Annual report pursuant to Section 13 and 15(d)

Debt (Details)

v3.24.0.1
Debt (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 22, 2022
Mar. 04, 2019
Dec. 31, 2023
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Oct. 01, 2022
Jul. 16, 2021
Dec. 31, 2020
Jul. 03, 2019
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     $ 2,462.9 $ 2,462.9 $ 2,544.7          
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net     (32.5) (32.5) (35.7)          
Other Long-term Debt     12.2 12.2 13.9          
Current Maturities of Long-term Debt     (454.7) (454.7) (89.0)          
Long-Term Debt, Net     1,975.7 1,975.7 2,420.0          
Proceeds from Issuance of Long-term Debt, Current and Long-term       4.7            
Maturities of Long-term Debt [Abstract]                    
2019     455.4 455.4            
2020     2.2 2.2            
2021     2.2 2.2            
2022     162.2 162.2            
2023     0.9 0.9            
Thereafter     1,840.0 1,840.0            
Total Long-Term Debt Including Current Maturities     2,462.9 2,462.9 2,544.7          
Line of Credit Facility [Abstract]                    
Letters of Credit Outstanding, Amount     8.5 8.5            
Proceeds from Issuance of Commercial Paper       485.0 500.0          
Commercial Paper, Maximum Amount Utilized       125.0 300.0          
Proceeds from Notes Payable $ 741.8     992.9            
Less: Restricted Cash     11.1 11.1 12.9 $ 12.2        
Proceeds from Issuance of Long-term Debt, Excluding Current Maturities       0.0            
Repayments of Long-term Debt, Current       (90.5)            
Repayments of Long-term Debt, Current and Long-term       (90.9)            
Other Debt Activity, Excluding Current Maturities       6.8            
Other Debt Activity, Current       0.8            
Other Debt Activity, Current and Long-term       7.6            
Debt, Long-term and Short-term, Combined Amount     2,430.4 2,430.4 2,509.0          
Proceeds from Issuance of Long-term Debt, Current       4.7            
Repayments of Long-term Debt, Excluding Current Maturities       (0.4)            
Short-Term Debt, Refinanced, Amount       (450.7)            
Reclassification of total debt       0.0            
Payments of Debt Issuance Costs         8.2 7.1        
Transaction Financing Charges       0.0 0.1 4.2        
Line of Credit Facility, Maximum Amount Outstanding During Period     127.8              
Commercial Paper, Maximum Amount Allowed to be Utilized       500.0            
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]                    
Line of Credit Facility [Abstract]                    
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount     71.3 71.3 52.8 97.9     $ 93.4  
Recoveries       0.0 0.0 $ 0.0        
Trustee Bank [Domain]                    
Line of Credit Facility [Abstract]                    
Less: Restricted Cash     8.3 8.3 8.0          
Commercial Paper [Member]                    
Line of Credit Facility [Abstract]                    
Line of Credit Facility, Maximum Borrowing Capacity             $ 300.0      
6.375% Senior Notes due 2049 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     230.0 230.0 230.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     230.0 230.0 230.0          
Debentures Due 2023 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     0.0 [1] 0.0 [1] 80.1          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     $ 0.0 [1] $ 0.0 [1] $ 80.1          
Loan With Fond Du Lac County Economic Development Corporation Due 2021 [Member]                    
Long-term Debt [Abstract]                    
Interest Rate     7.375% 7.375% 7.375%          
Notes Due 2027 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     $ 160.7 $ 160.7 $ 160.7          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     160.7 160.7 160.7          
Term Loan Due 2023 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities         56.3          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities         56.3          
6.625% Senior Notes due 2049 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     125.0 125.0 125.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     125.0 125.0 125.0          
6.500% Senior Notes due 2048 [Member]                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     185.0 185.0 185.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     185.0 185.0 185.0          
Senior Notes, 2.4% due 2031                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     550.0 550.0 550.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     550.0 550.0 550.0          
0.85% Senior Note Due 2024                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     450.0 450.0 450.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     450.0 450.0 450.0          
5.100% Senior Notes due 2052                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     300.0 300.0 300.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     300.0 300.0 300.0          
4.400% Senior Notes due 2032                    
Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     450.0 450.0 450.0          
Maturities of Long-term Debt [Abstract]                    
Total Long-Term Debt Including Current Maturities     450.0 450.0 450.0          
Line of Credit [Member]                    
Line of Credit Facility [Abstract]                    
Line of Credit Facility, Maximum Borrowing Capacity               $ 750.0    
Line of Credit Facility, Remaining Borrowing Capacity     741.9 741.9 747.2          
Letters of Credit Outstanding, Amount     8.1 8.1 2.8          
Line of Credit Facility, Increase (Decrease), Other, Net       100.0            
Line of Credit Facility, Current Borrowing Capacity         $ 125.0          
Senior Notes Due 2021 [Member] | Unsecured Debt [Member]                    
Line of Credit Facility [Abstract]                    
Senior Notes                   $ 150.0
Senior Notes Due 2049 [Member] | Unsecured Debt [Member]                    
Line of Credit Facility [Abstract]                    
Debt Instrument, Face Amount   $ 230.0                
Proceeds from Issuance of Debt   $ 222.0                
Term Loan Due 2023 [Member] | Unsecured Debt [Member]                    
Line of Credit Facility [Abstract]                    
Repayments of Other Debt       95.0            
0.850% Senior Notes due 2024                    
Line of Credit Facility [Abstract]                    
Senior Notes     450.0 450.0            
2,400% Senior Notes due 2031                    
Line of Credit Facility [Abstract]                    
Senior Notes     550.0 550.0            
Debentures Due 2023 [Member]                    
Line of Credit Facility [Abstract]                    
Debt Instrument, Face Amount     103.1 103.1            
Repayments of Other Debt       79.7            
Debt Instrument, Repurchase Amount     23.4 23.4            
Notes Due 2027 [Member]                    
Line of Credit Facility [Abstract]                    
Debt Instrument, Repurchase Amount     $ 2.5 $ 2.5            
4.400% Senior Notes due 2032                    
Line of Credit Facility [Abstract]                    
Senior Notes 450.0                  
5.100% Senior Notes due 2052                    
Line of Credit Facility [Abstract]                    
Senior Notes $ 300.0                  
[1]
(A) Included in Debentures, 7.375% due 2023 as of December 31, 2022, are the aggregate fair values related to the fixed-to-floating interest rate swaps as discussed in Note 12 – Financial Instruments. During the third quarter of 2022, the Debentures were reclassified from Long-term debt to Current maturities of long-term debt, of which the remaining principal payments were paid during the third quarter of 2023.