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Pension and Postretirement Benefit Plans (Net Periodic Pension Costs Included in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Before Tax [Roll Forward]      
Prior service cost arising during the year     $ (25.5)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Tax [Roll Forward]      
Prior service cost arising during the year     (6.4)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Net of Tax [Roll Forward]      
Prior service cost arising during the year $ (0.9) $ 0.0 (19.1)
Net actuarial gain (loss) arising during the year (2.2) (16.1) 12.3
Amortization of prior service cost 1.1 1.3 0.0
Amortization of net actuarial losses 7.8 7.0 6.4
Postretirement benefits | Defined Benefit Pension Plans      
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Before Tax [Roll Forward]      
Accumulated other comprehensive loss, beginning of period (314.4) (304.4) (302.4)
Prior service cost arising during the year (1.4)    
Net gain (loss) recognized due to settlement 18.8 0.4 (0.4)
Net actuarial gain (loss) arising during the year (2.7) (21.5) 15.0
Amortization of prior service cost 1.5 1.7 0.2
Amortization of net actuarial losses 10.5 9.4 8.7
Accumulated other comprehensive loss, end of period (287.7) (314.4) (304.4)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Tax [Roll Forward]      
Accumulated other comprehensive loss, beginning of period (75.8) (73.2) (72.0)
Prior service cost arising during the year (0.5)    
Net gain (loss) recognized due to settlement 4.8 0.0 0.0
Net actuarial gain (loss) arising during the year (0.5) (5.4) 2.7
Amortization of prior service cost 0.4 0.4 0.2
Amortization of net actuarial losses 2.7 2.4 2.3
Accumulated other comprehensive loss, end of period (68.9) (75.8) (73.2)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges in Period, Net of Tax [Roll Forward]      
Accumulated other comprehensive loss, beginning of period (238.6) (231.2) (230.4)
Prior service cost arising during the year (0.9)    
Net gain (loss) recognized due to settlement 14.0 0.4 (0.4)
Net actuarial gain (loss) arising during the year (2.2) (16.1) 12.3
Amortization of prior service cost 1.1 1.3 0.0
Amortization of net actuarial losses 7.8 7.0 6.4
Accumulated other comprehensive loss, end of period $ (218.8) $ (238.6) $ (231.2)