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Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures (Details) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Pension [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets $ 745.7 $ 759.4 $ 699.6
Pension [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 12.2 3.2  
Pension [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 711.9 731.2  
Pension [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 21.6 25.0  
Pension [Member] | U.S. Large-cap [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 113.8 [1] 91.7 [2]  
Pension [Member] | U.S. Large-cap [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | U.S. Large-cap [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 113.8 [1] 91.7 [2]  
Pension [Member] | U.S. Large-cap [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | U.S. Mid-cap Growth [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 47.6 [1] 40.0 [2]  
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 47.6 [1] 40.0 [2]  
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | U.S. Small-cap [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 46.2 [1] 40.7 [2]  
Pension [Member] | U.S. Small-cap [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | U.S. Small-cap [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 46.2 [1] 40.7 [2]  
Pension [Member] | U.S. Small-cap [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | International [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 158.2 97.1  
Pension [Member] | International [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | International [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 158.2 97.1  
Pension [Member] | International [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Fixed Income [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 346.1 [1] 461.7 [2]  
Pension [Member] | Fixed Income [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | Fixed Income [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 346.1 [1] 461.7 [2]  
Pension [Member] | Fixed Income [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [1] 0.0 [2]  
Pension [Member] | Cash and Cash Equivalents [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 12.2 3.2  
Pension [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 12.2 3.2  
Pension [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Cash and Cash Equivalents [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Private Equity [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 7.0  
Pension [Member] | Private Equity [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Private Equity [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Private Equity [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 7.0 8.0
Pension [Member] | Real Estate [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 21.6 18.0  
Pension [Member] | Real Estate [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Real Estate [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Pension [Member] | Real Estate [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 21.6 18.0 18.0
Postretirement Health and Life [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 201.8 186.0 173.7
Postretirement Health and Life [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 198.0 182.1  
Postretirement Health and Life [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 1.8 2.2  
Postretirement Health and Life [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 2.0 1.7  
Postretirement Health and Life [Member] | U.S. Large-cap [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 40.1 [3] 34.2 [4]  
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 40.1 [3] 34.2 [4]  
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 37.3 [3] 31.4 [4]  
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 37.3 [3] 31.4 [4]  
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | U.S. Small-cap [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 19.3 [3] 16.6 [4]  
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 19.3 [3] 16.6 [4]  
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | International [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 43.7 [3] 41.5 [4]  
Postretirement Health and Life [Member] | International [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 43.7 [3] 41.5 [4]  
Postretirement Health and Life [Member] | International [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | International [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 [3] 0.0 [4]  
Postretirement Health and Life [Member] | Mutual Funds [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 56.7 57.3  
Postretirement Health and Life [Member] | Mutual Funds [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 56.7 57.3  
Postretirement Health and Life [Member] | Mutual Funds [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Mutual Funds [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Fixed Income [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 1.8 2.2  
Postretirement Health and Life [Member] | Fixed Income [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Fixed Income [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 1.8 2.2  
Postretirement Health and Life [Member] | Fixed Income [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.9 1.1  
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.9 1.1  
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Private Equity [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 2.0 1.7  
Postretirement Health and Life [Member] | Private Equity [Member] | Level 1 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Private Equity [Member] | Level 2 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets 0.0 0.0  
Postretirement Health and Life [Member] | Private Equity [Member] | Level 3 [Member]      
Recurring Fair Value Measures [Line Items]      
Fair Value of Assets $ 2.0 $ 1.7 $ 1.7
[1] The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.
[2] The underlying investments consist of actively-managed funds managed to achieve the returns of certain U.S. equity and fixed income securities indexes.
[3] The underlying investments consist of mutual funds (Level 1). 
[4] The underlying investments consist of mutual funds (Level 1).