Benefit Plans and Other Postretirement Benefits, Fair value measurements of plan assets (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 481.6	$ 470.6	$ 644.0
U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	29.0	44.1
U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	8.7	13.0
International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.1	28.7
International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.7	38.4
Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	5.6	14.6
U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	113.5	83.6
Fixed Income Securities - Long Term [Member]
Defined Benefit Plan Disclosure
Fair value of pension plan assets	210.9	181.3
International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	39.7	34.0
Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	19.5	24.3
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	6.9	8.6
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	19.2	28.3
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	12.3	19.7
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed Income Securities - Long Term [Member]
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	6.9	8.6
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	437.3	403.4
Significant Observable Inputs (Level 2) | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	29.0	44.1
Significant Observable Inputs (Level 2) | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	8.7	13.0
Significant Observable Inputs (Level 2) | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	9.8	9.0
Significant Observable Inputs (Level 2) | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.7	38.4
Significant Observable Inputs (Level 2) | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Observable Inputs (Level 2) | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	113.5	83.6
Significant Observable Inputs (Level 2) | Fixed Income Securities - Long Term [Member]
Defined Benefit Plan Disclosure
Fair value of pension plan assets	210.9	181.3
Significant Observable Inputs (Level 2) | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	39.7	34.0
Significant Observable Inputs (Level 2) | Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	19.5	24.3	$ 34.1
Significant Unobservable Inputs (Level 3) | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Fixed Income Securities - Long Term [Member]
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	19.5	24.3
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure
Fair value of pension plan assets	5.6	14.6
Fair Value Measured At Net Asset Value | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	5.6	14.6
Fair Value Measured At Net Asset Value | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | Fixed Income Securities - Long Term [Member]
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	0.0	0.0
Fair Value Measured At Net Asset Value | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 0.0	$ 0.0