Benefit Plans and Other Postretirement Benefits, Fair Value Measurements (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 439.9	$ 392.2	$ 409.4
U.S. equities — large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	118.8	108.2
U.S. equities — small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.8	22.7
International equities — growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.5	46.0
International equities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	60.6	52.3
Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	12.6	31.5
U.S. fixed income securities — short term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	6.0
U.S. fixed income securities — intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	58.4	58.7
U.S. fixed income securities — high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.2	18.9
International fixed income securities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	43.0	37.2
Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	34.0
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	12.0	16.7
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	212.6	210.6
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	88.7	82.3
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities — growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.5	46.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	7.0	6.9
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	58.4	58.7
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	12.0	16.7
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	155.0	150.1
Significant Observable Inputs (Level 2) | U.S. equities — large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	30.1	25.9
Significant Observable Inputs (Level 2) | U.S. equities — small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.8	22.7
Significant Observable Inputs (Level 2) | International equities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	33.9	45.4
Significant Observable Inputs (Level 2) | U.S. fixed income securities — high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.2	18.9
Significant Observable Inputs (Level 2) | International fixed income securities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	43.0	37.2
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	34.0
Significant Unobservable Inputs (Level 3) | Insurance contracts
Defined Benefit Plan Disclosure
Fair value of pension plan assets	34.0
Assets Measured at Net Asset Value
Defined Benefit Plan Disclosure
Fair value of pension plan assets	38.3	31.5
Assets Measured at Net Asset Value | International equities — other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	19.7
Assets Measured at Net Asset Value | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	12.6	$ 31.5
Assets Measured at Net Asset Value | U.S. fixed income securities — short term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 6.0