Benefit Plans and Other Postretirement Benefits - Fair Value - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 392.2	$ 409.4	$ 392.5
Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	229.2	227.2
U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	108.2	106.6
U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.7	23.0
International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.0	46.9
International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	52.3	50.7
Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	114.8	119.9
U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	58.7	59.1
U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	18.9	20.2
International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	37.2	40.6
Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	31.5	40.1
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	16.7	22.2
Level 1
Defined Benefit Plan Disclosure
Fair value of pension plan assets	210.6	209.1
Level 1 | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	135.2	127.8
Level 1 | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	82.3	80.9
Level 1 | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.0	46.9
Level 1 | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	6.9
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	58.7	59.1
Level 1 | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	58.7	59.1
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	16.7	22.2
Level 2
Defined Benefit Plan Disclosure
Fair value of pension plan assets	181.6	200.3
Level 2 | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	94.0	99.4
Level 2 | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.9	25.7
Level 2 | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.7	23.0
Level 2 | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	45.4	50.7
Level 2 | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	56.1	60.8
Level 2 | U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	18.9	20.2
Level 2 | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	37.2	40.6
Level 2 | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 31.5	$ 40.1