Benefit Plans and Other Postretirement Benefits (Details 4) (Pension Benefits, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 409.4	$ 392.5	$ 334.4
Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	227.2	255.0
U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	106.6	122.2
U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	23.0	24.7
International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.9	51.8
International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	50.7	56.3
Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	119.9	126.3
U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59.1	62.2
U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	20.2	24.4
International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	40.6	39.7
Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	40.1
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.2	11.2
Level 1
Defined Benefit Plan Disclosure
Fair value of pension plan assets	209.1	228.3
Level 1 | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	127.8	154.6
Level 1 | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	80.9	93.1
Level 1 | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets		1.6
Level 1 | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	46.9	51.8
Level 1 | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets		8.1
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59.1	62.5
Level 1 | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59.1	62.2
Level 1 | U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets		0.3
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22.2	11.2
Level 2
Defined Benefit Plan Disclosure
Fair value of pension plan assets	200.3	164.2
Level 2 | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	99.4	100.4
Level 2 | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25.7	29.1
Level 2 | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	23.0	23.1
Level 2 | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	50.7	48.2
Level 2 | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	60.8	63.8
Level 2 | U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	20.2	24.1
Level 2 | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	40.6	39.7
Level 2 | Alternative investment funds
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 40.1