Pension and Other Postretirement Benefits - Plan Assets (Details 4) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	2,863.6		$ 2,808.5		$ 2,591.1
Equity Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocations percentage	60.00%
Fixed Income Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocations percentage	38.00%
Cash and Cash Equivalents [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocations percentage	2.00%
Private Equity Funds [Member]
Level 3 Assets [Roll Forward]
Beginning of year	0.6		3.2
Distribution to master pension trust			(2.6)
Gains (losses) recognized in other comprehensive income (loss)	0.3
End of year	0.9		0.6
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	2,863.6		2,808.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	239.0		301.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	2,623.7		2,506.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0.9		0.6
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	39.6		45.5
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	39.6		45.5
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | US Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	199.4		176.6
Fair Value, Measurements, Recurring [Member] | US Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	199.4		176.6
Fair Value, Measurements, Recurring [Member] | US Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | US Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	862.4		840.5
Fair Value, Measurements, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	862.4		840.5
Fair Value, Measurements, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | EAFE Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	272.9		277.6
Fair Value, Measurements, Recurring [Member] | EAFE Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | EAFE Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	272.9		277.6
Fair Value, Measurements, Recurring [Member] | EAFE Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		79.4
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		79.4
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	125.7		128.1
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	125.7		128.1
Fair Value, Measurements, Recurring [Member] | Emerging Market Equity Securities Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	210.7		230.8
Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	210.7		230.8
Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Investment-Grade Corporate Fixed Income Investments Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	421.8		378.4
Fair Value, Measurements, Recurring [Member] | U.S. Investment-Grade Corporate Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Investment-Grade Corporate Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	421.8		378.4
Fair Value, Measurements, Recurring [Member] | U.S. Investment-Grade Corporate Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Treasuries Fixed Income Investments Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	98.4		88.1
Fair Value, Measurements, Recurring [Member] | U.S. Treasuries Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. Treasuries Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	98.4		88.1
Fair Value, Measurements, Recurring [Member] | U.S. Treasuries Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Fixed Income Investments Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	18.0		20.5
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	18.0		20.5
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed Fixed Income Investments Common/Collective Trusts [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	435.4		350.8
Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	435.4		350.8
Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	178.4		191.6
Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	178.4		191.6
Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0.9	[1]	0.6	[1]
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0.9	[1]	$ 0.6	[1]

[1] Consists of private equity funds that have no remaining capital commitments due from the Company.