Pension and Other Postretirement Benefits - Expected Benefit Payments (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Future Benefit Payments in 2015	$ 286.5
Expected Future Benefit Payments in 2016	289.1
Expected Future Benefit Payments in 2017	302.6
Expected Future Benefit Payments in 2018	261.7
Expected Future Benefit Payments in 2019	254.5
Expected Future Benefit Payments in 2020 through 2024	1,154.8
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Future Benefit Payments in 2015	53.5	[1]
Expected Future Benefit Payments in 2016	49.8	[1]
Expected Future Benefit Payments in 2017	46.9	[1]
Expected Future Benefit Payments in 2018	44.6	[1]
Expected Future Benefit Payments in 2019	43.2	[1]
Expected Future Benefit Payments in 2020 through 2024	194.3	[1]
Expected Medicare Subsidy Receipts in 2015	(3.1)	[1]
Expected Medicare Subsidy Receipts in 2016	(1.6)	[1]
Expected Medicare Subsidy Receipts in 2017	(1.6)	[1]
Expected Medicare Subsidy Receipts in 2018	(1.6)	[1]
Expected Medicare Subsidy Receipts in 2019	(1.6)	[1]
Expected Medicare Subsidy Receipts in 2020 through 2024	$ (8.8)	[1]

[1] The amounts shown do not include the lump sum payment in 2015 to the VEBA trust related to the Zanesville Retiree Settlement. These amounts reflect the fact that the Company has eliminated its OPEB liability related to the group of retirees covered by the Butler Retiree Settlement after 2014 and the Zanesville Retiree Settlement after 2015.