Fair Value Measurements Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Financial Assets
Derivative Asset, Netting Adjustments	[1]	$ (16.7)	$ (19.4)
Derivative Asset, Net		7.7	3.5
Financial liabilities
Derivative Liability, Netting Adjustments	[1]	(16.7)	(19.4)
Derivative Liability, Net		149.7	135.4
Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		0.0	0.0
Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		24.4	22.9
Financial liabilities
Derivative Liability, Fair Value, Gross		166.4	154.8
Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		0.0	0.0
Short-term [Member]
Financial Assets
Derivative Asset, Netting Adjustments	[1]	(13.1)	(17.2)
Derivative Asset, Net		3.2	3.4
Financial liabilities
Derivative Liability, Netting Adjustments	[1]	(13.1)	(17.2)
Derivative Liability, Net		116.9	103.6
Short-term [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		0.0	0.0
Short-term [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		16.3	20.6
Financial liabilities
Derivative Liability, Fair Value, Gross		130.0	120.8
Short-term [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		0.0	0.0
Long-term [Member]
Financial Assets
Derivative Asset, Netting Adjustments	[1]	(3.6)	(2.2)
Derivative Asset, Net		4.5	0.1
Financial liabilities
Derivative Liability, Netting Adjustments	[1]	(3.6)	(2.2)
Derivative Liability, Net		32.8	31.8
Long-term [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		0.0	0.0
Long-term [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		8.1	2.3
Financial liabilities
Derivative Liability, Fair Value, Gross		36.4	34.0
Long-term [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross		0.0	0.0
Financial liabilities
Derivative Liability, Fair Value, Gross		$ 0.0	$ 0.0

[1] The Company nets its derivative contract assets and liabilities outstanding with the same counterparty on the Condensed Consolidated Balance Sheets, for the contracts that contain netting provisions. Refer to Note 7 – Derivative Contracts for additional information regarding the Company's derivative contracts.