Fair Value Measurements - Fair Value of Financial Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Financial Assets
Derivative Asset, Fair Value, Gross	$ 49.7		$ 6.5
Financial liabilities
Derivative Liability, Fair Value, Gross	9.1		32.0
Fair Value, Measurements, Recurring [Member]
Financial Assets
Net amount of derivative assets presented on condensed consolidated balance sheets	45.3		1.2
Financial liabilities
Net amount of derivative liabilities presented on condensed consolidated balance sheets	4.7		26.7
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	49.7		6.5
Financial liabilities
Derivative Liability, Fair Value, Gross	9.1		32.0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	(4.4)	[1]	(5.3)	[1]
Financial liabilities
Derivative Liability, Fair Value, Gross	(4.4)	[1]	(5.3)	[1]
Long-term [Member] | Interest Rate Swap [Member]
Financial Assets
Derivative Asset, Fair Value, Gross			0.6
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Long-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Net amount of derivative assets presented on condensed consolidated balance sheets	3.5		0.6
Long-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Long-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	3.5		0.6
Long-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Long-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0	[1]	0	[1]
Long-term [Member] | Commodity Contract [Member]
Financial Assets
Derivative Asset, Fair Value, Gross			0.4
Financial liabilities
Derivative Liability, Fair Value, Gross			0
Long-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Net amount of derivative assets presented on condensed consolidated balance sheets	9.2		0.4
Financial liabilities
Net amount of derivative liabilities presented on condensed consolidated balance sheets	0.2
Long-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0
Long-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	9.6		0.4
Financial liabilities
Derivative Liability, Fair Value, Gross	0.6
Long-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0
Long-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	(0.4)	[1]	0	[1]
Financial liabilities
Derivative Liability, Fair Value, Gross	(0.4)	[1]
Short-term [Member] | Interest Rate Swap [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross			2.6
Short-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member]
Financial liabilities
Net amount of derivative liabilities presented on condensed consolidated balance sheets	4.3		2.6
Short-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Short-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial liabilities
Derivative Liability, Fair Value, Gross	4.3		2.6
Short-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Short-term [Member] | Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Financial liabilities
Derivative Liability, Fair Value, Gross	0	[1]	0	[1]
Short-term [Member] | Commodity Contract [Member]
Financial Assets
Derivative Asset, Fair Value, Gross			5.5
Financial liabilities
Derivative Liability, Fair Value, Gross			29.4
Short-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Net amount of derivative assets presented on condensed consolidated balance sheets	32.6		0.2
Financial liabilities
Net amount of derivative liabilities presented on condensed consolidated balance sheets	0.2		24.1
Short-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Short-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	36.6		5.5
Financial liabilities
Derivative Liability, Fair Value, Gross	4.2		29.4
Short-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	0		0
Financial liabilities
Derivative Liability, Fair Value, Gross	0		0
Short-term [Member] | Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Financial Assets
Derivative Asset, Fair Value, Gross	(4.0)	[1]	(5.3)	[1]
Financial liabilities
Derivative Liability, Fair Value, Gross	$ (4.0)	[1]	$ (5.3)	[1]

[1] The Company nets its derivative contract assets and liabilities outstanding with the same counterparty on the Condensed Consolidated Balance Sheets as the contracts contain netting provisions. Refer to Note 8 - Derivative Contracts, for additional information regarding the Company's derivative contracts.