Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Variable Interest Entity [Line Items]
Document Period End Date	Sep. 30, 2013
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 136.3		$ 111.4
Carrying amounts of assets and liabilities of the VIE
Non-Recourse Debt	75.2		130.6
Variable Interest, Held by Entity [Member]
Carrying amounts of assets and liabilities of the VIE
Operating assets, net of accumulated depreciation	94.4	[1]	98.4	[1]
Non-Recourse Debt	27.9		35.1
Investments in affiliates [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 135.7		$ 110.7

[1] All operating assets are pledged as collateral on the nonrecourse debt.