Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Carrying amounts of assets and liabilities of the VIE
Non-Recourse Debt	$ 127.9		$ 130.6
Variable Interest, Held by Entity [Member]
Carrying amounts of assets and liabilities of the VIE
Operating assets, net of accumulated depreciation	97.0	[1]	98.4	[1]
Non-Recourse Debt	$ 32.8		$ 35.1

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