Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Type of Entity	one
Variable Interest, Held by Entity [Member]
Carrying amounts of assets and liabilities of the VIE
Operating assets, net of accumulated depreciation	88.1	[1]	$ 93.0	[1]
Nonrecourse debt	15.9		$ 25.4

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