Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
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	86.9	[1]	$ 88.1	[1]
Nonrecourse debt	13.7		$ 15.9

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