Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Unamortized discount on recourse debt	$ 84.2	[1]	$ 87.5
Preferred stock, shares authorized	1,500,000	[1]	1,500,000
Preferred stock, shares unissued	1,500,000	[1]	1,500,000
Common stock, shares authorized	200,000,000	[1]	200,000,000
Restricted cash	215.3	[1]	223.2
Property, plant, and equipment, at cost	5,854.6	[1]	5,642.0
Less accumulated depreciation	(1,392.6)	[1]	(1,343.0)
Partially-owned subsidiary
Restricted cash	50.9	[1]	50.3
Property, plant, and equipment, at cost	1,272.5	[1]	1,272.4
Less accumulated depreciation	$ 162.4	[1]	$ 153.8

[1] (unaudited)