Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Unamortized discount on recourse debt	$ 81.0	[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	227.0	[1]	223.2
Property, plant, and equipment, at cost	6,026.4	[1]	5,642.0
Less accumulated depreciation	1,441.8	[1]	1,343.0
Partially-owned subsidiaries
Restricted cash	69.1	[1]	57.8
Property, plant, and equipment, at cost	1,703.0	[1]	1,703.1
Less accumulated depreciation	$ 177.0	[1]	$ 153.8

[1] (unaudited)