Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Unamortized discount	$ 63.7	[1]	$ 74.1
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	237.9	[1]	260.7
Property, plant, and equipment, at cost	6,493.4	[1]	6,275.8
Less accumulated depreciation	1,638.1	[1]	1,505.2
Partially-owned subsidiaries
Restricted cash	94.3	[1]	77.1
Property, plant, and equipment, at cost	2,260.0	[1]	1,887.2
Less accumulated depreciation	$ 245.3	[1]	$ 202.1

[1] (unaudited)