Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	[1]	Dec. 31, 2014
Unamortized discount	$ 48.3		$ 60.0
Preferred stock, shares authorized	1,500,000.0		1,500,000.0
Preferred stock, shares issued	0		0
Common stock, shares authorized	400,000,000		200,000,000
Restricted cash	$ 211.8		$ 234.7
Property, plant, and equipment	7,111.0		6,586.0
Less accumulated depreciation	1,802.6		1,683.1
Partially-owned subsidiaries
Restricted cash	90.5		91.9
Property, plant, and equipment	2,261.3		2,261.2
Less accumulated depreciation	$ 308.8		$ 261.3

[1] (unaudited)