Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Receivables, allowance for doubtful accounts	$ 11.1	$ 4.5
Restricted cash	195.8	234.7
Property, plant and equipment, at cost	7,145.4	6,586.0
Less: accumulated depreciation	1,797.4	1,683.1
Unamortized discount on recourse debt	$ 44.2	$ 60.0
Preferred stock, shares authorized	1,500,000	1,500,000
Preferred stock, shares unissued	1,500,000	1,500,000
Common stock, shares authorized	400,000,000	200,000,000
Common stock, shares issued	152,900,000	155,700,000
Common stock, shares outstanding	152,900,000	155,700,000
Treasury stock, shares	100,000	100,000
Partially-owned subsidiaries
Restricted cash	$ 89.9	$ 91.9
Property, plant and equipment, at cost	2,078.9	2,073.6
Less: accumulated depreciation	$ 412.5	$ 356.2