Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Preferred stock, shares authorized	1.5	1.5
Preferred Stock, Shares Unissued	1.5	1.5
Common stock, shares authorized	400.0	400.0
Restricted cash	$ 96.3	$ 111.4
Property, Plant and Equipment, Gross	9,335.7	9,272.5
Less accumulated depreciation	(2,217.0)	(2,161.9)
Partially-owned subsidiaries
Restricted cash	27.3	33.0
Property, Plant and Equipment, Gross	2,069.6	2,065.3
Less accumulated depreciation	$ (540.5)	$ (527.7)