Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Jun. 30, 2019	Dec. 31, 2018
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	$ 113.7	$ 171.6
Property, plant and equipment, at cost	8,882.5	8,253.4
Less accumulated depreciation	(2,012.9)	(1,919.0)
Partially-owned subsidiaries
Restricted cash	30.8	36.6
Property, plant and equipment, at cost	2,048.3	2,032.0
Less accumulated depreciation	$ (499.8)	$ (472.0)