Earnings (Loss) per Share - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Calculation of basic earnings (loss) per share:
Net income (loss) applicable to common stock	$ 141.1	$ 43.9	$ (680.6)	$ 136.4
Weighted average common shares outstanding - basic (in shares)	138.2	115.2	126.9	115.8
Basic earnings (loss) per share (in dollars per share)	$ 1.02	$ 0.38	$ (5.36)	$ 1.18
Calculation of diluted earnings (loss) per share:
Net income (loss) applicable to common stock	$ 141.1	$ 43.9	$ (680.6)	$ 136.4
Convertible Notes	4.2	0.0	0.0	0.0
Diluted income (loss) applicable to common stock	$ 145.3	$ 43.9	$ (680.6)	$ 136.4
Weighted average common shares outstanding - diluted (in shares)	155.5	116.7	126.9	117.7
Diluted earnings (loss) per share (in dollars per share)	$ 0.93	$ 0.38	$ (5.36)	$ 1.16