Earnings per Share - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Calculation of basic EPS:
Net income applicable to common stock	$ (669.5)	$ 43.9	$ 93.5
Weighted-average common shares outstanding (in shares)	134.0	115.7	97.1
Basic EPS (in dollars per share)	$ (5.00)	$ 0.38	$ 0.96
Calculation of diluted EPS:
Diluted weighted-average common shares outstanding (in shares)	134.0	117.8	100.3
Diluted EPS (in dollars per share)	$ (5.00)	$ 0.37	$ 0.93