Stockholders' Equity - Repurchases of Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	6 Months Ended	9 Months Ended
	Feb. 08, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Class of Stock
Shares authorized for repurchase (in shares)	750,000,000
Payment for shares acquired	$ 434.0	$ 51.0	$ 62.5	$ 496.1	$ 0.0
Percentage of outstanding shares (percent)				13.00%
Common Stock
Class of Stock
Treasury shares acquired (in shares)	37,000,000	5,600,000	6,800,000
Treasury stock price (usd per share)	$ 11.72	$ 9.06	$ 9.20
Remaining shares authorized for repurchase		$ 254.0	$ 254.0	$ 254.0