Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Mar. 10, 2020	Jan. 23, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	44,900,000	3,000,000	0	5,989,279	47,736,847	11,424,755
Average purchase price per share (in usd per share)			$ 0	$ 10.04	$ 9.66	$ 10.51
Shares repurchased related to employee stock-based compensation plans (in shares)			908	24,036	1,106,027	1,313,427
Average purchase price per share (in usd per share)			$ 7.77	$ 10.05	$ 10.98	$ 10.93
Common shares issued (in shares)			147,735	181,020	2,985,297	3,651,684
Remaining authority under the share repurchase program			$ 75		$ 75