Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended		9 Months Ended
	Mar. 10, 2021	Jan. 28, 2021	Mar. 11, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	45,000,000	13,000,000	45,000,000	13,018,585	0	84,528,256	47,736,847
Average purchase price per share (in usd per share)				$ 18.75	$ 0	$ 17.17	$ 9.66
Shares repurchased related to employee stock-based compensation plans (in shares)				115,414	3,122	1,367,826	1,109,149
Average purchase price per share (in usd per share)				$ 18.83	$ 7.05	$ 14.70	$ 10.97
Common shares issued (in shares)				504,183	5,150	3,785,490	2,990,447
Remaining authority under the share repurchase program				$ 51		$ 51
Common stock repurchased and cancelled (in shares)						28,500,000