Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended		6 Months Ended
	Mar. 10, 2021	Jan. 28, 2021	Mar. 11, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	45,000,000	13,000,000	45,000,000	22,806,841	0	71,509,671	47,736,847
Average purchase price per share (in usd per share)				$ 19.27	$ 0	$ 16.87	$ 9.66
Shares repurchased related to employee stock-based compensation plans (in shares)				192,432	908	1,252,412	1,106,027
Average purchase price per share (in usd per share)				$ 18.80	$ 7.77	$ 14.32	$ 10.98
Common shares issued (in shares)				454,920	147,735	3,281,307	2,985,297
Remaining authority under the share repurchase program				$ 295		$ 295
Common stock repurchased and cancelled (in shares)						28,500,000