Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		9 Months Ended
	Mar. 10, 2020	Jan. 23, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	44,900,000	3,000,000	0	4,436,963	47,736,847	15,861,718
Average purchase price per share (in usd per share)			$ 0	$ 8.45	$ 9.66	$ 9.94
Shares repurchased related to employee stock-based compensation plans (in shares)			3,122	15,238	1,109,149	1,328,665
Average purchase price per share (in usd per share)			$ 7.05	$ 9.54	$ 10.97	$ 10.92
Common shares issued (in shares)			5,150	26,137	2,990,447	3,677,821
Remaining authority under the share repurchase program			$ 75		$ 75