Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	4,436,963	0	15,861,718	0
Average purchase price per share (in usd per share)	$ 8.45	$ 0	$ 9.94	$ 0
Shares repurchased related to employee stock-based compensation plans (in shares)	15,238	116,151	1,328,665	3,056,746
Average purchase price per share (in usd per share)	$ 9.54	$ 11.54	$ 10.92	$ 11.34
Common shares issued (in shares)	26,137	397,004	3,677,821	6,341,950
Remaining authority under the share repurchase program	$ 43		$ 43