Stockholders' Equity - Common Stock Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Common stock repurchased under repurchase program (in shares)	5,989,279	0	11,424,755	0
Average purchase price per share (in usd per share)	$ 10.04	$ 0	$ 10.51	$ 0
Shares repurchased related to employee stock-based compensation plans (in shares)	24,036	200,577	1,313,427	2,940,595
Average purchase price per share (in usd per share)	$ 10.05	$ 11.60	$ 10.93	$ 11.33
Common shares issued (in shares)	181,020	384,955	3,651,684	5,944,946
Average purchase price per share under repurchase program	$ 80		$ 80