Earnings Per Share - Computation of Basic and Diluted Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 58	$ 63	$ 61	$ 36	$ 54	$ 48	$ 50	$ 35	$ 218	$ 187	$ 63
Weighted Average Shares
Weighted average common shares outstanding (in shares)									56,584,238	57,520,289	57,093,868
Effect of dilutive securities
May investor warrants (in shares)									0	0	12,287
Stock-based Awards (in shares)									654,740	802,661	1,072,188
Weighted average diluted common shares (in shares)									57,238,978	58,322,950	58,178,343
Earnings per common share
Basic income (loss) per share (in usd per share)	$ 1.01	$ 1.12	$ 1.08	$ 0.64	$ 0.94	$ 0.84	$ 0.86	$ 0.61	$ 3.85	$ 3.26	$ 1.11
Effect of dilutive securities
May Investor Warrants (in usd per share)									0	0	0
Stock-based awards (in usd per share)									(0.05)	(0.05)	(0.02)
Diluted earnings per common share (in usd per share)	$ 1.00	$ 1.11	$ 1.06	$ 0.63	$ 0.93	$ 0.83	$ 0.85	$ 0.60	$ 3.80	$ 3.21	$ 1.09