Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 178	$ 198
Denominator:
Shares outstanding at the beginning of the period (in shares)			61.9	62.1
Weighted-average number of shares issued:
Stock purchases (in shares)	(1.7)	0.0
Stock-based compensation (in shares)	0.0	0.0
Denominator for net income per share, basic (in shares)	60.2	62.1
Effect of dilutive securities:
Warrants (in shares)	0.1	3.5
Stock-based compensation (in shares)	0.7	0.6
Denominator for net income per share, diluted (in shares)	61.0	66.2
Net income per share:
Basic (in dollars per share)	$ 2.95	$ 3.19
Diluted (in dollars per share)	$ 2.92	$ 2.99
Potentially dilutive common shares (in shares)		0.1