Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net income available to common stockholders	$ 173	$ 175
Denominator:
Denominator for basic earnings per share—weighted-average common shares (in shares)	74,041	79,401
Effect of dilutive securities:
Denominator for diluted earnings per share—adjusted weighted-average common shares (in shares)	74,266	80,047
Basic earnings per share (in dollars per share)	$ 2.33	$ 2.21
Diluted earnings per share (in dollars per share)	$ 2.33	$ 2.19
Employee stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	15	294
Restricted stock units
Effect of dilutive securities:
Effect of dilutive securities (in shares)	210	352