Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income available to common stockholders	$ 293	$ 212	$ 496	$ 385
Denominator:
Denominator for basic earnings per share—weighted-average common shares (in shares)	72,455	72,161	72,397	73,101
Effect of dilutive securities:
Denominator for diluted earnings per share—adjusted weighted-average common shares (in shares)	72,717	72,275	72,693	73,270
Basic earnings per share (in dollars per share)	$ 4.03	$ 2.94	$ 6.85	$ 5.26
Diluted earnings per share (in dollars per share)	$ 4.02	$ 2.93	$ 6.82	$ 5.25
Employee stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	4	12	5	14
Restricted stock units
Effect of dilutive securities:
Effect of dilutive securities (in shares)	258	102	291	155