Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator:
Net income available to common stockholders									$ 1,174	$ 1,096	$ 1,346
Denominator:
Denominator for basic earnings per share—weighted-average common shares (in shares)									77,341	82,652	84,599
Effect of dilutive securities:
Denominator for diluted earnings per share—adjusted weighted-average common shares (in shares)									77,710	83,530	85,562
Basic earnings per share (in dollars per share)	$ 4.51	$ 5.10	$ 3.45	$ 2.21	$ 3.84	$ 4.05	$ 3.22	$ 2.18	$ 15.18	$ 13.26	$ 15.91
Diluted earnings per share (in dollars per share)	$ 4.49	$ 5.08	$ 3.44	$ 2.19	$ 3.80	$ 4.01	$ 3.20	$ 2.15	$ 15.11	$ 13.12	$ 15.73
Employee stock options
Effect of dilutive securities:
Share-based payment arrangements (in shares)									114	379	403
Restricted stock units
Effect of dilutive securities:
Share-based payment arrangements (in shares)									255	499	560