Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings available to common stockholders	$ 1,024	$ 833		$ 2,368	$ 1,661
Basic weighted-average shares outstanding (in shares)	255.3	272.4		261.0	277.0
Effect of employee stock awards (in shares)	1.1	1.2		1.0	1.0
Diluted weighted-average shares outstanding (in shares)	256.4	273.6		262.0	278.0
Earnings per share, basic (in dollars per share)	$ 4.01	$ 3.06	[1]	$ 9.07	$ 6.00	[1]
Earnings per share, diluted (in dollars per share)	$ 3.99	$ 3.05	[1]	$ 9.04	$ 5.98	[1]

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.