Stockholders' Equity - Schedule of Changes in Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Class Of Stock [Line Items]
Balance		$ 8,994			$ 8,994
Net income	$ 1,305		$ 1,405		2,522	$ 2,771
Other comprehensive income (loss), net of taxes	8		21		16	13
Balance	8,486				8,486
Common Stock
Class Of Stock [Line Items]
Balance	1,741	1,741	1,741	$ 1,741	1,741	1,741
Net income	0	0	0	0
Dividends declared and paid ($0.77 and $0.62 per share)	0	0	0	0
Common stock issued for stock-based awards	0	0	0	0
Stock repurchases	0	0	0	0
Stock compensation	0	0	0	0
Other comprehensive income (loss), net of taxes	0	0	0	0
Dividend equivalents on RSUs	0	0	0	0
Cumulative effect of accounting changes				0
Other	0	0	0	0
Balance	1,741	1,741	1,741	1,741	1,741	1,741
Paid-in Capital
Class Of Stock [Line Items]
Balance	1,927	1,950	1,770	1,776	1,950	1,776
Net income	0	0	0	0
Dividends declared and paid ($0.77 and $0.62 per share)	0	0	0	0
Common stock issued for stock-based awards	10	(84)	22	(75)
Stock repurchases	0	0	0	0
Stock compensation	67	61	74	70
Other comprehensive income (loss), net of taxes	0	0	0	0
Dividend equivalents on RSUs	0	0	0	0
Cumulative effect of accounting changes				0
Other	(1)	0	1	(1)
Balance	2,003	1,927	1,867	1,770	2,003	1,867
Retained Earnings
Class Of Stock [Line Items]
Balance	38,396	37,906	35,619	34,662	37,906	34,662
Net income	1,305	1,217	1,405	1,366
Dividends declared and paid ($0.77 and $0.62 per share)	(722)	(724)	(606)	(611)
Common stock issued for stock-based awards	0	0	0	0
Stock repurchases	0	0	0	0
Stock compensation	0	0	0	0
Other comprehensive income (loss), net of taxes	0	0	0	0
Dividend equivalents on RSUs	(4)	(4)	(5)	(4)
Cumulative effect of accounting changes				206
Other	(1)	1	0	0
Balance	38,974	38,396	36,413	35,619	38,974	36,413
Treasury Common Stock
Class Of Stock [Line Items]
Balance	(33,080)	(32,130)	(28,096)	(27,458)	(32,130)	(27,458)
Net income	0	0	0	0
Dividends declared and paid ($0.77 and $0.62 per share)	0	0	0	0
Common stock issued for stock-based awards	136	235	80	253
Stock repurchases	(830)	(1,185)	(1,000)	(891)
Stock compensation	0	0	0	0
Other comprehensive income (loss), net of taxes	0	0	0	0
Dividend equivalents on RSUs	0	0	0	0
Cumulative effect of accounting changes				0
Other	(1)	0	0	0
Balance	(33,775)	(33,080)	(29,016)	(28,096)	(33,775)	(29,016)
AOCI
Class Of Stock [Line Items]
Balance	(465)	(473)	(392)	(384)	(473)	(384)
Net income	0	0	0	0
Dividends declared and paid ($0.77 and $0.62 per share)	0	0	0	0
Common stock issued for stock-based awards	0	0	0	0
Stock repurchases	0	0	0	0
Stock compensation	0	0	0	0
Other comprehensive income (loss), net of taxes	8	8	21	(8)
Dividend equivalents on RSUs	0	0	0	0
Cumulative effect of accounting changes				0
Other	0	0	0	0
Balance	$ (457)	$ (465)	$ (371)	$ (392)	$ (457)	$ (371)