Income Taxes - Items Accounting for Differences Between Income Taxes Computed at Federal Statutory Rate and Provision Recorded for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes computed at the federal statutory rate									$ 1,332	$ 1,362	$ 549
Effect of:
Impact of foreign tax differential									1,178	(69)	350
State taxes, net of federal benefits									114	110	37
Tax credits									(220)	(119)	(99)
Stock-based compensation									(917)	189	149
Domestic production activities deduction									0	(94)	(44)
Impact of 2017 Tax Act									(789)	0	0
Other, net									71	46	8
Provision for income taxes, net	$ 16	$ 58	$ 467	$ 229	$ 414	$ 229	$ 307	$ 475	769	$ 1,425	$ 950
Excess tax benefits from stock-based compensation									$ 1,300