Income Taxes - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2017	Dec. 21, 2017
Income Tax Disclosure [Abstract]
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense	$ 180
Tax cuts and jobs act of 2017, incomplete accounting, transition tax for accumulated foreign earnings, provisional income tax expense	1,468
Tax cuts and jobs act of 2017, incomplete accounting, transition tax for accumulated foreign earnings, provisional benefit	1,295
Tax cuts and jobs act of 2017, incomplete accounting, changes in tax rate and valuation allowance, deferred tax asset (liability), provisional income tax expense	$ 7
U.S. Federal statutory income tax rate, percentage	35.00%	35.00%	35.00%
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase, amount	$ 50	$ 11
Indefinitely reinvested foreign earnings	10,000			$ 10,000	$ 10,000
Accrued Income Taxes	39				$ 1,334
Tax cuts and jobs act of 2017, incomplete accounting, change in tax rate, deferred tax asset, provisional income tax expense (benefit)	1,295
Tax cuts and jobs act of 2017, incomplete accounting, change in tax rate, deferred tax liability, provisional income tax expense (benefit)	1,468
Income tax savings	$ 443	$ 310	$ 285
Benefit of tax rulings on net income per share (in usd per share)	$ 0.36	$ 0.25	$ 0.23
Unrecognized tax benefits that would impact effective tax rate, if realized	$ 406
Interest and penalties related to uncertain tax positions recognized in income tax expense	13
Interest and penalties accrued	75	$ 67
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	64
Tax credit carryforward	25
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	332
Tax credit carryforward	101
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	177
Foreign | Expiring In 2034
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 26