Income Taxes - Results from Non-U.S. Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of Income Tax Expense (Benefit) [Line Items]
U.S.	$ 26,651	$ 23,191	$ 23,422
Non-U.S.	7,885	7,511	7,277
Income before income tax expense	34,536	30,702	$ 30,699
Pretax earnings to be reinvested in subsidiaries	3,800
Cumulative amount of undistributed pretax earnings	38,400
Deferred tax liability from undistributed earnings, if recorded	$ 4,572	$ 4,285
UNITED KINGDOM
Components of Income Tax Expense (Benefit) [Line Items]
Statutory foreign tax rate	28.00%
Pro Forma
Components of Income Tax Expense (Benefit) [Line Items]
Deferred tax liability from undistributed earnings, if recorded	$ 8,800