Income Taxes - Results from Non-U.S. Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Income Tax Expense (Benefit) [Line Items]
U.S.	$ 23,191	$ 23,422	$ 17,990
Non-U.S.	7,511	7,277	8,685
Income before income tax expense	30,702	30,699	$ 26,675
Pretax earnings to be reinvested in subsidiaries	3,500
Cumulative amount of undistributed pretax earnings	34,600
Deferred tax liability from undistributed earnings, if recorded	$ 4,285	$ 4,444
UNITED KINGDOM
Components of Income Tax Expense (Benefit) [Line Items]
Statutory foreign tax rate	20.25%
Pro Forma
Components of Income Tax Expense (Benefit) [Line Items]
Deferred tax liability from undistributed earnings, if recorded	$ 8,200