Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,219	$ 21,103
Ending balance	22,068	22,073
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,040)	(1,442)
Other comprehensive income (loss) before reclassifications	785	442
Amounts reclassified into (out of) earnings	(15)	3
Other comprehensive income (loss)	770	445
Ending balance	(1,270)	(997)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	229	293
Other comprehensive income (loss) before reclassifications	(247)	(174)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(247)	(174)
Ending balance	(18)	119
Net Unrealized Gains (Losses) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(286)	(128)
Other comprehensive income (loss) before reclassifications	505	522
Amounts reclassified into (out of) earnings	(24)	2
Other comprehensive income (loss)	481	524
Ending balance	195	396
Net Unrealized Losses on Hedges of Net Investments in Non-U.S. Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	95	(14)
Other comprehensive income (loss) before reclassifications	(101)	51
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(101)	51
Ending balance	(6)	37
Other-Than-Temporary Impairment on Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9)	(16)
Other comprehensive income (loss) before reclassifications	2	4
Amounts reclassified into (out of) earnings	0	(1)
Other comprehensive income (loss)	2	3
Ending balance	(7)	(13)
Net Unrealized Losses on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(194)	(183)
Other comprehensive income (loss) before reclassifications	(1)	(4)
Amounts reclassified into (out of) earnings	9	2
Other comprehensive income (loss)	8	(2)
Ending balance	(186)	(185)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,875)	(1,394)
Other comprehensive income (loss) before reclassifications	627	43
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	627	43
Ending balance	$ (1,248)	$ (1,351)