Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,219	$ 21,103
Ending balance	22,497	22,150
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	1,069	445
Amounts reclassified into (out of) earnings	(13)	4
Other comprehensive income (loss)	1,056	449
Ending balance	(984)	(993)
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	(274)	(213)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(274)	(213)
Ending balance	(45)	80
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	555	520
Amounts reclassified into (out of) earnings	(23)	4
Other comprehensive income (loss)	532	524
Ending balance	246	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	(147)	55
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(147)	55
Ending balance	(52)	41
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	3	6
Amounts reclassified into (out of) earnings	0	(1)
Other comprehensive income (loss)	3	5
Ending balance	(6)	(11)
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	0	0
Amounts reclassified into (out of) earnings	10	1
Other comprehensive income (loss)	10	1
Ending balance	(184)	(182)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,875)	(1,394)
Other comprehensive income (loss) before reclassifications	932	77
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	932	77
Ending balance	$ (943)	$ (1,317)