Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,219	$ 21,103
Other comprehensive income (loss) before reclassifications	253	474
Amounts reclassified into (out of) earnings	(18)	4
Ending balance	21,294	21,496
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,040)	(1,442)
Other comprehensive income (loss)	235	478
Ending balance	(1,805)	(964)
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	(70)	(68)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(70)	(68)
Ending balance	159	225
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	231	238
Amounts reclassified into (out of) earnings	(24)	3
Other comprehensive income (loss)	207	241
Ending balance	(79)	113
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	(14)	0
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(14)	0
Ending balance	81	(14)
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	1	1
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	1	1
Ending balance	(8)	(15)
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	(3)
Amounts reclassified into (out of) earnings	6	1
Other comprehensive income (loss)	6	(2)
Ending balance	(188)	(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	105	306
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	105	306
Ending balance	$ (1,770)	$ (1,088)