Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 22,317	$ 21,219
Ending balance	24,553	22,497
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,009)	(2,040)
Other comprehensive income (loss) before reclassifications	(719)	1,069
Amounts reclassified into (out of) earnings	17	(13)
Other comprehensive income (loss)	(702)	1,056
Ending balance	(1,711)	(984)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(56)	229
Other comprehensive income (loss) before reclassifications	(27)	(274)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(27)	(274)
Ending balance	(83)	(45)
Net Unrealized Gains (Losses) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	103	(286)
Other comprehensive income (loss) before reclassifications	(452)	555
Amounts reclassified into (out of) earnings	6	(23)
Other comprehensive income (loss)	(446)	532
Ending balance	(343)	246
Net Unrealized Losses on Hedges of Net Investments in Non-U.S. Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(65)	95
Other comprehensive income (loss) before reclassifications	54	(147)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	54	(147)
Ending balance	(11)	(52)
Other-Than-Temporary Impairment on Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(6)	(9)
Other comprehensive income (loss) before reclassifications	4	3
Amounts reclassified into (out of) earnings	(3)	0
Other comprehensive income (loss)	1	3
Ending balance	(5)	(6)
Net Unrealized Losses on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(170)	(194)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified into (out of) earnings	14	10
Other comprehensive income (loss)	14	10
Ending balance	(156)	(184)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(815)	(1,875)
Other comprehensive income (loss) before reclassifications	(298)	932
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(298)	932
Ending balance	$ (1,113)	$ (943)