Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 22,317	$ 21,219
Ending balance	22,571	22,068
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	(496)	785
Amounts reclassified into (out of) earnings	17	(15)
Other comprehensive income (loss)	(479)	770
Ending balance	(1,488)	(1,270)
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	(57)	(247)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(57)	(247)
Ending balance	(113)	(18)
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	(254)	505
Amounts reclassified into (out of) earnings	6	(24)
Other comprehensive income (loss)	(248)	481
Ending balance	(145)	195
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	35	(101)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	35	(101)
Ending balance	(30)	(6)
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	1	2
Amounts reclassified into (out of) earnings	(2)	0
Other comprehensive income (loss)	(1)	2
Ending balance	(7)	(7)
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	1	(1)
Amounts reclassified into (out of) earnings	13	9
Other comprehensive income (loss)	14	8
Ending balance	(156)	(186)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(815)	(1,875)
Other comprehensive income (loss) before reclassifications	(222)	627
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(222)	627
Ending balance	$ (1,037)	$ (1,248)