Shareholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,219	$ 21,103	$ 21,328
Other comprehensive income (loss)			(935)
Ending balance	22,317	21,219	21,103
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,040)	(1,442)	(507)
Other comprehensive income (loss) before reclassifications	1,029	(589)
Amounts reclassified into (out of) earnings	2	(9)
Other comprehensive income (loss)	1,031	(598)	(935)
Ending balance	(1,009)	(2,040)	(1,442)
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	(285)	(64)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(285)	(64)
Ending balance	(56)	229	293
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	412	(164)
Amounts reclassified into (out of) earnings	(23)	6
Other comprehensive income (loss)	389	(158)
Ending balance	103	(286)	(128)
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	(160)	109
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	(160)	109
Ending balance	(65)	95	(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	3	8
Amounts reclassified into (out of) earnings	0	(1)
Other comprehensive income (loss)	3	7
Ending balance	(6)	(9)	(16)
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	24	(11)
Other comprehensive income (loss)	24	(11)
Ending balance	(170)	(194)	(183)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,875)	(1,394)
Other comprehensive income (loss) before reclassifications	1,059	(478)
Amounts reclassified into (out of) earnings	1	(3)
Other comprehensive income (loss)	1,060	(481)
Ending balance	$ (815)	$ (1,875)	$ (1,394)