Stockholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,103	$ 21,328
Other comprehensive income (loss)	449	(594)
Ending balance	22,150	21,343
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,442)	(507)
Other comprehensive income (loss) before reclassifications	445	(611)
Amounts reclassified into (out of) earnings	4	17
Other comprehensive income (loss)	449	(594)
Ending balance	(993)	(1,101)
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	293	276
Other comprehensive income (loss) before reclassifications	(213)	44
Amounts reclassified into (out of) earnings	0	2
Other comprehensive income (loss)	(213)	46
Ending balance	80	322
Net Unrealized Gains (Losses) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(128)	192
Other comprehensive income (loss) before reclassifications	520	(112)
Amounts reclassified into (out of) earnings	4	(3)
Other comprehensive income (loss)	524	(115)
Ending balance	396	77
Net Unrealized Losses on Hedges of Net Investments in Non-U.S. Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14)	(14)
Other comprehensive income (loss) before reclassifications	55	0
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	55	0
Ending balance	41	(14)
Other-Than-Temporary Impairment on Held-to-Maturity Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(16)	(29)
Other comprehensive income (loss) before reclassifications	6	12
Amounts reclassified into (out of) earnings	(1)	(1)
Other comprehensive income (loss)	5	11
Ending balance	(11)	(18)
Net Unrealized Losses on Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(183)	(272)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified into (out of) earnings	1	19
Other comprehensive income (loss)	1	19
Ending balance	(182)	(253)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,394)	(660)
Other comprehensive income (loss) before reclassifications	77	(555)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	77	(555)
Ending balance	$ (1,317)	$ (1,215)