Stockholders' Equity - Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 21,103	$ 21,328
Other comprehensive income (loss) before reclassifications	474	(504)
Amounts reclassified into (out of) earnings	4	5
Other comprehensive income (loss)	478	(499)
Ending balance	21,496	20,670
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,442)	(507)
Other comprehensive income (loss)	478	(499)
Ending balance	(964)	(1,006)
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	(68)	11
Amounts reclassified into (out of) earnings	0	1
Other comprehensive income (loss)	(68)	12
Ending balance	225	288
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	238	179
Amounts reclassified into (out of) earnings	3	0
Other comprehensive income (loss)	241	179
Ending balance	113	371
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	0	0
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	0	0
Ending balance	(14)	(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	1	5
Amounts reclassified into (out of) earnings	0	(1)
Other comprehensive income (loss)	1	4
Ending balance	(15)	(25)
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	(3)	0
Amounts reclassified into (out of) earnings	1	5
Other comprehensive income (loss)	(2)	5
Ending balance	(185)	(267)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,394)	(660)
Other comprehensive income (loss) before reclassifications	306	(699)
Amounts reclassified into (out of) earnings	0	0
Other comprehensive income (loss)	306	(699)
Ending balance	$ (1,088)	$ (1,359)