Shareholders' Equity - Accumulated Other Comprehensive Income/(Loss), Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 90,185
Other comprehensive income/(loss) adjustments, net of tax	$ 331	$ (881)	(1,177)	$ 41
Ending balance	92,012	86,762	92,012	86,762
Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(610)	(625)	(621)	(625)
Other comprehensive income/(loss) adjustments, net of tax	(9)	3	2	3
Ending balance	(619)	(628)	(619)	(628)
Debt Valuation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(221)	102	1,507	(1,046)
Other comprehensive income/(loss) adjustments, net of tax	278	(787)	(1,450)	361
Ending balance	57	(685)	57	(685)
Pension and Postretirement Liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(90)	(205)	(81)	(200)
Other comprehensive income/(loss) adjustments, net of tax	(5)	(1)	(14)	(6)
Ending balance	(95)	(206)	(95)	(206)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	106	(230)	(112)	(9)
Other comprehensive income/(loss) adjustments, net of tax	67	(90)	285	(311)
Ending balance	173	(320)	173	(320)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(815)	(958)	693	(1,880)
Other comprehensive income/(loss) adjustments, net of tax	331	(881)	(1,177)	41
Ending balance	$ (484)	$ (1,839)	$ (484)	$ (1,839)