Shareholders' Equity - Accumulated Other Comprehensive Income/(Loss), Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 90,265
Other comprehensive income/(loss) adjustments, net of tax	$ (294)	$ 331	849	$ (1,177)
Ending balance	92,650	92,012	92,650	92,012
Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(677)	(610)	(616)	(621)
Other comprehensive income/(loss) adjustments, net of tax	(13)	(9)	(74)	2
Ending balance	(690)	(619)	(690)	(619)
Debt Valuation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	124	(221)	(572)	1,507
Other comprehensive income/(loss) adjustments, net of tax	(268)	278	428	(1,450)
Ending balance	(144)	57	(144)	57
Pension and Postretirement Liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(339)	(90)	(342)	(81)
Other comprehensive income/(loss) adjustments, net of tax	(2)	(5)	1	(14)
Ending balance	(341)	(95)	(341)	(95)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	551	106	46	(112)
Other comprehensive income/(loss) adjustments, net of tax	(11)	67	494	285
Ending balance	540	173	540	173
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(341)	(815)	(1,484)	693
Other comprehensive income/(loss) adjustments, net of tax	(294)	331	849	(1,177)
Ending balance	$ (635)	$ (484)	$ (635)	$ (484)