Shareholders' Equity - Accumulated Other Comprehensive Income/(Loss), Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 90,185	$ 82,243
Other comprehensive income/(loss) adjustments, net of tax	(2,177)	2,573	$ (664)
Ending balance	90,265	90,185	82,243
Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(621)	(625)	(647)
Other comprehensive income/(loss) adjustments, net of tax	5	4	22
Ending balance	(616)	(621)	(625)
Debt Valuation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,507	(1,046)	(239)
Other comprehensive income/(loss) adjustments, net of tax	(2,079)	2,553	(807)
Ending balance	(572)	1,507	(1,046)
Pension and Postretirement Liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(81)	(200)	(330)
Other comprehensive income/(loss) adjustments, net of tax	(261)	119	130
Ending balance	(342)	(81)	(200)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(112)	(9)
Other comprehensive income/(loss) adjustments, net of tax	158	(103)	(9)
Ending balance	46	(112)	(9)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	693	(1,880)	(1,216)
Other comprehensive income/(loss) adjustments, net of tax	(2,177)	2,573	(664)
Ending balance	$ (1,484)	$ 693	$ (1,880)