Accumulated Other Comprehensive Income (Loss) - Reconciliation of Transactions Affecting Accumulated Other Comprehensive Income (Loss) Included in Shareholders' Equity (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (1,019)	$ (896)
Changes in unrealized gains and losses	488	208
Changes in unrealized gains and losses	392	180
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(96)	(28)
Other-than-temporary impairment not recognized in earnings on securities available-for-sale	(2)
Foreign currency translation adjustment	(16)	17
Reclassification to earnings of realized gains and losses	76	99
Applicable income taxes	(175)	(114)
Balance at end of period	(744)	(714)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(43)	(62)
Foreign currency translation adjustment	(16)	17
Applicable income taxes	5	(7)
Balance at end of period	(54)	(52)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,056)	(1,106)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Retirement Plans	0	0
Reclassification to earnings of realized gains and losses	41	56
Applicable income taxes	(16)	(22)
Balance at end of period	(1,031)	(1,072)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(67)	(172)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(96)	(28)
Reclassification to earnings of realized gains and losses	43	50
Applicable income taxes	21	(8)
Balance at end of period	(99)	(158)
Unrealized Gains (Losses) on Securities Transferred From Available For Sale to Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	36	52
Reclassification to earnings of realized gains and losses	(5)	(7)
Applicable income taxes	2	3
Balance at end of period	33	48
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	111	392
Changes in unrealized gains and losses	488	208
Other-than-temporary impairment not recognized in earnings on securities available-for-sale	(2)
Reclassification to earnings of realized gains and losses	(3)
Applicable income taxes	(187)	(80)
Balance at end of period	$ 407	$ 520