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, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (1,535)	$ (1,019)
Changes in unrealized gains and losses	127	488
Changes in unrealized gains and losses	7	(96)
Changes in unrealized gains and losses	134	392
Other-than-temporary impairment not recognized in earnings on securities available-for-sale		(2)
Foreign currency translation adjustment	10	(16)
Reclassification to earnings of realized gains and losses	11	76
Applicable income taxes	(59)	(175)
Balance at end of period	(1,439)	(744)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(71)	(43)
Foreign currency translation adjustment	10	(16)
Applicable income taxes	(3)	5
Balance at end of period	(64)	(54)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,113)	(1,056)
Changes in unrealized gains and losses	0	0
Reclassification to earnings of realized gains and losses	29	41
Applicable income taxes	(11)	(16)
Balance at end of period	(1,095)	(1,031)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	55	(67)
Changes in unrealized gains and losses	7	(96)
Reclassification to earnings of realized gains and losses	14	43
Applicable income taxes	(8)	21
Balance at end of period	68	(99)
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	25	36
Reclassification to earnings of realized gains and losses	(3)	(5)
Applicable income taxes	1	2
Balance at end of period	23	33
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(431)	111
Changes in unrealized gains and losses	127	488
Other-than-temporary impairment not recognized in earnings on securities available-for-sale		(2)
Reclassification to earnings of realized gains and losses	(29)	(3)
Applicable income taxes	(38)	(187)
Balance at end of period	$ (371)	$ 407