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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (562)	$ (865)	$ (1,019)	$ (896)
Changes in unrealized gains and losses	(105)	202	716	54
Changes in unrealized gains and losses	(74)	164	564	(7)
Changes in unrealized gains and losses	31	(38)	(152)	(61)
Other-than-temporary impairment not recognized in earnings on securities available-for-sale			(1)
Foreign currency translation adjustment	6	(28)	(30)	(3)
Reclassification to earnings of realized gains and losses	54	98	196	295
Applicable income taxes	(3)	(90)	(289)	(110)
Balance at end of period	(579)	(721)	(579)	(721)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(66)	(47)	(43)	(62)
Foreign currency translation adjustment	6	(28)	(30)	(3)
Applicable income taxes	(10)	11	3	1
Balance at end of period	(70)	(64)	(70)	(64)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,006)	(1,037)	(1,056)	(1,106)
Reclassification to earnings of realized gains and losses	41	55	122	167
Applicable income taxes	(16)	(21)	(47)	(64)
Balance at end of period	(981)	(1,003)	(981)	(1,003)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(133)	(125)	(67)	(172)
Changes in unrealized gains and losses	31	(38)	(152)	(61)
Reclassification to earnings of realized gains and losses	28	48	104	147
Applicable income taxes	(22)	(4)	19	(33)
Balance at end of period	(96)	(119)	(96)	(119)
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	31	43	36	52
Reclassification to earnings of realized gains and losses	(5)	(6)	(14)	(20)
Applicable income taxes	1	2	5	7
Balance at end of period	27	39	27	39
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	612	301	111	392
Changes in unrealized gains and losses	(105)	202	716	54
Other-than-temporary impairment not recognized in earnings on securities available-for-sale			(1)
Reclassification to earnings of realized gains and losses	(10)	1	(16)	1
Applicable income taxes	44	(78)	(269)	(21)
Balance at end of period	$ 541	$ 426	$ 541	$ 426