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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (865)	$ (682)	$ (896)	$ (1,071)
Changes in unrealized gains and losses	202	(21)	54	486
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(38)	16	(61)	(19)
Changes in unrealized gains and losses	164	(5)	(7)	467
Other-than-temporary impairment not recognized in earnings on securities available-for-sale				1
Foreign currency translation adjustment	(28)	4	(3)	18
Reclassification to earnings of realized gains and losses	98	76	295	221
Applicable income taxes	(90)	(29)	(110)	(272)
Balance at end of period	(721)	(636)	(721)	(636)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(47)	(51)	(62)	(60)
Foreign currency translation adjustment	(28)	4	(3)	18
Applicable income taxes	11	(2)	1	(7)
Balance at end of period	(64)	(49)	(64)	(49)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,037)	(699)	(1,106)	(743)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Retirement Plans	0	0	0	0
Reclassification to earnings of realized gains and losses	55	35	167	107
Applicable income taxes	(21)	(14)	(64)	(42)
Balance at end of period	(1,003)	(678)	(1,003)	(678)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(125)	(225)	(172)	(261)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(38)	16	(61)	(19)
Reclassification to earnings of realized gains and losses	48	45	147	139
Applicable income taxes	(4)	(23)	(33)	(46)
Balance at end of period	(119)	(187)	(119)	(187)
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	43	60	52	70
Reclassification to earnings of realized gains and losses	(6)	(7)	(20)	(23)
Applicable income taxes	2	3	7	9
Balance at end of period	39	56	39	56
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	301	233	392	(77)
Changes in unrealized gains and losses	202	(21)	54	486
Other-than-temporary impairment not recognized in earnings on securities available-for-sale				1
Reclassification to earnings of realized gains and losses	1	3	1	(2)
Applicable income taxes	(78)	7	(21)	(186)
Balance at end of period	$ 426	$ 222	$ 426	$ 222