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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (714)	$ (850)	$ (896)	$ (1,071)
Changes in unrealized gains and losses	(356)	206	(148)	507
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	5	(24)	(23)	(35)
Changes in unrealized gains and losses	(351)	182	(171)	472
Other-than-temporary impairment not recognized in earnings on securities available-for-sale		1		1
Foreign currency translation adjustment	8	18	25	14
Reclassification to earnings of realized gains and losses	98	72	197	145
Applicable income taxes	94	(105)	(20)	(243)
Balance at end of period	(865)	(682)	(865)	(682)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(52)	(63)	(62)	(60)
Foreign currency translation adjustment	8	18	25	14
Applicable income taxes	(3)	(6)	(10)	(5)
Balance at end of period	(47)	(51)	(47)	(51)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,072)	(721)	(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	56	36	112	72
Applicable income taxes	(21)	(14)	(43)	(28)
Balance at end of period	(1,037)	(699)	(1,037)	(699)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(158)	(238)	(172)	(261)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	5	(24)	(23)	(35)
Reclassification to earnings of realized gains and losses	49	45	99	94
Applicable income taxes	(21)	(8)	(29)	(23)
Balance at end of period	(125)	(225)	(125)	(225)
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	48	66	52	70
Reclassification to earnings of realized gains and losses	(7)	(9)	(14)	(16)
Applicable income taxes	2	3	5	6
Balance at end of period	43	60	43	60
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	520	106	392	(77)
Changes in unrealized gains and losses	(356)	206	(148)	507
Other-than-temporary impairment not recognized in earnings on securities available-for-sale		1		1
Reclassification to earnings of realized gains and losses				(5)
Applicable income taxes	137	(80)	57	(193)
Balance at end of period	$ 301	$ 233	$ 301	$ 233