Accumulated Other Comprehensive Income (Loss) - Reconciliation of Transactions Affecting Accumulated Other Comprehensive Income (Loss) Included in Shareholders' Equity (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (896)	$ (1,071)
Changes in unrealized gains and losses	208	301
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(28)	(11)
Changes in unrealized gains and losses	180	290
Foreign currency translation adjustment	17	(4)
Reclassification to earnings of realized gains and losses	99	73
Applicable income taxes	(114)	(138)
Balance at end of period	(714)	(850)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(62)	(60)
Foreign currency translation adjustment	17	(4)
Applicable income taxes	(7)	1
Balance at end of period	(52)	(63)
Unrealized Gains (Losses) on Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,106)	(743)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Retirement Plans	0	0
Reclassification to earnings of realized gains and losses	56	36
Applicable income taxes	(22)	(14)
Balance at end of period	(1,072)	(721)
Unrealized Gains (Losses) on Derivative Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(172)	(261)
Changes in unrealized gains and losses, Unrealized Gains (Losses) on Derivative Hedges	(28)	(11)
Reclassification to earnings of realized gains and losses	50	49
Applicable income taxes	(8)	(15)
Balance at end of period	(158)	(238)
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	52	70
Reclassification to earnings of realized gains and losses	(7)	(7)
Applicable income taxes	3	3
Balance at end of period	48	66
Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	392	(77)
Changes in unrealized gains and losses	208	301
Reclassification to earnings of realized gains and losses		(5)
Applicable income taxes	(80)	(113)
Balance at end of period	$ 520	$ 106