Accumulated Other Comprehensive Income - Reconciliation of Transactions Affecting Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Balance at beginning of period, Unrealized gains (losses) on securities available-for-sale	$ 679	$ 360
Changes in unrealized gains and losses, Unrealized gains (losses) on securities available-for-sale	(120)	306
Other-than-temporary impairment not recognized in earnings on securities available-for-sale, Unrealized gains (losses) on securities available-for-sale	6
Reclassification to earnings of realized gains and losses, Unrealized gains (losses) on securities available-for-sale	(5)
Applicable income taxes, Unrealized gains (losses) on securities available-for-sale	43	(116)
Balance at end of period, Unrealized gains (losses) on securities available-for-sale	603	550
Balance at beginning of period, Unrealized gains (losses) on securities transferred from available-for-sale to held-to-maturity	107
Reclassification to earnings of realized gains and losses, Unrealized gains (losses) on securities transferred from available-for-sale to held-to-maturity	(20)
Applicable income taxes, Unrealized gains (losses) on securities transferred from available-for-sale to held-to-maturity	7
Balance at end of period, Unrealized gains (losses) on securities transferred from available-for-sale to held-to-maturity	94
Balance at beginning of period, Unrealized gains (losses) on derivative hedges	(404)	(489)
Changes in unrealized gains and losses, Unrealized gains (losses) on derivative hedges	(3)	2
Reclassification to earnings of realized gains and losses, Unrealized gains (losses) on derivative hedges	54	53
Applicable income taxes, Unrealized gains (losses) on derivative hedges	(18)	(21)
Balance at end of period, Unrealized gains (losses) on derivative hedges	(371)	(455)
Balance at beginning of period, Unrealized gains (losses) on retirement plans	(1,265)	(1,022)
Changes in unrealized gains and losses, Unrealized gains (losses) on retirement plans	(1)
Reclassification to earnings of realized gains and losses, Unrealized gains (losses) on retirement plans	62	38
Applicable income taxes, Unrealized gains (losses) on retirement plans	(17)	(15)
Balance at end of period, Unrealized gains (losses) on retirement plans	(1,221)	(999)
Balance at beginning of period, Foreign currency translation	(40)	(49)
Foreign currency translation adjustment, Foreign currency translation	(10)	14
Applicable income taxes, Foreign currency translation	4	(5)
Balance at end of period, Foreign currency translation	(46)	(40)
Balance at beginning of period, Total	(923)	(1,200)
Changes in unrealized gains and losses, Total	(124)	308
Other-than-temporary impairment not recognized in earnings on securities available-for-sale, Total	6
Foreign currency translation adjustment, Total	(10)	14
Reclassification to earnings of realized gains and losses, Total	91	91
Applicable income taxes, Total	19	(157)
Balance at end of period, Total	$ (941)	$ (944)