Accumulated Other Comprehensive Income (Loss) - Impact to Consolidated Statement of Income for Items Reclassified Out of Accumulated Other Comprehensive Income and into Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of securities		$ 16	$ 21	$ 46
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Interest income	3,068	3,227	9,217	9,687
Gains (Losses) on derivative hedges	2,658	2,726	7,927	8,018
Actuarial gains (losses), prior service cost (credit) and transition obligation (asset) amortization	(278)	(225)	(865)	(714)
Total securities gains (losses), net	(3)	1	8	(18)
Applicable income taxes	(542)	(593)	(1,629)	(1,684)
Net income	1,430	1,432	4,261	4,115
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(61)		(165)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available-For-Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of securities			21
Other-than-temporary impairment recognized in earnings	(3)		(13)
Total securities gains (losses), net	(3)		8
Applicable income taxes	1		(3)
Net income	(2)		5
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Transferred From Available For Sale to Held To Maturity [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Interest income	13		50
Applicable income taxes	(5)		(19)
Net income	8		31
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (Losses) on derivative hedges	(47)		(142)
Applicable income taxes	18		55
Net income	(29)		(87)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Retirement Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains (losses), prior service cost (credit) and transition obligation (asset) amortization	(62)		(186)
Applicable income taxes	24		72
Net income	$ (38)		$ (114)