Accumulated Other Comprehensive Income (Loss) - Impact to Net Income for Items Reclassified out of Accumulated Other Comprehensive Income and into Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of securities		$ 5
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Interest income	3,061	3,022
Gains (Losses) on derivative hedges	2,698	2,650
Actuarial gains (losses), prior service cost (credit) and transition obligation (asset) amortization	(317)	(289)
Applicable income taxes	(479)	(496)
Net income	1,444	1,412
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(61)	(45)
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		5
Applicable income taxes		(2)
Net income		3
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	7	7
Applicable income taxes	(3)	(3)
Net income	4	4
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	(50)	(49)
Applicable income taxes	19	19
Net income	(31)	(30)
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	(56)	(36)
Applicable income taxes	22	14
Net income	$ (34)	$ (22)