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	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of securities				$ 8
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Interest income	$ 3,117	$ 3,057	$ 9,246	9,126
Gains (Losses) on derivative hedges	2,768	2,692	8,182	8,031
Actuarial gains (losses) and prior service cost (credit) amortization	(285)	(250)	(895)	(796)
Total securities gains (losses), net	(1)	(3)	(1)	2
Applicable income taxes	(534)	(523)	(1,541)	(1,566)
Net income	1,503	1,486	4,444	4,407
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(60)	(47)	(181)	(136)
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				8
Other-than-temporary impairment recognized in earnings	(1)	(3)	(1)	(6)
Total securities gains (losses), net	(1)	(3)	(1)	2
Applicable income taxes		1		(1)
Net income	(1)	(2)	(1)	1
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	6	7	20	23
Applicable income taxes	(2)	(3)	(7)	(9)
Net income	4	4	13	14
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	(48)	(45)	(147)	(139)
Applicable income taxes	19	17	57	53
Net income	(29)	(28)	(90)	(86)
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) and prior service cost (credit) amortization	(55)	(35)	(167)	(107)
Applicable income taxes	21	14	64	42
Net income	$ (34)	$ (21)	$ (103)	$ (65)