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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains (losses) on sale of securities	$ 9	$ 4	$ 38	$ 7
Amortization of unrealized gains on securities transferred from available-for-sale to held-to-maturity, Interest income	3,531	3,252	6,931	6,473
Realized gains (losses) on derivative hedges	(514)	(407)	(969)	(793)
Actuarial gains (losses) and prior service cost (credit) amortization	(287)	(278)	(601)	(578)
Total securities gains (losses), net	9	3	38	6
Applicable income taxes	(551)	(542)	(1,050)	(1,046)
Net income	1,512	1,536	2,998	2,937
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(16)	(41)	(23)	(88)
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	9	4	38	7
Other-than-temporary impairment recognized in earnings		(1)		(1)
Total securities gains (losses), net	9	3	38	6
Applicable income taxes	(3)	(1)	(14)	(2)
Net income	6	2	24	4
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	4	4	7	9
Applicable income taxes	(2)	(2)	(3)	(4)
Net income	2	2	4	5
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]
Realized gains (losses) on derivative hedges	(10)	(33)	(24)	(76)
Applicable income taxes	4	13	9	29
Net income	(6)	(20)	(15)	(47)
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	(29)	(40)	(58)	(81)
Applicable income taxes	11	15	22	31
Net income	$ (18)	$ (25)	$ (36)	$ (50)