Regulation and Capital Adequacy - CET1, Tier 1 Capital and Tier 2 Capital (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET 1, Beginning balance	$ 74,850	$ 73,116
Change in common shareholders' equity	2,385	80
Change in Impact of CECL transition	1,100
Change in deduction for goodwill	(115)	(432)
Change in deduction for identifiable intangible assets	5	(307)
Change in other adjustments	(722)	2,393
CET 1, Ending balance	77,503	74,850
Tier 1 Capital, Beginning balance	85,440	83,702
Change in CET1	2,653	1,734
Change in deduction for investments in covered funds	481	5
Change in other adjustments	(8)	(1)
Tier 1 Capital, Ending balance	88,566	85,440
Tier 2 capital, Beginning balance	14,925	14,926
Change in qualifying subordinated debt	25	(300)
Change in junior subordinated debt	(96)	(158)
Risk-based capital change in allowance for losses	1,217	449
Change in other adjustments	(53)	8
Tier 2 Capital, Ending balance	16,018	14,925
Total capital	104,584	100,365
Advanced Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET 1, Beginning balance	74,850	73,116
Change in common shareholders' equity	2,385	80
Change in Impact of CECL transition	1,100
Change in deduction for goodwill	(115)	(432)
Change in deduction for identifiable intangible assets	5	(307)
Change in other adjustments	(722)	2,393
CET 1, Ending balance	77,503	74,850
Tier 1 Capital, Beginning balance	85,440	83,702
Change in CET1	2,653	1,734
Change in deduction for investments in covered funds	481	5
Change in other adjustments	(8)	(1)
Tier 1 Capital, Ending balance	88,566	85,440
Tier 2 capital, Beginning balance	13,473	13,743
Change in qualifying subordinated debt	25	(300)
Change in junior subordinated debt	(96)	(158)
Change in other adjustments	665	188
Tier 2 Capital, Ending balance	14,067	13,473
Total capital	$ 102,633	$ 98,913