Regulation and Capital Adequacy - CET1, Tier 1 Capital and Tier 2 Capital (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 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	2,114	80
Change in Impact of CECL transition	819
Change in deduction for goodwill	1	(432)
Change in deduction for identifiable intangible assets	20	(307)
Change in other adjustments	(3,254)	2,393
CET 1, Ending balance	74,550	74,850
Tier 1 Capital, Beginning balance	85,440	83,702
Change in CET1	(300)	1,734
Change in deduction for investments in covered funds	453	5
Change in other adjustments	(4)	(1)
Tier 1 Capital, Ending balance	85,589	85,440
Tier 2 capital, Beginning balance	14,925	14,926
Change in qualifying subordinated debt	(27)	(300)
Change in junior subordinated debt	(96)	(158)
Change in allowance for credit losses	372	449
Change in other adjustments	(43)	8
Tier 2 Capital, Ending balance	15,131	14,925
Total capital	100,720	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	2,114	80
Change in Impact of CECL transition	819
Change in deduction for goodwill	1	(432)
Change in deduction for identifiable intangible assets	20	(307)
Change in other adjustments	(3,254)	2,393
CET 1, Ending balance	74,550	74,850
Tier 1 Capital, Beginning balance	85,440	83,702
Change in CET1	(300)	1,734
Change in deduction for investments in covered funds	453	5
Change in other adjustments	(4)	(1)
Tier 1 Capital, Ending balance	85,589	85,440
Tier 2 capital, Beginning balance	13,473	13,743
Change in qualifying subordinated debt	(27)	(300)
Change in junior subordinated debt	(96)	(158)
Change in allowance for credit losses	0
Change in other adjustments	120	188
Tier 2 Capital, Ending balance	13,470	13,473
Total capital	$ 99,059	$ 98,913