v3.21.2
Regulation and Capital Adequacy - CET1, Tier 1 Capital and Tier 2 Capital (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]          
Change in allowance for credit losses $ (72) $ 62 $ 266 $ (2,530)  
Standardized Capital Rules [Member]          
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]          
CET 1, Beginning balance     81,641 74,850 $ 74,850
Change in Impact of CECL transition     (67)   1,126
Change in common shareholders' equity     11,615   5,667
Change in deduction for goodwill         (123)
Change in deduction for identifiable intangible assets     123   3
Change in other adjustments     (20)   118
CET 1, Ending balance 93,292   93,292   81,641
Tier 1 Capital, Beginning balance     92,730 85,440 85,440
Change in CET1     11,651   6,791
Change in deduction for investments in covered funds     (556)   504
Change in preferred stock     (1,250)    
Change in other adjustments     5   (5)
Tier 1 Capital, Ending balance 102,580   102,580   92,730
Tier 2 capital, Beginning balance     15,424 14,925 14,925
Change in qualifying subordinated debt     (152)   (651)
Change in junior subordinated debt     (94)   (96)
Change in allowance for credit losses     (199)   1,293
Change in other adjustments     3   (47)
Tier 2 Capital, Ending balance 14,982   14,982   15,424
Total capital 117,562   117,562   108,154
Advanced Capital Rules [Member]          
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]          
CET 1, Beginning balance     81,641 74,850 74,850
Change in Impact of CECL transition     (67)   1,126
Change in common shareholders' equity     11,615   5,667
Change in deduction for goodwill         (123)
Change in deduction for identifiable intangible assets     123   3
Change in other adjustments     (20)   118
CET 1, Ending balance 93,292   93,292   81,641
Tier 1 Capital, Beginning balance     92,730 85,440 85,440
Change in CET1     11,651   6,791
Change in deduction for investments in covered funds     (556)   504
Change in preferred stock     (1,250)    
Change in other adjustments     5   (5)
Tier 1 Capital, Ending balance 102,580   102,580   92,730
Tier 2 capital, Beginning balance     13,279 $ 13,473 13,473
Change in qualifying subordinated debt     (152)   (651)
Change in junior subordinated debt     (94)   (96)
Change in other adjustments     (408)   553
Tier 2 Capital, Ending balance 12,625   12,625   13,279
Total capital $ 115,205   $ 115,205   $ 106,009