Regulation and Capital Adequacy - Changes in Risk-weighted Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk-Weighted Assets, Beginning balance	$ 547,910	$ 555,611
Change in deduction due to transitional provisions		7,766
Change in Credit RWAs	25,649	5,108
Change in Market RWAs	(9,984)	(12,809)
Change in operational risk	0
Risk-Weighted Assets, end of period	563,575	547,910
Standardized Capital Rules [Member] | Derivatives [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	(1,605)	(3,565)
Standardized Capital Rules [Member] | Commitments Guarantees and Loans [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	19,435	15,201
Standardized Capital Rules [Member] | Securities Financing Transactions [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	(496)	(11,599)
Standardized Capital Rules [Member] | Equity Investments [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	3,251	(2,241)
Standardized Capital Rules [Member] | Other [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	5,064	(454)
Standardized Capital Rules [Member] | Regulatory VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	1,151	250
Standardized Capital Rules [Member] | Stressed VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	2,959	(4,801)
Standardized Capital Rules [Member] | Incremental Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	(6,161)	2,028
Standardized Capital Rules [Member] | Comprehensive Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	(1,377)	373
Standardized Capital Rules [Member] | Specific Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	(6,556)	(10,659)
Advanced Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Risk-Weighted Assets, Beginning balance	558,111	617,646
Change in deduction due to transitional provisions		8,232
Change in Credit RWAs	(7,672)	(44,566)
Change in Market RWAs	(10,186)	(12,282)
Change in operational risk	4,400	(2,687)
Risk-Weighted Assets, end of period	544,653	558,111
Advanced Capital [Member] | Derivatives [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	(9,670)	(20,685)
Advanced Capital [Member] | Commitments Guarantees and Loans [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	(8,900)	(20,019)
Advanced Capital [Member] | Securities Financing Transactions [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	(4,425)	(1,103)
Advanced Capital [Member] | Equity Investments [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	6,738	(4,580)
Advanced Capital [Member] | Other [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Credit RWAs	8,585	(6,411)
Advanced Capital [Member] | Regulatory VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	1,151	250
Advanced Capital [Member] | Stressed VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	2,959	(4,801)
Advanced Capital [Member] | Incremental Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	(6,161)	2,028
Advanced Capital [Member] | Comprehensive Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	(1,579)	900
Advanced Capital [Member] | Specific Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Change in Market RWAs	$ (6,556)	$ (10,659)