Regulation and Capital Adequacy - Risk-weighted Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	$ 420,933	$ 420,118
Market RWAs	92,087	103,989
Total RWAs	513,020	524,107	$ 619,216
Standardized Capital Rules [Member] | Derivatives [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	126,732	136,841
Standardized Capital Rules [Member] | Commitments Guarantees and Loans [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	116,966	111,391
Standardized Capital Rules [Member] | Securities Financing Transactions [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	78,050	71,392
Standardized Capital Rules [Member] | Equity Investments [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	40,423	37,687
Standardized Capital Rules [Member] | Other [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	58,762	62,807
Standardized Capital Rules [Member] | Regulatory VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	9,525	12,000
Standardized Capital Rules [Member] | Stressed VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	24,925	21,738
Standardized Capital Rules [Member] | Incremental Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	9,188	9,513
Standardized Capital Rules [Member] | Comprehensive Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	5,638	5,725
Standardized Capital Rules [Member] | Specific Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	42,811	55,013
Basel III Advanced Transitional [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	362,609	344,082
Market RWAs	91,262	102,981
Total Operational RWAs	126,125	130,588
Total RWAs	579,996	577,651	$ 570,313
Basel III Advanced Transitional [Member] | Derivatives [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	123,920	113,671
Basel III Advanced Transitional [Member] | Commitments Guarantees and Loans [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	116,582	114,523
Basel III Advanced Transitional [Member] | Securities Financing Transactions [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	16,863	14,901
Basel III Advanced Transitional [Member] | Equity Investments [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	42,961	40,110
Basel III Advanced Transitional [Member] | Other [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Credit RWAs	62,283	60,877
Basel III Advanced Transitional [Member] | Regulatory VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	9,525	12,000
Basel III Advanced Transitional [Member] | Stressed VaR [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	24,925	21,738
Basel III Advanced Transitional [Member] | Incremental Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	9,188	9,513
Basel III Advanced Transitional [Member] | Comprehensive Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	4,813	4,717
Basel III Advanced Transitional [Member] | Specific Risk [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Market RWAs	$ 42,811	$ 55,013