Regulation and Capital Adequacy - Consolidated Regulatory Capital Ratios (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock	$ 11,203	$ 11,200
Tier 1 leverage ratio	9.30%	9.30%
Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common shareholders' equity	$ 75,907	$ 75,528
Deductions for goodwill and identifiable intangible assets, net of deferred tax liabilities	(2,879)	(2,814)
Deductions for investments in nonconsolidated financial institutions	(650)	(864)
Other adjustments	(681)	(487)
Total Common Equity Tier 1	71,697	71,363	$ 69,830
Preferred stock	11,203	11,200
Junior subordinated debt issued to trusts		330
Deduction for investments in covered funds	(587)	(413)
Other adjustments	(569)	(969)
Tier 1 capital	81,744	81,511	78,433
Qualifying subordinated debt	14,808	15,132
Junior subordinated debt issued to trusts	792	990
Allowance for losses on loans and lending commitments	699	602
Other adjustments	(4)	(19)
Tier 2 capital	16,295	16,705	12,861
Total capital	98,039	98,216
RWAs	$ 513,020	$ 524,107	619,216
CET1 ratio	14.00%	13.60%
Tier 1 capital ratio	15.90%	15.60%
Total capital ratio	19.10%	18.70%
Basel III Advanced Transitional [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Common Equity Tier 1	$ 71,697	$ 71,363	69,830
Tier 1 capital	81,744	81,511	78,433
Allowance for losses on loans and lending commitments	(699)	(602)
Tier 2 capital	15,596	16,103	12,545
Total capital	97,340	97,614
Standardized Tier 2 capital	16,295	16,705
RWAs	$ 579,996	$ 577,651	$ 570,313
CET1 ratio	12.40%	12.40%
Tier 1 capital ratio	14.10%	14.10%
Total capital ratio	16.80%	16.90%