Variable interest entities - Firm Sponsored Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Firm-sponsored mortgage and other consumer securitization trusts
Total assets held by securitization VIEs	$ 239,500	$ 254,300
Retained securitization interests, risk-rated 'A' or better, at fair value	76.00%	77.00%
Corporate & Investment Bank
Firm-sponsored mortgage and other consumer securitization trusts
Senior securities purchased in connection with CIB's secondary market-making activities	$ 132	$ 136
Subordinated securities purchased in connection with CIB's secondary market-making activities	64	34
Residential mortgage | Prime / Alt-A & Option ARMs
Firm-sponsored mortgage and other consumer securitization trusts
Total assets held by securitization VIEs	88,700	96,300
Residential mortgage | Subprime
Firm-sponsored mortgage and other consumer securitization trusts
Total assets held by securitization VIEs	25,200	28,400
Residential mortgage | Investment-grade
Firm-sponsored mortgage and other consumer securitization trusts
Fair value of retained interests	2,100	1,100
Residential mortgage | Noninvestment-grade
Firm-sponsored mortgage and other consumer securitization trusts
Fair value of retained interests	115	185
Commercial and other
Firm-sponsored mortgage and other consumer securitization trusts
Total assets held by securitization VIEs	125,600	129,600
Commercial and other | Investment-grade
Firm-sponsored mortgage and other consumer securitization trusts
Fair value of retained interests	3,800	3,700
Commercial and other | Noninvestment-grade
Firm-sponsored mortgage and other consumer securitization trusts
Fair value of retained interests	239	194
VIEs consolidated by the Firm
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in consolidated securitization VIEs	1,800	3,700
VIEs consolidated by the Firm | Residential mortgage | Prime / Alt-A & Option ARMs
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in consolidated securitization VIEs	1,500	2,700
VIEs consolidated by the Firm | Residential mortgage | Subprime
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in consolidated securitization VIEs	100	800
VIEs consolidated by the Firm | Commercial and other
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in consolidated securitization VIEs	200	200
Not Primary Beneficiary
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in nonconsolidated securitization VIEs with continuing involvement	184,448	198,391
Interest in securitized assets in nonconsolidated VIEs	6,400	5,200
Not Primary Beneficiary | Loans reported as trading assets
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	1,100	1,000
Not Primary Beneficiary | AFS securities
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	5,300	4,200
Not Primary Beneficiary | Residential mortgage | Prime / Alt-A & Option ARMs
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in nonconsolidated securitization VIEs with continuing involvement	73,779	78,294
Interest in securitized assets in nonconsolidated VIEs	2,200	1,200
Not Primary Beneficiary | Residential mortgage | Subprime
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in nonconsolidated securitization VIEs with continuing involvement	23,300	25,659
Interest in securitized assets in nonconsolidated VIEs	100	100
Not Primary Beneficiary | Residential mortgage | Loans reported as trading assets | Prime / Alt-A & Option ARMs
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	500	500
Not Primary Beneficiary | Residential mortgage | Loans reported as trading assets | Subprime
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	100	100
Not Primary Beneficiary | Residential mortgage | AFS securities | Prime / Alt-A & Option ARMs
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	1,700	700
Not Primary Beneficiary | Residential mortgage | AFS securities | Subprime
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	0	0
Not Primary Beneficiary | Commercial and other
Firm-sponsored mortgage and other consumer securitization trusts
Assets held in nonconsolidated securitization VIEs with continuing involvement	87,369	94,438
Interest in securitized assets in nonconsolidated VIEs	4,100	3,900
Not Primary Beneficiary | Commercial and other | Loans reported as trading assets
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	500	400
Not Primary Beneficiary | Commercial and other | AFS securities
Firm-sponsored mortgage and other consumer securitization trusts
Interest in securitized assets in nonconsolidated VIEs	$ 3,600	$ 3,500