Variable interest entities and securitization - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Nonredeemable noncontrolling interests	$ 251	$ 102
VME classification of carrying amount, assets	226	50
VME classification of carrying amount, liabilities	1	1
Noncontrolling interest in VME	31	1
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Trading assets	979	629
Other assets	9	16
Total assets	988	645
Other liabilities	404	388
Total liabilities	404	388
Nonredeemable noncontrolling interests	251	102
Variable Interest Entity, Primary Beneficiary | Investment Management funds
Variable Interest Entity [Line Items]
Trading assets	579	229
Other assets	9	16
Total assets	588	245
Other liabilities	4	1
Total liabilities	4	1
Nonredeemable noncontrolling interests	251	102
Variable Interest Entity, Primary Beneficiary | Securitization
Variable Interest Entity [Line Items]
Trading assets	400	400
Other assets	0	0
Total assets	400	400
Other liabilities	400	387
Total liabilities	400	387
Nonredeemable noncontrolling interests	$ 0	$ 0