Variable interest entities and securitization - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Nonredeemable noncontrolling interests	$ 112	$ 102
VME classification of carrying amount, assets	283	50
VME classification of carrying amount, liabilities	1	1
Noncontrolling interest in VME	37	1
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Trading assets	850	629
Other assets	10	16
Total assets	860	645
Other liabilities	403	388
Total liabilities	403	388
Nonredeemable noncontrolling interests	112	102
Variable Interest Entity, Primary Beneficiary | Investment Management funds
Variable Interest Entity [Line Items]
Trading assets	450	229
Other assets	10	16
Total assets	460	245
Other liabilities	4	1
Total liabilities	4	1
Nonredeemable noncontrolling interests	112	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	399	387
Total liabilities	399	387
Nonredeemable noncontrolling interests	$ 0	$ 0