Variable interest entities and securitization - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Nonredeemable noncontrolling interests	$ 94	$ 102
VME classification of carrying amount, assets	44	50
VME classification of carrying amount, liabilities	1	1
Noncontrolling interest in VME	1	1
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Trading assets	615	629
Other assets	14	16
Total assets	629	645
Other liabilities	398	388
Total liabilities	398	388
Nonredeemable noncontrolling interests	94	102
Variable Interest Entity, Primary Beneficiary | Investment Management funds
Variable Interest Entity [Line Items]
Trading assets	215	229
Other assets	14	16
Total assets	229	245
Other liabilities	1	1
Total liabilities	1	1
Nonredeemable noncontrolling interests	94	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	397	387
Total liabilities	397	387
Nonredeemable noncontrolling interests	$ 0	$ 0