Variable interest entities and securitization - Non-consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 428,398	$ 381,508
Liabilities	383,051	339,780
Variable Interest Entity, Not Primary Beneficiary | Securities available-for-sale
Variable Interest Entity [Line Items]
Assets	206	208
Liabilities	0	0
Maximum loss exposure	206	208
Variable Interest Entity, Not Primary Beneficiary | Other
Variable Interest Entity [Line Items]
Assets	2,278	2,400
Liabilities	388	422
Maximum loss exposure	$ 2,675	$ 2,822