Variable interest entities and securitization - Non-consolidated VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 442,316	$ 381,508
Liabilities	398,350	339,780
Variable Interest Entity, Not Primary Beneficiary | Securities available-for-sale
Variable Interest Entity [Line Items]
Assets	199	208
Liabilities	0	0
Maximum loss exposure	199	208
Variable Interest Entity, Not Primary Beneficiary | Other
Variable Interest Entity [Line Items]
Assets	2,237	2,400
Liabilities	363	422
Maximum loss exposure	$ 2,609	$ 2,822