Variable interest entities and securitization - Non-consolidated VIEs (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 468,155	$ 381,508
Liabilities	426,776	339,780
Variable Interest Entity, Not Primary Beneficiary | Securities available-for-sale
Variable Interest Entity [Line Items]
Assets	180	208
Liabilities	0	0
Maximum loss exposure	180	208
Variable Interest Entity, Not Primary Beneficiary | Other
Variable Interest Entity [Line Items]
Assets	2,287	2,400
Liabilities	390	422
Maximum loss exposure	$ 2,677	$ 2,822