Variable interest entities and securitization - Non-consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 470,533	$ 469,633
Liabilities	426,481	423,513
Securities available-for-sale | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	208	217
Liabilities	0	0
Maximum loss exposure	208	217
Other | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	2,380	2,565
Liabilities	480	514
Maximum loss exposure	$ 2,882	$ 3,096