Leases - Operating Lease Income and Related Depreciation Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Leases [Abstract]
Operating Lease, Income, Comprehensive Income [Extensible List]	us-gaap:NoninterestIncomeOther	us-gaap:NoninterestIncomeOther	us-gaap:NoninterestIncomeOther	us-gaap:NoninterestIncomeOther
Operating lease income	$ 1,277	$ 1,413	$ 2,602	$ 2,810
Assets subject to operating leases
Lessee, Lease, Description [Line Items]
Depreciation expense	$ 876	$ 1,084	$ 1,809	$ 2,224