Leases - Operating Lease Income and Related Depreciation Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating Lease, Income, Comprehensive Income [Extensible List]	us-gaap:NoninterestIncomeOther	us-gaap:NoninterestIncomeOther
Operating lease income	$ 1,325	$ 1,413
Assets subject to operating leases
Lessee, Lease, Description [Line Items]
Depreciation expense	$ 934	$ 1,140