Leases - Operating Lease Income and Related Depreciation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease income	$ 5,539	$ 5,455
Operating lease income			$ 4,540
Lessee, Lease, Description [Line Items]
Depreciation expense			$ 3,522
Assets subject to operating leases
Lessee, Lease, Description [Line Items]
Depreciation expense	$ 4,257	$ 4,157