Leasing (Depreciation Expense on Operating Lease Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases, Operating [Abstract]
Operating Lease, Lease Income	$ 1,435	$ 1,470	$ 1,489
Depreciation expense on operating lease assets	978	1,050	1,115
Remarketing gains, net	(127)	(69)	(90)
Net depreciation expense on operating lease assets	851	981	1,025
Variable lease payments, excessive wear and tear	$ 23	$ 19	$ 24