Leasing Leasing (Depreciation Expense on Operating Lease Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases, Operating [Abstract]
Operating Lease, Lease Income	$ 1,470	$ 1,489	$ 1,867
Depreciation expense on operating lease assets	1,050	1,115	1,368
Remarketing (gains) and losses, net	(69)	(90)	(124)
Net depreciation expense on operating lease assets	981	1,025	1,244
Variable lease payments, excessive wear and tear	$ 19	$ 24	$ 32