Leasing Leasing (Depreciation Expense on Operating Lease Assets) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Leases, Operating [Abstract]
Operating Lease, Lease Income	$ 367	$ 361
Depreciation expense on operating lease assets	250	261
Remarketing (gains) and losses, net	(2)	(15)
Net depreciation expense on operating lease assets	248	246
Variable lease payments, excessive wear and tear	$ 6	$ 4