Leasing Leasing (Depreciation Expense on Operating Lease Assets) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases, Operating [Abstract]
Operating Lease, Lease Income	$ 368	$ 368	$ 1,092	$ 1,124
Depreciation expense on operating lease assets	262	274	785	846
Remarketing (gains) and losses, net	(28)	(27)	(66)	(61)
Net depreciation expense on operating lease assets	234	247	719	785
Variable lease payments, excessive wear and tear	$ 5	$ 6	$ 14	$ 19