Leasing Leasing (Depreciation Expense on Operating Lease Assets) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Leases, Operating [Abstract]
Operating Lease, Lease Income	$ 363	$ 374	$ 724	$ 756
Depreciation expense on operating lease assets	262	281	523	572
Remarketing (gains) and losses, net	(23)	(16)	(38)	(34)
Net depreciation expense on operating lease assets	239	265	485	538
Variable lease payments, excessive wear and tear	$ 5	$ 6	$ 9	$ 13