Other Assets and Liabilites - Schedule of Assets Held Under Operating Leases and Related Activities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Other Assets and Liabilities
Net	$ 2,078		$ 2,118
Assets held under operating leases
Other Assets and Liabilities
Assets held under operating leases	1,365		1,378
Accumulated depreciation	(389)		(374)
Net	976		$ 1,004
Depreciation expense for assets under operating leases	$ 29	$ 30