Other Assets and Liabilites - Schedule of Assets Held Under Operating Leases and Related Activities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Other Assets and Liabilities
Assets held under operating leases	$ 1,359		$ 1,359		$ 1,378
Accumulated depreciation	(375)		(375)		(374)
Net	984		984		$ 1,004
Assets held under operating leases
Other Assets and Liabilities
Depreciation expense for assets under operating leases	$ 29	$ 30	$ 58	$ 60