Leases Lessee Disclosure - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets and Liabilities, Lessee [Abstract]
Operating lease assets, net		$ 538	$ 567	$ 0
Property and equipment, net	[1]	38
Total lease assets, net		576
Current portion of operating lease liabilities		129	126	0
Current portion of finance/capital lease liabilities		12		12
Long-term operating lease liabilities		471	$ 500	$ 0
Non-current portion of finance lease liabilities		20
Total lease liabilities		$ 632
Operating leases, Weighted Average Remaining Lease Term		5 years 8 months 12 days
Finance leases, Weighted Average Remaining Lease Term		3 years 2 months 12 days
Operating leases, Weighted Average Discount Rate		5.20%
Finance leases, Weighted Average Discount Rate		4.00%
Finance lease assets, Amortization		$ 36

[1] Finance lease assets are recorded net of accumulated amortization of $36 million.