Leases - Supplemental Cash Flow Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 7	$ 15
Operating cash flows from finance leases	2	3
Finance cash flows from finance leases	5	9
Operating leases	20	26
Finance leases	$ 1	$ 2
Operating leases, weighted-average remaining lease terms	8 years 6 months 25 days	8 years 6 months 25 days
Finance leases, weighted-average remaining lease terms	4 years 9 months	4 years 9 months
Operating leases, weighted-average discount rate	4.91%	4.91%
Finance leases, weighted-average discount rate	3.45%	3.45%
Operating lease assets, net of accumulated amortization of $11 million	$ 188	$ 188
Finance lease assets, net of accumulated amortization of $89 million	74	74
Leased Asset	262	262
Operating liability, current	31	31
Finance liability, current	16	16
Operating liability, noncurrent	196	196
Finance liability, noncurrent	51	51
Total leased liabilities	294	294
Operating lease assets, accumulated amortization	11	11
Financing lease, accumulated amortization	$ 89	$ 89