Leases - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease expense	$ 17	$ 52
Short-term lease expense	31	80
Variable lease expense	4	10
Total lease costs	$ 52	$ 142