Basis of Presentation and Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Right-of-use assets – operating leases	$ 165		$ 165		$ 171
Operating lease obligation, current	15		15		12
Operating lease obligation, long-term	164		164		170
Finance lease obligation, current	10		10		10
Finance lease obligation, long-term	58		58		63
Operating lease, lease income	57	$ 70	105	$ 139
Property Subject to Finance Lease
Lessee, Lease, Description [Line Items]
Right-of-use assets – finance leases	$ 102		$ 102		$ 107