Leases - Supplemental Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating cash flows from operating leases	$ 0	$ 0
Operating cash flows from finance leases	(3)	(4)
Financing cash flows from finance leases	$ (1)	$ (1)	$ 0
Weighted-average remaining lease term - operating leases	19 years	20 years
Weighted-average remaining lease term - finance leases	10 years	11 years
Weighted-average discount rate - operating leases	5.80%	5.80%
Weighted-average discount rate - finance leases	14.30%	14.30%