Leases - Other Quantitative Information (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Operating Leases
Weighted-average remaining lease term		8 years 7 months 6 days		8 years 4 months 24 days
Weighted-average discount rate	[1]	7.40%		5.20%
Finance Leases
Weighted-average remaining lease term		18 years 2 months 12 days		18 years 8 months 12 days
Weighted-average discount rate	[1]	16.20%		16.20%
Operating cash flows from operating leases		$ 157	$ 174
Operating cash flows from finance leases		5	5
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 246	$ 106

[1] The finance leases commenced prior to the adoption of the current leasing standard under GAAP. In accordance with previous accounting guidance, the implied rate is based on the fair value of the underlying assets.