Leases - Summary of Information Related to Leases (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Leases [Abstract]
Operating leases, assets	$ 539
Finance leases, assets	193
Operating leases, current liabilities	249		$ 0
Finance leases, current liabilities	31
Operating leases, long-term liabilities	308
Finance leases, long-term liabilities	230
Operating leases, total lease liabilities	557
Finance leases, total lease liabilities	$ 261
Weighted-average remaining lease term, operating leases	5 years
Weighted-average remaining lease term, finance leases	16 years
Weighted-average discount rate, operating leases	4.30%
Weighted-average discount rate, finance leases	15.10%
Operating leases, additions to ROU assets and lease liabilities	$ 126
Finance leases, additions to ROU assets and lease liabilities	$ 22	$ 0