Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Rental income	$ 52	$ 47	$ 153	$ 143
Percent of operating revenue	2.50%	2.30%	2.50%	2.30%