Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Leases starting expiration date	2019
Leases ending expiration date	2030
Operating leases, rent expense	$ 6	$ 24
Operating leases legally binding minimum lease payments, signed but not yet commenced	$ 2