Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
ROU asset	$ 133	$ 0
Operating lease liability	142	$ 0
Finance lease liability	3
Sublease income (less than $1)	$ 0
Minimum
Lessee, Lease, Description [Line Items]
Term of lease	1 year
Term of extension	3 years
Maximum
Lessee, Lease, Description [Line Items]
Term of lease	9 years
Term of extension	5 years