New Accounting Standard - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Lessee Disclosure [Abstract]
Lease right-of-use assets	$ 245,000,000		$ 243,000,000
Lease liability	256,000,000		$ 243,000,000
Lease costs	33,000,000	$ 80,000,000
Lease payments	$ 10,000,000
Lease weighted-average discount rate	5.70%
Lease,weighted average remaining lease term	9 years 3 months 18 days