Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure
Interest cost	$ 1	$ 1	$ 1
Expected return on plan assets	(6)	(6)	(5)
Prior service credit amortization	1	1	1
Actuarial loss amortization	(1)	(1)	(1)
Net periodic benefit cost	$ (5)	$ (5)	$ (4)