Postretirement Benefit Plans (Summary of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net periodic benefit cost:
Amortization of net actuarial loss	$ 1	$ 1
Net periodic benefit cost	1	2
Domestic defined benefit pension plans
Net periodic benefit cost:
Service cost	1	1
Interest cost	1	1
Expected return on plan assets	(2)	(2)
Amortization of net actuarial loss	0	1
Net periodic benefit cost	0	1
International defined benefit pension plans
Net periodic benefit cost:
Service cost	3	2
Interest cost	5	5
Expected return on plan assets	(9)	(9)
Amortization of net actuarial loss	2	2
Settlement/Curtailment	0	1
Net periodic benefit cost	$ 1	$ 1