Pension Plan and Other Postretirement Benefits (Pension and Other Postretirement Benefit Costs) (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3
Interest cost	1	2
Expected return on plan assets	(2)	(2)
Amortization of prior service cost	0	0
Amortization of net loss	1	0
Net periodic benefit cost	$ 2	$ 3