Pension Plan and Other Postretirement Benefits (Pension and Other Postretirement Benefit Costs) (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 4	$ 6
Interest cost	1	1	2	3
Expected return on plan assets	(1)	(2)	(3)	(4)
Amortization of prior service cost	0	0	0	0
Amortization of net loss	0	0	1	0
Settlement loss	4	0	4	0
Net periodic benefit cost	$ 6	$ 2	$ 8	$ 5