Pension Plan and Other Postretirement Benefits (Pension and Other Postretirement Benefit Costs) (Details) - Pension - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 2	$ 5	$ 8
Interest cost	2	1	4	4
Expected return on plan assets	(1)	(2)	(4)	(6)
Amortization of prior service cost	0	0	0	0
Amortization of net loss	0	1	1	1
Settlement loss	1	0	5	0
Net periodic benefit cost	$ 3	$ 2	$ 11	$ 7