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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 1	$ 6	$ 5
Interest cost	1	2	3	4
Expected return on plan assets	(2)	(1)	(5)	(4)
Amortization of prior service cost	0	0	0	0
Amortization of net loss	1	0	1	1
Settlement loss	0	1	0	5
Net periodic benefit cost	$ 2	$ 3	$ 5	$ 11