Pension Plan and Other Postretirement Benefits (Pension and Other Postretirement Benefit Costs) (Details) - Pension - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 2
Interest cost	1	1
Expected return on plan assets	(1)	(1)
Net periodic benefit cost	$ 0	$ 2