Pension Plan and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 5
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	1	$ 1
Benefit obligation	13		$ 13
Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	0	$ 2
Expected future employer contributions, remainder of fiscal year	7
Benefit obligation	$ 28		$ 33
Non-Qualified Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Treasury stock acquired (in shares)	2,035		3,632