Pension Plan and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 5
Additional contributions for remainder of year	$ 7
Treasury stock acquired (in shares)	5,260,687
Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost (gain)	$ 2	$ 2
Benefit obligation	27		$ 30
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost (gain)	1	$ 1
Benefit obligation	$ 13		$ 13
Non-Qualified Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Treasury stock acquired (in shares)	3,632		5,115