Pension Plan and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Employer contributions						$ 12
Treasury stock acquired (in shares)	44,000,000		5,260,687		39,061,269
Pension
Defined Benefit Plan Disclosure [Line Items]
Settlement loss		$ 1		$ 0		5	$ 0
Lump sum payments for settlement						19
Net periodic benefit cost (gain)		3		2		11	7
Benefit obligation	$ 34	26			$ 34	26		$ 34
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost (gain)		1		$ 1		1	$ 2
Benefit obligation	$ 13	$ 13			$ 13	$ 13		$ 13
Non-Qualified Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Treasury stock acquired (in shares)						5,115		10,653