Pension Plan and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended			12 Months Ended
	Dec. 31, 2018	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Employer contributions					$ 9
Additional contributions for remainder of year		$ 3			3
Treasury stock acquired (in shares)	44,000,000		5,260,687			39,061,269
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement loss		4		$ 0	4		$ 0
Payments for pension plan					16
Net periodic benefit cost (gain)		6		2	8		5
Benefit obligation	$ 34	28			28	$ 34		$ 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