Benefit Plans: (Components of Pension and Other Employee Benefits Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension and other employee benefit costs	$ 6	$ 5	$ 28	$ 9
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension and other employee benefit costs	(25)	(24)	(37)	(49)
Postemployment Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension and other employee benefit costs	29	27	59	54
Postretirement Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension and other employee benefit costs	$ 2	$ 2	$ 6	$ 4