Benefit Plans: (Pension and Other Employee Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	$ 46	$ 60	$ 45
Pension
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	(88)	(76)	(84)
Post- employment
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	118	123	117
Post- retirement
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	$ 16	$ 13	$ 12