Income Taxes: (Schedule of Unrecognized Tax Benefits and Liability for Contingent Income Taxes, Interest and Penalties) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 105	$ 56	$ 55	$ 72
Accrued interest and penalties	25	11	9
Tax credits and other indirect benefits	(1)	(1)	(1)
Liability for tax contingencies	$ 129	$ 66	$ 63