Income Taxes: (Schedule of Unrecognized Tax Benefits and Liability for Contingent Income Taxes, Interest and Penalties) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 72	$ 89	$ 72	$ 63
Accrued interest and penalties	13	18	17
Tax credits and other indirect benefits	(3)	(7)	(9)
Liability for tax contingencies	$ 82	$ 100	$ 80