Income Taxes: (Schedule of Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Beginning balance	$ 56	$ 55	$ 72
Additions based on tax positions related to the current year	40	6	7
Additions for tax positions of previous years	42	1	1
Reductions for tax positions of prior years	(34)	0	(23)
Reductions due to lapse of statute of limitations	(4)	(2)	(3)
Other	5	(4)	1
Ending balance	$ 105	$ 56	$ 55