Benefit Plans: (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 240	$ 218	$ 174
Interest cost	209	234	258
Expected return on plan assets	(437)	(403)	(365)
Amortization:
Net losses	145	93	18
Prior service cost (credit)	(2)	(2)	(2)
Settlement and curtailment	(3)	2	7
Net periodic pension and postretirement costs	152	142	90
Post- retirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3	4
Interest cost	12	13	12
Expected return on plan assets	0	0	0
Amortization:
Net losses	3	(1)	(1)
Prior service cost (credit)	0	0	0
Settlement and curtailment	1	1	1
Net periodic pension and postretirement costs	$ 20	$ 16	$ 16