Benefit Plans: (Amounts Recorded in Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	$ (1,688)	$ (2,973)	$ (3,131)
Prior service (cost) credit	48	55	57
Net transition (obligation) asset	(3)	(3)	(3)
Deferred income taxes	238	460	488
Losses to be amortized	(1,405)	(2,461)	(2,589)
Pension
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	(888)	(2,122)	(2,325)
Prior service (cost) credit	68	75	77
Net transition (obligation) asset	(3)	(3)	(3)
Deferred income taxes	36	246	283
Losses to be amortized	(787)	(1,804)	(1,968)
Post- retirement
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	(43)	(36)	(36)
Prior service (cost) credit	1	1	1
Net transition (obligation) asset	0	0	0
Deferred income taxes	21	19	19
Losses to be amortized	(21)	(16)	(16)
Post- employment
Defined Benefit Plan Disclosure [Line Items]
Net (losses) gains	(757)	(815)	(770)
Prior service (cost) credit	(21)	(21)	(21)
Net transition (obligation) asset	0	0	0
Deferred income taxes	181	195	186
Losses to be amortized	$ (597)	$ (641)	$ (605)