Benefit Plans: (Net Pension and Postretirement Cost Weighted-Average Assumptions) (Details)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate - service cost (as a percent)	2.39%	2.68%	3.27%
Discount rate - interest cost (as a percent)	1.97%	2.34%	3.03%
Expected rate of return on plan assets (as a percent)	4.65%	4.63%	4.42%
Rate of compensation increase (as a percent)	1.89%	2.05%	1.98%
Interest crediting rate (as a percent)	3.05%	2.99%	2.97%
Post- retirement
Defined Benefit Plan Disclosure [Line Items]
Discount rate - service cost (as a percent)	5.35%	5.19%	5.89%
Discount rate - interest cost (as a percent)	5.35%	5.19%	5.89%
Health care cost trend rate (as a percent)	6.82%	6.54%	6.14%