Benefit Plans: (Net Pension and Postretirement Cost Weighted-Average Assumptions) (Details) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
|
| Pension Plan | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Discount rate - service cost (as a percent) | 3.27% | 1.03% | 0.72% |
| Discount rate - interest cost (as a percent) | 3.03% | 0.71% | 0.44% |
| Expected rate of return on plan assets (as a percent) | 4.42% | 4.17% | 4.43% |
| Rate of compensation increase (as a percent) | 1.98% | 1.77% | 1.79% |
| Interest crediting rate (as a percent) | 2.97% | 3.15% | 3.20% |
| Postretirement | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Discount rate - service cost (as a percent) | 5.89% | 3.08% | 2.84% |
| Discount rate - interest cost (as a percent) | 5.89% | 3.08% | 2.84% |
| Health care cost trend rate (as a percent) | 6.14% | 6.27% | 6.21% |