Benefit Plans: (Components of Pension and Other Employee Benefit (Income) Costs) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||||
| Total pension and other employee benefit (income) costs | $ (5) | $ 11 | $ (10) | $ 23 |
| Pension Plan | ||||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||||
| Total pension and other employee benefit (income) costs | (40) | (22) | (81) | (42) |
| Postemployment Benefit Plans | ||||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||||
| Total pension and other employee benefit (income) costs | 31 | 29 | 63 | 58 |
| Postretirement Benefit Costs | ||||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||||
| Total pension and other employee benefit (income) costs | $ 4 | $ 4 | $ 8 | $ 7 |