Benefit Plans: (Pension and Other Employee Benefit Costs) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
|
| Defined Benefit Plan Disclosure [Line Items] | |||
| Total pension and other employee benefit costs | $ 45 | $ 24 | $ 115 |
| Pension Plan | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Total pension and other employee benefit costs | (84) | (93) | (1) |
| Postemployment Benefit Plans | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Total pension and other employee benefit costs | 117 | 107 | 108 |
| Postretirement Benefit Costs | |||
| Defined Benefit Plan Disclosure [Line Items] | |||
| Total pension and other employee benefit costs | $ 12 | $ 10 | $ 8 |