Indebtedness: (Fair Value of Outstanding Long-Term Debt, Excluding Finance Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of outstanding long-term debt, excluding finance leases	$ 45,288	$ 41,431
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of outstanding long-term debt, excluding finance leases	$ 3,085	$ 3,011