Indebtedness: (Fair Value of Outstanding Long-Term Debt, Excluding Finance Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Quoted Prices In Active Markets for Identical Assets/Liabilities (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	$ 38,259	$ 28,919
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	$ 6,687	$ 6,142

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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