Benefit Plans: (Fair Value of Pension Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
U S and International Equities
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	59.00%	57.00%
U S and International Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	11.00%	13.00%
Investment Funds Holding Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	14.00%	14.00%
Real Estate and Other Money Markets
Defined Benefit Plan Disclosure [Line Items]
Investment in securities, percent	16.00%	16.00%
Pension
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 10,816	$ 9,030	$ 8,851
Pension | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Total assets	10,539	8,747
Pension | Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets	10	83
Pension | Fair Value, Inputs, Level 1, 2 and 3 | U.S. securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	155	144
Pension | Fair Value, Inputs, Level 1, 2 and 3 | International securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	632	525
Pension | Fair Value, Inputs, Level 1, 2 and 3 | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Total assets	8,876	7,317
Pension | Fair Value, Inputs, Level 1, 2 and 3 | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	293	238
Pension | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	501	409
Pension | Fair Value, Inputs, Level 1, 2 and 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Total assets	72	31
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total assets	7,912	6,572
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets	10	83
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | U.S. securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	155	144
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | International securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	632	525
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Total assets	6,407	5,245
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	207	166
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	501	409
Pension | Quoted Prices In Active Markets for Identical Assets/Liabilities (Level 1) | Other
Defined Benefit Plan Disclosure [Line Items]
Total assets	0	0
Pension | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total assets	2,559	2,147
Pension | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Other Observable Inputs (Level 2) | U.S. securities
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Other Observable Inputs (Level 2) | International securities
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Other Observable Inputs (Level 2) | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Total assets	2,469	2,072
Pension | Significant Other Observable Inputs (Level 2) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	86	72
Pension | Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Total assets	4	3
Pension | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total assets	68	28
Pension | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | U.S. securities
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | International securities
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | Investment funds
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets
Pension | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Total assets	68	28
Pension | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 277	$ 283