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Statement - CONSOLIDATED BALANCE SHEETS - Southwest link:presentationLink link:calculationLink link:definitionLink 0000010 - Statement - CONSOLIDATED STATEMENTS OF INCOME - Southwest link:presentationLink link:calculationLink link:definitionLink 0000011 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - Southwest link:presentationLink link:calculationLink link:definitionLink 0000012 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS - Southwest link:presentationLink link:calculationLink link:definitionLink 0000013 - Statement - CONSOLIDATED STATEMENTS OF EQUITY - Southwest link:presentationLink link:calculationLink link:definitionLink 0000014 - Disclosure - Background, Organization, and Summary of Significant Accounting Policies link:presentationLink link:calculationLink link:definitionLink 0000015 - Disclosure - Regulated Operations Plant and Leases link:presentationLink link:calculationLink link:definitionLink 0000016 - Disclosure - Revenue link:presentationLink link:calculationLink link:definitionLink 0000017 - 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Redeemable Noncontrolling Interests (Tables) link:presentationLink link:calculationLink link:definitionLink 9954485 - Disclosure - Acquisitions and Dispositions (Tables) link:presentationLink link:calculationLink link:definitionLink 9954486 - Disclosure - Background, Organization, and Summary of Significant Accounting Policies - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954487 - Disclosure - Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Details) link:presentationLink link:calculationLink link:definitionLink 9954488 - Disclosure - Background, Organization, and Summary of Significant Accounting Policies - Summary of Intangible Assets (Details) link:presentationLink link:calculationLink link:definitionLink 9954489 - Disclosure - Background, Organization, and Summary of Significant Accounting Policies - Schedule of Estimated Future Amortization of Intangible Assets (Details) link:presentationLink link:calculationLink link:definitionLink 9954490 - 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Disclosure - Regulated Operations Plant and Leases - Schedule of Maturities of Lease Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 9954501 - Disclosure - Revenue - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954501 - Disclosure - Revenue - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954502 - Disclosure - Revenue - Schedule of Regulated Operations Revenues: Natural Gas Distribution Segment (Details) link:presentationLink link:calculationLink link:definitionLink 9954503 - Disclosure - Revenue - Schedule of Regulated Operations Revenues: Utility Infrastructure Services Segment (Details) link:presentationLink link:calculationLink link:definitionLink 9954504 - Disclosure - Revenue - Summary of Information about Receivables (Details) link:presentationLink link:calculationLink link:definitionLink 9954505 - Disclosure - Revenue - Schedule of Utility Infrastructure Services Contracts Receivable (Details) link:presentationLink link:calculationLink link:definitionLink 9954506 - 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Disclosure - Regulatory Assets and Liabilities - Schedule of Components of Other Regulatory Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 9954513 - Disclosure - Other Comprehensive Income and Accumulated Other Comprehensive Income ("AOCI") - Related Tax Effects Allocated to OCI (Detail) link:presentationLink link:calculationLink link:definitionLink 9954514 - Disclosure - Other Comprehensive Income and Accumulated Other Comprehensive Income ("AOCI") - AOCI Rollforward (Details) link:presentationLink link:calculationLink link:definitionLink 9954515 - Disclosure - Other Comprehensive Income and Accumulated Other Comprehensive Income ("AOCI") - Amount Recognized Before Income Tax Associated with Defined Benefit Plans in Accumulated Other Comprehensive Income (Detail) link:presentationLink link:calculationLink link:definitionLink 9954516 - Disclosure - Common Stock - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 9954517 - 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