101 - Document - Document and Entity Information
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103 - Statement - Condensed Consolidated Balance Sheets
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104 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)
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105 - Statement - Condensed Consolidated Statements of Income
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106 - Statement - Condensed Consolidated Statements of Comprehensive Income
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107 - Statement - Condensed Consolidated Statements of Cash Flows
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108 - Disclosure - Nature of Operations and Basis of Presentation
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109 - Disclosure - Components of Net Periodic Benefit Cost
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110 - Disclosure - Segment Information
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111 - Disclosure - Derivatives and Fair Value Measurements
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112 - Disclosure - Common Stock
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113 - Disclosure - Long-Term Debt
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114 - Disclosure - Short-Term Debt
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115 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income
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116 - Disclosure - Construction Services Redeemable Noncontrolling Interest
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117 - Disclosure - Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation
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118 - Disclosure - Nature of Operations and Basis of Presentation (Policies)
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119 - Disclosure - Nature of Operations and Basis of Presentation (Tables)
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120 - Disclosure - Components of Net Periodic Benefit Cost (Tables)
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121 - Disclosure - Segment Information (Tables)
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122 - Disclosure - Derivatives and Fair Value Measurements (Tables)
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123 - Disclosure - Long-Term Debt (Tables)
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124 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income (Tables)
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125 - Disclosure - Construction Services Redeemable Noncontrolling Interest (Tables)
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126 - Disclosure - Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation (Tables)
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127 - Disclosure - Nature of Operations and Basis of Presentation - Additional Information (Detail)
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128 - Disclosure - Nature of Operations and Basis of Presentation - Schedule of Goodwill (Detail)
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129 - Disclosure - Nature of Operations and Basis of Presentation - Accounts Receivable for Services (Detail)
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130 - Disclosure - Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail)
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131 - Disclosure - Nature of Operations and Basis of Presentation - Other Income (Deductions) (Detail)
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132 - Disclosure - Components of Net Periodic Benefit Cost - Schedule of Net Periodic Benefit Costs (Detail)
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133 - Disclosure - Segment Information - Additional Information (Detail)
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134 - Disclosure - Segment Information - Schedule of Segment Reporting Information (Detail)
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135 - Disclosure - Derivatives and Fair Value Measurements - Additional Information (Detail)
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136 - Disclosure - Derivatives and Fair Value Measurements - Notional Amounts under Swaps Contracts (Detail)
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137 - Disclosure - Derivatives and Fair Value Measurements - Amount of Gain or Losses Recognized in Income on Derivatives (Detail)
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138 - Disclosure - Derivatives and Fair Value Measurements - Fair Values of Swaps in Consolidated Balance Sheets (Detail)
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139 - Disclosure - Derivatives and Fair Value Measurements - Paid to and Received from Counterparties for Settlements of Matured Swaps (Detail)
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140 - Disclosure - Derivatives and Fair Value Measurements - Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets (Detail)
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141 - Disclosure - Derivatives and Fair Value Measurements - Summary of Financial Assets and Liabilities at Fair Value (Detail)
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142 - Disclosure - Common Stock - Additional Information (Detail)
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143 - Disclosure - Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Detail)
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144 - Disclosure - Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Parenthetical) (Detail)
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145 - Disclosure - Long-Term Debt - Additional Information (Detail)
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146 - Disclosure - Short-Term Debt - Additional Information (Detail)
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147 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Detail)
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148 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Parenthetical) (Detail)
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149 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Detail)
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150 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Parenthetical) (Detail)
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151 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Additional Information (Detail)
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152 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Detail)
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153 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Parenthetical) (Detail)
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154 - Disclosure - Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Amount Recognized Before Income Tax Associated with Defined Benefit Plans in Accumulated Other Comprehensive Income (Detail)
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155 - Disclosure - Construction Services Redeemable Noncontrolling Interest - Additional Information (Detail)
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156 - Disclosure - Construction Services Redeemable Noncontrolling Interest - Summary of Redeemable Noncontrolling Interest (Detail)
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157 - Disclosure - Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Summary of Assets and Liabilities within Amounts Reported as Discontinued Operations - Construction Services in Condensed Consolidated Balance Sheet (Detail)
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158 - Disclosure - Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Components of Discontinued Operations - Construction Services Non-Owner Equity Amount in Condensed Consolidated Balance Sheet (Detail)
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159 - Disclosure - Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Summary of Income Statement Components of Discontinued Operations - Construction Services in Condensed Consolidated Income Statements (Detail)
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