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Activity in Company's Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance at Beginning of Period |  | $ 3.3 | $ 3.3 | $ 1.0
Provision |  | 6.7 | 5.6 | 5.5
Recoveries |  | 0.9 | 0.8 | 0.6
Accounts Written Off |  | 7.6 | 6.5 | 4.4
Regulatory Defferals | [1] | (0.7) | 0.1 | 0.6
Balance at End of Period |  | 2.6 | 3.3 | 3.3
Electric |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance at Beginning of Period |  | 2.0 | 1.6 | 0.6
Provision |  | 4.2 | 3.3 | 2.9
Recoveries |  | 0.3 | 0.4 | 0.3
Accounts Written Off |  | 4.4 | 3.4 | 2.6
Regulatory Defferals | [1] | (0.5) | 0.1 | 0.4
Balance at End of Period |  | 1.6 | 2.0 | 1.6
Gas |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance at Beginning of Period |  | 1.3 | 1.7 | 0.4
Provision |  | 2.5 | 2.3 | 2.6
Recoveries |  | 0.6 | 0.4 | 0.3
Accounts Written Off |  | 3.2 | 3.1 | 1.8
Regulatory Defferals | [1] | (0.2) |  | 0.2
Balance at End of Period |  | $ 1.0 | $ 1.3 | $ 1.7
[1] | In 2021 and 2020, the Company recorded higher than normal expected bad debt expense due to the coronavirus pandemic. The incremental bad debt expense amounts were previously deferred as regulatory assets based on certain regulatory proceedings and management’s view that such amounts were probable of recovery. Based on actual billing and collections experience, the Company has not deferred any incremental bad debt expense as a regulatory asset as of December 31, 2022.

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- Definition Amount of allowance for credit loss on accounts receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(4)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Amount of direct write-downs of accounts receivable charged against the allowance. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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