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Components of Gas and Electric Operating Revenue (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | $ 178.7 | $ 220.2
Billed and Unbilled Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 171.4 | 219.5
Rate Adjustment Mechanism Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 7.3 | 0.7
Electric |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 73.6 | 108.2
Electric | Billed and Unbilled Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 71.0 | 97.6
Electric | Rate Adjustment Mechanism Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 2.6 | 10.6
Gas Segment |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 105.1 | 112.0
Gas Segment | Billed and Unbilled Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 100.4 | 121.9
Gas Segment | Rate Adjustment Mechanism Revenue |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 4.7 | (9.9)
Residential |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 81.6 | 109.2
Residential | Electric |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 40.5 | 60.1
Residential | Gas Segment |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 41.1 | 49.1
Commercial & Industrial |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 83.3 | 104.0
Commercial & Industrial | Electric |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 28.1 | 34.8
Commercial & Industrial | Gas Segment |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 55.2 | 69.2
Other |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 6.5 | 6.3
Other | Electric |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | 2.4 | 2.7
Other | Gas Segment |  |
Operating Revenues [Line Items] |  |
Total Electric and Gas Operating Revenues | $ 4.1 | $ 3.6

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- Definition Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 924 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 11.L) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479806/606-10-50-5 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 30 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-30 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 42 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-42 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-22 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 32 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-32 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 40 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-40 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-22 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 32 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-32 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 41 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482810/280-10-50-41 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479806/606-10-50-4 + Details
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