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Significant Segment Financial Data (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Other Operating Revenue - Non-Regulated | $ 0.0 | $ 0.9 |
Total Operating Revenues | 130.4 | 152.1 |
Segment Profit (Loss) | 15.2 | 26.5 |
Identifiable Segment Assets | 1,378.4 | 1,290.2 | $ 1,370.8
Capital Expenditures | 16.8 | 10.9 |
Billed and Unbilled Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | 136.9 | 161.9 |
Rate Adjustment Mechanism Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | (6.5) | (10.7) |
Gas Segment |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | 70.2 | 86.4 |
Segment Profit (Loss) | 12.3 | 13.7 |
Identifiable Segment Assets | 821.4 | 771.6 |
Capital Expenditures | 5.8 | 3.3 |
Gas Segment | Billed and Unbilled Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | 76.4 | 99.2 |
Gas Segment | Rate Adjustment Mechanism Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | (6.2) | (12.8) |
Electric |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | 60.2 | 64.8 |
Segment Profit (Loss) | 2.6 | 1.9 |
Identifiable Segment Assets | 537.7 | 502.3 |
Capital Expenditures | 9.9 | 6.6 |
Electric | Billed and Unbilled Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | 60.5 | 62.7 |
Electric | Rate Adjustment Mechanism Revenue |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total Operating Revenues | (0.3) | 2.1 |
All Other Segments |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Segment Profit (Loss) | 0.3 | 0.8 |
Identifiable Segment Assets | 19.2 | 16.2 |
Capital Expenditures | 1.1 | 1.0 |
Unregulated Operation |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Other Operating Revenue - Non-Regulated | 0.0 | 0.9 |
Total Operating Revenues | 0.0 | 0.9 |
Segment Profit (Loss) | 0.0 | 10.1 |
Identifiable Segment Assets | $ 0.1 | $ 0.1 |

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