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REVENUE - DISAGGREGATED REVENUE - PRODUCT (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | $ 833,677 | $ 782,331 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 15,750 | 10,364 |
Derivative Instruments |  |  |  |  |  |  |  |  | 1,105,357 | 1,807,588 |
Revenues out of scope |  |  |  |  |  |  |  |  | 1,119,991 | 1,809,714 |
Total operating revenues | $ 400,044 | $ 298,974 | $ 639,614 | $ 615,036 | $ 479,081 | $ 434,942 | $ 866,255 | $ 811,767 | 1,953,668 | 2,592,045 | $ 2,915,109
Natural gas utility sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 695,858 | 680,151 |
Wholesale natural gas services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 69,239 |  |
Wholesale natural gas services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 31,459 |
Service contracts |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 32,455 | 31,499 |
Installations and maintenance |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 18,562 | 19,403 |
Renewable Energy Certificates |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 1,384 |  |
Electricity sales |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 20,099 | 22,121 |
Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total operating revenues |  |  |  |  |  |  |  |  | 1,907,687 | 2,551,683 | $ 2,916,044
Operating Segments | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 695,858 | 680,151 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 15,750 | 10,364 |
Derivative Instruments |  |  |  |  |  |  |  |  | 18,315 | 20,278 |
Revenues out of scope |  |  |  |  |  |  |  |  | 34,065 | 30,642 |
Total operating revenues |  |  |  |  |  |  |  |  | 729,923 | 710,793 |
Operating Segments | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 21,483 | 22,121 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative Instruments |  |  |  |  |  |  |  |  | 81,134 | 75,978 |
Revenues out of scope |  |  |  |  |  |  |  |  | 81,134 | 75,978 |
Total operating revenues |  |  |  |  |  |  |  |  | 102,617 | 98,099 |
Operating Segments | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 24,511 | 31,459 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative Instruments |  |  |  |  |  |  |  |  | 1,005,908 | 1,711,332 |
Revenues out of scope |  |  |  |  |  |  |  |  | 1,004,792 | 1,703,094 |
Total operating revenues |  |  |  |  |  |  |  |  | 1,029,303 | 1,734,553 |
Operating Segments | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 42,015 | 0 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative Instruments |  |  |  |  |  |  |  |  | 0 | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Total operating revenues |  |  |  |  |  |  |  |  | 42,015 | 0 |
Operating Segments | Natural gas utility sales | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 695,858 | 680,151 |
Operating Segments | Natural gas utility sales | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Natural gas utility sales | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Natural gas utility sales | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Wholesale natural gas services | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Operating Segments | Wholesale natural gas services | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Operating Segments | Wholesale natural gas services | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 24,511 |  |
Operating Segments | Wholesale natural gas services | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 44,728 |  |
Operating Segments | Wholesale natural gas services | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 0 |
Operating Segments | Wholesale natural gas services | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 0 |
Operating Segments | Wholesale natural gas services | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 31,459 |
Operating Segments | Wholesale natural gas services | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 0 |
Operating Segments | Service contracts | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Service contracts | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Service contracts | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Service contracts | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Installations and maintenance | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Installations and maintenance | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Installations and maintenance | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Installations and maintenance | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Renewable Energy Certificates | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Operating Segments | Renewable Energy Certificates | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 1,384 |  |
Operating Segments | Renewable Energy Certificates | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Operating Segments | Renewable Energy Certificates | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Operating Segments | Electricity sales | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Electricity sales | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 20,099 | 22,121 |
Operating Segments | Electricity sales | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Operating Segments | Electricity sales | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Total operating revenues |  |  |  |  |  |  |  |  | 49,810 | 48,600 |
Home Services and Other | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 49,810 | 48,600 |
Alternative revenue programs (2) |  |  |  |  |  |  |  |  | 0 | 0 |
Derivative Instruments |  |  |  |  |  |  |  |  | 0 | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Total operating revenues |  |  |  |  |  |  |  |  | 49,810 | 48,600 |
Home Services and Other | Natural gas utility sales | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Home Services and Other | Wholesale natural gas services | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Home Services and Other | Wholesale natural gas services | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  |  | 0 |
Home Services and Other | Service contracts | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 32,455 | 31,499 |
Home Services and Other | Installations and maintenance | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 18,562 | 19,403 |
Home Services and Other | Renewable Energy Certificates | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 |  |
Home Services and Other | Electricity sales | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Eliminations |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | (3,920) | (2,302) |
Revenues out of scope |  |  |  |  |  |  |  |  | (1,116) | (8,238) |
Eliminations | Natural Gas Distribution |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Eliminations | Clean Energy Ventures |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Eliminations | Energy Services |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | 0 | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | (1,116) | (8,238) |
Eliminations | Storage and Transportation |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | (2,713) | 0 |
Revenues out of scope |  |  |  |  |  |  |  |  | 0 | 0 |
Eliminations | Home Services and Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues from contracts with customers |  |  |  |  |  |  |  |  | (1,207) | (2,302) |
Revenues out of scope |  |  |  |  |  |  |  |  | $ 0 | $ 0 |

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- Definition Amount of revenue that is not accounted for under Topic 606. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(1)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
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