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Operating Revenues - Disaggregation of Natural Gas Utility Operating Revenues by Customer Class (Details) - Revenues from contracts with customers - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | $ 7,169.3 | $ 7,449.3 | $ 7,680.3
Natural gas |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 2,826.9 | 3,071.4 | 3,194.9
Natural gas | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 2,824.5 | 3,068.1 | 3,185.9
Natural gas | Transferred over time | Total retail revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 2,450.5 | 2,784.2 | 2,818.9
Natural gas | Transferred over time | Residential |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,775.6 | 1,953.9 | 1,975.3
Natural gas | Transferred over time | Commercial and industrial |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 674.9 | 830.3 | 843.6
Natural gas | Transferred over time | Transport |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 326.2 | 349.5 | 346.7
Natural gas | Transferred over time | Other utility revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 47.8 | (65.6) | 20.3
Wisconsin | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 5,461.7 | 5,631.8 | 5,783.0
Wisconsin | Natural gas | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,195.6 | 1,324.1 | 1,350.6
Wisconsin | Natural gas | Transferred over time | Total retail revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,090.7 | 1,257.8 | 1,271.2
Wisconsin | Natural gas | Transferred over time | Residential |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 752.6 | 837.9 | 834.5
Wisconsin | Natural gas | Transferred over time | Commercial and industrial |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 338.1 | 419.9 | 436.7
Wisconsin | Natural gas | Transferred over time | Transport |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 79.1 | 72.6 | 70.8
Wisconsin | Natural gas | Transferred over time | Other utility revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 25.8 | (6.3) | 8.6
Illinois | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,267.9 | 1,332.5 | 1,407.1
Illinois | Natural gas | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,267.9 | 1,332.4 | 1,406.9
Illinois | Natural gas | Transferred over time | Total retail revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 1,023.2 | 1,119.5 | 1,144.4
Illinois | Natural gas | Transferred over time | Residential |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 802.2 | 857.8 | 877.5
Illinois | Natural gas | Transferred over time | Commercial and industrial |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 221.0 | 261.7 | 266.9
Illinois | Natural gas | Transferred over time | Transport |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 215.6 | 245.3 | 244.1
Illinois | Natural gas | Transferred over time | Other utility revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 29.1 | (32.4) | 18.4
Other States | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 378.1 | 428.2 | 444.5
Other States | Natural gas | Transferred over time |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 361.0 | 411.6 | 428.4
Other States | Natural gas | Transferred over time | Total retail revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 336.6 | 406.9 | 403.3
Other States | Natural gas | Transferred over time | Residential |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 220.8 | 258.2 | 263.3
Other States | Natural gas | Transferred over time | Commercial and industrial |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 115.8 | 148.7 | 140.0
Other States | Natural gas | Transferred over time | Transport |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | 31.5 | 31.6 | 31.8
Other States | Natural gas | Transferred over time | Other utility revenues |  |  |
Disaggregation of Operating Revenues |  |  |
Revenues from contracts with customers | $ (7.1) | $ (26.9) | $ (6.7)

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- Definition Amount, excluding 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 -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 40 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 32 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 42 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 924 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 11.L) -URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856 + Details
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