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INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Investment in transmission affiliates |  |  |  |
Charges to ATC for services and construction | $ 5.5 | $ 5.7 | $ 17.2 | $ 18.7
Charges from ATC for network transmission services | 90.3 | 87.8 | 270.7 | 262.7
Net refund from ATC related to FERC ROE orders | $ 8.7 | $ 2.3 | $ 7.4 | $ 10.7

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- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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- Definition Net refunds of transmission charges received from American Transmission Company LLC as a result of return on equity orders issued by the Federal Energy Regulatory Commission. + References No definition available. + Details
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- Definition Charges to related parties for services, construction, and/or operations (excluding transactions that are eliminated in consolidated or combined financial statements) during the period. + References No definition available. + Details
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- Details
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