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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, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Investment in transmission affiliates |  |  |  |
Charges to ATC for services and construction | $ 5.0 | $ 4.4 | $ 13.7 | $ 12.3
Charges from ATC for network transmission services | 84.4 | 87.4 | 253.5 | 262.0
Refund from ATC related to a FERC audit | 0.0 | 0.0 | 22.0 | 0.0
Refund from ATC per FERC ROE order | $ 0.0 | $ 0.0 | $ 0.0 | $ 28.3

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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 Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The amount of the refund received from ATC due to a FERC audit. + References No definition available. + Details
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- Definition Refund of previous year's revenue that wasn't distributed by ATC. This resulted from an order by the FERC. + 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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