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REGULATORY ASSETS AND LIABILITIES - REGULATORY LIABILITIES (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
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Regulatory liabilities |  |
Current liabilities | $ 25.6 | $ 41.8
Regulatory liabilities | 3,960.3 | 3,718.6
Total regulatory liabilities | 3,985.9 | 3,760.4
Income tax |  |
Regulatory liabilities |  |
Total regulatory liabilities | 2,279.1 | 2,134.1
Removal costs |  |
Regulatory liabilities |  |
Total regulatory liabilities | 1,313.4 | 1,294.9
Mines deferral |  |
Regulatory liabilities |  |
Total regulatory liabilities | 115.4 | 95.1
Unrecognized pension and OPEB costs |  |
Regulatory liabilities |  |
Total regulatory liabilities | 106.5 | 114.2
Energy efficiency programs |  |
Regulatory liabilities |  |
Total regulatory liabilities | 30.0 | 21.1
Energy costs refundable through rate adjustments |  |
Regulatory liabilities |  |
Total regulatory liabilities | 25.2 | 42.0
Uncollectible expense |  |
Regulatory liabilities |  |
Total regulatory liabilities | 23.9 | 24.7
Decoupling |  |
Regulatory liabilities |  |
Total regulatory liabilities | 22.8 | 1.8
Earnings sharing mechanisms |  |
Regulatory liabilities |  |
Total regulatory liabilities | 20.6 | 2.5
Other, net |  |
Regulatory liabilities |  |
Total regulatory liabilities | $ 49.0 | $ 30.0

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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