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Regulatory Assets and Liabilities - Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Regulatory Liabilities |  |
Other current liabilities | $ 33.4 | $ 33.8
Regulatory liabilities | 1,563.8 | 1,392.2
Total regulatory liabilities | 1,597.2 | 1,426.0
Removal costs |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 1,262.7 | 1,209.6
Mines deferral |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 70.2 | 31.6
Energy costs refundable through rate adjustments |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 88.7 | 76.9
Unrecognized pension and OPEB costs |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 63.0 | 26.3
Derivatives |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 41.1 | 12.6
Uncollectible expense |  |
Regulatory Liabilities |  |
Total regulatory liabilities | 36.1 | 31.8
Other, net |  |
Regulatory Liabilities |  |
Total regulatory liabilities | $ 35.4 | $ 37.2

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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://www.xbrl.org/2003/role/presentationRef -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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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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