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Regulatory Matters - MISO Return on Equity Complaints (Details) $ in Millions | Sep. 30, 2015 USD ($)
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FERC Complaint 1 [Member] |
Loss Contingencies [Line Items] |
Proposed Return on Common Equity | 9.15%
FERC Complaint 2 [Member] |
Loss Contingencies [Line Items] |
Proposed Return on Common Equity | 8.67%
Minnesota Power [Member] |
Loss Contingencies [Line Items] |
Estimated Refund for MISO Revenue | $ 6.2
Estimated Refund for MISO Transmission Expense | 4.1
Reserve | 2.1
Reserve, Portion Attributable to Prior Years | $ 1.5

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