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Regulatory Matters - MISO Return on Equity Complaints (Details) - FERC [Member]	Sep. 30, 2018
Regulatory Matters [Line Items]
FERC Authorized Return on Common Equity	10.32%
FERC Authorized Return on Equity Including Incentive Adder	10.82%
Return on Equity Complaint [Member]
Regulatory Matters [Line Items]
Proposed Return on Equity by Federal Administrative Law Judge	9.70%
Proposed Return on Equity by Federal Administrative Law Judge Including Incentive Adder	10.20%