Regulatory Matters - Boswell Mercury Emission Reduction Plan (Details) - Boswell Unit 4 [Member] $ in Millions	Dec. 31, 2015 USD ($)
Regulatory Matters [Line Items]
Total Project Costs	$ 220
MPUC [Member] \| Boswell Mercury Emissions Reduction Plan [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Total Project Costs	$ 220

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