Document Type Amendment Flag Amendment Description Document Period End Date Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Filer Category Entity Public Float Entity Common Stock, Shares Outstanding Assets Current Assets Cash and Cash Equivalents Cash and Cash Equivalents at Beginning of Period Cash and Cash Equivalents at End of Period Accounts Receivable (Less Allowance of $0.9 at June 30, 2010 and December 31, 2009) Inventories Inventory Net Prepayments and Other Prepaid Expense Current Total Current Assets Property, Plant and Equipment - Net Investment in ATC Equity Method Investments Other Investments Other Non-Current Assets Other Assets Noncurrent Total Assets Liabilities and Equity Liabilities Current Liabilities Accounts Payable Accounts Payable Current Accrued Taxes Accrued Interest Long-Term Debt Due Within One Year Notes Payable Other Other Liabilities Current Total Current Liabilities Long-Term Debt Deferred Income Taxes Other Non-Current Liabilities Other Liabilities Noncurrent Total Liabilities Commitments and Contingencies (Note 14) Equity ALLETE's Equity Common Stock Without Par Value, 80.0 Shares Authorized, 35.7 and 35.2 Shares Outstanding Unearned ESOP Shares Unearned ESOP Shares Accumulated Other Comprehensive Loss Retained Earnings Total ALLETE Equity Non-Controlling Interest in Subsidiaries Total Equity Total Liabilities and Equity Operating Revenue Operating Expenses Operating Revenue Regulated And Unregulated Operating Revenue Prior Year Rate Refunds Total Operating Revenue Total Operating Revenue Fuel and Purchased Power Operating and Maintenance Depreciation Total Operating Expenses Operating Income Other Income (Expense) Interest Expense Interest Expense Equity Earnings in ATC Other Other Nonoperating Income Expense Total Other Expense Net Income Income Loss From Continuing Operations Before Income Taxes Minority Interest Income Before Non-Controlling Interest and Income Taxes Income Tax Expense Income Tax Expense Benefit Net Income Profit Loss Less: Non-Controlling Interest in Subsidiaries Net Income Attributable to ALLETE Average Shares of Common Stock Basic Diluted Basic Earnings Per Share of Common Stock Diluted Earnings Per Share of Common Stock Dividends Per Share of Common Stock Cash and Cash Equivalents, Period Increase (Decrease) [Abstract] Operating Activities Investing Activities Financing Activities Allowance for Funds Used During Construction (Income) Loss from Equity Investments, Net of Dividends Gain on Real Estate Foreclosure Income from Equity Investments, Net of Dividends Depreciation Expense Amortization of Debt Issuance Costs Deferred Income Tax Expense Stock Compensation Expense Bad Debt Expense Changes in Operating Assets and Liabilities Accounts Receivable Inventories Increase Decrease In Inventories Prepayments and Other Increase Decrease In Prepaid Deferred Expense And Other Assets Accounts Payable Increase Decrease In Accounts Payable Increase Decrease In Operating Liabilities Current The net change during the reporting period in other current operating liabilities not otherwise defined in the taxonomy Other Current Liabilities Changes in Regulatory and Other Non-Current Liabilities Changes in Regulatory and Other Non-Current Assets Increase Decrease In Other Operating Assets Cash from Operating Activities Proceeds from Sale of Available-for-Sale Securities Payments for Purchase of Available-for-Sale Securities Payments To Acquire Available For Sale Securities Payments for Purchase of Available-for-Sale Securities Payments for Purchase of Available-for-Sale Securities Payments To Acquire Equity Method Investments Other Investment In Subsidiary Investment in ATC Changes to Other Investments Changes to Other Investments Additions to Property, Plant and Equipment Additions to Property, Plant and Equipment Proceeds from Sale of Assets Cash for Investing Activities Proceeds from Issuance of Common Stock Proceeds from Issuance of Long-Term Debt Reductions of Long-Term Debt Reductions of Long-Term Debt Debt Issuance Costs Debt Issuance Costs Dividends on Common Stock Dividends on Common Stock Changes in Notes Payable Cash from (for) Financing Activities Change in Cash and Cash Equivalents Notes To Financial Statements [Abstract] Commitments, Guarantees and Contingencies Pension and Other Postretirement Benefit Plans Earnings Per Share and Common Stock Other Comprehensive Income Income Tax Expense Income Tax Disclosure [Text Block] Other Income Expense Short-term and Long-term Debt Investment in ATC Equity Method Investments [Text Block] Regulatory Matters Fair Value Derivatives Investments Investments In Debt And Marketable Equity Securities And Certain Trading Assets Disclosure Text Block Business Segments Significant Accounting Policies Regulatory Assets Regulatory Liabilities Statement of Financial Position [Abstract] Statement of Cash Flows [Abstract] Income Statement [Abstract] Accounts Receivable, Allowance Common Stock Par Value Common Stock Shares Authorized Common Stock Shares Outstanding Entity [Text Block] Document Information [Text Block] Document Fiscal Year Focus Document Fiscal Period Focus