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Schedule II | 12 Months Ended
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Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] |
Schedule II [Text Block] | Schedule II ALLETE Valuation and Qualifying Accounts and Reserves
| Balance at Beginning of Period | Additions | Deductions from Reserves (a) | Balance at End of Period
| Charged to Income | Other Charges
Millions |  |  |  |  |
Reserve Deducted from Related Assets |  |  |  |  |
Reserve For Uncollectible Accounts |  |  |  |  |
2016 Trade Accounts Receivable |  | $1.0 |  |  | $4.1 |  | — |  |  | $2.0 |  |  | $3.1 |
Finance Receivables – Long-Term |  | $0.6 |  | — |  | — |  | $0.6 | — |
2017 Trade Accounts Receivable |  | $3.1 |  |  | $0.8 |  | — |  |  | $1.8 |  |  | $2.1 |
Finance Receivables – Long-Term | — |  | — |  | — |  | — |  | — |
2018 Trade Accounts Receivable |  | $2.1 |  | $0.9 | — |  |  | $1.3 |  |  | $1.7 |
Finance Receivables – Long-Term | — |  | — |  | — |  | — |  | — |
Deferred Asset Valuation Allowance |  |  |  |  |
2016 Deferred Tax Assets |  | $31.6 |  | $11.4 | — |  | — |  |  | $43.0 |
2017 Deferred Tax Assets |  | $43.0 |  | $17.0 | — |  | — |  |  | $60.0 |
2018 Deferred Tax Assets |  | $60.0 |  |  | $6.5 |  | — |  | — |  |  | $66.5 |
(a) | Includes uncollectible accounts written-off.

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- Definition The entire disclosure for valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- References No definition available. + Details
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