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Pension and Other Postretirement Benefit Plans | 9 Months Ended
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Sep. 30, 2017
Retirement Benefits [Abstract] |
Pension and Other Postretirement Benefit Plans [Text Block] | PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS
| Pension |  | Other Postretirement
Components of Net Periodic Benefit Cost (Income) | 2017 |  | 2016 |  | 2017 |  | 2016
Millions |  |  |  |  |  |  |
Quarter Ended September 30, |  |  |  |  |  |  |
Service Cost |  | $2.6 |  |  |  | $2.0 |  |  |  | $1.1 |  |  |  | $1.0 |
Interest Cost | 8.1 |  |  | 8.2 |  |  | 2.0 |  |  | 1.9 |
Expected Return on Plan Assets | (10.6 | ) |  | (10.7 | ) |  | (2.6 | ) |  | (2.8 | )
Amortization of Prior Service Credits | — |  |  | — |  |  | (0.5 | ) |  | (0.7 | )
Amortization of Net Loss | 2.5 |  |  | 2.4 |  |  | — |  |  | — |
Net Periodic Benefit Cost (Income) |  | $2.6 |  |  |  | $1.9 |  |  | — |  |  | $(0.6)
Nine Months Ended September 30, |  |  |  |  |  |  |
Service Cost |  | $7.7 |  |  |  | $6.1 |  |  |  | $3.3 |  |  |  | $3.0 |
Interest Cost | 24.4 |  |  | 24.4 |  |  | 5.8 |  |  | 5.6 |
Expected Return on Plan Assets | (31.8 | ) |  | (32.0 | ) |  | (7.9 | ) |  | (8.4 | )
Amortization of Prior Service Credits | — |  |  | — |  |  | (1.5 | ) |  | (2.2 | )
Amortization of Net Loss | 7.4 |  |  | 7.3 |  |  | 0.2 |  |  | 0.1 |
Net Periodic Benefit Cost (Income) |  | $7.7 |  |  |  | $5.8 |  |  | $(0.1) |  | $(1.9)
Employer Contributions. For the nine months ended September 30, 2017, we contributed $1.7 million in cash and $13.5 million in ALLETE common stock to the defined benefit pension plans ($6.3 million in cash for the nine months ended September 30, 2016); we do not expect to make additional contributions to our defined benefit pension plans in 2017. For the nine months ended September 30, 2017, and 2016, we made no contributions to our other postretirement benefit plans; we do not expect to make any contributions to our other postretirement benefit plans in 2017.

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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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