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Pension and Other Postretirement Benefit Plans | 3 Months Ended
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Mar. 31, 2018
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 | 2018 |  | 2017 |  | 2018 |  | 2017
Millions |  |  |  |  |  |  |
Three Months Ended March 31, |  |  |  |  |  |  |
Service Cost |  | $2.7 |  |  |  | $2.5 |  |  |  | $1.2 |  |  |  | $1.1 |
Interest Cost (a) | 7.4 |  |  | 8.1 |  |  | 1.8 |  |  | 1.9 |
Expected Return on Plan Assets (a) | (11.0 | ) |  | (10.6 | ) |  | (2.7 | ) |  | (2.6 | )
Amortization of Prior Service Credits (a) | — |  |  | — |  |  | (0.4 | ) |  | (0.5 | )
Amortization of Net Loss (a) | 3.0 |  |  | 2.5 |  |  | 0.2 |  |  | 0.1 |
Net Periodic Benefit Cost |  | $2.1 |  |  |  | $2.5 |  |  |  | $0.1 |  |  | — |
(a) | These components of net periodic benefit cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.
Employer Contributions. For the three months ended March 31, 2018, we contributed $15.0 million in cash to the defined benefit pension plans ($1.7 million in cash and $13.5 million in ALLETE common stock for the three months ended March 31, 2017); we do not expect to make additional contributions to our defined benefit pension plans in 2018. For the three months ended March 31, 2018, and 2017, 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 2018.

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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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