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Pension And Other Postretirement Benefits (Tables) | 3 Months Ended
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Mar. 31, 2017
Pension and Other Postretirement Benefit Expense [Abstract] |
Components Of The Plans' Net Periodic Benefits Cost | The following tables provide the components of the plans’ actuarially determined net periodic benefit cost for the three months ended March 31, 2017 and 2016:
| Pension Benefits |  | Other Postretirement Benefits
Three Months Ended March 31, (in millions) | 2017 |  | 2016 |  | 2017 |  | 2016
Components of Net Periodic Benefit Cost |  |  |  |  |  |  |
Service cost(1) | $ | 7.5 |  |  | $ | 7.7 |  |  | $ | 1.2 |  |  | $ | 1.2 |
Interest cost(1) | 17.2 |  |  | 22.4 |  |  | 4.5 |  |  | 5.5 |
Expected return on assets | (30.3 | ) |  | (33.2 | ) |  | (4.0 | ) |  | (4.3 | )
Amortization of prior service credit | (0.2 | ) |  | (0.1 | ) |  | (1.1 | ) |  | (1.2 | )
Recognized actuarial loss | 13.4 |  |  | 15.3 |  |  | 0.8 |  |  | 0.8 |
Total Net Periodic Benefit Cost | $ | 7.6 |  |  | $ | 12.1 |  |  | $ | 1.4 |  |  | $ | 2.0 |
(1)Effective January 1, 2017, NiSource adopted the methodology of using a full yield curve (spot rate) approach to estimate the service and interest components of net periodic benefit cost. This change in accounting estimate resulted in a decrease in these costs for the three months ended March 31, 2017 when compared to the same period in 2016.

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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