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Pension And Other Postretirement Benefits | 3 Months Ended
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Mar. 31, 2017
Pension and Other Postretirement Benefit Expense [Abstract] |
Pension And Other Postretirement Benefits | Pension and Other Postretirement Benefits NiSource provides defined contribution plans and noncontributory defined benefit retirement plans that cover certain of its employees. Benefits under the defined benefit retirement plans reflect the employees’ compensation, years of service and age at retirement. Additionally, NiSource provides health care and life insurance benefits for certain retired employees. The majority of employees may become eligible for these benefits if they reach retirement age while working for NiSource. The expected cost of such benefits is accrued during the employees’ years of service. For most plans, cash contributions are remitted to grantor trusts. For the three months ended March 31, 2017, NiSource contributed $1.1 million to its pension plans and $7.6 million to its other postretirement benefit plans. 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 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 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2410-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39675-114964 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66047640&loc=d3e39622-114963 + Details
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