Regulatory Matters	3 Months Ended
Mar. 31, 2017
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Gas Distribution Operations Regulatory Matters Cost Recovery and Trackers. Comparability of Gas Distribution Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as those described below. Increases in the expenses that are the subject of trackers result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results. Certain operating costs of the NiSource distribution companies are significant, recurring in nature, and generally outside the control of the distribution companies. Some states allow the recovery of such costs through cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for the distribution companies to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include GCR adjustment mechanisms, tax riders, and bad debt recovery mechanisms. A portion of the distribution companies' revenue is related to the recovery of gas costs, the review and recovery of which occurs through standard regulatory proceedings. All states in NiSource's operating area require periodic review of actual gas procurement activity to determine prudence and to permit the recovery of prudently incurred costs related to the supply of gas for customers. NiSource distribution companies have historically been found prudent in the procurement of gas supplies to serve customers. Certain of the NiSource distribution companies have completed rate proceedings involving infrastructure replacement or are embarking upon regulatory initiatives to replace significant portions of their operating systems that are nearing the end of their useful lives. Each LDC's approach to cost recovery may be unique, given the different laws, regulations and precedent that exist in each jurisdiction. Columbia of Ohio. On November 28, 2012, the PUCO approved Columbia of Ohio’s application to extend its IRP for an additional five years (2013-2017), allowing Columbia of Ohio to continue to invest and recover on its accelerated main replacements. Columbia of Ohio filed its application to adjust rates associated with its IRP and DSM Riders on February 27, 2017, which requested authority to increase revenues by approximately $31.5 million. On March 23, 2017, the PUCO Staff filed comments which recommended approval of the application with only minor revisions. The PUCO issued an order on April 26, 2017, approving Columbia of Ohio's application. New rates went into effect on May 1, 2017. On December 27, 2016, Columbia of Ohio filed its Notice of Intent to file an application that will request authority for Columbia of Ohio to extend its IRP for an additional five years (2018-2022). Columbia of Ohio’s application was filed on February 27, 2017. An order is expected by the end of 2017. NIPSCO Gas. On April 30, 2013, then Indiana Governor Pence signed Senate Enrolled Act 560, the TDSIC statute, into law. Among other provisions, this legislation provides for cost recovery outside of a base rate proceeding for new or replacement electric and gas transmission, distribution, and storage projects that a public utility undertakes for the purposes of safety, reliability, system modernization, or economic development. Provisions of the TDSIC statute require that, among other things, requests for recovery include a seven-year plan of eligible investments. Once the plan is approved by the IURC, eighty percent of eligible costs can be recovered using a periodic rate adjustment mechanism. The cost recovery mechanism is referred to as a TDSIC mechanism. Recoverable costs include a return on, and of, the investment, including AFUDC, post-in-service carrying charges, operation and maintenance expenses, depreciation and property taxes. The remaining twenty percent of recoverable costs are to be deferred for future recovery in the public utility’s next general rate case. The periodic rate adjustment mechanism is capped at an annual increase of no more than two percent of total retail revenues. On December 28, 2016, the IURC issued an order on the seven-year plan (2014-2020) within TDSIC-5 approving NIPSCO’s updated estimate of TDSIC-eligible investments of $824 million. The order also included approval to begin recovery of $211.6 million of cumulative net capital spend through June 30, 2016. New rates went into effect on January 1, 2017. On February 28, 2017, NIPSCO filed TDSIC-6 requesting approval of $271.3 million of cumulative net capital spend through December 31, 2016. An order is expected in June 2017, with new rates effective July 1, 2017. Columbia of Massachusetts. On July 7, 2014, the Governor of Massachusetts signed into law Chapter 149 of the Acts of 2014, An Act Relative to Natural Gas Leaks (“the Act”). The Act authorizes natural gas distribution companies to file gas infrastructure replacement plans with the Massachusetts DPU to address the replacement of aging natural gas pipeline infrastructure. In addition, the Act provides that the Massachusetts DPU may, after review of the plans, allow the proposed estimated costs of the plan into rates as of May 1 of the subsequent year. On October 31, 2016, Columbia of Massachusetts filed its GSEP for the 2017 construction year. Columbia of Massachusetts is proposing to recover an incremental $8.4 million for a cumulative revenue requirement of $17.2 million. An order was received from the Massachusetts DPU on April 28, 2017, and rates went into effect on May 1, 2017. Columbia of Virginia. On April 29, 2016, Columbia of Virginia filed a request with the VSCC, seeking an annual revenue increase of $37.0 million. The case was driven by Columbia of Virginia's ongoing capital program to modernize its infrastructure and to expand and upgrade its facilities to meet customer growth, as well as expenditures related to employee training and compliance with pipeline safety regulations. On September 28, 2016, Columbia of Virginia implemented updated interim base rates subject to refund. On January 17, 2017, Columbia of Virginia presented a stipulation and proposed recommendation, representing a settlement by all parties to the proceeding that included a base revenue increase of $28.5 million. On February 8, 2017, the hearing examiner in the case filed a report recommending approval of the stipulation and proposed recommendation. On March 17, 2017, by final order, the VSCC approved the settlement agreement without modification. Under terms of the final order, Columbia of Virginia will refund within 90 days the difference between the interim customer rates implemented in 2016 and the rates approved by the final order. Columbia of Maryland. On April 14, 2017, Columbia of Maryland filed a request with the MPSC to adjust its base rates so it can continue to expedite the replacement of aging pipe as well as adopt pipeline safety upgrades. If approved as filed, the rate adjustment would result in an annual revenue increase of approximately $6 million. An order is expected by the end of 2017. Electric Operations Regulatory Matters Cost Recovery and Trackers. Comparability of Electric Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as those described below. Increases in the expenses that are the subject of trackers result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results. Certain operating costs of the Electric Operations are significant, recurring in nature, and generally outside the control of NIPSCO. The IURC allows for recovery of such costs through cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for NIPSCO to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include electric energy efficiency programs, MISO non-fuel costs and revenues, resource capacity charges, federally mandated costs and environmental related costs. A portion of NIPSCO's revenue is related to the recovery of fuel costs to generate power and the fuel costs related to purchased power. These costs are recovered through a FAC, a quarterly regulatory proceeding in Indiana. NIPSCO has approval from the IURC to recover certain environmental related costs through an ECT. Under the ECT, NIPSCO is permitted to recover (1) AFUDC and a return on the capital investment expended by NIPSCO to implement environmental compliance plan projects and (2) related operation and maintenance and depreciation expenses once the environmental facilities become operational. On January 31, 2017, NIPSCO filed ECR-29 which included $261.1 million of net capital expenditures for the period ended December 31, 2016. An order was received from the IURC on April 26, 2017. NIPSCO made a TDSIC rate adjustment mechanism filing on June 30, 2016 seeking recovery and ratemaking relief associated with $45.5 million of cumulative net capital expenditures invested through April 30, 2016. An IURC order approving NIPSCO's filing was received on January 25, 2017. New rates went into effect with the first billing cycle of February 2017. On November 1, 2016, NIPSCO filed a petition with the IURC for relief regarding the construction of additional environmental projects required to comply with the final rules for regulation of CCRs and the ELG. An order is expected by the end of 2017. Refer to Note 14-C, “Environmental Matters,” for more information.

Regulatory Matters

Gas Distribution Operations Regulatory Matters

Cost Recovery and Trackers. Comparability of Gas Distribution Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as those described below. Increases in the expenses that are the subject of trackers result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results.

Certain operating costs of the NiSource distribution companies are significant, recurring in nature, and generally outside the control of the distribution companies. Some states allow the recovery of such costs through cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for the distribution companies to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include GCR adjustment mechanisms, tax riders, and bad debt recovery mechanisms.

A portion of the distribution companies' revenue is related to the recovery of gas costs, the review and recovery of which occurs through standard regulatory proceedings. All states in NiSource's operating area require periodic review of actual gas procurement activity to determine prudence and to permit the recovery of prudently incurred costs related to the supply of gas for customers. NiSource distribution companies have historically been found prudent in the procurement of gas supplies to serve customers.

Certain of the NiSource distribution companies have completed rate proceedings involving infrastructure replacement or are embarking upon regulatory initiatives to replace significant portions of their operating systems that are nearing the end of their useful lives. Each LDC's approach to cost recovery may be unique, given the different laws, regulations and precedent that exist in each jurisdiction.

Columbia of Ohio. On November 28, 2012, the PUCO approved Columbia of Ohio’s application to extend its IRP for an additional five years (2013-2017), allowing Columbia of Ohio to continue to invest and recover on its accelerated main replacements. Columbia of Ohio filed its application to adjust rates associated with its IRP and DSM Riders on February 27, 2017, which requested authority to increase revenues by approximately $31.5 million. On March 23, 2017, the PUCO Staff filed comments which recommended approval of the application with only minor revisions. The PUCO issued an order on April 26, 2017, approving Columbia of Ohio's application. New rates went into effect on May 1, 2017.

On December 27, 2016, Columbia of Ohio filed its Notice of Intent to file an application that will request authority for Columbia of Ohio to extend its IRP for an additional five years (2018-2022). Columbia of Ohio’s application was filed on February 27, 2017. An order is expected by the end of 2017.

NIPSCO Gas. On April 30, 2013, then Indiana Governor Pence signed Senate Enrolled Act 560, the TDSIC statute, into law. Among other provisions, this legislation provides for cost recovery outside of a base rate proceeding for new or replacement electric and gas transmission, distribution, and storage projects that a public utility undertakes for the purposes of safety, reliability, system modernization, or economic development. Provisions of the TDSIC statute require that, among other things, requests for recovery include a seven-year plan of eligible investments. Once the plan is approved by the IURC, eighty percent of eligible costs can be recovered using a periodic rate adjustment mechanism. The cost recovery mechanism is referred to as a TDSIC mechanism. Recoverable costs include a return on, and of, the investment, including AFUDC, post-in-service carrying charges, operation and maintenance expenses, depreciation and property taxes. The remaining twenty percent of recoverable costs are to be deferred for future recovery in the public utility’s next general rate case. The periodic rate adjustment mechanism is capped at an annual increase of no more than two percent of total retail revenues. On December 28, 2016, the IURC issued an order on the seven-year plan (2014-2020) within TDSIC-5 approving NIPSCO’s updated estimate of TDSIC-eligible investments of $824 million. The order also included approval to begin recovery of $211.6 million of cumulative net capital spend through June 30, 2016. New rates went into effect on January 1, 2017. On February 28, 2017, NIPSCO filed TDSIC-6 requesting approval of $271.3 million of cumulative net capital spend through December 31, 2016. An order is expected in June 2017, with new rates effective July 1, 2017.

Columbia of Massachusetts. On July 7, 2014, the Governor of Massachusetts signed into law Chapter 149 of the Acts of 2014, An Act Relative to Natural Gas Leaks (“the Act”). The Act authorizes natural gas distribution companies to file gas infrastructure replacement plans with the Massachusetts DPU to address the replacement of aging natural gas pipeline infrastructure. In addition, the Act provides that the Massachusetts DPU may, after review of the plans, allow the proposed estimated costs of the plan into rates as of May 1 of the subsequent year. On October 31, 2016, Columbia of Massachusetts filed its GSEP for the 2017 construction year. Columbia of Massachusetts is proposing to recover an incremental $8.4 million for a cumulative revenue requirement of $17.2 million. An order was received from the Massachusetts DPU on April 28, 2017, and rates went into effect on May 1, 2017.

Columbia of Virginia. On April 29, 2016, Columbia of Virginia filed a request with the VSCC, seeking an annual revenue increase of $37.0 million. The case was driven by Columbia of Virginia's ongoing capital program to modernize its infrastructure and to expand and upgrade its facilities to meet customer growth, as well as expenditures related to employee training and compliance with pipeline safety regulations. On September 28, 2016, Columbia of Virginia implemented updated interim base rates subject to refund. On January 17, 2017, Columbia of Virginia presented a stipulation and proposed recommendation, representing a settlement by all parties to the proceeding that included a base revenue increase of $28.5 million. On February 8, 2017, the hearing examiner in the case filed a report recommending approval of the stipulation and proposed recommendation. On March 17, 2017, by final order, the VSCC approved the settlement agreement without modification. Under terms of the final order, Columbia of Virginia will refund within 90 days the difference between the interim customer rates implemented in 2016 and the rates approved by the final order.

Columbia of Maryland. On April 14, 2017, Columbia of Maryland filed a request with the MPSC to adjust its base rates so it can continue to expedite the replacement of aging pipe as well as adopt pipeline safety upgrades. If approved as filed, the rate adjustment would result in an annual revenue increase of approximately $6 million. An order is expected by the end of 2017.

Electric Operations Regulatory Matters

Cost Recovery and Trackers. Comparability of Electric Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as those described below. Increases in the expenses that are the subject of trackers result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results.

Certain operating costs of the Electric Operations are significant, recurring in nature, and generally outside the control of NIPSCO. The IURC allows for recovery of such costs through cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for NIPSCO to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include electric energy efficiency programs, MISO non-fuel costs and revenues, resource capacity charges, federally mandated costs and environmental related costs.

A portion of NIPSCO's revenue is related to the recovery of fuel costs to generate power and the fuel costs related to purchased power. These costs are recovered through a FAC, a quarterly regulatory proceeding in Indiana.

NIPSCO has approval from the IURC to recover certain environmental related costs through an ECT. Under the ECT, NIPSCO is permitted to recover (1) AFUDC and a return on the capital investment expended by NIPSCO to implement environmental compliance plan projects and (2) related operation and maintenance and depreciation expenses once the environmental facilities become operational. On January 31, 2017, NIPSCO filed ECR-29 which included $261.1 million of net capital expenditures for the period ended December 31, 2016. An order was received from the IURC on April 26, 2017.

NIPSCO made a TDSIC rate adjustment mechanism filing on June 30, 2016 seeking recovery and ratemaking relief associated with $45.5 million of cumulative net capital expenditures invested through April 30, 2016. An IURC order approving NIPSCO's filing was received on January 25, 2017. New rates went into effect with the first billing cycle of February 2017.

On November 1, 2016, NIPSCO filed a petition with the IURC for relief regarding the construction of additional environmental projects required to comply with the final rules for regulation of CCRs and the ELG. An order is expected by the end of 2017. Refer to Note 14-C, “Environmental Matters,” for more information.