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Property, Plant, and Equipment	3 Months Ended
Property, Plant, and Equipment	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure	Property, Plant and Equipment In 2020, the MISO approved NIPSCO's plan to retire the R.M. Schahfer Generating Station in 2023. The December 2019 NIPSCO electric rate case order included approval to create a regulatory asset upon the retirement of the R.M. Schahfer Generating Station. The order allows for the recovery of and on the net book value of the station by the end of 2032. In connection with the MISO's approval of NIPSCO's planned retirement of the R.M. Schahfer Generating Station, we recorded plant retirement-related charges during 2020 comprised of write downs of certain capital projects that have been cancelled and materials and supplies inventory balances deemed obsolete due to the planned retirement. As more information becomes available, the retirement date of the R.M. Schahfer Generating Station will be finalized, and additional plant retirement-related charges may be incurred. An immaterial amount of plant retirement-related charges were included within "Operation and maintenance" in the Condensed Statement of Consolidated Income (unaudited) during the three months ended March 31, 2021. On March 11, 2021, NIPSCO submitted modified Attachment Y Notices to MISO requesting an updated retirement date for two of the four coal fired units at R.M. Schahfer Generating Station. The two units are now expected to be retired by the end of 2021, with the remaining two units still scheduled to be retired in 2023. At retirement, the net book value of the retired units will be reclassified from "Net Property, Plant and Equipment", to current and long-term “Regulatory Assets.” The total net book value of R.M. Schahfer Generating Station's coal units and other associated plant was $861.6 million at March 31, 2021. On April 28, 2021, in response to a Motion filed by certain parties in NIPSCO's quarterly FAC proceeding, the IURC created a sub-docket proceeding in order to receive additional information related to the planned retirements of Units 14 and 15 by the end of 2021 and any resulting cost impacts to customers. NIPSCO does not anticipate that the sub-docket proceeding will impact the planned timing of end of year 2021 for the unit retirements.