v3.25.2
Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 12, 2025
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Disaggregation of Revenue [Line Items]          
Customer revenues   $ 1,246,500,000 $ 1,054,100,000 $ 3,396,000,000 $ 2,697,100,000
Other revenues   36,500,000 30,600,000 70,200,000 93,900,000
Total Operating Revenues   1,283,000,000 1,084,700,000 3,466,200,000 2,791,000,000
NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   777,900,000 605,300,000 2,448,400,000 1,834,100,000
NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   468,600,000 448,800,000 947,600,000 863,000,000.0
Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues $ 2,518,393 0 0 0 0
Other revenues   1,200,000 100,000 2,400,000 300,000
Corporate and Other | Unaffiliated          
Disaggregation of Revenue [Line Items]          
Revenues   1,200,000 100,000 2,400,000 300,000
NIPSCO Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   654,200,000 576,800,000 1,563,800,000 1,309,500,000
Other revenues   26,400,000 20,400,000 58,200,000 40,100,000
Total Operating Revenues   680,600,000 597,200,000    
NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   185,600,000 128,000,000.0 616,200,000 446,500,000
NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   468,600,000 448,800,000 947,600,000 863,000,000.0
NIPSCO Operations | Unaffiliated          
Disaggregation of Revenue [Line Items]          
Revenues       1,622,000,000 1,349,600,000
Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   592,300,000 477,300,000 1,832,200,000 1,387,600,000
Other revenues   8,900,000 10,100,000 9,600,000 53,500,000
Columbia Operations | Unaffiliated          
Disaggregation of Revenue [Line Items]          
Revenues       1,841,800,000 1,441,100,000
Residential | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   511,200,000 410,900,000 1,653,800,000 1,251,000,000
Residential | NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   163,900,000 156,900,000 331,800,000 300,700,000
Residential | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Residential | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   114,200,000 78,600,000 405,600,000 290,700,000
Residential | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   163,900,000 156,900,000 331,800,000 300,700,000
Residential | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   397,000,000.0 332,300,000 1,248,200,000 960,300,000
Commercial | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   171,700,000 127,600,000 581,300,000 422,700,000
Commercial | NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   161,000,000.0 154,400,000 321,100,000 297,300,000
Commercial | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Commercial | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   45,500,000 30,700,000 148,600,000 105,400,000
Commercial | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   161,000,000.0 154,400,000 321,100,000 297,300,000
Commercial | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   126,200,000 96,900,000 432,700,000 317,300,000
Industrial | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   60,200,000 49,100,000 139,500,000 113,000,000.0
Industrial | NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   133,500,000 119,700,000 276,100,000 235,600,000
Industrial | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Industrial | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   22,600,000 16,100,000 54,000,000.0 39,900,000
Industrial | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   133,500,000 119,700,000 276,100,000 235,600,000
Industrial | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   37,600,000 33,000,000.0 85,500,000 73,100,000
Off-system | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   22,800,000 10,600,000 45,100,000 23,400,000
Off-system | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Off-system | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Off-system | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   22,800,000 10,600,000 45,100,000 23,400,000
Miscellaneous | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   12,000,000.0 6,900,000 28,700,000 23,000,000.0
Miscellaneous | NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   (1,700,000) 4,700,000 (900,000) 7,900,000
Miscellaneous | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues   0 0 0 0
Miscellaneous | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues   3,300,000 2,600,000 8,000,000.0 10,500,000
Miscellaneous | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   (1,700,000) 4,700,000 (900,000) 7,900,000
Miscellaneous | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues   8,700,000 4,300,000 20,700,000 12,500,000
Wholesale | NiSource Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues     200,000   1,000,000.0
Wholesale | NiSource Electric Generation and Power Delivery          
Disaggregation of Revenue [Line Items]          
Customer revenues   11,900,000 11,200,000 19,500,000 17,500,000
Wholesale | Corporate and Other          
Disaggregation of Revenue [Line Items]          
Customer revenues     0   0
Wholesale | NIPSCO Operations | Gas Distribution          
Disaggregation of Revenue [Line Items]          
Customer revenues     0   0
Wholesale | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues   $ 11,900,000 11,200,000 $ 19,500,000 17,500,000
Wholesale | Columbia Operations          
Disaggregation of Revenue [Line Items]          
Customer revenues     200,000   1,000,000.0
Public Authority          
Disaggregation of Revenue [Line Items]          
Customer revenues     1,900,000   4,000,000.0
Public Authority | NIPSCO Operations | NIPSCO Electric Generation          
Disaggregation of Revenue [Line Items]          
Customer revenues     $ 1,900,000   $ 4,000,000.0