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Long-Term Debt (Schedule of Consolidated Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 09, 2024	Jun. 24, 2024	May 16, 2024	Mar. 14, 2024	Dec. 31, 2023	Jun. 08, 2023
Debt Instrument [Line Items]
Medium-Term Notes	$ 102.0					$ 102.0
Finance Lease, Liability	246.2					205.4
Senior Notes	12,103.0					10,853.0
Junior Subordinated Notes	1,000.0					0.0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	(95.5)					(81.1)
Long-Term Debt, Current Maturities	(1,281.2)					(23.8)
Long-term Debt, Excluding Current Maturities	13,355.7					11,079.3
Long-term Debt and Lease Obligation	$ 12,074.5					11,055.5
NiSource
Debt Instrument [Line Items]
Senior Notes							$ 450.0
NiSource \| 0.95% Notes Due 2025
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	0.95%
Senior Notes	$ 1,250.0					1,250.0
NiSource \| 3.49% Notes due 2027
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.49%
Senior Notes	$ 1,000.0					1,000.0
NiSource \| 6.78% Notes Due 2027
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.78%
Senior Notes	$ 3.0					3.0
NiSource \| 2.95% Notes Due 2029
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	2.95%
Senior Notes	$ 750.0					750.0
NiSource \| 3.60% Notes Due 2030
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.60%
Senior Notes	$ 1,000.0					1,000.0
NiSource \| 1.70% Notes Due 2031
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	1.70%
Senior Notes	$ 750.0					750.0
NiSource \| 6.25% Notes Due 2040
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.25%
Senior Notes	$ 152.6					152.6
NiSource \| 5.95% Notes Due 2041
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.95%
Senior Notes	$ 347.4					347.4
NiSource \| 5.80% Notes Due 2042
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.80%
Senior Notes	$ 250.0					250.0
NiSource \| 5.25% Notes Due 2043
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.25%
Senior Notes	$ 500.0					500.0
NiSource \| 4.80% Notes due 2044
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.80%
Senior Notes	$ 750.0					750.0
NiSource \| 5.65% Notes Due 2045
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.65%
Senior Notes	$ 500.0					500.0
NiSource \| 4.375% Notes due 2047
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.375%
Senior Notes	$ 1,000.0					1,000.0
NiSource \| 3.95% Notes Due 2048
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.95%
Senior Notes	$ 750.0					750.0
NiSource \| Medium-Term Note
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	7.99%
Medium-Term Notes	$ 29.0					29.0
NiSource \| 5.00% Notes Due 2052
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.00%
Senior Notes	$ 350.0					350.0
NiSource \| 5.25% Notes Due 2028
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.25%
Senior Notes	$ 1,050.0					1,050.0
NiSource \| 5.40% Notes Due 2033
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.40%
Senior Notes	$ 450.0					450.0
NiSource \| 5.20% Notes Due 2029
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.20%		5.20%
Senior Notes	$ 600.0		$ 600.0			0.0
NiSource \| 5.35% Notes Due 2034
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.35%				5.35%
Senior Notes	$ 650.0				$ 650.0	0.0
NiSource \| 6.95% Notes due 2054
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.95%			6.95%
Junior Subordinated Notes	$ 500.0			$ 500.0		0.0
NiSource \| 6.375% Notes due 2054
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.375%	6.375%
Junior Subordinated Notes	$ 500.0	$ 500.0				0.0
Columbia Of Massachusetts \| Medium-Term Note
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.373%
Medium-Term Notes	$ 15.0					15.0
NIPSCO \| Medium-Term Note
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	7.644%
Medium-Term Notes	$ 58.0					58.0
NIPSCO \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.25%
Finance Lease, Liability	$ 124.3					61.2
Columbia Of Ohio \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.15%
Finance Lease, Liability	$ 85.6					90.3
NiSource Corporate Services \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.47%
Finance Lease, Liability	$ 14.6					30.5
Columbia Of Virginia \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.19%
Finance Lease, Liability	$ 15.2					16.1
Columbia Of Kentucky \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.36%
Finance Lease, Liability	$ 0.1					0.2
Columbia Of Pennsylvania \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.47%
Finance Lease, Liability	$ 6.4					$ 7.1