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Long-Term Debt (Schedule of Consolidated Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Jun. 08, 2023	Dec. 31, 2022	Aug. 30, 2022	Apr. 01, 2022
Debt Instrument [Line Items]
Medium-Term Notes	$ 102.0		$ 102.0
Finance Lease, Liability	205.4		174.7
Senior Notes	10,853.0		9,353.0
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	(81.1)		(76.1)
Long-term Debt, Excluding Current Maturities	$ 11,079.3		9,553.6
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	4.38%
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 Notes
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	7.99%			7.40%	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		0.0
NiSource \| 5.40% Notes Due 2033
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	5.40%
Senior Notes	$ 450.0		0.0
Columbia Of Massachusetts \| Medium-term Notes
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.37%
Medium-Term Notes	$ 15.0		15.0
NIPSCO \| Medium-term Notes
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	7.64%
Medium-Term Notes	$ 58.0		58.0
NIPSCO \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.77%
Finance Lease, Liability	$ 61.2		16.5
Columbia Of Ohio \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.16%
Finance Lease, Liability	$ 90.3		83.5
NiSource Corporate Services \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	2.89%
Finance Lease, Liability	$ 30.5		48.6
Columbia Of Virginia \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.23%
Finance Lease, Liability	$ 16.1		17.0
Columbia Of Kentucky \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	3.79%
Finance Lease, Liability	$ 0.2		0.2
Columbia Of Pennsylvania \| Finance Leases
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	4.49%
Finance Lease, Liability	$ 7.1		$ 8.9