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Risk Management Activities (Narrative) (Details) mMDth in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) mMDth	Jun. 08, 2023 USD ($)	Mar. 24, 2023 USD ($)	Dec. 31, 2022 USD ($) mMDth	Jun. 07, 2022 USD ($)
Derivative [Line Items]
Limit of GCA Volumes	20.00%
Derivative Asset	$ 23.3			$ 84.8
Senior Notes	10,853.0			9,353.0
Derivative Asset, Subject to Master Netting Arrangement, after Offset	$ 13.9			81.8
Customer annual demand	20.00%
Other Current Assets
Derivative [Line Items]
Derivative Asset	$ 1.1			$ 18.8
NiSource
Derivative [Line Items]
Senior Notes		$ 450.0
Senior Notes \| NiSource
Derivative [Line Items]
Senior Notes	$ 1,050.0	$ 300.0	$ 750.0		$ 350.0
Debt, Weighted Average Interest Rate		5.25%	5.25%		5.00%
Minimum
Derivative [Line Items]
Commodity Contract Length	1 year
Maximum
Derivative [Line Items]
Commodity Contract Length	4 years
Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount \| mMDth	76.1			99.0