Regulatory Matters (Rate Case Action) (Details) - USD ($) $ in Millions		May 22, 2019	Oct. 31, 2018	Aug. 28, 2018	Sep. 27, 2017
Rate Case Action [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Adjustment				$ 5.2
NIPSCO - Gas
Rate Case Action [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[1]				$ 138.1
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 107.3
Columbia Of Virginia
Rate Case Action [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[2]			14.2
Public Utilities, Approved Rate Increase (Decrease), Amount				$ 1.3
NIPSCO - Electric
Rate Case Action [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[3]		$ 21.4
Public Utilities, Approved Rate Increase (Decrease), Amount			(45.0)
Public Utilities, Requested Rate Increase (Decrease), Adjustment			83.6
Public Utilities, Approved Rate Increase (Decrease), Adjustment			$ 85.3
Columbia Of Maryland
Rate Case Action [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 2.5

[1] Rates will be implemented in three steps, with implementation of step 1 rates effective October 1, 2018. Step 2 rates were effective on March 1, 2019, and step 3 rates will be effective on January 1, 2020. The IURC’s order also dismissed NIPSCO from phase 2 of the IURC’s TCJA investigation.

[2] Rates as originally filed were implemented in February 2019 on an interim basis, subject to refund. The final approved rates, which replaced interim rates, were implemented in July 2019.

[3] An order on the partial settlement agreement, including the resolution of outstanding TCJA impacts to rates is currently pending before the IURC. The as-filed request and partial settlement agreement also includes $83.6 million and $85.3 million, respectively, of reductions to the fuel component of base rates related to a proposed change in service structure.