Commitments and Contingencies - Narrative (Details) $ in Millions	1 Months Ended	6 Months Ended
	Dec. 31, 2018 lawsuit	Jun. 30, 2021 USD ($) ashPond gasManufacturingAndStorageSite warrantyObligation suretyBond lawsuit MW	Dec. 31, 2020 USD ($)	Aug. 31, 2018 lawsuit	Jul. 31, 2018 lawsuit
Loss Contingencies [Line Items]
Number of surety bond obligations outstanding | suretyBond		47
Performance guarantee obligations outstanding face amount		$ 484
Percentage of work yet to be completed on projects with open surety bonds		34.00%
Number of warranty obligations outstanding | warrantyObligation		34
Warranty obligations outstanding face amount		$ 553
Energy savings commitments not guaranteed		1,200
Guarantor obligations, maximum exposure, undiscounted		$ 517
Number of owned coal ash ponds | ashPond		3
F.B. Culley
Loss Contingencies [Line Items]
Number of owned coal ash ponds | ashPond		2
A.B. Brown
Loss Contingencies [Line Items]
Number of owned coal ash ponds | ashPond		1
Indiana Gas Service Territory
Loss Contingencies [Line Items]
Environmental remediation number of sites with potential remedial responsibility | gasManufacturingAndStorageSite		26
SIGECO
Loss Contingencies [Line Items]
Environmental remediation number of sites with potential remedial responsibility | gasManufacturingAndStorageSite		5
Vectren Proxy Statement Materially Incomplete Related to Merger
Loss Contingencies [Line Items]
Pending lawsuits | lawsuit				7	7
Number of claims dismissed | lawsuit	2
February 2021 Winter Storm
Loss Contingencies [Line Items]
Pending lawsuits | lawsuit		65
Shell Energy North America (US), L.P.
Loss Contingencies [Line Items]
Guarantor obligations, maximum exposure, undiscounted		$ 40
Houston Electric | February 2021 Winter Storm
Loss Contingencies [Line Items]
Pending lawsuits | lawsuit		65
Indiana Electric
Loss Contingencies [Line Items]
Asset retirement obligation		$ 88
Indiana Electric | Minimum
Loss Contingencies [Line Items]
Estimated capital expenditure to clean ash ponds		60
Indiana Electric | Maximum
Loss Contingencies [Line Items]
Estimated capital expenditure to clean ash ponds		80
Energy Services Disposal Group
Loss Contingencies [Line Items]
Guarantor obligation, current carrying value		$ 0	$ 0
Energy Services Disposal Group | CERC Corp
Loss Contingencies [Line Items]
Exposure period after closing		90 days
Annualized fee received for retained CES guarantee exposure		3.00%
Quarterly increase of fee received for retained CES guarantee exposure		1.00%
Exposure period until increased fee		3 months
Estimated remaining exposure		$ 35
Additional guarantees		0
Guarantor obligation, current carrying value		0	$ 0
ESG
Loss Contingencies [Line Items]
Fair value of guarantees		$ 0
Posey Solar
Loss Contingencies [Line Items]
Solar array generating capacity (in MW) | MW		300