Income Taxes Merger with Vectren (Details) - USD ($) $ in Millions		12 Months Ended
	Feb. 01, 2019	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Deferred tax assets, valuation allowance		$ 26	$ 25
Unrecognized tax benefits assumed through the Merger		0	9
CERC Corp [Member]
Business Acquisition [Line Items]
Deferred tax assets, valuation allowance		15
State and Local Jurisdiction
Business Acquisition [Line Items]
Operating loss carryforwards		979
Deferred tax assets tax credit carryforwards		22
State and Local Jurisdiction | CERC Corp [Member]
Business Acquisition [Line Items]
Operating loss carryforwards		592
Deferred tax assets tax credit carryforwards		17
Domestic Tax Authority | CERC Corp [Member]
Business Acquisition [Line Items]
Deferred tax assets tax credit carryforwards		425
Vectren [Member]
Business Acquisition [Line Items]
Cash paid to acquire Vectren	$ 6,000		5,982
Operating loss carryforwards		177
Unrecognized tax benefits assumed through the Merger		9	$ 9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		2
Unrecognized Tax benefit, impacting ETR if recognized		3
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		6
Charitable Contribution [Member] | Vectren [Member]
Business Acquisition [Line Items]
Deferred tax assets tax credit carryforwards		$ 60