CONDENSED CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Cash and cash equivalents	$ 168.0	$ 241.0
Accounts receivable, less bad debt reserve	735.0	702.0
Bad debt reserve	39.0	21.0
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	2.0	0.0
Prepaid expenses and other current assets	108.0	123.0
Regulatory assets	$ 2,149.0	$ 2,117.0
Cumulative preferred stock authorized (in shares)	20,000,000
Common stock par value (in dollars per share)	$ 0.01	$ 0.01
Common stock authorized (in shares)	1,000,000,000	1,000,000,000
Common stock outstanding (in shares)	544,709,048	502,242,061
Houston Electric [Member]
Cash and cash equivalents	$ 151.0	$ 216.0
Bad debt reserve	1.0	1.0
Prepaid expenses and other current assets	33.0	49.0
Regulatory assets	879.0	915.0
CERC Corp [Member]
Cash and cash equivalents	1.0	2.0
Accounts receivable, less bad debt reserve	265.0	322.0
Bad debt reserve	32.0	15.0
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	1.0	0.0
Prepaid expenses and other current assets	0.0	9.0
Regulatory assets	$ 201.0	$ 191.0
Cumulative Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Cumulative preferred stock authorized (in shares)	20,000,000	20,000,000
Series A Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock aggregate liquidation preference	$ 800.0	$ 800.0
Preferred stock outstanding (in shares)	800,000	800,000
Series B Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock aggregate liquidation preference	$ 977.5	$ 977.5
Preferred stock outstanding (in shares)	977,500	977,500
Series C Preferred Stock [Member]
Preferred stock par value (in dollars per share)	$ 0.01
Preferred stock aggregate liquidation preference	$ 725.0
Preferred stock outstanding (in shares)	725,000
Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	$ 149.0	$ 216.0
Accounts receivable, less bad debt reserve	27.0	26.0
Prepaid expenses and other current assets	19.0	19.0
Regulatory assets	719.0	788.0
Variable Interest Entity, Primary Beneficiary [Member] | Houston Electric [Member]
Cash and cash equivalents	149.0	216.0
Accounts receivable, less bad debt reserve	27.0	26.0
Prepaid expenses and other current assets	19.0	19.0
Regulatory assets	$ 719.0	$ 788.0