CONDENSED CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Cash and cash equivalents	$ 220.0	$ 241.0
Accounts receivable, less bad debt reserve	711.0	702.0
Bad debt reserve	30.0	21.0
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	3.0	0.0
Prepaid expenses and other current assets	120.0	123.0
Regulatory assets	$ 2,120.0	$ 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)	502,647,495	502,242,061
Houston Electric [Member]
Cash and cash equivalents	$ 196.0	$ 216.0
Bad debt reserve	1.0	1.0
Prepaid expenses and other current assets	36.0	49.0
Regulatory assets	891.0	915.0
CERC Corp [Member]
Cash and cash equivalents	1.0	2.0
Accounts receivable, less bad debt reserve	324.0	322.0
Bad debt reserve	24.0	15.0
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	2.0	0.0
Prepaid expenses and other current assets	8.0	9.0
Regulatory assets	$ 192.0	$ 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
Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	$ 190.0	$ 216.0
Accounts receivable, less bad debt reserve	22.0	26.0
Prepaid expenses and other current assets	19.0	19.0
Regulatory assets	758.0	788.0
Variable Interest Entity, Primary Beneficiary [Member] | Houston Electric [Member]
Cash and cash equivalents	190.0	216.0
Accounts receivable, less bad debt reserve	22.0	26.0
Prepaid expenses and other current assets	19.0	19.0
Regulatory assets	$ 758.0	$ 788.0