CONDENSED CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Cash and cash equivalents	$ 271.0	$ 4,231.0
Accounts receivable, less bad debt reserve	1,173.0	1,190.0
Bad debt reserve	27.0	18.0
Prepaid expenses and other current assets	181.0	192.0
Regulatory assets	$ 2,228.0	$ 1,967.0
Preferred stock par value (in dollars per share)	$ 0.01
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)	502,214,639	501,197,784
Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	$ 260.0	$ 335.0
Accounts receivable, less bad debt reserve	77.0	56.0
Prepaid expenses and other current assets	33.0	34.0
Regulatory assets	895.0	1,059.0
Houston Electric [Member]
Cash and cash equivalents	260.0	335.0
Bad debt reserve	1.0	1.0
Prepaid expenses and other current assets	41.0	61.0
Regulatory assets	1,016.0	1,124.0
Houston Electric [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Cash and cash equivalents	260.0	335.0
Accounts receivable, less bad debt reserve	77.0	56.0
Prepaid expenses and other current assets	33.0	34.0
Regulatory assets	895.0	1,059.0
CERC Corp [Member]
Cash and cash equivalents	1.0	14.0
Accounts receivable, less bad debt reserve	506.0	894.0
Bad debt reserve	21.0	17.0
Prepaid expenses and other current assets	39.0	115.0
Regulatory assets	$ 187.0	$ 181.0
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

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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