Indexed Debt Securities (ZENS) and Securities Related to ZENS (CenterPoint Energy) (Tables)

3 Months Ended

Mar. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Schedule of Indexed Debt Securities and Marketable Securities [Table Text Block]

A subsidiary of CenterPoint Energy holds shares of certain securities detailed in the table below, which are securities with a readily determinable fair value and are expected to be held to facilitate CenterPoint Energy’s ability to meet its obligation under the ZENS. Unrealized gains and losses resulting from changes in the market value of the ZENS-Related Securities are recorded in CenterPoint Energy’s Condensed Statements of Consolidated Income.

	Shares Held
	March 31, 2021	December 31, 2020
AT&T Common	10,212,945	10,212,945
Charter Common	872,503	872,503

(b) ZENS

In September 1999, CenterPoint Energy issued ZENS having an original principal amount of $1.0 billion of which $828 million remained outstanding as of March 31, 2021. Each ZENS is exchangeable at the holder’s option at any time for an amount of cash equal to 95% of the market value of the reference shares attributable to such note. The number and identity of the reference shares attributable to each ZENS are adjusted for certain corporate events.

CenterPoint Energy’s reference shares for each ZENS consisted of the following:

	March 31, 2021	December 31, 2020
	(in shares)
AT&T Common	0.7185	0.7185
Charter Common	0.061382	0.061382