Intangible Assets and Liabilities - Narrative (Details) - USD ($)		9 Months Ended	12 Months Ended
	Aug. 01, 2021	Sep. 30, 2021	Dec. 31, 2008	Dec. 31, 2020	Mar. 31, 2020	Apr. 13, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets		$ 88,635,000		$ 111,731,000
Goodwill		1,490,797,000		$ 1,490,797,000		$ 1,490,000,000
Goodwill impairment	$ 0
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets, residual value		0
Impairment of intangible assets		3,800,000
Intangible assets		$ 0
Power supply agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		7 years
Power supply agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		19 years
Cleco Katrina/Rita
Finite-Lived Intangible Assets [Line Items]
Intangible assets, residual value					$ 0
Cleco Katrina/Rita | Cleco Katrina/Rita right to bill and collect storm recovery charges
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired			$ 177,500,000
Cleco Katrina/Rita | Cleco Katrina/Rita right to bill and collect storm recovery charges from customers, net of financing costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired			176,000,000
Cleco Katrina/Rita | Financing costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired			$ 1,500,000
Cleco Cajun | LTSA
Finite-Lived Intangible Assets [Line Items]
Intangible liabilities, remaining life		7 years
Cleco Cajun | Power supply agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, residual value		$ 0
Cleco Cajun | Power supply agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, remaining life		6 years
Cleco Cajun | Power supply agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Intangible assets, remaining life		8 years