Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2008	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 52,917,000			$ 45,948,000
Reduction in revenue on intangible assets for power supply agreements	2,400,000	$ 3,500,000
Trade name
Finite-Lived Intangible Assets [Line Items]
Residual value	0
Amortization of intangible assets (less than)	$ 100,000	100,000
Finite-lived intangible asset, useful life	20 years
Power supply agreements
Finite-Lived Intangible Assets [Line Items]
Residual value	$ 0
Power supply agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	5 years
Power supply agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	17 years
Cleco Power
Finite-Lived Intangible Assets [Line Items]
Residual value	$ 0
Accumulated amortization	140,321,000		$ 0	$ 135,836,000
Cleco Power | 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
Amortization of intangible assets (less than)	$ 4,500,000	$ 3,500,000
Cleco Power | 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 Power | Financing costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired			$ 1,500,000