Intangible Assets and Goodwill - Summary of Intangible Assets (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2008
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 160,798,000	$ 160,798,000
Accumulated amortization	(69,016,000)	(45,948,000)
Net intangible assets subject to amortization	91,782,000	114,850,000
Cleco Katrina/Rita right to bill and collect storm recovery charges
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	70,594,000	70,594,000
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	5,100,000	5,100,000
Power supply agreements
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	85,104,000	85,104,000
CLECO POWER
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	(151,453,000)	(135,836,000)	$ 0
Net intangible assets subject to amortization	26,084,000	41,701,000
CLECO POWER | Cleco Katrina/Rita right to bill and collect storm recovery charges
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 177,537,000	$ 177,537,000