Fair Value Accounting and Financial Instruments - Fair Value of Financial Assets and Liabilities Measured On A Recurring Basis (Details) - Measured on a Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Asset description
Institutional money market funds	$ 252,807	$ 86,001
Total assets	395,037	99,405
Liability description
Total liabilities	1,589	3,237
CLECO POWER
Asset description
Institutional money market funds	135,763	25,357
Total assets	141,791	29,694
Liability description
Total liabilities	1,330	1,121
FTRs
Asset description
Derivative assets	9,338	4,805
Liability description
Derivative liabilities	1,589	1,625
FTRs | CLECO POWER
Asset description
Derivative assets	6,028	4,337
Liability description
Derivative liabilities	1,330	1,121
Natural gas derivatives*
Asset description
Derivative assets	132,892	8,599
Liability description
Derivative liabilities	0	1,612
QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)
Asset description
Institutional money market funds	0	0
Total assets	0	0
Liability description
Total liabilities	0	0
QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) | CLECO POWER
Asset description
Institutional money market funds	0	0
Total assets	0	0
Liability description
Total liabilities	0	0
QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) | FTRs
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	0	0
QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) | FTRs | CLECO POWER
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	0	0
QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) | Natural gas derivatives*
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	0	0
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2)
Asset description
Institutional money market funds	252,807	86,001
Total assets	385,699	94,600
Liability description
Total liabilities	0	1,612
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) | CLECO POWER
Asset description
Institutional money market funds	135,763	25,357
Total assets	135,763	25,357
Liability description
Total liabilities	0	0
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) | FTRs
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	0	0
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) | FTRs | CLECO POWER
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	0	0
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) | Natural gas derivatives*
Asset description
Derivative assets	132,892	8,599
Liability description
Derivative liabilities	0	1,612
SIGNIFICANT UNOBSERVABLE INPUTS (LEVEL 3)
Asset description
Institutional money market funds	0	0
Derivative assets	9,338	4,805
Total assets	9,338	4,805
Liability description
Derivative liabilities	1,589	1,625
Total liabilities	1,589	1,625
SIGNIFICANT UNOBSERVABLE INPUTS (LEVEL 3) | CLECO POWER
Asset description
Institutional money market funds	0	0
Derivative assets	6,028	4,337
Total assets	6,028	4,337
Liability description
Derivative liabilities	1,330	1,121
Total liabilities	1,330	1,121
SIGNIFICANT UNOBSERVABLE INPUTS (LEVEL 3) | FTRs
Asset description
Derivative assets	9,338	4,805
Liability description
Derivative liabilities	1,589	1,625
SIGNIFICANT UNOBSERVABLE INPUTS (LEVEL 3) | FTRs | CLECO POWER
Asset description
Derivative assets	6,028	4,337
Liability description
Derivative liabilities	1,330	1,121
SIGNIFICANT UNOBSERVABLE INPUTS (LEVEL 3) | Natural gas derivatives*
Asset description
Derivative assets	0	0
Liability description
Derivative liabilities	$ 0	$ 0