Leases - Cottonwood Sale Leaseback Agreement (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Fixed lease payments per year	$ 40.0
Sale leaseback transaction, depreciation expense	$ 29.3	$ 22.7

Sales-Type And Direct Financing Leases, Lease Receivable, Payments To Be Received, Annual Payments

No definition available.

Name:	cnl_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedAnnualPayments
Namespace Prefix:	cnl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant