COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 04, 2021	Mar. 30, 2024	Dec. 30, 2023
Loss Contingencies [Line Items]
Anticipated costs		$ 173.3	$ 141.8
Tax incentive receivable			460.0
Tax incentive liability			460.0
Payments for tax incentive financing			27.1
Term of purchase commitments		1 year
Site Restoration Obligations | Other noncurrent liabilities
Loss Contingencies [Line Items]
Site restoration obligation, non-current		$ 45.3	44.8
Site Restoration Obligations | Accrued expenses.
Loss Contingencies [Line Items]
Site restoration obligation, current		$ 5.9	5.1
Argos USA
Loss Contingencies [Line Items]
Payment for legal penalty	$ 20.0
Deferred Prosecution Agreement, term	3 years
Summit Materials, LLC
Loss Contingencies [Line Items]
Term of purchase commitments		1 year
Summit Materials, LLC | Site Restoration Obligations
Loss Contingencies [Line Items]
Anticipated costs		$ 173.3	141.8
Summit Materials, LLC | Site Restoration Obligations | Other noncurrent liabilities
Loss Contingencies [Line Items]
Site restoration obligation, non-current		45.3	44.8
Summit Materials, LLC | Site Restoration Obligations | Accrued expenses.
Loss Contingencies [Line Items]
Site restoration obligation, current		$ 5.9	$ 5.1