Goodwill and Intangibles - Schedule of Carrying Value of Goodwill by Reportable Segment Appearing in Accompanying Consolidated Balance Sheets (Details) $ in Thousands	12 Months Ended
	Sep. 26, 2025 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 4,788,181
Foreign currency translation and other	(7,363)
Ending balance	4,780,818
Infrastructure & Advanced Facilities
Goodwill [Roll Forward]
Beginning balance	3,362,760
Foreign currency translation and other	(11,270)
Ending balance	3,351,490
PA Consulting
Goodwill [Roll Forward]
Beginning balance	1,425,421
Foreign currency translation and other	3,907
Ending balance	$ 1,429,328