Segment Information - Schedule of Total Services Revenues for Reportable Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 29, 2023	Sep. 30, 2022	Oct. 01, 2021
Segment Reporting Information [Line Items]
Revenues	$ 16,352,414	$ 14,922,825	$ 14,092,632
Critical Mission Solutions | Operating Segments
Segment Reporting Information [Line Items]
Revenues	4,693,499	4,376,562	4,251,690
People & Places Solutions | Operating Segments
Segment Reporting Information [Line Items]
Revenues	9,553,857	8,534,650	8,364,640
Divergent Solutions | Operating Segments
Segment Reporting Information [Line Items]
Revenues	946,914	892,317	848,901
PA Consulting | Operating Segments
Segment Reporting Information [Line Items]
Revenues	$ 1,158,144	$ 1,119,296	$ 627,401