Pension and Other Postretirement Benefit Plans - Schedule of Change in Combined Fair Value of Plans' Assets (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2022	Oct. 01, 2021
U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	$ 385,521	$ 382,250
Actual (loss) return on plan assets	(68,585)	35,152
Employer contributions	93	88
Participants’ contributions	0	0
Gross benefits paid	(25,565)	(25,582)
Curtailments/settlements/plan amendments	(5,271)	(6,387)
Acquisition of PA Consulting Plans, net of post-deal transfers	0	0
Effect of exchange rate changes and other, net	0	0
Fair value of plan assets at the end of the year	286,193	385,521
Non-U.S. Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	2,203,495	2,043,356
Actual (loss) return on plan assets	(557,972)	60,040
Employer contributions	33,032	39,085
Participants’ contributions	249	212
Gross benefits paid	(74,378)	(74,477)
Curtailments/settlements/plan amendments	(2,641)	(13,932)
Acquisition of PA Consulting Plans, net of post-deal transfers	0	60,160
Effect of exchange rate changes and other, net	(304,160)	89,051
Fair value of plan assets at the end of the year	$ 1,297,625	$ 2,203,495

Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment, Settlements and Plan Amendments 1

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- Definition

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of increase in plan assets of defined benefit plan from business combination.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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- Definition

Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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Amount of contributions received by defined benefit plan from participant which increases plan assets.

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- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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