Pension and Other Postretirement Benefit Plans - Summary of Changes in the Fair Value of Plans' Level 3 Assets (Details) - Pension Plan - Non-U.S. Plans - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2022	Oct. 01, 2021
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
Effect of exchange rate changes	304,160	(89,051)
Fair value of plan assets at the end of the year	1,297,625	2,203,495
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	482,057
Fair value of plan assets at the end of the year	321,702	482,057
Real estate investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	187,689
Fair value of plan assets at the end of the year	143,903	187,689
Real estate investments \| Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	116,936	105,422
Purchases, sales, and settlements	(8,686)	6,288
Realized and unrealized losses	14,701	398
Acquisition of PA Consulting Plans, net of post-deal transfers		0
Effect of exchange rate changes	(20,083)	4,828
Fair value of plan assets at the end of the year	102,868	116,936
Insurance contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	133,802
Fair value of plan assets at the end of the year	80,231	133,802
Insurance contracts \| Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	133,802	67,709
Purchases, sales, and settlements	(6,312)	2,413
Realized and unrealized losses	(24,770)	1,448
Acquisition of PA Consulting Plans, net of post-deal transfers		60,160
Effect of exchange rate changes	(22,489)	2,072
Fair value of plan assets at the end of the year	80,231	133,802
Hedge funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	247,339
Fair value of plan assets at the end of the year	150,171	247,339
Hedge funds \| Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	231,319	171,730
Purchases, sales, and settlements	(11,553)	51,513
Realized and unrealized losses	(42,964)	864
Acquisition of PA Consulting Plans, net of post-deal transfers		0
Effect of exchange rate changes	(38,199)	7,212
Fair value of plan assets at the end of the year	$ 138,603	$ 231,319

Defined Benefit Plan, Plan Assets, Increase from Business Combinations, Net

No definition available.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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- Definition

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 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

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