Employee Benefits - U.S. and Canadian Other Post-Retirement Benefits Narrative (Details) - Other Post-Retirement Benefits $ in Millions	Dec. 31, 2023 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected amortization of prior service credit, next fiscal year	$ 0.7
Amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost in next fiscal year	0.2
Expected employer contributions during next fiscal year	6.0
Expected future benefit payments 2024 through 2028	6.0
Expected future benefit payments 2029-2033	$ 28.0

Defined Benefit Plan, Expected Future Benefit Payment, Year One To Year Five

No definition available.

Name:	aon_DefinedBenefitPlanExpectedFutureBenefitPaymentYearOneToYearFive
Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount included in accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan expected to be recognized in net periodic benefit (cost) credit for fiscal year following most recent annual statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount included in accumulated other comprehensive (income) loss for prior service cost (credit) expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-18

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: