Number Of Credit Facilities

No definition available.

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Namespace Prefix:	aon_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

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+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=aon_CreditFacilityExpiringSeptember2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=aon_CreditFacilityExpiringOctober2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A285SeniorNotesDueMay2027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A390SeniorNotesDueFebruary2052Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A260SeniorNotesDueDecember2031Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A220SeniorNotesDueNovember2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A205SeniorNotesDueAugust2031Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A290SeniorNotesDueAugust2051Member
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A280SeniorNotesDueMarch2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_USCommercialPaperProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_EuropeanMultiCurrencyCommercialPaperProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Narrative (Details)	Mar. 31, 2022 USD ($) credit_facility	Mar. 31, 2022 EUR (€) credit_facility	Feb. 28, 2022 USD ($)	Dec. 02, 2021 USD ($)	Nov. 30, 2021 USD ($)	Aug. 23, 2021 USD ($)	Jan. 13, 2021 USD ($)
Debt Instrument [Line Items]
Number of credit facilities \| credit_facility	2	2
Borrowings under credit facilities	$ 0
Line of Credit
Debt Instrument [Line Items]
Line of credit facility, available credit	1,750,000,000
Line of Credit \| Credit Facility Expiring September 2026
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,000,000,000
Line of Credit \| Credit Facility Expiring October 2023
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	750,000,000
2.85% Senior Notes Due May 2027 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount			$ 600,000,000
Debt interest rate percentage (as a percent)			2.85%
3.90% Senior Notes Due February 2052 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount			$ 900,000,000
Debt interest rate percentage (as a percent)			3.90%
2.60% Senior Notes Due December 2031 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount				$ 500,000,000
Debt interest rate percentage (as a percent)				2.60%
2.20% Senior Notes due November 2022 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount					$ 500,000,000
Debt interest rate percentage (as a percent)					2.20%
2.05% Senior Notes Due August 2031 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount						$ 400,000,000
Debt interest rate percentage (as a percent)						2.05%
2.90% Senior Notes Due August 2051 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount						$ 600,000,000
Debt interest rate percentage (as a percent)						2.90%
2.80% Senior Notes Due March 2021 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 400,000,000
Debt interest rate percentage (as a percent)							2.80%
U.S. Program \| Commercial paper outstanding
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,000,000,000
European Program \| Commercial paper outstanding
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 686,000,000	€ 625,000,000