Number Of Credit Facilities

No definition available.

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- Definition

Payment For Regulatory Termination Fee

+ References

No definition available.

+ Details

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Namespace Prefix:	aon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

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+ Details

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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

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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

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Balance Type:	na
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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.

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+ Details

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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

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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

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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:
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- Details

Name:	us-gaap_CreditFacilityAxis=aon_CreditFacilityExpiringSeptember2026Member
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Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=aon_CreditFacilityExpiringOctober2023Member
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A205SeniorNotesDueAugust2031Member
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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A290SeniorNotesDueAugust2051Member
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- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A280SeniorNotesDueMarch2021Member
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- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A5.00SeniorNotesDueSeptember2020Member
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- Details

Name:	us-gaap_DebtInstrumentAxis=aon_A280SeniorNotesDueMay2030Member
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- Details

Name:	us-gaap_DebtInstrumentAxis=aon_USCommercialPaperProgramMember
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- Details

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Name:	us-gaap_DebtInstrumentAxis=aon_EuropeanMultiCurrencyCommercialPaperProgramMember
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Debt - Narrative (Details)			3 Months Ended		9 Months Ended
Debt - Narrative (Details)	Jul. 27, 2021 USD ($)	May 29, 2020 USD ($)	Sep. 30, 2021 USD ($) credit_facility	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) credit_facility	Sep. 30, 2020 USD ($)	Sep. 30, 2021 EUR (€) credit_facility	Sep. 28, 2021 USD ($)	Aug. 23, 2021 USD ($)	Jan. 13, 2021 USD ($)	May 12, 2020 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 0	$ 0	$ 0	$ 7,000,000
Number of credit facilities \| credit_facility			2		2		2
Line of credit facility, maximum borrowing capacity								$ 900,000,000
Borrowings under credit facilities			$ 0		$ 0
Payment for regulatory termination fee	$ 400,000,000
Line of Credit
Debt Instrument [Line Items]
Line of credit facility, available credit			1,750,000,000		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		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		750,000,000
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%
5.00% Senior Notes Due September 2020 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount		$ 600,000,000
Debt interest rate percentage (as a percent)		5.00%		5.00%		5.00%
Loss on extinguishment of debt		$ 7,000,000
2.80% Senior Notes Due May 2030 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount											$ 1,000,000,000
Debt interest rate percentage (as a percent)											2.80%
U.S. Program \| Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 900,000,000		$ 900,000,000
European Program \| Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity \| €							€ 625,000,000