Number Of Credit Facilities

No definition available.

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

- Definition

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

+ References

+ 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

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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.

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+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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

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

- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Debt - Narrative (Details)		3 Months Ended		9 Months Ended
Debt - Narrative (Details)	Apr. 25, 2024 USD ($)	Sep. 30, 2024 USD ($) credit_facility	Jun. 30, 2024 USD ($)	Sep. 30, 2024 USD ($) credit_facility	Sep. 30, 2024 EUR (€) credit_facility	Apr. 02, 2024 USD ($)	Mar. 01, 2024 USD ($)	Dec. 31, 2023 USD ($)	Nov. 30, 2023 USD ($)	Feb. 28, 2023 USD ($)
Debt Instrument [Line Items]
Proceeds from long-term lines of credit	$ 2,000,000,000
Borrowings under credit facilities		$ 0		$ 0				$ 0
Extinguishment of debt			$ 6,000,000
Number of credit facilities \| credit_facility		2		2	2
Line of Credit
Debt Instrument [Line Items]
Debt instrument, repurchased face amount						$ 3,300,000,000
Line of credit facility, available credit		$ 2,000,000,000		$ 2,000,000,000
Line of Credit \| Delayed Draw Term Loan
Debt Instrument [Line Items]
Proceeds from long-term lines of credit	$ 2,000,000,000
Repayments of long-term lines of credit				850,000,000
Borrowings under credit facilities		1,200,000,000		1,200,000,000
Extinguishment of debt		1,000,000
Line of Credit \| Credit Facility Expiring September 2027
Debt Instrument [Line Items]
Maximum borrowing capacity		1,000,000,000.0		1,000,000,000.0
Line of Credit \| Credit Facility Expiring October 2028
Debt Instrument [Line Items]
Maximum borrowing capacity		1,000,000,000.0		1,000,000,000.0
Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 6,000,000,000
3.50% Senior Notes Due June 2024 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount			$ 600,000,000
Debt interest rate percentage			3.50%
6.875% Senior Notes Due 2028 \| Senior Notes \| NFP
Debt Instrument [Line Items]
Debt interest rate percentage						6.875%
4.875% Senior Notes Due 2028 \| Senior Notes \| NFP
Debt Instrument [Line Items]
Debt interest rate percentage						4.875%
7.500% Senior Secured Notes Due 2030 \| Senior Notes \| NFP
Debt Instrument [Line Items]
Debt interest rate percentage						7.50%
8.500% Senior Secured Notes Due 2031 \| Senior Notes \| NFP
Debt Instrument [Line Items]
Debt interest rate percentage						8.50%
5.125% Senior Notes Due March 2027 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 600,000,000
Debt interest rate percentage							5.125%
5.150% Senior Notes Due March 2029 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 1,000,000,000
Debt interest rate percentage							5.15%
5.300% Senior Notes Due March 2031 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 650,000,000
Debt interest rate percentage							5.30%
5.450% Senior Notes Due March 2034 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 1,750,000,000
Debt interest rate percentage							5.45%
5.750% Senior Notes Due March 2054 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount							$ 2,000,000,000
Debt interest rate percentage							5.75%
4.00% Senior Notes Due November 2023 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount									$ 350,000,000
Debt interest rate percentage									4.00%
5.350% Senior Notes Due February 2033 \| Senior Notes
Debt Instrument [Line Items]
Debt, face amount										$ 750,000,000
Debt interest rate percentage										5.35%
U.S. Program \| Commercial paper outstanding
Debt Instrument [Line Items]
Maximum borrowing capacity		1,300,000,000		1,300,000,000
European Program \| Commercial paper outstanding
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 699,000,000		$ 699,000,000	€ 625,000,000