Number Of Credit Facilities

No definition available.

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- Definition

Payment For Regulatory Termination Fee

+ References

No definition available.

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Balance Type:	credit
Period Type:	duration

- Definition

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

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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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- 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.

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- 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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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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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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Balance Type:	credit
Period Type:	instant

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

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- Details

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- Details

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- Details

Name:	us-gaap_CreditFacilityAxis=aon_CreditFacilityExpiringFebruary2022Member
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Debt - Narrative (Details)			3 Months Ended		6 Months Ended
Debt - Narrative (Details)	Jul. 27, 2021 USD ($)	May 29, 2020 USD ($)	Jun. 30, 2021 USD ($) credit_facility	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) credit_facility	Jun. 30, 2020 USD ($)	Jun. 30, 2021 EUR (€) credit_facility	Jan. 13, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020	May 12, 2020 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 0	$ 7,000,000	$ 0	$ 7,000,000
Number of credit facilities \| credit_facility			2		2		2
Borrowings under credit facilities			$ 0		$ 0
Subsequent Event
Debt Instrument [Line Items]
Payment for Regulatory Termination Fee	$ 400,000,000
Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			1,650,000,000		1,650,000,000
Commercial paper outstanding			0		0				$ 0
Line of Credit
Debt Instrument [Line Items]
Line of credit facility, available credit			1,650,000,000		1,650,000,000
Line of Credit \| Credit Facility Expiring February 2022
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			900,000,000		900,000,000
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
2.80% Senior Notes Due March 2021 \| Senior Notes
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)								2.80%
Debt face value								$ 400,000,000
5.00% Senior Notes Due September 2020 \| Senior Notes
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)		5.00%								5.00%
Debt face value		$ 600,000,000
Loss on extinguishment of debt		$ 7,000,000
2.80% Senior Notes Due May 2030 \| Senior Notes
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)											2.80%
Debt face value											$ 1,000,000,000
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