Income Taxes (Tables)

12 Months Ended

Dec. 31, 2024

Income Tax Disclosure [Abstract]

Schedule of Income From Continuing Operations Before Income Tax

Income before income tax and the provision for income tax consist of the following (in millions):

	Years Ended December 31
	2024		2023		2022
Income (loss) before income taxes:
Ireland	$	52	$	31	$	85
U.K.	782		338		502
U.S.	854		219		161
Other	1,774		2,581		2,408
Total	$	3,462	$	3,169	$	3,156
Income tax expense:
Current:
Ireland	$	13	$	4	$	2
U.K.	233		185		206
U.S. federal	292		240		195
U.S. state and local	79		74		43
Other	436		411		316
Total current tax expense	$	1,053	$	914	$	762
Deferred tax expense (benefit):
Ireland	$	—	$	—	$	—
U.K.	(169)		(116)		(152)
U.S. federal	(83)		(126)		(69)
U.S. state and local	(71)		(39)		(21)
Other	12		(92)		(10)
Total deferred tax expense (benefit)	$	(311)	$	(373)	$	(252)
Total income tax expense	$	742	$	541	$	510

Schedule of Reconciliation of the Income Tax Provisions based on the U.S. Statutory Corporate Tax Rate to the Provisions Reflected in the Consolidated Financial Statements

	Years Ended December 31
	2024	2023	2022
Statutory tax rate	25.0%	25.0%	25.0%
U.S. state income taxes, net of U.S. federal benefit	0.7	0.6	0.4
Taxes on international operations (1)	(9.3)	(11.2)	(11.6)
Nondeductible expenses	1.8	3.2	2.4
Adjustments to prior year tax requirements	0.8	0.5	(7.0)
Deferred tax adjustments, including statutory rate changes	(0.1)	(0.3)	(0.5)
Deferred tax adjustments, international earnings	1.1	0.7	0.2
Adjustments to valuation allowances	(0.1)	(2.5)	1.9
Change in uncertain tax positions	2.3	2.6	8.6
Excess tax benefits related to shared based compensation (2)	(0.7)	(1.6)	(1.5)
Capital and other losses	—	—	(1.4)
Other — net	(0.1)	0.1	(0.3)
Effective tax rate	21.4%	17.1%	16.2%

(1)The Company determines the adjustment for taxes on international operations based on the difference between the statutory tax rate applicable to earnings in each foreign jurisdiction and the enacted rate of 25.0%, 25.0% and 25.0% at December 31, 2024, 2023, and 2022, respectively. The benefit to the Company’s effective income tax rate from taxes on international operations relates to benefits from lower-taxed global operations, primarily due to the use of global funding structures and the tax holiday in Singapore.

(2)Excess tax benefits and deficiencies from share-based payment transactions are recognized as income tax expense or benefit in the Company’s Consolidated Statements of Income.

Schedule of Components of Aon's Deferred Tax Assets and Liabilities

The components of the Company’s deferred tax assets and liabilities are as follows (in millions):

As of December 31	2024		2023
Deferred tax assets:
Net operating loss, capital loss, interest, and tax credit carryforwards	$	1,576	$	1,049
Employee benefit plans	359		337
Lease liabilities	171		164
Other accrued expenses	176		155
Federal and state benefit of interest from uncertain tax positions	99		75
Accrued interest	102		52
Deferred revenue	31		25
Other	56		40
Total	2,570		1,897
Valuation allowance on deferred tax assets	(202)		(197)
Total	$	2,368	$	1,700
Deferred tax liabilities:
Intangibles and property, plant and equipment	$	(1,512)	$	(254)
Deferred costs	(160)		(149)
Lease right-of-use asset	(139)		(135)
Unremitted earnings	(66)		(44)
Other accrued expenses	(21)		(20)
Unrealized foreign exchange gains	(36)		(18)
Investment basis differences (1)	(42)		49
Other	(57)		(49)
Total	$	(2,033)	$	(620)
Net deferred tax asset	$	335	$	1,080

(1)The balance was in an asset position for the comparable period.

Schedule of Deferred Income Taxes (Assets and Liabilities Netted by Jurisdiction) as Classified in the Consolidated Statements of Financial Position

Deferred income taxes (assets and liabilities have been netted by jurisdiction) have been classified in the Consolidated Statements of Financial Position as follows (in millions):

As of December 31	2024		2023
Deferred tax assets — non-current	$	654	$	1,195
Deferred tax liabilities — non-current	(319)		(115)
Net deferred tax asset	$	335	$	1,080

Schedule of Operating and Capital Loss Carryforwards

The Company had the following carryforwards (in millions):

As of December 31	2024		2023
U.K.
Operating loss carryforwards	$	1,499	$	1,033
Capital loss carryforwards	$	557	$	550
Interest carryforwards	$	85	$	—
U.S.
Federal operating loss carryforwards	$	2	$	1
Federal interest carryforwards	$	3,743	$	2,303
Federal foreign tax credit carryforwards	$	29	$	24
State operating loss carryforwards	$	1,822	$	493
State interest carryforwards	$	2,303	$	1,209
Other Non-U.S.
Operating loss carryforwards	$	339	$	461
Capital loss carryforwards	$	9	$	7
Interest carryforwards	$	126	$	129
Other carryforwards	$	—	$	3

Schedule of Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits

The following is a reconciliation of the Company’s beginning and ending amount of uncertain tax positions (in millions):

	2024		2023
Balance at January 1	$	637	$	601
Additions based on tax positions related to the current year	39		40
Additions for tax positions of prior years	1		2
Reductions for tax positions of prior years	(5)		(3)
Settlements	(1)		—
Business combinations	61		—
Lapse of statute of limitations	(10)		(3)
Foreign currency translation	—		—
Balance at December 31	$	722	$	637