Aon (AON) 10-K 17 Feb 23 2022 FY Annual report Financial data

Cover

Cover - USD ($)	12 Months Ended
	Dec. 31, 2022	Feb. 16, 2023	Jun. 30, 2022
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-7933
Entity Registrant Name	Aon plc
Entity Incorporation, State or Country Code	L2
Entity Tax Identification Number	98-1539969
Entity Address, Address Line One	Metropolitan Building, James Joyce Street
Entity Address, City or Town	Dublin 1
Entity Address, Country	IE
Entity Address, Postal Zip Code	D01 K0Y8
City Area Code	1
Local Phone Number	266 6000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 57,066,496,679
Entity Common Stock, Shares Outstanding		205,142,379
Documents Incorporated by Reference	Portions of the registrant’s proxy statement for its 2023 Annual General Meeting of Shareholders are incorporated by reference in this report in response to Part III, Items 10, 11, 12, 13, and 14.
Entity Central Index Key	0000315293
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Class A Ordinary Shares $0.01 nominal value
Entity Information [Line Items]
Title of 12(b) Security	Class A Ordinary Shares $0.01 nominal value
Trading Symbol	AON
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.00% Senior Notes due 2023
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.00% Senior Notes due 2023
Trading Symbol	AON23
Security Exchange Name	NYSE
Guarantees of Aon plc’s 3.50% Senior Notes due 2024
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 3.50% Senior Notes due 2024
Trading Symbol	AON24
Security Exchange Name	NYSE
Guarantees of Aon plc’s 3.875% Senior Notes due 2025
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 3.875% Senior Notes due 2025
Trading Symbol	AON25
Security Exchange Name	NYSE
Guarantees of Aon plc’s 2.875% Senior Notes due 2026
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 2.875% Senior Notes due 2026
Trading Symbol	AON26
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.85% Senior Notes due 2027
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.85% Senior Notes due 2027
Trading Symbol	AON27
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.05% Senior Notes due 2031
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.05% Senior Notes due 2031
Trading Symbol	AON31
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.60% Senior Notes due 2031
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.60% Senior Notes due 2031
Trading Symbol	AON31A
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 5.00% Senior Notes due 2032
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 5.00% Senior Notes due 2032
Trading Symbol	AON32
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.25% Senior Notes due 2042
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.25% Senior Notes due 2042
Trading Symbol	AON42
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.45% Senior Notes due 2043
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.45% Senior Notes due 2043
Trading Symbol	AON43
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.60% Senior Notes due 2044
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.60% Senior Notes due 2044
Trading Symbol	AON44
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.75% Senior Notes due 2045
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.75% Senior Notes due 2045
Trading Symbol	AON45
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.90% Senior Notes due 2051
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 2.90% Senior Notes due 2051
Trading Symbol	AON51
Security Exchange Name	NYSE
Guarantees of Aon Corporation and Aon Global Holdings plc’s 3.90% Senior Notes due 2052
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon Corporation and Aon Global Holdings plc’s 3.90% Senior Notes due 2052
Trading Symbol	AON52
Security Exchange Name	NYSE

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2022
Audit Information [Abstract]
Auditor Location	Chicago, Illinois
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue
Total revenue	$ 12,479	$ 12,193	$ 11,066
Expenses
Compensation and benefits	6,477	6,738	5,905
Information technology	509	477	444
Premises	289	327	291
Depreciation of fixed assets	151	179	167
Amortization and impairment of intangible assets	113	147	246
Other general expense	1,271	2,235	1,232
Total operating expenses	8,810	10,103	8,285
Operating income	3,669	2,090	2,781
Interest income	18	11	6
Interest expense	(406)	(322)	(334)
Other income (expense)	(125)	152	13
Income before income taxes	3,156	1,931	2,466
Income tax expense	510	623	448
Net income	2,646	1,308	2,018
Less: Net income attributable to noncontrolling interests	57	53	49
Net income attributable to Aon shareholders	$ 2,589	$ 1,255	$ 1,969
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ 12.23	$ 5.59	$ 8.49
Diluted net income per share attributable to Aon shareholders (in dollars per share)	$ 12.14	$ 5.55	$ 8.45
Weighted average ordinary shares outstanding - basic (in shares)	211.7	224.7	231.9
Weighted average ordinary shares outstanding - diluted (in shares)	213.2	226.1	233.1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 2,646	$ 1,308	$ 2,018
Less: Net income attributable to noncontrolling interests	57	53	49
Net income attributable to Aon shareholders	2,589	1,255	1,969
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(13)	1	13
Foreign currency translation adjustments	(528)	(289)	263
Postretirement benefit obligation	(211)	277	(101)
Total other comprehensive income (loss)	(752)	(11)	175
Less: Other comprehensive income (loss) attributable to noncontrolling interests	0	(1)	3
Total other comprehensive income (loss) attributable to Aon shareholders	(752)	(10)	172
Comprehensive income attributable to Aon shareholders	$ 1,837	$ 1,245	$ 2,141

Consolidated Statements of Fina

Consolidated Statements of Financial Position - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 690	$ 544
Short-term investments	452	292
Receivables, net	3,035	3,094
Fiduciary assets	15,900	14,386
Other current assets	646	716
Total current assets	20,723	19,032
Goodwill	8,292	8,434
Intangible assets, net	447	492
Fixed assets, net	558	529
Operating lease right-of-use assets	699	786
Deferred tax assets	824	766
Prepaid pension	652	1,366
Other non-current assets	509	512
Total assets	32,704	31,917
Current liabilities
Accounts payable and accrued liabilities	2,114	2,192
Short-term debt and current portion of long-term debt	945	1,164
Fiduciary liabilities	15,900	14,386
Other current liabilities	1,347	1,331
Total current liabilities	20,306	19,073
Long-term debt	9,825	8,228
Non-current operating lease liabilities	693	772
Deferred tax liabilities	99	401
Pension, other postretirement, and postemployment liabilities	1,186	1,375
Other non-current liabilities	1,024	910
Total liabilities	33,133	30,759
Equity (deficit)
Ordinary shares - $0.01 nominal value Authorized: 500.0 shares (issued: 2022 - 205.4; 2021 - 214.8)	2	2
Additional paid-in capital	6,864	6,624
Accumulated deficit	(2,772)	(1,694)
Accumulated other comprehensive loss	(4,623)	(3,871)
Total Aon shareholders' equity (deficit)	(529)	1,061
Noncontrolling interests	100	97
Total equity (deficit)	(429)	1,158
Total liabilities and equity (deficit)	$ 32,704	$ 31,917

Consolidated Statements of Fi_2

Consolidated Statements of Financial Position (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Ordinary shares, nominal value (in dollars per share)	$ 0.01	$ 0.01
Ordinary shares, authorized shares (in Shares)	500,000,000	500,000,000
Ordinary shares, issued shares (in Shares)	205,400,000	214,800,000

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity (Deficit) - USD ($) shares in Millions, $ in Millions	Total	Ordinary Shares and Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Loss, Net of Tax	Non-controlling Interests
Beginning Balance (in shares) at Dec. 31, 2019		232.1
Beginning Balance at Dec. 31, 2019	$ 3,443	$ 6,154	$ 1,248	$ (4,033)	$ 74
Increase (Decrease) in Shareholders' Equity
Net income	2,018		1,969		49
Shares issued — employee stock compensation plans (in shares)		1.9
Shares issued — employee stock compensation plans	(154)	$ (154)
Shares repurchased (in shares)		(8.5)
Shares repurchased	(1,763)		(1,763)
Share-based compensation expense	317	$ 317
Dividends to shareholders	(412)		(412)
Net change in fair value of financial instruments	13			13
Net foreign currency translation adjustments	263			260	3
Net postretirement benefit obligation	(101)			(101)
Net purchases of shares from noncontrolling interests	(9)	$ (3)			(6)
Dividends paid to noncontrolling interests on subsidiary common stock	(32)				(32)
Ending Balance (in shares) at Dec. 31, 2020		225.5
Ending Balance at Dec. 31, 2020	3,583	$ 6,314	1,042	(3,861)	88
Increase (Decrease) in Shareholders' Equity
Net income	1,308		1,255		53
Shares issued — employee stock compensation plans (in shares)		1.7
Shares issued — employee stock compensation plans	(130)	$ (129)	(1)
Shares repurchased (in shares)		(12.4)
Shares repurchased	(3,543)		(3,543)
Share-based compensation expense	449	$ 449
Dividends to shareholders	(447)		(447)
Net change in fair value of financial instruments	1			1
Net foreign currency translation adjustments	(289)			(288)	(1)
Net postretirement benefit obligation	277			277
Net purchases of shares from noncontrolling interests	(13)	$ (8)			(5)
Dividends paid to noncontrolling interests on subsidiary common stock	$ (38)				(38)
Ending Balance (in shares) at Dec. 31, 2021	214.8	214.8
Ending Balance at Dec. 31, 2021	$ 1,158	$ 6,626	(1,694)	(3,871)	97
Increase (Decrease) in Shareholders' Equity
Net income	2,646		2,589		57
Shares issued — employee stock compensation plans (in shares)		1.7
Shares issued — employee stock compensation plans	(157)	$ (156)	(1)
Shares repurchased (in shares)		(11.1)
Shares repurchased	(3,203)		(3,203)
Share-based compensation expense	397	$ 397
Dividends to shareholders	(463)		(463)
Net change in fair value of financial instruments	(13)			(13)
Net foreign currency translation adjustments	(528)			(528)	0
Net postretirement benefit obligation	(211)			(211)
Net purchases of shares from noncontrolling interests	(2)	$ (1)			(1)
Dividends paid to noncontrolling interests on subsidiary common stock	$ (53)				(53)
Ending Balance (in shares) at Dec. 31, 2022	205.4	205.4
Ending Balance at Dec. 31, 2022	$ (429)	$ 6,866	$ (2,772)	$ (4,623)	$ 100

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Deficit) (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Stockholders' Equity [Abstract]
Dividends (in dollars per share)	$ 2.19	$ 1.99	$ 1.78

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net income	$ 2,646	$ 1,308	$ 2,018
Adjustments to reconcile net income to cash provided by operating activities:
Gain from sales of businesses	(54)	(142)	(25)
Depreciation of fixed assets	151	179	167
Amortization and impairment of intangible assets	113	147	246
Share-based compensation expense	397	449	312
Deferred income taxes	(252)	11	9
Other, net	170	5	2
Change in assets and liabilities:
Receivables, net	(96)	(119)	108
Accounts payable and accrued liabilities	(22)	264	186
Current income taxes	216	200	(17)
Pension, other postretirement and postemployment liabilities	(53)	(124)	(143)
Other assets and liabilities	3	4	(80)
Cash provided by operating activities	3,219	2,182	2,783
Cash flows from investing activities
Proceeds from investments	110	58	64
Payments for investments	(107)	(91)	(97)
Net sales (purchases) of short-term investments - non fiduciary	(175)	15	(167)
Acquisition of businesses, net of cash and funds held on behalf of clients	(162)	(14)	(368)
Sale of businesses, net of cash and funds held on behalf of clients	81	218	30
Capital expenditures	(196)	(137)	(141)
Cash provided by (used for) investing activities	(449)	49	(679)
Cash flows from financing activities
Share repurchase	(3,203)	(3,543)	(1,763)
Proceeds from issuance of shares	58	55	44
Cash paid for employee taxes on withholding shares	(215)	(185)	(193)
Commercial paper issuances, net of repayments	(65)	671	(113)
Issuance of debt	1,967	1,495	991
Repayment of debt	(500)	(413)	(607)
Increase in fiduciary liabilities, net of fiduciary receivables	702	568	316
Cash dividends to shareholders	(463)	(447)	(412)
Noncontrolling interests and other financing activities	(71)	(125)	(35)
Cash used for financing activities	(1,790)	(1,924)	(1,772)
Effect of exchange rates on cash and cash equivalents and funds held on behalf of clients	(549)	(235)	297
Net increase in cash and cash equivalents and funds held on behalf of clients	431	72	629
Cash and cash equivalents and funds held on behalf of clients at beginning of year	6,645	6,573	5,944
Cash and cash equivalents and funds held on behalf of clients at end of year	7,076	6,645	6,573
Reconciliation of cash and cash equivalents and funds held on behalf of clients:
Cash and cash equivalents	690	544	884
Funds held on behalf of clients	6,386	6,101	5,689
Total cash and cash equivalents and funds held on behalf of clients	7,076	6,645	6,573
Supplemental disclosures:
Interest paid	351	328	326
Income taxes paid, net of refunds	$ 546	$ 412	$ 455

Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying Consolidated Financial Statements and Notes thereto have been prepared in accordance with U.S. GAAP. The Consolidated Financial Statements include the accounts of Aon plc and all of its controlled subsidiaries (“Aon” or the “Company”). Intercompany accounts and transactions have been eliminated. The Consolidated Financial Statements include, in the opinion of management, all adjustments (consisting of normal recurring adjustments and reclassifications) necessary to present fairly the Company’s consolidated financial position, results of operations, and cash flows for all periods presented. Use of Estimates The preparation of the accompanying Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosures of contingent assets and liabilities at the date of the Consolidated Financial Statements, and the reported amounts of reserves and expenses. These estimates and assumptions are based on management’s best estimates and judgments. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment. Management believes its estimates to be reasonable given the current facts available. Aon adjusts such estimates and assumptions when facts and circumstances dictate. Illiquid credit markets, volatile equity markets, and foreign currency exchange rate movements increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment would, if applicable, be reflected in the Consolidated Financial Statements in future periods. Reclassification Certain amounts in prior periods' Consolidated Financial Statements have been reclassified to conform to the current year presentation. In prior periods, commercial paper issuances and repayments were included in Issuance of debt and Repayment of debt, respectively, in the Consolidated Statements of Cash Flows. The net amount of commercial paper activity is now disclosed separately in Commercial paper issuances, net of repayments in the Consolidated Statements of Cash Flows. For the year ended December 31, 2021 and December 31, 2020, commercial paper issuances reclassified from Issuance of debt was $4,478 million and $3,162 million, respectively, and commercial paper repayments reclassified from Repayment of debt was $3,807 million and $3,275 million, respectively. Further information on the gross commercial paper activity for the current and prior year periods is included within the Liquidity and Financial Conditions section of Part II Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations. In November 2022, Aon incurred a non-cash pension settlement charge of $170 million in connection with the purchase of an annuity for portions of its U.S. pension plans. Aon has separately classified the non-cash pension settlement charge within Other, net on the Consolidated Statement of Cash Flows as an adjustment to reconcile Net income to Cash provided by operating activities for the period ended December 31, 2022. Prior year comparable balances have been reclassified to conform with current year presentation. For the years ended December 31, 2021 and 2020, Aon incurred insignificant non-cash pension settlement charges of $5 million and $2 million, respectively, which were presented as changes in assets and liabilities held within Pension, other postretirement and other postemployment liabilities in the Consolidated Statements of Cash Flows. See Note 11 “Employee Benefits” for further information regarding the non-cash settlement charges incurred. In prior periods, Cash paid for employee taxes on withholding shares were included with Proceeds from issuance of shares, and presented as Issuance of shares for employee benefit plans in the Consolidated Statements of Cash Flows. These items are now presented separately and prior year balances have been reclassified to conform to current year presentation. For the year ended December 31, 2021 and December 31, 2020, Proceeds from issuance of shares was $55 million and $44 million, respectively, and Cash paid for employee taxes on withholding shares was $185 million and $193 million, respectively.

Summary of Significant Accounti

Summary of Significant Accounting Principles and Practices	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Principles and Practices	Summary of Significant Accounting Principles and Practices Revenue Recognition The Company generates revenues primarily through commissions, compensation from insurance and reinsurance companies for services provided to them, and fees from customers. Commissions and fees for brokerage services vary depending upon several factors, which may include the amount of premium, the type of insurance or reinsurance coverage provided, the particular services provided to a client, insurer, or reinsurer, and the capacity in which the Company acts. Compensation from insurance and reinsurance companies includes: (1) fees for consulting and analytics services and (2) fees and commissions for administrative and other services provided to or on behalf of insurers. In Aon’s capacity as an insurance and reinsurance broker, the service promised to the customer is placement of an effective insurance or reinsurance policy, respectively. The customer obtains control over the services promised by the Company at the completion of the insurance or reinsurance policy placement process once coverage is effective. Judgment is not typically required when assessing whether the coverage is effective. Fees from clients for advice and consulting services are dependent on the extent and value of the services provided. Payment terms for the Company’s principal service lines are discussed below; the Company believes these terms are consistent with current industry practices. Significant financing components are typically not present in Aon’s arrangements. The Company recognizes revenue when control of the promised services is transferred to the customer in the amount that best reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements where control is transferred over time, an input or output method is applied that represents a faithful depiction of the progress towards completion of the performance obligation. For arrangements that include variable consideration, the Company assesses whether any amounts should be constrained. For arrangements that include multiple performance obligations, the Company allocates consideration based on their relative fair values. Costs incurred by the Company in obtaining a contract are capitalized and amortized on a systematic basis that is consistent with the transfer of control of the services to which the asset relates, considering anticipated renewals when applicable. Certain contract related costs, including pre-placement brokerage costs, are capitalized as a cost to fulfill and are amortized on a systematic basis consistent with the transfer of control of the services to which the asset relates, which is generally less than one year. The Company has elected to apply practical expedients to not disclose the revenue related to unsatisfied performance obligations if (1) the contract has an original duration of 1 year or less, (2) the Company has recognized revenue for the amount in which it has the right to bill, and (3) the variable consideration is allocated entirely to an unsatisfied performance obligation which is recognized as a series of distinct goods or services that form a single performance obligation. Disaggregation of Revenue The following is a description of principal service lines from which the Company generates its revenue: Commercial Risk Solutions includes retail brokerage, specialty solutions, global risk consulting and captives management, and Affinity programs. Revenue primarily includes insurance commissions and fees for services rendered. Revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement using output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements recognized over time, various output measures, including units delivered and time elapsed, are utilized to provide a faithful depiction of the progress towards completion of the performance obligation. Revenue is recorded net of allowances for estimated policy cancellations, which are determined based on an evaluation of historical and current cancellation data. Reimbursements received for out-of-pocket expenses are generally recorded as a component of revenue. Commissions and fees for brokerage services may be invoiced near the effective date of the underlying policy or over the term of the arrangement in installments during the policy period. Reinsurance Solutions includes treaty reinsurance, facultative reinsurance, Strategy and Technology Group, and capital markets. Revenue primarily includes reinsurance commissions and fees for services rendered. Revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement using output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements recognized over time, various output measures, including units delivered and time elapsed, are utilized to provide a faithful depiction of the progress towards completion of the performance obligation. Commissions and fees for brokerage services may be invoiced at the inception of the reinsurance period for certain reinsurance brokerage, or more commonly, over the term of the arrangement in installments based on deposit or minimum premiums for most treaty reinsurance arrangements. Health Solutions includes consulting and brokerage, Human Capital, and Consumer Benefits Solutions. Revenue primarily includes insurance commissions and fees for services rendered. For brokerage commissions, revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services using input or output measures, including units delivered or time elapsed, to provide a faithful depiction of the progress towards completion of the performance obligation. Revenue from health care exchange arrangements is typically recognized upon successful enrollment of participants. Commissions and fees for brokerage services may be invoiced at the effective date of the underlying policy or over the term of the arrangement in installments during the policy period. Payment terms for other services vary but are typically over the contract term in installments. Wealth Solutions includes retirement consulting and pension administration, as well as investments. Revenue recognized for these arrangements is predominantly recognized over the term of the arrangement using input or output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services, or for certain arrangements, at a point in time upon completion of the services. For consulting arrangements recognized over time, revenue will be recognized based on a measure of progress that depicts the transfer of control of the services to the customer, utilizing an appropriate input or output measure to provide a reasonable assessment of the progress towards completion of the performance obligation including units delivered or time elapsed. Fees paid by customers for consulting services are typically charged on an hourly, project or fixed-fee basis, and revenue for these arrangements is typically recognized based on time incurred, days elapsed, or reports delivered. Revenue from time-and-materials or cost-plus arrangements are recognized as services are performed using input or output measures to provide a reasonable assessment of the progress towards completion of the performance obligation including hours worked, and revenue for these arrangements is typically recognized based on time and materials incurred. Revenue generated from the Company’s delegated investment business is generally earned as an agreed percentage based on AUM and, to a lesser extent, based on performance fees. Reimbursements received for out-of-pocket expenses are generally recorded as a component of revenue. Payment terms vary but are typically over the contract term in installments. Share-based Compensation Expense Share-based payments to employees, including grants of RSUs and PSAs, are measured based on grant date fair value. For purposes of measuring share-based compensation expense, the Company considered whether an adjustment to the observable market price is necessary to reflect material nonpublic information that is known to us at the time the award is granted. No adjustments were necessary for the years ended December 31, 2022, 2021, or 2020. The Company recognizes compensation expense over the requisite service period for awards expected to ultimately vest. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates. Pension and Other Postretirement Benefits The Company records net periodic cost relating to its pension and other postretirement benefit plans based on calculations that include various actuarial assumptions, including discount rates, assumed rates of return on plan assets, inflation rates, mortality rates, compensation increases, and turnover rates. The Company reviews its actuarial assumptions on an annual basis and modifies these assumptions based on current rates and trends. The effects of gains, losses, and prior service costs and credits are amortized over future service periods or future estimated lives if the plans are frozen as reflected in Other income (expense) within the Consolidated Statements of Income. The funded status of each plan, calculated as the fair value of plan assets less the benefit obligation, is reflected in the Company’s Consolidated Statements of Financial Position using a December 31 measurement date. Earnings per Share Basic earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, including participating securities, which consist of unvested share awards with non-forfeitable rights to dividends. Diluted earnings per share is computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding, which have been adjusted for the dilutive effect of potentially issuable ordinary shares, including certain contingently issuable shares. The diluted earnings per share calculation reflects the more dilutive effect of either (1) the two-class method that assumes that the participating securities have not been exercised, or (2) the treasury stock method. Potentially issuable shares are not included in the computation of diluted earnings per share if their inclusion would be antidilutive. Cash and Cash Equivalents and Short-term Investments Cash and cash equivalents include cash balances and all highly liquid investments with initial maturities of three months or less. Short-term investments generally consist of money market funds. The estimated fair value of Cash and cash equivalents and Short-term investments approximates their carrying values. At December 31, 2022, Cash and cash equivalents and Short-term investments totaled $1,142 million compared to $836 million at December 31, 2021, an increase of $306 million. Of the total balance, $115 million and $160 million was restricted as to its use at December 31, 2022 and 2021, respectively. Included within Short-term investments as of December 31, 2022 and 2021 balances, respectively, were £60.1 million ($72.5 million at December 31, 2022 exchanges rates) and £84.3 million ($112.8 million at December 31, 2021 exchange rates) of operating funds required to be held by the Company in the U.K. by the FCA, a U.K.-based regulator. Fiduciary Assets and Liabilities In its capacity as an insurance agent and broker, Aon collects premiums from insureds and, after deducting its commission, remits the premiums to the respective insurers. Aon also collects claims or refunds from insurers on behalf of insureds. Uncollected premiums from insureds and uncollected claims or refunds from insurers are recorded as Fiduciary assets in the Company’s Consolidated Statements of Financial Position. Unremitted insurance premiums and claims are held in a fiduciary capacity and the obligation to remit these funds is recorded as Fiduciary liabilities in the Consolidated Statements of Financial Position. Funds held on behalf of clients represent fiduciary assets held by Aon for premiums collected from insureds but not yet remitted to insurance companies and claims collected from insurance companies but not yet remitted to insureds of $6.4 billion and $6.1 billion at December 31, 2022 and 2021, respectively. Fiduciary receivables were $9.5 billion and $8.3 billion at December 31, 2022 and 2021, respectively. These funds and a corresponding liability are included in Fiduciary assets and Fiduciary liabilities, respectively, in the accompanying Consolidated Statements of Financial Position. Allowance for Doubtful Accounts The Company’s estimate for allowance for credit losses with respect to receivables is based on a combination of factors, including evaluation of forward-looking information, historical write-offs, aging of balances, and other qualitative and quantitative analyses. Receivables, net included an allowance for doubtful accounts of $76 million and $90 million at December 31, 2022 and 2021, respectively. Fixed Assets Fixed assets are stated at cost, less accumulated depreciation. Included in this category are certain capitalized costs incurred during the application development stage related to directly obtaining, developing, or enhancing internal use software. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Estimated Useful Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years Goodwill and Intangible Assets Goodwill represents the excess of purchase price over the fair value of the net assets acquired in the acquisition of a business. Goodwill is allocated to applicable reporting units. Upon disposition of a business entity, goodwill is allocated to the disposed entity based on the relative fair value of that entity compared to the fair value of the reporting unit in which it was included. Goodwill is not amortized, but instead is tested for impairment at least annually. The goodwill impairment test is performed at the reporting unit level. The Company may initially perform a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If a qualitative assessment is not performed or if a determination is made that it is not more likely than not that the value of the reporting unit exceeds its carrying amount, then the Company will perform a quantitative analysis. If the fair value of a reporting unit is determined to be greater than the carrying value of the reporting unit, goodwill is deemed not to be impaired and no further testing is necessary. If the fair value of a reporting unit is less than the carrying value, a goodwill impairment loss is recognized for the amount that the carrying amount of a reporting unit, including goodwill, exceeds its fair value limited to the total amount of the goodwill allocated to the reporting unit. Any resulting difference will be a charge to Amortization and impairment of intangible assets in the Consolidated Statements of Income in the period in which the determination is made. Fair value is determined using a combination of present value techniques and market prices of comparable businesses. We classify our intangible assets acquired as either customer-related and contract based, technology, tradenames, or other intangibles. Amortization basis and estimated useful lives by intangible asset type are generally as follows: Intangible Asset Description Amortization Basis Estimated Useful Life Customer-related and contract-based In line with underlying cash flows 7 to 20 years Technology and other Straight-line 5 to 7 years Tradenames Straight-line 1 to 3 years Derivatives Derivative instruments are recognized in the Consolidated Statements of Financial Position at fair value. Where the Company has entered into master netting agreements with counterparties, the derivative positions are netted by counterparties and are reported accordingly in other assets or other liabilities. Changes in the fair value of derivative instruments are recognized in earnings each period, unless the derivative is designated and qualifies as a cash flow or net investment hedge. The Company has historically designated the following hedging relationships for certain transactions: (1) a hedge of the change in fair value of a recognized asset or liability or firm commitment (“fair value hedge”), (2) a hedge of the variability in cash flows from a recognized variable-rate asset or liability or forecasted transaction (“cash flow hedge”), and (3) a hedge of the net investment in a foreign operation (“net investment hedge”). In order for a derivative to qualify for hedge accounting, the derivative must be formally designated as a fair value, cash flow, or a net investment hedge by documenting the relationship between the derivative and the hedged item. The documentation must include a description of the hedging instrument, the hedged item, the risk being hedged, Aon’s risk management objective and strategy for undertaking the hedge, and the method for assessing the effectiveness of the hedge. Additionally, the hedge relationship must be expected to be highly effective at offsetting changes in either the fair value or cash flows of the hedged item at both the inception of the hedge and on an ongoing basis. Aon assesses the ongoing effectiveness of its hedges quarterly or more frequently if facts and circumstances require. For a derivative designated as a fair value hedging instrument, the gain or loss is recognized in earnings in the period of change together with the offsetting loss or gain on the hedged item attributable to the risk being hedged. The effect is to reflect in earnings the extent to which the hedge is not effective in achieving offsetting changes in fair value. For a cash flow hedge that qualifies for hedge accounting, the change in fair value of a hedging instrument is recognized in Accumulated Other Comprehensive Income and subsequently reclassified to earnings in the same period the hedged item impacts earnings. For a net investment hedge, the change in fair value of the hedging instrument is recognized in Accumulate Other Comprehensive Income as part of the cumulative translation adjustment. Changes in the fair value of a derivative that is not designated as part of a hedging relationship (commonly referred to as an “economic hedge”) are recorded in Other income in the Consolidated Statements of Income in the period of change. The Company discontinues hedge accounting prospectively when (1) the derivative expires or is sold, terminated, or exercised, (2) the qualifying criteria are no longer met, or (3) management removes the designation of the hedging relationship. Foreign Currency Certain of the Company’s non-U.S. operations use their respective local currency as their functional currency. These operations that do not have the U.S. dollar as their functional currency translate their financial statements at the current rates of exchange in effect at the balance sheet date and revenues and expenses using rates that approximate those in effect during the period. The resulting translation adjustments are included in Net foreign currency translation adjustments within the Consolidated Statements of Shareholders’ Equity. Further, gains and losses from the remeasurement of monetary assets and liabilities that are denominated in a non-functional currency of that entity are included in Other income (expense) within the Consolidated Statements of Income. Income Taxes Deferred income taxes are recognized for the effect of temporary differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted marginal tax rates and laws that are currently in effect. The effect on deferred tax assets and liabilities from a change in tax rates is recognized in the period when the rate change is enacted. Deferred tax assets are reduced by valuation allowances if, based on the consideration of all available evidence, it is more likely than not that some portion of the deferred tax asset will not be realized. Deferred tax assets are realized by having sufficient future taxable income to allow the related tax benefits to reduce taxes otherwise payable. The sources of taxable income that may be available to realize the benefit of deferred tax assets are future reversals of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences and carry-forwards, taxable income in carry-back years, and tax planning strategies that are both prudent and feasible. The Company recognizes the effect of income tax positions only if sustaining those positions is more likely than not. Tax positions that meet the more likely than not recognition threshold but are not highly certain are initially and subsequently measured based on the largest amount of benefit that is greater than 50% likely of being realized upon settlement with the taxing authority. Only information that is available at the reporting date is considered in the Company’s recognition and measurement analysis, and events or changes in facts and circumstances are accounted for in the period in which the event or change in circumstance occurs. The Company records penalties and interest related to unrecognized tax benefits in Income taxes in the Company’s Consolidated Statements of Income. The Company releases income tax effects from Accumulated other comprehensive loss using the portfolio approach. Leases The Company leases office facilities, equipment, and automobiles under operating and finance leases. The Company’s lease obligations are primarily for the use of office facilities. The Company evaluates if a leasing arrangement exists upon inception of a contract. A contract contains a lease if the contract conveys the right to control the use of identified tangible assets for a period of time in exchange for consideration. Identified property, plant, or equipment may include a physically distinct portion of a larger asset, or a portion of an asset that represents substantially all of the capacity of the asset but is not physically distinct. The Company assesses whether a contract implicitly contains the right to control the use of a tangible asset that is not already owned. In addition, the Company subleases certain real estate properties to third parties, which are classified as operating leases. The Company’s leases expire at various dates and may contain renewal, expansion or termination options. The exercise of lease renewal and expansion options are typically at the Company’s sole discretion and are only included in the determination of the lease term if the Company is reasonably certain to exercise the option. In addition, the Company’s lease agreements typically do not contain any material residual value guarantees or restrictive covenants. ROU assets and lease liabilities are based on the present value of the minimum lease payments over the lease term. The Company has elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease components from lease components and instead account for consideration received in a contract as a single lease component. The Company’s lease agreements may include initial direct costs and lease incentives. Initial direct costs are incremental costs of a lease that would not have been incurred if the lease had not been obtained and are included in the measurement of the ROU asset. Payments made to or on behalf of the Company, such as tenant improvement allowances, represent incentives that are considered reductions to the ROU asset and lease expense over the lease term. The Company made a policy election to not recognize ROU assets and lease liabilities that arise from leases with an initial term of twelve months or less in the Consolidated Statements of Financial Position. However, the Company recognized these lease payments in the Consolidated Statements of Income on a straight-line basis over the lease term and variable lease payments in the period in which the expense was incurred. The Company applies this accounting policy across all classes of underlying assets. A portion of the Company’s lease agreements include variable lease payments that are not recorded in the initial measurement of the lease liability and ROU asset balances. For real estate arrangements, base rental payments may be escalated according to annual changes in the CPI or other indices. The escalated rental payments based on the estimated CPI at the lease commencement date are included within minimum rental payments; however, changes in CPI are considered variable in nature and are recognized as variable lease costs in the period in which the obligation is incurred. Additionally, real estate lease agreements may include other variable payments related to operating expenses charged by the landlord based on actual expenditures. Information technology equipment agreements may include variable payments based on usage of the equipment. These expenses are also recognized as variable lease costs in the period in which the expense is incurred. The Company utilizes discount rates to determine the present value of the lease payments based on information available at the commencement date of the lease. As the rate implicit in each lease is not typically readily available, the Company uses an incremental borrowing rate based on factors such as the lease term and the economic environment where the lease exists to determine the appropriate present value of future lease payments. When determining the incremental borrowing rate, the Company considers the rate of interest it would pay on a secured borrowing in an amount equal to the lease payments for the underlying asset under similar terms. Operating leases are included in Operating lease ROU assets, Other current liabilities, and Non-current operating lease liabilities in the Consolidated Statements of Financial Position. Finance leases are included in Other non-current assets, Other current liabilities, and Other non-current liabilities in the Consolidated Statements of Financial Position. Principles of Consolidation The accompanying Consolidated Financial Statements include the accounts of Aon plc and those entities in which the Company has a controlling financial interest. To determine if Aon holds a controlling financial interest in an entity, the Company first evaluates if it is required to apply the variable interest model to the entity, otherwise, the entity is evaluated under the voting interest model. When Aon holds rights that give it the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance, combined with a variable interest that gives the right to receive potentially significant benefits or the obligation to absorb potentially significant losses, the Company has a controlling financial interest in that VIE. The Company does not hold a controlling financial interest over any VIEs that significantly impacts the VIE’s economic performance and the Company does not have rights to any significant benefits or obligations to absorb potentially significant losses. Thus, the Company does not consolidate any VIEs and Aon’s interest in VIEs as of December 31, 2022 was insignificant. Aon holds a controlling financial interest in entities that are not VIEs when it, directly or indirectly holds more than 50% of the voting rights and the noncontrolling interest holders do not hold substantive participating rights. New Accounting Pronouncements All issued, but not yet effective, guidance has been deemed not applicable or not significant to the Consolidated Financial Statements.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Disaggregation of Revenue The following table summarizes revenue from contracts with customers by principal service line (in millions): Years Ended December 31 2022 2021 2020 Commercial Risk Solutions $ 6,715 $ 6,635 $ 5,861 Reinsurance Solutions 2,190 1,997 1,814 Health Solutions 2,224 2,154 2,067 Wealth Solutions 1,367 1,426 1,341 Elimination (17) (19) (17) Total revenue $ 12,479 $ 12,193 $ 11,066 Consolidated revenue from contracts with customers by geographic area, which is attributed on the basis of where the services are performed, is as follows (in millions): Years Ended December 31 2022 2021 2020 U.S. $ 5,666 $ 5,459 $ 5,032 Americas other than U.S. 1,137 1,027 911 U.K. 1,660 1,681 1,579 Ireland 99 127 84 Europe, Middle East, & Africa other than U.K. and Ireland 2,443 2,565 2,236 Asia Pacific 1,474 1,334 1,224 Total revenue $ 12,479 $ 12,193 $ 11,066 Contract Costs Changes in the net carrying amount of costs to fulfill contracts with customers are as follows (in millions): 2022 2021 Balance at beginning of period $ 361 $ 339 Additions 1,479 1,504 Amortization (1,480) (1,478) Impairment — — Foreign currency translation and other (5) (4) Balance at end of period $ 355 $ 361 Changes in the net carrying amount of costs to obtain contracts with customers are as follows (in millions): 2022 2021 Balance at beginning of period $ 179 $ 184 Additions 56 59 Amortization (49) (48) Impairment — — Foreign currency translation and other (1) (16) Balance at end of period $ 185 $ 179

Other Financial Data

Other Financial Data	12 Months Ended
	Dec. 31, 2022
Other Financial Data [Abstract]
Other Financial Data	Other Financial Data Consolidated Statements of Income Information Other Income (Expense) The components of Other income (expense) are as follows (in millions): Years Ended December 31 2022 2021 2020 Pension and other postretirement (1) $ (179) $ 21 $ 13 Foreign currency remeasurement (14) 26 (12) Extinguishment of debt — — (7) Financial instruments and other 4 (45) (10) Equity earnings 10 8 4 Gain from disposals of business 54 142 25 Total $ (125) $ 152 $ 13 (1) Refer to Note 11 “Employee Benefits” for further information. Consolidated Statements of Financial Position Information Allowance for Doubtful Accounts Changes in the net carrying amount of allowance for doubtful accounts are as follows (in millions): 2022 2021 2020 Balance at beginning of period $ 90 $ 98 $ 77 Provision 8 26 29 Accounts written off, net of recoveries (18) (37) (6) Foreign currency translation and other (4) 3 (2) Balance at end of period $ 76 $ 90 $ 98 Other Current Assets The components of Other current assets are as follows (in millions): As of December 31 2022 2021 Costs to fulfill contracts with customers (1) $ 355 $ 361 Prepaid expenses 109 137 Taxes receivable 74 53 Other 108 165 Total $ 646 $ 716 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. Fixed Assets, net The components of Fixed assets, net are as follows (in millions): As of December 31 2022 2021 Software $ 861 $ 797 Leasehold improvements 409 425 Computer equipment 269 268 Furniture, fixtures, and equipment 267 279 Construction in progress 109 45 Other 34 33 Fixed assets, gross 1,949 1,847 Less: Accumulated depreciation 1,391 1,318 Fixed assets, net $ 558 $ 529 Depreciation expense, which includes software amortization, was $151 million, $179 million, and $167 million for the years ended December 31, 2022, 2021, and 2020, respectively. Other Non-current Assets The components of Other non-current assets are as follows (in millions): As of December 31 2022 2021 Costs to obtain contracts with customers (1) $ 185 $ 179 Taxes receivable 109 95 Investments 60 64 Leases (2) 43 63 Other 112 111 Total $ 509 $ 512 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) Refer to Note 8 “Lease Commitments” for further information. Other Current Liabilities The components of Other current liabilities are as follows (in millions): As of December 31 2022 2021 Deferred revenue (1) $ 250 $ 321 Taxes payable 193 149 Leases (2) 186 213 Other 718 648 Total $ 1,347 $ 1,331 (1) $653 million and $553 million was recognized in the Consolidated Statements of Income during the years ended December 31, 2022 and December 31, 2021, respectively. (2) Refer to Note 8 “Lease Commitments” for further information. Other Non-current Liabilities The components of Other non-current liabilities are as follows (in millions): As of December 31 2022 2021 Taxes payable (1) $ 795 $ 609 Compensation and benefits 69 58 Deferred revenue 37 70 Leases (2) 28 46 Other 95 127 Total $ 1,024 $ 910 (1) Includes $129 million and $145 million for the non-current portion of the transition tax as of December 31, 2022 and December 31, 2021, respectively. Refer to Note 9 “Income Taxes” for further information on the transition tax. (2) Refer to Note 8 “Lease Commitments” for further information.

Acquisitions and Dispositions o

Acquisitions and Dispositions of Businesses	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Acquisitions and Dispositions of Businesses	Acquisitions and Dispositions of Businesses Completed Acquisitions The Company completed five acquisitions during the year ended December 31, 2022 and two acquisitions during the year ended December 31, 2021. The following table includes the preliminary fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Year Ended Consideration transferred Cash $ 161 Deferred and contingent consideration 9 Aggregate consideration transferred $ 170 Assets acquired Goodwill $ 87 Intangible assets 78 Other assets (1) 25 Total assets acquired 190 Liabilities assumed Total liabilities assumed 20 Net assets acquired $ 170 (1) Includes Cash and cash equivalents o f $2 million and funds held on behalf of clients of an insignificant amount . Intangible assets acquired include technology as well as customer-related and contract-based assets. The intangible assets acquired as part of business acquisitions in 2022 had a weighted average useful economic life of 9 years . Acquisition related costs for completed acquisitions incurred and recognized within Other general expense for the year ended December 31, 2022 were insignificant . Total revenue for these acquisitions included in the Company’s Consolidated Statement of Income for the year ended December 31, 2022 was approximately $25 million . The results of operations of these acquisitions are included in the Consolidated Financial Statements as of the respective acquisition dates. The Company’s results of operations would not have been materially different if these acquisitions had been reported from the beginning of the period in which they were acquired. 2022 Acquisitions On November 1, 2022, the Company completed the acquisition of 100% of the share capital of E.R.N. Evaluacion de Riesgos Naturales y Antropogenicos, S.A. de C.V., a Mexico-based firm in risk assessment modeling. On September 12, 2022, the Company completed the purchase of certain assets of Praxiom Risk Management, a provider of professional risk management in the U.S. On August 1, 2022, the Company completed the purchase of certain assets of U.S. Advisors, Inc., a broker based in the U.S. On May 3, 2022, the Company completed the acquisition of 100% of the share capital of Karl Köllner group companies, a marine hull broker based in Germany. On March 1, 2022, the Company completed the acquisition of Tyche, an actuarial software platform based in the U.K. 2021 Acquisitions On December 22, 2021, the Company completed the transaction to acquire 100% share capital of For Welfare S.r.l, a company focused on bancassurance programs in Italy. On September 1, 2021, the Company completed the transaction to acquire 51% of Aon India Insurance Brokers Limited (formerly known as Anviti Insurance Brokers Private Limited). Prior to the acquisition date, the Company accounted for its 49% interest in Anviti as an equity-method investment. The acquisition-date fair value of the previous equity interest was $15 million and is included in the measurement of consideration transferred. There was no significant impact as a result of remeasuring the carrying value of the Company’s prior equity interest in Anviti held before the business combination. Completed Dispositions The Company completed three dispositions during the year ended December 31, 2022. The Company completed six dispositions during the year ended December 31, 2021 and one disposition during the year ended December 31, 2020. The pretax gains recognized related to dispositions were $54 million, $142 million, and $25 million for the years ended December 31, 2022, December 31, 2021 and December 31, 2020, respectively. Gains recognized as a result of a disposition are included in Other income in the Consolidated Statements of Income. The pretax losses recognized in the Consolidated Statements of Income related to dispositions were insignificant for the years ended December 31, 2022, December 31, 2021, and December 31, 2020, respectively.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The changes in the net carrying amount of goodwill for the years ended December 31, 2022 and 2021, respectively, are as follows (in millions): Balance as of January 1, 2021 $ 8,666 Goodwill related to current year acquisitions 17 Goodwill related to current year disposals (37) Foreign currency translation and other (212) Balance as of December 31, 2021 $ 8,434 Goodwill related to current year acquisitions 87 Goodwill related to current year disposals (11) Foreign currency translation and other (218) Balance as of December 31, 2022 $ 8,292 Other intangible assets by asset class are as follows (in millions): As of December 31 2022 2021 Gross Accumulated Amortization and Impairment Net Gross Accumulated Amortization and Impairment Net Customer-related and contract-based $ 2,207 $ 1,833 $ 374 $ 2,289 $ 1,848 $ 441 Technology and other 436 363 73 407 357 50 Tradenames 14 14 — 14 13 1 Total $ 2,657 $ 2,210 $ 447 $ 2,710 $ 2,218 $ 492 Amortization expense and impairment charges from finite lived intangible assets were $113 million, $147 million, and $246 million for the years ended December 31, 2022, 2021, and 2020, respectively. The estimated future amortization for finite-lived intangible assets as of December 31, 2022 is as follows (in millions): Estimated Future Amortization For the years ended 2023 $ 99 2024 82 2025 68 2026 47 2027 34 Thereafter 117 Total $ 447

Debt

Debt	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Debt	Debt The following is a summary of outstanding debt (in millions): As of December 31 2022 2021 Commercial paper $ 592 $ 665 2.20% Senior Notes due November 2022 (1) — 499 4.00% Senior Notes due November 2023 (2) 350 349 3.50% Senior Notes due June 2024 599 598 3.875% Senior Notes due December 2025 748 748 2.875% Senior Notes due May 2026 (EUR 500M) 530 563 8.205% Junior Subordinated Notes due January 2027 521 521 2.85% Senior Notes due May 2027 596 — 4.50% Senior Notes due December 2028 348 347 3.75% Senior Notes due May 2029 746 745 2.80% Senior Notes due May 2030 994 993 2.05% Senior Notes due August 2031 396 396 2.60% Senior Notes due December 2031 496 496 5.00% Senior Notes due September 2032 495 — 6.25% Senior Notes due September 2040 297 296 4.25% Senior Notes due December 2042 203 201 4.45% Senior Notes due May 2043 247 247 4.60% Senior Notes due June 2044 545 544 4.75% Senior Notes due May 2045 594 593 2.90% Senior Notes due August 2051 591 591 3.90% Senior Notes due February 2052 877 — Other 5 — Total debt 10,770 9,392 Less: Short-term debt and current portion of long-term debt 945 1,164 Total long-term debt $ 9,825 $ 8,228 (1) The 2.20% Senior Notes due November 2022 were repaid in full on November 1, 2022. (2) The 4.00% Senior Notes due November 2023 were reclassified as Short-term debt and current portion of long-term debt in the Consolidated Statement of Financial Position as of December 31, 2022. Notes In November 2022, Aon Global Limited’s $350 million 4.00% Senior Notes due November 2023 were classified as Short-term debt and current portion of long-term debt in the Consolidated Statement of Financial Position as the date of maturity is in less than one year as of December 31, 2022. In November 2022, Aon Corporation’s $500 million 2.20% Senior Notes matured and were repaid in full. In November 2021, the Company’s $500 million 2.20% Senior Notes due November 2022 were classified as Short-term debt and current portion of long-term debt in the Consolidated Statement of Financial Position as the date of maturity is in less than one year as of December 31, 2021. On September 12, 2022, Aon Corporation, a Delaware corporation, and Aon Global Holdings plc, a public limited company formed under the laws of England and Wales, both wholly owned subsidiaries of the Company, co-issued $500 million of 5.00% Senior Notes due September 2032. The Company intends to use the net proceeds from the offering for general corporate purposes. On February 28, 2022, Aon Corporation and Aon Global Holdings plc co-issued $600 million of 2.85% Senior Notes due May 2027 and $900 million of 3.90% Senior Notes due February 2052. The Company intends to use the net proceeds from the offering for general corporate purposes. On December 2, 2021, Aon Corporation and Aon Global Holdings plc co-issued $500 million aggregate principal amount of 2.60% Senior Notes set to mature on December 2, 2031. The Company intends to use the net proceeds of the offering for general corporate purposes. On August 23, 2021, Aon Corporation and Aon Global Holdings plc co-issued $400 million 2.05% Senior Notes due August 2031 and $600 million of 2.90% Senior Notes due August 2051. The Company intends to use the net proceeds of the offering for general corporate purposes. On January 13, 2021, Aon Global Limited issued an irrevocable notice of redemption to holders of its 2.80% Senior Notes for the redemption of all $400 million outstanding aggregate principal amount of the notes, which were set to mature in March 2021. The redemption date was on February 16, 2021 and resulted in an insignificant loss due to extinguishment. Each of the notes issued by Aon Corporation is fully and unconditionally guaranteed by Aon Global Limited, Aon plc, and Aon Global Holding plc. Each of the notes issued by Aon Global Limited is fully and unconditionally guaranteed by Aon plc, Aon Global Holdings plc, and Aon Corporation. Each of the notes co-issued by Aon Corporation and Aon Global Holdings plc is fully and unconditionally guaranteed by Aon plc and Aon Global Limited. All guarantees of Aon plc and Aon Global Limited of the Co-Issued Notes are joint and several as well as full and unconditional. Senior Notes rank pari passu in right of payment with all other present and future unsecured debt which is not expressed to be subordinate or junior in rank to any other unsecured debt of the Co-Issuers. Refer to “Guarantee of Registered Securities” within Part II Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations for further information regarding guarantees of outstanding debt securities. Each of the notes described and identified in the table above contains customary representations, warranties, and covenants, and the Company was in compliance with all such covenants as of December 31, 2022. Repayments of total debt as of December 31, 2022 are as follows (in millions): 2023 $ 946 2024 604 2025 750 2026 532 2027 1,121 Thereafter 6,956 Total Repayments 10,909 Unamortized discounts, premiums, and debt issuance costs (139) Total Debt $ 10,770 Revolving Credit Facilities As of December 31, 2022, Aon plc had two primary committed credit facilities outstanding: its Each of these primary committed credit facilities includes customary representations, warranties, and covenants, including financial covenants that require Aon to maintain specified ratios of adjusted consolidated EBITDA to consolidated interest expense and consolidated debt to adjusted consolidated EBITDA, in each case, tested quarterly. At December 31, 2022, Aon did not have borrowings under either of these primary committed credit facilities, and was in compliance with the financial covenants and all other covenants contained therein during the rolling year ended December 31, 2022. Commercial Paper Commercial paper may be issued in aggregate principal amounts of up to $1 billion under the U.S. Program and €625 million ($665 million at December 31, 2022 exchange rates) under the European Program, not to exceed the amount of the Company’s committed credit facilities, which was approximately $1.8 billion at December 31, 2022. The aggregate capacity of the Commercial Paper Program remains fully backed by the Company’s committed credit facilities. The U.S. Program was fully and unconditionally guaranteed by Aon plc, Aon Global Limited, and Aon Global Holdings plc and the European Program was fully and unconditionally guaranteed by Aon plc, Aon Global Limited, and Aon Corporation. Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Company’s Consolidated Statements of Financial Position, is as follows (in millions): As of December 31 2022 2021 Commercial paper outstanding $ 592 $ 665 The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Years Ended December 31 2022 2021 Weighted average commercial paper outstanding $ 499 $ 273 Weighted average interest rate of commercial paper outstanding 1.42 % 0.01 %

Lease Commitments

Lease Commitments	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Lease Commitments	Lease Commitments The classification of operating and finance lease asset and liability balances within the Consolidated Statements of Financial Position are as follows (in millions): As of December 31 2022 2021 Assets Operating lease assets Operating lease right-of-use assets $ 699 $ 786 Finance lease assets Other non-current assets 43 63 Total lease assets $ 742 $ 849 Liabilities Current lease liabilities Operating Other current liabilities $ 163 $ 194 Finance Other current liabilities 23 19 Non-current lease liabilities Operating Non-current operating lease liabilities 693 772 Finance Other non-current liabilities 28 46 Total lease liabilities $ 907 $ 1,031 The components of lease costs are as follows (in millions): Years Ended December 31 2022 2021 Operating lease cost $ 204 $ 217 Finance lease costs Amortization of leased assets 28 26 Interest on lease liabilities 1 1 Variable lease cost 38 49 Short-term lease cost (1) 11 11 Sublease income (29) (31) Net lease cost $ 253 $ 273 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less. Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of December 31 2022 2021 Weighted average remaining lease term (years) Operating leases 6.7 6.9 Finance leases 2.5 3.6 Weighted average discount rate Operating leases 3.1 % 2.8 % Finance leases 1.0 % 1.0 % Other cash and non-cash related activities are as follows (in millions): Years Ended December 31 2022 2021 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 231 $ 244 Financing cash flows for finance leases $ 14 $ 23 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 110 $ 44 ROU assets obtained in exchange for new finance lease liabilities $ — $ — Operating lease ROU asset expense (1) $ 162 $ 142 Changes in Non-current operating lease liabilities (1) $ (79) $ (125) (1) The Company has recorded non-cash changes in Operating lease ROU assets and Non-current operating lease liabilities through Other assets and liabilities in Cash flows from operations within the Consolidated Statements of Cash Flows. Maturity analysis of operating and finance leases as of December 31, 2022 are as follows (in millions): Operating Leases Finance Leases Total 2023 $ 175 $ 23 $ 198 2024 164 18 182 2025 135 10 145 2026 123 — 123 2027 108 — 108 Thereafter 235 — 235 Total undiscounted future minimum lease payments 940 51 991 Less: Imputed interest (84) — (84) Present value of lease liabilities $ 856 $ 51 $ 907
Lease Commitments	Lease Commitments The classification of operating and finance lease asset and liability balances within the Consolidated Statements of Financial Position are as follows (in millions): As of December 31 2022 2021 Assets Operating lease assets Operating lease right-of-use assets $ 699 $ 786 Finance lease assets Other non-current assets 43 63 Total lease assets $ 742 $ 849 Liabilities Current lease liabilities Operating Other current liabilities $ 163 $ 194 Finance Other current liabilities 23 19 Non-current lease liabilities Operating Non-current operating lease liabilities 693 772 Finance Other non-current liabilities 28 46 Total lease liabilities $ 907 $ 1,031 The components of lease costs are as follows (in millions): Years Ended December 31 2022 2021 Operating lease cost $ 204 $ 217 Finance lease costs Amortization of leased assets 28 26 Interest on lease liabilities 1 1 Variable lease cost 38 49 Short-term lease cost (1) 11 11 Sublease income (29) (31) Net lease cost $ 253 $ 273 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less. Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of December 31 2022 2021 Weighted average remaining lease term (years) Operating leases 6.7 6.9 Finance leases 2.5 3.6 Weighted average discount rate Operating leases 3.1 % 2.8 % Finance leases 1.0 % 1.0 % Other cash and non-cash related activities are as follows (in millions): Years Ended December 31 2022 2021 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 231 $ 244 Financing cash flows for finance leases $ 14 $ 23 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 110 $ 44 ROU assets obtained in exchange for new finance lease liabilities $ — $ — Operating lease ROU asset expense (1) $ 162 $ 142 Changes in Non-current operating lease liabilities (1) $ (79) $ (125) (1) The Company has recorded non-cash changes in Operating lease ROU assets and Non-current operating lease liabilities through Other assets and liabilities in Cash flows from operations within the Consolidated Statements of Cash Flows. Maturity analysis of operating and finance leases as of December 31, 2022 are as follows (in millions): Operating Leases Finance Leases Total 2023 $ 175 $ 23 $ 198 2024 164 18 182 2025 135 10 145 2026 123 — 123 2027 108 — 108 Thereafter 235 — 235 Total undiscounted future minimum lease payments 940 51 991 Less: Imputed interest (84) — (84) Present value of lease liabilities $ 856 $ 51 $ 907

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income before income tax and the provision for income tax consist of the following (in millions): Years Ended December 31 2022 2021 2020 Income (loss) before income taxes: Ireland $ 85 $ 15 $ (86) U.K. 502 549 634 U.S. 161 (818) (28) Other 2,408 2,185 1,946 Total $ 3,156 $ 1,931 $ 2,466 Income tax expense: Current: Ireland $ 2 $ 2 $ 2 U.K. 206 50 30 U.S. federal 195 197 126 U.S. state and local 43 72 22 Other 316 291 259 Total current tax expense $ 762 $ 612 $ 439 Deferred tax expense (benefit): Ireland $ — $ (1) $ (1) U.K. (152) 131 39 U.S. federal (69) (83) (72) U.S. state and local (21) (30) (4) Other (10) (6) 47 Total deferred tax expense (benefit) $ (252) $ 11 $ 9 Total income tax expense $ 510 $ 623 $ 448 Income before income taxes shown above is based on the location of the business unit to which such earnings are attributable for tax purposes. In addition, because the earnings shown above may, in some cases, be subject to taxation in more than one country, the income tax provision shown above as Ireland, U.K., U.S. or Other may not correspond to the geographic attribution of the earnings. The Company performs a reconciliation of the income tax provisions based on its domicile and statutory rate at each reporting period. The reconciliation of the income tax provisions based on the Irish statutory corporate tax rate of 25% to the provisions reflected in the Consolidated Financial Statements is as follows: Years Ended December 31 2022 2021 2020 Statutory tax rate 25.0% 25.0% 25.0% U.S. state income taxes, net of U.S. federal benefit 0.4 1.5 1.0 Taxes on international operations (1) (2) (11.6) (15.4) (9.8) Nondeductible expenses 2.4 3.3 2.1 Adjustments to prior year tax requirements (7.0) (0.2) — Deferred tax adjustments, including statutory rate changes (0.5) 3.2 0.7 Deferred tax adjustments, international earnings 0.2 1.8 0.7 Adjustments to valuation allowances 1.9 (0.2) — Change in uncertain tax positions 8.6 2.1 1.5 Excess tax benefits related to shared based compensation (3) (1.5) (2.4) (2.2) Capital and other losses (1.4) — (1.8) Non-deductible transaction costs — 1.1 1.3 Non-deductible termination fee — 12.9 — Other — net (0.3) (0.4) (0.3) Effective tax rate 16.2% 32.3% 18.2% (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, 2022, 2021, and 2020, 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) In July 2020, final U.S. tax regulations were issued regarding the GILTI high tax election, allowing taxpayers to exclude from GILTI the income of a Controlled Foreign Corporation that incurs a foreign tax rate more than 90% of the top U.S. corporate tax rate. A GILTI high tax election may be made on an annual basis, and taxpayers may choose to apply the election to taxable years beginning after December 31, 2017. The Company expects to make the GILTI high-tax election for 2022 and therefore recorded the impact of making the election. (3) 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. The Company has elected to account for GILTI in the period in which it is incurred, and therefore has not provided deferred tax impacts of GILTI in its Consolidated Financial Statements. The components of the Company’s deferred tax assets and liabilities are as follows (in millions): As of December 31 2022 2021 Deferred tax assets: Net operating loss, capital loss, interest, and tax credit carryforwards $ 952 $ 581 Lease liabilities 178 207 Employee benefit plans 297 160 Other accrued expenses 100 132 Accrued interest — 97 Federal and state benefit of interest from uncertain tax positions 57 45 Deferred revenue 26 36 Investment basis differences 30 25 Lease and service guarantees 1 1 Other 38 25 Total 1,679 1,309 Valuation allowance on deferred tax assets (275) (230) Total $ 1,404 $ 1,079 Deferred tax liabilities: Intangibles and property, plant and equipment $ (258) $ (243) Lease right-of-use asset (151) (173) Deferred costs (147) (159) Unremitted earnings (38) (58) Other accrued expenses (20) (27) Unrealized foreign exchange gains (23) (22) Other (42) (32) Total $ (679) $ (714) Net deferred tax asset $ 725 $ 365 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 2022 2021 Deferred tax assets — non-current $ 824 $ 766 Deferred tax liabilities — non-current (99) (401) Net deferred tax asset $ 725 $ 365 In assessing the realizability of deferred tax assets, the Company considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized and adjusts the valuation allowance accordingly. Considerations with respect to the realizability of deferred tax assets include the period of expiration of the deferred tax asset, historical earnings and projected future taxable income by jurisdiction as well as tax liabilities for the tax jurisdiction to which the tax asset relates. Significant management judgment is required in determining the assumptions and estimates related to the amount and timing of future taxable income. Valuation allowances have been established primarily with regard to the tax benefits of certain tax credits and net operating losses, capital losses, and interest carryforwards. Valuation allowances increased by $45 million as of December 31, 2022, when compared to December 31, 2021. The change is primarily attributable to an increase in valuation allowances related to net operating losses and foreign tax credits. The Company generally intends to limit distributions from foreign subsidiaries in excess of U.S. tax earnings and profits (except where distributions would be limited by available cash) and to limit repatriations from certain other jurisdictions that would otherwise generate a U.S. tax liability. As of December 31, 2022, the Company has accrued $38 million for local country income taxes, withholding taxes and state income taxes on those undistributed earnings that are not indefinitely reinvested. The Company has not provided for deferred taxes on outside basis differences in our investments in our foreign subsidiaries that are unrelated to these accumulated undistributed earnings, as these outside basis differences are indefinitely reinvested. A determination of the unrecognized deferred taxes related to these other components of our outside basis differences is not practicable. The Company had the following carryforwards (in millions): As of December 31 2022 2021 U.K. Operating loss carryforwards $ 608 $ 41 Capital loss carryforwards $ 533 $ 573 U.S. Federal operating loss carryforwards $ 1 $ 25 Federal capital loss carryforwards $ 112 $ 112 Federal interest carryforwards $ 2,269 $ 1,140 Federal foreign tax credit carryforwards $ 20 $ 18 State operating loss carryforwards $ 473 $ 398 State capital loss carryforwards $ 123 $ 123 State interest carryforwards $ 1,187 $ 551 Other Non-U.S. Operating loss carryforwards $ 490 $ 301 Capital loss carryforwards $ 8 $ 35 Interest carryforwards $ 26 $ 26 Other carryforwards $ 5 $ 5 The U.K. operating losses and capital losses have an indefinite carryforward period. The federal operating loss carryforwards generated through December 31, 2017 expire at various dates between 2034 and 2036 while federal operating loss carryforwards generated after this date have indefinite carryforward periods. State net operating losses as of December 31, 2022 have various carryforward periods and will begin to expire in 2023. Federal and state capital losses can be carried forward until 2023. Federal and state interest carryforwards have indefinite carryforward periods. Foreign tax credits can be carried forward for ten years and will begin to expire in 2028. Operating, capital losses, and other carryforwards in other non-U.S. jurisdictions have various carryforward periods and will begin to expire in 2023. The interest carryforwards in other non-U.S. jurisdictions have an indefinite carryforward period. During 2012, the Company was granted a tax holiday for the period from October 1, 2012 through September 30, 2022, with respect to withholding taxes and certain income derived from services in Singapore. The Company has been granted a new incentive for the period October 1, 2022 to September 30, 2032. The new incentive provides for a reduced withholding tax rate and a reduced tax rate on certain income derived from services in Singapore, as long as certain conditions are met. The benefit realized was approximately $115 million, $104 million, and $97 million during the years ended December 31, 2022, 2021, and 2020, respectively. The impact of this tax holiday on diluted earnings per share was $0.54, $0.46, and $0.42 during the years ended December 31, 2022, 2021, and 2020, respectively. Uncertain Tax Positions The following is a reconciliation of the Company’s beginning and ending amount of uncertain tax positions (in millions): 2022 2021 Balance at January 1 $ 347 $ 321 Additions based on tax positions related to the current year 35 33 Additions for tax positions of prior years 226 7 Reductions for tax positions of prior years (1) (4) Settlements (1) — Business combinations — — Lapse of statute of limitations (5) (10) Foreign currency translation — — Balance at December 31 $ 601 $ 347 The Company’s liability for uncertain tax positions as of December 31, 2022, 2021, and 2020, includes $535 million, $295 million, and $270 million, respectively, related to amounts that would impact the effective tax rate if recognized. It is possible that the amount of unrecognized tax benefits may change in the next twelve months; however, the Company does not expect the change to have a significant impact on its consolidated statements of income or consolidated balance sheets. These changes may be the result of settlements of ongoing audits. At this time, an estimate of the range of the reasonably possible outcomes within the next twelve months cannot be made. The Company recognizes interest and penalties related to uncertain tax positions in its provision for income taxes. The Company accrued potential interest and penalties of $40 million, $22 million, and $21 million in 2022, 2021, and 2020, respectively. The Company recorded a liability for interest and penalties of $181 million, $142 million, and $120 million as of December 31, 2022, 2021, and 2020, respectively. The Company and its subsidiaries file income tax returns in their respective jurisdictions. The Company has substantially concluded all U.S. federal income tax matters for years through 2007. Material U.S. state and local income tax jurisdiction examinations have been concluded for years through 2014. The Company has concluded income tax examinations in its primary non-U.S. jurisdictions through 2008.

Shareholders' Equity (Deficit)

Shareholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Shareholders' Equity (Deficit)	Shareholders’ Equity (Deficit) Distributable Profits The Company is required under Irish law to have available “distributable profits” to make share repurchases or pay dividends to shareholders. Distributable profits are created through the earnings of the Irish parent company and, among other methods, through intercompany dividends or a reduction in share capital approved by the High Court of Ireland. Distributable profits are not linked to a U.S. GAAP reported amount (e.g., accumulated deficit). As of December 31, 2022 and 2021, the Company had distributable profits in excess of $29.0 billion and $32.7 billion, respectively. We believe that we have the ability to create sufficient distributable profits for the foreseeable future. Ordinary Shares Aon has a share repurchase program authorized by the Company’s Board of Directors. The Repurchase Program was established in April 2012 with $5.0 billion in authorized repurchases and was increased by $5.0 billion in authorized repurchases in each of November 2014, June 2017, and November 2020, and by $7.5 billion in February 2022 for a total of $27.5 billion in repurchase authorizations. Under the Repurchase Program, the Company’s class A ordinary shares may be repurchased through the open market or in privately negotiated transactions, from time to time, based on prevailing market conditions and will be funded from available capital. The following table summarizes the Company’s share repurchase activity (in millions, except per share data): Years Ended December 31 2022 2021 Shares repurchased 11.1 12.4 Average price per share $ 289.76 $ 286.82 Repurchase costs recorded to accumulated deficit $ 3,203 $ 3,543 At December 31, 2022, the remaining authorized amount for share repurchases under the Repurchase Program was approximately $6.0 billion. Under the Repurchase Program, the Company has repurchased a total of 160.7 million shares for an aggregate cost of approximately $21.5 billion. Weighted Average Ordinary Shares Weighted average ordinary shares outstanding are as follows (in millions): Years Ended December 31 2022 2021 2020 Basic weighted average ordinary shares outstanding 211.7 224.7 231.9 Dilutive effect of potentially issuable shares 1.5 1.4 1.2 Diluted weighted average ordinary shares outstanding 213.2 226.1 233.1 Potentially issuable shares are not included in the computation of Diluted net income per share attributable to Aon shareholders if their inclusion would be antidilutive. There were 0.8 million and 0.3 million shares excluded from the calculation in 2022 and 2021, respectively, and no shares excluded from the calculation in 2020. Accumulated Other Comprehensive Loss Changes in Accumulated other comprehensive loss by component, net of related tax, are as follows (in millions): Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Postretirement Benefit Obligation (2) Total Balance at December 31, 2019 $ (12) $ (1,305) $ (2,716) $ (4,033) Other comprehensive income (loss) before reclassifications: Other comprehensive income (loss) before reclassifications 1 258 (255) 4 Tax benefit — 2 60 62 Other comprehensive income (loss) before reclassifications, net 1 260 (195) 66 Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income 15 — 125 140 Tax expense (3) — (31) (34) Amounts reclassified from accumulated other comprehensive income, net 12 — 94 106 Net current period other comprehensive income (loss) 13 260 (101) 172 Balance at December 31, 2020 $ 1 $ (1,045) $ (2,817) $ (3,861) Other comprehensive income (loss) before reclassifications: Other comprehensive income (loss) before reclassifications — (290) 227 (63) Tax benefit (expense) — 2 (58) (56) Other comprehensive income (loss) before reclassifications, net — (288) 169 (119) Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income 2 — 142 144 Tax expense (1) — (34) (35) Amounts reclassified from accumulated other comprehensive income, net 1 — 108 109 Net current period other comprehensive income (loss) 1 (288) 277 (10) Balance at December 31, 2021 $ 2 $ (1,333) $ (2,540) $ (3,871) Other comprehensive income (loss) before reclassifications: Other comprehensive loss before reclassifications (15) (528) (569) (1,112) Tax benefit (expense) 4 — 149 153 Other comprehensive loss before reclassifications, net (11) (528) (420) (959) Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income (loss) (2) — 282 280 Tax expense — — (73) (73) Amounts reclassified from accumulated other comprehensive income (loss), net (2) — 209 207 Net current period other comprehensive loss (13) (528) (211) (752) Balance at December 31, 2022 $ (11) $ (1,861) $ (2,751) $ (4,623) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Total revenue, Interest expense, and Compensation and benefits in the Consolidated Statements of Income. Refer to Note 13 “Derivatives and Hedging” for further information regarding the Company’s derivative and hedging activity. (2) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Other income (expense) in the Consolidated Statements of Income.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Employee Benefits	Employee Benefits Defined Contribution Savings Plans Aon maintains defined contribution savings plans for the benefit of its employees. The expense recognized for these plans is included in Compensation and benefits in the Consolidated Statements of Income. The expense for the significant plans in the U.S., U.K., Netherlands, and Canada is as follows (in millions): Years Ended December 31 2022 2021 2020 U.S. $ 108 $ 103 $ 87 U.K. 47 46 42 Netherlands and Canada 33 35 26 Total $ 188 $ 184 $ 155 Pension and Other Postretirement Benefits The Company sponsors defined benefit pension and postretirement health and welfare plans that provide retirement, medical, and life insurance benefits. The postretirement health care plans are contributory, with retiree contributions adjusted annually, and the life insurance and pension plans are generally noncontributory. The significant U.S., U.K., Netherlands, and Canada pension plans are closed to new entrants. Pension Plans The following tables provide a reconciliation of the changes in the projected benefit obligations and fair value of assets for the years ended December 31, 2022 and 2021, and a statement of the funded status as of December 31, 2022 and 2021, for Aon’s significant U.K., U.S., and other major pension plans, which are located in the Netherlands and Canada. These plans represent approximately 88% of the Company’s projected benefit obligations. U.K. U.S. Other (millions) 2022 2021 2022 2021 2022 2021 Change in projected benefit obligation At January 1 $ 4,919 $ 5,406 $ 3,164 $ 3,380 $ 1,531 $ 1,625 Service cost 1 1 — — — — Interest cost 83 65 73 57 19 12 Settlements — (14) (283) — — — Actuarial (gain) loss (1,418) (292) (607) (103) (322) 24 Benefit payments (195) (189) (167) (170) (45) (47) Foreign currency impact (444) (58) — — (89) (83) As of December 31 $ 2,946 $ 4,919 $ 2,180 $ 3,164 $ 1,094 $ 1,531 Accumulated benefit obligation at end of year $ 2,946 $ 4,919 $ 2,180 $ 3,164 $ 1,079 $ 1,504 Change in fair value of plan assets At January 1 $ 6,246 $ 6,652 $ 2,378 $ 2,276 $ 1,430 $ 1,497 Actual return on plan assets (1,961) (136) (484) 211 (284) 46 Employer contributions 7 9 37 61 15 17 Settlements — (14) (283) — — — Benefit payments (195) (189) (167) (170) (45) (47) Foreign currency impact (559) (76) — — (83) (83) As of December 31 $ 3,537 $ 6,246 $ 1,481 $ 2,378 $ 1,032 $ 1,430 Market related value at end of year $ 3,537 $ 6,246 $ 1,794 $ 2,174 $ 1,032 $ 1,430 Amount recognized in Statement of Financial Position as of December 31 Funded status $ 591 $ 1,327 $ (699) $ (786) $ (62) $ (101) Unrecognized prior-service cost 35 40 — — (6) (6) Unrecognized loss 1,726 1,215 1,305 1,551 443 489 Net amount recognized $ 2,352 $ 2,582 $ 606 $ 765 $ 375 $ 382 The benefit obligation decreased primarily as a result of increases in the discount rates in 2022 as compared to 2021. The value of plan assets decreased as a result of negative asset returns, predominately in the U.K, and overall weaker exchange rates versus the U.S. Dollar. The U.K. pension assets are concentrated in fixed income and annuities which were disproportionately negatively impacted by the rising interest rate environment. The U.K. hedging strategy continues to perform as expected and the related pension plans remain over-funded. Net actuarial gains decreased the benefit obligation in 2021 primarily due to the increase in the discount rates. In November 2022, to further its pension de-risking strategy the Company purchased an annuity for portions of its U.S. pension plans that will settle certain obligations. The transaction settled $280 million of benefit obligations using $280 million of assets. In November 2020, the Company entered into an insurance contract that covers a portion of the assets within a select U.K. pension scheme. The transaction resulted in a decrease in Prepaid pension assets and Accumulated other comprehensive income of $94 million. Amounts recognized in the Consolidated Statements of Financial Position consist of (in millions): U.K. U.S. Other 2022 2021 2022 2021 2022 2021 Prepaid benefit cost (1) $ 612 $ 1,344 $ — $ — $ — $ — Accrued benefit liability - current (2) (1) (1) (42) (52) (5) (5) Accrued benefit liability - non-current (3) (20) (16) (657) (734) (57) (96) Accumulated other comprehensive loss 1,761 1,255 1,305 1,551 437 483 Net amount recognized $ 2,352 $ 2,582 $ 606 $ 765 $ 375 $ 382 (1) Included in Prepaid pension. (2) Included in Other current liabilities. (3) Included in Pension, other postretirement, and postemployment liabilities. Amounts recognized in Accumulated other comprehensive loss (income) that have not yet been recognized as components of net periodic benefit cost at December 31, 2022 and 2021 consist of (in millions): U.K. U.S. Other 2022 2021 2022 2021 2022 2021 Net loss $ 1,726 $ 1,215 $ 1,305 $ 1,551 $ 443 $ 489 Prior service cost (income) 35 40 — — (6) (6) Total $ 1,761 $ 1,255 $ 1,305 $ 1,551 $ 437 $ 483 In 2022, U.S. plans with a PBO and an ABO in excess of the fair value of plan assets had a PBO of $2.2 billion, an ABO of $2.2 billion, and plan assets with a fair value of $1.5 billion. U.K. plans with a PBO and an ABO in excess of the fair value of plan assets had a PBO of $114 million, an ABO of $114 million and, plan assets with a fair value of $93 million. Other plans with a PBO in excess of the fair value of plan assets had a PBO of $1.1 billion and plan assets with a fair value of $1.0 billion, and other plans with an ABO in excess of the fair value of plan assets had an ABO of $220 million and plan assets with a fair value of $166 million. In 2021, U.S. plans with a PBO and an ABO in excess of the fair value of plan assets had a PBO of $3.2 billion, an ABO of $3.2 billion, and plan assets with a fair value of $2.4 billion. U.K. plans with a PBO and an ABO in excess of the fair value of plan assets had a PBO of $17 million, an ABO of $17 million and no plan assets. Other plans with a PBO in excess of the fair value of plan assets had a PBO of $1.5 billion and plan assets with a fair value of $1.4 billion, and other plans with an ABO in excess of the fair value of plan assets had an ABO of $409 million and plan assets with a fair value of $326 million. Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): U.K. U.S. Other 2022 2021 2020 2022 2021 2020 2022 2021 2020 Service cost $ 1 $ 1 $ — $ — $ — $ — $ — $ — $ — Interest cost 83 65 88 73 57 85 19 12 19 Expected return on plan assets, net of administration expenses (134) (137) (159) (108) (130) (134) (33) (32) (34) Amortization of prior-service cost 2 2 2 — — 1 — — — Amortization of net actuarial loss 29 32 30 61 78 68 13 15 12 Net periodic benefit (income) cost (19) (37) (39) 26 5 20 (1) (5) (3) Settlement expense — 5 2 170 — — — — — Total net periodic benefit cost (income) $ (19) $ (32) $ (37) $ 196 $ 5 $ 20 $ (1) $ (5) $ (3) The Company uses a full-yield curve approach in the estimation of the service and interest cost components of net periodic pension and postretirement benefit cost for its major pension and other postretirement benefit plans. This estimation was obtained by applying the specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. In November 2022, to further its pension de-risking strategy the Company purchased an annuity for portions of its U.S. pension plans that will settle certain obligations. This triggered settlement accounting which required immediate recognition of a portion of the accumulated losses associated with the plan. Consequently, the Company recognized a non-cash settlement charge of approximately $170 million in 2022. Transfer payments from certain U.K. pension plans exceeded the plan’s service and interest cost in 2021 and 2020. This triggered settlement accounting which required immediate recognition of a portion of the accumulated losses associated with the plan. Consequently, the Company recognized a non-cash settlement charge for approximately £3 million in 2021 ($5 million using December 31, 2021 exchange rates), and approximately £2 million in 2020 ($2 million using December 31, 2020 exchange rates). The weighted-average assumptions used to determine benefit obligations are as follows: U.K. U.S. (1) Other 2022 2021 2022 2021 2022 2021 Discount rate 4.89% 1.96% 4.82 - 5.03% 2.23 - 2.8% 3.23 - 5.19% 1.00 - 2.97% Rate of compensation increase 3.59 - 4.09% 3.62 - 4.12% N/A N/A 1.00 - 3.00% 1.00 - 3.00% Underlying price inflation 2.44% 2.52% N/A N/A 2.00% 2.00% (1) U.S. pension plans are frozen and therefore not impacted by compensation increases or price inflation. The weighted-average assumptions used to determine the net periodic benefit cost are as follows: U.K. U.S. Other 2022 2021 2020 2022 2021 2020 2022 2021 2020 Discount rate 1.85% 1.20% 1.89% 1.67 - 2.25% 1.12 - 1.79% 2.36 - 2.76% 0.84 - 2.58% 0.28 - 2.00% 0.74 - 2.90% Expected return on plan assets, net of administration expenses 2.34% 2.04% 2.74% 2.03 - 5.28% 2.65- 6.56% 3.30%-7.04% 1.80 - 3.15% 1.70 - 2.65% 2.10 - 3.10% Rate of compensation increase 3.62 - 4.12% 3.22 - 3.72% 3.24 - 3.74% N/A N/A N/A 1.00 - 3.00% 1.00 - 3.00% 1.00 - 3.00% Expected Return on Plan Assets To determine the expected long-term rate of return on plan assets, the historical performance, investment community forecasts, and current market conditions are analyzed to develop expected returns for each asset class used by the plans. The expected returns for each asset class are weighted by the target allocations of the plans. The expected return of 5.28% on U.S. plan assets reflects a portfolio that is seeking asset growth through a higher equity allocation while maintaining prudent risk levels. The portfolio contains certain assets that have historically resulted in higher returns, as well as other financial instruments to minimize downside risk. No plan assets are expected to be returned to the Company during 2023. Fair value of plan assets The Company determined the fair value of plan assets through numerous procedures based on the asset class and available information. Refer to Note 14 “Fair Value Measurements and Financial Instruments” for a description of the procedures performed to determine the fair value of the plan assets. The fair values of the Company’s U.S. pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Asset Category Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 42 $ 42 $ — $ — Equity investments: Equity securities 64 64 — — Equity derivatives (6) — (6) — Pooled funds (2) 293 — — — Fixed income investments: Corporate bonds 192 — 192 — Government and agency bonds 149 124 25 — Pooled funds (2) 507 — — — Other investments: Real estate (2) (3) 113 — — — Alternative investments (2) (4) 127 — — — Total $ 1,481 $ 230 $ 211 $ — Fair Value Measurements Using Asset Category Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 93 $ 93 $ — $ — Equity investments: Equity securities 86 86 — — Equity derivatives 19 — 19 — Pooled funds (2) 548 — — — Fixed income investments: Corporate bonds 249 — 249 — Government and agency bonds 230 192 38 — Pooled funds (2) 838 — — — Other investments: Real estate (2)(3) 156 — — — Alternative investments (2) (4) 159 — — — Total $ 2,378 $ 371 $ 306 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of property funds and trusts holding direct real estate investments. (4) Consists of limited partnerships, private equity, and hedge funds. The fair values of the Company’s major U.K. pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 336 $ 336 $ — $ — Equity investments: Pooled funds (2) — — — — Fixed income investments: Derivatives (3) (548) — (548) — Government and agency bonds 1,593 1,593 — — Annuities 1,403 — — 1,403 Pooled funds (2) 139 — — — Other investments: Real estate (2) (4) 97 — — — Pooled funds (2) (5) 517 — — — Total $ 3,537 $ 1,929 $ (548) $ 1,403 Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 872 $ 872 $ — $ — Equity investments: Pooled funds (2) — — — — Fixed income investments: Derivatives (3) (1,640) — (1,640) — Government and agency bonds 2,969 2,969 — — Annuities 2,305 — — 2,305 Pooled funds (2) 463 — — — Other investments: Real estate (2) (4) 130 — — — Pooled funds (2) (5) 1,147 — — — Total $ 6,246 $ 3,841 $ (1,640) $ 2,305 (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of equity securities and equity derivatives, including repurchase agreements. (4) Consists of property funds and trusts holding direct real estate investments. (5) Consists of multi-strategy limited partnerships, private equity, hedge funds, and collective investment schemes with a diversified portfolio of cash, equities, equity related securities, derivatives, and/or fixed income securities. The following table presents the changes in the Level 3 fair-value category in the Company’s U.K. pension plans for the years ended December 31, 2022 and December 31, 2021 (in millions): Fair Value Measurements Using Level 3 Inputs Annuities Balance at January 1, 2021 $ 2,625 Actual return on plan assets: Relating to assets still held at December 31, 2021 (286) Purchase, sales and settlements-net — Foreign exchange (34) Balance at December 31, 2021 2,305 Actual return on plan assets: Relating to assets still held at December 31, 2022 (674) Purchases, sales and settlements-net — Foreign exchange (228) Balance at December 31, 2022 $ 1,403 The fair values of the Company’s other major pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 30 $ 30 $ — $ — Equity investments: Equity securities 53 53 — — Pooled funds (2) 211 — — — Fixed income investments: Government and agency bonds 225 225 — — Derivatives (3) — (3) — Pooled funds (2) 462 — — — Other investments: Alternative investments (2) (3) 42 — — — Real estate (2) (4) 12 — — — Total $ 1,032 $ 308 $ (3) $ — Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 29 $ 29 $ — $ — Equity investments: Equity securities 72 72 — — Pooled funds (2) 316 — — — Fixed income investments: Government and agency bonds 350 350 — — Pooled funds (2) 597 — — — Other investments: Alternative investments (2) (3) 55 — — — Real estate (2) (4) 11 — — — Total $ 1,430 $ 451 $ — $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of limited partnerships, private equity, and hedge funds. (4) Consists of property funds and trusts holding direct real estate investments. Investment Policy and Strategy The U.S. investment policy, as established by the RPGIC, seeks reasonable asset growth at prudent risk levels within weighted average target allocations. At December 31, 2022, the weighted average targeted allocation for the U.S. plans was 30% for equity investments, 54% for fixed income investments, and 16% for other investments. Aon believes that plan assets are well-diversified and are of appropriate quality. The investment portfolio asset allocation is reviewed quarterly and re-balanced to be within policy target allocations. The investment policy is reviewed at least annually and revised, as deemed appropriate by the RPGIC. The investment policies for international plans are generally established by the local pension plan trustees and seek to maintain the plans’ ability to meet liabilities and to comply with local minimum funding requirements. Plan assets are invested in diversified portfolios that provide adequate levels of return at an acceptable level of risk. The investment policies are reviewed at least annually and revised, as deemed appropriate to ensure that the objectives are being met. At December 31, 2022, the weighted average targeted allocation for the U.K. and non-U.S. plans was 6% for equity investments, 86% for fixed income investments, and 8% for other investments. Cash Flows Contributions Based on current assumptions, in 2023, the Company expects to contribute approximately $4 million, $43 million, and $14 million to its significant U.K., U.S., and other major pension plans, respectively. Estimated Future Benefit Payments Estimated future benefit payments for plans, not including voluntary one-time lump sum payments, are as follows at December 31, 2022 (in millions): U.K. U.S. Other 2023 $ 153 $ 157 $ 46 2024 $ 157 $ 158 $ 47 2025 $ 161 $ 158 $ 49 2026 $ 166 $ 162 $ 50 2027 $ 170 $ 155 $ 51 2028 - 2032 $ 905 $ 754 $ 274 U.S. and Canadian Other Postretirement Benefits The following table provides an overview of the accumulated PBO, fair value of plan assets, funded status and net amount recognized as of December 31, 2022 and 2021 for the Company’s other significant postretirement benefit plans located in the U.S. and Canada (in millions): 2022 2021 Accumulated projected benefit obligation $ 83 $ 109 Fair value of plan assets 14 17 Funded status (69) (92) Unrecognized prior-service credit (1) (1) Unrecognized (gain) loss (19) 2 Net amount recognized $ (89) $ (91) Other information related to the Company’s other postretirement benefit plans are as follows: 2022 2021 2020 Net periodic benefit cost recognized (millions) $3 $5 $4 Weighted-average discount rate used to determine future benefit obligations 4.94 - 5.19% 2.52 - 3.06% 2.10 - 2.58% Weighted-average discount rate used to determine net periodic benefit costs 1.97 - 2.69% 1.45 - 2.68% 2.93 - 3.25% Based on current assumptions, the Company expects: • The amount in Accumulated other comprehensive income expected to be recognized as a component of net periodic benefit cost during 2023 is $0.8 million net gain and $0.2 million of prior-service credit. • To contribute $5 million to fund significant other postretirement benefit plans during 2023. • Estimated future benefit payments will be approximately $5 million each year for 2023 through 2027, and $27 million in aggregate for 2028-2032.

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The following table summarizes share-based compensation expense recognized in the Consolidated Statements of Income in Compensation and benefits (in millions): Years Ended December 31 2022 2021 2020 Restricted share units $ 251 $ 204 $ 186 Performance share awards 134 189 116 Employee share purchase plans and other (1) 12 56 10 Total share-based compensation expense 397 449 312 Tax benefit 83 87 61 Share-based compensation expense, net of tax $ 314 $ 362 $ 251 (1) 2021 includes expenses related to the Aon United Growth Ownership Plan. Restricted Share Units RSUs generally vest between three The following table summarizes the status of the Company’s RSUs (shares in thousands, except fair value): Shares Fair Value (1) Non-vested balance at December 31, 2021 3,075 $ 203 Granted 1,117 $ 279 Vested (1,154) $ 187 Forfeited (175) $ 219 Non-vested balance at December 31, 2022 2,863 $ 238 (1) Represents per share weighted average fair value of award at date of grant. The weighted-average grant date fair value of the Company's RSU awards granted during the years ended December 31, 2022, December 31, 2021, and December 31, 2020 was $279, $253, and $185, respectively. The fair value of RSUs that vested during 2022, 2021, and 2020 was $216 million, $189 million, and $190 million, respectively. Unamortized deferred compensation expense amounted to $466 million as of December 31, 2022, with a remaining weighted average amortization period of approximately 2.0 years. Performance Share Awards The vesting of PSAs is contingent upon meeting a cumulative level of adjusted diluted earnings per share related performance over a three-year period. The actual issuance of shares may range from 0-200% of the target number of PSAs granted, based on the terms of the plan and level of achievement of the related performance target. The grant date fair value of PSAs is based upon the market price of the Company’s class A ordinary shares at the date of grant, reduced by the present value of estimated dividends foregone during the vesting period. The performance conditions are not considered in the determination of the grant date fair value for these awards. Compensation expense is recognized over the performance period based on management’s estimate of the number of units expected to vest. Management evaluates its estimate of the actual number of shares expected to be issued at the end of the programs on a quarterly basis. The cumulative effect of the change in estimate is recognized in the period of change as an adjustment to Compensation and benefits in the Consolidated Statements of Income, if necessary. Dividend equivalents are not paid on PSAs. The following table summarizes the status of the Company's PSAs at 100% of the targeted amount (shares in thousands, except fair value): Shares Fair Value (1) Non-vested balance at December 31, 2021 1,298 $ 181 Granted 300 $ 311 Vested (444) $ 163 Forfeited (18) $ 217 Non-vested balance at December 31, 2022 1,136 $ 222 (1) Represents per share weighted average fair value of award at date of grant. The per share weighted-average grant date fair value of the Company's PSA awards granted during the years ended December 31, 2022, December 31, 2021, and December 31, 2020 was $311, $225, and $163, respectively. The payout of shares in 2022 with respect to the PSA awards granted in 2019 based on performance for the three-year performance period ended 2021 was, in aggregate, 888 thousand shares. The fair value of PSAs that vested during 2022, 2021, and 2020 was $145 million, $112 million, and $121 million, respectively. Unamortized compensation expense, based on current performance levels, amounted to $126 million as of December 31, 2022, with a remaining weighted average amortization period of approximately 1.3 years.

Derivatives and Hedging

Derivatives and Hedging	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging	Derivatives and HedgingThe Company is exposed to market risks, including changes in foreign currency exchange rates and interest rates. To manage the risk related to these exposures, the Company enters into various derivative instruments that reduce these risks by creating offsetting exposures. The Company does not enter into derivative transactions for trading or speculative purposes. Foreign Exchange Risk Management The Company is exposed to foreign exchange risk when it earns revenues, pays expenses, enters into monetary intercompany transfers or other transactions denominated in a currency that differs from its functional currency. The Company uses foreign exchange derivatives, typically forward contracts, options and cross-currency swaps, to reduce its overall exposure to the effects of currency fluctuations on cash flows. These exposures are hedged, on average, for less than two years. These derivatives are accounted for as hedges, and changes in fair value are recorded each period in Other comprehensive income (loss) in the Consolidated Statements of Comprehensive Income. The Company also uses foreign exchange derivatives, typically forward contracts and options, to economically hedge the currency exposure of the Company’s global liquidity profile, including monetary assets or liabilities that are denominated in a non-functional currency of an entity, typically on a rolling 90-day basis, but may be for up to one year in the future. These derivatives are not accounted for as hedges, and changes in fair value are recorded each period in Other income (expense) in the Consolidated Statements of Income. The notional and fair values of derivative instruments are as follows (in millions): Notional Amount Net Amount of Derivative Assets Presented in the Statements of Financial Position (1) Net Amount of Derivative Liabilities Presented in the Statements of Financial Position As of December 31 2022 2021 2022 2021 2022 2021 Foreign exchange contracts Accounted for as hedges $ 618 $ 629 $ 12 $ 27 $ 2 $ — Not accounted for as hedges (3) 312 412 — 2 1 — Total $ 930 $ 1,041 $ 12 $ 29 $ 3 $ — (1) Included within Other current assets ($3 million in 2022 and $21 million in 2021) or Other non-current assets ($9 million in 2022 and $8 million in 2021). (2) Included within Other current liabilities ($2 million in 2022) or Other non-current liabilities ($1 million in 2022). (3) These contracts typically are for 90-day durations and executed close to the last day of the most recent reporting month, thereby resulting in nominal fair values at the balance sheet date. The amounts of derivative gains (losses) recognized in the Consolidated Financial Statements are as follows (in millions): 2022 2021 2020 (Loss) gain recognized in Accumulated other comprehensive loss $ (15) $ — $ 1 The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss to the Consolidated Statements of Income are as follows (in millions): Years Ended December 31 2022 2021 2020 Total revenue $ 2 $ (3) $ (14) Compensation and benefits — 1 — Interest expense — — (1) Total $ 2 $ (2) $ (15) The Company estimates that approximately $10 million of pretax loss currently included within Accumulated other comprehensive loss will be reclassified into earnings in the next twelve months. The Company recorded a gain of $11 million in 2022, a loss of $24 million in 2021, and a gain of $1 million in 2020 in Other income (expense) for foreign exchange derivatives not designated or qualifying as hedges.

Fair Value Measurements and Fin

Fair Value Measurements and Financial Instruments	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements and Financial Instruments	Fair Value Measurements and Financial Instruments Accounting standards establish a three-tier fair value hierarchy that prioritizes the inputs used in measuring fair values as follows: • Level 1 — observable inputs such as quoted prices for identical assets in active markets; • Level 2 — inputs other than quoted prices for identical assets in active markets, that are observable either directly or indirectly; and • Level 3 — unobservable inputs in which there is little or no market data which requires the use of valuation techniques and the development of assumptions. The following methods and assumptions are used to estimate the fair values of the Company’s financial instruments, including pension assets (refer to Note 11 “Employee Benefits”): Money market funds consist of institutional prime, treasury, and government money market funds. The Company reviews treasury and government money market funds to obtain reasonable assurance that the fund net asset value is $1 per share and reviews the floating net asset value of institutional prime money market funds for reasonableness. Cash and cash equivalents consist of cash and institutional short-term investment funds. The Company reviews the short-term investment funds to obtain reasonable assurance that the fund net asset value is $1 per share. Equity investments consist of equity securities and equity derivatives valued using the closing stock price on a national securities exchange. Over the counter equity derivatives are valued using observable inputs such as underlying prices of the underlying security and volatility. On a sample basis the Company reviews the listing of Level 1 equity securities in the portfolio, agrees the closing stock prices to a national securities exchange, and independently verifies the observable inputs for Level 2 equity derivatives and securities. Fixed income investments consist of certain categories of bonds and derivatives. Corporate, government, and agency bonds are valued by pricing vendors who estimate fair value using recently executed transactions and proprietary models based on observable inputs, such as interest rate spreads, yield curves, and credit risk. Asset-backed securities are valued by pricing vendors who estimate fair value using DCF models utilizing observable inputs based on trade and quote activity of securities with similar features. Fixed income derivatives are valued by pricing vendors using observable inputs such as interest rates and yield curves. The Company obtains an understanding of the models, inputs, and assumptions used in developing prices provided by its vendors through discussions with the fund managers. The Company independently verifies the observable inputs, as well as assesses assumptions used for reasonableness based on relevant market conditions and internal Company guidelines. If an assumption is deemed unreasonable, based on internal Company guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates used in the Consolidated Financial Statements. Pooled funds consist of various equity, fixed income, and real estate mutual fund type investment vehicles. Pooled investment funds fair value is estimated based on the proportionate share ownership in the underlying net assets of the investment, which is based on the fair value of the underlying securities. The underlying securities typically trade on a national securities exchange or may be valued by the fund managers using applicable models, inputs, and assumptions. The Company gains an understanding of the investment guidelines and valuation policies of the fund and discusses fund performance with pooled fund managers. The Company obtains audited fund manager financial statements, when available. If the pooled fund is designed to replicate a publicly traded index, the Company compares the performance of the fund to the index to assess the reasonableness of the fair value measurement. Alternative investments consist of limited partnerships, private equity, and hedge funds. Alternative investment fair value is generally estimated based on the proportionate share ownership in the underlying net assets of the investment as determined by the general partner or investment manager. The valuations are based on various factors depending on investment strategy, proprietary models, and specific financial data or projections. The Company obtains audited fund manager financial statements, when available. The Company obtains a detailed understanding of the models, inputs, and assumptions used in developing prices provided by the investment managers, or appropriate party, through regular discussions. The Company also obtains the investment manger’s valuation policies and assesses the assumptions used for reasonableness based on relevant market conditions and internal Company guidelines. If an assumption is deemed unreasonable, based on the Company’s guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates in the Consolidated Financial Statements. Derivatives are carried at fair value, based upon industry standard valuation techniques that use, where possible, current market-based or independently sourced pricing inputs, such as interest rates, currency exchange rates, or implied volatility. Annuity contracts consist of insurance group annuity contracts purchased to match the pension benefit payment stream owed to certain selected plan participant demographics within a few major U.K. defined benefit plans. Annuity contracts are valued using a DCF model utilizing assumptions such as discount rate, mortality, and inflation. Real estate and REITs consist of publicly traded REITs and direct real estate investments. Level 1 REITs are valued using the closing stock price on a national securities exchange. Non-Level 1 values are based on the proportionate share of ownership in the underlying net asset value as determined by the investment manager. The Company independently reviews the listing of Level 1 REIT securities in the portfolio and agrees the closing stock prices to a national securities exchange. The Company gains an understanding of the investment guidelines and valuation policies of the non-Level 1 real estate funds and discusses performance with the fund managers. The Company obtains audited fund manager financial statements, when available. See the description of “Alternative investments” for further detail on valuation procedures surrounding non-Level 1 REITs. Debt is carried at outstanding principal balance, less any unamortized issuance costs, discount or premium. Fair value is based on quoted market prices or estimates using DCF analyses based on current borrowing rates for similar types of borrowing arrangements. The following tables present the categorization of the Company’s assets and liabilities that are measured at fair value on a recurring basis at December 31, 2022 and December 31, 2021 (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Significant Significant Assets Money market funds (1) $ 3,323 $ 3,323 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 19 $ — $ 19 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 9 $ — $ 9 $ — Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Significant Significant Assets Money market funds (1) $ 2,918 $ 2,918 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 40 $ — $ 40 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 11 $ — $ 11 $ — (1) Included within Fiduciary assets or Short-term investments in the Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 13 “Derivatives and Hedging” for additional information regarding the Company’s derivatives and hedging activity. There were no transfers of assets or liabilities between fair value hierarchy levels during 2022 or 2021. The Company recognized no realized or unrealized gains or losses in the Consolidated Statements of Income related to assets and liabilities measured at fair value using unobservable inputs in 2022, 2021, or 2020. The fair value of debt is classified as Level 2 of the fair value hierarchy. The following table provides the carrying value and fair value for the Company’s term debt (in millions): 2022 2021 As of December 31 Carrying Fair Carrying Fair Current portion of long-term debt $ 350 $ 347 $ 499 $ 507 Long-term debt $ 9,825 $ 8,745 $ 8,228 $ 9,204

Claims, Lawsuits and Other Cont

Claims, Lawsuits and Other Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Claims, Lawsuits, and Other Contingencies	Claims, Lawsuits, and Other Contingencies Legal Aon and its subsidiaries are subject to numerous claims, tax assessments, lawsuits and proceedings that arise in the ordinary course of business, which frequently include E&O claims. The damages claimed in these matters are or may be substantial, including, in many instances, claims for punitive, treble, or extraordinary damages. While Aon maintains meaningful E&O insurance and other insurance programs to provide protection against certain losses that arise in such matters, Aon has exhausted or materially depleted its coverage under some of the policies that protect the Company and, consequently, is self-insured or materially self-insured for some claims. Accruals for these exposures, and related insurance receivables, when applicable, are included in the Consolidated Statements of Financial Position and have been recognized in Other general expense in the Consolidated Statements of Income to the extent that losses are deemed probable and are reasonably estimable. These amounts are adjusted from time to time as developments warrant. Matters that are not probable and reasonably estimable are not accrued for in the financial statements. The Company is not subject to current matters in connection with which the Company believes (1) material loss (including interest and costs) is probable, (2) material loss (including interest and costs) is reasonably possible (that is, more than remote but not probable), or (3) there exists the reasonable possibility of material loss (including interest and costs) greater than the accrued amount. The Company includes in the current matters described below certain matters in which it believes a material loss is remote but in which the claimed amounts are significant. Although management at present believes that the ultimate outcome of such matters, individually or in the aggregate, will not have a material adverse effect on the consolidated financial position of Aon, legal proceedings are subject to inherent uncertainties and unfavorable rulings or other events. Unfavorable resolutions could include substantial monetary or punitive damages imposed on Aon or its subsidiaries. If unfavorable outcomes of these matters were to occur, future results of operations or cash flows for any particular quarterly or annual period could be materially adversely affected. Current Matters Aon Hewitt Investment Consulting, Inc, now known as Aon Investments USA, Inc. (“Aon Investments”), Lowe’s Companies, Inc. and the Administrative Committee of Lowe’s Companies, Inc. (collectively “Lowe’s”) were sued on April 27, 2018 in the U.S. District Court for the Western District of North Carolina (the “Court”) in a class action lawsuit brought on behalf of participants in the Lowe’s 401(k) Plan (the “Plan”). Aon Investments provided investment consulting services to Lowe’s under ERISA. The plaintiffs contend that in 2015 Lowe’s imprudently placed the Hewitt Growth Fund in the Plan’s lineup of investments, the Hewitt Growth Fund underperformed its benchmarks, and that Aon had a conflict of interest in recommending the proprietary fund for the Plan. The plaintiffs allege the Plan suffered over $200 million in investment losses when compared to the eight funds it replaced. The plaintiffs allege that Aon Investments breached its duties of loyalty and prudence pursuant to ERISA. The matter was tried to the Court the last week of June 2021, and the Court entered judgment in favor of Aon on all claims on October 12, 2021. Plaintiffs have filed an appeal with the United States Court of Appeals for the Fourth Circuit, and oral argument took place on December 7, 2022. Aon believes it has meritorious defenses and intends to vigorously defend itself against these claims and appeal. Aon faces legal action arising out of a fatal plane crash in November 2016. Aon U.K. Limited placed an aviation civil liability reinsurance policy for the Bolivian insurer of the airline. After the crash, the insurer determined that there was no coverage under the airline’s insurance policy due to the airline’s breach of various policy conditions. In November 2018, the owner of the aircraft filed a claim in Bolivia against Aon, the airline, the insurer and the insurance broker. The claim is for $16 million plus any liability the owner has to third parties. In November 2019, a federal prosecutor in Brazil filed a public civil action naming three Aon entities as defendants, along with the airline, the insurer, and the lead reinsurer. That claim seeks pecuniary damages for families affected by the crash in the sum of $300 million; or, in the alternative, $50 million; or, in the alternative, $25 million; plus “moral damages” of an equivalent sum. Separately, in March 2020, the Brazilian Federal Senate invited Aon to give evidence to a Parliamentary Commission of Inquiry in an investigation into the accident. Aon cooperated with that inquiry. In August 2020, 43 individuals (surviving passengers and estates of the deceased) filed a motion in the Circuit Court of the 11th Judicial Circuit in and for Miami-Dade County, Florida, seeking permission to commence proceedings against Aon (and the insurer and reinsurers) for claims totaling $844 million. Finally, in April 2021, representatives of 16 passengers issued a claim against Aon in the High Court in England seeking damages under the Fatal Accidents Act 1976 in the sum of £29 million ($35 million at December 31, 2022 exchange rates). In December 2022, the High Court in England granted an anti-suit injunction, restricting the 43 individuals who previously filed a motion in the Circuit Court of the 11th Judicial Circuit in and for Miami-Dade County, Florida, from continuing litigation in the Circuit Court of the 11th Judicial Circuit against Aon. Aon believes that it has meritorious defenses and intends to vigorously defend itself against the remaining claims. Settled/Closed Matters On October 3, 2017, CCC invoked arbitration to pursue a claim that it asserts against Aon New Zealand. Aon provided insurance broking services to CCC in relation to CCC’s 2010-2011 material damage and business interruption program. In December 2015, CCC settled its property and business interruption claim for its losses arising from the 2010-2011 Canterbury earthquakes against the underwriter of its material damage and business interruption program and the reinsurers of that underwriter. CCC contends that acts and omissions by Aon caused CCC to recover less in that settlement than it otherwise would have. CCC claimed damages of approximately NZD 320 million ($202 million at December 31, 2022 exchange rates) plus interest and costs. In December 2022, the case was settled with no admission of liability on the part of Aon. Guarantees and Indemnifications The Company provides a variety of guarantees and indemnifications to its customers and others. The maximum potential amount of future payments represents the notional amounts that could become payable under the guarantees and indemnifications if there were a total default by the guaranteed parties, without consideration of possible recoveries under recourse provisions or other methods. These amounts may bear no relationship to the expected future payments, if any, for these guarantees and indemnifications. Any anticipated amounts payable are included in the Financial Statements and are recorded at fair value. The Company expects that, as prudent business interests dictate, additional guarantees and indemnifications may be issued from time to time. Guarantee of Registered Securities In connection with the Ireland Reorganization, on April 1, 2020, Aon plc and Aon Global Holdings plc entered into various agreements pursuant to which they agreed to guarantee the obligations of Aon Corporation arising under issued and outstanding debt securities, which were previously guaranteed solely by Aon Global Limited and the obligations of Aon Global Limited arising under issued and outstanding debt securities, which were previously guaranteed solely by Aon Corporation. Those agreements include: (1) Second Amended and Restated Indenture, dated April 1, 2020, among Aon Corporation, Aon Global Limited, Aon plc, and Aon Global Holdings plc and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”) (amending and restating the Amended and Restated Indenture, dated April 2, 2012, among Aon Corporation, Aon Global Limited and the Trustee); (2) Amended and Restated Indenture, dated April 1, 2020, among Aon Corporation, Aon Global Limited, Aon plc, Aon Global Holdings plc and the Trustee (amending and restating the Indenture, dated December 12, 2012, among Aon Corporation, Aon Global Limited plc and the Trustee); (3) Second Amended and Restated Indenture, dated April 1, 2020, among Aon Corporation, Aon Global Limited, Aon plc, Aon Global Holdings plc and the Trustee (amending and restating the Amended and Restated Indenture, dated May 20, 2015, among Aon Corporation, Aon Global Limited and the Trustee); (4) Amended and Restated Indenture, dated April 1, 2020, among Aon Corporation, Aon Global Limited, Aon plc, Aon Global Holdings plc and the Trustee (amending and restating the Indenture, dated November 13, 2015, among Aon Corporation, Aon Global Limited and the Trustee); and (5) Amended and Restated Indenture, dated April 1, 2020, among Aon Corporation, Aon Global Limited, Aon plc, Aon Global Holdings plc and the Trustee (amending and restating the Indenture, dated December 3, 2018, among Aon Corporation, Aon Global Limited and the Trustee). Letters of Credit Aon has entered into a number of arrangements whereby the Company’s performance on certain obligations is guaranteed by a third party through the issuance of LOCs. The Company had total LOCs outstanding of approximately $74 million at December 31, 2022, and $75 million at December 31, 2021. These LOCs cover the beneficiaries related to certain of Aon’s U.S. and Canadian non-qualified pension plan schemes and secure deductible retentions for Aon’s own workers compensation program. The Company has also obtained LOCs to cover contingent payments for taxes and other business obligations to third parties, and other guarantees for miscellaneous purposes at its international subsidiaries. Premium Payments The Company has certain contractual contingent guarantees for premium payments owed by clients to certain insurance companies. The maximum exposure with respect to such contractual contingent guarantees was approximately $173 million at December 31, 2022 compared to $153 million at December 31, 2021.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Segment Information	Segment Information The Company operates as one segment that includes all of Aon’s operations, which as a global professional services firm provides a broad range of risk, health, and wealth solutions through four solution lines which make up its principal products and services. The CODM assesses the performance of the Company and allocates resources based on one segment: Aon United. The Company’s reportable operating segment has been determined using a management approach, which is consistent with the basis and manner in which the CODM uses financial information for the purposes of allocating resources and evaluating performance. The CODM assesses performance and allocates resources based on total Aon results against its key four metrics, expense discipline, and collaborative behaviors that maximize value for Aon and its shareholders, regardless of which solution line it benefits. As Aon operates as one segment, segment profit or loss is consistent with consolidated reporting as disclosed in the Consolidated Statements of Income. Refer to Note 3 “Revenue from Contracts with Customers” for further information on revenue by principal service line. Consolidated long-lived assets, net by geographic area are as follows (in millions): As of December 31 Total United Americas other United Ireland Other Europe, Middle East, & Africa Asia 2022 $ 1,300 $ 519 $ 120 $ 155 $ 9 $ 279 $ 218 2021 $ 1,378 $ 563 $ 121 $ 180 $ 7 $ 293 $ 214

Summary of Significant Accoun_2

Summary of Significant Accounting Principles and Practices (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Accounting	Basis of PresentationThe accompanying Consolidated Financial Statements and Notes thereto have been prepared in accordance with U.S. GAAP. The Consolidated Financial Statements include the accounts of Aon plc and all of its controlled subsidiaries (“Aon” or the “Company”). Intercompany accounts and transactions have been eliminated. The Consolidated Financial Statements include, in the opinion of management, all adjustments (consisting of normal recurring adjustments and reclassifications) necessary to present fairly the Company’s consolidated financial position, results of operations, and cash flows for all periods presented.
Use of Estimates	Use of Estimates The preparation of the accompanying Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosures of contingent assets and liabilities at the date of the Consolidated Financial Statements, and the reported amounts of reserves and expenses. These estimates and assumptions are based on management’s best estimates and judgments. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment. Management believes its estimates to be reasonable given the current facts available. Aon adjusts such estimates and assumptions when facts and circumstances dictate. Illiquid credit markets, volatile equity markets, and foreign currency exchange rate movements increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment would, if applicable, be reflected in the Consolidated Financial Statements in future periods.
Revenue Recognition	Revenue Recognition The Company generates revenues primarily through commissions, compensation from insurance and reinsurance companies for services provided to them, and fees from customers. Commissions and fees for brokerage services vary depending upon several factors, which may include the amount of premium, the type of insurance or reinsurance coverage provided, the particular services provided to a client, insurer, or reinsurer, and the capacity in which the Company acts. Compensation from insurance and reinsurance companies includes: (1) fees for consulting and analytics services and (2) fees and commissions for administrative and other services provided to or on behalf of insurers. In Aon’s capacity as an insurance and reinsurance broker, the service promised to the customer is placement of an effective insurance or reinsurance policy, respectively. The customer obtains control over the services promised by the Company at the completion of the insurance or reinsurance policy placement process once coverage is effective. Judgment is not typically required when assessing whether the coverage is effective. Fees from clients for advice and consulting services are dependent on the extent and value of the services provided. Payment terms for the Company’s principal service lines are discussed below; the Company believes these terms are consistent with current industry practices. Significant financing components are typically not present in Aon’s arrangements. The Company recognizes revenue when control of the promised services is transferred to the customer in the amount that best reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements where control is transferred over time, an input or output method is applied that represents a faithful depiction of the progress towards completion of the performance obligation. For arrangements that include variable consideration, the Company assesses whether any amounts should be constrained. For arrangements that include multiple performance obligations, the Company allocates consideration based on their relative fair values. Costs incurred by the Company in obtaining a contract are capitalized and amortized on a systematic basis that is consistent with the transfer of control of the services to which the asset relates, considering anticipated renewals when applicable. Certain contract related costs, including pre-placement brokerage costs, are capitalized as a cost to fulfill and are amortized on a systematic basis consistent with the transfer of control of the services to which the asset relates, which is generally less than one year. The Company has elected to apply practical expedients to not disclose the revenue related to unsatisfied performance obligations if (1) the contract has an original duration of 1 year or less, (2) the Company has recognized revenue for the amount in which it has the right to bill, and (3) the variable consideration is allocated entirely to an unsatisfied performance obligation which is recognized as a series of distinct goods or services that form a single performance obligation. Disaggregation of Revenue The following is a description of principal service lines from which the Company generates its revenue: Commercial Risk Solutions includes retail brokerage, specialty solutions, global risk consulting and captives management, and Affinity programs. Revenue primarily includes insurance commissions and fees for services rendered. Revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement using output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements recognized over time, various output measures, including units delivered and time elapsed, are utilized to provide a faithful depiction of the progress towards completion of the performance obligation. Revenue is recorded net of allowances for estimated policy cancellations, which are determined based on an evaluation of historical and current cancellation data. Reimbursements received for out-of-pocket expenses are generally recorded as a component of revenue. Commissions and fees for brokerage services may be invoiced near the effective date of the underlying policy or over the term of the arrangement in installments during the policy period. Reinsurance Solutions includes treaty reinsurance, facultative reinsurance, Strategy and Technology Group, and capital markets. Revenue primarily includes reinsurance commissions and fees for services rendered. Revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement using output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services. For arrangements recognized over time, various output measures, including units delivered and time elapsed, are utilized to provide a faithful depiction of the progress towards completion of the performance obligation. Commissions and fees for brokerage services may be invoiced at the inception of the reinsurance period for certain reinsurance brokerage, or more commonly, over the term of the arrangement in installments based on deposit or minimum premiums for most treaty reinsurance arrangements. Health Solutions includes consulting and brokerage, Human Capital, and Consumer Benefits Solutions. Revenue primarily includes insurance commissions and fees for services rendered. For brokerage commissions, revenue is predominantly recognized at a point in time upon the effective date of the underlying policy (or policies), or for a limited number of arrangements, over the term of the arrangement to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services using input or output measures, including units delivered or time elapsed, to provide a faithful depiction of the progress towards completion of the performance obligation. Revenue from health care exchange arrangements is typically recognized upon successful enrollment of participants. Commissions and fees for brokerage services may be invoiced at the effective date of the underlying policy or over the term of the arrangement in installments during the policy period. Payment terms for other services vary but are typically over the contract term in installments. Wealth Solutions includes retirement consulting and pension administration, as well as investments. Revenue recognized for these arrangements is predominantly recognized over the term of the arrangement using input or output measures to depict the transfer of control of the services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those services, or for certain arrangements, at a point in time upon completion of the services. For consulting arrangements recognized over time, revenue will be recognized based on a measure of progress that depicts the transfer of control of the services to the customer, utilizing an appropriate input or output measure to provide a reasonable assessment of the progress towards completion of the performance obligation including units delivered or time elapsed. Fees paid by customers for consulting services are typically charged on an hourly, project or fixed-fee basis, and revenue for these arrangements is typically recognized based on time incurred, days elapsed, or reports delivered. Revenue from time-and-materials or cost-plus arrangements are recognized as services are performed using input or output measures to provide a reasonable assessment of the progress towards completion of the performance obligation including hours worked, and revenue for these arrangements is typically recognized based on time and materials incurred. Revenue generated from the Company’s delegated investment business is generally earned as an agreed percentage based on AUM and, to a lesser extent, based on performance fees. Reimbursements received for out-of-pocket expenses are generally recorded as a component of revenue. Payment terms vary but are typically over the contract term in installments.
Share-based Compensation Expense	Share-based Compensation Expense Share-based payments to employees, including grants of RSUs and PSAs, are measured based on grant date fair value. For purposes of measuring share-based compensation expense, the Company considered whether an adjustment to the observable market price is necessary to reflect material nonpublic information that is known to us at the time the award is granted. No adjustments were necessary for the years ended December 31, 2022, 2021, or 2020. The Company recognizes compensation expense over the requisite service period for awards expected to ultimately vest. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates.
Pension and Other Post-Retirement Benefits	Pension and Other Postretirement Benefits The Company records net periodic cost relating to its pension and other postretirement benefit plans based on calculations that include various actuarial assumptions, including discount rates, assumed rates of return on plan assets, inflation rates, mortality rates, compensation increases, and turnover rates. The Company reviews its actuarial assumptions on an annual basis and modifies these assumptions based on current rates and trends. The effects of gains, losses, and prior service costs and credits are amortized over future service periods or future estimated lives if the plans are frozen as reflected in Other income (expense) within the Consolidated Statements of Income. The funded status of each plan, calculated as the fair value of plan assets less the benefit obligation, is reflected in the Company’s Consolidated Statements of Financial Position using a December 31 measurement date.
Earnings per Share	Earnings per Share Basic earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, including participating securities, which consist of unvested share awards with non-forfeitable rights to dividends. Diluted earnings per share is computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding, which have been adjusted for the dilutive effect of potentially issuable ordinary shares, including certain contingently issuable shares. The diluted earnings per share calculation reflects the more dilutive effect of either (1) the two-class method that assumes that the participating securities have not been exercised, or (2) the treasury stock method. Potentially issuable shares are not included in the computation of diluted earnings per share if their inclusion would be antidilutive.
Cash and Cash Equivalents and Short-term Investments	Cash and Cash Equivalents and Short-term Investments Cash and cash equivalents include cash balances and all highly liquid investments with initial maturities of three months or less. Short-term investments generally consist of money market funds. The estimated fair value of Cash and cash equivalents and Short-term investments approximates their carrying values.
Fiduciary Assets and Liabilities	Fiduciary Assets and Liabilities In its capacity as an insurance agent and broker, Aon collects premiums from insureds and, after deducting its commission, remits the premiums to the respective insurers. Aon also collects claims or refunds from insurers on behalf of insureds. Uncollected premiums from insureds and uncollected claims or refunds from insurers are recorded as Fiduciary assets in the Company’s Consolidated Statements of Financial Position. Unremitted insurance premiums and claims are held in a fiduciary capacity and the obligation to remit these funds is recorded as Fiduciary liabilities in the Consolidated Statements of Financial Position.
Allowance for Doubtful Accounts	Allowance for Doubtful AccountsThe Company’s estimate for allowance for credit losses with respect to receivables is based on a combination of factors, including evaluation of forward-looking information, historical write-offs, aging of balances, and other qualitative and quantitative analyses.
Fixed Assets	Fixed Assets Fixed assets are stated at cost, less accumulated depreciation. Included in this category are certain capitalized costs incurred during the application development stage related to directly obtaining, developing, or enhancing internal use software. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Estimated Useful Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill represents the excess of purchase price over the fair value of the net assets acquired in the acquisition of a business. Goodwill is allocated to applicable reporting units. Upon disposition of a business entity, goodwill is allocated to the disposed entity based on the relative fair value of that entity compared to the fair value of the reporting unit in which it was included. Goodwill is not amortized, but instead is tested for impairment at least annually. The goodwill impairment test is performed at the reporting unit level. The Company may initially perform a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If a qualitative assessment is not performed or if a determination is made that it is not more likely than not that the value of the reporting unit exceeds its carrying amount, then the Company will perform a quantitative analysis. If the fair value of a reporting unit is determined to be greater than the carrying value of the reporting unit, goodwill is deemed not to be impaired and no further testing is necessary. If the fair value of a reporting unit is less than the carrying value, a goodwill impairment loss is recognized for the amount that the carrying amount of a reporting unit, including goodwill, exceeds its fair value limited to the total amount of the goodwill allocated to the reporting unit. Any resulting difference will be a charge to Amortization and impairment of intangible assets in the Consolidated Statements of Income in the period in which the determination is made. Fair value is determined using a combination of present value techniques and market prices of comparable businesses. We classify our intangible assets acquired as either customer-related and contract based, technology, tradenames, or other intangibles. Amortization basis and estimated useful lives by intangible asset type are generally as follows: Intangible Asset Description Amortization Basis Estimated Useful Life Customer-related and contract-based In line with underlying cash flows 7 to 20 years Technology and other Straight-line 5 to 7 years Tradenames Straight-line 1 to 3 years
Derivatives	Derivatives Derivative instruments are recognized in the Consolidated Statements of Financial Position at fair value. Where the Company has entered into master netting agreements with counterparties, the derivative positions are netted by counterparties and are reported accordingly in other assets or other liabilities. Changes in the fair value of derivative instruments are recognized in earnings each period, unless the derivative is designated and qualifies as a cash flow or net investment hedge. The Company has historically designated the following hedging relationships for certain transactions: (1) a hedge of the change in fair value of a recognized asset or liability or firm commitment (“fair value hedge”), (2) a hedge of the variability in cash flows from a recognized variable-rate asset or liability or forecasted transaction (“cash flow hedge”), and (3) a hedge of the net investment in a foreign operation (“net investment hedge”). In order for a derivative to qualify for hedge accounting, the derivative must be formally designated as a fair value, cash flow, or a net investment hedge by documenting the relationship between the derivative and the hedged item. The documentation must include a description of the hedging instrument, the hedged item, the risk being hedged, Aon’s risk management objective and strategy for undertaking the hedge, and the method for assessing the effectiveness of the hedge. Additionally, the hedge relationship must be expected to be highly effective at offsetting changes in either the fair value or cash flows of the hedged item at both the inception of the hedge and on an ongoing basis. Aon assesses the ongoing effectiveness of its hedges quarterly or more frequently if facts and circumstances require. For a derivative designated as a fair value hedging instrument, the gain or loss is recognized in earnings in the period of change together with the offsetting loss or gain on the hedged item attributable to the risk being hedged. The effect is to reflect in earnings the extent to which the hedge is not effective in achieving offsetting changes in fair value. For a cash flow hedge that qualifies for hedge accounting, the change in fair value of a hedging instrument is recognized in Accumulated Other Comprehensive Income and subsequently reclassified to earnings in the same period the hedged item impacts earnings. For a net investment hedge, the change in fair value of the hedging instrument is recognized in Accumulate Other Comprehensive Income as part of the cumulative translation adjustment. Changes in the fair value of a derivative that is not designated as part of a hedging relationship (commonly referred to as an “economic hedge”) are recorded in Other income in the Consolidated Statements of Income in the period of change. The Company discontinues hedge accounting prospectively when (1) the derivative expires or is sold, terminated, or exercised, (2) the qualifying criteria are no longer met, or (3) management removes the designation of the hedging relationship.
Foreign Currency	Foreign Currency Certain of the Company’s non-U.S. operations use their respective local currency as their functional currency. These operations that do not have the U.S. dollar as their functional currency translate their financial statements at the current rates of exchange in effect at the balance sheet date and revenues and expenses using rates that approximate those in effect during the period. The resulting translation adjustments are included in Net foreign currency translation adjustments within the Consolidated Statements of Shareholders’ Equity. Further, gains and losses from the remeasurement of monetary assets and liabilities that are denominated in a non-functional currency of that entity are included in Other income (expense) within the Consolidated Statements of Income.
Income Taxes	Income Taxes Deferred income taxes are recognized for the effect of temporary differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted marginal tax rates and laws that are currently in effect. The effect on deferred tax assets and liabilities from a change in tax rates is recognized in the period when the rate change is enacted. Deferred tax assets are reduced by valuation allowances if, based on the consideration of all available evidence, it is more likely than not that some portion of the deferred tax asset will not be realized. Deferred tax assets are realized by having sufficient future taxable income to allow the related tax benefits to reduce taxes otherwise payable. The sources of taxable income that may be available to realize the benefit of deferred tax assets are future reversals of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences and carry-forwards, taxable income in carry-back years, and tax planning strategies that are both prudent and feasible. The Company recognizes the effect of income tax positions only if sustaining those positions is more likely than not. Tax positions that meet the more likely than not recognition threshold but are not highly certain are initially and subsequently measured based on the largest amount of benefit that is greater than 50% likely of being realized upon settlement with the taxing authority. Only information that is available at the reporting date is considered in the Company’s recognition and measurement analysis, and events or changes in facts and circumstances are accounted for in the period in which the event or change in circumstance occurs. The Company records penalties and interest related to unrecognized tax benefits in Income taxes in the Company’s Consolidated Statements of Income. The Company releases income tax effects from Accumulated other comprehensive loss using the portfolio approach.
Leases	Leases The Company leases office facilities, equipment, and automobiles under operating and finance leases. The Company’s lease obligations are primarily for the use of office facilities. The Company evaluates if a leasing arrangement exists upon inception of a contract. A contract contains a lease if the contract conveys the right to control the use of identified tangible assets for a period of time in exchange for consideration. Identified property, plant, or equipment may include a physically distinct portion of a larger asset, or a portion of an asset that represents substantially all of the capacity of the asset but is not physically distinct. The Company assesses whether a contract implicitly contains the right to control the use of a tangible asset that is not already owned. In addition, the Company subleases certain real estate properties to third parties, which are classified as operating leases. The Company’s leases expire at various dates and may contain renewal, expansion or termination options. The exercise of lease renewal and expansion options are typically at the Company’s sole discretion and are only included in the determination of the lease term if the Company is reasonably certain to exercise the option. In addition, the Company’s lease agreements typically do not contain any material residual value guarantees or restrictive covenants. ROU assets and lease liabilities are based on the present value of the minimum lease payments over the lease term. The Company has elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease components from lease components and instead account for consideration received in a contract as a single lease component. The Company’s lease agreements may include initial direct costs and lease incentives. Initial direct costs are incremental costs of a lease that would not have been incurred if the lease had not been obtained and are included in the measurement of the ROU asset. Payments made to or on behalf of the Company, such as tenant improvement allowances, represent incentives that are considered reductions to the ROU asset and lease expense over the lease term. The Company made a policy election to not recognize ROU assets and lease liabilities that arise from leases with an initial term of twelve months or less in the Consolidated Statements of Financial Position. However, the Company recognized these lease payments in the Consolidated Statements of Income on a straight-line basis over the lease term and variable lease payments in the period in which the expense was incurred. The Company applies this accounting policy across all classes of underlying assets. A portion of the Company’s lease agreements include variable lease payments that are not recorded in the initial measurement of the lease liability and ROU asset balances. For real estate arrangements, base rental payments may be escalated according to annual changes in the CPI or other indices. The escalated rental payments based on the estimated CPI at the lease commencement date are included within minimum rental payments; however, changes in CPI are considered variable in nature and are recognized as variable lease costs in the period in which the obligation is incurred. Additionally, real estate lease agreements may include other variable payments related to operating expenses charged by the landlord based on actual expenditures. Information technology equipment agreements may include variable payments based on usage of the equipment. These expenses are also recognized as variable lease costs in the period in which the expense is incurred. The Company utilizes discount rates to determine the present value of the lease payments based on information available at the commencement date of the lease. As the rate implicit in each lease is not typically readily available, the Company uses an incremental borrowing rate based on factors such as the lease term and the economic environment where the lease exists to determine the appropriate present value of future lease payments. When determining the incremental borrowing rate, the Company considers the rate of interest it would pay on a secured borrowing in an amount equal to the lease payments for the underlying asset under similar terms.
Principles of Consolidation	Principles of Consolidation The accompanying Consolidated Financial Statements include the accounts of Aon plc and those entities in which the Company has a controlling financial interest. To determine if Aon holds a controlling financial interest in an entity, the Company first evaluates if it is required to apply the variable interest model to the entity, otherwise, the entity is evaluated under the voting interest model. When Aon holds rights that give it the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance, combined with a variable interest that gives the right to receive potentially significant benefits or the obligation to absorb potentially significant losses, the Company has a controlling financial interest in that VIE. The Company does not hold a controlling financial interest over any VIEs that significantly impacts the VIE’s economic performance and the Company does not have rights to any significant benefits or obligations to absorb potentially significant losses. Thus, the Company does not consolidate any VIEs and Aon’s interest in VIEs as of December 31, 2022 was insignificant. Aon holds a controlling financial interest in entities that are not VIEs when it, directly or indirectly holds more than 50% of the voting rights and the noncontrolling interest holders do not hold substantive participating rights.
Fair Value Measurements	Accounting standards establish a three-tier fair value hierarchy that prioritizes the inputs used in measuring fair values as follows: • Level 1 — observable inputs such as quoted prices for identical assets in active markets; • Level 2 — inputs other than quoted prices for identical assets in active markets, that are observable either directly or indirectly; and • Level 3 — unobservable inputs in which there is little or no market data which requires the use of valuation techniques and the development of assumptions. The following methods and assumptions are used to estimate the fair values of the Company’s financial instruments, including pension assets (refer to Note 11 “Employee Benefits”): Money market funds consist of institutional prime, treasury, and government money market funds. The Company reviews treasury and government money market funds to obtain reasonable assurance that the fund net asset value is $1 per share and reviews the floating net asset value of institutional prime money market funds for reasonableness. Cash and cash equivalents consist of cash and institutional short-term investment funds. The Company reviews the short-term investment funds to obtain reasonable assurance that the fund net asset value is $1 per share. Equity investments consist of equity securities and equity derivatives valued using the closing stock price on a national securities exchange. Over the counter equity derivatives are valued using observable inputs such as underlying prices of the underlying security and volatility. On a sample basis the Company reviews the listing of Level 1 equity securities in the portfolio, agrees the closing stock prices to a national securities exchange, and independently verifies the observable inputs for Level 2 equity derivatives and securities. Fixed income investments consist of certain categories of bonds and derivatives. Corporate, government, and agency bonds are valued by pricing vendors who estimate fair value using recently executed transactions and proprietary models based on observable inputs, such as interest rate spreads, yield curves, and credit risk. Asset-backed securities are valued by pricing vendors who estimate fair value using DCF models utilizing observable inputs based on trade and quote activity of securities with similar features. Fixed income derivatives are valued by pricing vendors using observable inputs such as interest rates and yield curves. The Company obtains an understanding of the models, inputs, and assumptions used in developing prices provided by its vendors through discussions with the fund managers. The Company independently verifies the observable inputs, as well as assesses assumptions used for reasonableness based on relevant market conditions and internal Company guidelines. If an assumption is deemed unreasonable, based on internal Company guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates used in the Consolidated Financial Statements. Pooled funds consist of various equity, fixed income, and real estate mutual fund type investment vehicles. Pooled investment funds fair value is estimated based on the proportionate share ownership in the underlying net assets of the investment, which is based on the fair value of the underlying securities. The underlying securities typically trade on a national securities exchange or may be valued by the fund managers using applicable models, inputs, and assumptions. The Company gains an understanding of the investment guidelines and valuation policies of the fund and discusses fund performance with pooled fund managers. The Company obtains audited fund manager financial statements, when available. If the pooled fund is designed to replicate a publicly traded index, the Company compares the performance of the fund to the index to assess the reasonableness of the fair value measurement. Alternative investments consist of limited partnerships, private equity, and hedge funds. Alternative investment fair value is generally estimated based on the proportionate share ownership in the underlying net assets of the investment as determined by the general partner or investment manager. The valuations are based on various factors depending on investment strategy, proprietary models, and specific financial data or projections. The Company obtains audited fund manager financial statements, when available. The Company obtains a detailed understanding of the models, inputs, and assumptions used in developing prices provided by the investment managers, or appropriate party, through regular discussions. The Company also obtains the investment manger’s valuation policies and assesses the assumptions used for reasonableness based on relevant market conditions and internal Company guidelines. If an assumption is deemed unreasonable, based on the Company’s guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates in the Consolidated Financial Statements. Derivatives are carried at fair value, based upon industry standard valuation techniques that use, where possible, current market-based or independently sourced pricing inputs, such as interest rates, currency exchange rates, or implied volatility. Annuity contracts consist of insurance group annuity contracts purchased to match the pension benefit payment stream owed to certain selected plan participant demographics within a few major U.K. defined benefit plans. Annuity contracts are valued using a DCF model utilizing assumptions such as discount rate, mortality, and inflation. Real estate and REITs consist of publicly traded REITs and direct real estate investments. Level 1 REITs are valued using the closing stock price on a national securities exchange. Non-Level 1 values are based on the proportionate share of ownership in the underlying net asset value as determined by the investment manager. The Company independently reviews the listing of Level 1 REIT securities in the portfolio and agrees the closing stock prices to a national securities exchange. The Company gains an understanding of the investment guidelines and valuation policies of the non-Level 1 real estate funds and discusses performance with the fund managers. The Company obtains audited fund manager financial statements, when available. See the description of “Alternative investments” for further detail on valuation procedures surrounding non-Level 1 REITs. Debt is carried at outstanding principal balance, less any unamortized issuance costs, discount or premium. Fair value is based on quoted market prices or estimates using DCF analyses based on current borrowing rates for similar types of borrowing arrangements.
New Accounting Pronouncements	New Accounting Pronouncements All issued, but not yet effective, guidance has been deemed not applicable or not significant to the Consolidated Financial Statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Principles and Practices (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Schedule of Estimated Useful Lives of Assets	Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Estimated Useful Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years
Schedule of Other Intangible Assets by Asset Class	Amortization basis and estimated useful lives by intangible asset type are generally as follows: Intangible Asset Description Amortization Basis Estimated Useful Life Customer-related and contract-based In line with underlying cash flows 7 to 20 years Technology and other Straight-line 5 to 7 years Tradenames Straight-line 1 to 3 years Other intangible assets by asset class are as follows (in millions): As of December 31 2022 2021 Gross Accumulated Amortization and Impairment Net Gross Accumulated Amortization and Impairment Net Customer-related and contract-based $ 2,207 $ 1,833 $ 374 $ 2,289 $ 1,848 $ 441 Technology and other 436 363 73 407 357 50 Tradenames 14 14 — 14 13 1 Total $ 2,657 $ 2,210 $ 447 $ 2,710 $ 2,218 $ 492

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Years Ended December 31 2022 2021 2020 Commercial Risk Solutions $ 6,715 $ 6,635 $ 5,861 Reinsurance Solutions 2,190 1,997 1,814 Health Solutions 2,224 2,154 2,067 Wealth Solutions 1,367 1,426 1,341 Elimination (17) (19) (17) Total revenue $ 12,479 $ 12,193 $ 11,066 Consolidated revenue from contracts with customers by geographic area, which is attributed on the basis of where the services are performed, is as follows (in millions): Years Ended December 31 2022 2021 2020 U.S. $ 5,666 $ 5,459 $ 5,032 Americas other than U.S. 1,137 1,027 911 U.K. 1,660 1,681 1,579 Ireland 99 127 84 Europe, Middle East, & Africa other than U.K. and Ireland 2,443 2,565 2,236 Asia Pacific 1,474 1,334 1,224 Total revenue $ 12,479 $ 12,193 $ 11,066
Schedule of Capitalized Contract Cost	Changes in the net carrying amount of costs to fulfill contracts with customers are as follows (in millions): 2022 2021 Balance at beginning of period $ 361 $ 339 Additions 1,479 1,504 Amortization (1,480) (1,478) Impairment — — Foreign currency translation and other (5) (4) Balance at end of period $ 355 $ 361 Changes in the net carrying amount of costs to obtain contracts with customers are as follows (in millions): 2022 2021 Balance at beginning of period $ 179 $ 184 Additions 56 59 Amortization (49) (48) Impairment — — Foreign currency translation and other (1) (16) Balance at end of period $ 185 $ 179

Other Financial Data (Tables)

Other Financial Data (Tables)	12 Months Ended
	Dec. 31, 2022
Other Financial Data [Abstract]
Schedule of Components of Other Income (Expense)	The components of Other income (expense) are as follows (in millions): Years Ended December 31 2022 2021 2020 Pension and other postretirement (1) $ (179) $ 21 $ 13 Foreign currency remeasurement (14) 26 (12) Extinguishment of debt — — (7) Financial instruments and other 4 (45) (10) Equity earnings 10 8 4 Gain from disposals of business 54 142 25 Total $ (125) $ 152 $ 13 (1) Refer to Note 11 “Employee Benefits” for further information.
Schedule of Allowance for Doubtful Accounts	Changes in the net carrying amount of allowance for doubtful accounts are as follows (in millions): 2022 2021 2020 Balance at beginning of period $ 90 $ 98 $ 77 Provision 8 26 29 Accounts written off, net of recoveries (18) (37) (6) Foreign currency translation and other (4) 3 (2) Balance at end of period $ 76 $ 90 $ 98
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions): As of December 31 2022 2021 Costs to fulfill contracts with customers (1) $ 355 $ 361 Prepaid expenses 109 137 Taxes receivable 74 53 Other 108 165 Total $ 646 $ 716 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information.
Schedule of Components of Fixed Assets, Net	The components of Fixed assets, net are as follows (in millions): As of December 31 2022 2021 Software $ 861 $ 797 Leasehold improvements 409 425 Computer equipment 269 268 Furniture, fixtures, and equipment 267 279 Construction in progress 109 45 Other 34 33 Fixed assets, gross 1,949 1,847 Less: Accumulated depreciation 1,391 1,318 Fixed assets, net $ 558 $ 529
Schedule of Other Non-current Assets	The components of Other non-current assets are as follows (in millions): As of December 31 2022 2021 Costs to obtain contracts with customers (1) $ 185 $ 179 Taxes receivable 109 95 Investments 60 64 Leases (2) 43 63 Other 112 111 Total $ 509 $ 512 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) Refer to Note 8 “Lease Commitments” for further information.
Schedule of Other Current Liabilities	The components of Other current liabilities are as follows (in millions): As of December 31 2022 2021 Deferred revenue (1) $ 250 $ 321 Taxes payable 193 149 Leases (2) 186 213 Other 718 648 Total $ 1,347 $ 1,331 (1) $653 million and $553 million was recognized in the Consolidated Statements of Income during the years ended December 31, 2022 and December 31, 2021, respectively. (2) Refer to Note 8 “Lease Commitments” for further information.
Schedule of Other Non-current Liabilities	The components of Other non-current liabilities are as follows (in millions): As of December 31 2022 2021 Taxes payable (1) $ 795 $ 609 Compensation and benefits 69 58 Deferred revenue 37 70 Leases (2) 28 46 Other 95 127 Total $ 1,024 $ 910 (1) Includes $129 million and $145 million for the non-current portion of the transition tax as of December 31, 2022 and December 31, 2021, respectively. Refer to Note 9 “Income Taxes” for further information on the transition tax. (2) Refer to Note 8 “Lease Commitments” for further information.

Acquisitions and Dispositions_2

Acquisitions and Dispositions of Businesses (Tables)	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Schedule of Consideration Transferred and Preliminary Value of Intangible Assets	The following table includes the preliminary fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Year Ended Consideration transferred Cash $ 161 Deferred and contingent consideration 9 Aggregate consideration transferred $ 170 Assets acquired Goodwill $ 87 Intangible assets 78 Other assets (1) 25 Total assets acquired 190 Liabilities assumed Total liabilities assumed 20 Net assets acquired $ 170 (1) Includes Cash and cash equivalents o f $2 million and funds held on behalf of clients of an insignificant amount .

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in the Net Carrying Amount of Goodwill by Operating Segment	The changes in the net carrying amount of goodwill for the years ended December 31, 2022 and 2021, respectively, are as follows (in millions): Balance as of January 1, 2021 $ 8,666 Goodwill related to current year acquisitions 17 Goodwill related to current year disposals (37) Foreign currency translation and other (212) Balance as of December 31, 2021 $ 8,434 Goodwill related to current year acquisitions 87 Goodwill related to current year disposals (11) Foreign currency translation and other (218) Balance as of December 31, 2022 $ 8,292
Schedule of Other Intangible Assets by Asset Class	Amortization basis and estimated useful lives by intangible asset type are generally as follows: Intangible Asset Description Amortization Basis Estimated Useful Life Customer-related and contract-based In line with underlying cash flows 7 to 20 years Technology and other Straight-line 5 to 7 years Tradenames Straight-line 1 to 3 years Other intangible assets by asset class are as follows (in millions): As of December 31 2022 2021 Gross Accumulated Amortization and Impairment Net Gross Accumulated Amortization and Impairment Net Customer-related and contract-based $ 2,207 $ 1,833 $ 374 $ 2,289 $ 1,848 $ 441 Technology and other 436 363 73 407 357 50 Tradenames 14 14 — 14 13 1 Total $ 2,657 $ 2,210 $ 447 $ 2,710 $ 2,218 $ 492
Schedule of Estimated Future Amortization Expense on Intangible Assets	The estimated future amortization for finite-lived intangible assets as of December 31, 2022 is as follows (in millions): Estimated Future Amortization For the years ended 2023 $ 99 2024 82 2025 68 2026 47 2027 34 Thereafter 117 Total $ 447

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The following is a summary of outstanding debt (in millions): As of December 31 2022 2021 Commercial paper $ 592 $ 665 2.20% Senior Notes due November 2022 (1) — 499 4.00% Senior Notes due November 2023 (2) 350 349 3.50% Senior Notes due June 2024 599 598 3.875% Senior Notes due December 2025 748 748 2.875% Senior Notes due May 2026 (EUR 500M) 530 563 8.205% Junior Subordinated Notes due January 2027 521 521 2.85% Senior Notes due May 2027 596 — 4.50% Senior Notes due December 2028 348 347 3.75% Senior Notes due May 2029 746 745 2.80% Senior Notes due May 2030 994 993 2.05% Senior Notes due August 2031 396 396 2.60% Senior Notes due December 2031 496 496 5.00% Senior Notes due September 2032 495 — 6.25% Senior Notes due September 2040 297 296 4.25% Senior Notes due December 2042 203 201 4.45% Senior Notes due May 2043 247 247 4.60% Senior Notes due June 2044 545 544 4.75% Senior Notes due May 2045 594 593 2.90% Senior Notes due August 2051 591 591 3.90% Senior Notes due February 2052 877 — Other 5 — Total debt 10,770 9,392 Less: Short-term debt and current portion of long-term debt 945 1,164 Total long-term debt $ 9,825 $ 8,228 (1) The 2.20% Senior Notes due November 2022 were repaid in full on November 1, 2022. (2) The 4.00% Senior Notes due November 2023 were reclassified as Short-term debt and current portion of long-term debt in the Consolidated Statement of Financial Position as of December 31, 2022.
Schedule of Repayments of Long-term Debt	Repayments of total debt as of December 31, 2022 are as follows (in millions): 2023 $ 946 2024 604 2025 750 2026 532 2027 1,121 Thereafter 6,956 Total Repayments 10,909 Unamortized discounts, premiums, and debt issuance costs (139) Total Debt $ 10,770
Schedule of Commercial Paper	Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Company’s Consolidated Statements of Financial Position, is as follows (in millions): As of December 31 2022 2021 Commercial paper outstanding $ 592 $ 665 The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Years Ended December 31 2022 2021 Weighted average commercial paper outstanding $ 499 $ 273 Weighted average interest rate of commercial paper outstanding 1.42 % 0.01 %

Lease Commitments (Tables)

Lease Commitments (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Schedule of Assets And Liabilities Of Lessee	The classification of operating and finance lease asset and liability balances within the Consolidated Statements of Financial Position are as follows (in millions): As of December 31 2022 2021 Assets Operating lease assets Operating lease right-of-use assets $ 699 $ 786 Finance lease assets Other non-current assets 43 63 Total lease assets $ 742 $ 849 Liabilities Current lease liabilities Operating Other current liabilities $ 163 $ 194 Finance Other current liabilities 23 19 Non-current lease liabilities Operating Non-current operating lease liabilities 693 772 Finance Other non-current liabilities 28 46 Total lease liabilities $ 907 $ 1,031
Schedule of Lease, Cost	The components of lease costs are as follows (in millions): Years Ended December 31 2022 2021 Operating lease cost $ 204 $ 217 Finance lease costs Amortization of leased assets 28 26 Interest on lease liabilities 1 1 Variable lease cost 38 49 Short-term lease cost (1) 11 11 Sublease income (29) (31) Net lease cost $ 253 $ 273 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less. Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of December 31 2022 2021 Weighted average remaining lease term (years) Operating leases 6.7 6.9 Finance leases 2.5 3.6 Weighted average discount rate Operating leases 3.1 % 2.8 % Finance leases 1.0 % 1.0 % Other cash and non-cash related activities are as follows (in millions): Years Ended December 31 2022 2021 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 231 $ 244 Financing cash flows for finance leases $ 14 $ 23 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 110 $ 44 ROU assets obtained in exchange for new finance lease liabilities $ — $ — Operating lease ROU asset expense (1) $ 162 $ 142 Changes in Non-current operating lease liabilities (1) $ (79) $ (125) (1) The Company has recorded non-cash changes in Operating lease ROU assets and Non-current operating lease liabilities through Other assets and liabilities in Cash flows from operations within the Consolidated Statements of Cash Flows.
Schedule of Lessee Operating Lease Liability Maturity	Maturity analysis of operating and finance leases as of December 31, 2022 are as follows (in millions): Operating Leases Finance Leases Total 2023 $ 175 $ 23 $ 198 2024 164 18 182 2025 135 10 145 2026 123 — 123 2027 108 — 108 Thereafter 235 — 235 Total undiscounted future minimum lease payments 940 51 991 Less: Imputed interest (84) — (84) Present value of lease liabilities $ 856 $ 51 $ 907
Schedule of Finance Lease, Liability, Maturity	Maturity analysis of operating and finance leases as of December 31, 2022 are as follows (in millions): Operating Leases Finance Leases Total 2023 $ 175 $ 23 $ 198 2024 164 18 182 2025 135 10 145 2026 123 — 123 2027 108 — 108 Thereafter 235 — 235 Total undiscounted future minimum lease payments 940 51 991 Less: Imputed interest (84) — (84) Present value of lease liabilities $ 856 $ 51 $ 907

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
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 2022 2021 2020 Income (loss) before income taxes: Ireland $ 85 $ 15 $ (86) U.K. 502 549 634 U.S. 161 (818) (28) Other 2,408 2,185 1,946 Total $ 3,156 $ 1,931 $ 2,466 Income tax expense: Current: Ireland $ 2 $ 2 $ 2 U.K. 206 50 30 U.S. federal 195 197 126 U.S. state and local 43 72 22 Other 316 291 259 Total current tax expense $ 762 $ 612 $ 439 Deferred tax expense (benefit): Ireland $ — $ (1) $ (1) U.K. (152) 131 39 U.S. federal (69) (83) (72) U.S. state and local (21) (30) (4) Other (10) (6) 47 Total deferred tax expense (benefit) $ (252) $ 11 $ 9 Total income tax expense $ 510 $ 623 $ 448
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 2022 2021 2020 Statutory tax rate 25.0% 25.0% 25.0% U.S. state income taxes, net of U.S. federal benefit 0.4 1.5 1.0 Taxes on international operations (1) (2) (11.6) (15.4) (9.8) Nondeductible expenses 2.4 3.3 2.1 Adjustments to prior year tax requirements (7.0) (0.2) — Deferred tax adjustments, including statutory rate changes (0.5) 3.2 0.7 Deferred tax adjustments, international earnings 0.2 1.8 0.7 Adjustments to valuation allowances 1.9 (0.2) — Change in uncertain tax positions 8.6 2.1 1.5 Excess tax benefits related to shared based compensation (3) (1.5) (2.4) (2.2) Capital and other losses (1.4) — (1.8) Non-deductible transaction costs — 1.1 1.3 Non-deductible termination fee — 12.9 — Other — net (0.3) (0.4) (0.3) Effective tax rate 16.2% 32.3% 18.2% (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, 2022, 2021, and 2020, 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) In July 2020, final U.S. tax regulations were issued regarding the GILTI high tax election, allowing taxpayers to exclude from GILTI the income of a Controlled Foreign Corporation that incurs a foreign tax rate more than 90% of the top U.S. corporate tax rate. A GILTI high tax election may be made on an annual basis, and taxpayers may choose to apply the election to taxable years beginning after December 31, 2017. The Company expects to make the GILTI high-tax election for 2022 and therefore recorded the impact of making the election. (3) 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 2022 2021 Deferred tax assets: Net operating loss, capital loss, interest, and tax credit carryforwards $ 952 $ 581 Lease liabilities 178 207 Employee benefit plans 297 160 Other accrued expenses 100 132 Accrued interest — 97 Federal and state benefit of interest from uncertain tax positions 57 45 Deferred revenue 26 36 Investment basis differences 30 25 Lease and service guarantees 1 1 Other 38 25 Total 1,679 1,309 Valuation allowance on deferred tax assets (275) (230) Total $ 1,404 $ 1,079 Deferred tax liabilities: Intangibles and property, plant and equipment $ (258) $ (243) Lease right-of-use asset (151) (173) Deferred costs (147) (159) Unremitted earnings (38) (58) Other accrued expenses (20) (27) Unrealized foreign exchange gains (23) (22) Other (42) (32) Total $ (679) $ (714) Net deferred tax asset $ 725 $ 365
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 2022 2021 Deferred tax assets — non-current $ 824 $ 766 Deferred tax liabilities — non-current (99) (401) Net deferred tax asset $ 725 $ 365
Schedule of Operating and Capital Loss Carryforwards	The Company had the following carryforwards (in millions): As of December 31 2022 2021 U.K. Operating loss carryforwards $ 608 $ 41 Capital loss carryforwards $ 533 $ 573 U.S. Federal operating loss carryforwards $ 1 $ 25 Federal capital loss carryforwards $ 112 $ 112 Federal interest carryforwards $ 2,269 $ 1,140 Federal foreign tax credit carryforwards $ 20 $ 18 State operating loss carryforwards $ 473 $ 398 State capital loss carryforwards $ 123 $ 123 State interest carryforwards $ 1,187 $ 551 Other Non-U.S. Operating loss carryforwards $ 490 $ 301 Capital loss carryforwards $ 8 $ 35 Interest carryforwards $ 26 $ 26 Other carryforwards $ 5 $ 5
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): 2022 2021 Balance at January 1 $ 347 $ 321 Additions based on tax positions related to the current year 35 33 Additions for tax positions of prior years 226 7 Reductions for tax positions of prior years (1) (4) Settlements (1) — Business combinations — — Lapse of statute of limitations (5) (10) Foreign currency translation — — Balance at December 31 $ 601 $ 347

Shareholders' Equity (Deficit)

Shareholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Schedule of Repurchase Agreements	The following table summarizes the Company’s share repurchase activity (in millions, except per share data): Years Ended December 31 2022 2021 Shares repurchased 11.1 12.4 Average price per share $ 289.76 $ 286.82 Repurchase costs recorded to accumulated deficit $ 3,203 $ 3,543
Schedule of Components of Weighted Average Number of Shares Outstanding	Weighted average ordinary shares outstanding are as follows (in millions): Years Ended December 31 2022 2021 2020 Basic weighted average ordinary shares outstanding 211.7 224.7 231.9 Dilutive effect of potentially issuable shares 1.5 1.4 1.2 Diluted weighted average ordinary shares outstanding 213.2 226.1 233.1
Schedule of Components of Accumulated Other Comprehensive Loss, Net of Related Tax	Changes in Accumulated other comprehensive loss by component, net of related tax, are as follows (in millions): Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Postretirement Benefit Obligation (2) Total Balance at December 31, 2019 $ (12) $ (1,305) $ (2,716) $ (4,033) Other comprehensive income (loss) before reclassifications: Other comprehensive income (loss) before reclassifications 1 258 (255) 4 Tax benefit — 2 60 62 Other comprehensive income (loss) before reclassifications, net 1 260 (195) 66 Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income 15 — 125 140 Tax expense (3) — (31) (34) Amounts reclassified from accumulated other comprehensive income, net 12 — 94 106 Net current period other comprehensive income (loss) 13 260 (101) 172 Balance at December 31, 2020 $ 1 $ (1,045) $ (2,817) $ (3,861) Other comprehensive income (loss) before reclassifications: Other comprehensive income (loss) before reclassifications — (290) 227 (63) Tax benefit (expense) — 2 (58) (56) Other comprehensive income (loss) before reclassifications, net — (288) 169 (119) Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income 2 — 142 144 Tax expense (1) — (34) (35) Amounts reclassified from accumulated other comprehensive income, net 1 — 108 109 Net current period other comprehensive income (loss) 1 (288) 277 (10) Balance at December 31, 2021 $ 2 $ (1,333) $ (2,540) $ (3,871) Other comprehensive income (loss) before reclassifications: Other comprehensive loss before reclassifications (15) (528) (569) (1,112) Tax benefit (expense) 4 — 149 153 Other comprehensive loss before reclassifications, net (11) (528) (420) (959) Amounts reclassified from accumulated other comprehensive income (loss): Amounts reclassified from accumulated other comprehensive income (loss) (2) — 282 280 Tax expense — — (73) (73) Amounts reclassified from accumulated other comprehensive income (loss), net (2) — 209 207 Net current period other comprehensive loss (13) (528) (211) (752) Balance at December 31, 2022 $ (11) $ (1,861) $ (2,751) $ (4,623) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Total revenue, Interest expense, and Compensation and benefits in the Consolidated Statements of Income. Refer to Note 13 “Derivatives and Hedging” for further information regarding the Company’s derivative and hedging activity. (2) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Other income (expense) in the Consolidated Statements of Income.

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Schedule of Expense Recognized for Defined Contribution Savings Plans, Included in Compensation and Benefits and Discontinued Operations in the Consolidated Statements of Income	The expense for the significant plans in the U.S., U.K., Netherlands, and Canada is as follows (in millions): Years Ended December 31 2022 2021 2020 U.S. $ 108 $ 103 $ 87 U.K. 47 46 42 Netherlands and Canada 33 35 26 Total $ 188 $ 184 $ 155
Schedule of Changes in Projected Benefit Obligations Fair Value of Plan Assets, Funded Status and Amount Recognized	The following tables provide a reconciliation of the changes in the projected benefit obligations and fair value of assets for the years ended December 31, 2022 and 2021, and a statement of the funded status as of December 31, 2022 and 2021, for Aon’s significant U.K., U.S., and other major pension plans, which are located in the Netherlands and Canada. These plans represent approximately 88% of the Company’s projected benefit obligations. U.K. U.S. Other (millions) 2022 2021 2022 2021 2022 2021 Change in projected benefit obligation At January 1 $ 4,919 $ 5,406 $ 3,164 $ 3,380 $ 1,531 $ 1,625 Service cost 1 1 — — — — Interest cost 83 65 73 57 19 12 Settlements — (14) (283) — — — Actuarial (gain) loss (1,418) (292) (607) (103) (322) 24 Benefit payments (195) (189) (167) (170) (45) (47) Foreign currency impact (444) (58) — — (89) (83) As of December 31 $ 2,946 $ 4,919 $ 2,180 $ 3,164 $ 1,094 $ 1,531 Accumulated benefit obligation at end of year $ 2,946 $ 4,919 $ 2,180 $ 3,164 $ 1,079 $ 1,504 Change in fair value of plan assets At January 1 $ 6,246 $ 6,652 $ 2,378 $ 2,276 $ 1,430 $ 1,497 Actual return on plan assets (1,961) (136) (484) 211 (284) 46 Employer contributions 7 9 37 61 15 17 Settlements — (14) (283) — — — Benefit payments (195) (189) (167) (170) (45) (47) Foreign currency impact (559) (76) — — (83) (83) As of December 31 $ 3,537 $ 6,246 $ 1,481 $ 2,378 $ 1,032 $ 1,430 Market related value at end of year $ 3,537 $ 6,246 $ 1,794 $ 2,174 $ 1,032 $ 1,430 Amount recognized in Statement of Financial Position as of December 31 Funded status $ 591 $ 1,327 $ (699) $ (786) $ (62) $ (101) Unrecognized prior-service cost 35 40 — — (6) (6) Unrecognized loss 1,726 1,215 1,305 1,551 443 489 Net amount recognized $ 2,352 $ 2,582 $ 606 $ 765 $ 375 $ 382 The following table provides an overview of the accumulated PBO, fair value of plan assets, funded status and net amount recognized as of December 31, 2022 and 2021 for the Company’s other significant postretirement benefit plans located in the U.S. and Canada (in millions): 2022 2021 Accumulated projected benefit obligation $ 83 $ 109 Fair value of plan assets 14 17 Funded status (69) (92) Unrecognized prior-service credit (1) (1) Unrecognized (gain) loss (19) 2 Net amount recognized $ (89) $ (91)
Schedule of Amounts Recognized in the Consolidated Statements of Financial Position	Amounts recognized in the Consolidated Statements of Financial Position consist of (in millions): U.K. U.S. Other 2022 2021 2022 2021 2022 2021 Prepaid benefit cost (1) $ 612 $ 1,344 $ — $ — $ — $ — Accrued benefit liability - current (2) (1) (1) (42) (52) (5) (5) Accrued benefit liability - non-current (3) (20) (16) (657) (734) (57) (96) Accumulated other comprehensive loss 1,761 1,255 1,305 1,551 437 483 Net amount recognized $ 2,352 $ 2,582 $ 606 $ 765 $ 375 $ 382 (1) Included in Prepaid pension. (2) Included in Other current liabilities.
Schedule of Amounts Recognized in Accumulated Other Comprehensive Loss that have not yet been Recognized as Components of net Periodic Benefit Cost	Amounts recognized in Accumulated other comprehensive loss (income) that have not yet been recognized as components of net periodic benefit cost at December 31, 2022 and 2021 consist of (in millions): U.K. U.S. Other 2022 2021 2022 2021 2022 2021 Net loss $ 1,726 $ 1,215 $ 1,305 $ 1,551 $ 443 $ 489 Prior service cost (income) 35 40 — — (6) (6) Total $ 1,761 $ 1,255 $ 1,305 $ 1,551 $ 437 $ 483
Schedule of Components of Net Periodic Benefit Cost for the Pension Plans	Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): U.K. U.S. Other 2022 2021 2020 2022 2021 2020 2022 2021 2020 Service cost $ 1 $ 1 $ — $ — $ — $ — $ — $ — $ — Interest cost 83 65 88 73 57 85 19 12 19 Expected return on plan assets, net of administration expenses (134) (137) (159) (108) (130) (134) (33) (32) (34) Amortization of prior-service cost 2 2 2 — — 1 — — — Amortization of net actuarial loss 29 32 30 61 78 68 13 15 12 Net periodic benefit (income) cost (19) (37) (39) 26 5 20 (1) (5) (3) Settlement expense — 5 2 170 — — — — — Total net periodic benefit cost (income) $ (19) $ (32) $ (37) $ 196 $ 5 $ 20 $ (1) $ (5) $ (3)
Schedule of Weighted-Average Assumptions Used to Determine Future Benefit Obligations and Net Periodic Benefit Cost	The weighted-average assumptions used to determine benefit obligations are as follows: U.K. U.S. (1) Other 2022 2021 2022 2021 2022 2021 Discount rate 4.89% 1.96% 4.82 - 5.03% 2.23 - 2.8% 3.23 - 5.19% 1.00 - 2.97% Rate of compensation increase 3.59 - 4.09% 3.62 - 4.12% N/A N/A 1.00 - 3.00% 1.00 - 3.00% Underlying price inflation 2.44% 2.52% N/A N/A 2.00% 2.00% (1) U.S. pension plans are frozen and therefore not impacted by compensation increases or price inflation. The weighted-average assumptions used to determine the net periodic benefit cost are as follows: U.K. U.S. Other 2022 2021 2020 2022 2021 2020 2022 2021 2020 Discount rate 1.85% 1.20% 1.89% 1.67 - 2.25% 1.12 - 1.79% 2.36 - 2.76% 0.84 - 2.58% 0.28 - 2.00% 0.74 - 2.90% Expected return on plan assets, net of administration expenses 2.34% 2.04% 2.74% 2.03 - 5.28% 2.65- 6.56% 3.30%-7.04% 1.80 - 3.15% 1.70 - 2.65% 2.10 - 3.10% Rate of compensation increase 3.62 - 4.12% 3.22 - 3.72% 3.24 - 3.74% N/A N/A N/A 1.00 - 3.00% 1.00 - 3.00% 1.00 - 3.00%
Schedule of Fair Values of Pension Plan Assets	The fair values of the Company’s U.S. pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Asset Category Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 42 $ 42 $ — $ — Equity investments: Equity securities 64 64 — — Equity derivatives (6) — (6) — Pooled funds (2) 293 — — — Fixed income investments: Corporate bonds 192 — 192 — Government and agency bonds 149 124 25 — Pooled funds (2) 507 — — — Other investments: Real estate (2) (3) 113 — — — Alternative investments (2) (4) 127 — — — Total $ 1,481 $ 230 $ 211 $ — Fair Value Measurements Using Asset Category Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 93 $ 93 $ — $ — Equity investments: Equity securities 86 86 — — Equity derivatives 19 — 19 — Pooled funds (2) 548 — — — Fixed income investments: Corporate bonds 249 — 249 — Government and agency bonds 230 192 38 — Pooled funds (2) 838 — — — Other investments: Real estate (2)(3) 156 — — — Alternative investments (2) (4) 159 — — — Total $ 2,378 $ 371 $ 306 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of property funds and trusts holding direct real estate investments. (4) Consists of limited partnerships, private equity, and hedge funds. The fair values of the Company’s major U.K. pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 336 $ 336 $ — $ — Equity investments: Pooled funds (2) — — — — Fixed income investments: Derivatives (3) (548) — (548) — Government and agency bonds 1,593 1,593 — — Annuities 1,403 — — 1,403 Pooled funds (2) 139 — — — Other investments: Real estate (2) (4) 97 — — — Pooled funds (2) (5) 517 — — — Total $ 3,537 $ 1,929 $ (548) $ 1,403 Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 872 $ 872 $ — $ — Equity investments: Pooled funds (2) — — — — Fixed income investments: Derivatives (3) (1,640) — (1,640) — Government and agency bonds 2,969 2,969 — — Annuities 2,305 — — 2,305 Pooled funds (2) 463 — — — Other investments: Real estate (2) (4) 130 — — — Pooled funds (2) (5) 1,147 — — — Total $ 6,246 $ 3,841 $ (1,640) $ 2,305 (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of equity securities and equity derivatives, including repurchase agreements. (4) Consists of property funds and trusts holding direct real estate investments. (5) Consists of multi-strategy limited partnerships, private equity, hedge funds, and collective investment schemes with a diversified portfolio of cash, equities, equity related securities, derivatives, and/or fixed income securities. The fair values of the Company’s other major pension plan assets at December 31, 2022 and December 31, 2021, by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 30 $ 30 $ — $ — Equity investments: Equity securities 53 53 — — Pooled funds (2) 211 — — — Fixed income investments: Government and agency bonds 225 225 — — Derivatives (3) — (3) — Pooled funds (2) 462 — — — Other investments: Alternative investments (2) (3) 42 — — — Real estate (2) (4) 12 — — — Total $ 1,032 $ 308 $ (3) $ — Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Cash and cash equivalents (1) $ 29 $ 29 $ — $ — Equity investments: Equity securities 72 72 — — Pooled funds (2) 316 — — — Fixed income investments: Government and agency bonds 350 350 — — Pooled funds (2) 597 — — — Other investments: Alternative investments (2) (3) 55 — — — Real estate (2) (4) 11 — — — Total $ 1,430 $ 451 $ — $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of limited partnerships, private equity, and hedge funds. (4) Consists of property funds and trusts holding direct real estate investments.
Schedule of Changes in the Level 3 Fair-Value Category	The following table presents the changes in the Level 3 fair-value category in the Company’s U.K. pension plans for the years ended December 31, 2022 and December 31, 2021 (in millions): Fair Value Measurements Using Level 3 Inputs Annuities Balance at January 1, 2021 $ 2,625 Actual return on plan assets: Relating to assets still held at December 31, 2021 (286) Purchase, sales and settlements-net — Foreign exchange (34) Balance at December 31, 2021 2,305 Actual return on plan assets: Relating to assets still held at December 31, 2022 (674) Purchases, sales and settlements-net — Foreign exchange (228) Balance at December 31, 2022 $ 1,403
Schedule of Estimated Future Benefit Payments	Estimated future benefit payments for plans, not including voluntary one-time lump sum payments, are as follows at December 31, 2022 (in millions): U.K. U.S. Other 2023 $ 153 $ 157 $ 46 2024 $ 157 $ 158 $ 47 2025 $ 161 $ 158 $ 49 2026 $ 166 $ 162 $ 50 2027 $ 170 $ 155 $ 51 2028 - 2032 $ 905 $ 754 $ 274
Schedule of Other Information Related to the Company's Other Post-Retirement Benefit Plans	Other information related to the Company’s other postretirement benefit plans are as follows: 2022 2021 2020 Net periodic benefit cost recognized (millions) $3 $5 $4 Weighted-average discount rate used to determine future benefit obligations 4.94 - 5.19% 2.52 - 3.06% 2.10 - 2.58% Weighted-average discount rate used to determine net periodic benefit costs 1.97 - 2.69% 1.45 - 2.68% 2.93 - 3.25%

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Share-based Compensation Expense Recognized in Continuing Operations	The following table summarizes share-based compensation expense recognized in the Consolidated Statements of Income in Compensation and benefits (in millions): Years Ended December 31 2022 2021 2020 Restricted share units $ 251 $ 204 $ 186 Performance share awards 134 189 116 Employee share purchase plans and other (1) 12 56 10 Total share-based compensation expense 397 449 312 Tax benefit 83 87 61 Share-based compensation expense, net of tax $ 314 $ 362 $ 251 (1) 2021 includes expenses related to the Aon United Growth Ownership Plan.
Schedule of Restricted Share Unit Activity	The following table summarizes the status of the Company’s RSUs (shares in thousands, except fair value): Shares Fair Value (1) Non-vested balance at December 31, 2021 3,075 $ 203 Granted 1,117 $ 279 Vested (1,154) $ 187 Forfeited (175) $ 219 Non-vested balance at December 31, 2022 2,863 $ 238 (1) Represents per share weighted average fair value of award at date of grant.
Schedule of Performance-based Plans Information	The following table summarizes the status of the Company's PSAs at 100% of the targeted amount (shares in thousands, except fair value): Shares Fair Value (1) Non-vested balance at December 31, 2021 1,298 $ 181 Granted 300 $ 311 Vested (444) $ 163 Forfeited (18) $ 217 Non-vested balance at December 31, 2022 1,136 $ 222 (1) Represents per share weighted average fair value of award at date of grant.

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional and Fair Values of Derivative Instruments	The notional and fair values of derivative instruments are as follows (in millions): Notional Amount Net Amount of Derivative Assets Presented in the Statements of Financial Position (1) Net Amount of Derivative Liabilities Presented in the Statements of Financial Position As of December 31 2022 2021 2022 2021 2022 2021 Foreign exchange contracts Accounted for as hedges $ 618 $ 629 $ 12 $ 27 $ 2 $ — Not accounted for as hedges (3) 312 412 — 2 1 — Total $ 930 $ 1,041 $ 12 $ 29 $ 3 $ — (1) Included within Other current assets ($3 million in 2022 and $21 million in 2021) or Other non-current assets ($9 million in 2022 and $8 million in 2021). (2) Included within Other current liabilities ($2 million in 2022) or Other non-current liabilities ($1 million in 2022). (3) These contracts typically are for 90-day durations and executed close to the last day of the most recent reporting month, thereby resulting in nominal fair values at the balance sheet date.
Schedule of Derivative Gains (Losses)	The amounts of derivative gains (losses) recognized in the Consolidated Financial Statements are as follows (in millions): 2022 2021 2020 (Loss) gain recognized in Accumulated other comprehensive loss $ (15) $ — $ 1 The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss to the Consolidated Statements of Income are as follows (in millions): Years Ended December 31 2022 2021 2020 Total revenue $ 2 $ (3) $ (14) Compensation and benefits — 1 — Interest expense — — (1) Total $ 2 $ (2) $ (15)

Fair Value Measurements and F_2

Fair Value Measurements and Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities that are Measured at Fair Value on a Recurring Basis	The following tables present the categorization of the Company’s assets and liabilities that are measured at fair value on a recurring basis at December 31, 2022 and December 31, 2021 (in millions): Fair Value Measurements Using Balance at December 31, 2022 Quoted Prices in Significant Significant Assets Money market funds (1) $ 3,323 $ 3,323 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 19 $ — $ 19 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 9 $ — $ 9 $ — Fair Value Measurements Using Balance at December 31, 2021 Quoted Prices in Significant Significant Assets Money market funds (1) $ 2,918 $ 2,918 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 40 $ — $ 40 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 11 $ — $ 11 $ — (1) Included within Fiduciary assets or Short-term investments in the Consolidated Statements of Financial Position, depending on their nature and initial maturity.
Schedule of Financial Instruments where the Carrying Amounts and Fair Values Differ	The fair value of debt is classified as Level 2 of the fair value hierarchy. The following table provides the carrying value and fair value for the Company’s term debt (in millions): 2022 2021 As of December 31 Carrying Fair Carrying Fair Current portion of long-term debt $ 350 $ 347 $ 499 $ 507 Long-term debt $ 9,825 $ 8,745 $ 8,228 $ 9,204

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Schedule of Disclosure on Geographic Areas of Fixed Assets and Operating Lease Right-of-Use Asset	Consolidated long-lived assets, net by geographic area are as follows (in millions): As of December 31 Total United Americas other United Ireland Other Europe, Middle East, & Africa Asia 2022 $ 1,300 $ 519 $ 120 $ 155 $ 9 $ 279 $ 218 2021 $ 1,378 $ 563 $ 121 $ 180 $ 7 $ 293 $ 214

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Issuance of debt		$ (1,967)	$ (1,495)	$ (991)
Repayment of debt		(500)	(413)	(607)
Non-cash pension settlement charges	$ 170		5	2
Proceeds from issuance of shares		58	55	44
Cash paid for employee taxes on withholding shares		$ 215	185	193
Revision of Prior Period, Reclassification, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Issuance of debt			4,478	3,162
Repayment of debt			3,807	3,275
Proceeds from issuance of shares			55	44
Cash paid for employee taxes on withholding shares			$ 185	$ 193

Summary of Significant Accoun_4

Summary of Significant Accounting Principles and Practices - Additional Information (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 GBP (£)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Cash and cash equivalents and short-term investments	$ 1,142		$ 836
Cash and cash equivalents and short term investments, period increase (decrease)	306
Restricted cash and investments, current	115		160
Operating funds required to be held by the Company in the U.K.	72.5	£ 60.1	112.8	£ 84.3
Premium trust balances	6,400		6,100
Fiduciary receivables	9,500		8,300
Allowance for doubtful accounts	$ 76		$ 90		$ 98	$ 77

Summary of Significant Accoun_5

Summary of Significant Accounting Principles and Practices - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2022
Software | Minimum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	4 years
Software | Maximum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	7 years
Leasehold improvements
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	10 years
Furniture, fixtures and equipment | Minimum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	4 years
Furniture, fixtures and equipment | Maximum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	10 years
Computer equipment | Minimum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	4 years
Computer equipment | Maximum
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	6 years
Buildings
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	35 years
Automobiles
Fixed Assets, net [Line Items]
Fixed assets, original life, weighted-average	6 years

Summary of Significant Accoun_6

Summary of Significant Accounting Principles and Practices - Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2022
Customer-related and contract-based | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	7 years
Customer-related and contract-based | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	20 years
Technology and other | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	5 years
Technology and other | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	7 years
Tradenames | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	1 year
Tradenames | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life of finite-lived intangible assets	3 years

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 12,479	$ 12,193	$ 11,066
U.S.
Disaggregation of Revenue [Line Items]
Total revenue	5,666	5,459	5,032
Americas other than U.S.
Disaggregation of Revenue [Line Items]
Total revenue	1,137	1,027	911
U.K.
Disaggregation of Revenue [Line Items]
Total revenue	1,660	1,681	1,579
Ireland
Disaggregation of Revenue [Line Items]
Total revenue	99	127	84
Europe, Middle East, & Africa other than U.K. and Ireland
Disaggregation of Revenue [Line Items]
Total revenue	2,443	2,565	2,236
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	1,474	1,334	1,224
Elimination
Disaggregation of Revenue [Line Items]
Total revenue	(17)	(19)	(17)
Commercial Risk Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	6,715	6,635	5,861
Reinsurance Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	2,190	1,997	1,814
Health Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	2,224	2,154	2,067
Wealth Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,367	$ 1,426	$ 1,341

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 361	$ 339
Additions	1,479	1,504
Amortization	(1,480)	(1,478)
Impairment	0	0
Foreign currency translation and other	(5)	(4)
Balance at end of period	355	361
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	179	184
Additions	56	59
Amortization	(49)	(48)
Impairment	0	0
Foreign currency translation and other	(1)	(16)
Balance at end of period	$ 185	$ 179

Other Financial Data - Schedule

Other Financial Data - Schedule of Other Income (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other Financial Data [Abstract]
Pension and other postretirement	$ (179)	$ 21	$ 13
Foreign currency remeasurement	(14)	26	(12)
Extinguishment of debt	0	0	(7)
Financial instruments and other	4	(45)	(10)
Equity earnings	10	8	4
Gain from disposals of business	54	142	25
Total	$ (125)	$ 152	$ 13
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total

Other Financial Data - Schedu_2

Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 90	$ 98	$ 77
Provision	8	26	29
Accounts written off, net of recoveries	(18)	(37)	(6)
Foreign currency translation and other	(4)	3	(2)
Balance at end of period	$ 76	$ 90	$ 98

Other Financial Data - Schedu_3

Other Financial Data - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Other Financial Data [Abstract]
Costs to fulfill contracts with customers	$ 355	$ 361
Prepaid expenses	109	137
Taxes receivable	74	53
Other	108	165
Total	$ 646	$ 716

Other Financial Data - Componen

Other Financial Data - Components of Fixed Assets, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 1,949	$ 1,847
Less: Accumulated depreciation	1,391	1,318
Fixed assets, net	558	529
Depreciation of fixed assets	151	179	$ 167
Software
Fixed Assets, net [Line Items]
Fixed assets, gross	861	797
Leasehold improvements
Fixed Assets, net [Line Items]
Fixed assets, gross	409	425
Computer equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	269	268
Furniture, fixtures and equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	267	279
Construction in progress
Fixed Assets, net [Line Items]
Fixed assets, gross	109	45
Other
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 34	$ 33

Other Financial Data - Schedu_4

Other Financial Data - Schedule of Other Non-current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Other Financial Data [Abstract]
Costs to obtain contracts with customers	$ 185	$ 179
Taxes receivable	109	95
Investments	60	64
Leases	43	63
Other	112	111
Total	$ 509	$ 512

Other Financial Data - Schedu_5

Other Financial Data - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Other Financial Data [Abstract]
Deferred revenue	$ 250	$ 321
Taxes payable	193	149
Leases	186	213
Other	718	648
Total	1,347	1,331
Deferred revenue recognized	$ 653	$ 553

Other Financial Data - Schedu_6

Other Financial Data - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Other Financial Data [Abstract]
Taxes payable	$ 795	$ 609
Compensation and benefits	69	58
Deferred revenue	37	70
Leases	28	46
Other	95	127
Other non-current liabilities	1,024	910
Taxes payable, noncurrent, transition tax	$ 129	$ 145

Acquisitions and Dispositions_3

Acquisitions and Dispositions of Businesses - Completed Acquisitions (Details) $ in Millions		12 Months Ended
	Sep. 01, 2021 USD ($)	Dec. 31, 2022 USD ($) acquisition	Dec. 31, 2021 acquisition	Nov. 01, 2022	May 03, 2022	Dec. 22, 2021	Aug. 31, 2021
Business Acquisition [Line Items]
Number of business acquired under business combination | acquisition		5	2
Weighted average useful life		9 years
Revenues from acquisitions included in the Company's Consolidated Statement of Income		$ 25
E.R.N. Evaluacion de Riesgos Naturales y Antropogenicos, S.A. de C.V
Business Acquisition [Line Items]
Percentage of capital acquired				100%
Karl Köllner Group
Business Acquisition [Line Items]
Percentage of capital acquired					100%
For Welfare S.r.l
Business Acquisition [Line Items]
Percentage of capital acquired						100%
Aon India Insurance Brokers Limited
Business Acquisition [Line Items]
Percentage of capital acquired	51%
Equity interest in acquiree, percentage							49%
Equity interest in acquiree	$ 15

Acquisitions and Dispositions_4

Acquisitions and Dispositions of Businesses - Schedule of Net Assets Acquired (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets acquired
Goodwill	$ 8,292	$ 8,434	$ 8,666
2022 And 2021 Acquisitions
Consideration transferred
Cash	161
Deferred and contingent consideration	9
Aggregate consideration transferred	170
Assets acquired
Goodwill	87
Intangible assets	78
Other assets	25
Total assets acquired	190
Liabilities assumed
Total liabilities assumed	20
Net assets acquired	170
Cash and cash equivalents	$ 2

Acquisitions and Dispositions_5

Acquisitions and Dispositions of Businesses - Completed Dispositions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) disposition	Dec. 31, 2021 USD ($) disposition	Dec. 31, 2020 USD ($) disposition
Business Combination and Asset Acquisition [Abstract]
Number of dispositions | disposition	3	6	1
Gain from disposals of business | $	$ 54	$ 142	$ 25

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Schedule of changes in the net carrying amount of goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Balance at the beginning of the period	$ 8,434	$ 8,666
Goodwill related to current year acquisitions	87	17
Goodwill related to current year disposals	(11)	(37)
Foreign currency translation and other	(218)	(212)
Balance at the end of the period	$ 8,292	$ 8,434

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Schedule of other intangible assets by asset class (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,657	$ 2,710
Accumulated Amortization and Impairment	2,210	2,218
Net Carrying Amount	447	492
Amortization and impairment of intangible assets	113	147	$ 246
Customer-related and contract-based
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,207	2,289
Accumulated Amortization and Impairment	1,833	1,848
Net Carrying Amount	374	441
Technology and other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	436	407
Accumulated Amortization and Impairment	363	357
Net Carrying Amount	73	50
Tradenames
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	14	14
Accumulated Amortization and Impairment	14	13
Net Carrying Amount	$ 0	$ 1

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of estimated future amortization expense on intangible assets (Details) $ in Millions	Dec. 31, 2022 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2023	$ 99
2024	82
2025	68
2026	47
2027	34
Thereafter	117
Total	$ 447

Debt - Summary of outstanding d

Debt - Summary of outstanding debt (Details)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 EUR (€)	Sep. 12, 2022 USD ($)	Feb. 28, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 02, 2021 USD ($)	Aug. 23, 2021 USD ($)
Debt Instrument [Line Items]
Total debt	$ 10,770,000,000				$ 9,392,000,000
Less: Short-term debt and current portion of long-term debt	945,000,000				1,164,000,000
Total long-term debt	9,825,000,000				8,228,000,000
Other
Debt Instrument [Line Items]
Total debt	5,000,000				$ 0
2.20% Senior Notes due November 2022 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt					2.20%
Total debt	$ 0				$ 499,000,000
4.00% Senior Notes due November 2023 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4%	4%
Total debt	$ 350,000,000				349,000,000
3.50% Senior Notes due June 2024 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	3.50%	3.50%
Total debt	$ 599,000,000				598,000,000
3.875% Senior Notes due December 2025 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	3.875%	3.875%
Total debt	$ 748,000,000				748,000,000
2.875% Senior Notes due May 2026 (EUR 500M) | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.875%	2.875%
Total debt	$ 530,000,000				563,000,000
Debt face value | €		€ 500,000,000
8.205% Junior Subordinated Notes due January 2027 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	8.205%	8.205%
Total debt	$ 521,000,000				521,000,000
2.85% Senior Notes due May 2027 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.85%	2.85%		2.85%
Total debt	$ 596,000,000				0
Debt face value				$ 600,000,000
4.50% Senior Notes due December 2028 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4.50%	4.50%
Total debt	$ 348,000,000				347,000,000
3.75% Senior Notes due May 2029 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	3.75%	3.75%
Total debt	$ 746,000,000				745,000,000
2.80% Senior Notes due May 2030 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.80%	2.80%
Total debt	$ 994,000,000				993,000,000
2.05% Senior Notes due August 2031 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.05%	2.05%					2.05%
Total debt	$ 396,000,000				396,000,000
Debt face value							$ 400,000,000
2.60% Senior Notes due December 2031 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.60%	2.60%				2.60%
Total debt	$ 496,000,000				496,000,000
Debt face value						$ 500,000,000
5.00% Senior Notes due September 2032 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	5%	5%	5%
Total debt	$ 495,000,000				0
Debt face value			$ 500,000,000
6.25% Senior Notes due September 2040 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	6.25%	6.25%
Total debt	$ 297,000,000				296,000,000
4.25% Senior Notes due December 2042 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4.25%	4.25%
Total debt	$ 203,000,000				201,000,000
4.45% Senior Notes due May 2043 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4.45%	4.45%
Total debt	$ 247,000,000				247,000,000
4.60% Senior Notes due June 2044 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4.60%	4.60%
Total debt	$ 545,000,000				544,000,000
4.75% Senior Notes due May 2045 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	4.75%	4.75%
Total debt	$ 594,000,000				593,000,000
2.90% Senior Notes due August 2051 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	2.90%	2.90%					2.90%
Total debt	$ 591,000,000				591,000,000
Debt face value							$ 600,000,000
3.90% Senior Notes due February 2052 | Senior Notes
Debt Instrument [Line Items]
Interest rate on debt	3.90%	3.90%		3.90%
Total debt	$ 877,000,000				0
Debt face value				$ 900,000,000
Commercial paper
Debt Instrument [Line Items]
Total debt	$ 592,000,000				$ 665,000,000

Debt - Narrative (Details)

Debt - Narrative (Details)	Dec. 31, 2022 EUR (€) credit_facility	Dec. 31, 2022 USD ($) credit_facility	Sep. 12, 2022 USD ($)	Feb. 28, 2022 USD ($)	Dec. 31, 2021 USD ($)	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
4.00% Senior Notes due November 2023 | Senior Notes
Debt Instrument [Line Items]
Debt face value		$ 350,000,000
Debt interest rate percentage (as a percent)	4%	4%
2.20% Senior Notes due November 2022 | Senior Notes
Debt Instrument [Line Items]
Debt face value					$ 500,000,000		$ 500,000,000
Debt interest rate percentage (as a percent)					2.20%
U. S. Program | Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,000,000,000
European Program | Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	€ 625,000,000	$ 665,000,000
Senior Notes | 4.00% Senior Notes due November 2023
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)	4%	4%
Senior Notes | 2.20% Senior Notes due November 2022
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)					2.20%
Senior Notes | 5.00% Senior Notes due September 2032
Debt Instrument [Line Items]
Debt face value			$ 500,000,000
Debt interest rate percentage (as a percent)	5%	5%	5%
Senior Notes | 2.85% Senior Notes due May 2027
Debt Instrument [Line Items]
Debt face value				$ 600,000,000
Debt interest rate percentage (as a percent)	2.85%	2.85%		2.85%
Senior Notes | 3.90% Senior Notes due February 2052
Debt Instrument [Line Items]
Debt face value				$ 900,000,000
Debt interest rate percentage (as a percent)	3.90%	3.90%		3.90%
Senior Notes | 2.60% Senior Notes due December 2031
Debt Instrument [Line Items]
Debt face value						$ 500,000,000
Debt interest rate percentage (as a percent)	2.60%	2.60%				2.60%
Senior Notes | 2.05% Senior Notes due August 2031
Debt Instrument [Line Items]
Debt face value								$ 400,000,000
Debt interest rate percentage (as a percent)	2.05%	2.05%						2.05%
Senior Notes | 2.90% Senior Notes due August 2051
Debt Instrument [Line Items]
Debt face value								$ 600,000,000
Debt interest rate percentage (as a percent)	2.90%	2.90%						2.90%
Senior Notes | 2.80% Senior Notes due March 2021
Debt Instrument [Line Items]
Debt face value									$ 400,000,000
Debt interest rate percentage (as a percent)									2.80%
Line of Credit
Debt Instrument [Line Items]
Line of credit facility, available credit		$ 1,800,000,000
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

Debt - Repayments of long-term

Debt - Repayments of long-term debt (Details) $ in Millions	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
2023	$ 946
2024	604
2025	750
2026	532
2027	1,121
Thereafter	6,956
Total Repayments	10,909
Unamortized discounts, premiums, and debt issuance costs	(139)
Total Debt	$ 10,770

Debt - Schedule of Commercial P

Debt - Schedule of Commercial Paper (Details) - Commercial paper - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Line of Credit Facility [Line Items]
Commercial paper outstanding	$ 592	$ 665
Weighted average commercial paper outstanding	$ 499	$ 273
Weighted average interest rate of commercial paper outstanding	1.42%	0.01%

Lease Commitments - Assets and

Lease Commitments - Assets and Liabilities of Lessee (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Assets
Operating lease assets	$ 699	$ 786
Finance lease assets	43	63
Total lease assets	$ 742	$ 849
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other non-current assets	Other non-current assets
Current lease liabilities
Operating	$ 163	$ 194
Finance	$ 23	$ 19
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Non-current lease liabilities
Operating	$ 693	$ 772
Finance	$ 28	$ 46
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other non-current liabilities	Other non-current liabilities
Total lease liabilities	$ 907	$ 1,031

Lease Commitments - Lease Costs

Lease Commitments - Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease cost	$ 204	$ 217
Finance lease costs
Amortization of leased assets	28	26
Interest on lease liabilities	1	1
Variable lease cost	38	49
Short-term lease cost	11	11
Sublease income	(29)	(31)
Net lease cost	$ 253	$ 273

Lease Commitments - Lease Terms

Lease Commitments - Lease Terms and Assumptions (Details)	Dec. 31, 2022	Dec. 31, 2021
Weighted average remaining lease term (years)
Operating leases	6 years 8 months 12 days	6 years 10 months 24 days
Finance leases	2 years 6 months	3 years 7 months 6 days
Weighted average discount rate
Operating leases	3.10%	2.80%
Finance leases	1%	1%

Lease Commitments - Cash Flow o

Lease Commitments - Cash Flow of Lessee (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 231	$ 244
Financing cash flows for finance leases	14	23
Non-cash related activities
ROU assets obtained in exchange for new operating lease liabilities	110	44
ROU assets obtained in exchange for new finance lease liabilities	0	0
Operating lease ROU asset expense	162	142
Changes in Non-current operating lease liabilities	$ (79)	$ (125)

Lease Commitments - Lease Matur

Lease Commitments - Lease Maturity (Details) $ in Millions	Dec. 31, 2022 USD ($)
Operating Leases
2023	$ 175
2024	164
2025	135
2026	123
2027	108
Thereafter	235
Total undiscounted future minimum lease payments	940
Less: Imputed interest	(84)
Present value of lease liabilities	856
Finance Leases
2023	23
2024	18
2025	10
2026	0
2027	0
Thereafter	0
Less: Imputed interest	51
Less: Imputed interest	0
Present value of lease liabilities	51
Total
2023	198
2024	182
2025	145
2026	123
2027	108
Thereafter	235
Total undiscounted future minimum lease payments	991
Less: Imputed interest	(84)
Present value of lease liabilities	$ 907

Income Taxes - Income from cont

Income Taxes - Income from continuing operations before income tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income (loss) before income taxes:
Income before income taxes	$ 3,156	$ 1,931	$ 2,466
Current:
Total current tax expense	762	612	439
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	(252)	11	9
Total income tax expense	510	623	448
Ireland
Income (loss) before income taxes:
Income before income taxes	85	15	(86)
Current:
Total current tax expense	2	2	2
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	0	(1)	(1)
U.K.
Income (loss) before income taxes:
Income before income taxes	502	549	634
Current:
Total current tax expense	206	50	30
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	(152)	131	39
U.S. federal
Income (loss) before income taxes:
Income before income taxes	161	(818)	(28)
Current:
Total current tax expense	195	197	126
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	(69)	(83)	(72)
U.S. state and local
Current:
Total current tax expense	43	72	22
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	(21)	(30)	(4)
Other
Income (loss) before income taxes:
Income before income taxes	2,408	2,185	1,946
Current:
Total current tax expense	316	291	259
Deferred tax expense (benefit):
Total deferred tax expense (benefit)	$ (10)	$ (6)	$ 47

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory tax rate	25%	25%	25%
Increase in valuation allowance	$ 45
Unremitted earnings	38	$ 58
Benefit realized from tax holiday granted	$ 115	$ 104	$ 97
Earnings per share impact of tax holiday (in dollars per share)	$ 0.54	$ 0.46	$ 0.42
Unrecognized tax benefits that would impact effective tax rate	$ 535	$ 295	$ 270
Accrued potential interest and penalties	40	22	21
Liability recorded for interest and penalties	$ 181	$ 142	$ 120

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the income tax provisions based on the U.S. statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of the income tax provisions based on the statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements
Statutory tax rate	25%	25%	25%
U.S. state income taxes, net of U.S. federal benefit	0.40%	1.50%	1%
Taxes on international operations	(11.60%)	(15.40%)	(9.80%)
Nondeductible expenses	2.40%	3.30%	2.10%
Adjustments to prior year tax requirements	(7.00%)	(0.20%)	0%
Deferred tax adjustments, including statutory rate changes	(0.50%)	3.20%	0.70%
Deferred tax adjustments, international earnings	0.20%	1.80%	0.70%
Adjustments to valuation allowances	1.90%	(0.20%)	0%
Change in uncertain tax positions	8.60%	2.10%	1.50%
Excess tax benefits related to shared based compensation	(1.50%)	(2.40%)	(2.20%)
Capital and other losses	(0.014)	0	(0.018)
Non-deductible transaction costs	0	0.011	0.013
Non-deductible termination fee	0%	12.90%	0%
Other — net	(0.30%)	(0.40%)	(0.30%)
Effective tax rate	16.20%	32.30%	18.20%

Income Taxes - Components of Ao

Income Taxes - Components of Aon's deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss, capital loss, interest, and tax credit carryforwards	$ 952	$ 581
Lease liabilities	178	207
Employee benefit plans	297	160
Other accrued expenses	100	132
Accrued interest	0	97
Federal and state benefit of interest from uncertain tax positions	57	45
Deferred revenue	26	36
Investment basis differences	30	25
Lease and service guarantees	1	1
Other	38	25
Total	1,679	1,309
Valuation allowance on deferred tax assets	(275)	(230)
Total	1,404	1,079
Deferred tax liabilities:
Intangibles and property, plant and equipment	(258)	(243)
Lease right-of-use asset	(151)	(173)
Deferred costs	(147)	(159)
Unremitted earnings	(38)	(58)
Other accrued expenses	(20)	(27)
Unrealized foreign exchange gains	(23)	(22)
Other	(42)	(32)
Total	(679)	(714)
Net deferred tax asset	$ 725	$ 365

Income Taxes - Deferred income

Income Taxes - Deferred income taxes (assets and liabilities netted by jurisdiction) as classified in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Deferred tax assets — non-current	$ 824	$ 766
Deferred tax liabilities — non-current	(99)	(401)
Net deferred tax asset	$ 725	$ 365

Income Taxes Operating Loss Car

Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
U.K.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 608	$ 41
Capital loss carryforwards	533	573
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1	25
Capital loss carryforwards	112	112
Interest Carryforward	2,269	1,140
Foreign tax credit carryforwards	20	18
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	473	398
Capital loss carryforwards	123	123
Interest Carryforward	1,187	551
Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	490	301
Capital loss carryforwards	8	35
Interest Carryforward	26	26
Other carryforwards	$ 5	$ 5

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of the Company's beginning and ending amount of unrecognized tax benefits
Balance at the beginning of the period	$ 347	$ 321
Additions based on tax positions related to the current year	35	33
Additions for tax positions of prior years	226	7
Reductions for tax positions of prior years	(1)	(4)
Settlements	(1)	0
Business combinations	0	0
Lapse of statute of limitations	(5)	(10)
Foreign currency translation	0	0
Balance at the end of the period	$ 601	$ 347

Shareholders' Equity (Deficit_2

Shareholders' Equity (Deficit) - Distributable Profits (Details) - USD ($) $ in Billions	Dec. 31, 2022	Dec. 31, 2021
Equity [Abstract]
Distributable reserves available amount	$ 29	$ 32.7

Shareholders' Equity (Deficit_3

Shareholders' Equity (Deficit) - Ordinary Shares (Details) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended				12 Months Ended		129 Months Ended
	Feb. 18, 2022	Nov. 30, 2020	Jun. 30, 2017	Nov. 30, 2014	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Apr. 30, 2012
Equity [Abstract]
Share repurchase authorization amount					$ 27,500,000,000		$ 27,500,000,000	$ 5,000,000,000
Share repurchase authorization amount, increase during period	$ 7,500,000,000	$ 5,000,000,000	$ 5,000,000,000	$ 5,000,000,000
Number of shares repurchased (in shares)					11.1	12.4	160.7
Average price per share (in dollars per share)					$ 289.76	$ 286.82
Repurchase costs recorded to accumulated deficit					$ 3,203,000,000	$ 3,543,000,000	$ 21,500,000,000
Remaining authorized repurchase amount					$ 6,000,000,000		$ 6,000,000,000

Shareholders' Equity (Deficit_4

Shareholders' Equity (Deficit) - Schedule of weighted average shares outstanding (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Equity [Abstract]
Basic weighted average ordinary shares outstanding (in shares)	211.7	224.7	231.9
Dilutive effect of potentially issuable shares (in shares)	1.5	1.4	1.2
Diluted weighted average ordinary shares outstanding (in shares)	213.2	226.1	233.1
Antidilutive securities excluded from computation of earnings per share (in shares)	0.8	0.3	0

Shareholders' Equity (Deficit_5

Shareholders' Equity (Deficit) - Components of Accumulated other comprehensive loss, net of related tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 1,158	$ 3,583	$ 3,443
Other comprehensive income (loss) before reclassifications	(1,112)	(63)	4
Tax benefit	153	(56)	62
Other comprehensive income (loss) before reclassifications, net	(959)	(119)	66
Amounts reclassified from accumulated other comprehensive income	280	144	140
Tax expense	(73)	(35)	(34)
Amounts reclassified from accumulated other comprehensive income (loss), net	207	109	106
Total other comprehensive income (loss) attributable to Aon shareholders	(752)	(10)	172
Ending Balance	(429)	1,158	3,583
Change in Fair Value of Investments
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	2	1	(12)
Other comprehensive income (loss) before reclassifications	(15)	0	1
Tax benefit	4	0	0
Other comprehensive income (loss) before reclassifications, net	(11)	0	1
Amounts reclassified from accumulated other comprehensive income	(2)	2	15
Tax expense	0	(1)	(3)
Amounts reclassified from accumulated other comprehensive income (loss), net	(2)	1	12
Total other comprehensive income (loss) attributable to Aon shareholders	(13)	1	13
Ending Balance	(11)	2	1
Foreign Currency Translation Adjustments
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(1,333)	(1,045)	(1,305)
Other comprehensive income (loss) before reclassifications	(528)	(290)	258
Tax benefit	0	2	2
Other comprehensive income (loss) before reclassifications, net	(528)	(288)	260
Amounts reclassified from accumulated other comprehensive income	0	0	0
Tax expense	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net	0	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(528)	(288)	260
Ending Balance	(1,861)	(1,333)	(1,045)
Post-retirement Benefit Obligations
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(2,540)	(2,817)	(2,716)
Other comprehensive income (loss) before reclassifications	(569)	227	(255)
Tax benefit	149	(58)	60
Other comprehensive income (loss) before reclassifications, net	(420)	169	(195)
Amounts reclassified from accumulated other comprehensive income	282	142	125
Tax expense	(73)	(34)	(31)
Amounts reclassified from accumulated other comprehensive income (loss), net	209	108	94
Total other comprehensive income (loss) attributable to Aon shareholders	(211)	277	(101)
Ending Balance	(2,751)	(2,540)	(2,817)
AOCI attributable to parent
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(3,871)	(3,861)	(4,033)
Ending Balance	$ (4,623)	$ (3,871)	$ (3,861)

Employee Benefits - Schedule of

Employee Benefits - Schedule of expense recognized in Compensation and benefit in the Consolidated Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expense recognized for defined contribution savings plans	$ 188	$ 184	$ 155
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expense recognized for defined contribution savings plans	108	103	87
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expense recognized for defined contribution savings plans	47	46	42
Netherlands and Canada
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expense recognized for defined contribution savings plans	$ 33	$ 35	$ 26

Employee Benefits - Pension Pla

Employee Benefits - Pension Plans Narrative (Details) £ in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Nov. 30, 2022 USD ($)	Nov. 30, 2020 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 GBP (£)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 GBP (£)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of the Company's projected benefit obligation			88%
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement expense			$ 170
Non-cash settlement charge			(170)
Pension Plan | U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefits obligations settled	$ 280
Defined benefit plan, plan assets for settlements	$ 280		283	$ 0
Plans with PBO in excess of plan assets, PBO			2,200	3,200
Plans with ABO in excess of the fair value of plan assets, ABO			2,200	3,200
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets			1,500	2,400
Settlement expense			(170)	0		$ 0
Non-cash settlement charge			170	0		0
Pension Plan | U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets for settlements			0	14
Insurance contract, decrease in Prepaid pension assets		$ 94
Plans with PBO in excess of plan assets, PBO			114	17
Plans with ABO in excess of the fair value of plan assets, ABO			114	17
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets			93
Settlement expense			0	(5)	£ (3)	(2)	£ (2)
Non-cash settlement charge			0	5	£ 3	2	£ 2
Pension Plan | Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets for settlements			0	0
Plans with PBO in excess of plan assets, PBO			1,100	1,500
Plans with ABO in excess of the fair value of plan assets, ABO			220	409
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets			166	326
Plans with PBO in excess of plan assets, plan assets			1,000	1,400
Settlement expense			0	0		0
Non-cash settlement charge			$ 0	$ 0		$ 0

Employee Benefits - Reconciliat

Employee Benefits - Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status (Details) - Pension Plan - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
U.S.
Change in projected benefit obligation
Balance at the beginning of the Period		$ 3,164	$ 3,380
Service cost		0	0	$ 0
Interest cost		73	57	85
Settlements		(283)	0
Actuarial (gain) loss		(607)	(103)
Benefit payments		(167)	(170)
Foreign currency impact		0	0
Balance at the end of the period		2,180	3,164	3,380
Accumulated benefit obligation at end of year		2,180	3,164
Change in fair value of plan assets
Balance at the beginning of the period		2,378	2,276
Actual return on plan assets		(484)	211
Employer contributions		37	61
Settlements	$ (280)	(283)	0
Benefit payments		(167)	(170)
Foreign currency impact		0	0
Balance at the end of the period		1,481	2,378	2,276
Market related value at end of year		1,794	2,174
Funded status		(699)	(786)
Unrecognized prior-service cost		0	0
Unrecognized loss		1,305	1,551
Net amount recognized		606	765
U.K.
Change in projected benefit obligation
Balance at the beginning of the Period		4,919	5,406
Service cost		1	1	0
Interest cost		83	65	88
Settlements		0	(14)
Actuarial (gain) loss		(1,418)	(292)
Benefit payments		(195)	(189)
Foreign currency impact		(444)	(58)
Balance at the end of the period		2,946	4,919	5,406
Accumulated benefit obligation at end of year		2,946	4,919
Change in fair value of plan assets
Balance at the beginning of the period		6,246	6,652
Actual return on plan assets		(1,961)	(136)
Employer contributions		7	9
Settlements		0	(14)
Benefit payments		(195)	(189)
Foreign currency impact		(559)	(76)
Balance at the end of the period		3,537	6,246	6,652
Market related value at end of year		3,537	6,246
Funded status		591	1,327
Unrecognized prior-service cost		35	40
Unrecognized loss		1,726	1,215
Net amount recognized		2,352	2,582
Other
Change in projected benefit obligation
Balance at the beginning of the Period		1,531	1,625
Service cost		0	0	0
Interest cost		19	12	19
Settlements		0	0
Actuarial (gain) loss		(322)	24
Benefit payments		(45)	(47)
Foreign currency impact		(89)	(83)
Balance at the end of the period		1,094	1,531	1,625
Accumulated benefit obligation at end of year		1,079	1,504
Change in fair value of plan assets
Balance at the beginning of the period		1,430	1,497
Actual return on plan assets		(284)	46
Employer contributions		15	17
Settlements		0	0
Benefit payments		(45)	(47)
Foreign currency impact		(83)	(83)
Balance at the end of the period		1,032	1,430	$ 1,497
Market related value at end of year		1,032	1,430
Funded status		(62)	(101)
Unrecognized prior-service cost		(6)	(6)
Unrecognized loss		443	489
Net amount recognized		$ 375	$ 382

Employee Benefits - Amounts rec

Employee Benefits - Amounts recognized in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid pension	$ 652	$ 1,366
Pension Plan | U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid pension	0	0
Accrued benefit liability - current	(42)	(52)
Accrued benefit liability - non-current	(657)	(734)
Accumulated other comprehensive loss	1,305	1,551
Net amount recognized	606	765
Pension Plan | U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid pension	612	1,344
Accrued benefit liability - current	(1)	(1)
Accrued benefit liability - non-current	(20)	(16)
Accumulated other comprehensive loss	1,761	1,255
Net amount recognized	2,352	2,582
Pension Plan | Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid pension	0	0
Accrued benefit liability - current	(5)	(5)
Accrued benefit liability - non-current	(57)	(96)
Accumulated other comprehensive loss	437	483
Net amount recognized	$ 375	$ 382

Employee Benefits - Amounts r_2

Employee Benefits - Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
U.S.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	$ 1,305	$ 1,551
Prior service cost (income)	0	0
Net amount recognized	1,305	1,551
U.K.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	1,726	1,215
Prior service cost (income)	35	40
Net amount recognized	1,761	1,255
Other
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	443	489
Prior service cost (income)	(6)	(6)
Net amount recognized	$ 437	$ 483

Employee Benefits - Components

Employee Benefits - Components of net periodic benefit cost (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 GBP (£)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 GBP (£)
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement expense	$ (170)
Pension Plan | U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	$ 0		$ 0
Interest cost	73	57		85
Expected return on plan assets, net of administration expenses	(108)	(130)		(134)
Amortization of prior-service cost	0	0		1
Amortization of net actuarial loss	61	78		68
Net periodic benefit (income) cost	26	5		20
Settlement expense	170	0		0
Total net periodic benefit cost (income)	196	5		20
Pension Plan | U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1	1		0
Interest cost	83	65		88
Expected return on plan assets, net of administration expenses	(134)	(137)		(159)
Amortization of prior-service cost	2	2		2
Amortization of net actuarial loss	29	32		30
Net periodic benefit (income) cost	(19)	(37)		(39)
Settlement expense	0	5	£ 3	2	£ 2
Total net periodic benefit cost (income)	(19)	(32)		(37)
Pension Plan | Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0		0
Interest cost	19	12		19
Expected return on plan assets, net of administration expenses	(33)	(32)		(34)
Amortization of prior-service cost	0	0		0
Amortization of net actuarial loss	13	15		12
Net periodic benefit (income) cost	(1)	(5)		(3)
Settlement expense	0	0		0
Total net periodic benefit cost (income)	$ (1)	$ (5)		$ (3)

Employee Benefits - Weighted-av

Employee Benefits - Weighted-average assumptions used to determine future benefit obligations (Details) - Pension Plan	Dec. 31, 2022	Dec. 31, 2021
U.S. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.82%	2.23%
U.S. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	5.03%	2.80%
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.89%	1.96%
Underlying price inflation	2.44%	2.52%
U.K. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.59%	3.62%
U.K. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.09%	4.12%
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Underlying price inflation	2%	2%
Other | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.23%	1%
Rate of compensation increase	1%	1%
Other | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	5.19%	2.97%
Rate of compensation increase	3%	3%

Employee Benefits - Weighted-_2

Employee Benefits - Weighted-average assumptions used to determine the net periodic benefit cost (Details) - Pension Plan	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets, net of administration expenses	5.28%
U.S. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	1.67%	1.12%	2.36%
Expected return on plan assets, net of administration expenses	2.03%	2.65%	3.30%
U.S. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.25%	1.79%	2.76%
Expected return on plan assets, net of administration expenses	5.28%	6.56%	7.04%
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	1.85%	1.20%	1.89%
Expected return on plan assets, net of administration expenses	2.34%	2.04%	2.74%
U.K. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.62%	3.22%	3.24%
U.K. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.12%	3.72%	3.74%
Other | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	0.84%	0.28%	0.74%
Expected return on plan assets, net of administration expenses	1.80%	1.70%	2.10%
Rate of compensation increase	1%	1%	1%
Other | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.58%	2%	2.90%
Expected return on plan assets, net of administration expenses	3.15%	2.65%	3.10%
Rate of compensation increase	3%	3%	3%

Employee Benefits - Expected Re

Employee Benefits - Expected Return on Plan Assets Narrative (Details)	12 Months Ended
	Dec. 31, 2022
Pension Plan | U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets, net of administration expenses	5.28%

Employee Benefits - Schedule _2

Employee Benefits - Schedule of Fair Value of U.S Plan Assets (Details) - Pension Plan - U.S. - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	$ 1,481	$ 2,378	$ 2,276
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	42	93
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	64	86
Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	(6)	19
Equity investments, Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	293	548
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	192	249
Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	149	230
Fixed Income Investments, Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	507	838
Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	113	156
Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	127	159
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	230	371
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	42	93
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	64	86
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity investments, Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	124	192
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed Income Investments, Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	211	306
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	(6)	19
Significant Other Observable Inputs (Level 2) | Equity investments, Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	192	249
Significant Other Observable Inputs (Level 2) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	25	38
Significant Other Observable Inputs (Level 2) | Fixed Income Investments, Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Other Observable Inputs (Level 2) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity investments, Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Fixed Income Investments, Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	0	0
Significant Unobservable Inputs (Level 3) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets	$ 0	$ 0

Employee Benefits - Schedule _3

Employee Benefits - Schedule of Fair Value of U.K. Plan Assets (Details) - Pension Plan - U.K. - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	$ 3,537	$ 6,246	$ 6,652
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,929	3,841
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(548)	(1,640)
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,403	2,305	$ 2,625
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	336	872
Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	336	872
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(548)	(1,640)
Derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Derivatives | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(548)	(1,640)
Derivatives | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Government and agency bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,593	2,969
Government and agency bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,593	2,969
Government and agency bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Government and agency bonds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Annuities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,403	2,305
Annuities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Annuities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Annuities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	1,403	2,305
Fixed Income Investments, Pooled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	139	463
Fixed Income Investments, Pooled Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Fixed Income Investments, Pooled Funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Fixed Income Investments, Pooled Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	97	130
Real estate | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Other Investments, Pooled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	517	1,147
Other Investments, Pooled Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Other Investments, Pooled Funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Other Investments, Pooled Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	$ 0	$ 0

Employee Benefits - Schedule _4

Employee Benefits - Schedule of changes in Level 3 fair value for U.K. Pension Plans (Details) - Pension Plan - U.K. - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Actual return on plan assets:
Balance at the beginning of the period	$ 6,246	$ 6,652
Foreign exchange	(559)	(76)
Balance at the end of the period	3,537	6,246
Significant Unobservable Inputs (Level 3)
Actual return on plan assets:
Balance at the beginning of the period	2,305	2,625
Relating to assets still held at the end of the year	(674)	(286)
Purchases, sales and settlements-net	0	0
Foreign exchange	(228)	(34)
Balance at the end of the period	$ 1,403	$ 2,305

Employee Benefits - Schedule _5

Employee Benefits - Schedule of Fair Value of Other Plan Assets (Details) - Pension Plan - Other - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	$ 1,032	$ 1,430	$ 1,497
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	308	451
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(3)	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	30	29
Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	30	29
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	53	72
Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	53	72
Equity securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	211	316
Equity investments, Pooled funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Equity investments, Pooled funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Government and agency bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	225	350
Government and agency bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	225	350
Government and agency bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Government and agency bonds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(3)
Derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0
Derivatives | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	(3)
Derivatives | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0
Fixed Income Investments, Pooled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	462	597
Fixed Income Investments, Pooled Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Fixed Income Investments, Pooled Funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Fixed Income Investments, Pooled Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	42	55
Alternative investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Alternative investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Alternative investments | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	12	11
Real estate | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate | Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	0	0
Real estate | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, plan assets	$ 0	$ 0

Employee Benefits - Investment

Employee Benefits - Investment Policy and Strategy Narrative (Details)	Dec. 31, 2022
Foreign Plan | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	6%
Foreign Plan | Fixed income investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	86%
Foreign Plan | Other Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	8%
Pension Plan | U.S. | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	30%
Pension Plan | U.S. | Fixed income investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	54%
Pension Plan | U.S. | Other Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	16%

Employee Benefits - Cash Flows

Employee Benefits - Cash Flows Narrative (Details) - Pension Plan $ in Millions	Dec. 31, 2022 USD ($)
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	$ 43
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	4
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	$ 14

Employee Benefits - Estimated F

Employee Benefits - Estimated Future Benefit Payments (Details) - Pension Plan $ in Millions	Dec. 31, 2022 USD ($)
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2023	$ 157
2024	158
2025	158
2026	162
2027	155
2028 - 2032	754
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2023	153
2024	157
2025	161
2026	166
2027	170
2028 - 2032	905
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2023	46
2024	47
2025	49
2026	50
2027	51
2028 - 2032	$ 274

Employee Benefits - Overview of

Employee Benefits - Overview of the accumulated benefit obligation, fair value of plan assets, funded status and net amount recognized for U.S. and Canadian Other Post-Retirement Benefits (Details) - Other Post-Retirement Benefits - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated projected benefit obligation	$ 83	$ 109
Fair value of plan assets	14	17
Funded status	(69)	(92)
Unrecognized prior-service credit	(1)	(1)
Unrecognized loss	(19)	2
Net amount recognized	$ (89)	$ (91)

Employee Benefits - Schedule _6

Employee Benefits - Schedule of Other information related to Company's other post-retirement plan's (Details) - Other Post-Retirement Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost recognized (millions)	$ 3	$ 5	$ 4
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average discount rate used to determine future benefit obligations	4.94%	2.52%	2.10%
Weighted-average discount rate used to determine net periodic benefit costs		1.45%	2.93%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average discount rate used to determine future benefit obligations	5.19%	3.06%	2.58%
Weighted-average discount rate used to determine net periodic benefit costs		2.68%	3.25%

Employee Benefits - U.S. and Ca

Employee Benefits - U.S. and Canadian Other Post-Retirement Benefits Narrative (Details) - Other Post-Retirement Benefits $ in Millions	Dec. 31, 2022 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected amortization of prior service credit, next fiscal year	$ 0.8
Amounts in Accumulated other comprehensive income (loss) expected to be recognized as components of net periodic benefit cost in next fiscal year	0.2
Expected employer contributions during next fiscal year	5
Expected future benefit payments 2023	5
Expected future benefit payments 2028 – 2032	$ 27

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Share-based compensation expense recognized in continuing operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 397	$ 449	$ 312
Tax benefit	83	87	61
Share-based compensation expense, net of tax	314	362	251
Employee share purchase plans and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	12	56	10
Restricted share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	251	204	186
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 134	$ 189	$ 116

Share-Based Compensation Plan_3

Share-Based Compensation Plans - Restricted Share Units Narrative (Details) - Restricted share units (RSUs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 279	$ 253	$ 185
Fair value of RSUs vested during the period	$ 216	$ 189	$ 190
Unamortized deferred compensation	$ 466
Weighted average remaining amortization period (in years)	2 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years

Share-Based Compensation Plan_4

Share-Based Compensation Plans - Summary of the status of the Company's RSUs and PSAs (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restricted share units
Non-vested share awards
Non-vested at beginning of period (in shares)	3,075
Granted (in shares)	1,117
Vested (in shares)	(1,154)
Forfeited (in shares)	(175)
Non-vested at end of period (in shares)	2,863	3,075
Fair Value at Date of Grant
Non-vested at beginning of period (in dollars per share)	$ 203
Granted (in dollars per share)	279	$ 253	$ 185
Vested (in dollars per share)	187
Forfeited (in dollars per share)	219
Non-vested at end of period (in dollars per share)	$ 238	$ 203
Performance-based Awards
Non-vested share awards
Non-vested at beginning of period (in shares)	1,298
Granted (in shares)	300
Vested (in shares)	(444)
Forfeited (in shares)	(18)
Non-vested at end of period (in shares)	1,136	1,298
Fair Value at Date of Grant
Non-vested at beginning of period (in dollars per share)	$ 181
Granted (in dollars per share)	311	$ 225	$ 163,000,000
Vested (in dollars per share)	163
Forfeited (in dollars per share)	217
Non-vested at end of period (in dollars per share)	$ 222	$ 181

Share-Based Compensation Plan_5

Share-Based Compensation Plans - Performance Share Awards Narrative (Details) - Performance-based Awards - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, vesting conditions period (in years)	3 years
Granted (in dollars per share)	$ 311	$ 225	$ 163,000,000
Shares issued (in shares)	888
Fair value of PSAs vested during the period	$ 145	$ 112	$ 121
Unamortized deferred compensation	$ 126
Weighted average remaining amortization period (in years)	1 year 3 months 18 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, actual shares issued, percent	0%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, actual shares issued, percent	200%

Derivatives and Hedging - Narra

Derivatives and Hedging - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	$ 10
Gain (loss) on derivative	$ 4	$ (45)	$ (10)
Gross foreign exchange contracts | Not accounted for as hedges
Derivative [Line Items]
Derivative term of contract	90 days
Gain (loss) on derivative	$ (11)	$ 24	$ (1)
Gross foreign exchange contracts | Not accounted for as hedges | Maximum
Derivative [Line Items]
Derivative term of contract	1 year
Cash Flow Hedging
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period (in years)	2 years

Derivatives and Hedging - Notio

Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Other Current Assets
Derivative [Line Items]
Derivative assets	$ 3	$ 21
Other Noncurrent Assets
Derivative [Line Items]
Derivative assets	9	8
Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	2
Other Noncurrent Liabilities
Derivative [Line Items]
Derivative liabilities	1
Accounted for as hedges | Gross foreign exchange contracts
Derivative [Line Items]
Derivative, Notional Amount	618	629
Derivative assets	12	27
Derivative liabilities	2	0
Not accounted for as hedges
Derivative [Line Items]
Derivative, Notional Amount	930	1,041
Derivative assets	12	29
Derivative liabilities	3	0
Not accounted for as hedges | Gross foreign exchange contracts
Derivative [Line Items]
Derivative, Notional Amount	312	412
Derivative assets	0	2
Derivative liabilities	$ 1	$ 0
Derivative term of contract	90 days

Derivatives and Hedging - Sched

Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
(Loss) gain recognized in Accumulated other comprehensive loss	$ (15)	$ 0	$ 1
Gain (loss) reclassified from accumulated other comprehensive loss, after adoption of ASU 2017-02	2	(2)	(15)
Total revenue
Derivative [Line Items]
Gain (loss) reclassified from accumulated other comprehensive loss, after adoption of ASU 2017-02	2	(3)	(14)
Compensation and benefits
Derivative [Line Items]
Gain (loss) reclassified from accumulated other comprehensive loss, after adoption of ASU 2017-02	0	1	0
Interest expense
Derivative [Line Items]
Gain (loss) reclassified from accumulated other comprehensive loss, after adoption of ASU 2017-02	$ 0	$ 0	$ (1)

Fair Value Measurements and F_3

Fair Value Measurements and Financial Instruments - Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Money market funds
Assets
Money market funds	$ 3,323	$ 2,918
Government bonds
Assets
Other investments	1	1
Gross foreign exchange contracts
Assets
Gross foreign exchange contracts	19	40
Liabilities
Gross foreign exchange contracts	9	11
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets
Money market funds	3,323	2,918
Quoted Prices in Active Markets for Identical Assets (Level 1) | Government bonds
Assets
Other investments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Gross foreign exchange contracts
Assets
Gross foreign exchange contracts	0	0
Liabilities
Gross foreign exchange contracts	0	0
Significant Other Observable Inputs (Level 2) | Money market funds
Assets
Money market funds	0	0
Significant Other Observable Inputs (Level 2) | Government bonds
Assets
Other investments	1	1
Significant Other Observable Inputs (Level 2) | Gross foreign exchange contracts
Assets
Gross foreign exchange contracts	19	40
Liabilities
Gross foreign exchange contracts	9	11
Significant Unobservable Inputs (Level 3) | Money market funds
Assets
Money market funds	0	0
Significant Unobservable Inputs (Level 3) | Government bonds
Assets
Other investments	0	0
Significant Unobservable Inputs (Level 3) | Gross foreign exchange contracts
Assets
Gross foreign exchange contracts	0	0
Liabilities
Gross foreign exchange contracts	$ 0	$ 0

Fair Value Measurements and F_4

Fair Value Measurements and Financial Instruments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Unrealized gain (loss) related to assets and liabilities measured at fair value using unobservable inputs	$ 0	$ 0	$ 0

Fair Value Measurements and F_5

Fair Value Measurements and Financial Instruments - Schedule of Financial Instruments where the Carrying Amounts and Fair Values Differ (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Fair value of assets and liabilities [Line Items]
Long-term debt	$ 9,825	$ 8,228
Carrying Value
Fair value of assets and liabilities [Line Items]
Current portion of long-term debt	350	499
Long-term debt	9,825	8,228
Fair Value | Fair Value, Inputs, Level 2
Fair value of assets and liabilities [Line Items]
Current portion of long-term debt, fair value	347	507
Long term debt, fair value	$ 8,745	$ 9,204

Claims, Lawsuits, and Other Con

Claims, Lawsuits, and Other Contingencies - Legal Narrative (Details) £ in Millions, $ in Millions, $ in Millions			1 Months Ended
	Oct. 03, 2017 USD ($)	Oct. 03, 2017 NZD ($)	Dec. 31, 2022 plaintiff	Apr. 30, 2021 USD ($) plaintiff	Apr. 30, 2021 GBP (£) plaintiff	Aug. 31, 2020 USD ($) plaintiff	Nov. 30, 2019 USD ($) defendant	Nov. 30, 2018 USD ($)	Apr. 27, 2018 USD ($)
Pending Litigation | Aon Hewitt Investment Consulting, Inc.
Loss Contingencies [Line Items]
Investment losses suffered by plaintiff									$ 200
Pending Litigation | Fatal Plain Crash In November2016
Loss Contingencies [Line Items]
Value of damages sought				$ 35	£ 29	$ 844		$ 16
Loss contingency, number of defendants | defendant							3
Damages sought option 1							$ 300
Damages sought option 2							50
Damages sought option 3							$ 25
Loss contingency, number of plaintiffs | plaintiff			43	16	16	43
Settled Litigation | Christchurch City Council
Loss Contingencies [Line Items]
Value of damages sought	$ 202	$ 320

Claims, Lawsuits, and Other C_2

Claims, Lawsuits, and Other Contingencies - Guarantees and Indemnifications Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Maximum potential funding under commitments	$ 173	$ 153

Claims, Lawsuits, and Other C_3

Claims, Lawsuits, and Other Contingencies - Letters of Credit Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 74	$ 75

Claims, Lawsuits, and Other C_4

Claims, Lawsuits, and Other Contingencies - Premium Payments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Maximum potential funding under commitments	$ 173	$ 153

Segment Information - Narrative

Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2022 segment revenue_line performance_metric
Segment Reporting [Abstract]
Number of reportable segments | segment	1
Number of revenue lines | revenue_line	4
Number of performance metrics measured | performance_metric	4

Segment Information - Schedule

Segment Information - Schedule of consolidated non-current assets by geographic area (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	$ 1,300	$ 1,378
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	519	563
Americas other than U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	120	121
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	155	180
Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	9	7
Other Europe, Middle East, & Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	279	293
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including operating lease ROU assets	$ 218	$ 214