Aon (AON) 10-Q 1 May 20 2020 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
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	00-0000000
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		231,084,584
Entity Central Index Key	0000315293
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
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 2.800% Senior Notes due 2021
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 2.800% Senior Notes due 2021
Trading Symbol	AON21
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.000% Senior Notes due 2023
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.000% Senior Notes due 2023
Trading Symbol	AON23
Security Exchange Name	NYSE
Guarantees of Aon plc’s 3.500% Senior Notes due 2024
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 3.500% 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 plc’s 4.250% Senior Notes due 2042
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.250% Senior Notes due 2042
Trading Symbol	AON24
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.450% Senior Notes due 2043
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.450% Senior Notes due 2043
Trading Symbol	AON43
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.600% Senior Notes due 2044
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.600% Senior Notes due 2044
Trading Symbol	AON44
Security Exchange Name	NYSE
Guarantees of Aon plc’s 4.750% Senior Notes due 2045
Entity Information [Line Items]
Title of 12(b) Security	Guarantees of Aon plc’s 4.750% Senior Notes due 2045
Trading Symbol	AON45
Security Exchange Name	NYSE

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue
Total revenue	$ 3,219	$ 3,143
Expenses
Compensation and benefits	1,522	1,584
Information technology	111	117
Premises	73	87
Depreciation of fixed assets	41	40
Amortization of intangible assets	97	97
Other general expenses	342	346
Total operating expenses	2,186	2,271
Operating income	1,033	872
Interest income	2	2
Interest expense	(83)	(72)
Other income (expense)	29	0
Income from continuing operations before income taxes	981	802
Income tax expense	189	126
Net income from continuing operations	792	676
Net income (loss) from discontinued operations	(1)	0
Net income	791	676
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	$ 772	$ 659
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 3.31	$ 2.72
Discontinued operations (in dollars per share)	0	0
Net income (in dollars per share)	3.31	2.72
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	3.29	2.70
Discontinued operations (in dollars per share)	0	0
Net income (in dollars per share)	$ 3.29	$ 2.70
Weighted average ordinary shares outstanding - basic (in shares)	233.2	242.2
Weighted average ordinary shares outstanding - diluted (in shares)	234.5	243.7

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 791	$ 676
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	772	659
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(5)	7
Foreign currency translation adjustments	(397)	133
Postretirement benefit obligation	24	31
Total other comprehensive income (loss)	(378)	171
Less: Other comprehensive income attributable to noncontrolling interests	(2)	2
Total other comprehensive income (loss) attributable to Aon shareholders	(376)	169
Comprehensive income (loss) attributable to Aon shareholders	$ 396	$ 828

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Financial Position - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 690	$ 790
Short-term investments	170	138
Receivables, net	3,554	3,112
Fiduciary assets	12,401	11,834
Other current assets	530	602
Total current assets	17,345	16,476
Goodwill	8,293	8,165
Intangible assets, net	746	783
Fixed assets, net	666	621
Operating lease right-of-use assets	897	929
Deferred tax assets	638	645
Prepaid pension	1,164	1,216
Other non-current assets	533	570
Total assets	30,282	29,405
Current liabilities
Accounts payable and accrued liabilities	1,549	1,939
Short-term debt and current portion of long-term debt	1,884	712
Fiduciary liabilities	12,401	11,834
Other current liabilities	1,277	1,086
Total current liabilities	17,111	15,571
Long-term debt	6,227	6,627
Non-current operating lease liabilities	910	944
Deferred tax liabilities	189	199
Pension, other postretirement, and postemployment liabilities	1,655	1,738
Other non-current liabilities	930	877
Total liabilities	27,022	25,956
Equity
Ordinary shares - $0.01 nominal value Authorized: 750 shares (issued: 2020 - 231.1; 2019 - 232.1)	2	2
Additional paid-in capital	6,121	6,152
Retained earnings	1,455	1,254
Accumulated other comprehensive loss	(4,409)	(4,033)
Total Aon shareholders' equity	3,169	3,375
Noncontrolling interests	91	74
Total equity	3,260	3,449
Total liabilities and equity	$ 30,282	$ 29,405

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Financial Position (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Common stock, nominal or par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	750,000,000	750,000,000
Common stock, issued shares (in shares)	234,100,000	240,100,000

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Ordinary Shares and Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Tax	Non- controlling Interests
Beginning Balance (in shares) at Dec. 31, 2018		240.1
Beginning Balance at Dec. 31, 2018	$ 4,219	$ 5,967	$ 2,093	$ (3,909)	$ 68
Increase (Decrease) in Shareholders' Equity
Net income	676		659		17
Shares issued - employee stock compensation plans (in shares)		1.4
Shares issued - employee stock compensation plans	(96)	$ (96)
Shares purchased (in shares)		(0.6)
Shares purchased	(101)		(101)
Share-based compensation expense	89	$ 89
Dividends to shareholders	(96)		(96)
Net change in fair value of financial instruments	7			7
Net foreign currency translation adjustments	133			131	2
Net postretirement benefit obligation	31			31
Ending Balance (in shares) at Mar. 31, 2019		240.9
Ending Balance at Mar. 31, 2019	$ 4,862	$ 5,960	2,555	(3,740)	87
Beginning Balance (in shares) at Dec. 31, 2019	240.1	232.1
Beginning Balance at Dec. 31, 2019	$ 3,449	$ 6,154	1,254	(4,033)	74
Increase (Decrease) in Shareholders' Equity
Net income	791		772		19
Shares issued - employee stock compensation plans (in shares)		1.2
Shares issued - employee stock compensation plans	(112)	$ (112)
Shares purchased (in shares)		(2.2)
Shares purchased	(463)		(463)
Share-based compensation expense	81	$ 81
Dividends to shareholders	(102)		(102)
Net change in fair value of financial instruments	(5)			(5)
Net foreign currency translation adjustments	(397)			(395)	(2)
Net postretirement benefit obligation	$ 24			24
Ending Balance (in shares) at Mar. 31, 2020	234.1	231.1
Ending Balance at Mar. 31, 2020	$ 3,260	$ 6,123	$ 1,455	$ (4,409)	$ 91

Condensed Consolidated Statem_6

Condensed Consolidated Statement of Shareholders' Equity Unaudited (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Stockholders' Equity [Abstract]
Dividends (in dollars per share)	$ 0.44	$ 400,000

Condensed Consolidated Statem_7

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net income	$ 791	$ 676
Net income (loss) from discontinued operations	(1)	0
Adjustments to reconcile net income to cash provided by operating activities:
(Gain) loss from sales of businesses, net	(25)	(4)
Depreciation of fixed assets	41	40
Amortization and impairment of intangible assets	97	97
Share-based compensation expense	76	89
Deferred income taxes	(6)	(25)
Change in assets and liabilities:
Fiduciary receivables	(808)	(609)
Short-term investments — funds held on behalf of clients	(237)	(541)
Fiduciary liabilities	1,045	1,150
Receivables, net	(543)	(458)
Accounts payable and accrued liabilities	(275)	(454)
Restructuring reserves	(60)	(25)
Current income taxes	141	118
Pension, other postretirement and postemployment liabilities	(41)	(54)
Other assets and liabilities	141	74
Cash provided by operating activities	338	74
Cash flows from investing activities
Proceeds from investments	6	12
Payments for investments	(43)	(14)
Net sales (purchases) of short-term investments — non-fiduciary	(38)	41
Acquisition of businesses, net of cash acquired	(334)	(15)
Sale of businesses, net of cash sold	30	6
Capital expenditures	(59)	(57)
Cash used for investing activities	(438)	(27)
Cash flows from financing activities
Share repurchase	(463)	(100)
Issuance of shares for employee benefit plans	(112)	(98)
Issuance of debt	2,060	871
Repayment of debt	(1,341)	(694)
Cash dividends to shareholders	(102)	(96)
Noncontrolling interests and other financing activities	40	(23)
Cash provided by (used for) financing activities	82	(140)
Effect of exchange rates on cash and cash equivalents	(82)	37
Net increase (decrease) in cash and cash equivalents	(100)	(56)
Cash and cash equivalents at beginning of period	790	656
Cash and cash equivalents at end of period	690	600
Supplemental disclosures:
Interest paid	51	27
Income taxes paid, net of refunds	$ 53	$ 33

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements and Notes thereto (the “Financial Statements”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). The Financial Statements include the accounts of Aon plc and all of its controlled subsidiaries. Intercompany accounts and transactions have been eliminated. The 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. Certain information and disclosures normally included in the Financial Statements prepared in accordance with U.S. GAAP have been condensed or omitted. The Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 , including amendments and additions disclosed on Form 8-K issued April 1, 2020. The results for the three months ended March 31, 2020 are not necessarily indicative of operating results that may be expected for the full year ending December 31, 2020 , particularly in light of the continuing effect of the COVID-19 pandemic. On April 1, 2020, a scheme of arrangement under English law was completed pursuant to which the Class A ordinary shares of Aon plc, a public limited company incorporated under the laws of England and Wales and the publicly traded parent company of the Aon group (“Aon UK”), were cancelled and the holders thereof received, on a one-for-one basis, Class A ordinary shares of Aon plc, an Irish public limited company formerly known as Aon Limited (“Aon Ireland”), as described in the proxy statement filed with the U.S. Securities and Exchange Commission (“SEC”) on December 20, 2019 (the “Ireland Reorganization”). Aon Ireland is a tax resident of Ireland. References in the Financial Statements to “Aon” or the “Company” for time periods prior to April 1, 2020 refer to Aon UK. References in the Financial Statements to “Aon” or the “Company” for time periods on or after April 1, 2020, refer to Aon Ireland. Use of Estimates The preparation of the 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 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, foreign currency exchange rate movements, and, recently, impacts from the COVID-19 pandemic 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 Financial Statements in future periods.

Accounting Principles and Pract

Accounting Principles and Practices	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Accounting Principles and Practices	Accounting Principles and Practices Adoption of New Accounting Standards Cloud Computing Arrangements In August 2018, the Financial Accounting Standards Board (“FASB”) issued new accounting guidance on implementation costs incurred in a cloud computing arrangement that is a service contract. The new guidance aligns capitalization requirements for certain implementation costs incurred in cloud computing arrangements with existing requirements for capitalizing implementation costs for internal-use software. These costs will be deferred over the term of the hosting arrangement, including any optional renewal periods the entity is reasonably certain to exercise. An entity may apply the new guidance on either a prospective or retrospective basis. The new guidance was effective for Aon in the first quarter of 2020 and was adopted on a prospective basis for all implementation costs incurred after the date of initial adoption. The adoption of this guidance had no significant impact on the Financial Statements. Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued new accounting guidance on simplifying the test for goodwill impairment. Currently the standard requires an entity to perform a two-step test to determine the amount, if any, of goodwill impairment. In Step 1, an entity compares the fair value of a reporting unit with its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the entity performs Step 2 and compares the implied fair value of goodwill with the carrying amount of that goodwill for that reporting unit. An impairment charge equal to the amount by which the carrying amount of goodwill for the reporting unit exceeds the implied fair value of that goodwill is recorded, limited to the amount of goodwill allocated to that reporting unit. The new guidance removes Step 2. An entity will apply a one-step quantitative test and record the amount of goodwill impairment as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment of goodwill impairment. The new guidance was effective for Aon in the first quarter of 2020 and was adopted on a prospective basis. The adoption of this guidance had no significant impact on the Financial Statements. Credit Losses In June 2016, the FASB issued a new accounting standard on the measurement of credit losses on financial instruments. The new standard replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The Company adopted the new standard as of January 1, 2020 using the modified retrospective approach. Under this approach, prior periods were not restated. Rather, the cumulative effect of initially applying the new standard was recognized as an adjustment to retained earnings. Upon the adoption of this guidance on January 1, 2020, the Company recognized a cumulative adjustment of $6 million to decrease retained earnings. 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. Accounting Standards Issued But Not Yet Adopted Simplifying the Accounting for Income Taxes In December 2019, the FASB issued new accounting guidance that simplifies the accounting for income taxes by eliminating some exceptions to the general approach in the existing guidance. It also clarifies certain aspects of the existing guidance to promote more consistent application. The new guidance is effective for Aon in the first quarter of 2021, with early adoption permitted. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption. Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued new accounting guidance related to the disclosure requirements for employers that sponsor defined benefit pension and other postretirement benefit plans. The guidance requires sponsors of these plans to provide additional disclosures, including weighted average interest rates used in the entity’s cash balance pension plans and a narrative description of reasons for any significant gains or losses impacting the benefit obligation for the period, and eliminates certain previous disclosure requirements. The new guidance is effective for Aon in the first quarter of 2021, with early adoption permitted and will be applied retrospectively. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption. Securities and Exchange Commission Final Rules Financial Disclosures about Guarantors In March 2020, the SEC passed changes to the disclosure requirements in Rules 3-10 and 3-16 of Regulation S-X to better align those requirements with the needs of investors and to simplify and streamline the disclosure obligations of registrants. The amendments are effective January 4, 2021, with early adoption permitted. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2020
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): Three Months Ended March 31, 2020 2019 Commercial Risk Solutions $ 1,146 $ 1,118 Reinsurance Solutions 848 788 Retirement Solutions 397 420 Health Solutions 502 486 Data & Analytic Services 331 336 Elimination (5 ) (5 ) Total revenue $ 3,219 $ 3,143 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): Three Months Ended March 31, 2020 2019 United States $ 1,227 $ 1,161 Americas other than United States 228 226 United Kingdom 500 452 Europe, Middle East, & Africa other than United Kingdom 978 1,009 Asia Pacific 286 295 Total revenue $ 3,219 $ 3,143 Contract Costs An analysis of the changes in the net carrying amount of costs to fulfill contracts with customers are as follows (in millions): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 335 $ 329 Additions 318 346 Amortization (416 ) (439 ) Impairment — — Foreign currency translation and other (8 ) — Balance at end of period $ 229 $ 236 An analysis of the changes in the net carrying amount of costs to obtain contracts with customers are as follows (in millions): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 171 $ 156 Additions 12 9 Amortization (12 ) (11 ) Impairment — — Foreign currency translation and other (4 ) 1 Balance at end of period $ 167 $ 155

Cash and Cash Equivalents and S

Cash and Cash Equivalents and Short-term Investments	3 Months Ended
	Mar. 31, 2020
Cash, Cash Equivalents, and Short-term Investments [Abstract]
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 instruments with initial maturities of three months or less. Short-term investments consist of money market funds. The estimated fair value of cash and cash equivalents and short-term investments approximates their carrying values. At March 31, 2020 , Cash and cash equivalents and Short-term investments were $860 million compared to $928 million at December 31, 2019 , a decrease of $68 million . Of the total balances, $95 million and $110 million were restricted as to their use at March 31, 2020 and December 31, 2019 , respectively. Included within Short-term investments as of March 31, 2020 and December 31, 2019 were £42.7 million ( $52.1 million at March 31, 2020 exchange rates and $55.5 million at December 31, 2019 exchange rates) of operating funds required to be held by the Company in the United Kingdom (the “U.K.”) by the Financial Conduct Authority (the “FCA”), a U.K.-based regulator.

Other Financial Data

Other Financial Data	3 Months Ended
	Mar. 31, 2020
Other Financial Data [Abstract]
Other Financial Data	Other Financial Data Condensed Consolidated Statements of Income Information Other Income (Expense) Other income (expense) consists of the following (in millions): Three Months Ended March 31, 2020 2019 Foreign currency remeasurement $ 42 $ (11 ) Disposal of businesses 25 5 Pension and other postretirement 4 4 Equity earnings 1 1 Financial instruments (44 ) 1 Other 1 — Total $ 29 $ — Condensed Consolidated Statements of Financial Position Information Allowance for Doubtful Accounts An analysis of the allowance for doubtful accounts is as follows (in millions): Three Months Ended March 31, 2020 (1) 2019 Balance at December 31 $ 70 $ 64 Adoption of new accounting guidance (2) 7 — Balance at January 1 77 64 Provision 9 8 Accounts written off, net of recoveries (8 ) (8 ) Foreign currency translation and other 3 — Balance at end of period $ 81 $ 64 (1) 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. Refer to Note 2 “Accounting Principles and Practices” for further information. (2) The allowance for doubtful accounts resulted in a $7 million charge from the adoption of the new accounting standard on the measurement of credit losses. After tax impacts, this resulted in a $6 million decrease to Retained earnings. Refer to Note 2 “Accounting Principles and Practices” for further information. Other Current Assets The components of Other current assets are as follows (in millions): As of March 31, December 31, Costs to fulfill contracts with customers (1) $ 229 $ 335 Prepaid expenses 156 97 Taxes receivable 79 88 Other (2) 66 82 Total $ 530 $ 602 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) December 31, 2019 includes $4 million previously classified as “Receivables from the Divested Business”. Other Non-Current Assets The components of Other non-current assets are as follows (in millions): As of March 31, December 31, Costs to obtain contracts with customers (1) $ 167 $ 171 Taxes receivable 101 102 Leases 93 100 Investments 52 53 Other 120 144 Total $ 533 $ 570 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. Other Current Liabilities The components of Other current liabilities are as follows (in millions): As of March 31, December 31, Deferred revenue (1) $ 309 $ 270 Leases 200 210 Taxes payable 196 93 Other 572 513 Total $ 1,277 $ 1,086 (1) During the three months ended March 31, 2020 , $117 million was recognized in the Condensed Consolidated Statement of Income. During the 12 months ended December 31, 2019 , $532 million was recognized in the Consolidated Statement of Income. Other Non-Current Liabilities The components of Other non-current liabilities are as follows (in millions): As of March 31, December 31, Taxes payable (1) $ 544 $ 525 Leases 74 76 Deferred revenue 72 62 Compensation and benefits 41 49 Other 199 165 Total $ 930 $ 877 (1) Includes $145 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of March 31, 2020 and December 31, 2019 .

Restructuring

Restructuring	3 Months Ended
	Mar. 31, 2020
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring In 2017, Aon initiated a global restructuring plan (the “Restructuring Plan”) in connection with the sale of the benefits administration and business process outsourcing business (the “Divested Business”). The Restructuring Plan was intended to streamline operations across the organization and deliver greater efficiency, insight, and connectivity. The Company incurred all remaining costs for the Restructuring Plan, and the Restructuring Plan was closed in the fourth quarter of 2019. As such, for the three months ended March 31, 2020, no charges were taken under the Restructuring Plan. For the three months ended March 31, 2019, $91 million of restructuring expenses were charged under the Restructuring Plan. As of December 31, 2019, the remaining liabilities for the Restructuring Plan were $204 million . During the three months ended March 31, 2020, the Company made cash payments of $60 million , and the effect of foreign currency translation and other non-cash activity was $17 million , resulting in restructuring liabilities of $127 million as of March 31, 2020.

Acquisitions and Dispositions o

Acquisitions and Dispositions of Businesses	3 Months Ended
	Mar. 31, 2020
Business Combinations [Abstract]
Acquisitions and Dispositions of Businesses	Acquisitions and Dispositions of Businesses Completed Acquisitions The Company completed five acquisitions during the three months ended March 31, 2020 and one acquisition during the three months ended March 31, 2019 . 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): Consideration Transferred Three Months Ended March 31, 2020 Cash $ 351 Deferred, contingent, and other consideration 35 Aggregate consideration transferred $ 386 Assets acquired Cash and cash equivalents $ 17 Receivables 7 Goodwill 303 Intangible assets 74 Current assets 2 Non-current assets 5 Total assets acquired 408 Liabilities assumed Current liabilities 11 Non-current liabilities 11 Total liabilities assumed 22 Net assets acquired $ 386 The results of operations of these acquisitions are included in the 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. 2020 Acquisitions On January 1, 2020, the Company completed the acquisition of 100% share capital of Apollo Conseil et Courtage, an insurance broker based in France. On January 1, 2020, the Company completed the acquisition of 100% share capital of Assimedia SA, an insurance broker based in Switzerland. On January 1, 2020, the Company completed the acquisition of 100% share capital of TRIUM GmbH Insurance Broker, an insurance broker based in Germany. On January 3, 2020, the Company completed the acquisition of 100% share capital of CoverWallet, Inc., a U.S.-based digital insurance platform for small- and medium-sized businesses. On January 31, 2020, the Company completed the acquisition of 100% share capital of Cytelligence Inc., a Canadian-based cyber security firm that provides incident response advisory, digital forensic expertise, security consulting services, and cyber security training for employees to help organizations respond to cyber security threats and strengthen their security position. 2019 Acquisitions On July 31, 2019, the Company completed the acquisition of 100% share capital of Ovatio Courtage SAS, an insurance broker based in France. On July 31, 2019, the Company completed the acquisition of 100% share capital of Zalba-Caldu Correduria de Seguros, S.A., a Spanish insurance broker. On January 1, 2019, the Company completed the acquisition of 100% share capital of Chapka Assurances SAS, based in France. Completed Dispositions The Company completed one disposition during the three months ended March 31, 2020 . The Company completed one disposition during the three months ended March 31, 2019 . Total pretax gains recognized for the three months ended March 31, 2020 were $25 million . Total pretax gains recognized for the three months ended March 31, 2019 were $5 million . Gains and losses recognized as a result of a disposition are included in Other income (expense) in the Condensed Consolidated Statements of Income. Other Significant Activity On March 9, 2020, Aon and Willis Towers Watson Public Limited Company, an Irish public limited company (“WTW”), entered into a business combination agreement (the “Business Combination Agreement”) with respect to a combination of the parties (the “Combination”). Refer to “Business Combination Agreement” within Management’s Discussion and Analysis of Financial Condition and Results of Operations for further information.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2020
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 three months ended March 31, 2020 are as follows (in millions): Balance as of December 31, 2019 $ 8,165 Goodwill related to current year acquisitions 303 Goodwill related to disposals (3 ) Goodwill related to prior year acquisitions — Foreign currency translation (172 ) Balance as of March 31, 2020 $ 8,293 Other intangible assets by asset class are as follows (in millions): March 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization and Impairment Net Carrying Amount Gross Carrying Amount Accumulated Net Carrying Amount Customer-related and contract-based $ 2,227 $ 1,590 $ 637 $ 2,264 $ 1,600 $ 664 Tradenames 1,026 1,005 21 1,029 956 73 Technology and other 408 320 88 380 334 46 Total $ 3,661 $ 2,915 $ 746 $ 3,673 $ 2,890 $ 783 The estimated future amortization for finite-lived intangible assets as of March 31, 2020 is as follows (in millions): Remainder of 2020 $ 139 2021 136 2022 96 2023 85 2024 69 2025 51 Thereafter 170 Total $ 746

Debt

Debt	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt Notes In March 2020, the Company’s $400 million 2.80% Senior Notes due March 2021 were classified as Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position as the date of maturity is in less than one year. On November 15, 2019, Aon Corporation, a Delaware corporation and a wholly owned subsidiary of the Company, issued $500 million 2.20% Senior Notes due November 2022. The Company used the net proceeds of the offering to pay down a portion of outstanding commercial paper and for general corporate purposes. In September 2019, the Company’s $600 million 5.00% Senior Notes due September 2020 were classified as Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position as the date of maturity is in less than one year. On May 2, 2019, Aon Corporation issued $750 million 3.75% Senior Notes due May 2029. The Company used the net proceeds of the offering to pay down a portion of outstanding commercial paper and for general corporate purposes. Revolving Credit Facilities As of March 31, 2020 , Aon plc had two primary committed credit facilities outstanding: its $900 million multi-currency U.S. credit facility expiring in February 2022 and its $750 million multi-currency U.S. credit facility expiring in October 2023 . Effective February 27, 2020 , the $750 million multi-currency U.S. credit facility was increased by $350 million from the original $400 million . In aggregate, these two facilities provide $1.65 billion in available credit. 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 earnings before interest, taxes, depreciation, and amortization (“EBITDA”) to consolidated interest expense and consolidated debt to adjusted consolidated EBITDA, in each case, tested quarterly. At March 31, 2020 , 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 12 months ended March 31, 2020 . Commercial Paper Aon Corporation has established a U.S. commercial paper program (the “U.S. Program”) and Aon UK has established a European multi-currency commercial paper program (the “European Program” and, together with the U.S. Program, the “Commercial Paper Programs”). Commercial paper may be issued in aggregate principal amounts of up to $600 million under the U.S. Program and €525 million under the European Program, not to exceed the amount of the Company’s committed credit, which was $1.65 billion at March 31, 2020 . As of March 31, 2020 , the U.S. Program was fully and unconditionally guaranteed by Aon UK and the European Program was fully and unconditionally guaranteed by Aon Corporation. In connection with the Ireland Reorganization, on April 1, 2020, a new guarantee structure for the Commercial Paper Programs was established. Refer to Note 18 “Guarantee of Registered Securities” for further information. Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position, is as follows (in millions): As of March 31, 2020 December 31, 2019 Commercial paper outstanding $ 833 $ 112 The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Three Months Ended March 31, 2020 2019 Weighted average commercial paper outstanding $ 456 $ 323 Weighted average interest rate of commercial paper outstanding 0.96 % 0.49 %

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate on Net income from continuing operations was 19.3% for the three months ended March 31, 2020 . The effective tax rate on Net income from continuing operations was 15.7% for the three months ended March 31, 2019 . For the three months ended March 31, 2020 , the tax rate was primarily driven by the geographical distribution of income and certain discrete items, primarily the favorable impact of share-based payments. For the three months ended March 31, 2019 , the tax rate was primarily driven by the geographical distribution of income and certain discrete items, primarily the favorable impact of shared-based payments.

Shareholders' Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity Ordinary Shares Aon has a share repurchase program authorized by the Company’s Board of Directors (the “Repurchase Program”). 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 and June 2017 for a total of $15.0 billion in repurchase authorizations. The Repurchase Program was adopted by Aon Ireland’s Board of Directors on April 1, 2020. 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): Three Months Ended March 31, 2020 2019 Shares repurchased 2.2 0.6 Average price per share $ 212.78 $ 161.16 Costs recorded to retained earnings Total repurchase cost $ 461 $ 100 Additional associated costs 2 1 Total costs recorded to retained earnings $ 463 $ 101 At March 31, 2020 , the remaining authorized amount for share repurchases under the Repurchase Program was $1.6 billion . Under the Repurchase Program, the Company has repurchased a total of 130.9 million shares for an aggregate cost of approximately $13.4 billion . Due to COVID-19, the Company has temporarily suspended share repurchase. Net Income Per Share Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended March 31, 2020 2019 Basic weighted average ordinary shares outstanding 233.2 242.2 Dilutive effect of potentially issuable shares 1.3 1.5 Diluted weighted average ordinary shares outstanding 234.5 243.7 Potentially issuable shares are not included in the computation of Diluted net income per share if their inclusion would be antidilutive. There were no shares and 0.1 million shares excluded from the calculation for the three months ended March 31, 2020 and March 31, 2019 , respectively. 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, net (9 ) (395 ) 1 (403 ) Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 5 — 30 35 Tax expense (1 ) — (7 ) (8 ) Amounts reclassified from accumulated other comprehensive income, net (3) 4 — 23 27 Net current period other comprehensive income (loss) (5 ) (395 ) 24 (376 ) Balance at March 31, 2020 $ (17 ) $ (1,700 ) $ (2,692 ) $ (4,409 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the Condensed Consolidated Statements of Income. Refer to Note 14 “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 Condensed Consolidated Statements of Income. (3) It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach. Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Postretirement Benefit Obligation (2) Total Balance at December 31, 2018 $ (15 ) $ (1,319 ) $ (2,575 ) $ (3,909 ) Other comprehensive income before reclassifications, net 4 131 11 146 Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 5 — 26 31 Tax expense (2 ) — (6 ) (8 ) Amounts reclassified from accumulated other comprehensive income, net (3) 3 — 20 23 Net current period other comprehensive income 7 131 31 169 Balance at March 31, 2019 $ (8 ) $ (1,188 ) $ (2,544 ) $ (3,740 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the Condensed Consolidated Statements of Income. Refer to Note 14 “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 Condensed Consolidated Statements of Income. (3) It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach.

Employee Benefits

Employee Benefits	3 Months Ended
	Mar. 31, 2020
Retirement Benefits [Abstract]
Employee Benefits	Employee Benefits The following table provides the components of the net periodic (benefit) cost recognized in the Condensed Consolidated Statements of Income for Aon’s significant U.K., U.S., and other major pension plans, which are located in the Netherlands and Canada. Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): Three Months Ended March 31, U.K. U.S. Other 2020 2019 2020 2019 2020 2019 Service cost $ — $ — $ — $ — $ — $ — Interest cost 22 28 21 27 4 7 Expected return on plan assets, net of administration expenses (39 ) (49 ) (33 ) (34 ) (8 ) (10 ) Amortization of prior-service cost — 1 — 1 — — Amortization of net actuarial loss 7 7 17 13 3 3 Total net periodic (benefit) cost $ (10 ) $ (13 ) $ 5 $ 7 $ (1 ) $ — Contributions Assuming no additional contributions are agreed to with, or required by, the pension plan trustees, the Company expects to make total cash contributions of approximately $5 million , $99 million , and $19 million , (at December 31, 2019 exchange rates) to its significant U.K., U.S., and other major pension plans, respectively, during 2020. The following table summarizes contributions made to the Company’s significant pension plans (in millions): Three Months Ended March 31, 2020 2019 Contributions to U.K. pension plans $ 2 $ 23 Contributions to U.S. pension plans 31 17 Contributions to other major pension plans 2 7 Total contributions $ 35 $ 47

Share-Based Compensation Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The following table summarizes share-based compensation expense recognized in the Condensed Consolidated Statements of Income in Compensation and benefits (in millions): Three Months Ended March 31, 2020 2019 Restricted share units (“RSUs”) $ 58 $ 63 Performance share awards (“PSAs”) 14 23 Employee share purchase plans 4 3 Total share-based compensation expense $ 76 $ 89 Restricted Share Units RSUs generally vest between three and five years . The fair value of RSUs is based upon the market value of the Company’s Class A ordinary shares at the date of grant. With certain limited exceptions, any break in continuous employment will cause the forfeiture of all non-vested awards. Compensation expense associated with RSUs is recognized on a straight-line basis over the requisite service period. Dividend equivalents are paid on certain RSUs, based on the initial grant amount. The following table summarizes the status of the Company’s RSUs (shares in thousands, except fair value): Three Months Ended March 31, 2020 2019 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 3,634 $ 143 4,208 $ 120 Granted 432 $ 179 517 $ 170 Vested (583 ) $ 141 (677 ) $ 117 Forfeited (79 ) $ 146 (41 ) $ 121 Non-vested at end of period 3,403 $ 147 4,007 $ 127 (1) Represents per share weighted average fair value of award at date of grant. Unamortized deferred compensation expense amounted to $359 million as of March 31, 2020 , with a remaining weighted average amortization period of approximately two years . Performance Share Awards The vesting of PSAs is contingent upon meeting a cumulative level of 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. 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 Condensed Consolidated Statements of Income, if necessary. Dividend equivalents are not paid on PSAs. The following table summarizes the Company’s target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the three months ended March 31, 2020 and the years ended December 31, 2019 and 2018 , respectively (shares in thousands and dollars in millions, except fair value): March 31, December 31, December 31, Target PSAs granted during period 487 467 564 Weighted average fair value per share at date of grant $ 160 $ 165 $ 134 Number of shares that would be issued based on current performance levels 487 451 818 Unamortized expense, based on current performance levels $ 78 $ 42 $ 24

Derivatives and Hedging

Derivatives and Hedging	3 Months Ended
	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging	Derivatives and Hedging The 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, and 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 Condensed 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 30 -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 Condensed 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 (2) March 31, December 31, March 31, December 31, March 31, December 31, Foreign exchange contracts Accounted for as hedges $ 537 $ 579 $ 8 $ 16 $ (3 ) $ 1 Not accounted for as hedges (3) 385 297 4 2 (1 ) — Total $ 922 $ 876 $ 12 $ 18 $ (4 ) $ 1 (1) Included within Other current assets ( $7 million at March 31, 2020 and $7 million at December 31, 2019 ) or Other non-current assets ( $5 million at March 31, 2020 and $11 million at December 31, 2019 ). (2) Included within Other current liabilities ( $3 million at March 31, 2020 and $1 million at December 31, 2019 ) or Other non-current liabilities ( $1 million at March 31, 2020 and $0 million at December 31, 2019 ). (3) These contracts typically are for 30 -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 Condensed Consolidated Financial Statements are as follows (in millions): Three Months Ended March 31, 2020 2019 (Loss) Gain recognized in Accumulated other comprehensive loss $ (11 ) $ 4 The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss in the Condensed Consolidated Statements of Income are as follows (in millions): Three Months Ended March 31, 2020 2019 Total revenue $ (4 ) $ (4 ) Interest expense (1 ) (1 ) Total $ (5 ) $ (5 ) The Company estimates that approximately $14 million of pretax losses currently included within Accumulated other comprehensive loss will be reclassified into earnings in the next 12 months. The Company recorded a loss of $35 million and a gain of $5 million in Other income (expense) during the three months ended March 31, 2020 and March 31, 2019, respectively, for foreign exchange derivatives not designated or qualifying as hedges. Net Investments in Foreign Operations Risk Management The Company uses non-derivative financial instruments to protect the value of its investments in a number of foreign subsidiaries. The Company has designated a portion of its euro-denominated commercial paper issuances as a non-derivative hedge of the foreign currency exposure of a net investment in its European operations. The change in fair value of the designated portion of the euro-denominated commercial paper due to changes in foreign currency exchange rates is recorded in Foreign currency translation adjustment, a component of Accumulated other comprehensive loss, to the extent it is effective as a hedge. The foreign currency translation adjustment of the hedged net investments is also recorded in Accumulated other comprehensive loss. Ineffective portions of net investment hedges, if any, are reclassified from Accumulated other comprehensive loss into earnings during the period of change. The Company had €101 million ( $112 million at March 31, 2020 exchange rates) and € 101 million ( $112 million at December 31, 2019 exchange rates) of outstanding euro-denominated commercial paper at March 31, 2020 and December 31, 2019, respectively, designated as a hedge of the foreign currency exposure of its net investment in its European operations. The unrealized gain recognized in Accumulated other comprehensive loss related to the net investment non-derivative hedging instrument was $30 million and $29 million , as of March 31, 2020 and December 31, 2019, respectively. The Company did not reclassify any deferred gains or losses related to net investment hedges from Accumulated other comprehensive loss to earnings during the three months ended March 31, 2020

Fair Value Measurements and Fin

Fair Value Measurements and Financial Instruments	3 Months Ended
	Mar. 31, 2020
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: 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. 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 discounted cash flow 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 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 volatilities. 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 discounted cash flow 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 March 31, 2020 and December 31, 2019 (in millions): Fair Value Measurements Using Balance at March 31, 2020 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds (1) $ 2,252 $ 2,252 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 13 $ — $ 13 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 5 $ — $ 5 $ — Fair Value Measurements Using Balance at December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds (1) $ 2,007 $ 2,007 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities 0 Derivatives (2) Gross foreign exchange contracts $ 4 $ — $ 4 $ — (1) Included within Fiduciary assets or Short-term investments in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 14 “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 in the three months ended March 31, 2020 and 2019 . The Company recognized no realized or unrealized gains or losses in the Condensed Consolidated Statements of Income during the three months ended March 31, 2020 and 2019 related to assets and liabilities measured at fair value using unobservable inputs. 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): March 31, 2020 December 31, 2019 Carrying Value Fair Value Carrying Value Fair Value Current portion of long-term debt $ 999 $ 1,004 $ 600 $ 614 Long-term debt $ 6,227 $ 6,837 $ 6,627 $ 7,442

Claims, Lawsuits and Other Cont

Claims, Lawsuits and Other Contingencies	3 Months Ended
	Mar. 31, 2020
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 errors and omissions (“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 Condensed Consolidated Statements of Financial Position and have been recognized in Other general expense in the Condensed 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 has included in the current matters described below certain matters in which (1) loss is probable, (2) loss is reasonably possible (that is, more than remote but not probable), or (3) there exists the reasonable possibility of loss greater than the accrued amount. In addition, the Company may from time to time disclose matters for which the probability of loss could be remote but the claim amounts associated with such matters are potentially significant. The reasonably possible range of loss for the matters described below for which loss is estimable, in excess of amounts that are deemed probable and estimable and therefore already accrued, is estimated to be between $0 and $0.1 billion , exclusive of any insurance coverage. These estimates are based on available information as of the date of this filing. As available information changes, the matters for which Aon is able to estimate, and the estimates themselves, may change. In addition, many estimates involve significant judgment and uncertainty. For example, at the time of making an estimate, Aon may only have limited information about the facts underlying the claim, and predictions and assumptions about future court rulings and outcomes may prove to be inaccurate. Although management at present believes that the ultimate outcome of all matters described below, 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 On October 3, 2017, Christchurch City Council (“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 claims damages of approximately NZD 528 million ( $315 million at March 31, 2020 exchange rates) plus interest and costs. Aon believes that it has meritorious defenses and intends to vigorously defend itself against these claims. A retail insurance brokerage subsidiary of Aon was sued on September 6, 2018 in the United States District Court for the Southern District of New York by a client, Pilkington North America, Inc., that sustained damage from a tornado to its Ottawa, Illinois property. The lawsuit seeks between $45 million and $85 million in property and business interruption damages from either its insurer or Aon. The insurer contends that insurance proceeds were limited to $15 million in coverage by a windstorm sub-limit purportedly contained in the policy procured by Aon for Pilkington. The insurer therefore has tendered $15 million to Pilkington and denied coverage for the remainder of the loss. Pilkington sued the insurer and Aon seeking full coverage for the loss from the insurer or, in the alternative, seeking the same damages against Aon on various theories of professional liability if the court finds that the $15 million sub-limit applies to the claim. Aon believes it has meritorious defenses and intends to vigorously defend itself against these claims. In April 2017, the FCA announced an investigation relating to suspected competition law breaches in the aviation and aerospace broking industry, which, for Aon in 2016, represented less than $100 million in global revenue. The European Commission has now assumed jurisdiction over the investigation in place of the FCA. Other antitrust agencies outside the European Union are also conducting formal or informal investigations regarding these matters. Aon intends to work diligently with all antitrust agencies concerned to ensure they can carry out their work as efficiently as possible. At this time, in light of the uncertainties and many variables involved, Aon cannot estimate the ultimate impact on the Company from these investigations or any related private litigation, nor any damages, penalties, or fines related to them. There can be no assurance that the ultimate resolution of these matters will not have a material adverse effect on the Company’s consolidated financial position, results of operations, or liquidity. 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 See Note 18 “Guarantee of Registered Securities” for information regarding the Company’s guarantees of obligations of its subsidiaries arising under issued and outstanding debt securities. Sale of the Divested Business In connection with the sale of the Divested Business, the Company guaranteed future operating lease commitments related to certain facilities assumed by the Buyer. The Company is obligated to perform under the guarantees if the Divested Business defaults on such leases at any time during the remainder of the lease agreements, which expire on various dates through 2025. As of March 31, 2020 , the undiscounted maximum potential future payments under the lease guarantee is $66 million , with an estimated fair value of $11 million . No cash payments were made in connection to the lease commitments during the three months ended March 31, 2020 . Additionally, the Company is subject to performance guarantee requirements under certain client arrangements that were assumed by the Buyer. Should the Divested Business fail to perform as required by the terms of the arrangements, the Company would be required to fulfill the remaining contract terms, which expire on various dates through 2023. As of March 31, 2020 , the undiscounted maximum potential future payments under the performance guarantees were $139 million , with an estimated fair value of $1 million . No cash payments were made in connection to the performance guarantees during the three months ended March 31, 2020 . 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 letters of credit (“LOCs”). The Company had total LOCs outstanding of approximately $71 million at March 31, 2020 , compared to $73 million at December 31, 2019 . 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 $70 million at March 31, 2020 compared to $110 million at December 31, 2019 .

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information The Company operates as one segment that includes all of Aon’s continuing operations, which as a global professional services firm provides advice and solutions to clients focused on risk, retirement, and health through five revenue lines which make up its principal products and services. The Chief Operating Decision Maker (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, including organic revenue growth, expense discipline, and collaborative behaviors, that maximize value for Aon and its shareholders, regardless of which revenue line it benefits. As Aon operates as one segment, segment profit or loss is consistent with consolidated reporting as disclosed in the Condensed Consolidated Statements of Income. Refer to Note 3 “Revenue from Contracts with Customers” for further information on revenue by principal service line.

Guarantee of Registered Securit

Guarantee of Registered Securities	3 Months Ended
	Mar. 31, 2020
Guarantee of Registered Securities [Abstract]
Guarantee of Registered Securities	Guarantee of Registered Securities In connection with the Company’s 2012 redomestication to the U.K. (the “2012 Redomestication”), the Company on April 2, 2012 entered into various agreements pursuant to which it agreed to guarantee the obligations of its subsidiaries arising under issued and outstanding debt securities. Those agreements included the: (1) Amended and Restated Indenture, dated April 2, 2012, among Aon Corporation, Aon UK, and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”) (amending and restating the Indenture, dated September 10, 2010, between Aon Corporation and the Trustee); (2) Amended and Restated Indenture, dated April 2, 2012, among Aon Corporation, Aon UK and the Trustee (amending and restating the Indenture, dated December 16, 2002, between Aon Corporation and the Trustee); and (3) Amended and Restated Indenture, dated April 2, 2012, among Aon Corporation, Aon UK and the Trustee (amending and restating the Indenture, dated January 13, 1997, between Aon Corporation and the Trustee, as supplemented by the First Supplemental Indenture, dated January 13, 1997). In connection with the Ireland Reorganization, on April 1, 2020 Aon Ireland and Aon Global Holdings Limited, a company incorporated under the laws of England and Wales, 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 UK, including the: 5.00% Notes due September 2020; 2.20% Notes due November 2022; 8.205% Notes due January 2027; 4.50% Senior Notes due December 2028; 3.75% Senior Notes due May 2029; and 6.25% Notes due September 2040 (collectively, the “Aon Corporation Notes). Aon Corporation, Aon UK, and Aon Global Holdings Limited are indirect wholly owned subsidiaries of Aon Ireland. All guarantees of Aon Ireland, Aon UK, and Aon Global Holdings Limited of the Aon Corporation Notes are joint and several as well as full and unconditional. There are no subsidiaries other than those listed above that guarantee the Aon Corporation Notes. In addition, in connection with the Ireland Reorganization, on April 1, 2020 Aon Ireland and Aon Global Holdings Limited entered into various agreements pursuant to which they guaranteed the obligations of Aon UK arising under issued and outstanding debt securities, which were previously guaranteed solely by Aon Corporation, including the: 4.25% Notes due December 2042 exchanged for Aon Corporation’s 8.205% Notes due January 2027; 4.45% Notes due May 2043; 4.00% Notes due November 2023; 2.875% Notes due May 2026; 3.50% Notes due June 2024; 4.60% Notes due June 2044; 4.75% Notes due May 2045; 2.80% Notes due March 2021; and 3.875% Notes due December 2025 (collectively, the “Aon UK Notes”). All guarantees of Aon Ireland, Aon Global Holdings Limited, and Aon Corporation of the Aon UK Notes are joint and several as well as full and unconditional. There are no subsidiaries other than those listed above that guarantee the Aon UK Notes. The Company has reflected these new guarantees in the Condensed Consolidating Statements of Income, Condensed Consolidating Statements of Comprehensive Income, and Condensed Consolidating Statements of Cash Flows for the three months ended March 31, 2020 and 2019, and in the Condensed Consolidating Statements of Financial Position as of March 31, 2020 and December 31, 2019. In 2019, Aon Corporation obtained indirect ownership of subsidiaries that were previously indirectly owned by Aon UK. The financial results of both subsidiaries are included in the Other Non-Guarantor Subsidiaries column of the Condensed Consolidating Financial Statements. Aon Ireland was not part of the Aon group until November 2019, therefore no balances are reflected in the Condensed Consolidating Statement of Income, Condensed Consolidating Statement of Comprehensive Income, and the Condensed Consolidating Statement of Cash Flows for the period ended March 31, 2019. The following tables set forth the Condensed Consolidating Statements of Income and Condensed Consolidating Statements of Comprehensive Income for the three months ended March 31, 2020 and 2019, Condensed Consolidating Statements of Financial Position as of March 31, 2020 and December 31, 2019, and Condensed Consolidating Statements of Cash Flows for the three months ended March 31, 2020 and 2019, in accordance with Rule 3-10 of Regulation S-X. The Condensed Consolidating Financial Information includes the accounts of Aon Ireland, the accounts of Aon UK, the accounts of Aon Global Holdings Limited, the accounts of Aon Corporation, and the combined accounts of the Other Non-Guarantor Subsidiaries. The Condensed Consolidating Financial Statements are presented in all periods as a merger under common control. The principal consolidating adjustments are to eliminate the investment in subsidiaries and intercompany balances and transactions. Condensed Consolidating Statement of Income Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ — $ — $ 3,219 $ — $ 3,219 Expenses Compensation and benefits — 12 — (12 ) 1,522 — 1,522 Information technology — — — — 111 — 111 Premises — — — 5 68 — 73 Depreciation of fixed assets — — — — 41 — 41 Amortization and impairment of intangible assets — — — — 97 — 97 Other general expense — 26 — 1 315 — 342 Total operating expenses — 38 — (6 ) 2,154 — 2,186 Operating income (loss) — (38 ) — 6 1,065 — 1,033 Interest income — — — 10 14 (22 ) 2 Interest expense — (54 ) (11 ) (39 ) (1 ) 22 (83 ) Intercompany interest income (expense) — 8 — (113 ) 105 — — Intercompany other income (expense) — 81 — (128 ) 47 — — Other income (expense) — — — (42 ) 72 (1 ) 29 Income (loss) from continuing operations before income taxes — (3 ) (11 ) (306 ) 1,302 (1 ) 981 Income tax expense (benefit) — (17 ) (2 ) (48 ) 256 — 189 Net income (loss) from continuing operations — 14 (9 ) (258 ) 1,046 (1 ) 792 Net income (loss) from discontinued operations — — — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries — 14 (9 ) (258 ) 1,045 (1 ) 791 Equity in earnings of subsidiaries 773 759 614 862 — (3,008 ) — Net income 773 773 605 604 1,045 (3,009 ) 791 Less: Net income attributable to noncontrolling interests — — — — 19 — 19 Net income attributable to Aon shareholders $ 773 $ 773 $ 605 $ 604 $ 1,026 $ (3,009 ) $ 772 Condensed Consolidating Statement of Income Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ — $ — $ 3,143 $ — $ 3,143 Expenses Compensation and benefits — 20 — 8 1,556 — 1,584 Information technology — — — — 117 — 117 Premises — — — 4 83 — 87 Depreciation of fixed assets — — — — 40 — 40 Amortization and impairment of intangible assets — — — — 97 — 97 Other general expense — — — 1 345 — 346 Total operating expenses — 20 — 13 2,238 — 2,271 Operating income (loss) — (20 ) — (13 ) 905 — 872 Interest income — — — 9 20 (27 ) 2 Interest expense — (46 ) (24 ) (28 ) (1 ) 27 (72 ) Intercompany interest income (expense) — 4 — (116 ) 112 — — Intercompany other income (expense) — 31 — (94 ) 63 — — Other income (expense) — 5 — (11 ) 8 (2 ) — Income (loss) from continuing operations before income taxes — (26 ) (24 ) (253 ) 1,107 (2 ) 802 Income tax expense (benefit) — (5 ) (5 ) (42 ) 178 — 126 Net income (loss) from continuing operations — (21 ) (19 ) (211 ) 929 (2 ) 676 Net income (loss) from discontinued operations — — — — — — — Net income (loss) before equity in earnings of subsidiaries — (21 ) (19 ) (211 ) 929 (2 ) 676 Equity in earnings of subsidiaries — 682 619 724 — (2,025 ) — Net income — 661 600 513 929 (2,027 ) 676 Less: Net income attributable to noncontrolling interests — — — — 17 — 17 Net income attributable to Aon shareholders $ — $ 661 $ 600 $ 513 $ 912 $ (2,027 ) $ 659 Condensed Consolidating Statement of Comprehensive Income Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 773 $ 773 $ 605 $ 604 $ 1,045 $ (3,009 ) $ 791 Less: Net income attributable to noncontrolling interests — — — — 19 — 19 Net income attributable to Aon shareholders 773 773 605 604 1,026 (3,009 ) 772 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — — (2 ) (3 ) — (5 ) Foreign currency translation adjustments — — — — (398 ) 1 (397 ) Postretirement benefit obligation — — — 13 11 — 24 Total other comprehensive income (loss) — — — 11 (390 ) 1 (378 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (377 ) (377 ) (370 ) (381 ) — 1,505 — Less: Other comprehensive loss attributable to noncontrolling interests — — — — (2 ) — (2 ) Total other comprehensive income (loss) attributable to Aon shareholders (377 ) (377 ) (370 ) (370 ) (388 ) 1,506 (376 ) Comprehensive income attributable to Aon shareholders $ 396 $ 396 $ 235 $ 234 $ 638 $ (1,503 ) $ 396 Condensed Consolidating Statement of Comprehensive Income Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ — $ 661 $ 600 $ 513 $ 929 $ (2,027 ) $ 676 Less: Net income attributable to noncontrolling interests — — — — 17 — 17 Net income attributable to Aon shareholders — 661 600 513 912 (2,027 ) 659 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — — 2 5 — 7 Foreign currency translation adjustments — — — — 131 2 133 Postretirement benefit obligation — — — 22 9 — 31 Total other comprehensive income (loss) — — — 24 145 2 171 Equity in other comprehensive income (loss) of subsidiaries, net of tax — 167 139 115 — (421 ) — Less: Other comprehensive loss attributable to noncontrolling interests — — — — 2 — 2 Total other comprehensive income (loss) attributable to Aon shareholders — 167 139 139 143 (419 ) 169 Comprehensive income attributable to Aon shareholders $ — $ 828 $ 739 $ 652 $ 1,055 $ (2,446 ) $ 828 Condensed Consolidating Statement of Financial Position As of March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ — $ 36 $ 194 $ 1,698 $ (1,238 ) $ 690 Short-term investments — — — 57 113 — 170 Receivables, net — — — — 3,554 — 3,554 Fiduciary assets — — — — 12,401 — 12,401 Current intercompany receivables — 208 90 2,710 14,875 (17,883 ) — Other current assets — — — 4 526 — 530 Total current assets — 208 126 2,965 33,167 (19,121 ) 17,345 Goodwill — — — — 8,293 — 8,293 Intangible assets, net — — — — 746 — 746 Fixed assets, net — — — — 666 — 666 Operating lease right-of-use assets — — — 103 794 — 897 Deferred tax assets — 89 4 589 150 (194 ) 638 Prepaid pension — — — 7 1,157 — 1,164 Non-current intercompany receivables — 397 — 261 7,044 (7,702 ) — Other non-current assets — — — 25 508 — 533 Investment in subsidiary 3,169 8,650 8,871 19,973 — (40,663 ) — Total assets $ 3,169 $ 9,344 $ 9,001 $ 23,923 $ 52,525 $ (67,680 ) $ 30,282 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ — $ 1,345 $ — $ 49 $ 1,393 $ (1,238 ) $ 1,549 Short-term debt and current portion of long-term debt — 696 — 1,136 52 — 1,884 Fiduciary liabilities — — — — 12,401 — 12,401 Current intercompany payables — 310 61 16,321 1,191 (17,883 ) — Other current liabilities — — — 82 1,195 — 1,277 Total current liabilities — 2,351 61 17,588 16,232 (19,121 ) 17,111 Long-term debt — 3,822 — 2,405 — — 6,227 Non-current operating lease liabilities — — — 136 774 — 910 Deferred tax liabilities — — — — 383 (194 ) 189 Pension, other postretirement, and postemployment liabilities — — — 1,287 368 — 1,655 Non-current intercompany payables — — — 7,210 492 (7,702 ) — Other non-current liabilities — 2 — 115 813 — 930 Total liabilities — 6,175 61 28,741 19,062 (27,017 ) 27,022 Equity Total Aon shareholders’ equity 3,169 3,169 8,940 (4,818 ) 33,372 (40,663 ) 3,169 Noncontrolling interests — — — — 91 — 91 Total equity 3,169 3,169 8,940 (4,818 ) 33,463 (40,663 ) 3,260 Total liabilities and equity $ 3,169 $ 9,344 $ 9,001 $ 23,923 $ 52,525 $ (67,680 ) $ 30,282 Condensed Consolidating Statement of Financial Position As of December 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ — $ — $ 2,271 $ 2,619 $ (4,100 ) $ 790 Short-term investments — — — 28 110 — 138 Receivables, net — — — — 3,112 — 3,112 Fiduciary assets — — — — 11,834 — 11,834 Current intercompany receivables — 246 89 1,214 12,710 (14,259 ) — Other current assets — — — 7 595 — 602 Total current assets — 246 89 3,520 30,980 (18,359 ) 16,476 Goodwill — — — — 8,165 — 8,165 Intangible assets, net — — — — 783 — 783 Fixed assets, net — — — — 621 — 621 Operating lease right-of-use assets — — — 110 819 — 929 Deferred tax assets — 89 4 577 165 (190 ) 645 Prepaid pension — — — 7 1,209 — 1,216 Non-current intercompany receivables — 868 — 261 7,046 (8,175 ) — Other non-current assets — — — 32 538 — 570 Investment in subsidiary 3,375 8,899 12,211 19,470 — (43,955 ) — Total assets $ 3,375 $ 10,102 $ 12,304 $ 23,977 $ 50,326 $ (70,679 ) $ 29,405 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ — $ 2,157 $ 1,994 $ 56 $ 1,832 $ (4,100 ) $ 1,939 Short-term debt and current portion of long-term debt — 112 — 600 — — 712 Fiduciary liabilities — — — — 11,834 — 11,834 Current intercompany payables — 234 61 12,978 986 (14,259 ) — Other current liabilities — — — 80 1,006 — 1,086 Total current liabilities — 2,503 2,055 13,714 15,658 (18,359 ) 15,571 Long-term debt — 4,223 — 2,404 — — 6,627 Non-current operating lease liabilities — — — 143 801 — 944 Deferred tax liabilities — — — — 389 (190 ) 199 Pension, other postretirement, and postemployment liabilities — — — 1,348 390 — 1,738 Non-current intercompany payables — — — 7,212 963 (8,175 ) — Other non-current liabilities — 1 — 113 763 — 877 Total liabilities — 6,727 2,055 24,934 18,964 (26,724 ) 25,956 Equity Total Aon shareholders’ equity 3,375 3,375 10,249 (957 ) 31,288 (43,955 ) 3,375 Noncontrolling interests — — — — 74 — 74 Total equity 3,375 3,375 10,249 (957 ) 31,362 (43,955 ) 3,449 Total liabilities and equity $ 3,375 $ 10,102 $ 12,304 $ 23,977 $ 50,326 $ (70,679 ) $ 29,405 Condensed Consolidating Statement of Cash Flows Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ — $ 1,561 $ 3,648 $ (512 ) $ 852 $ (5,211 ) $ 338 Cash flows from investing activities Proceeds from investments — — — 2 4 — 6 Payments for investments — (450 ) (518 ) (30 ) (13 ) 968 (43 ) Net sales (purchases) of short-term investments - non-fiduciary — — — (28 ) (10 ) — (38 ) Acquisition of businesses, net of cash acquired — — — — (334 ) — (334 ) Sale of businesses, net of cash sold — — — — 30 — 30 Capital expenditures — — — — (59 ) — (59 ) Cash provided by (used for) investing activities — (450 ) (518 ) (56 ) (382 ) 968 (438 ) Cash flows from financing activities Share repurchase — (463 ) — — — — (463 ) Advances from (to) affiliates — (618 ) (3,094 ) (2,044 ) (1,349 ) 7,105 — Issuance of shares for employee benefit plans — (112 ) — — — — (112 ) Issuance of debt — 457 — 1,603 — 2,060 Repayment of debt — (273 ) — (1,068 ) — — (1,341 ) Cash dividends to shareholders — (102 ) — — — — (102 ) Noncontrolling interests and other financing activities — — — — 40 — 40 Cash provided by (used for) financing activities — (1,111 ) (3,094 ) (1,509 ) (1,309 ) 7,105 82 Effect of exchange rate changes on cash and cash equivalents — — — — (82 ) — (82 ) Net increase (decrease) in cash and cash equivalents — — 36 (2,077 ) (921 ) 2,862 (100 ) Cash and cash equivalents at beginning of period — — — 2,271 2,619 (4,100 ) 790 Cash and cash equivalents at end of period $ — $ — $ 36 $ 194 $ 1,698 $ (1,238 ) $ 690 Condensed Consolidating Statement of Cash Flows Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ — $ (11 ) $ 529 $ (34 ) $ 143 $ (553 ) $ 74 Cash flows from investing activities Proceeds from investments — — 72 8 4 (72 ) 12 Payments for investments — — — (9 ) (77 ) 72 (14 ) Net sales (purchases) of short-term investments - non-fiduciary — — — 9 32 — 41 Acquisition of businesses, net of cash acquired — — — — (15 ) — (15 ) Sale of businesses, net of cash sold — — — — 6 — 6 Capital expenditures — (57 ) — (57 ) Cash provided by (used for) investing activities — — 72 8 (107 ) — (27 ) Cash flows from financing activities Share repurchase — (100 ) — — — — (100 ) Advances from (to) affiliates — 305 (601 ) (265 ) (550 ) 1,111 — Issuance of shares for employee benefit plans — (98 ) — — — — (98 ) Issuance of debt — 384 — 485 2 — 871 Repayment of debt — (384 ) — (310 ) — — (694 ) Cash dividends to shareholders — (96 ) — — — — (96 ) Noncontrolling interests and other financing activities — — — — (23 ) — (23 ) Cash provided by (used for) financing activities — 11 (601 ) (90 ) (571 ) 1,111 (140 ) Effect of exchange rate changes on cash and cash equivalents — — — — 37 — 37 Net increase (decrease) in cash and cash equivalents — — — (116 ) (498 ) 558 (56 ) Cash and cash equivalents at beginning of period — — — 862 3,473 (3,679 ) 656 Cash and cash equivalents at end of period $ — $ — $ — $ 746 $ 2,975 $ (3,121 ) $ 600

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Ireland Reorganization On April 1, 2020, a scheme of arrangement under English law was completed pursuant to which the Class A ordinary shares of Aon UK were cancelled and the holders thereof received, on a one -for-one basis, Class A ordinary shares of Aon Ireland, as described in the proxy statement filed with the SEC on December 20, 2019. Equity incentive and compensation plans were assumed by Aon Ireland and amended to provide that those plans will now provide for the award and issuance of Class A ordinary shares of Aon Ireland instead of Class A ordinary shares of Aon UK, on a one -for-one basis. Beginning on April 1, 2020, Aon Ireland’s principal executive office address is Metropolitan Building, James Joyce Street, Dublin 1, Ireland, not 122 Leadenhall Street, London, England. Aon Ireland is a tax resident of Ireland. The Share Repurchase Program, which related to Class A ordinary shares of Aon UK and preceded the Ireland Reorganization, was adopted by Aon Ireland’s Board of Directors. Commercial Paper On April 1, 2020 the Company entered into an agreement increasing the aggregate outstanding borrowings under its U.S. commercial paper program by $300 million , to an aggregate amount equal to $900 million . The U.S. program remains fully backed by Aon’s committed credit facilities. Colleague Compensatory Arrangements On April 24, 2020, due to the COVID-19 pandemic and the resulting economic disruption, the Board of Directors of the Company determined to temporarily reduce the annual base salaries of the Company’s named executive officers and the cash compensation of each of the Company’s non-executive directors. Each of the named executive officers and non-executive directors have agreed to a temporary 50% reduction in his or her cash compensation from May 1, 2020 through December 31, 2020, or until such other date as decided by the Company. Additionally, on April 27, 2020 the Company announced it will apply a temporary salary reduction of up to 20%

Accounting Principles and Pra_2

Accounting Principles and Practices (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited Condensed Consolidated Financial Statements and Notes thereto (the “Financial Statements”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). The Financial Statements include the accounts of Aon plc and all of its controlled subsidiaries. Intercompany accounts and transactions have been eliminated. The 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 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 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, foreign currency exchange rate movements, and, recently, impacts from the COVID-19 pandemic 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 Financial Statements in future periods.
New Accounting Standards	Adoption of New Accounting Standards Cloud Computing Arrangements In August 2018, the Financial Accounting Standards Board (“FASB”) issued new accounting guidance on implementation costs incurred in a cloud computing arrangement that is a service contract. The new guidance aligns capitalization requirements for certain implementation costs incurred in cloud computing arrangements with existing requirements for capitalizing implementation costs for internal-use software. These costs will be deferred over the term of the hosting arrangement, including any optional renewal periods the entity is reasonably certain to exercise. An entity may apply the new guidance on either a prospective or retrospective basis. The new guidance was effective for Aon in the first quarter of 2020 and was adopted on a prospective basis for all implementation costs incurred after the date of initial adoption. The adoption of this guidance had no significant impact on the Financial Statements. Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued new accounting guidance on simplifying the test for goodwill impairment. Currently the standard requires an entity to perform a two-step test to determine the amount, if any, of goodwill impairment. In Step 1, an entity compares the fair value of a reporting unit with its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the entity performs Step 2 and compares the implied fair value of goodwill with the carrying amount of that goodwill for that reporting unit. An impairment charge equal to the amount by which the carrying amount of goodwill for the reporting unit exceeds the implied fair value of that goodwill is recorded, limited to the amount of goodwill allocated to that reporting unit. The new guidance removes Step 2. An entity will apply a one-step quantitative test and record the amount of goodwill impairment as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment of goodwill impairment. The new guidance was effective for Aon in the first quarter of 2020 and was adopted on a prospective basis. The adoption of this guidance had no significant impact on the Financial Statements. Credit Losses In June 2016, the FASB issued a new accounting standard on the measurement of credit losses on financial instruments. The new standard replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The Company adopted the new standard as of January 1, 2020 using the modified retrospective approach. Under this approach, prior periods were not restated. Rather, the cumulative effect of initially applying the new standard was recognized as an adjustment to retained earnings. Upon the adoption of this guidance on January 1, 2020, the Company recognized a cumulative adjustment of $6 million to decrease retained earnings. 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. Accounting Standards Issued But Not Yet Adopted Simplifying the Accounting for Income Taxes In December 2019, the FASB issued new accounting guidance that simplifies the accounting for income taxes by eliminating some exceptions to the general approach in the existing guidance. It also clarifies certain aspects of the existing guidance to promote more consistent application. The new guidance is effective for Aon in the first quarter of 2021, with early adoption permitted. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption. Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued new accounting guidance related to the disclosure requirements for employers that sponsor defined benefit pension and other postretirement benefit plans. The guidance requires sponsors of these plans to provide additional disclosures, including weighted average interest rates used in the entity’s cash balance pension plans and a narrative description of reasons for any significant gains or losses impacting the benefit obligation for the period, and eliminates certain previous disclosure requirements. The new guidance is effective for Aon in the first quarter of 2021, with early adoption permitted and will be applied retrospectively. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption.
Derivatives	The 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, and 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 Condensed 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 30 -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 Condensed Consolidated Statements of Income.
Fair Value Measurement	The following methods and assumptions are used to estimate the fair values of the Company’s financial instruments: 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. 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 discounted cash flow 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 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 volatilities. 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 discounted cash flow analyses based on current borrowing rates for similar types of borrowing arrangements.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table summarizes revenue from contracts with customers by principal service line (in millions): Three Months Ended March 31, 2020 2019 Commercial Risk Solutions $ 1,146 $ 1,118 Reinsurance Solutions 848 788 Retirement Solutions 397 420 Health Solutions 502 486 Data & Analytic Services 331 336 Elimination (5 ) (5 ) Total revenue $ 3,219 $ 3,143 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): Three Months Ended March 31, 2020 2019 United States $ 1,227 $ 1,161 Americas other than United States 228 226 United Kingdom 500 452 Europe, Middle East, & Africa other than United Kingdom 978 1,009 Asia Pacific 286 295 Total revenue $ 3,219 $ 3,143
Capitalized Contract Cost	An analysis of the changes in the net carrying amount of costs to fulfill contracts with customers are as follows (in millions): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 335 $ 329 Additions 318 346 Amortization (416 ) (439 ) Impairment — — Foreign currency translation and other (8 ) — Balance at end of period $ 229 $ 236 An analysis of the changes in the net carrying amount of costs to obtain contracts with customers are as follows (in millions): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 171 $ 156 Additions 12 9 Amortization (12 ) (11 ) Impairment — — Foreign currency translation and other (4 ) 1 Balance at end of period $ 167 $ 155

Other Financial Data (Tables)

Other Financial Data (Tables)	3 Months Ended
	Mar. 31, 2020
Other Financial Data [Abstract]
Schedule of Other Income (Expense)	Other income (expense) consists of the following (in millions): Three Months Ended March 31, 2020 2019 Foreign currency remeasurement $ 42 $ (11 ) Disposal of businesses 25 5 Pension and other postretirement 4 4 Equity earnings 1 1 Financial instruments (44 ) 1 Other 1 — Total $ 29 $ —
Schedule of Allowance for Doubtful Accounts	An analysis of the allowance for doubtful accounts is as follows (in millions): Three Months Ended March 31, 2020 (1) 2019 Balance at December 31 $ 70 $ 64 Adoption of new accounting guidance (2) 7 — Balance at January 1 77 64 Provision 9 8 Accounts written off, net of recoveries (8 ) (8 ) Foreign currency translation and other 3 — Balance at end of period $ 81 $ 64 (1) 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. Refer to Note 2 “Accounting Principles and Practices” for further information. (2) The allowance for doubtful accounts resulted in a $7 million charge from the adoption of the new accounting standard on the measurement of credit losses. After tax impacts, this resulted in a $6 million decrease to Retained earnings. Refer to Note 2 “Accounting Principles and Practices” for further information.
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions): As of March 31, December 31, Costs to fulfill contracts with customers (1) $ 229 $ 335 Prepaid expenses 156 97 Taxes receivable 79 88 Other (2) 66 82 Total $ 530 $ 602 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) December 31, 2019 includes $4 million previously classified as “Receivables from the Divested Business”.
Schedule of Other Non-current Assets	The components of Other non-current assets are as follows (in millions): As of March 31, December 31, Costs to obtain contracts with customers (1) $ 167 $ 171 Taxes receivable 101 102 Leases 93 100 Investments 52 53 Other 120 144 Total $ 533 $ 570 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information.
Schedule of Other Current Liabilities	The components of Other current liabilities are as follows (in millions): As of March 31, December 31, Deferred revenue (1) $ 309 $ 270 Leases 200 210 Taxes payable 196 93 Other 572 513 Total $ 1,277 $ 1,086 (1) During the three months ended March 31, 2020 , $117 million was recognized in the Condensed Consolidated Statement of Income. During the 12 months ended December 31, 2019 , $532 million was recognized in the Consolidated Statement of Income.
Schedule of Other Non-current Liabilities	The components of Other non-current liabilities are as follows (in millions): As of March 31, December 31, Taxes payable (1) $ 544 $ 525 Leases 74 76 Deferred revenue 72 62 Compensation and benefits 41 49 Other 199 165 Total $ 930 $ 877 (1) Includes $145 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of March 31, 2020 and December 31, 2019 .

Acquisitions and Dispositions_2

Acquisitions and Dispositions of Businesses (Tables)	3 Months Ended
	Mar. 31, 2020
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	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): Consideration Transferred Three Months Ended March 31, 2020 Cash $ 351 Deferred, contingent, and other consideration 35 Aggregate consideration transferred $ 386 Assets acquired Cash and cash equivalents $ 17 Receivables 7 Goodwill 303 Intangible assets 74 Current assets 2 Non-current assets 5 Total assets acquired 408 Liabilities assumed Current liabilities 11 Non-current liabilities 11 Total liabilities assumed 22 Net assets acquired $ 386

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2020
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 three months ended March 31, 2020 are as follows (in millions): Balance as of December 31, 2019 $ 8,165 Goodwill related to current year acquisitions 303 Goodwill related to disposals (3 ) Goodwill related to prior year acquisitions — Foreign currency translation (172 ) Balance as of March 31, 2020 $ 8,293
Schedule of Other Intangible Assets by Asset Class	Other intangible assets by asset class are as follows (in millions): March 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization and Impairment Net Carrying Amount Gross Carrying Amount Accumulated Net Carrying Amount Customer-related and contract-based $ 2,227 $ 1,590 $ 637 $ 2,264 $ 1,600 $ 664 Tradenames 1,026 1,005 21 1,029 956 73 Technology and other 408 320 88 380 334 46 Total $ 3,661 $ 2,915 $ 746 $ 3,673 $ 2,890 $ 783
Schedule of Estimated Future Amortization Expense on Intangible Assets	The estimated future amortization for finite-lived intangible assets as of March 31, 2020 is as follows (in millions): Remainder of 2020 $ 139 2021 136 2022 96 2023 85 2024 69 2025 51 Thereafter 170 Total $ 746

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Three Months Ended March 31, 2020 2019 Weighted average commercial paper outstanding $ 456 $ 323 Weighted average interest rate of commercial paper outstanding 0.96 % 0.49 % Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position, is as follows (in millions): As of March 31, 2020 December 31, 2019 Commercial paper outstanding $ 833 $ 112

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Schedule of Share Repurchase Agreements	The following table summarizes the Company’s share repurchase activity (in millions, except per share data): Three Months Ended March 31, 2020 2019 Shares repurchased 2.2 0.6 Average price per share $ 212.78 $ 161.16 Costs recorded to retained earnings Total repurchase cost $ 461 $ 100 Additional associated costs 2 1 Total costs recorded to retained earnings $ 463 $ 101
Schedule of Components of Weighted Average Number of Shares	Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended March 31, 2020 2019 Basic weighted average ordinary shares outstanding 233.2 242.2 Dilutive effect of potentially issuable shares 1.3 1.5 Diluted weighted average ordinary shares outstanding 234.5 243.7
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, net (9 ) (395 ) 1 (403 ) Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 5 — 30 35 Tax expense (1 ) — (7 ) (8 ) Amounts reclassified from accumulated other comprehensive income, net (3) 4 — 23 27 Net current period other comprehensive income (loss) (5 ) (395 ) 24 (376 ) Balance at March 31, 2020 $ (17 ) $ (1,700 ) $ (2,692 ) $ (4,409 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the Condensed Consolidated Statements of Income. Refer to Note 14 “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 Condensed Consolidated Statements of Income. (3) It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach. Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Postretirement Benefit Obligation (2) Total Balance at December 31, 2018 $ (15 ) $ (1,319 ) $ (2,575 ) $ (3,909 ) Other comprehensive income before reclassifications, net 4 131 11 146 Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 5 — 26 31 Tax expense (2 ) — (6 ) (8 ) Amounts reclassified from accumulated other comprehensive income, net (3) 3 — 20 23 Net current period other comprehensive income 7 131 31 169 Balance at March 31, 2019 $ (8 ) $ (1,188 ) $ (2,544 ) $ (3,740 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the Condensed Consolidated Statements of Income. Refer to Note 14 “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 Condensed Consolidated Statements of Income. (3) It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach.

Employee Benefits (Tables)

Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2020
Retirement Benefits [Abstract]
Components of net periodic benefit cost for the pension plans	The following table provides the components of the net periodic (benefit) cost recognized in the Condensed Consolidated Statements of Income for Aon’s significant U.K., U.S., and other major pension plans, which are located in the Netherlands and Canada. Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): Three Months Ended March 31, U.K. U.S. Other 2020 2019 2020 2019 2020 2019 Service cost $ — $ — $ — $ — $ — $ — Interest cost 22 28 21 27 4 7 Expected return on plan assets, net of administration expenses (39 ) (49 ) (33 ) (34 ) (8 ) (10 ) Amortization of prior-service cost — 1 — 1 — — Amortization of net actuarial loss 7 7 17 13 3 3 Total net periodic (benefit) cost $ (10 ) $ (13 ) $ 5 $ 7 $ (1 ) $ —
Schedule of employer's contributions	The following table summarizes contributions made to the Company’s significant pension plans (in millions): Three Months Ended March 31, 2020 2019 Contributions to U.K. pension plans $ 2 $ 23 Contributions to U.S. pension plans 31 17 Contributions to other major pension plans 2 7 Total contributions $ 35 $ 47

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-based compensation expense recognized in continuing operations	The following table summarizes share-based compensation expense recognized in the Condensed Consolidated Statements of Income in Compensation and benefits (in millions): Three Months Ended March 31, 2020 2019 Restricted share units (“RSUs”) $ 58 $ 63 Performance share awards (“PSAs”) 14 23 Employee share purchase plans 4 3 Total share-based compensation expense $ 76 $ 89
Restricted share unit activity	The following table summarizes the status of the Company’s RSUs (shares in thousands, except fair value): Three Months Ended March 31, 2020 2019 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 3,634 $ 143 4,208 $ 120 Granted 432 $ 179 517 $ 170 Vested (583 ) $ 141 (677 ) $ 117 Forfeited (79 ) $ 146 (41 ) $ 121 Non-vested at end of period 3,403 $ 147 4,007 $ 127 (1) Represents per share weighted average fair value of award at date of grant.
Performance-based plans	The following table summarizes the Company’s target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the three months ended March 31, 2020 and the years ended December 31, 2019 and 2018 , respectively (shares in thousands and dollars in millions, except fair value): March 31, December 31, December 31, Target PSAs granted during period 487 467 564 Weighted average fair value per share at date of grant $ 160 $ 165 $ 134 Number of shares that would be issued based on current performance levels 487 451 818 Unamortized expense, based on current performance levels $ 78 $ 42 $ 24

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	3 Months Ended
	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
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 (2) March 31, December 31, March 31, December 31, March 31, December 31, Foreign exchange contracts Accounted for as hedges $ 537 $ 579 $ 8 $ 16 $ (3 ) $ 1 Not accounted for as hedges (3) 385 297 4 2 (1 ) — Total $ 922 $ 876 $ 12 $ 18 $ (4 ) $ 1 (1) Included within Other current assets ( $7 million at March 31, 2020 and $7 million at December 31, 2019 ) or Other non-current assets ( $5 million at March 31, 2020 and $11 million at December 31, 2019 ). (2) Included within Other current liabilities ( $3 million at March 31, 2020 and $1 million at December 31, 2019 ) or Other non-current liabilities ( $1 million at March 31, 2020 and $0 million at December 31, 2019 ). (3) These contracts typically are for 30 -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.
Derivative gains (losses)	The amounts of derivative gains (losses) recognized in the Condensed Consolidated Financial Statements are as follows (in millions): Three Months Ended March 31, 2020 2019 (Loss) Gain recognized in Accumulated other comprehensive loss $ (11 ) $ 4 The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss in the Condensed Consolidated Statements of Income are as follows (in millions): Three Months Ended March 31, 2020 2019 Total revenue $ (4 ) $ (4 ) Interest expense (1 ) (1 ) Total $ (5 ) $ (5 )

Fair Value Measurements and F_2

Fair Value Measurements and Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2020
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 March 31, 2020 and December 31, 2019 (in millions): Fair Value Measurements Using Balance at March 31, 2020 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds (1) $ 2,252 $ 2,252 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 13 $ — $ 13 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 5 $ — $ 5 $ — Fair Value Measurements Using Balance at December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds (1) $ 2,007 $ 2,007 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities 0 Derivatives (2) Gross foreign exchange contracts $ 4 $ — $ 4 $ — (1) Included within Fiduciary assets or Short-term investments in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2)
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): March 31, 2020 December 31, 2019 Carrying Value Fair Value Carrying Value Fair Value Current portion of long-term debt $ 999 $ 1,004 $ 600 $ 614 Long-term debt $ 6,227 $ 6,837 $ 6,627 $ 7,442

Guarantee of Registered Secur_2

Guarantee of Registered Securities (Tables)	3 Months Ended
	Mar. 31, 2020
Guarantee of Registered Securities [Abstract]
Condensed Consolidating Statements of Income	Condensed Consolidating Statement of Income Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ — $ — $ 3,219 $ — $ 3,219 Expenses Compensation and benefits — 12 — (12 ) 1,522 — 1,522 Information technology — — — — 111 — 111 Premises — — — 5 68 — 73 Depreciation of fixed assets — — — — 41 — 41 Amortization and impairment of intangible assets — — — — 97 — 97 Other general expense — 26 — 1 315 — 342 Total operating expenses — 38 — (6 ) 2,154 — 2,186 Operating income (loss) — (38 ) — 6 1,065 — 1,033 Interest income — — — 10 14 (22 ) 2 Interest expense — (54 ) (11 ) (39 ) (1 ) 22 (83 ) Intercompany interest income (expense) — 8 — (113 ) 105 — — Intercompany other income (expense) — 81 — (128 ) 47 — — Other income (expense) — — — (42 ) 72 (1 ) 29 Income (loss) from continuing operations before income taxes — (3 ) (11 ) (306 ) 1,302 (1 ) 981 Income tax expense (benefit) — (17 ) (2 ) (48 ) 256 — 189 Net income (loss) from continuing operations — 14 (9 ) (258 ) 1,046 (1 ) 792 Net income (loss) from discontinued operations — — — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries — 14 (9 ) (258 ) 1,045 (1 ) 791 Equity in earnings of subsidiaries 773 759 614 862 — (3,008 ) — Net income 773 773 605 604 1,045 (3,009 ) 791 Less: Net income attributable to noncontrolling interests — — — — 19 — 19 Net income attributable to Aon shareholders $ 773 $ 773 $ 605 $ 604 $ 1,026 $ (3,009 ) $ 772 Condensed Consolidating Statement of Income Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ — $ — $ 3,143 $ — $ 3,143 Expenses Compensation and benefits — 20 — 8 1,556 — 1,584 Information technology — — — — 117 — 117 Premises — — — 4 83 — 87 Depreciation of fixed assets — — — — 40 — 40 Amortization and impairment of intangible assets — — — — 97 — 97 Other general expense — — — 1 345 — 346 Total operating expenses — 20 — 13 2,238 — 2,271 Operating income (loss) — (20 ) — (13 ) 905 — 872 Interest income — — — 9 20 (27 ) 2 Interest expense — (46 ) (24 ) (28 ) (1 ) 27 (72 ) Intercompany interest income (expense) — 4 — (116 ) 112 — — Intercompany other income (expense) — 31 — (94 ) 63 — — Other income (expense) — 5 — (11 ) 8 (2 ) — Income (loss) from continuing operations before income taxes — (26 ) (24 ) (253 ) 1,107 (2 ) 802 Income tax expense (benefit) — (5 ) (5 ) (42 ) 178 — 126 Net income (loss) from continuing operations — (21 ) (19 ) (211 ) 929 (2 ) 676 Net income (loss) from discontinued operations — — — — — — — Net income (loss) before equity in earnings of subsidiaries — (21 ) (19 ) (211 ) 929 (2 ) 676 Equity in earnings of subsidiaries — 682 619 724 — (2,025 ) — Net income — 661 600 513 929 (2,027 ) 676 Less: Net income attributable to noncontrolling interests — — — — 17 — 17 Net income attributable to Aon shareholders $ — $ 661 $ 600 $ 513 $ 912 $ (2,027 ) $ 659
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statement of Comprehensive Income Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 773 $ 773 $ 605 $ 604 $ 1,045 $ (3,009 ) $ 791 Less: Net income attributable to noncontrolling interests — — — — 19 — 19 Net income attributable to Aon shareholders 773 773 605 604 1,026 (3,009 ) 772 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — — (2 ) (3 ) — (5 ) Foreign currency translation adjustments — — — — (398 ) 1 (397 ) Postretirement benefit obligation — — — 13 11 — 24 Total other comprehensive income (loss) — — — 11 (390 ) 1 (378 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (377 ) (377 ) (370 ) (381 ) — 1,505 — Less: Other comprehensive loss attributable to noncontrolling interests — — — — (2 ) — (2 ) Total other comprehensive income (loss) attributable to Aon shareholders (377 ) (377 ) (370 ) (370 ) (388 ) 1,506 (376 ) Comprehensive income attributable to Aon shareholders $ 396 $ 396 $ 235 $ 234 $ 638 $ (1,503 ) $ 396 Condensed Consolidating Statement of Comprehensive Income Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ — $ 661 $ 600 $ 513 $ 929 $ (2,027 ) $ 676 Less: Net income attributable to noncontrolling interests — — — — 17 — 17 Net income attributable to Aon shareholders — 661 600 513 912 (2,027 ) 659 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — — 2 5 — 7 Foreign currency translation adjustments — — — — 131 2 133 Postretirement benefit obligation — — — 22 9 — 31 Total other comprehensive income (loss) — — — 24 145 2 171 Equity in other comprehensive income (loss) of subsidiaries, net of tax — 167 139 115 — (421 ) — Less: Other comprehensive loss attributable to noncontrolling interests — — — — 2 — 2 Total other comprehensive income (loss) attributable to Aon shareholders — 167 139 139 143 (419 ) 169 Comprehensive income attributable to Aon shareholders $ — $ 828 $ 739 $ 652 $ 1,055 $ (2,446 ) $ 828
Condensed Consolidating Statements of Financial Position	Condensed Consolidating Statement of Financial Position As of March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ — $ 36 $ 194 $ 1,698 $ (1,238 ) $ 690 Short-term investments — — — 57 113 — 170 Receivables, net — — — — 3,554 — 3,554 Fiduciary assets — — — — 12,401 — 12,401 Current intercompany receivables — 208 90 2,710 14,875 (17,883 ) — Other current assets — — — 4 526 — 530 Total current assets — 208 126 2,965 33,167 (19,121 ) 17,345 Goodwill — — — — 8,293 — 8,293 Intangible assets, net — — — — 746 — 746 Fixed assets, net — — — — 666 — 666 Operating lease right-of-use assets — — — 103 794 — 897 Deferred tax assets — 89 4 589 150 (194 ) 638 Prepaid pension — — — 7 1,157 — 1,164 Non-current intercompany receivables — 397 — 261 7,044 (7,702 ) — Other non-current assets — — — 25 508 — 533 Investment in subsidiary 3,169 8,650 8,871 19,973 — (40,663 ) — Total assets $ 3,169 $ 9,344 $ 9,001 $ 23,923 $ 52,525 $ (67,680 ) $ 30,282 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ — $ 1,345 $ — $ 49 $ 1,393 $ (1,238 ) $ 1,549 Short-term debt and current portion of long-term debt — 696 — 1,136 52 — 1,884 Fiduciary liabilities — — — — 12,401 — 12,401 Current intercompany payables — 310 61 16,321 1,191 (17,883 ) — Other current liabilities — — — 82 1,195 — 1,277 Total current liabilities — 2,351 61 17,588 16,232 (19,121 ) 17,111 Long-term debt — 3,822 — 2,405 — — 6,227 Non-current operating lease liabilities — — — 136 774 — 910 Deferred tax liabilities — — — — 383 (194 ) 189 Pension, other postretirement, and postemployment liabilities — — — 1,287 368 — 1,655 Non-current intercompany payables — — — 7,210 492 (7,702 ) — Other non-current liabilities — 2 — 115 813 — 930 Total liabilities — 6,175 61 28,741 19,062 (27,017 ) 27,022 Equity Total Aon shareholders’ equity 3,169 3,169 8,940 (4,818 ) 33,372 (40,663 ) 3,169 Noncontrolling interests — — — — 91 — 91 Total equity 3,169 3,169 8,940 (4,818 ) 33,463 (40,663 ) 3,260 Total liabilities and equity $ 3,169 $ 9,344 $ 9,001 $ 23,923 $ 52,525 $ (67,680 ) $ 30,282 Condensed Consolidating Statement of Financial Position As of December 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ — $ — $ 2,271 $ 2,619 $ (4,100 ) $ 790 Short-term investments — — — 28 110 — 138 Receivables, net — — — — 3,112 — 3,112 Fiduciary assets — — — — 11,834 — 11,834 Current intercompany receivables — 246 89 1,214 12,710 (14,259 ) — Other current assets — — — 7 595 — 602 Total current assets — 246 89 3,520 30,980 (18,359 ) 16,476 Goodwill — — — — 8,165 — 8,165 Intangible assets, net — — — — 783 — 783 Fixed assets, net — — — — 621 — 621 Operating lease right-of-use assets — — — 110 819 — 929 Deferred tax assets — 89 4 577 165 (190 ) 645 Prepaid pension — — — 7 1,209 — 1,216 Non-current intercompany receivables — 868 — 261 7,046 (8,175 ) — Other non-current assets — — — 32 538 — 570 Investment in subsidiary 3,375 8,899 12,211 19,470 — (43,955 ) — Total assets $ 3,375 $ 10,102 $ 12,304 $ 23,977 $ 50,326 $ (70,679 ) $ 29,405 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ — $ 2,157 $ 1,994 $ 56 $ 1,832 $ (4,100 ) $ 1,939 Short-term debt and current portion of long-term debt — 112 — 600 — — 712 Fiduciary liabilities — — — — 11,834 — 11,834 Current intercompany payables — 234 61 12,978 986 (14,259 ) — Other current liabilities — — — 80 1,006 — 1,086 Total current liabilities — 2,503 2,055 13,714 15,658 (18,359 ) 15,571 Long-term debt — 4,223 — 2,404 — — 6,627 Non-current operating lease liabilities — — — 143 801 — 944 Deferred tax liabilities — — — — 389 (190 ) 199 Pension, other postretirement, and postemployment liabilities — — — 1,348 390 — 1,738 Non-current intercompany payables — — — 7,212 963 (8,175 ) — Other non-current liabilities — 1 — 113 763 — 877 Total liabilities — 6,727 2,055 24,934 18,964 (26,724 ) 25,956 Equity Total Aon shareholders’ equity 3,375 3,375 10,249 (957 ) 31,288 (43,955 ) 3,375 Noncontrolling interests — — — — 74 — 74 Total equity 3,375 3,375 10,249 (957 ) 31,362 (43,955 ) 3,449 Total liabilities and equity $ 3,375 $ 10,102 $ 12,304 $ 23,977 $ 50,326 $ (70,679 ) $ 29,405
Condensed Consolidating Statements of Cash Flows	Condensed Consolidating Statement of Cash Flows Three Months Ended March 31, 2020 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ — $ 1,561 $ 3,648 $ (512 ) $ 852 $ (5,211 ) $ 338 Cash flows from investing activities Proceeds from investments — — — 2 4 — 6 Payments for investments — (450 ) (518 ) (30 ) (13 ) 968 (43 ) Net sales (purchases) of short-term investments - non-fiduciary — — — (28 ) (10 ) — (38 ) Acquisition of businesses, net of cash acquired — — — — (334 ) — (334 ) Sale of businesses, net of cash sold — — — — 30 — 30 Capital expenditures — — — — (59 ) — (59 ) Cash provided by (used for) investing activities — (450 ) (518 ) (56 ) (382 ) 968 (438 ) Cash flows from financing activities Share repurchase — (463 ) — — — — (463 ) Advances from (to) affiliates — (618 ) (3,094 ) (2,044 ) (1,349 ) 7,105 — Issuance of shares for employee benefit plans — (112 ) — — — — (112 ) Issuance of debt — 457 — 1,603 — 2,060 Repayment of debt — (273 ) — (1,068 ) — — (1,341 ) Cash dividends to shareholders — (102 ) — — — — (102 ) Noncontrolling interests and other financing activities — — — — 40 — 40 Cash provided by (used for) financing activities — (1,111 ) (3,094 ) (1,509 ) (1,309 ) 7,105 82 Effect of exchange rate changes on cash and cash equivalents — — — — (82 ) — (82 ) Net increase (decrease) in cash and cash equivalents — — 36 (2,077 ) (921 ) 2,862 (100 ) Cash and cash equivalents at beginning of period — — — 2,271 2,619 (4,100 ) 790 Cash and cash equivalents at end of period $ — $ — $ 36 $ 194 $ 1,698 $ (1,238 ) $ 690 Condensed Consolidating Statement of Cash Flows Three Months Ended March 31, 2019 (millions) Aon Ireland Aon UK Aon Global Holdings Limited Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ — $ (11 ) $ 529 $ (34 ) $ 143 $ (553 ) $ 74 Cash flows from investing activities Proceeds from investments — — 72 8 4 (72 ) 12 Payments for investments — — — (9 ) (77 ) 72 (14 ) Net sales (purchases) of short-term investments - non-fiduciary — — — 9 32 — 41 Acquisition of businesses, net of cash acquired — — — — (15 ) — (15 ) Sale of businesses, net of cash sold — — — — 6 — 6 Capital expenditures — (57 ) — (57 ) Cash provided by (used for) investing activities — — 72 8 (107 ) — (27 ) Cash flows from financing activities Share repurchase — (100 ) — — — — (100 ) Advances from (to) affiliates — 305 (601 ) (265 ) (550 ) 1,111 — Issuance of shares for employee benefit plans — (98 ) — — — — (98 ) Issuance of debt — 384 — 485 2 — 871 Repayment of debt — (384 ) — (310 ) — — (694 ) Cash dividends to shareholders — (96 ) — — — — (96 ) Noncontrolling interests and other financing activities — — — — (23 ) — (23 ) Cash provided by (used for) financing activities — 11 (601 ) (90 ) (571 ) 1,111 (140 ) Effect of exchange rate changes on cash and cash equivalents — — — — 37 — 37 Net increase (decrease) in cash and cash equivalents — — — (116 ) (498 ) 558 (56 ) Cash and cash equivalents at beginning of period — — — 862 3,473 (3,679 ) 656 Cash and cash equivalents at end of period $ — $ — $ — $ 746 $ 2,975 $ (3,121 ) $ 600

Accounting Principles and Pra_3

Accounting Principles and Practices (Details) $ in Millions	Jan. 01, 2020USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment to decrease retained earnings	$ 6
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment to decrease retained earnings	$ 6

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 3,219	$ 3,143
United States
Disaggregation of Revenue [Line Items]
Total revenue	1,227	1,161
Americas other than United States
Disaggregation of Revenue [Line Items]
Total revenue	228	226
United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	500	452
Europe, Middle East, & Africa other than United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	978	1,009
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	286	295
Operating Segments | Commercial Risk Solutions
Disaggregation of Revenue [Line Items]
Total revenue	1,146	1,118
Operating Segments | Reinsurance Solutions
Disaggregation of Revenue [Line Items]
Total revenue	848	788
Operating Segments | Retirement Solutions
Disaggregation of Revenue [Line Items]
Total revenue	397	420
Operating Segments | Health Solutions
Disaggregation of Revenue [Line Items]
Total revenue	502	486
Operating Segments | Data & Analytic Services
Disaggregation of Revenue [Line Items]
Total revenue	331	336
Elimination
Disaggregation of Revenue [Line Items]
Total revenue	$ (5)	$ (5)

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 335	$ 329
Additions	318	346
Amortization	(416)	(439)
Impairment	0	0
Foreign currency translation and other	(8)	0
Balance at end of period	229	236
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	171	156
Additions	12	9
Amortization	(12)	(11)
Impairment	0	0
Foreign currency translation and other	(4)	1
Balance at end of period	$ 167	$ 155

Cash and Cash Equivalents and_2

Cash and Cash Equivalents and Short-term Investments (Details) £ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)	Mar. 31, 2020GBP (£)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents and short-term investments			$ 860	$ 928
Cash and cash equivalents and short term investments, period increase (decrease)	$ (68)
Restricted cash and investments			95	110
Operating funds in U.K.		£ 42.7	$ 52.1	$ 55.5

Other Financial Data - Schedule

Other Financial Data - Schedule of Other Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other (Expense) Income
Foreign currency remeasurement	$ 42	$ (11)
Disposal of businesses	25	5
Pension and other postretirement	4	4
Equity earnings	1	1
Financial instruments	(44)	1
Other	1	0
Total	$ 29	$ 0

Other Financial Data - Schedu_2

Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 70	$ 64
Provision	9	8
Accounts written off, net of recoveries	(8)	(8)
Foreign currency translation and other	3	0
Balance at end of period	81	$ 64
Cumulative Effect, Period Of Adoption, Adjustment
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7
Cumulative Effect, Period Of Adoption, Adjustment | Accounting Standards Update 2016-13
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7
Cumulative Effect, Period Of Adoption, Adjusted Balance
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 77

Other Financial Data - Schedu_3

Other Financial Data - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Financial Data [Abstract]
Cost to fulfill contracts with customers	$ 229	$ 335
Prepaid expenses	156	97
Taxes receivable	79	88
Other	66	82
Total	$ 530	602
Receivables from divested business		$ 4

Other Financial Data - Schedu_4

Other Financial Data - Schedule of Other Non-current Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Financial Data [Abstract]
Cost to obtain contracts with customers	$ 167	$ 171
Taxes receivable	101	102
Leases	93	100
Investments	52	53
Other	120	144
Total	$ 533	$ 570

Other Financial Data - Schedu_5

Other Financial Data - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Other Financial Data [Abstract]
Deferred revenue	$ 309	$ 270
Leases	200	210
Taxes payable	196	93
Other	572	513
Total	1,277	1,086
Revenue recognized from deferred revenue	$ 117	$ 532

Other Financial Data - Schedu_6

Other Financial Data - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Financial Data [Abstract]
Taxes payable	$ 544	$ 525
Leases	74	76
Deferred revenue	72	62
Compensation and benefits	41	49
Other	199	165
Total	930	877
Noncurrent portion of transition tax	$ 145	$ 145

Restructuring (Details)

Restructuring (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Restructuring and Related Activities [Abstract]
Restructuring charges	$ 0	$ 91,000,000
Restructuring liabilities	127,000,000		$ 204,000,000
Cash payments	60,000,000
Foreign currency translation and other non-cash activity	$ 17,000,000

Acquisitions and Dispositions_3

Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)acquisition	Mar. 31, 2019acquisition	Jan. 31, 2020	Jan. 03, 2020	Jan. 01, 2020	Dec. 31, 2019USD ($)	Jul. 31, 2019	Jan. 01, 2019
Business Acquisition [Line Items]
Number of business acquired under business combination | acquisition	5	1
Assets acquired
Goodwill	$ 8,293					$ 8,165
2019 and 2020 acquisitions
Business Combination, Consideration Transferred [Abstract]
Cash	351
Deferred, contingent, and other consideration	35
Aggregate consideration transferred	386
Assets acquired
Cash and cash equivalents	17
Receivables	7
Goodwill	303
Intangible assets	74
Current assets	2
Non-current assets	5
Total assets acquired	408
Liabilities assumed
Current liabilities	11
Other non-current liabilities	11
Total liabilities assumed	22
Net assets acquired	$ 386
Apollo Conseil et Courtage
Liabilities assumed
Percentage of capital acquired					100.00%
Assimedia SA
Liabilities assumed
Percentage of capital acquired					100.00%
TRIUM GmbH Insurance Broker
Liabilities assumed
Percentage of capital acquired					100.00%
CoverWallet, Inc.
Liabilities assumed
Percentage of capital acquired				100.00%
Cytelligence Inc.
Liabilities assumed
Percentage of capital acquired			100.00%
Ovatio Courtage SAS
Liabilities assumed
Percentage of capital acquired							100.00%
Zalba-Caldu Correduria de Seguros, S.A.
Liabilities assumed
Percentage of capital acquired							100.00%
Chapka Assurances SAS
Liabilities assumed
Percentage of capital acquired								100.00%

Acquisitions and Dispositions_4

Acquisitions and Dispositions of Businesses - Dispositions (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)disposal	Mar. 31, 2019USD ($)disposal
Dispositions
Pretax gains (losses) recognized on disposal of businesses | $	$ 25	$ 5
Disposal Group, Not Discontinued Operations
Dispositions
Number of dispositions | disposal	1	1

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Schedule of Goodwill Rollforward (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)
Changes in the net carrying amount of goodwill by operating segment
Beginning balance	$ 8,165
Goodwill related to current year acquisitions	303
Goodwill related to disposals	(3)
Goodwill related to prior year acquisitions	0
Foreign currency translation	(172)
Ending balance	$ 8,293

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Intangible assets with finite lives
Gross Carrying Amount	$ 3,661	$ 3,673
Accumulated Amortization and Impairment	2,915	2,890
Net Carrying Amount	746	783
Estimated amortization for intangible assets
Remainder of 2020	139
2021	136
2022	96
2023	85
2024	69
2025	51
Thereafter	170
Total	746
Customer-related and contract-based
Intangible assets with finite lives
Gross Carrying Amount	2,227	2,264
Accumulated Amortization and Impairment	1,590	1,600
Net Carrying Amount	637	664
Tradenames
Intangible assets with finite lives
Gross Carrying Amount	1,026	1,029
Accumulated Amortization and Impairment	1,005	956
Net Carrying Amount	21	73
Technology and other
Intangible assets with finite lives
Gross Carrying Amount	408	380
Accumulated Amortization and Impairment	320	334
Net Carrying Amount	$ 88	$ 46

Debt - Narrative (Details)

Debt - Narrative (Details)	Mar. 31, 2020EUR (€)credit_facility	Mar. 31, 2020USD ($)credit_facility	Feb. 27, 2020USD ($)	Feb. 26, 2020USD ($)	May 02, 2019USD ($)
Debt Instrument [Line Items]
Number of credit facilities | credit_facility	2	2
Borrowings under credit facilities		$ 0
Line of Credit
Debt Instrument [Line Items]
Line of credit facility, available credit		1,650,000,000
2.80% Senior Notes Due March 2021 | Senior Notes
Debt Instrument [Line Items]
Debt face value		$ 400,000,000
Debt interest rate percentage (as a percent)	2.80%	2.80%
2.20% Senior Notes Due November 2022 | Senior Notes
Debt Instrument [Line Items]
Debt face value					$ 500,000,000
Debt interest rate percentage (as a percent)					2.20%
5.00% Senior Notes Due September 2020
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)	5.00%	5.00%
5.00% Senior Notes Due September 2020 | Senior Notes
Debt Instrument [Line Items]
Debt face value		$ 600,000,000
Debt interest rate percentage (as a percent)	5.00%	5.00%
3.75% Senior Notes Due May 2, 2029
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)	3.75%	3.75%
3.75% Senior Notes Due May 2, 2029 | Senior Notes
Debt Instrument [Line Items]
Debt face value					$ 750,000,000
Debt interest rate percentage (as a percent)					3.75%
Credit Facility Expiring February 2022 | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 900,000,000
Credit Facility Expiring October 2023 | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		750,000,000	$ 750,000,000	$ 400,000,000
Line of credit facility, increase of maximum borrowing capacity			$ 350,000,000
Commercial paper
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		1,650,000,000
Commercial paper | U.S. Program
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 600,000,000
Commercial paper | European Program
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity | €	€ 525,000,000

Debt - Schedule of Commercial P

Debt - Schedule of Commercial Paper (Details) - Commercial paper - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Commercial paper outstanding	$ 833		$ 112
Weighted average commercial paper outstanding	$ 456	$ 323
Weighted average interest rate of commercial paper outstanding	0.96%	0.49%

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Effective income tax rate	19.30%	15.70%

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Details) - USD ($)	3 Months Ended		96 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Feb. 28, 2017	Nov. 30, 2014	Apr. 30, 2012
Equity, Class of Treasury Stock [Line Items]
Total cost of shares purchased	$ 463,000,000	$ 101,000,000
Number of shares excluded from the calculation of diluted earnings per share (in shares)	0	100,000
2012 - Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization limit (up to)	$ 15,000,000,000		$ 15,000,000,000	$ 5,000,000,000	$ 5,000,000,000	$ 5,000,000,000
Share repurchase, remaining authorization limit (in shares)	$ 1,600,000,000		$ 1,600,000,000
Shares purchased (in shares)	2,200,000	600,000	130,900,000
Total cost of shares purchased	$ 461,000,000	$ 100,000,000	$ 13,400,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		96 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020
Equity, Class of Treasury Stock [Line Items]
Total repurchase cost	$ 463	$ 101
2012 - Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares purchased (in shares)	2.2	0.6	130.9
Average price per share of stock repurchased (in dollars per share)	$ 212.78	$ 161.16
Total repurchase cost	$ 461	$ 100	$ 13,400
Additional associated costs	2	1
Total costs recorded to retained earnings	$ 463	$ 101

Shareholders' Equity - Weighted

Shareholders' Equity - Weighted Average Ordinary Shares Outstanding (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted average shares outstanding
Basic weighted average ordinary shares outstanding (in shares)	233.2	242.2
Dilutive effect of potentially issuable shares (in shares)	1.3	1.5
Diluted weighted average ordinary shares outstanding (in shares)	234.5	243.7

Shareholders' Equity - Accumula

Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 3,449	$ 4,219
Other comprehensive income (loss) before reclassifications, net	(403)	146
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income	35	31
Tax expense	(8)	(8)
Amounts reclassified from accumulated other comprehensive income, net (3)	27	23
Total other comprehensive income (loss) attributable to Aon shareholders	(376)	169
Ending Balance	3,260	4,862
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(4,033)	(3,909)
Amounts reclassified from accumulated other comprehensive income
Ending Balance	(4,409)	(3,740)
Change in Fair Value of Financial Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(12)	(15)
Other comprehensive income (loss) before reclassifications, net	(9)	4
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income	5	5
Tax expense	(1)	(2)
Amounts reclassified from accumulated other comprehensive income, net (3)	4	3
Total other comprehensive income (loss) attributable to Aon shareholders	(5)	7
Ending Balance	(17)	(8)
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(1,305)	(1,319)
Other comprehensive income (loss) before reclassifications, net	(395)	131
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income	0	0
Tax expense	0	0
Amounts reclassified from accumulated other comprehensive income, net (3)	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(395)	131
Ending Balance	(1,700)	(1,188)
Postretirement Benefit Obligation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(2,716)	(2,575)
Other comprehensive income (loss) before reclassifications, net	1	11
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income	30	26
Tax expense	(7)	(6)
Amounts reclassified from accumulated other comprehensive income, net (3)	23	20
Total other comprehensive income (loss) attributable to Aon shareholders	24	31
Ending Balance	$ (2,692)	$ (2,544)

Employee Benefits - Components

Employee Benefits - Components of Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0
Interest cost	21	27
Expected return on plan assets, net of administration expenses	(33)	(34)
Amortization of prior-service cost	0	1
Amortization of net actuarial loss	17	13
Total net periodic (benefit) cost	5	7
U.K.
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	22	28
Expected return on plan assets, net of administration expenses	(39)	(49)
Amortization of prior-service cost	0	1
Amortization of net actuarial loss	7	7
Total net periodic (benefit) cost	(10)	(13)
Other
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	4	7
Expected return on plan assets, net of administration expenses	(8)	(10)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	3	3
Total net periodic (benefit) cost	$ (1)	$ 0

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) $ in Millions	Dec. 31, 2019USD ($)
UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Estimate of contributions to defined benefit pension plans for the current fiscal year	$ 99
U.K.
Defined Benefit Plan Disclosure [Line Items]
Estimate of contributions to defined benefit pension plans for the current fiscal year	5
Other
Defined Benefit Plan Disclosure [Line Items]
Estimate of contributions to defined benefit pension plans for the current fiscal year	$ 19

Employee Benefits - Summary of

Employee Benefits - Summary of Employer Contributions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 35	$ 47
U.S.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	31	17
U.K.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	2	23
Other
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 2	$ 7

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Share-based compensation expenses recognized (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 76	$ 89
Restricted share units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	58	63
Performance share awards (“PSAs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	14	23
Employee share purchase plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 4	$ 3

Share-Based Compensation Plan_3

Share-Based Compensation Plans - Restricted share unit activity (Details) - Restricted share units (“RSUs”) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Non-vested share awards (in shares)
Non-vested at beginning of period (in shares)	3,634	4,208	4,208
Granted (in shares)	432	517
Vested (in shares)	(583)	(677)
Forfeited (in shares)	(79)	(41)
Non-vested at end of period (in shares)	3,403	4,007	3,634
Weighted Average Fair value
Non-vested at beginning of period (in dollars per share)	$ 143	$ 120	$ 120
Granted (in dollars per share)	179	170
Vested (in dollars per share)	141	117
Forfeited (in dollars per share)	146	121
Non-vested at end of period (in dollars per share)	$ 147	$ 127	$ 143
Unamortized deferred compensation expense	$ 359
Remaining weighted-average amortization period (in years)	2 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years

Share-Based Compensation Plan_4

Share-Based Compensation Plans - Performance Share Awards Narrative (Details) - Performance Shares	3 Months Ended
	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting conditions period (in years)	3 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, percent	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, percent	200.00%

Share-Based Compensation Plan_5

Share-Based Compensation Plans - Schedule of Performance-based plans (Details) - Performance Shares - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target PSAs granted during period (in shares)	487	467	564
Weighted average fair value per share at date of grant (in dollars per share)	$ 160	$ 165	$ 134
Number of shares that would be issued based on current performance levels (in shares)	487	451	818
Unamortized expense, based on current performance levels	$ 78	$ 42	$ 24

Derivatives and Hedging - Forei

Derivatives and Hedging - Foreign Exchange Risk Management Narrative (Details) - Foreign exchange contracts	3 Months Ended
	Mar. 31, 2020
Derivative [Line Items]
Term of derivative contract	30 days
Cash Flow Hedging
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period (less than)	2 years
Not Designated as Hedging Instrument
Derivative [Line Items]
Foreign currency exposures, maximum hedging period (up to)	1 year

Derivatives and Hedging - Notio

Derivatives and Hedging - Notional and Fair Values of Derivative Instruments (Details) - Foreign exchange contracts - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value
Notional Amount	$ 922,000,000	$ 876,000,000
Derivative Assets	12,000,000	18,000,000
Derivative Liabilities	$ (4,000,000)	1,000,000
Term of derivative contract	30 days
Other Current Assets
Derivatives, Fair Value
Derivative Assets	$ 7,000,000	7,000,000
Other non-current assets
Derivatives, Fair Value
Derivative Assets	5,000,000	11,000,000
Other current liabilities
Derivatives, Fair Value
Derivative Liabilities	3,000,000	1,000,000
Other non-current liabilities
Derivatives, Fair Value
Derivative Liabilities	1,000,000	0
Derivatives accounted for as hedges
Derivatives, Fair Value
Notional Amount	537,000,000	579,000,000
Derivative Assets	8,000,000	16,000,000
Derivative Liabilities	(3,000,000)	1,000,000
Not Designated as Hedging Instrument
Derivatives, Fair Value
Notional Amount	385,000,000	297,000,000
Derivative Assets	4,000,000	2,000,000
Derivative Liabilities	$ (1,000,000)	$ 0

Derivatives and Hedging - Sched

Derivatives and Hedging - Schedule of Derivative Gains (Losses) Recognized in the Consolidated Financial Statements (Details) - Foreign exchange contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Gain (loss) recognized in Accumulated other comprehensive loss	$ (11)	$ 4
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(5)	(5)
Total revenue
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(4)	(4)
Interest expense
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	$ (1)	$ (1)

Derivatives and Hedging - Inter

Derivatives and Hedging - Interest Rate Management Risk Narrative (Details) - Foreign exchange contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	$ 14
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative gain (loss)	$ (35)	$ 5

Derivatives and Hedging - Net I

Derivatives and Hedging - Net Investments in Foreign Operations Risk Management Narrative (Details) - Net Investment Hedging € in Millions, $ in Millions	Mar. 31, 2020EUR (€)	Mar. 31, 2020USD ($)	Dec. 31, 2019EUR (€)	Dec. 31, 2019USD ($)
Derivatives, Fair Value
European denominated commercial paper	€ 101	$ 112	€ 101	$ 112
Effective portion of loss reclassified from Accumulated OCI		$ 30		$ 29

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	Mar. 31, 2020	Dec. 31, 2019
Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	$ 2,252	$ 2,007
Government bonds
Assets
Other investments	1	1
Equity investments
Assets
Other investments	1	1
Gross foreign exchange contracts
Assets
Derivatives	13	21
Liabilities
Derivatives	5	4
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	2,252	2,007
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) | Equity investments
Assets
Other investments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Gross foreign exchange contracts
Assets
Derivatives	0	0
Liabilities
Derivatives	0	0
Significant Other Observable Inputs (Level 2) | Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	0	0
Significant Other Observable Inputs (Level 2) | Government bonds
Assets
Other investments	1	1
Significant Other Observable Inputs (Level 2) | Equity investments
Assets
Other investments	1	1
Significant Other Observable Inputs (Level 2) | Gross foreign exchange contracts
Assets
Derivatives	13	21
Liabilities
Derivatives	5	4
Significant Unobservable Inputs (Level 3) | Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	0	0
Significant Unobservable Inputs (Level 3) | Government bonds
Assets
Other investments	0	0
Significant Unobservable Inputs (Level 3) | Equity investments
Assets
Other investments	0	0
Significant Unobservable Inputs (Level 3) | Gross foreign exchange contracts
Assets
Derivatives	0	0
Liabilities
Derivatives	$ 0	$ 0

Fair Value Measurements and F_4

Fair Value Measurements and Financial Instruments - Schedule of financial instruments where the carrying amounts and fair values differ (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Carrying Value
Fair value of financial instrument
Current portion of long-term debt	$ 999	$ 600
Long-term debt	6,227	6,627
Fair Value | Fair Value, Inputs, Level 2
Fair value of financial instrument
Current portion of long-term debt	1,004	614
Long-term debt	$ 6,837	$ 7,442

Claims, Lawsuits and Other Co_2

Claims, Lawsuits and Other Contingencies - Narrative (Details) $ in Millions	Mar. 31, 2020USD ($)	Sep. 06, 2018USD ($)	Oct. 03, 2017NZD ($)	Mar. 31, 2020USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2019USD ($)
Legal, Guarantees and Indemnifications
Revenue				$ 3,219,000,000	$ 3,143,000,000
Maximum potential funding under commitments	$ 70,000,000			70,000,000			$ 110,000,000
Letters of credit outstanding	71,000,000			71,000,000			$ 73,000,000
Pending Litigation | Christchurch City Council
Legal, Guarantees and Indemnifications
Damages sought	315,000,000		$ 528
Minimum
Legal, Guarantees and Indemnifications
Estimate of possible loss	0			0
Minimum | Pilkington North America, Inc.
Legal, Guarantees and Indemnifications
Damages sought		$ 45,000,000
Maximum
Legal, Guarantees and Indemnifications
Estimate of possible loss	100,000,000			100,000,000
Maximum | Pilkington North America, Inc.
Legal, Guarantees and Indemnifications
Damages sought		85,000,000
Damages awarded		$ 15,000,000
Aviation and Aerospace Broking Industry
Legal, Guarantees and Indemnifications
Revenue						$ 100,000,000
Discontinued Operations, Disposed of by Sale | Tempo Business | Property Lease Guarantee
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	66,000,000			66,000,000
Guarantor obligations, current carrying value	11,000,000			11,000,000
Loss contingency accrual payments				0
Discontinued Operations, Disposed of by Sale | Tempo Business | Performance Guarantee
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	139,000,000			139,000,000
Guarantor obligations, current carrying value	$ 1,000,000			1,000,000
Loss contingency accrual payments				$ 0

Segment Information (Details)

Segment Information (Details)	3 Months Ended
	Mar. 31, 2020segmentmetricrevenue_line
Segment Reporting [Abstract]
Number of reportable segments	1
Number of revenue lines | revenue_line	5
Number of performance metrics | metric	4
Number of operating segments	1

Guarantee of Registered Secur_3

Guarantee of Registered Securities - Narrative (Details)	Mar. 31, 2020
5.00% notes due September 2020
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	5.00%
2.20% Notes due November 2020
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.20%
8.205% Notes due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	8.205%
4.50% Senior Notes Due December 2028
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.50%
4.75% Notes due May 2045
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.75%
3.75% Senior Notes due May 2, 2029
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.75%
6.25% Senior notes due September 2040
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	6.25%
4.250% Senior notes due 2042
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.25%
4.45% notes due 2043
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.45%
4.00% notes due 2023
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.00%
2.875% notes due 2026
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.875%
3.50% Notes due June 2024
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.50%
4.60% Senior Notes due June 2044
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.60%
2.80% Senior Notes due 2021
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.80%
3.875% Senior Notes due December 2025
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.875%

Guarantee of Registered Secur_4

Guarantee of Registered Securities - Condensed Consolidating Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue
Total revenue	$ 3,219	$ 3,143
Expenses
Compensation and benefits	1,522	1,584
Information technology	111	117
Premises	73	87
Depreciation of fixed assets	41	40
Amortization and impairment of intangible assets	97	97
Other general expenses	342	346
Total operating expenses	2,186	2,271
Operating income	1,033	872
Interest income	2	2
Interest expense	(83)	(72)
Intercompany interest income (expense)	0	0
Intercompany other income (expense)	0	0
Other income (expense)	29	0
Income from continuing operations before income taxes	981	802
Income tax expense (benefit)	189	126
Net income from continuing operations	792	676
Net income (loss) from discontinued operations	(1)	0
Net income (loss) before equity in earnings of subsidiaries	791	676
Equity in earnings of subsidiaries	0	0
Net income	791	676
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	772	659
Aon Ireland
Revenue
Total revenue	0	0
Expenses
Compensation and benefits	0	0
Information technology	0	0
Premises	0	0
Depreciation of fixed assets	0	0
Amortization and impairment of intangible assets	0	0
Other general expenses	0	0
Total operating expenses	0	0
Operating income	0	0
Interest income	0	0
Interest expense	0	0
Intercompany interest income (expense)	0	0
Intercompany other income (expense)	0	0
Other income (expense)	0	0
Income from continuing operations before income taxes	0	0
Income tax expense (benefit)	0	0
Net income from continuing operations	0	0
Net income (loss) from discontinued operations	0	0
Net income (loss) before equity in earnings of subsidiaries	0	0
Equity in earnings of subsidiaries	773	0
Net income	773	0
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	773	0
Aon UK
Revenue
Total revenue	0	0
Expenses
Compensation and benefits	12	20
Information technology	0	0
Premises	0	0
Depreciation of fixed assets	0	0
Amortization and impairment of intangible assets	0	0
Other general expenses	26	0
Total operating expenses	38	20
Operating income	(38)	(20)
Interest income	0	0
Interest expense	(54)	(46)
Intercompany interest income (expense)	8	4
Intercompany other income (expense)	81	31
Other income (expense)	0	5
Income from continuing operations before income taxes	(3)	(26)
Income tax expense (benefit)	(17)	(5)
Net income from continuing operations	14	(21)
Net income (loss) from discontinued operations	0	0
Net income (loss) before equity in earnings of subsidiaries	14	(21)
Equity in earnings of subsidiaries	759	682
Net income	773	661
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	773	661
Aon Global Holdings Limited
Revenue
Total revenue	0	0
Expenses
Compensation and benefits	0	0
Information technology	0	0
Premises	0	0
Depreciation of fixed assets	0	0
Amortization and impairment of intangible assets	0	0
Other general expenses	0	0
Total operating expenses	0	0
Operating income	0	0
Interest income	0	0
Interest expense	(11)	(24)
Intercompany interest income (expense)	0	0
Intercompany other income (expense)	0	0
Other income (expense)	0	0
Income from continuing operations before income taxes	(11)	(24)
Income tax expense (benefit)	(2)	(5)
Net income from continuing operations	(9)	(19)
Net income (loss) from discontinued operations	0	0
Net income (loss) before equity in earnings of subsidiaries	(9)	(19)
Equity in earnings of subsidiaries	614	619
Net income	605	600
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	605	600
Aon Corporation
Revenue
Total revenue	0	0
Expenses
Compensation and benefits	(12)	8
Information technology	0	0
Premises	5	4
Depreciation of fixed assets	0	0
Amortization and impairment of intangible assets	0	0
Other general expenses	1	1
Total operating expenses	(6)	13
Operating income	6	(13)
Interest income	10	9
Interest expense	(39)	(28)
Intercompany interest income (expense)	(113)	(116)
Intercompany other income (expense)	(128)	(94)
Other income (expense)	(42)	(11)
Income from continuing operations before income taxes	(306)	(253)
Income tax expense (benefit)	(48)	(42)
Net income from continuing operations	(258)	(211)
Net income (loss) from discontinued operations	0	0
Net income (loss) before equity in earnings of subsidiaries	(258)	(211)
Equity in earnings of subsidiaries	862	724
Net income	604	513
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	604	513
Other Non-Guarantor Subsidiaries
Revenue
Total revenue	3,219	3,143
Expenses
Compensation and benefits	1,522	1,556
Information technology	111	117
Premises	68	83
Depreciation of fixed assets	41	40
Amortization and impairment of intangible assets	97	97
Other general expenses	315	345
Total operating expenses	2,154	2,238
Operating income	1,065	905
Interest income	14	20
Interest expense	(1)	(1)
Intercompany interest income (expense)	105	112
Intercompany other income (expense)	47	63
Other income (expense)	72	8
Income from continuing operations before income taxes	1,302	1,107
Income tax expense (benefit)	256	178
Net income from continuing operations	1,046	929
Net income (loss) from discontinued operations	(1)	0
Net income (loss) before equity in earnings of subsidiaries	1,045	929
Equity in earnings of subsidiaries	0	0
Net income	1,045	929
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	1,026	912
Consolidation Adjustments
Revenue
Total revenue	0	0
Expenses
Compensation and benefits	0	0
Information technology	0	0
Premises	0	0
Depreciation of fixed assets	0	0
Amortization and impairment of intangible assets	0	0
Other general expenses	0	0
Total operating expenses	0	0
Operating income	0	0
Interest income	(22)	(27)
Interest expense	22	27
Intercompany interest income (expense)	0	0
Intercompany other income (expense)	0	0
Other income (expense)	(1)	(2)
Income from continuing operations before income taxes	(1)	(2)
Income tax expense (benefit)	0	0
Net income from continuing operations	(1)	(2)
Net income (loss) from discontinued operations	0	0
Net income (loss) before equity in earnings of subsidiaries	(1)	(2)
Equity in earnings of subsidiaries	(3,008)	(2,025)
Net income	(3,009)	(2,027)
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	$ (3,009)	$ (2,027)

Guarantee of Registered Secur_5

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net income	$ 791	$ 676
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	772	659
Change in fair value of financial instruments	(5)	7
Foreign currency translation adjustments	(397)	133
Postretirement benefit obligation	24	31
Total other comprehensive income (loss)	(378)	171
Equity in other comprehensive income (loss) of subsidiaries, net of tax	0	0
Less: Other comprehensive loss attributable to noncontrolling interests	(2)	2
Total other comprehensive income (loss) attributable to Aon shareholders	(376)	169
Comprehensive income (loss) attributable to Aon shareholders	396	828
Aon Ireland
Condensed Financial Statements, Captions [Line Items]
Net income	773	0
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	773	0
Change in fair value of financial instruments	0	0
Foreign currency translation adjustments	0	0
Postretirement benefit obligation	0	0
Total other comprehensive income (loss)	0	0
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(377)	0
Less: Other comprehensive loss attributable to noncontrolling interests	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(377)	0
Comprehensive income (loss) attributable to Aon shareholders	396	0
Aon UK
Condensed Financial Statements, Captions [Line Items]
Net income	773	661
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	773	661
Change in fair value of financial instruments	0	0
Foreign currency translation adjustments	0	0
Postretirement benefit obligation	0	0
Total other comprehensive income (loss)	0	0
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(377)	167
Less: Other comprehensive loss attributable to noncontrolling interests	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(377)	167
Comprehensive income (loss) attributable to Aon shareholders	396	828
Aon Global Holdings Limited
Condensed Financial Statements, Captions [Line Items]
Net income	605	600
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	605	600
Change in fair value of financial instruments	0	0
Foreign currency translation adjustments	0	0
Postretirement benefit obligation	0	0
Total other comprehensive income (loss)	0	0
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(370)	139
Less: Other comprehensive loss attributable to noncontrolling interests	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(370)	139
Comprehensive income (loss) attributable to Aon shareholders	235	739
Aon Corporation
Condensed Financial Statements, Captions [Line Items]
Net income	604	513
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	604	513
Change in fair value of financial instruments	(2)	2
Foreign currency translation adjustments	0	0
Postretirement benefit obligation	13	22
Total other comprehensive income (loss)	11	24
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(381)	115
Less: Other comprehensive loss attributable to noncontrolling interests	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(370)	139
Comprehensive income (loss) attributable to Aon shareholders	234	652
Other Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	1,045	929
Less: Net income attributable to noncontrolling interests	19	17
Net income attributable to Aon shareholders	1,026	912
Change in fair value of financial instruments	(3)	5
Foreign currency translation adjustments	(398)	131
Postretirement benefit obligation	11	9
Total other comprehensive income (loss)	(390)	145
Equity in other comprehensive income (loss) of subsidiaries, net of tax	0	0
Less: Other comprehensive loss attributable to noncontrolling interests	(2)	2
Total other comprehensive income (loss) attributable to Aon shareholders	(388)	143
Comprehensive income (loss) attributable to Aon shareholders	638	1,055
Consolidation Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income	(3,009)	(2,027)
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	(3,009)	(2,027)
Change in fair value of financial instruments	0	0
Foreign currency translation adjustments	1	2
Postretirement benefit obligation	0	0
Total other comprehensive income (loss)	1	2
Equity in other comprehensive income (loss) of subsidiaries, net of tax	1,505	(421)
Less: Other comprehensive loss attributable to noncontrolling interests	0	0
Total other comprehensive income (loss) attributable to Aon shareholders	1,506	(419)
Comprehensive income (loss) attributable to Aon shareholders	$ (1,503)	$ (2,446)

Guarantee of Registered Secur_6

Guarantee of Registered Securities - Condensed Consolidating Statement of Financial Position (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 690,000,000	$ 790,000,000
Short-term investments	170,000,000	138,000,000
Receivables, net	3,554,000,000	3,112,000,000
Fiduciary assets	12,401,000,000	11,834,000,000
Current intercompany receivables	0	0
Other current assets	530,000,000	602,000,000
Total current assets	17,345,000,000	16,476,000,000
Goodwill	8,293,000,000	8,165,000,000
Intangible assets, net	746,000,000	783,000,000
Fixed assets, net	666,000,000	621,000,000
Operating lease right-of-use assets	897,000,000	929,000,000
Deferred tax assets	638,000,000	645,000,000
Prepaid pension	1,164,000,000	1,216,000,000
Non-current intercompany receivables	0	0
Other non-current assets	533,000,000	570,000,000
Investment in subsidiary	0	0
Total assets	30,282,000,000	29,405,000,000
Current liabilities
Accounts payable and accrued liabilities	1,549,000,000	1,939,000,000
Short-term debt and current portion of long-term debt	1,884,000,000	712,000,000
Fiduciary liabilities	12,401,000,000	11,834,000,000
Current intercompany payables	0	0
Other current liabilities	1,277,000,000	1,086,000,000
Total current liabilities	17,111,000,000	15,571,000,000
Long-term debt	6,227,000,000	6,627,000,000
Non-current operating lease liabilities	910,000,000	944,000,000
Deferred tax liabilities	189,000,000	199,000,000
Pension, other postretirement, and postemployment liabilities	1,655,000,000	1,738,000,000
Non-current intercompany payables	0	0
Other non-current liabilities	930,000,000	877,000,000
Total liabilities	27,022,000,000	25,956,000,000
Total Aon shareholders’ equity	3,169,000,000	3,375,000,000
Noncontrolling interests	91,000,000	74,000,000
Total equity	3,260,000,000	3,449,000,000	$ 4,862,000,000	$ 4,219,000,000
Total liabilities and equity	30,282,000,000	29,405,000,000
Aon Ireland
Current assets
Cash and cash equivalents	0	0
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Current intercompany receivables	0	0
Other current assets	0	0
Total current assets	0	0
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Operating lease right-of-use assets	0	0
Deferred tax assets	0	0
Prepaid pension	0	0
Non-current intercompany receivables	0	0
Other non-current assets	0	0
Investment in subsidiary	3,169,000,000	3,375,000,000
Total assets	3,169,000,000	3,375,000,000
Current liabilities
Accounts payable and accrued liabilities	0	0
Short-term debt and current portion of long-term debt	0	0
Fiduciary liabilities	0	0
Current intercompany payables	0	0
Other current liabilities	0	0
Total current liabilities	0	0
Long-term debt	0	0
Non-current operating lease liabilities	0	0
Deferred tax liabilities	0	0
Pension, other postretirement, and postemployment liabilities	0	0
Non-current intercompany payables	0	0
Other non-current liabilities	0	0
Total liabilities	0	0
Total Aon shareholders’ equity	3,169,000,000	3,375,000,000
Noncontrolling interests	0	0
Total equity	3,169,000,000	3,375,000,000
Total liabilities and equity	3,169,000,000	3,375,000,000
Aon UK
Current assets
Cash and cash equivalents	0	0
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Current intercompany receivables	208,000,000	246,000,000
Other current assets	0	0
Total current assets	208,000,000	246,000,000
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Operating lease right-of-use assets	0	0
Deferred tax assets	89,000,000	89,000,000
Prepaid pension	0	0
Non-current intercompany receivables	397,000,000	868,000,000
Other non-current assets	0	0
Investment in subsidiary	8,650,000,000	8,899,000,000
Total assets	9,344,000,000	10,102,000,000
Current liabilities
Accounts payable and accrued liabilities	1,345,000,000	2,157,000,000
Short-term debt and current portion of long-term debt	696,000,000	112,000,000
Fiduciary liabilities	0	0
Current intercompany payables	310,000,000	234,000,000
Other current liabilities	0	0
Total current liabilities	2,351,000,000	2,503,000,000
Long-term debt	3,822,000,000	4,223,000,000
Non-current operating lease liabilities	0	0
Deferred tax liabilities	0	0
Pension, other postretirement, and postemployment liabilities	0	0
Non-current intercompany payables	0	0
Other non-current liabilities	2,000,000	1,000,000
Total liabilities	6,175,000,000	6,727,000,000
Total Aon shareholders’ equity	3,169,000,000	3,375,000,000
Noncontrolling interests	0	0
Total equity	3,169,000,000	3,375,000,000
Total liabilities and equity	9,344,000,000	10,102,000,000
Aon Global Holdings Limited
Current assets
Cash and cash equivalents	36,000,000	0
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Current intercompany receivables	90,000,000	89,000,000
Other current assets	0	0
Total current assets	126,000,000	89,000,000
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Operating lease right-of-use assets	0	0
Deferred tax assets	4,000,000	4,000,000
Prepaid pension	0	0
Non-current intercompany receivables	0	0
Other non-current assets	0	0
Investment in subsidiary	8,871,000,000	12,211,000,000
Total assets	9,001,000,000	12,304,000,000
Current liabilities
Accounts payable and accrued liabilities	0	1,994,000,000
Short-term debt and current portion of long-term debt	0	0
Fiduciary liabilities	0	0
Current intercompany payables	61,000,000	61,000,000
Other current liabilities	0	0
Total current liabilities	61,000,000	2,055,000,000
Long-term debt	0	0
Non-current operating lease liabilities	0	0
Deferred tax liabilities	0	0
Pension, other postretirement, and postemployment liabilities	0	0
Non-current intercompany payables	0	0
Other non-current liabilities	0	0
Total liabilities	61,000,000	2,055,000,000
Total Aon shareholders’ equity	8,940,000,000	10,249,000,000
Noncontrolling interests	0	0
Total equity	8,940,000,000	10,249,000,000
Total liabilities and equity	9,001,000,000	12,304,000,000
Aon Corporation
Current assets
Cash and cash equivalents	194,000,000	2,271,000,000
Short-term investments	57,000,000	28,000,000
Receivables, net	0	0
Fiduciary assets	0	0
Current intercompany receivables	2,710,000,000	1,214,000,000
Other current assets	4,000,000	7,000,000
Total current assets	2,965,000,000	3,520,000,000
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Operating lease right-of-use assets	103,000,000	110,000,000
Deferred tax assets	589,000,000	577,000,000
Prepaid pension	7,000,000	7,000,000
Non-current intercompany receivables	261,000,000	261,000,000
Other non-current assets	25,000,000	32,000,000
Investment in subsidiary	19,973,000,000	19,470,000,000
Total assets	23,923,000,000	23,977,000,000
Current liabilities
Accounts payable and accrued liabilities	49,000,000	56,000,000
Short-term debt and current portion of long-term debt	1,136,000,000	600,000,000
Fiduciary liabilities	0	0
Current intercompany payables	16,321,000,000	12,978,000,000
Other current liabilities	82,000,000	80,000,000
Total current liabilities	17,588,000,000	13,714,000,000
Long-term debt	2,405,000,000	2,404,000,000
Non-current operating lease liabilities	136,000,000	143,000,000
Deferred tax liabilities	0	0
Pension, other postretirement, and postemployment liabilities	1,287,000,000	1,348,000,000
Non-current intercompany payables	7,210,000,000	7,212,000,000
Other non-current liabilities	115,000,000	113,000,000
Total liabilities	28,741,000,000	24,934,000,000
Total Aon shareholders’ equity	(4,818,000,000)	(957,000,000)
Noncontrolling interests	0	0
Total equity	(4,818,000,000)	(957,000,000)
Total liabilities and equity	23,923,000,000	23,977,000,000
Other Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	1,698,000,000	2,619,000,000
Short-term investments	113,000,000	110,000,000
Receivables, net	3,554,000,000	3,112,000,000
Fiduciary assets	12,401,000,000	11,834,000,000
Current intercompany receivables	14,875,000,000	12,710,000,000
Other current assets	526,000,000	595,000,000
Total current assets	33,167,000,000	30,980,000,000
Goodwill	8,293,000,000	8,165,000,000
Intangible assets, net	746,000,000	783,000,000
Fixed assets, net	666,000,000	621,000,000
Operating lease right-of-use assets	794,000,000	819,000,000
Deferred tax assets	150,000,000	165,000,000
Prepaid pension	1,157,000,000	1,209,000,000
Non-current intercompany receivables	7,044,000,000	7,046,000,000
Other non-current assets	508,000,000	538,000,000
Investment in subsidiary	0	0
Total assets	52,525,000,000	50,326,000,000
Current liabilities
Accounts payable and accrued liabilities	1,393,000,000	1,832,000,000
Short-term debt and current portion of long-term debt	52,000,000	0
Fiduciary liabilities	12,401,000,000	11,834,000,000
Current intercompany payables	1,191,000,000	986,000,000
Other current liabilities	1,195,000,000	1,006,000,000
Total current liabilities	16,232,000,000	15,658,000,000
Long-term debt	0	0
Non-current operating lease liabilities	774,000,000	801,000,000
Deferred tax liabilities	383,000,000	389,000,000
Pension, other postretirement, and postemployment liabilities	368,000,000	390,000,000
Non-current intercompany payables	492,000,000	963,000,000
Other non-current liabilities	813,000,000	763,000,000
Total liabilities	19,062,000,000	18,964,000,000
Total Aon shareholders’ equity	33,372,000,000	31,288,000,000
Noncontrolling interests	91,000,000	74,000,000
Total equity	33,463,000,000	31,362,000,000
Total liabilities and equity	52,525,000,000	50,326,000,000
Consolidation Adjustments
Current assets
Cash and cash equivalents	(1,238,000,000)	(4,100,000,000)
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Current intercompany receivables	(17,883,000,000)	(14,259,000,000)
Other current assets	0	0
Total current assets	(19,121,000,000)	(18,359,000,000)
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Operating lease right-of-use assets	0	0
Deferred tax assets	(194,000,000)	(190,000,000)
Prepaid pension	0	0
Non-current intercompany receivables	(7,702,000,000)	(8,175,000,000)
Other non-current assets	0	0
Investment in subsidiary	(40,663,000,000)	(43,955,000,000)
Total assets	(67,680,000,000)	(70,679,000,000)
Current liabilities
Accounts payable and accrued liabilities	(1,238,000,000)	(4,100,000,000)
Short-term debt and current portion of long-term debt	0	0
Fiduciary liabilities	0	0
Current intercompany payables	(17,883,000,000)	(14,259,000,000)
Other current liabilities	0	0
Total current liabilities	(19,121,000,000)	(18,359,000,000)
Long-term debt	0	0
Non-current operating lease liabilities	0	0
Deferred tax liabilities	(194,000,000)	(190,000,000)
Pension, other postretirement, and postemployment liabilities	0	0
Non-current intercompany payables	(7,702,000,000)	(8,175,000,000)
Other non-current liabilities	0	0
Total liabilities	(27,017,000,000)	(26,724,000,000)
Total Aon shareholders’ equity	(40,663,000,000)	(43,955,000,000)
Noncontrolling interests	0	0
Total equity	(40,663,000,000)	(43,955,000,000)
Total liabilities and equity	$ (67,680,000,000)	$ (70,679,000,000)

Guarantee of Registered Secur_7

Guarantee of Registered Securities - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Cash provided by (used for) operating activities	$ 338	$ 74
Cash flows from investing activities
Proceeds from investments	6	12
Payments for investments	(43)	(14)
Net sales (purchases) of short-term investments - non-fiduciary	(38)	41
Acquisition of businesses, net of cash acquired	(334)	(15)
Sale of businesses, net of cash sold	30	6
Capital expenditures	(59)	(57)
Cash used for investing activities	(438)	(27)
Cash flows from financing activities
Share repurchase	(463)	(100)
Advances from (to) affiliates	0	0
Issuance of shares for employee benefit plans	(112)	(98)
Issuance of debt	2,060	871
Repayment of debt	(1,341)	(694)
Cash dividends to shareholders	(102)	(96)
Noncontrolling interests and other financing activities	40	(23)
Cash provided by (used for) financing activities	82	(140)
Effect of exchange rates on cash and cash equivalents	(82)	37
Net increase (decrease) in cash and cash equivalents	(100)	(56)
Cash and cash equivalents at beginning of period	790	656
Cash and cash equivalents at end of period	690	600
Aon Ireland
Cash flows from operating activities
Cash provided by (used for) operating activities	0	0
Cash flows from investing activities
Proceeds from investments	0	0
Payments for investments	0	0
Net sales (purchases) of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0
Cash used for investing activities	0	0
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	0	0
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	0
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash provided by (used for) financing activities	0	0
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Aon UK
Cash flows from operating activities
Cash provided by (used for) operating activities	1,561	(11)
Cash flows from investing activities
Proceeds from investments		0
Payments for investments	(450)	0
Net sales (purchases) of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0
Cash used for investing activities	(450)	0
Cash flows from financing activities
Share repurchase	(463)	(100)
Advances from (to) affiliates	(618)	305
Issuance of shares for employee benefit plans	(112)	(98)
Issuance of debt	457	384
Repayment of debt	(273)	(384)
Cash dividends to shareholders	(102)	(96)
Noncontrolling interests and other financing activities	0	0
Cash provided by (used for) financing activities	(1,111)	11
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Aon Global Holdings Limited
Cash flows from operating activities
Cash provided by (used for) operating activities	3,648	529
Cash flows from investing activities
Proceeds from investments		72
Payments for investments	(518)	0
Net sales (purchases) of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0
Cash used for investing activities	(518)	72
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(3,094)	(601)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	0
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash provided by (used for) financing activities	(3,094)	(601)
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	36	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	36	0
Aon Corporation
Cash flows from operating activities
Cash provided by (used for) operating activities	(512)	(34)
Cash flows from investing activities
Proceeds from investments	2	8
Payments for investments	(30)	(9)
Net sales (purchases) of short-term investments - non-fiduciary	(28)	9
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0	0
Cash used for investing activities	(56)	8
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(2,044)	(265)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	1,603	485
Repayment of debt	(1,068)	(310)
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash provided by (used for) financing activities	(1,509)	(90)
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	(2,077)	(116)
Cash and cash equivalents at beginning of period	2,271	862
Cash and cash equivalents at end of period	194	746
Other Non-Guarantor Subsidiaries
Cash flows from operating activities
Cash provided by (used for) operating activities	852	143
Cash flows from investing activities
Proceeds from investments	4	4
Payments for investments	(13)	(77)
Net sales (purchases) of short-term investments - non-fiduciary	(10)	32
Acquisition of businesses, net of cash acquired	(334)	(15)
Sale of businesses, net of cash sold	30	6
Capital expenditures	(59)	(57)
Cash used for investing activities	(382)	(107)
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(1,349)	(550)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	2
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	40	(23)
Cash provided by (used for) financing activities	(1,309)	(571)
Effect of exchange rates on cash and cash equivalents	(82)	37
Net increase (decrease) in cash and cash equivalents	(921)	(498)
Cash and cash equivalents at beginning of period	2,619	3,473
Cash and cash equivalents at end of period	1,698	2,975
Consolidation Adjustments
Cash flows from operating activities
Cash provided by (used for) operating activities	(5,211)	(553)
Cash flows from investing activities
Proceeds from investments		(72)
Payments for investments	968	72
Net sales (purchases) of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0	0
Cash used for investing activities	968	0
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	7,105	1,111
Issuance of shares for employee benefit plans	0	0
Issuance of debt		0
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash provided by (used for) financing activities	7,105	1,111
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	2,862	558
Cash and cash equivalents at beginning of period	(4,100)	(3,679)
Cash and cash equivalents at end of period	$ (1,238)	$ (3,121)

Subsequent Events (Details)

Subsequent Events (Details)	Apr. 27, 2020	Apr. 24, 2020	Apr. 01, 2020USD ($)	Mar. 31, 2020USD ($)
Subsequent Event
Subsequent Event [Line Items]
Common stock exchange ratio, related to reorganization			1
Equity incentive and compensation plans, exchange ratio, related to reorganization			1
Subsequent Event | Named executive officers and non-executive directors
Subsequent Event [Line Items]
Temporary compensation reduction, percentage		50.00%
Subsequent Event | Employees
Subsequent Event [Line Items]
Temporary compensation reduction, percentage	20.00%
Commercial paper
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity				$ 1,650,000,000
Commercial paper | U.S. Program
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity				$ 600,000,000
Commercial paper | U.S. Program | Subsequent Event
Subsequent Event [Line Items]
Line of credit facility, increase of maximum borrowing capacity			$ 300,000,000
Line of credit facility, maximum borrowing capacity			$ 900,000,000

Uncategorized Items - q12020aon

Label	Element	Value
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	$ 3,443,000,000
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	1,248,000,000
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(6,000,000)
Noncontrolling Interest [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	74,000,000
AOCI Attributable to Parent [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	(4,033,000,000)
Common Stock Including Additional Paid in Capital [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance1	$ 6,154,000,000