Aon (AON) 10-Q 26 Jul 19 2019 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2019	Jul. 25, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	1-7933
Entity Registrant Name	Aon plc
Entity Incorporation, State or Country Code	X0
Entity Tax Identification Number	98-1030901
Entity Address, Address Line One	122 LEADENHALL STREET
Entity Address, City or Town	LONDON
Entity Address, Country	GB
Entity Address, Postal Zip Code	EC3V 4AN
City Area Code	20
Local Phone Number	7623 5500
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		235,841,886
Entity Central Index Key	0000315293
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Total revenue	$ 2,606	$ 2,561	$ 5,749	$ 5,651
Expenses
Compensation and benefits	1,501	1,494	3,085	3,110
Information technology	126	123	243	238
Premises	85	96	172	189
Depreciation of fixed assets	40	47	80	86
Amortization and impairment of intangible assets	97	282	194	392
Other general expenses	344	535	690	853
Total operating expenses	2,193	2,577	4,464	4,868
Operating income (loss)	413	(16)	1,285	783
Interest income	1	1	3	5
Interest expense	(77)	(69)	(149)	(139)
Other income (expense)	6	(3)	6	(18)
Income (loss) from continuing operations before income taxes	343	(87)	1,145	631
Income tax expense (benefit)	56	(144)	182	(30)
Net income from continuing operations	287	57	963	661
Net income from discontinued operations	0	1	0	7
Net income	287	58	963	668
Less: Net income attributable to noncontrolling interests	10	10	27	26
Net income attributable to Aon shareholders	$ 277	$ 48	$ 936	$ 642
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 1.15	$ 0.19	$ 3.88	$ 2.57
Discontinued operations (in dollars per share)	0	0.01	0	0.03
Net income (in dollars per share)	1.15	0.20	3.88	2.60
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	1.14	0.19	3.85	2.55
Discontinued operations (in dollars per share)	0	0	0	0.03
Net income (in dollars per share)	$ 1.14	$ 0.19	$ 3.85	$ 2.58
Weighted average ordinary shares outstanding - basic (in shares)	240.6	246	241.4	247.2
Weighted average ordinary shares outstanding - diluted (in shares)	242.8	247.4	243.2	248.8

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 287	$ 58	$ 963	$ 668
Less: Net income attributable to noncontrolling interests	10	10	27	26
Net income attributable to Aon shareholders	277	48	936	642
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(8)	(1)	(1)	13
Foreign currency translation adjustments	(103)	(460)	30	(213)
Postretirement benefit obligation	14	122	45	170
Total other comprehensive income (loss)	(97)	(339)	74	(30)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	0	(6)	2	(3)
Total other comprehensive income (loss) attributable to Aon shareholders	(97)	(333)	72	(27)
Comprehensive income (loss) attributable to Aon shareholders	$ 180	$ (285)	$ 1,008	$ 615

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Financial Position - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 581	$ 656
Short-term investments	235	172
Receivables, net	3,227	2,760
Fiduciary assets	12,071	10,166
Other current assets	631	618
Total current assets	16,745	14,372
Goodwill	8,198	8,171
Intangible assets, net	973	1,149
Fixed assets, net	599	588
Operating lease right-of-use assets	959
Deferred tax assets	599	561
Prepaid pension	1,213	1,133
Other non-current assets	521	448
Total assets	29,807	26,422
Current liabilities
Accounts payable and accrued liabilities	1,369	1,943
Short-term debt and current portion of long-term debt	844	251
Fiduciary liabilities	12,071	10,166
Other current liabilities	1,197	936
Total current liabilities	15,481	13,296
Long-term debt	6,740	5,993
Non-current operating lease liabilities	962
Deferred tax liabilities	211	181
Pension, other postretirement, and postemployment liabilities	1,576	1,636
Other non-current liabilities	924	1,097
Total liabilities	25,894	22,203
Equity
Ordinary shares - $0.01 nominal value Authorized: 750 shares (issued: 2019 - 235.7; 2018 - 240.1)	2	2
Additional paid-in capital	6,002	5,965
Retained earnings	1,669	2,093
Accumulated other comprehensive loss	(3,837)	(3,909)
Total Aon shareholders' equity	3,836	4,151
Noncontrolling interests	77	68
Total equity	3,913	4,219
Total liabilities and equity	$ 29,807	$ 26,422

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Financial Position (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
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)	235,700,000	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, 2017		247.6
Beginning Balance at Dec. 31, 2017	$ 5,140	$ 5,777	$ 2,795	$ (3,497)	$ 65
Increase (Decrease) in Shareholders' Equity
Net income	610		594		16
Shares issued - employee stock compensation plans (in shares)		1.5
Shares issued - employee stock compensation plans	(109)	$ (109)
Shares purchased (in shares)		(3.9)
Shares purchased	(553)		(553)
Share-based compensation expense	77	$ 77
Dividends to shareholders	(89)		(89)
Net change in fair value of financial instruments	14			14
Net foreign currency translation adjustments	247			244	3
Net postretirement benefit obligation	48			48
Ending Balance (in shares) at Mar. 31, 2018		245.2
Ending Balance at Mar. 31, 2018	5,385	$ 5,745	2,747	(3,191)	84
Beginning Balance (in shares) at Dec. 31, 2017		247.6
Beginning Balance at Dec. 31, 2017	5,140	$ 5,777	2,795	(3,497)	65
Increase (Decrease) in Shareholders' Equity
Net income	668
Net change in fair value of financial instruments	13
Net foreign currency translation adjustments	(213)
Net postretirement benefit obligation	170
Ending Balance (in shares) at Jun. 30, 2018		243
Ending Balance at Jun. 30, 2018	4,618	$ 5,774	2,295	(3,524)	73
Beginning Balance (in shares) at Mar. 31, 2018		245.2
Beginning Balance at Mar. 31, 2018	5,385	$ 5,745	2,747	(3,191)	84
Increase (Decrease) in Shareholders' Equity
Net income	58		48		10
Shares issued - employee stock compensation plans (in shares)		0.6
Shares issued - employee stock compensation plans	(41)	$ (41)
Shares purchased (in shares)		(2.8)
Shares purchased	(402)		(402)
Share-based compensation expense	70	$ 70
Dividends to shareholders	(98)		(98)
Net change in fair value of financial instruments	(1)			(1)
Net foreign currency translation adjustments	(460)			(454)	(6)
Net postretirement benefit obligation	122			122
Purchases of shares from noncontrolling interests	(1)				(1)
Dividends paid to noncontrolling interests on subsidiary common stock	(14)				(14)
Ending Balance (in shares) at Jun. 30, 2018		243
Ending Balance at Jun. 30, 2018	$ 4,618	$ 5,774	2,295	(3,524)	73
Beginning Balance (in shares) at Dec. 31, 2018	240.1	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, 2018	240.1	240.1
Beginning Balance at Dec. 31, 2018	$ 4,219	$ 5,967	2,093	(3,909)	68
Increase (Decrease) in Shareholders' Equity
Net income	963
Net change in fair value of financial instruments	(1)
Net foreign currency translation adjustments	30
Net postretirement benefit obligation	$ 45
Ending Balance (in shares) at Jun. 30, 2019	235.7	235.7
Ending Balance at Jun. 30, 2019	$ 3,913	$ 6,004	1,669	(3,837)	77
Beginning Balance (in shares) at Mar. 31, 2019		240.9
Beginning Balance at Mar. 31, 2019	4,862	$ 5,960	2,555	(3,740)	87
Increase (Decrease) in Shareholders' Equity
Net income	287		277		10
Shares issued - employee stock compensation plans (in shares)		0.6
Shares issued - employee stock compensation plans	(47)	$ (47)
Shares purchased (in shares)		(5.8)
Shares purchased	(1,056)		(1,056)
Share-based compensation expense	91	$ 91
Dividends to shareholders	(107)		(107)
Net change in fair value of financial instruments	(8)			(8)
Net foreign currency translation adjustments	(103)			(103)
Net postretirement benefit obligation	14			14
Dividends paid to noncontrolling interests on subsidiary common stock	$ (20)				(20)
Ending Balance (in shares) at Jun. 30, 2019	235.7	235.7
Ending Balance at Jun. 30, 2019	$ 3,913	$ 6,004	$ 1,669	$ (3,837)	$ 77

Condensed Consolidated Statem_6

Condensed Consolidated Statement of Shareholders' Equity Unaudited (Parenthetical) - $ / shares	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Dividends (in dollars per share)	$ 0.44	$ 0.40	$ 0.40	$ 0.36

Condensed Consolidated Statem_7

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net income	$ 963	$ 668
Net income from discontinued operations	0	7
Adjustments to reconcile net income to cash provided by operating activities:
(Gain) loss from sales of businesses, net	(7)	1
Depreciation of fixed assets	80	86
Amortization and impairment of intangible assets	194	392
Share-based compensation expense	180	147
Deferred income taxes	(25)	(93)
Change in assets and liabilities:
Fiduciary receivables	(926)	(883)
Short-term investments — funds held on behalf of clients	(961)	(154)
Fiduciary liabilities	1,887	1,037
Receivables, net	(477)	(371)
Accounts payable and accrued liabilities	(579)	(495)
Restructuring reserves	(18)	12
Current income taxes	10	(144)
Pension, other postretirement and postemployment liabilities	(92)	(84)
Other assets and liabilities	132	301
Cash provided by operating activities	361	413
Cash flows from investing activities
Proceeds from investments	14	23
Payments for investments	(60)	(36)
Net sales (purchases) of short-term investments — non-fiduciary	(62)	352
Acquisition of businesses, net of cash acquired	(15)	(50)
Sale of businesses, net of cash sold	7	1
Capital expenditures	(106)	(111)
Cash provided by (used for) investing activities	(222)	179
Cash flows from financing activities
Share repurchase	(1,155)	(971)
Issuance of shares for employee benefit plans	(144)	(150)
Issuance of debt	3,559	2,552
Repayment of debt	(2,228)	(2,027)
Cash dividends to shareholders	(203)	(187)
Noncontrolling interests and other financing activities	(61)	(15)
Cash used for financing activities	(232)	(798)
Effect of exchange rates on cash and cash equivalents	18	(63)
Net increase (decrease) in cash and cash equivalents	(75)	(269)
Cash and cash equivalents at beginning of period	656	756
Cash and cash equivalents at end of period	581	487
Supplemental disclosures:
Interest paid	147	145
Income taxes paid, net of refunds	$ 197	$ 207

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2019
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 (“Aon” or the “Company”). 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. These 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, 2018 . The results for the three and six months ended June 30, 2019 are not necessarily indicative of operating results that may be expected for the full year ending December 31, 2019 . Use of Estimates The preparation of the accompanying 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, and foreign currency exchange rate movements increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment would, if applicable, be reflected in the Financial Statements in future periods.

Accounting Principles and Pract

Accounting Principles and Practices	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Accounting Principles and Practices	Accounting Principles and Practices Adoption of New Accounting Standards Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued new accounting guidance related to reclassification of certain tax effects from accumulated other comprehensive income. The guidance allowed a reclassification from accumulated comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The guidance was effective for the Company in the first quarter of 2019. For the three and six months ended June 30, 2019 , there was no impact on the net income of the Company as Aon did not elect to reclassify stranded tax effects on the Condensed Consolidated Statement of Financial Position. It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach. Targeted Improvements to Accounting for Hedging Activities In August 2017, the FASB issued new accounting guidance on targeted improvements to accounting for hedging activities. The new guidance amended its hedge accounting model to enable entities to better portray their risk management activities in the financial statements. The guidance eliminated the requirement to separately measure and report hedge ineffectiveness and required the effect of a hedging instrument to be presented in the same income statement line as the hedged item. The new guidance was effective for Aon in the first quarter of 2019 and the Company adopted it on a modified retrospective basis with no cumulative effect adjustment to accumulated other comprehensive income or corresponding adjustment to Retained earnings. Changes to the Condensed Consolidated Statement of Income and financial statement disclosures were applied prospectively. Under the new guidance, gains or losses on certain derivative hedging instruments are recognized in revenue, as opposed to other income (expense) under the previous guidance. For the three and six months ended June 30, 2019 , the adoption of this guidance had no impact on the net income and an insignificant impact on the operating income of the Company. Leases In February 2016, the FASB issued a new accounting standard on leases, which requires lessees to recognize assets and liabilities for most leases. Under the new standard, a lessee is required to recognize in the Consolidated Statements of Financial Position, liabilities to make future lease payments and right-of-use (“ROU”) assets representing its right to use the underlying assets for the lease term. The recognition, measurement, timing, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from previous U.S. GAAP. The Company adopted the new standard as of January 1, 2019, using the modified retrospective approach for all leases existing at, or entered into after, the period of adoption. Under this approach, prior periods were not restated. Rather, lease balances and other disclosures for prior periods were provided in the notes to the financial statements as previously reported, and the cumulative effect of initially applying the guidance was recognized in the Condensed Consolidated Statement of Financial Position. The modified retrospective approach includes several optional practical expedients available that entities may elect to apply upon transition. These practical expedients relate to the identification and classification of leases that commenced before the effective date, initial direct costs for leases that commenced before the effective date, and the ability to use hindsight in evaluating lessee options to extend or terminate a lease or to purchase the underlying asset. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which allows a lessee to carryforward their population of existing leases, the classification of each lease, as well as the treatment of initial direct costs as of the period of adoption. In addition, the Company elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease from lease components and instead account for consideration paid in a contract as a single lease component. Lastly, the Company did not elect the practical expedient related to hindsight analysis which allows a lessee to use hindsight in determining the lease term and in assessing impairment of the entity’s ROU assets. The Company has made a policy election to not recognize ROU assets and lease liabilities that arise from leases with an initial term of twelve months or less on the Condensed Consolidated Statements of Financial Position. However, the Company will recognize these lease payments in the Condensed Consolidated Statements of Income on a straight-line basis over the lease term and variable lease payments in the period in which the obligation is incurred. The Company has chosen to apply this accounting policy across all classes of underlying assets. Additionally, upon adoption, the Company utilized a discount rate to determine the present value of the lease payments based on information available as of January 1, 2019. Beginning January 1, 2019, operating ROU assets and operating lease liabilities are recognized based on the present value of lease payments over the lease term at the commencement date. Operating leases in effect prior to January 1, 2019 were recognized at the present value of the remaining payments on the remaining lease term as of January 1, 2019. Upon adoption, the Company recognized ROU assets and lease liabilities of $1.1 billion and $1.3 billion , respectively. The standard had an insignificant impact on the Condensed Consolidated Statements of Income and no impact on the Condensed Consolidated Statements of Cash Flows. Refer to Note 20 “Lease Commitments” for further information including significant assumptions and judgments made. As a result of applying the modified retrospective approach to adopt the new leasing standard, the following adjustments were made to the Condensed Consolidated Statements of Financial Position as of January 1, 2019 (in millions): December 31, January 1, As Reported Adjustments As Adjusted Assets Operating lease right-of-use assets $ — $ 1,021 $ 1,021 Other non-current assets $ 448 $ 78 $ 526 Liabilities Other current liabilities $ 936 $ 219 $ 1,155 Non-current operating lease liabilities $ — $ 1,014 $ 1,014 Other non-current liabilities $ 1,097 $ (134 ) $ 963 Accounting Standards Issued But Not Yet Adopted 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. 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. An entity will apply the new guidance on a prospective basis. The new guidance is effective for Aon in the first quarter of 2020 and early adoption is permitted. The Company is currently evaluating the period of adoption, but does not expect a 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. An entity will apply the new standard through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the standard is effective. The new standard is effective for Aon in the first quarter of 2020 with early adoption permitted. The Company is currently evaluating the impact that the standard will have on the Financial Statements and will adopt the new accounting standard in the first quarter of 2020.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Commercial Risk Solutions $ 1,167 $ 1,166 $ 2,285 $ 2,350 Reinsurance Solutions 420 380 1,208 1,122 Retirement Solutions 419 431 839 855 Health Solutions 317 309 803 760 Data & Analytic Services 286 277 622 571 Elimination (3 ) (2 ) (8 ) (7 ) Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 United States $ 1,146 $ 1,125 $ 2,307 $ 2,241 Americas other than United States 241 243 467 480 United Kingdom 400 413 852 897 Europe, Middle East, & Africa other than United Kingdom 501 493 1,510 1,472 Asia Pacific 318 287 613 561 Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 236 $ 240 $ 329 $ 298 Additions 336 341 682 711 Amortization (357 ) (353 ) (796 ) (785 ) Impairment — — — — Foreign currency translation and other 1 (12 ) 1 (8 ) Balance at end of period $ 216 $ 216 $ 216 $ 216 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 155 $ 144 $ 156 $ 145 Additions 17 13 26 21 Amortization (11 ) (11 ) (22 ) (21 ) Impairment — — — — Foreign currency translation and other — (2 ) 1 (1 ) Balance at end of period $ 161 $ 144 $ 161 $ 144

Cash and Cash Equivalents and S

Cash and Cash Equivalents and Short-term Investments	6 Months Ended
	Jun. 30, 2019
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 June 30, 2019 , Cash and cash equivalents and Short-term investments were $816 million compared to $828 million at December 31, 2018 , a decrease of $12 million . Of the total balances, $99 million and $91 million were restricted as to their use at June 30, 2019 and December 31, 2018 , respectively. Included within Short-term investments as of June 30, 2019 and December 31, 2018 were £42.8 million ( $54.3 million at June 30, 2019 exchange rates) and £42.7 million ( $53.9 million at December 31, 2018 exchange rates), respectively, 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	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Foreign currency remeasurement $ 11 $ 29 $ — $ 13 Disposal of businesses 2 — 7 (1 ) Pension and other postretirement 5 (7 ) 9 (5 ) Equity earnings 1 1 2 2 Financial instruments (13 ) (27 ) (12 ) (27 ) Other — 1 — — Total $ 6 $ (3 ) $ 6 $ (18 ) Condensed Consolidated Statements of Financial Position Information Allowance for Doubtful Accounts An analysis of the allowance for doubtful accounts are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 64 $ 65 $ 64 $ 59 Provision charged to Other general expenses 4 3 12 11 Accounts written off, net of recoveries (3 ) (6 ) (11 ) (8 ) Balance at end of period $ 65 $ 62 $ 65 $ 62 Other Current Assets The components of Other current assets are as follows (in millions): As of June 30, December 31, Costs to fulfill contracts with customers (1) $ 216 $ 329 Prepaid expenses 128 97 Taxes receivable 145 113 Other (2) 142 79 Total $ 631 $ 618 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) December 31, 2018 includes $12 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 June 30, December 31, Costs to obtain contracts with customers (1) $ 161 $ 156 Taxes receivable 100 100 Leases (2) 65 — Investments 54 54 Other 141 138 Total $ 521 $ 448 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) Refer to Note 20 “Lease Commitments” for further information. Other Current Liabilities The components of Other current liabilities are as follows (in millions): As of June 30, December 31, Deferred revenue (1) $ 337 $ 251 Leases (2) 223 — Taxes payable 133 83 Other 504 602 Total $ 1,197 $ 936 (1) During the three and six months ended June 30, 2019 , $95 million and $241 million , respectively, was recognized in the Condensed Consolidated Statements of Income. During the three and six months ended June 30, 2018 , $115 million and $215 million , respectively, was recognized in the Condensed Consolidated Statements of Income. (2) Refer to Note 20 “Lease Commitments” for further information. Other Non-Current Liabilities The components of Other non-current liabilities are as follows (in millions): As of June 30, December 31, Taxes payable (1) $ 576 $ 585 Leases 37 169 Deferred revenue 59 65 Compensation and benefits 49 56 Other 203 222 Total $ 924 $ 1,097 (1) Includes $221 million and $240 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of June 30, 2019 and December 31, 2018 , respectively.

Discontinued Operations

Discontinued Operations	6 Months Ended
	Jun. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	Discontinued Operations On February 9, 2017, the Company entered into a Purchase Agreement with Tempo Acquisition, LLC (the “Purchase Agreement”) to sell its benefits administration and business process outsourcing business (the “Divested Business”) to an entity formed and controlled by affiliates of The Blackstone Group L.P. (the “Buyer”) and certain designated purchasers that are direct or indirect subsidiaries of the Buyer. On May 1, 2017, the Buyer purchased all of the outstanding equity interests of the Divested Business, plus certain related assets and liabilities, for a purchase price of $4.3 billion in cash paid at closing, subject to customary adjustments set forth in the Purchase Agreement, and deferred consideration of up to $500 million (the “Transaction”). Cash proceeds after customary adjustments and before taxes due were $4.2 billion . Aon and the Buyer entered into certain transaction related agreements at the closing, including two commercial agreements, a transition services agreement, certain intellectual property license agreements, subleases, and other customary agreements. Aon expects to continue to be a significant client of the Divested Business and the Divested Business has agreed to use Aon for its broking and other services for a specified period of time. The financial results of the Divested Business for the three and six months ended June 30, 2019 and 2018 are presented as Income from discontinued operations on the Company’s Condensed Consolidated Statements of Income. The following table presents the financial results of the Divested Business (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Expenses Total operating expenses $ 1 $ — $ 1 $ 3 Loss from discontinued operations before income taxes (1 ) — (1 ) (3 ) Income tax benefit (1 ) — (1 ) (1 ) Net loss from discontinued operations excluding gain — — — (2 ) Gain on sale of discontinued operations, net of tax — 1 — 9 Net income from discontinued operations $ — $ 1 $ — $ 7 There were no Cash and cash equivalents of discontinued operations at June 30, 2019 . Total proceeds received for the sale of the Divested Business and taxes paid as a result of the sale are recognized on the Condensed Consolidated Statements of Cash Flows in Cash provided by investing activities - continuing operations and Cash provided by operating activities - continuing operations, respectively.

Restructuring

Restructuring	6 Months Ended
	Jun. 30, 2019
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 Divested Business. The Restructuring Plan is intended to streamline operations across the organization and deliver greater efficiency, insight, and connectivity. The Company expects these restructuring activities and related expenses to affect continuing operations through the fourth quarter of 2019, including an estimated 5,000 to 5,600 total role eliminations. In the second quarter of 2019, Aon updated the Restructuring Plan for additional opportunities that were identified in the quarter, which are expected to result in additional estimated charges of $125 million in 2019. The Restructuring Plan is expected to result in cumulative charges of approximately $1,350 million through the end of the plan, consisting of approximately $530 million in employee termination costs, $130 million in technology rationalization costs, $80 million in lease consolidation costs, $45 million in non-cash asset impairments, and $565 million in other costs, including certain separation costs associated with the sale of the Divested Business. From the inception of the Restructuring Plan through June 30, 2019 , the Company has eliminated 5,091 positions and incurred total charges of $1,200 million for restructuring and related separation costs. These charges are included in Compensation and benefits, Information technology, Premises, Depreciation of fixed assets, and Other general expenses in the accompanying Condensed Consolidated Statements of Income. The following table summarizes restructuring and separation costs by type that have been incurred through June 30, 2019 and are estimated to be incurred through the end of the Restructuring Plan (in millions). Estimated costs by type may be revised in future periods as these assumptions are updated: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Inception to Date Estimated Remaining Costs Estimated Total Cost (1) Workforce reduction $ 78 $ 102 $ 516 $ 14 $ 530 Technology rationalization (2) 4 15 95 35 130 Lease consolidation (2) 5 14 50 30 80 Asset impairments 2 2 41 4 45 Other costs associated with restructuring and separation (2) (3) 38 85 498 67 565 Total restructuring and related expenses $ 127 $ 218 $ 1,200 $ 150 $ 1,350 (1) Actual costs, when incurred, may vary due to changes in the assumptions built into the Restructuring Plan. Significant assumptions that may change when plans are finalized and implemented include, but are not limited to, changes in severance calculations, changes in the assumptions underlying sublease loss calculations due to changing market conditions, and changes in the overall analysis that might cause the Company to add or cancel component initiatives. Estimated Total Cost includes $100 million of non-cash charges. (2) Total contract termination costs incurred under the Restructuring Plan associated with Technology rationalizations, Lease consolidations, and Other costs, respectively, associated with restructuring and separation were for the three months ended June 30, 2019 , $2 million , $4 million , and $1 million ; for the six months ended June 30, 2019 , were $3 million , $13 million , and $3 million ; and since inception of the Restructuring Plan, were $9 million , $46 million , and $91 million . Total estimated contract termination costs expected to be incurred under the Restructuring Plan associated with Technology rationalizations, Lease consolidations, and Other costs associated with restructuring and separation, are $15 million , $80 million , and $95 million , respectively. (3) Other costs associated with the Restructuring Plan include those to separate the Divested Business, as well as moving costs, and consulting and legal fees. These costs are generally recognized when incurred. The changes in the Company’s liabilities for the Restructuring Plan as of June 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 201 Expensed 204 Cash payments (222 ) Foreign currency translation 1 Balance as of June 30, 2019 $ 184

Acquisitions and Dispositions o

Acquisitions and Dispositions of Businesses	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Acquisitions and Dispositions of Businesses	Acquisitions and Dispositions of Businesses Completed Acquisitions The Company completed one acquisition during the six months ended June 30, 2019 and five acquisitions during the six months ended June 30, 2018 . The following table includes the fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Six Months Ended June 30, 2019 Consideration Transferred $ 17 Deferred and contingent consideration 5 Aggregate consideration transferred $ 22 Assets acquired Cash and cash equivalents $ 2 Goodwill 15 Intangible assets, net 9 Other assets 4 Total assets acquired 30 Liabilities assumed Current liabilities 6 Other non-current liabilities 2 Total liabilities assumed 8 Net assets acquired $ 22 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. 2019 Acquisitions On January 1, 2019, the Company completed the transaction to acquire Chapka Assurances SAS based in France. 2018 Acquisitions On May 9, 2018, the Company completed the transaction to acquire certain assets of 601West, a division of Lee & Hayes, P.L.L.C. based in the United States. On April 24, 2018, the Company completed the transaction to acquire Inspiring Benefits, S.L., a Spain-based firm specialized in employee loyalty, wellbeing, and rewards programs. On March 1, 2018, the Company completed the transaction to acquire the business and assets of the trade credit business of Niche International Business Proprietary Limited, a trade credit brokerage based in Johannesburg, South Africa. On March 1, 2018, the Company completed the transaction to acquire Affinity Risk Partners (Brokers) Pty. Ltd., an insurance broker in Victoria, Australia. On January 19, 2018, the Company completed the transaction to acquire substantially all of the assets of The Burchfield Group, a provider in pharmacy benefit consulting, auditing, and health plan compliance services based in the United States. Completed Dispositions The Company completed three dispositions during the three months ended June 30, 2019 and four dispositions during the six months ended June 30, 2019 . The Company completed one disposition during the three and six months ended June 30, 2018 . Total pretax gains recognized for the three and six months ended June 30, 2019 were $2 million and $7 million , respectively. There were no pretax gains or losses for the three months ended June 30, 2018 and total pretax losses, net of gains, were $1 million for the six months ended June 30, 2018 . Gains and losses recognized as a result of a disposition are included in Other income (expense) in the Condensed Consolidated Statements of Income.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	6 Months Ended
	Jun. 30, 2019
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 six months ended June 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 8,171 Goodwill related to current year acquisitions 15 Goodwill related to disposals (9 ) Goodwill related to prior year acquisitions 2 Foreign currency translation and other 19 Balance as of June 30, 2019 $ 8,198 Other intangible assets by asset class are as follows (in millions): June 30, 2019 December 31, 2018 Gross Carrying Amount Accumulated Amortization and Impairment Net Carrying Amount Gross Carrying Amount Accumulated Net Carrying Amount Customer related and contract based $ 2,254 $ 1,517 $ 737 $ 2,240 $ 1,444 $ 796 Tradenames 1,028 847 181 1,027 740 287 Technology and other 385 330 55 391 325 66 Total $ 3,667 $ 2,694 $ 973 $ 3,658 $ 2,509 $ 1,149 The estimated future amortization for finite lived intangible assets as of June 30, 2019 is as follows (in millions): Remainder of 2019 $ 192 2020 223 2021 128 2022 87 2023 74 2024 58 Thereafter 211 Total $ 973

Debt

Debt	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Debt	Debt Notes 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. On December 3, 2018, Aon Corporation issued $350 million 4.50% Senior Notes due December 2028. The Company used the net proceeds of the offering to pay down a portion of outstanding commercial paper and for general corporate purposes. On March 8, 2018, the Company’s CAD 375 million ( $291 million at March 8, 2018 exchange rates) 4.76% Senior Note due March 2018 issued by a Canadian subsidiary of Aon Corporation matured and was repaid in full. Revolving Credit Facilities As of June 30, 2019 , Aon plc had two primary committed credit facilities outstanding: its $900 million multi-currency United States (“U.S.”) credit facility expiring in February 2022 and its $400 million multi-currency U.S. credit facility expiring in October 2022 (collectively, the “2022 Facilities”). Each of these 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 June 30, 2019 , Aon did not have borrowings under the 2022 Facilities, and was in compliance with the financial covenants and all other covenants contained therein during the rolling twelve months ended June 30, 2019 . Commercial Paper Aon Corporation, a wholly owned subsidiary of Aon plc, has established a U.S. commercial paper program and Aon plc has established a European multi-currency commercial paper program (collectively, the “CP 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 $1.3 billion at June 30, 2019 . The U.S. commercial paper program is fully and unconditionally guaranteed by Aon plc and the European multi-currency commercial paper program is fully and unconditionally guaranteed by Aon Corporation. Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Company’s Condensed Consolidated Statements of Financial Position, is as follows (in millions): As of June 30, 2019 December 31, 2018 Commercial paper outstanding $ 843 $ 250 The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Weighted average commercial paper outstanding $ 639 $ 744 482 $ 437 Weighted average interest rate of commercial paper outstanding 0.70 % 0.92 % 0.63 % 0.85 %

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rates on net income from continuing operations were 16.3% and 15.9% for the three and six months ended June 30, 2019 , respectively. The effective tax rates on net income from continuing operations were 165.5% and (4.8)% for the three and six months ended June 30, 2018 , respectively. For the three and six months ended June 30, 2019 , the tax rate was primarily driven by the geographical distribution of income, including restructuring charges, and certain favorable discrete items, primarily the impact of shared-based payments and changes in the assertion for unremitted earnings. For the three and six months ended June 30, 2018 , the tax rate was primarily driven by the geographical distribution of income including restructuring charges, legacy litigation, and the impairment charge related to certain assets and liabilities classified as held for sale. In addition, certain discrete items impacted the 2018 tax rate including the net tax benefit associated with the anticipated sale of certain assets and liabilities classified as held for sale, the impact of share-based payments, changes in uncertain tax positions and the deferred remeasurement related to the anticipated acceleration of contributions to the qualified U.S. pension plan.

Shareholders' Equity

Shareholders' Equity	6 Months Ended
	Jun. 30, 2019
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 February 2017 for a total of $15.0 billion in repurchase authorizations. Under the Repurchase Program, 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Shares repurchased 5.8 2.8 6.4 6.7 Average price per share $ 183.23 $ 141.23 $ 181.07 $ 141.06 Costs recorded to retained earnings: Total repurchase cost $ 1,050 $ 400 $ 1,150 $ 950 Additional associated costs 6 2 7 5 Total costs recorded to retained earnings $ 1,056 $ 402 $ 1,157 $ 955 At June 30, 2019 , the remaining authorized amount for share repurchase under the Repurchase Program was $2.8 billion . Under the Repurchase Program, the Company has repurchased a total of 124.6 million shares for an aggregate cost of approximately $12.2 billion . Net Income Per Share Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Basic weighted average ordinary shares outstanding 240.6 246.0 241.4 247.2 Dilutive effect of potentially issuable shares 2.2 1.4 1.8 1.6 Diluted weighted average ordinary shares outstanding 242.8 247.4 243.2 248.8 Potentially issuable shares are not included in the computation of diluted net income per share if its inclusion would be antidilutive. There were no shares excluded from the calculation for the three and six months ended June 30, 2019 and June 30, 2018 . 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, 2018 $ (15 ) $ (1,319 ) $ (2,575 ) $ (3,909 ) Other comprehensive income (loss) before reclassifications, net (8 ) 28 5 25 Amounts reclassified from accumulated other comprehensive income: Amounts reclassified from accumulated other comprehensive income 8 — 52 60 Tax expense (1 ) — (12 ) (13 ) Amounts reclassified from accumulated other comprehensive income, net 7 — 40 47 Net current period other comprehensive income (loss) (1 ) 28 45 72 Balance at June 30, 2019 $ (16 ) $ (1,291 ) $ (2,530 ) $ (3,837 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the accompanying Condensed Consolidated Statements of Income. Refer to Note 15 “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).

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2019
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 international pension plans. 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 June 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 27 29 27 25 7 7 Expected return on plan assets, net of administration expenses (48 ) (50 ) (34 ) (36 ) (10 ) (11 ) Amortization of prior-service cost — — — 1 — — Amortization of net actuarial loss 8 7 14 15 3 3 Net periodic (benefit) cost (13 ) (14 ) 7 5 — (1 ) Loss on pension settlement — 16 — — — — Total net periodic (benefit) cost $ (13 ) $ 2 $ 7 $ 5 $ — $ (1 ) Six Months Ended June 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 55 58 54 50 14 14 Expected return on plan assets, net of administration expenses (97 ) (101 ) (68 ) (72 ) (20 ) (23 ) Amortization of prior-service cost 1 — 1 1 — — Amortization of net actuarial loss 15 15 27 30 6 6 Net periodic (benefit) cost (26 ) (28 ) 14 9 — (3 ) Loss on pension settlement — 23 — — — — Total net periodic (benefit) cost $ (26 ) $ (5 ) $ 14 $ 9 $ — $ (3 ) In March 2017, the Company approved a plan to offer a voluntary one-time lump sum payment option to certain eligible employees of the Company’s U.K. pension plans that, if accepted, would settle the Company’s pension obligations to them. The lump sum cash payment offer closed during 2018. For the six months ended June 30, 2018, lump sum payments from plan assets of £99 million ( $132 million using June 30, 2018 exchange rates) were paid. As a result of this settlement, the Company remeasured the assets and liabilities of the U.K. pension plan during the second quarter of 2018, which in aggregate resulted in a reduction to the projected benefit obligation of £87 million ( $115 million using June 30, 2018 exchange rates), as well as a non-cash settlement charge of £12 million ( $16 million using average June 30, 2018 exchange rates) in the second quarter of 2018 and £17 million ( $23 million using average exchange rates) for the six months ended June 30, 2018. Contributions The Company expects to make total cash contributions of approximately $80 million , $46 million , and $19 million , based on exchange rates as of December 31, 2018 , to its significant U.K., U.S., and other significant international pension plans, respectively, during 2019. During the three months ended June 30, 2019 , cash contributions of $23 million , $6 million , and $3 million were made to the Company’s significant U.K., U.S., and other significant international pension plans, respectively. During the six months ended June 30, 2019 , cash contributions of $46 million , $23 million , and $10 million were made to the Company’s significant U.K., U.S., and other significant international pension plans, respectively. During the three months ended June 30, 2018 , cash contributions of $25 million , $8 million , and $3 million were made to the Company’s significant U.K., U.S., and other significant international pension plans, respectively. During the six months ended June 30, 2018 , cash contributions of $48 million , $25 million , and $11 million were made to the Company’s significant U.K., U.S., and other significant international pension plans, respectively.

Share-Based Compensation Plans

Share-Based Compensation Plans	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Restricted share units (“RSUs”) $ 50 $ 46 $ 113 $ 104 Performance share awards (“PSAs”) 39 23 62 39 Employee share purchase plans 2 1 5 4 Total share-based compensation expense $ 91 $ 70 $ 180 $ 147 Restricted Share Units RSUs generally vest between three and five years . The fair value of RSUs is based upon the market value of Aon plc 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, including shares related to the Divested Business (shares in thousands, except fair value): Six Months Ended June 30, 2019 Six Months Ended June 30, 2018 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 4,208 $ 120 4,849 $ 104 Granted 1,178 $ 173 1,352 $ 140 Vested (1,451 ) $ 113 (1,664 ) $ 98 Forfeited (97 ) $ 124 (109 ) $ 109 Non-vested at end of period 3,838 $ 139 4,428 $ 117 (1) Represents per share weighted average fair value of award at date of grant. Unamortized deferred compensation expense amounted to $426 million as of June 30, 2019 , with a remaining weighted average amortization period of approximately 2.1 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 issue 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 Aon plc 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 six months ended June 30, 2019 and the years ended December 31, 2018 and 2017 , respectively (shares in thousands and dollars in millions, except fair value): June 30, December 31, December 31, Target PSAs granted during period 467 564 548 Weighted average fair value per share at date of grant $ 164 $ 134 $ 114 Number of shares that would be issued based on current performance levels 464 970 1,066 Unamortized expense, based on current performance levels $ 69 $ 67 $ 20

Derivatives and Hedging

Derivatives and Hedging	6 Months Ended
	Jun. 30, 2019
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, 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 2 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 1 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) June 30, December 31, June 30, December 31, June 30, December 31, Foreign exchange contracts: Accounted for as hedges $ 588 $ 646 $ 14 $ 17 $ 1 $ 2 Not accounted for as hedges (3) 285 269 5 1 — 6 Total $ 873 $ 915 $ 19 $ 18 $ 1 $ 8 (1) Included within Other current assets ( $8 million at June 30, 2019 and $3 million at December 31, 2018 ) or Other non-current assets ( $11 million at June 30, 2019 and $15 million at December 31, 2018 ). (2) Included within Other current liabilities ( $1 million at June 30, 2019 and $5 million at December 31, 2018 ) or Other non-current liabilities ( $3 million at December 31, 2018 ). (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 Financial Statements are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Loss recognized in Accumulated other comprehensive loss $ (12 ) $ (25 ) $ (8 ) $ (11 ) The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss into the Condensed Consolidated Statements of Income are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Revenue (1) $ (3 ) $ — $ (7 ) $ — Compensation and benefits — — — 1 Other general expenses — (1 ) — (2 ) Interest expense — — (1 ) (1 ) Other income (expense) (1) — (1 ) — (4 ) Total $ (3 ) $ (2 ) $ (8 ) $ (6 ) (1) With the adoption of new hedge accounting guidance in the first quarter of 2019, gains (losses) on derivatives accounted for as hedges are recognized in Total revenue in the Company’s Condensed Consolidated Statements of Income rather than Other income (expense). Refer to Note 2 “Accounting Principles and Practices” for additional details. 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 twelve months. During the three and six months ended June 30, 2019 , the Company recorded losses of $9 million and $4 million , respectively, in Other income (expense) for foreign exchange derivatives not accounted for as hedges. During the three and six months ended June 30, 2018 , the Company recorded losses of $20 million and $11 million , respectively, in Other income (expense) for foreign exchange derivatives not accounted for 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. As of June 30, 2019 , the Company has €500 million ( $568 million at June 30, 2019 exchange rates) of outstanding euro-denominated commercial paper designated as a hedge of the foreign currency exposure of its net investment in its European operations. As of June 30, 2019 , the unrealized gain recognized in Accumulated other comprehensive loss related to the net investment non derivative hedging instrument was $16 million . 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 and six months ended June 30, 2019

Fair Value Measurements and Fin

Fair Value Measurements and Financial Instruments	6 Months Ended
	Jun. 30, 2019
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 domestic and international 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 and 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 the Company’s guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates 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 June 30, 2019 and December 31, 2018 (in millions): Fair Value Measurements Using Balance at June 30, 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) $ 2,356 $ 2,356 $ — $ — Other investments: Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 3 $ — $ 3 $ — Fair Value Measurements Using Balance at December 31, 2018 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) $ 1,759 $ 1,759 $ — $ — Other investments: Government bonds $ 1 $ — $ 1 $ — Equity investments $ 2 $ — $ 2 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 12 $ — $ 12 $ — (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 15 “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 either the six months ended June 30, 2019 or 2018 . The Company recognized no realized or unrealized gains or losses in the Condensed Consolidated Statements of Income during either the six months ended June 30, 2019 or 2018 , 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): June 30, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value Long-term debt $ 6,740 $ 7,356 $ 5,993 $ 6,159

Claims, Lawsuits and Other Cont

Claims, Lawsuits and Other Contingencies	6 Months Ended
	Jun. 30, 2019
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 expenses 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 may change, 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 A pensions consulting and administration subsidiary of Aon provided advisory services to the Trustees of the Gleeds pension fund in the United Kingdom and, on occasion, to the relevant employer of the fund. In April 2014, the High Court, Chancery Division, London found that certain governing documents of the fund that sought to alter the fund’s benefit structure and that had been drafted by Aon were procedurally defective and therefore invalid. No lawsuit naming Aon as a party was filed, although a tolling agreement was entered. The High Court decision says that the additional liabilities in the pension fund resulting from the alleged defect in governing documents amount to approximately £45 million ( $57 million at June 30, 2019 exchange rates). In December 2014, the Court of Appeal granted the employer leave to appeal the High Court decision. At a hearing in October 2016, the Court of Appeal approved a settlement of the pending litigation. On October 31, 2016, the fund’s trustees and employer sued Aon in the High Court, Chancery Division, London, alleging negligence and breach of duty in relation to the governing documents. The proceedings were served on Aon on December 20, 2016. The claimants seek damages of approximately £70 million ( $89 million at June 30, 2019 exchange rates) plus interest and costs. In February 2018, the claimants instructed new lawyers and added their previous lawyers as defendants to the Aon lawsuit. Claimants have alleged that the previous lawyers were responsible for some of the losses sought from Aon because the lawyers gave negligent legal advice during the course of the High Court and Court of Appeal proceedings. Aon believes that it has meritorious defenses and intends to vigorously defend itself against this claim. 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 ( $353 million at June 30, 2019 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 our 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. Settled/Closed Matters On June 29, 2015, Lyttelton Port Company Limited (“LPC”) sued Aon New Zealand in the Christchurch Registry of the High Court of New Zealand. LPC alleges, among other things, that Aon was negligent and in breach of contract in arranging LPC’s property insurance program for the period covering June 30, 2010 to June 30, 2011. LPC contended that acts and omissions by Aon caused LPC to recover less than it otherwise would have from insurers for losses suffered in the 2010 and 2011 Canterbury earthquakes. LPC claimed damages of approximately NZD 184 million ( $123 million at June 30, 2019 exchange rates) plus interest and costs. In April 2019, the case was settled with no admission of liability on the part of Aon. The terms of this settlement did not have a significant impact on Aon’s results of operations or financial condition. 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 Company’s 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. Redomestication In connection with the 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 as of April 2, 2012, among Aon Corporation, Aon plc, and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”) (amending and restating the Indenture, dated as of September 10, 2010, between Aon Corporation and the Trustee), (2) Amended and Restated Indenture, dated as of April 2, 2012, among Aon Corporation, Aon plc and the Trustee (amending and restating the Indenture, dated as of December 16, 2002, between Aon Corporation and the Trustee), and (3) Amended and Restated Indenture, dated as of April 2, 2012, among Aon Corporation, Aon plc and the Trustee (amending and restating the Indenture, dated as of January 13, 1997, as supplemented by the First Supplemental Indenture, dated as of January 13, 1997). 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 June 30, 2019 , the undiscounted maximum potential future payments under the lease guarantee is $77 million , with an estimated fair value of $15 million . No cash payments were made in connection to the lease commitments during the six months ended June 30, 2019 . 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 June 30, 2019 , the undiscounted maximum potential future payments under the performance guarantees were $170 million , with an estimated fair value of $1 million . No cash payments were made in connection to the performance guarantees during the three and six months ended June 30, 2019 . 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 $74 million at June 30, 2019 , compared to $83 million at December 31, 2018 . 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 $102 million at June 30, 2019 compared to $103 million at December 31, 2018 .

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2019
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 Aon’s 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 on 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	6 Months Ended
	Jun. 30, 2019
Guarantee of Registered Securities [Abstract]
Guarantee of Registered Securities	Guarantee of Registered Securities As described in Note 17 “Claims, Lawsuits, and Other Contingencies,” in connection with the Redomestication, Aon plc entered into various agreements pursuant to which it agreed to guarantee the obligations of Aon Corporation arising under issued and outstanding debt securities, including the 5.00% Notes due September 2020, the 8.205% Notes due January 2027, and the 6.25% Notes due September 2040 (collectively, the “Aon Corporation Notes”). Additionally, Aon plc has guaranteed the obligations of Aon Corporation arising under the 4.50% Senior Notes due 2028 and the 3.75% Senior Notes due 2029. Aon Corporation is a 100% indirectly owned subsidiary of Aon plc. All guarantees of Aon plc are full and unconditional. There are no other subsidiaries of Aon plc that are guarantors of the Aon Corporation Notes. In addition, Aon Corporation entered into an agreement pursuant to which it guaranteed the obligations of Aon plc arising under the 4.25% Notes due 2042 exchanged for Aon Corporation’s outstanding 8.205% Notes due January 2027, and has also guaranteed the obligations of Aon plc arising under the 4.45% Notes due 2043, the 4.00% Notes due November 2023, the 2.875% Notes due May 2026, the 3.50% Notes due June 2024, the 4.60% Notes due June 2044, the 4.75% Notes due May 2045, the 2.80% Notes due March 2021, and the 3.875% Notes due December 2025 (collectively, the “Aon plc Notes”). In each case, the guarantee of Aon Corporation is full and unconditional. There are no subsidiaries of Aon plc, other than Aon Corporation, that are guarantors of the Aon plc Notes. As a result of the existence of these guarantees, the Company has elected to present the financial information set forth in this footnote in accordance with Rule 3-10 of Regulation S-X. In the fourth quarter of 2018, Aon plc obtained direct ownership in two subsidiaries that were previously indirectly owned by Aon Corporation. In the first quarter of 2019, Aon Corporation obtained indirect ownership of subsidiaries that were previously indirectly owned by Aon plc. The financial results of these subsidiaries are included in the Other Non-Guarantor Subsidiaries column of the Condensed Consolidating Financial Statements. The Company has retrospectively reflected the impact of these transactions on the Condensed Consolidating Statements of Income and Condensed Consolidating Statements of Comprehensive Income for the periods ended June 30, 2018 and the Condensed Consolidated Statement of Financial Position as of December 31, 2018. The following tables set forth Condensed Consolidating Statements of Income and Condensed Consolidating Statements of Comprehensive Income for the three and six months ended June 30, 2019 and 2018 , Condensed Consolidating Statements of Financial Position as of June 30, 2019 and December 31, 2018 , and Condensed Consolidating Statements of Cash Flows for the six months ended June 30, 2019 and 2018 in accordance with Rule 3-10 of Regulation S-X. The Condensed Consolidating Financial Information includes the accounts of Aon plc, 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 June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,606 $ — $ 2,606 Expenses Compensation and benefits 22 4 1,475 — 1,501 Information technology — — 126 — 126 Premises — 9 76 — 85 Depreciation of fixed assets — — 40 — 40 Amortization and impairment of intangible assets — — 97 — 97 Other general expenses 3 6 335 — 344 Total operating expenses 25 19 2,149 — 2,193 Operating income (loss) (25 ) (19 ) 457 — 413 Interest income — 9 — (8 ) 1 Interest expense (45 ) (34 ) (6 ) 8 (77 ) Intercompany interest income (expense) 3 (116 ) 113 — — Intercompany other income (expense) 137 (164 ) 27 — — Other income (expense) (11 ) (14 ) 24 7 6 Income (loss) from continuing operations before income taxes 59 (338 ) 615 7 343 Income tax expense (benefit) — (64 ) 120 — 56 Net income (loss) from continuing operations 59 (274 ) 495 7 287 Net income from discontinued operations — — — — — Net income (loss) before equity in earnings of subsidiaries 59 (274 ) 495 7 287 Equity in earnings of subsidiaries 211 301 27 (539 ) — Net income 270 27 522 (532 ) 287 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders $ 270 $ 27 $ 512 $ (532 ) $ 277 Condensed Consolidating Statement of Income Three Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,561 $ — $ 2,561 Expenses Compensation and benefits 15 1 1,478 — 1,494 Information technology — — 123 — 123 Premises — — 96 — 96 Depreciation of fixed assets — — 47 — 47 Amortization and impairment of intangible assets — — 282 — 282 Other general expenses 2 91 442 — 535 Total operating expenses 17 92 2,468 — 2,577 Operating income (loss) (17 ) (92 ) 93 — (16 ) Interest income — 15 — (14 ) 1 Interest expense (48 ) (25 ) (10 ) 14 (69 ) Intercompany interest income (expense) 3 (129 ) 126 — — Intercompany other income (expense) (93 ) 10 83 — — Other income (expense) 48 (20 ) (13 ) (18 ) (3 ) Income (loss) from continuing operations before income taxes (107 ) (241 ) 279 (18 ) (87 ) Income tax expense (benefit) (3 ) (50 ) (91 ) — (144 ) Net income (loss) from continuing operations (104 ) (191 ) 370 (18 ) 57 Net income from discontinued operations — — 1 — 1 Net income (loss) before equity in earnings of subsidiaries (104 ) (191 ) 371 (18 ) 58 Equity in earnings of subsidiaries 170 207 16 (393 ) — Net income 66 16 387 (411 ) 58 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders $ 66 $ 16 $ 377 $ (411 ) $ 48 Condensed Consolidating Statement of Income Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 5,749 $ — $ 5,749 Expenses Compensation and benefits 42 12 3,031 — 3,085 Information technology — — 243 — 243 Premises — 13 159 — 172 Depreciation of fixed assets — — 80 — 80 Amortization and impairment of intangible assets — — 194 — 194 Other general expenses 3 2 685 — 690 Total operating expenses 45 27 4,392 — 4,464 Operating income (loss) (45 ) (27 ) 1,357 — 1,285 Interest income — 18 — (15 ) 3 Interest expense (91 ) (62 ) (11 ) 15 (149 ) Intercompany interest income (expense) 7 (232 ) 225 — — Intercompany other income (expense) 168 (263 ) 95 — — Other income (expense) (6 ) (25 ) 32 5 6 Income (loss) from continuing operations before income taxes 33 (591 ) 1,698 5 1,145 Income tax expense (benefit) (5 ) (106 ) 293 — 182 Net income (loss) from continuing operations 38 (485 ) 1,405 5 963 Net income from discontinued operations — — — — — Net income (loss) before equity in earnings of subsidiaries 38 (485 ) 1,405 5 963 Equity in earnings of subsidiaries 893 1,025 540 (2,458 ) — Net income 931 540 1,945 (2,453 ) 963 Less: Net income attributable to noncontrolling interests — — 27 — 27 Net income attributable to Aon shareholders $ 931 $ 540 $ 1,918 $ (2,453 ) $ 936 Condensed Consolidating Statement of Income Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 5,651 $ — $ 5,651 Expenses Compensation and benefits 34 2 3,074 — 3,110 Information technology — — 238 — 238 Premises — — 189 — 189 Depreciation of fixed assets — — 86 — 86 Amortization and impairment of intangible assets — — 392 — 392 Other general expenses 3 91 759 — 853 Total operating expenses 37 93 4,738 — 4,868 Operating income (loss) (37 ) (93 ) 913 — 783 Interest income — 29 — (24 ) 5 Interest expense (97 ) (49 ) (17 ) 24 (139 ) Intercompany interest income (expense) 7 (257 ) 250 — — Intercompany other income (expense) (146 ) 5 141 — — Other income (expense) 23 (26 ) — (15 ) (18 ) Income (loss) from continuing operations before income taxes (250 ) (391 ) 1,287 (15 ) 631 Income tax expense (benefit) (19 ) (77 ) 66 — (30 ) Net income (loss) from continuing operations (231 ) (314 ) 1,221 (15 ) 661 Net income from discontinued operations — — 7 — 7 Net income (loss) before equity in earnings of subsidiaries (231 ) (314 ) 1,228 (15 ) 668 Equity in earnings of subsidiaries 888 912 598 (2,398 ) — Net income 657 598 1,826 (2,413 ) 668 Less: Net income attributable to noncontrolling interests — — 26 — 26 Net income attributable to Aon shareholders $ 657 $ 598 $ 1,800 $ (2,413 ) $ 642 Condensed Consolidating Statement of Comprehensive Income Three Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 270 $ 27 $ 522 $ (532 ) $ 287 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders 270 27 512 (532 ) 277 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (8 ) — (8 ) Foreign currency translation adjustments — — (96 ) (7 ) (103 ) Postretirement benefit obligation — 10 4 — 14 Total other comprehensive income (loss) — 10 (100 ) (7 ) (97 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (90 ) (118 ) (108 ) 316 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — — — — Total other comprehensive income (loss) attributable to Aon shareholders (90 ) (108 ) (208 ) 309 (97 ) Comprehensive income attributable (loss) to Aon shareholders $ 180 $ (81 ) $ 304 $ (223 ) $ 180 Condensed Consolidating Statement of Comprehensive Income Three Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 66 $ 16 $ 387 $ (411 ) $ 58 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders 66 16 377 (411 ) 48 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (4 ) 3 — (1 ) Foreign currency translation adjustments — — (478 ) 18 (460 ) Postretirement benefit obligation — 11 111 — 122 Total other comprehensive income (loss) — 7 (364 ) 18 (339 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (351 ) (345 ) (338 ) 1,034 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive income (loss) attributable to Aon shareholders (351 ) (338 ) (696 ) 1,052 (333 ) Comprehensive income attributable (loss) to Aon shareholders $ (285 ) $ (322 ) $ (319 ) $ 641 $ (285 ) Condensed Consolidating Statement of Comprehensive Income Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 931 $ 540 $ 1,945 $ (2,453 ) $ 963 Less: Net income attributable to noncontrolling interests — — 27 — 27 Net income attributable to Aon shareholders 931 540 1,918 (2,453 ) 936 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — 2 (3 ) — (1 ) Foreign currency translation adjustments — — 35 (5 ) 30 Postretirement benefit obligation — 32 13 — 45 Total other comprehensive income (loss) — 34 45 (5 ) 74 Equity in other comprehensive income (loss) of subsidiaries, net of tax 77 (3 ) 31 (105 ) — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — 2 — 2 Total other comprehensive income (loss) attributable to Aon shareholders 77 31 74 (110 ) 72 Comprehensive income attributable (loss) to Aon shareholders $ 1,008 $ 571 $ 1,992 $ (2,563 ) $ 1,008 Condensed Consolidating Statement of Comprehensive Income Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 657 $ 598 $ 1,826 $ (2,413 ) $ 668 Less: Net income attributable to noncontrolling interests — — 26 — 26 Net income attributable to Aon shareholders 657 598 1,800 (2,413 ) 642 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (1 ) 14 — 13 Foreign currency translation adjustments — — (228 ) 15 (213 ) Postretirement benefit obligation — 22 148 — 170 Total other comprehensive income (loss) — 21 (66 ) 15 (30 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (42 ) (60 ) (39 ) 141 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive income (loss) attributable to Aon shareholders (42 ) (39 ) (102 ) 156 (27 ) Comprehensive income attributable (loss) to Aon shareholders $ 615 $ 559 $ 1,698 $ (2,257 ) $ 615 Condensed Consolidating Statement of Financial Position As of June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 1,371 $ 537 $ (1,327 ) $ 581 Short-term investments — 125 110 — 235 Receivables, net — — 3,227 — 3,227 Fiduciary assets — — 12,071 — 12,071 Current intercompany receivables 167 3,421 12,843 (16,431 ) — Other current assets — 10 621 — 631 Total current assets 167 4,927 29,409 (17,758 ) 16,745 Goodwill — — 8,198 — 8,198 Intangible assets, net — — 973 — 973 Fixed assets, net — — 599 — 599 Operating lease right-of-use assets — 112 847 — 959 Deferred tax assets 93 498 150 (142 ) 599 Prepaid pension — 5 1,208 — 1,213 Non-current intercompany receivables 404 261 7,200 (7,865 ) — Other non-current assets 1 28 492 — 521 Investment in subsidiary 8,937 20,147 (424 ) (28,660 ) — Total assets $ 9,602 $ 25,978 $ 48,652 $ (54,425 ) $ 29,807 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 582 $ 57 $ 2,057 $ (1,327 ) $ 1,369 Short-term debt and current portion of long-term debt 569 275 — — 844 Fiduciary liabilities — — 12,071 — 12,071 Current intercompany payables 378 14,633 1,420 (16,431 ) — Other current liabilities — 78 1,119 — 1,197 Total current liabilities 1,529 15,043 16,667 (17,758 ) 15,481 Long-term debt 4,234 2,506 — — 6,740 Non-current operating lease liabilities — 149 813 — 962 Deferred tax liabilities — — 353 (142 ) 211 Pension, other postretirement, and postemployment liabilities — 1,232 344 — 1,576 Non-current intercompany payables — 7,366 499 (7,865 ) — Other non-current liabilities 3 106 815 — 924 Total liabilities 5,766 26,402 19,491 (25,765 ) 25,894 Equity Total Aon shareholders’ equity 3,836 (424 ) 29,084 (28,660 ) 3,836 Noncontrolling interests — — 77 — 77 Total equity 3,836 (424 ) 29,161 (28,660 ) 3,913 Total liabilities and equity $ 9,602 $ 25,978 $ 48,652 $ (54,425 ) $ 29,807 Condensed Consolidating Statement of Financial Position As of December 31, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 862 $ 575 $ (781 ) $ 656 Short-term investments — 56 116 — 172 Receivables, net — — 2,760 — 2,760 Fiduciary assets — — 10,166 — 10,166 Current intercompany receivables 191 897 11,634 (12,722 ) — Other current assets — 16 602 — 618 Total current assets 191 1,831 25,853 (13,503 ) 14,372 Goodwill — — 8,171 — 8,171 Intangible assets, net — — 1,149 — 1,149 Fixed assets, net — — 588 — 588 Operating lease right-of-use assets — — — — — Deferred tax assets 94 467 144 (144 ) 561 Prepaid pension — 5 1,128 — 1,133 Non-current intercompany receivables 403 261 7,225 (7,889 ) — Other non-current assets 1 30 417 — 448 Investment in subsidiary 8,433 19,132 (882 ) (26,683 ) — Total assets $ 9,122 $ 21,726 $ 43,793 $ (48,219 ) $ 26,422 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 274 $ 70 $ 2,380 $ (781 ) $ 1,943 Short-term debt and current portion of long-term debt 250 — 1 — 251 Fiduciary liabilities — — 10,166 — 10,166 Current intercompany payables 213 11,875 634 (12,722 ) — Other current liabilities — 69 867 — 936 Total current liabilities 737 12,014 14,048 (13,503 ) 13,296 Long-term debt 4,231 1,762 — — 5,993 Non-current operating lease liabilities — — — — — Deferred tax liabilities — — 325 (144 ) 181 Pension, other postretirement, and postemployment liabilities — 1,275 361 — 1,636 Non-current intercompany payables — 7,390 499 (7,889 ) — Other non-current liabilities 3 167 927 — 1,097 Total liabilities 4,971 22,608 16,160 (21,536 ) 22,203 Equity Total Aon shareholders’ equity 4,151 (882 ) 27,565 (26,683 ) 4,151 Noncontrolling interests — — 68 — 68 Total equity 4,151 (882 ) 27,633 (26,683 ) 4,219 Total liabilities and equity $ 9,122 $ 21,726 $ 43,793 $ (48,219 ) $ 26,422 Condensed Consolidating Statement of Cash Flows Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ 366 $ (110 ) $ 690 $ (585 ) $ 361 Cash flows from investing activities Proceeds from investments — 9 5 — 14 Payments for investments — (19 ) (41 ) — (60 ) Net sales (purchases) of short-term investments - non-fiduciary — (69 ) 7 — (62 ) Acquisition of businesses, net of cash acquired — — (15 ) — (15 ) Sale of businesses, net of cash sold — — 7 — 7 Capital expenditures — — (106 ) — (106 ) Cash provided by (used for) investing activities — (79 ) (143 ) — (222 ) Cash flows from financing activities Share repurchase (1,155 ) — — — (1,155 ) Advances from (to) affiliates 823 (320 ) (542 ) 39 — Issuance of shares for employee benefit plans (144 ) — — — (144 ) Issuance of debt 1,219 2,340 — — 3,559 Repayment of debt (906 ) (1,322 ) — — (2,228 ) Cash dividends to shareholders (203 ) — — — (203 ) Noncontrolling interests and other financing activities — — (61 ) — (61 ) Cash provided by (used for) financing activities (366 ) 698 (603 ) 39 (232 ) Effect of exchange rate changes on cash and cash equivalents — — 18 — 18 Net increase (decrease) in cash and cash equivalents — 509 (38 ) (546 ) (75 ) Cash and cash equivalents at beginning of period — 862 575 (781 ) 656 Cash and cash equivalents at end of period $ — $ 1,371 $ 537 $ (1,327 ) $ 581 Condensed Consolidating Statement of Cash Flows Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ (126 ) $ 582 $ 759 $ (802 ) $ 413 Cash flows from investing activities Proceeds from investments — 13 10 — 23 Payments for investments (12 ) (17 ) (19 ) 12 (36 ) Net sales (purchases) of short-term investments - non-fiduciary — 296 56 — 352 Acquisition of businesses, net of cash acquired — — (50 ) — (50 ) Sale of businesses, net of cash sold — — 1 — 1 Capital expenditures — — (111 ) — (111 ) Cash provided by (used for) investing activities (12 ) 292 (113 ) 12 179 Cash flows from financing activities Share repurchase (971 ) — — — (971 ) Advances from (to) affiliates 965 (810 ) (395 ) 240 — Issuance of shares for employee benefit plans (150 ) — — — (150 ) Issuance of debt 752 1,800 — — 2,552 Repayment of debt (272 ) (1,461 ) (294 ) — (2,027 ) Cash dividends to shareholders (187 ) — — — (187 ) Noncontrolling interests and other financing activities — — (15 ) — (15 ) Cash provided by (used for) financing activities 137 (471 ) (704 ) 240 (798 ) Effect of exchange rate changes on cash and cash equivalents — — (63 ) — (63 ) Net increase (decrease) in cash and cash equivalents (1 ) 403 (121 ) (550 ) (269 ) Cash and cash equivalents at beginning of period 1 2,524 793 (2,562 ) 756 Cash and cash equivalents at end of period $ — $ 2,927 $ 672 $ (3,112 ) $ 487

Lease Commitments

Lease Commitments	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Lease Commitments	Lease Commitments The Company leases office facilities, equipment, and automobiles under non-cancelable operating and finance leases. The Company’s lease obligations are primarily for the use of office space. The Company evaluates if a leasing arrangement exists upon inception of a contract. A contract contains a lease if the contract conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Identified property, plant, or equipment may include a physically distinct portion of a larger asset, or a portion of an asset that represents substantially all of the capacity of the asset but is not physically distinct. The Company assesses whether a contract implicitly contains the right to control the use of a tangible asset that is not already owned. In addition, the Company subleases certain real estate properties to third parties, which consist of operating leases. The Company’s leases expire at various dates and may contain renewal and expansion options. The exercise of lease renewal and expansion options are at the Company’s sole discretion and are only included in the determination of the lease term if the Company is reasonably certain to exercise the option. The Company’s leases do not typically contain termination options. In addition, the Company’s lease agreements typically do not contain any material residual value guarantees or restrictive covenants. ROU assets and lease liabilities are based on the present value of the minimum lease payments over the lease term. As stated in Note 2 “Accounting Principles and Practices”, the Company has elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease from lease components and instead account for consideration received in a contract as a single lease component. A portion of the Company’s lease agreements include variable lease payments that are not recorded in the initial measurement of the lease liability and ROU asset balances. For real estate arrangements, base rental payments may be escalated according to annual changes in the Consumer Price Index (“CPI”) or other indices. The escalated rental payments based on the estimated CPI at the lease commencement date are included within minimum rental payments; however, changes in CPI are considered variable in nature and are recognized as variable lease costs in the period in which the obligation is incurred. Additionally, real estate lease agreements may include other variable payments related to operating expenses charged by the landlord based on actual expenditures. Information technology equipment agreements may include variable payments based on usage of the equipment. The Company utilizes discount rates to determine the present value of the lease payments based on information available at the commencement date of the lease. The Company uses an incremental borrowing rate based on factors such as the lease term and the economic environment where the lease exists to determine the appropriate present value of future lease payments as the rate implicit in the lease is not always readily available. When determining the incremental borrowing rate, the Company considers the rate of interest it would pay on a secured borrowing in an amount equal to the lease payments for the underlying asset under similar terms. Operating leases are included in Operating lease right-of-use assets, Other current liabilities, and Non-current operating lease liabilities on the Condensed Consolidated Statements of Financial Position. Finance leases are included in Other non-current assets, Other current liabilities, and Other non-current liabilities on the Condensed Consolidated Statements of Financial Position. The classification of operating and finance lease asset and liability balances within the Condensed Consolidated Statements of Financial Position is as follows (in millions): As of June 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 959 Finance lease assets Other non-current assets 65 Total lease assets $ 1,024 Liabilities Current lease liabilities Operating Other current liabilities $ 199 Finance Other current liabilities 27 Non-current lease liabilities Operating Non-current operating lease liabilities 962 Finance Other non-current liabilities 37 Total lease liabilities $ 1,225 The components of lease costs are as follows (in millions): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 65 $ 133 Finance lease costs Amortization of leased assets 6 13 Interest on lease liabilities — 1 Variable lease cost 12 18 Short-term lease cost (1) 1 2 Sublease income (8 ) (16 ) Net lease cost $ 76 $ 151 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less. Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of June 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 2.5 Weighted average discount rate Operating leases 3.3 % Finance leases 2.4 % Other cash and non-cash related activities are as follows (in millions): Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 116 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 50 The Company has recorded non-cash changes in Operating lease ROU assets and Non-current operating lease liabilities through Other assets and liabilities in cash flows from operations within the Condensed Consolidated Statements of Cash Flows. Non-cash ROU asset lease expense was $68 million and the change in Non-current operating lease liabilities was a decrease of $52 million for the six months ended June 30, 2019 . Maturity analysis of operating and finance leases as of June 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 127 $ 14 $ (17 ) $ 124 2020 248 28 (34 ) 242 2021 224 22 (33 ) 213 2022 198 2 (34 ) 166 2023 144 — (15 ) 129 Thereafter 511 — (8 ) 503 Total undiscounted future minimum lease payments $ 1,452 $ 66 $ (141 ) $ 1,377 Less: Imputed interest (151 ) (1 ) — (152 ) Present value of lease liabilities $ 1,301 $ 65 $ (141 ) $ 1,225 At December 31, 2018, future minimum rental payments required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year are as follows (in millions): Year Ended December 31, 2018 Gross rental commitments Rentals from subleases Net rental commitments 2019 $ 303 $ (34 ) $ 269 2020 253 (30 ) 223 2021 221 (30 ) 191 2022 182 (30 ) 152 2023 148 (12 ) 136 Thereafter 472 (5 ) 467 Total minimum payments required $ 1,579 $ (141 ) $ 1,438
Lease Commitments	Lease Commitments The Company leases office facilities, equipment, and automobiles under non-cancelable operating and finance leases. The Company’s lease obligations are primarily for the use of office space. The Company evaluates if a leasing arrangement exists upon inception of a contract. A contract contains a lease if the contract conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Identified property, plant, or equipment may include a physically distinct portion of a larger asset, or a portion of an asset that represents substantially all of the capacity of the asset but is not physically distinct. The Company assesses whether a contract implicitly contains the right to control the use of a tangible asset that is not already owned. In addition, the Company subleases certain real estate properties to third parties, which consist of operating leases. The Company’s leases expire at various dates and may contain renewal and expansion options. The exercise of lease renewal and expansion options are at the Company’s sole discretion and are only included in the determination of the lease term if the Company is reasonably certain to exercise the option. The Company’s leases do not typically contain termination options. In addition, the Company’s lease agreements typically do not contain any material residual value guarantees or restrictive covenants. ROU assets and lease liabilities are based on the present value of the minimum lease payments over the lease term. As stated in Note 2 “Accounting Principles and Practices”, the Company has elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease from lease components and instead account for consideration received in a contract as a single lease component. A portion of the Company’s lease agreements include variable lease payments that are not recorded in the initial measurement of the lease liability and ROU asset balances. For real estate arrangements, base rental payments may be escalated according to annual changes in the Consumer Price Index (“CPI”) or other indices. The escalated rental payments based on the estimated CPI at the lease commencement date are included within minimum rental payments; however, changes in CPI are considered variable in nature and are recognized as variable lease costs in the period in which the obligation is incurred. Additionally, real estate lease agreements may include other variable payments related to operating expenses charged by the landlord based on actual expenditures. Information technology equipment agreements may include variable payments based on usage of the equipment. The Company utilizes discount rates to determine the present value of the lease payments based on information available at the commencement date of the lease. The Company uses an incremental borrowing rate based on factors such as the lease term and the economic environment where the lease exists to determine the appropriate present value of future lease payments as the rate implicit in the lease is not always readily available. When determining the incremental borrowing rate, the Company considers the rate of interest it would pay on a secured borrowing in an amount equal to the lease payments for the underlying asset under similar terms. Operating leases are included in Operating lease right-of-use assets, Other current liabilities, and Non-current operating lease liabilities on the Condensed Consolidated Statements of Financial Position. Finance leases are included in Other non-current assets, Other current liabilities, and Other non-current liabilities on the Condensed Consolidated Statements of Financial Position. The classification of operating and finance lease asset and liability balances within the Condensed Consolidated Statements of Financial Position is as follows (in millions): As of June 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 959 Finance lease assets Other non-current assets 65 Total lease assets $ 1,024 Liabilities Current lease liabilities Operating Other current liabilities $ 199 Finance Other current liabilities 27 Non-current lease liabilities Operating Non-current operating lease liabilities 962 Finance Other non-current liabilities 37 Total lease liabilities $ 1,225 The components of lease costs are as follows (in millions): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 65 $ 133 Finance lease costs Amortization of leased assets 6 13 Interest on lease liabilities — 1 Variable lease cost 12 18 Short-term lease cost (1) 1 2 Sublease income (8 ) (16 ) Net lease cost $ 76 $ 151 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less. Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of June 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 2.5 Weighted average discount rate Operating leases 3.3 % Finance leases 2.4 % Other cash and non-cash related activities are as follows (in millions): Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 116 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 50 The Company has recorded non-cash changes in Operating lease ROU assets and Non-current operating lease liabilities through Other assets and liabilities in cash flows from operations within the Condensed Consolidated Statements of Cash Flows. Non-cash ROU asset lease expense was $68 million and the change in Non-current operating lease liabilities was a decrease of $52 million for the six months ended June 30, 2019 . Maturity analysis of operating and finance leases as of June 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 127 $ 14 $ (17 ) $ 124 2020 248 28 (34 ) 242 2021 224 22 (33 ) 213 2022 198 2 (34 ) 166 2023 144 — (15 ) 129 Thereafter 511 — (8 ) 503 Total undiscounted future minimum lease payments $ 1,452 $ 66 $ (141 ) $ 1,377 Less: Imputed interest (151 ) (1 ) — (152 ) Present value of lease liabilities $ 1,301 $ 65 $ (141 ) $ 1,225 At December 31, 2018, future minimum rental payments required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year are as follows (in millions): Year Ended December 31, 2018 Gross rental commitments Rentals from subleases Net rental commitments 2019 $ 303 $ (34 ) $ 269 2020 253 (30 ) 223 2021 221 (30 ) 191 2022 182 (30 ) 152 2023 148 (12 ) 136 Thereafter 472 (5 ) 467 Total minimum payments required $ 1,579 $ (141 ) $ 1,438

Accounting Principles and Pra_2

Accounting Principles and Practices (Policies)	6 Months Ended
	Jun. 30, 2019
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 (“Aon” or the “Company”). 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 accompanying 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, and foreign currency exchange rate movements increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment would, if applicable, be reflected in the Financial Statements in future periods.
New Accounting Standards	Adoption of New Accounting Standards Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued new accounting guidance related to reclassification of certain tax effects from accumulated other comprehensive income. The guidance allowed a reclassification from accumulated comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The guidance was effective for the Company in the first quarter of 2019. For the three and six months ended June 30, 2019 , there was no impact on the net income of the Company as Aon did not elect to reclassify stranded tax effects on the Condensed Consolidated Statement of Financial Position. It is the Company’s policy to release income tax effects from accumulated other comprehensive loss using the portfolio approach. Targeted Improvements to Accounting for Hedging Activities In August 2017, the FASB issued new accounting guidance on targeted improvements to accounting for hedging activities. The new guidance amended its hedge accounting model to enable entities to better portray their risk management activities in the financial statements. The guidance eliminated the requirement to separately measure and report hedge ineffectiveness and required the effect of a hedging instrument to be presented in the same income statement line as the hedged item. The new guidance was effective for Aon in the first quarter of 2019 and the Company adopted it on a modified retrospective basis with no cumulative effect adjustment to accumulated other comprehensive income or corresponding adjustment to Retained earnings. Changes to the Condensed Consolidated Statement of Income and financial statement disclosures were applied prospectively. Under the new guidance, gains or losses on certain derivative hedging instruments are recognized in revenue, as opposed to other income (expense) under the previous guidance. For the three and six months ended June 30, 2019 , the adoption of this guidance had no impact on the net income and an insignificant impact on the operating income of the Company. Leases In February 2016, the FASB issued a new accounting standard on leases, which requires lessees to recognize assets and liabilities for most leases. Under the new standard, a lessee is required to recognize in the Consolidated Statements of Financial Position, liabilities to make future lease payments and right-of-use (“ROU”) assets representing its right to use the underlying assets for the lease term. The recognition, measurement, timing, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from previous U.S. GAAP. The Company adopted the new standard as of January 1, 2019, using the modified retrospective approach for all leases existing at, or entered into after, the period of adoption. Under this approach, prior periods were not restated. Rather, lease balances and other disclosures for prior periods were provided in the notes to the financial statements as previously reported, and the cumulative effect of initially applying the guidance was recognized in the Condensed Consolidated Statement of Financial Position. The modified retrospective approach includes several optional practical expedients available that entities may elect to apply upon transition. These practical expedients relate to the identification and classification of leases that commenced before the effective date, initial direct costs for leases that commenced before the effective date, and the ability to use hindsight in evaluating lessee options to extend or terminate a lease or to purchase the underlying asset. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which allows a lessee to carryforward their population of existing leases, the classification of each lease, as well as the treatment of initial direct costs as of the period of adoption. In addition, the Company elected the practical expedient related to lease and non-lease components, as an accounting policy election for all asset classes, which allows a lessee to not separate non-lease from lease components and instead account for consideration paid in a contract as a single lease component. Lastly, the Company did not elect the practical expedient related to hindsight analysis which allows a lessee to use hindsight in determining the lease term and in assessing impairment of the entity’s ROU assets. The Company has made a policy election to not recognize ROU assets and lease liabilities that arise from leases with an initial term of twelve months or less on the Condensed Consolidated Statements of Financial Position. However, the Company will recognize these lease payments in the Condensed Consolidated Statements of Income on a straight-line basis over the lease term and variable lease payments in the period in which the obligation is incurred. The Company has chosen to apply this accounting policy across all classes of underlying assets. Additionally, upon adoption, the Company utilized a discount rate to determine the present value of the lease payments based on information available as of January 1, 2019. Beginning January 1, 2019, operating ROU assets and operating lease liabilities are recognized based on the present value of lease payments over the lease term at the commencement date. Operating leases in effect prior to January 1, 2019 were recognized at the present value of the remaining payments on the remaining lease term as of January 1, 2019. Upon adoption, the Company recognized ROU assets and lease liabilities of $1.1 billion and $1.3 billion , respectively. The standard had an insignificant impact on the Condensed Consolidated Statements of Income and no impact on the Condensed Consolidated Statements of Cash Flows. Refer to Note 20 “Lease Commitments” for further information including significant assumptions and judgments made. As a result of applying the modified retrospective approach to adopt the new leasing standard, the following adjustments were made to the Condensed Consolidated Statements of Financial Position as of January 1, 2019 (in millions): December 31, January 1, As Reported Adjustments As Adjusted Assets Operating lease right-of-use assets $ — $ 1,021 $ 1,021 Other non-current assets $ 448 $ 78 $ 526 Liabilities Other current liabilities $ 936 $ 219 $ 1,155 Non-current operating lease liabilities $ — $ 1,014 $ 1,014 Other non-current liabilities $ 1,097 $ (134 ) $ 963 Accounting Standards Issued But Not Yet Adopted 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. 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. An entity will apply the new guidance on a prospective basis. The new guidance is effective for Aon in the first quarter of 2020 and early adoption is permitted. The Company is currently evaluating the period of adoption, but does not expect a 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. An entity will apply the new standard through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the standard is effective. The new standard is effective for Aon in the first quarter of 2020 with early adoption permitted. The Company is currently evaluating the impact that the standard will have on the Financial Statements and will adopt the new accounting standard in the first quarter of 2020.
Revenue from Contract with Customer	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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Commercial Risk Solutions $ 1,167 $ 1,166 $ 2,285 $ 2,350 Reinsurance Solutions 420 380 1,208 1,122 Retirement Solutions 419 431 839 855 Health Solutions 317 309 803 760 Data & Analytic Services 286 277 622 571 Elimination (3 ) (2 ) (8 ) (7 ) Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 United States $ 1,146 $ 1,125 $ 2,307 $ 2,241 Americas other than United States 241 243 467 480 United Kingdom 400 413 852 897 Europe, Middle East, & Africa other than United Kingdom 501 493 1,510 1,472 Asia Pacific 318 287 613 561 Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 236 $ 240 $ 329 $ 298 Additions 336 341 682 711 Amortization (357 ) (353 ) (796 ) (785 ) Impairment — — — — Foreign currency translation and other 1 (12 ) 1 (8 ) Balance at end of period $ 216 $ 216 $ 216 $ 216 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 155 $ 144 $ 156 $ 145 Additions 17 13 26 21 Amortization (11 ) (11 ) (22 ) (21 ) Impairment — — — — Foreign currency translation and other — (2 ) 1 (1 ) Balance at end of period $ 161 $ 144 $ 161 $ 144
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, 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 2 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 1 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 domestic and international 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 and 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 the Company’s guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates 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.

Accounting Principles and Pra_3

Accounting Principles and Practices Accounting Principles and Practices (Tables)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	As a result of applying the modified retrospective approach to adopt the new leasing standard, the following adjustments were made to the Condensed Consolidated Statements of Financial Position as of January 1, 2019 (in millions): December 31, January 1, As Reported Adjustments As Adjusted Assets Operating lease right-of-use assets $ — $ 1,021 $ 1,021 Other non-current assets $ 448 $ 78 $ 526 Liabilities Other current liabilities $ 936 $ 219 $ 1,155 Non-current operating lease liabilities $ — $ 1,014 $ 1,014 Other non-current liabilities $ 1,097 $ (134 ) $ 963

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Commercial Risk Solutions $ 1,167 $ 1,166 $ 2,285 $ 2,350 Reinsurance Solutions 420 380 1,208 1,122 Retirement Solutions 419 431 839 855 Health Solutions 317 309 803 760 Data & Analytic Services 286 277 622 571 Elimination (3 ) (2 ) (8 ) (7 ) Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 United States $ 1,146 $ 1,125 $ 2,307 $ 2,241 Americas other than United States 241 243 467 480 United Kingdom 400 413 852 897 Europe, Middle East, & Africa other than United Kingdom 501 493 1,510 1,472 Asia Pacific 318 287 613 561 Total revenue $ 2,606 $ 2,561 $ 5,749 $ 5,651
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 236 $ 240 $ 329 $ 298 Additions 336 341 682 711 Amortization (357 ) (353 ) (796 ) (785 ) Impairment — — — — Foreign currency translation and other 1 (12 ) 1 (8 ) Balance at end of period $ 216 $ 216 $ 216 $ 216 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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 155 $ 144 $ 156 $ 145 Additions 17 13 26 21 Amortization (11 ) (11 ) (22 ) (21 ) Impairment — — — — Foreign currency translation and other — (2 ) 1 (1 ) Balance at end of period $ 161 $ 144 $ 161 $ 144

Other Financial Data (Tables)

Other Financial Data (Tables)	6 Months Ended
	Jun. 30, 2019
Other Financial Data [Abstract]
Schedule of Other Income (Expense)	Other income (expense) consists of the following (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Foreign currency remeasurement $ 11 $ 29 $ — $ 13 Disposal of businesses 2 — 7 (1 ) Pension and other postretirement 5 (7 ) 9 (5 ) Equity earnings 1 1 2 2 Financial instruments (13 ) (27 ) (12 ) (27 ) Other — 1 — — Total $ 6 $ (3 ) $ 6 $ (18 )
Schedule of Allowance for Doubtful Accounts	An analysis of the allowance for doubtful accounts are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Balance at beginning of period $ 64 $ 65 $ 64 $ 59 Provision charged to Other general expenses 4 3 12 11 Accounts written off, net of recoveries (3 ) (6 ) (11 ) (8 ) Balance at end of period $ 65 $ 62 $ 65 $ 62
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions): As of June 30, December 31, Costs to fulfill contracts with customers (1) $ 216 $ 329 Prepaid expenses 128 97 Taxes receivable 145 113 Other (2) 142 79 Total $ 631 $ 618 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) December 31, 2018 includes $12 million
Schedule of Other Non-current Assets	The components of Other non-current assets are as follows (in millions): As of June 30, December 31, Costs to obtain contracts with customers (1) $ 161 $ 156 Taxes receivable 100 100 Leases (2) 65 — Investments 54 54 Other 141 138 Total $ 521 $ 448 (1) Refer to Note 3 “Revenue from Contracts with Customers” for further information. (2) Refer to Note 20 “Lease Commitments” for further information.
Schedule of Other Current Liabilities	The components of Other current liabilities are as follows (in millions): As of June 30, December 31, Deferred revenue (1) $ 337 $ 251 Leases (2) 223 — Taxes payable 133 83 Other 504 602 Total $ 1,197 $ 936 (1) During the three and six months ended June 30, 2019 , $95 million and $241 million , respectively, was recognized in the Condensed Consolidated Statements of Income. During the three and six months ended June 30, 2018 , $115 million and $215 million , respectively, was recognized in the Condensed Consolidated Statements of Income. (2) Refer to Note 20 “Lease Commitments” for further information.
Schedule of Other Non-current Liabilities	The components of Other non-current liabilities are as follows (in millions): As of June 30, December 31, Taxes payable (1) $ 576 $ 585 Leases 37 169 Deferred revenue 59 65 Compensation and benefits 49 56 Other 203 222 Total $ 924 $ 1,097 (1) Includes $221 million and $240 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of June 30, 2019 and December 31, 2018 , respectively.

Discontinued Operations (Tables

Discontinued Operations (Tables)	6 Months Ended
	Jun. 30, 2019
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	The following table presents the financial results of the Divested Business (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Expenses Total operating expenses $ 1 $ — $ 1 $ 3 Loss from discontinued operations before income taxes (1 ) — (1 ) (3 ) Income tax benefit (1 ) — (1 ) (1 ) Net loss from discontinued operations excluding gain — — — (2 ) Gain on sale of discontinued operations, net of tax — 1 — 9 Net income from discontinued operations $ — $ 1 $ — $ 7

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Jun. 30, 2019
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	The following table summarizes restructuring and separation costs by type that have been incurred through June 30, 2019 and are estimated to be incurred through the end of the Restructuring Plan (in millions). Estimated costs by type may be revised in future periods as these assumptions are updated: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Inception to Date Estimated Remaining Costs Estimated Total Cost (1) Workforce reduction $ 78 $ 102 $ 516 $ 14 $ 530 Technology rationalization (2) 4 15 95 35 130 Lease consolidation (2) 5 14 50 30 80 Asset impairments 2 2 41 4 45 Other costs associated with restructuring and separation (2) (3) 38 85 498 67 565 Total restructuring and related expenses $ 127 $ 218 $ 1,200 $ 150 $ 1,350 (1) Actual costs, when incurred, may vary due to changes in the assumptions built into the Restructuring Plan. Significant assumptions that may change when plans are finalized and implemented include, but are not limited to, changes in severance calculations, changes in the assumptions underlying sublease loss calculations due to changing market conditions, and changes in the overall analysis that might cause the Company to add or cancel component initiatives. Estimated Total Cost includes $100 million of non-cash charges. (2) Total contract termination costs incurred under the Restructuring Plan associated with Technology rationalizations, Lease consolidations, and Other costs, respectively, associated with restructuring and separation were for the three months ended June 30, 2019 , $2 million , $4 million , and $1 million ; for the six months ended June 30, 2019 , were $3 million , $13 million , and $3 million ; and since inception of the Restructuring Plan, were $9 million , $46 million , and $91 million . Total estimated contract termination costs expected to be incurred under the Restructuring Plan associated with Technology rationalizations, Lease consolidations, and Other costs associated with restructuring and separation, are $15 million , $80 million , and $95 million , respectively. (3) Other costs associated with the Restructuring Plan include those to separate the Divested Business, as well as moving costs, and consulting and legal fees. These costs are generally recognized when incurred.
Schedule of Restructuring Reserve by Type of Cost	The changes in the Company’s liabilities for the Restructuring Plan as of June 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 201 Expensed 204 Cash payments (222 ) Foreign currency translation 1 Balance as of June 30, 2019 $ 184

Acquisitions and Dispositions_2

Acquisitions and Dispositions of Businesses (Tables)	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table includes the fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Six Months Ended June 30, 2019 Consideration Transferred $ 17 Deferred and contingent consideration 5 Aggregate consideration transferred $ 22 Assets acquired Cash and cash equivalents $ 2 Goodwill 15 Intangible assets, net 9 Other assets 4 Total assets acquired 30 Liabilities assumed Current liabilities 6 Other non-current liabilities 2 Total liabilities assumed 8 Net assets acquired $ 22

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2019
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 six months ended June 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 8,171 Goodwill related to current year acquisitions 15 Goodwill related to disposals (9 ) Goodwill related to prior year acquisitions 2 Foreign currency translation and other 19 Balance as of June 30, 2019 $ 8,198
Schedule of Other Intangible Assets by Asset Class	Other intangible assets by asset class are as follows (in millions): June 30, 2019 December 31, 2018 Gross Carrying Amount Accumulated Amortization and Impairment Net Carrying Amount Gross Carrying Amount Accumulated Net Carrying Amount Customer related and contract based $ 2,254 $ 1,517 $ 737 $ 2,240 $ 1,444 $ 796 Tradenames 1,028 847 181 1,027 740 287 Technology and other 385 330 55 391 325 66 Total $ 3,667 $ 2,694 $ 973 $ 3,658 $ 2,509 $ 1,149
Schedule of Estimated Future Amortization Expense on Intangible Assets	The estimated future amortization for finite lived intangible assets as of June 30, 2019 is as follows (in millions): Remainder of 2019 $ 192 2020 223 2021 128 2022 87 2023 74 2024 58 Thereafter 211 Total $ 973

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Weighted average commercial paper outstanding $ 639 $ 744 482 $ 437 Weighted average interest rate of commercial paper outstanding 0.70 % 0.92 % 0.63 % 0.85 % Commercial paper outstanding, which is included in Short-term debt and current portion of long-term debt in the Company’s Condensed Consolidated Statements of Financial Position, is as follows (in millions): As of June 30, 2019 December 31, 2018 Commercial paper outstanding $ 843 $ 250

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Schedule of Repurchase Agreements	The following table summarizes the Company’s Share Repurchase activity (in millions, except per share data): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Shares repurchased 5.8 2.8 6.4 6.7 Average price per share $ 183.23 $ 141.23 $ 181.07 $ 141.06 Costs recorded to retained earnings: Total repurchase cost $ 1,050 $ 400 $ 1,150 $ 950 Additional associated costs 6 2 7 5 Total costs recorded to retained earnings $ 1,056 $ 402 $ 1,157 $ 955
Schedule of Components of Weighted Average Number of Shares	Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Basic weighted average ordinary shares outstanding 240.6 246.0 241.4 247.2 Dilutive effect of potentially issuable shares 2.2 1.4 1.8 1.6 Diluted weighted average ordinary shares outstanding 242.8 247.4 243.2 248.8
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, 2018 $ (15 ) $ (1,319 ) $ (2,575 ) $ (3,909 ) Other comprehensive income (loss) before reclassifications, net (8 ) 28 5 25 Amounts reclassified from accumulated other comprehensive income: Amounts reclassified from accumulated other comprehensive income 8 — 52 60 Tax expense (1 ) — (12 ) (13 ) Amounts reclassified from accumulated other comprehensive income, net 7 — 40 47 Net current period other comprehensive income (loss) (1 ) 28 45 72 Balance at June 30, 2019 $ (16 ) $ (1,291 ) $ (2,530 ) $ (3,837 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Revenue, Interest expense, and Compensation and benefits in the accompanying Condensed Consolidated Statements of Income. Refer to Note 15 “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).

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2019
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 international pension plans. 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 June 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 27 29 27 25 7 7 Expected return on plan assets, net of administration expenses (48 ) (50 ) (34 ) (36 ) (10 ) (11 ) Amortization of prior-service cost — — — 1 — — Amortization of net actuarial loss 8 7 14 15 3 3 Net periodic (benefit) cost (13 ) (14 ) 7 5 — (1 ) Loss on pension settlement — 16 — — — — Total net periodic (benefit) cost $ (13 ) $ 2 $ 7 $ 5 $ — $ (1 ) Six Months Ended June 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 55 58 54 50 14 14 Expected return on plan assets, net of administration expenses (97 ) (101 ) (68 ) (72 ) (20 ) (23 ) Amortization of prior-service cost 1 — 1 1 — — Amortization of net actuarial loss 15 15 27 30 6 6 Net periodic (benefit) cost (26 ) (28 ) 14 9 — (3 ) Loss on pension settlement — 23 — — — — Total net periodic (benefit) cost $ (26 ) $ (5 ) $ 14 $ 9 $ — $ (3 )

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	6 Months Ended
	Jun. 30, 2019
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 June 30 Six Months Ended June 30 2019 2018 2019 2018 Restricted share units (“RSUs”) $ 50 $ 46 $ 113 $ 104 Performance share awards (“PSAs”) 39 23 62 39 Employee share purchase plans 2 1 5 4 Total share-based compensation expense $ 91 $ 70 $ 180 $ 147
Restricted share unit activity	The following table summarizes the status of the Company’s RSUs, including shares related to the Divested Business (shares in thousands, except fair value): Six Months Ended June 30, 2019 Six Months Ended June 30, 2018 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 4,208 $ 120 4,849 $ 104 Granted 1,178 $ 173 1,352 $ 140 Vested (1,451 ) $ 113 (1,664 ) $ 98 Forfeited (97 ) $ 124 (109 ) $ 109 Non-vested at end of period 3,838 $ 139 4,428 $ 117 (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 six months ended June 30, 2019 and the years ended December 31, 2018 and 2017 , respectively (shares in thousands and dollars in millions, except fair value): June 30, December 31, December 31, Target PSAs granted during period 467 564 548 Weighted average fair value per share at date of grant $ 164 $ 134 $ 114 Number of shares that would be issued based on current performance levels 464 970 1,066 Unamortized expense, based on current performance levels $ 69 $ 67 $ 20

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	6 Months Ended
	Jun. 30, 2019
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) June 30, December 31, June 30, December 31, June 30, December 31, Foreign exchange contracts: Accounted for as hedges $ 588 $ 646 $ 14 $ 17 $ 1 $ 2 Not accounted for as hedges (3) 285 269 5 1 — 6 Total $ 873 $ 915 $ 19 $ 18 $ 1 $ 8 (1) Included within Other current assets ( $8 million at June 30, 2019 and $3 million at December 31, 2018 ) or Other non-current assets ( $11 million at June 30, 2019 and $15 million at December 31, 2018 ). (2) Included within Other current liabilities ( $1 million at June 30, 2019 and $5 million at December 31, 2018 ) or Other non-current liabilities ( $3 million at December 31, 2018 ). (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 Financial Statements are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Loss recognized in Accumulated other comprehensive loss $ (12 ) $ (25 ) $ (8 ) $ (11 ) The amounts of derivative gains (losses) reclassified from Accumulated other comprehensive loss into the Condensed Consolidated Statements of Income are as follows (in millions): Three Months Ended June 30 Six Months Ended June 30 2019 2018 2019 2018 Revenue (1) $ (3 ) $ — $ (7 ) $ — Compensation and benefits — — — 1 Other general expenses — (1 ) — (2 ) Interest expense — — (1 ) (1 ) Other income (expense) (1) — (1 ) — (4 ) Total $ (3 ) $ (2 ) $ (8 ) $ (6 ) (1) With the adoption of new hedge accounting guidance in the first quarter of 2019, gains (losses) on derivatives accounted for as hedges are recognized in Total revenue in the Company’s Condensed Consolidated Statements of Income rather than Other income (expense). Refer to Note 2 “Accounting Principles and Practices” for additional details.

Fair Value Measurements and F_2

Fair Value Measurements and Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
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 June 30, 2019 and December 31, 2018 (in millions): Fair Value Measurements Using Balance at June 30, 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) $ 2,356 $ 2,356 $ — $ — Other investments: Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 3 $ — $ 3 $ — Fair Value Measurements Using Balance at December 31, 2018 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) $ 1,759 $ 1,759 $ — $ — Other investments: Government bonds $ 1 $ — $ 1 $ — Equity investments $ 2 $ — $ 2 $ — Derivatives (2) Gross foreign exchange contracts $ 21 $ — $ 21 $ — Liabilities Derivatives (2) Gross foreign exchange contracts $ 12 $ — $ 12 $ — (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): June 30, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value Long-term debt $ 6,740 $ 7,356 $ 5,993 $ 6,159

Guarantee of Registered Secur_2

Guarantee of Registered Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Guarantee of Registered Securities [Abstract]
Condensed Consolidating Statements of Income	Condensed Consolidating Statement of Income Three Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,606 $ — $ 2,606 Expenses Compensation and benefits 22 4 1,475 — 1,501 Information technology — — 126 — 126 Premises — 9 76 — 85 Depreciation of fixed assets — — 40 — 40 Amortization and impairment of intangible assets — — 97 — 97 Other general expenses 3 6 335 — 344 Total operating expenses 25 19 2,149 — 2,193 Operating income (loss) (25 ) (19 ) 457 — 413 Interest income — 9 — (8 ) 1 Interest expense (45 ) (34 ) (6 ) 8 (77 ) Intercompany interest income (expense) 3 (116 ) 113 — — Intercompany other income (expense) 137 (164 ) 27 — — Other income (expense) (11 ) (14 ) 24 7 6 Income (loss) from continuing operations before income taxes 59 (338 ) 615 7 343 Income tax expense (benefit) — (64 ) 120 — 56 Net income (loss) from continuing operations 59 (274 ) 495 7 287 Net income from discontinued operations — — — — — Net income (loss) before equity in earnings of subsidiaries 59 (274 ) 495 7 287 Equity in earnings of subsidiaries 211 301 27 (539 ) — Net income 270 27 522 (532 ) 287 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders $ 270 $ 27 $ 512 $ (532 ) $ 277 Condensed Consolidating Statement of Income Three Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,561 $ — $ 2,561 Expenses Compensation and benefits 15 1 1,478 — 1,494 Information technology — — 123 — 123 Premises — — 96 — 96 Depreciation of fixed assets — — 47 — 47 Amortization and impairment of intangible assets — — 282 — 282 Other general expenses 2 91 442 — 535 Total operating expenses 17 92 2,468 — 2,577 Operating income (loss) (17 ) (92 ) 93 — (16 ) Interest income — 15 — (14 ) 1 Interest expense (48 ) (25 ) (10 ) 14 (69 ) Intercompany interest income (expense) 3 (129 ) 126 — — Intercompany other income (expense) (93 ) 10 83 — — Other income (expense) 48 (20 ) (13 ) (18 ) (3 ) Income (loss) from continuing operations before income taxes (107 ) (241 ) 279 (18 ) (87 ) Income tax expense (benefit) (3 ) (50 ) (91 ) — (144 ) Net income (loss) from continuing operations (104 ) (191 ) 370 (18 ) 57 Net income from discontinued operations — — 1 — 1 Net income (loss) before equity in earnings of subsidiaries (104 ) (191 ) 371 (18 ) 58 Equity in earnings of subsidiaries 170 207 16 (393 ) — Net income 66 16 387 (411 ) 58 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders $ 66 $ 16 $ 377 $ (411 ) $ 48 Condensed Consolidating Statement of Income Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 5,749 $ — $ 5,749 Expenses Compensation and benefits 42 12 3,031 — 3,085 Information technology — — 243 — 243 Premises — 13 159 — 172 Depreciation of fixed assets — — 80 — 80 Amortization and impairment of intangible assets — — 194 — 194 Other general expenses 3 2 685 — 690 Total operating expenses 45 27 4,392 — 4,464 Operating income (loss) (45 ) (27 ) 1,357 — 1,285 Interest income — 18 — (15 ) 3 Interest expense (91 ) (62 ) (11 ) 15 (149 ) Intercompany interest income (expense) 7 (232 ) 225 — — Intercompany other income (expense) 168 (263 ) 95 — — Other income (expense) (6 ) (25 ) 32 5 6 Income (loss) from continuing operations before income taxes 33 (591 ) 1,698 5 1,145 Income tax expense (benefit) (5 ) (106 ) 293 — 182 Net income (loss) from continuing operations 38 (485 ) 1,405 5 963 Net income from discontinued operations — — — — — Net income (loss) before equity in earnings of subsidiaries 38 (485 ) 1,405 5 963 Equity in earnings of subsidiaries 893 1,025 540 (2,458 ) — Net income 931 540 1,945 (2,453 ) 963 Less: Net income attributable to noncontrolling interests — — 27 — 27 Net income attributable to Aon shareholders $ 931 $ 540 $ 1,918 $ (2,453 ) $ 936 Condensed Consolidating Statement of Income Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 5,651 $ — $ 5,651 Expenses Compensation and benefits 34 2 3,074 — 3,110 Information technology — — 238 — 238 Premises — — 189 — 189 Depreciation of fixed assets — — 86 — 86 Amortization and impairment of intangible assets — — 392 — 392 Other general expenses 3 91 759 — 853 Total operating expenses 37 93 4,738 — 4,868 Operating income (loss) (37 ) (93 ) 913 — 783 Interest income — 29 — (24 ) 5 Interest expense (97 ) (49 ) (17 ) 24 (139 ) Intercompany interest income (expense) 7 (257 ) 250 — — Intercompany other income (expense) (146 ) 5 141 — — Other income (expense) 23 (26 ) — (15 ) (18 ) Income (loss) from continuing operations before income taxes (250 ) (391 ) 1,287 (15 ) 631 Income tax expense (benefit) (19 ) (77 ) 66 — (30 ) Net income (loss) from continuing operations (231 ) (314 ) 1,221 (15 ) 661 Net income from discontinued operations — — 7 — 7 Net income (loss) before equity in earnings of subsidiaries (231 ) (314 ) 1,228 (15 ) 668 Equity in earnings of subsidiaries 888 912 598 (2,398 ) — Net income 657 598 1,826 (2,413 ) 668 Less: Net income attributable to noncontrolling interests — — 26 — 26 Net income attributable to Aon shareholders $ 657 $ 598 $ 1,800 $ (2,413 ) $ 642
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statement of Comprehensive Income Three Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 270 $ 27 $ 522 $ (532 ) $ 287 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders 270 27 512 (532 ) 277 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (8 ) — (8 ) Foreign currency translation adjustments — — (96 ) (7 ) (103 ) Postretirement benefit obligation — 10 4 — 14 Total other comprehensive income (loss) — 10 (100 ) (7 ) (97 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (90 ) (118 ) (108 ) 316 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — — — — Total other comprehensive income (loss) attributable to Aon shareholders (90 ) (108 ) (208 ) 309 (97 ) Comprehensive income attributable (loss) to Aon shareholders $ 180 $ (81 ) $ 304 $ (223 ) $ 180 Condensed Consolidating Statement of Comprehensive Income Three Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 66 $ 16 $ 387 $ (411 ) $ 58 Less: Net income attributable to noncontrolling interests — — 10 — 10 Net income attributable to Aon shareholders 66 16 377 (411 ) 48 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (4 ) 3 — (1 ) Foreign currency translation adjustments — — (478 ) 18 (460 ) Postretirement benefit obligation — 11 111 — 122 Total other comprehensive income (loss) — 7 (364 ) 18 (339 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (351 ) (345 ) (338 ) 1,034 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive income (loss) attributable to Aon shareholders (351 ) (338 ) (696 ) 1,052 (333 ) Comprehensive income attributable (loss) to Aon shareholders $ (285 ) $ (322 ) $ (319 ) $ 641 $ (285 ) Condensed Consolidating Statement of Comprehensive Income Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 931 $ 540 $ 1,945 $ (2,453 ) $ 963 Less: Net income attributable to noncontrolling interests — — 27 — 27 Net income attributable to Aon shareholders 931 540 1,918 (2,453 ) 936 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — 2 (3 ) — (1 ) Foreign currency translation adjustments — — 35 (5 ) 30 Postretirement benefit obligation — 32 13 — 45 Total other comprehensive income (loss) — 34 45 (5 ) 74 Equity in other comprehensive income (loss) of subsidiaries, net of tax 77 (3 ) 31 (105 ) — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — 2 — 2 Total other comprehensive income (loss) attributable to Aon shareholders 77 31 74 (110 ) 72 Comprehensive income attributable (loss) to Aon shareholders $ 1,008 $ 571 $ 1,992 $ (2,563 ) $ 1,008 Condensed Consolidating Statement of Comprehensive Income Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 657 $ 598 $ 1,826 $ (2,413 ) $ 668 Less: Net income attributable to noncontrolling interests — — 26 — 26 Net income attributable to Aon shareholders 657 598 1,800 (2,413 ) 642 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (1 ) 14 — 13 Foreign currency translation adjustments — — (228 ) 15 (213 ) Postretirement benefit obligation — 22 148 — 170 Total other comprehensive income (loss) — 21 (66 ) 15 (30 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (42 ) (60 ) (39 ) 141 — Less: Other comprehensive income (loss) attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive income (loss) attributable to Aon shareholders (42 ) (39 ) (102 ) 156 (27 ) Comprehensive income attributable (loss) to Aon shareholders $ 615 $ 559 $ 1,698 $ (2,257 ) $ 615
Condensed Consolidating Statements of Financial Position	Condensed Consolidating Statement of Financial Position As of June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 1,371 $ 537 $ (1,327 ) $ 581 Short-term investments — 125 110 — 235 Receivables, net — — 3,227 — 3,227 Fiduciary assets — — 12,071 — 12,071 Current intercompany receivables 167 3,421 12,843 (16,431 ) — Other current assets — 10 621 — 631 Total current assets 167 4,927 29,409 (17,758 ) 16,745 Goodwill — — 8,198 — 8,198 Intangible assets, net — — 973 — 973 Fixed assets, net — — 599 — 599 Operating lease right-of-use assets — 112 847 — 959 Deferred tax assets 93 498 150 (142 ) 599 Prepaid pension — 5 1,208 — 1,213 Non-current intercompany receivables 404 261 7,200 (7,865 ) — Other non-current assets 1 28 492 — 521 Investment in subsidiary 8,937 20,147 (424 ) (28,660 ) — Total assets $ 9,602 $ 25,978 $ 48,652 $ (54,425 ) $ 29,807 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 582 $ 57 $ 2,057 $ (1,327 ) $ 1,369 Short-term debt and current portion of long-term debt 569 275 — — 844 Fiduciary liabilities — — 12,071 — 12,071 Current intercompany payables 378 14,633 1,420 (16,431 ) — Other current liabilities — 78 1,119 — 1,197 Total current liabilities 1,529 15,043 16,667 (17,758 ) 15,481 Long-term debt 4,234 2,506 — — 6,740 Non-current operating lease liabilities — 149 813 — 962 Deferred tax liabilities — — 353 (142 ) 211 Pension, other postretirement, and postemployment liabilities — 1,232 344 — 1,576 Non-current intercompany payables — 7,366 499 (7,865 ) — Other non-current liabilities 3 106 815 — 924 Total liabilities 5,766 26,402 19,491 (25,765 ) 25,894 Equity Total Aon shareholders’ equity 3,836 (424 ) 29,084 (28,660 ) 3,836 Noncontrolling interests — — 77 — 77 Total equity 3,836 (424 ) 29,161 (28,660 ) 3,913 Total liabilities and equity $ 9,602 $ 25,978 $ 48,652 $ (54,425 ) $ 29,807 Condensed Consolidating Statement of Financial Position As of December 31, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 862 $ 575 $ (781 ) $ 656 Short-term investments — 56 116 — 172 Receivables, net — — 2,760 — 2,760 Fiduciary assets — — 10,166 — 10,166 Current intercompany receivables 191 897 11,634 (12,722 ) — Other current assets — 16 602 — 618 Total current assets 191 1,831 25,853 (13,503 ) 14,372 Goodwill — — 8,171 — 8,171 Intangible assets, net — — 1,149 — 1,149 Fixed assets, net — — 588 — 588 Operating lease right-of-use assets — — — — — Deferred tax assets 94 467 144 (144 ) 561 Prepaid pension — 5 1,128 — 1,133 Non-current intercompany receivables 403 261 7,225 (7,889 ) — Other non-current assets 1 30 417 — 448 Investment in subsidiary 8,433 19,132 (882 ) (26,683 ) — Total assets $ 9,122 $ 21,726 $ 43,793 $ (48,219 ) $ 26,422 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 274 $ 70 $ 2,380 $ (781 ) $ 1,943 Short-term debt and current portion of long-term debt 250 — 1 — 251 Fiduciary liabilities — — 10,166 — 10,166 Current intercompany payables 213 11,875 634 (12,722 ) — Other current liabilities — 69 867 — 936 Total current liabilities 737 12,014 14,048 (13,503 ) 13,296 Long-term debt 4,231 1,762 — — 5,993 Non-current operating lease liabilities — — — — — Deferred tax liabilities — — 325 (144 ) 181 Pension, other postretirement, and postemployment liabilities — 1,275 361 — 1,636 Non-current intercompany payables — 7,390 499 (7,889 ) — Other non-current liabilities 3 167 927 — 1,097 Total liabilities 4,971 22,608 16,160 (21,536 ) 22,203 Equity Total Aon shareholders’ equity 4,151 (882 ) 27,565 (26,683 ) 4,151 Noncontrolling interests — — 68 — 68 Total equity 4,151 (882 ) 27,633 (26,683 ) 4,219 Total liabilities and equity $ 9,122 $ 21,726 $ 43,793 $ (48,219 ) $ 26,422
Condensed Consolidating Statements of Cash Flows	Condensed Consolidating Statement of Cash Flows Six Months Ended June 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ 366 $ (110 ) $ 690 $ (585 ) $ 361 Cash flows from investing activities Proceeds from investments — 9 5 — 14 Payments for investments — (19 ) (41 ) — (60 ) Net sales (purchases) of short-term investments - non-fiduciary — (69 ) 7 — (62 ) Acquisition of businesses, net of cash acquired — — (15 ) — (15 ) Sale of businesses, net of cash sold — — 7 — 7 Capital expenditures — — (106 ) — (106 ) Cash provided by (used for) investing activities — (79 ) (143 ) — (222 ) Cash flows from financing activities Share repurchase (1,155 ) — — — (1,155 ) Advances from (to) affiliates 823 (320 ) (542 ) 39 — Issuance of shares for employee benefit plans (144 ) — — — (144 ) Issuance of debt 1,219 2,340 — — 3,559 Repayment of debt (906 ) (1,322 ) — — (2,228 ) Cash dividends to shareholders (203 ) — — — (203 ) Noncontrolling interests and other financing activities — — (61 ) — (61 ) Cash provided by (used for) financing activities (366 ) 698 (603 ) 39 (232 ) Effect of exchange rate changes on cash and cash equivalents — — 18 — 18 Net increase (decrease) in cash and cash equivalents — 509 (38 ) (546 ) (75 ) Cash and cash equivalents at beginning of period — 862 575 (781 ) 656 Cash and cash equivalents at end of period $ — $ 1,371 $ 537 $ (1,327 ) $ 581 Condensed Consolidating Statement of Cash Flows Six Months Ended June 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Cash flows from operating activities Cash provided by (used for) operating activities $ (126 ) $ 582 $ 759 $ (802 ) $ 413 Cash flows from investing activities Proceeds from investments — 13 10 — 23 Payments for investments (12 ) (17 ) (19 ) 12 (36 ) Net sales (purchases) of short-term investments - non-fiduciary — 296 56 — 352 Acquisition of businesses, net of cash acquired — — (50 ) — (50 ) Sale of businesses, net of cash sold — — 1 — 1 Capital expenditures — — (111 ) — (111 ) Cash provided by (used for) investing activities (12 ) 292 (113 ) 12 179 Cash flows from financing activities Share repurchase (971 ) — — — (971 ) Advances from (to) affiliates 965 (810 ) (395 ) 240 — Issuance of shares for employee benefit plans (150 ) — — — (150 ) Issuance of debt 752 1,800 — — 2,552 Repayment of debt (272 ) (1,461 ) (294 ) — (2,027 ) Cash dividends to shareholders (187 ) — — — (187 ) Noncontrolling interests and other financing activities — — (15 ) — (15 ) Cash provided by (used for) financing activities 137 (471 ) (704 ) 240 (798 ) Effect of exchange rate changes on cash and cash equivalents — — (63 ) — (63 ) Net increase (decrease) in cash and cash equivalents (1 ) 403 (121 ) (550 ) (269 ) Cash and cash equivalents at beginning of period 1 2,524 793 (2,562 ) 756 Cash and cash equivalents at end of period $ — $ 2,927 $ 672 $ (3,112 ) $ 487

Lease Commitments - (Tables)

Lease Commitments - (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Assets And Liabilities Of Lessee	The classification of operating and finance lease asset and liability balances within the Condensed Consolidated Statements of Financial Position is as follows (in millions): As of June 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 959 Finance lease assets Other non-current assets 65 Total lease assets $ 1,024 Liabilities Current lease liabilities Operating Other current liabilities $ 199 Finance Other current liabilities 27 Non-current lease liabilities Operating Non-current operating lease liabilities 962 Finance Other non-current liabilities 37 Total lease liabilities $ 1,225
Lease, Cost	Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of June 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 2.5 Weighted average discount rate Operating leases 3.3 % Finance leases 2.4 % Other cash and non-cash related activities are as follows (in millions): Six Months Ended June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 116 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 50 The components of lease costs are as follows (in millions): Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating lease cost $ 65 $ 133 Finance lease costs Amortization of leased assets 6 13 Interest on lease liabilities — 1 Variable lease cost 12 18 Short-term lease cost (1) 1 2 Sublease income (8 ) (16 ) Net lease cost $ 76 $ 151 (1) Short-term lease cost does not include expenses related to leases with a lease term of one month or less.
Lessee Operating Lease Liability Maturity	Maturity analysis of operating and finance leases as of June 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 127 $ 14 $ (17 ) $ 124 2020 248 28 (34 ) 242 2021 224 22 (33 ) 213 2022 198 2 (34 ) 166 2023 144 — (15 ) 129 Thereafter 511 — (8 ) 503 Total undiscounted future minimum lease payments $ 1,452 $ 66 $ (141 ) $ 1,377 Less: Imputed interest (151 ) (1 ) — (152 ) Present value of lease liabilities $ 1,301 $ 65 $ (141 ) $ 1,225 At December 31, 2018, future minimum rental payments required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year are as follows (in millions): Year Ended December 31, 2018 Gross rental commitments Rentals from subleases Net rental commitments 2019 $ 303 $ (34 ) $ 269 2020 253 (30 ) 223 2021 221 (30 ) 191 2022 182 (30 ) 152 2023 148 (12 ) 136 Thereafter 472 (5 ) 467 Total minimum payments required $ 1,579 $ (141 ) $ 1,438
Finance Lease, Liability, Maturity	Maturity analysis of operating and finance leases as of June 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 127 $ 14 $ (17 ) $ 124 2020 248 28 (34 ) 242 2021 224 22 (33 ) 213 2022 198 2 (34 ) 166 2023 144 — (15 ) 129 Thereafter 511 — (8 ) 503 Total undiscounted future minimum lease payments $ 1,452 $ 66 $ (141 ) $ 1,377 Less: Imputed interest (151 ) (1 ) — (152 ) Present value of lease liabilities $ 1,301 $ 65 $ (141 ) $ 1,225 At December 31, 2018, future minimum rental payments required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year are as follows (in millions): Year Ended December 31, 2018 Gross rental commitments Rentals from subleases Net rental commitments 2019 $ 303 $ (34 ) $ 269 2020 253 (30 ) 223 2021 221 (30 ) 191 2022 182 (30 ) 152 2023 148 (12 ) 136 Thereafter 472 (5 ) 467 Total minimum payments required $ 1,579 $ (141 ) $ 1,438
Lessor, Operating Lease, Payments to be Received, Maturity	Maturity analysis of operating and finance leases as of June 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 127 $ 14 $ (17 ) $ 124 2020 248 28 (34 ) 242 2021 224 22 (33 ) 213 2022 198 2 (34 ) 166 2023 144 — (15 ) 129 Thereafter 511 — (8 ) 503 Total undiscounted future minimum lease payments $ 1,452 $ 66 $ (141 ) $ 1,377 Less: Imputed interest (151 ) (1 ) — (152 ) Present value of lease liabilities $ 1,301 $ 65 $ (141 ) $ 1,225 At December 31, 2018, future minimum rental payments required under operating leases that have initial or remaining non-cancelable lease terms in excess of one year are as follows (in millions): Year Ended December 31, 2018 Gross rental commitments Rentals from subleases Net rental commitments 2019 $ 303 $ (34 ) $ 269 2020 253 (30 ) 223 2021 221 (30 ) 191 2022 182 (30 ) 152 2023 148 (12 ) 136 Thereafter 472 (5 ) 467 Total minimum payments required $ 1,579 $ (141 ) $ 1,438

Accounting Principles and Pra_4

Accounting Principles and Practices - (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 959
Present value of lease liabilities	$ 1,301
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 1,100
Present value of lease liabilities		$ 1,300

Accounting Principles and Pra_5

Accounting Principles and Practices - Schedule of Changes to Balance Sheet for New Accounting Standards (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Operating lease right-of-use assets	$ 959
Other non-current assets	521		$ 448
Liabilities
Other current liabilities	1,197		936
Non-current operating lease liabilities	962
Other non-current liabilities	$ 924		$ 1,097
Accounting Standards Update 2016-02
Assets
Operating lease right-of-use assets		$ 1,100
Operating lease right-of-use assets
Assets
Operating lease right-of-use assets		1,021
Operating lease right-of-use assets | Accounting Standards Update 2016-02
Assets
Operating lease right-of-use assets		1,021
Other non-current assets
Assets
Other non-current assets		526
Other non-current assets | Accounting Standards Update 2016-02
Assets
Other non-current assets		78
Other current liabilities
Liabilities
Other current liabilities		1,155
Other current liabilities | Accounting Standards Update 2016-02
Liabilities
Other current liabilities		219
Non-current operating lease liabilities
Liabilities
Non-current operating lease liabilities		1,014
Non-current operating lease liabilities | Accounting Standards Update 2016-02
Liabilities
Non-current operating lease liabilities		1,014
Other non-current liabilities
Liabilities
Other non-current liabilities		963
Other non-current liabilities | Accounting Standards Update 2016-02
Liabilities
Other non-current liabilities		$ (134)

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,606	$ 2,561	$ 5,749	$ 5,651
United States
Disaggregation of Revenue [Line Items]
Total revenue	1,146	1,125	2,307	2,241
Americas other than United States
Disaggregation of Revenue [Line Items]
Total revenue	241	243	467	480
United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	400	413	852	897
Europe, Middle East, & Africa other than United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	501	493	1,510	1,472
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	318	287	613	561
Operating Segments | Commercial Risk Solutions
Disaggregation of Revenue [Line Items]
Total revenue	1,167	1,166	2,285	2,350
Operating Segments | Reinsurance Solutions
Disaggregation of Revenue [Line Items]
Total revenue	420	380	1,208	1,122
Operating Segments | Retirement Solutions
Disaggregation of Revenue [Line Items]
Total revenue	419	431	839	855
Operating Segments | Health Solutions
Disaggregation of Revenue [Line Items]
Total revenue	317	309	803	760
Operating Segments | Data & Analytic Services
Disaggregation of Revenue [Line Items]
Total revenue	286	277	622	571
Elimination
Disaggregation of Revenue [Line Items]
Total revenue	$ (3)	$ (2)	$ (8)	$ (7)

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 236	$ 240	$ 329	$ 298
Additions	336	341	682	711
Amortization	(357)	(353)	(796)	(785)
Impairment	0	0	0	0
Foreign currency and other	1	(12)	1	(8)
Balance at end of period	216	216	216	216
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	155	144	156	145
Additions	17	13	26	21
Amortization	(11)	(11)	(22)	(21)
Impairment	0	0	0	0
Foreign currency and other	0	(2)	1	(1)
Balance at end of period	$ 161	$ 144	$ 161	$ 144

Cash and Cash Equivalents and_2

Cash and Cash Equivalents and Short-term Investments (Details) £ in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019GBP (£)	Jun. 30, 2019USD ($)	Dec. 31, 2018GBP (£)	Dec. 31, 2018USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents and short-term investments			$ 816		$ 828
Cash and cash equivalents and short term investments, period increase (decrease)	$ (12)
Restricted cash and investments			99		91
Operating funds in U.K.		£ 42.8	$ 54.3	£ 42.7	$ 53.9

Other Financial Data - Schedule

Other Financial Data - Schedule of Other Income (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other (Expense) Income
Foreign currency remeasurement	$ 11,000,000	$ 29,000,000	$ 0	$ 13,000,000
Disposal of businesses	2,000,000	0	7,000,000	(1,000,000)
Pension and other postretirement	5,000,000	(7,000,000)	9,000,000	(5,000,000)
Equity earnings	1,000,000	1,000,000	2,000,000	2,000,000
Financial instruments	(13,000,000)	(27,000,000)	(12,000,000)	(27,000,000)
Other	0	1,000,000	0	0
Total	$ 6,000,000	$ (3,000,000)	$ 6,000,000	$ (18,000,000)

Other Financial Data - Schedu_2

Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 64	$ 65	$ 64	$ 59
Provision charged to Other general expenses	4	3	12	11
Accounts written off, net of recoveries	(3)	(6)	(11)	(8)
Balance at end of period	$ 65	$ 62	$ 65	$ 62

Other Financial Data - Schedu_3

Other Financial Data - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Cost to fulfill contracts with customers	$ 216	$ 329
Prepaid expenses	128	97
Taxes receivable	145	113
Other	142	79
Total	$ 631	618
Receivables from divested business		$ 12

Other Financial Data - Schedu_4

Other Financial Data - Schedule of Other Non-current Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Cost to obtain contracts with customers	$ 161	$ 156
Taxes receivable	100	100
Finance lease assets	65
Investments	54	54
Other	141	138
Total	$ 521	$ 448

Other Financial Data - Schedu_5

Other Financial Data - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Other Financial Data [Abstract]
Deferred revenue	$ 337		$ 337		$ 251
Leases	223		223
Taxes payable	133		133		83
Other	504		504		602
Total	1,197		1,197		$ 936
Revenue recognized from deferred revenue	$ 95	$ 115	$ 241	$ 215

Other Financial Data - Schedu_6

Other Financial Data - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Taxes payable	$ 576	$ 585
Leases	37	169
Deferred revenue	59	65
Compensation and benefits	49	56
Other	203	222
Total	924	1,097
Noncurrent portion of transition tax	$ 221	$ 240

Discontinued Operations (Detail

Discontinued Operations (Details) - Tempo Business	May 01, 2017USD ($)agreement	Jun. 30, 2019USD ($)
Dispositions
Number of commercial agreements | agreement	2
Discontinued Operations, Disposed of by Sale
Dispositions
Purchase price	$ 4,300,000,000
Cash and cash equivalents from discontinued operations		$ 0
Maximum | Discontinued Operations, Disposed of by Sale
Dispositions
Purchase price	4,200,000,000
Deferred consideration	$ 500,000,000

Discontinued Operations Income

Discontinued Operations Income Statement (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Expenses
Net income from discontinued operations	$ 0	$ 1	$ 0	$ 7
Tempo Business | Discontinued Operations, Disposed of by Sale
Expenses
Total operating expenses	1	0	1	3
Loss from discontinued operations before income taxes	(1)	0	(1)	(3)
Income tax benefit	(1)	0	(1)	(1)
Net loss from discontinued operations excluding gain	0	0	0	(2)
Gain on sale of discontinued operations, net of tax	0	1	0	9
Net income from discontinued operations	$ 0	$ 1	$ 0	$ 7

Restructuring - Narrative (Det

Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	6 Months Ended	30 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)job_elimination	Jun. 30, 2019USD ($)job_elimination
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 125	$ 204
Expected total cost	1,350	1,350	$ 1,350
Number of positions eliminated to date | job_elimination			5,091
Costs incurred	127	218	$ 1,200
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost	530	530	530
Costs incurred	78	102	516
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost	130	130	130
Costs incurred	4	15	95
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost	80	80	80
Costs incurred	5	14	50
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost	45	45	45
Costs incurred	2	2	41
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost	565	565	565
Costs incurred	$ 38	$ 85	$ 498
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,000
Maximum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,600

Restructuring - Schedule of Re

Restructuring - Schedule of Restructuring and Related Expenses (Details) - 2017 Plan $ in Millions	3 Months Ended	6 Months Ended	30 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 127	$ 218	$ 1,200
Estimated Remaining Costs	150	150	150
Expected total cost	1,350	1,350	1,350
Expected non-cash expense	100	100	100
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Costs incurred	78	102	516
Estimated Remaining Costs	14	14	14
Expected total cost	530	530	530
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Costs incurred	4	15	95
Estimated Remaining Costs	35	35	35
Expected total cost	130	130	130
Contract termination costs incurred	2	3	9
Expected contract termination cost remaining	15	15	15
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Costs incurred	5	14	50
Estimated Remaining Costs	30	30	30
Expected total cost	80	80	80
Contract termination costs incurred	4	13	46
Expected contract termination cost remaining	80	80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Costs incurred	2	2	41
Estimated Remaining Costs	4	4	4
Expected total cost	45	45	45
Other costs associated with restructuring and separation
Restructuring Cost and Reserve [Line Items]
Costs incurred	38	85	498
Estimated Remaining Costs	67	67	67
Expected total cost	565	565	565
Contract termination costs incurred	1	3	91
Expected contract termination cost remaining	$ 95	$ 95	$ 95

Restructuring - Schedule of _2

Restructuring - Schedule of Restructuring Reserve (Details) - 2017 Plan - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Restructuring Plan
Balance as of December 31, 2018		$ 201
Expensed	$ 125	204
Cash payments		(222)
Foreign currency translation		1
Balance as of June 30, 2019	$ 184	$ 184

Acquisitions and Dispositions_3

Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)acquisition	Jun. 30, 2018acquisition	Dec. 31, 2018USD ($)
Business Acquisition
Number of business acquired under business combination | acquisition	1	5
Assets acquired
Goodwill	$ 8,198		$ 8,171
2019 Acquisitions
Business Combination, Consideration Transferred [Abstract]
Consideration Transferred	17
Deferred and contingent consideration	5
Aggregate consideration transferred	22
Assets acquired
Cash and cash equivalents	2
Goodwill	15
Intangible assets, net	9
Other assets	4
Total assets acquired	30
Liabilities assumed
Current liabilities	6
Other non-current liabilities	2
Total liabilities assumed	8
Net assets acquired	$ 22

Acquisitions and Dispositions_4

Acquisitions and Dispositions of Businesses - Dispositions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)disposal	Jun. 30, 2018USD ($)disposal	Jun. 30, 2019USD ($)disposal	Jun. 30, 2018USD ($)disposal
Dispositions
Disposal of businesses | $	$ 2,000,000	$ 0	$ 7,000,000	$ (1,000,000)
Disposal Group, Not Discontinued Operations
Dispositions
Number of dispositions | disposal	3	1	4	1

- Goodwill and Other Intangible

- Goodwill and Other Intangible Assets Rollforward (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)
Changes in the net carrying amount of goodwill by operating segment
Beginning balance	$ 8,171
Goodwill related to current year acquisitions	15
Goodwill related to disposals	(9)
Goodwill related to prior year acquisitions	2
Foreign currency translation and other	19
Ending balance	$ 8,198

- Goodwill and Other Intangib_2

- Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Intangible assets with finite lives
Gross Carrying Amount	$ 3,667	$ 3,658
Accumulated Amortization and Impairment	2,694	2,509
Net Carrying Amount	973	1,149
Estimated amortization for intangible assets
Remainder of 2019	192
2020	223
2021	128
2022	87
2023	74
2024	58
Thereafter	211
Total	973
Customer related and contract based
Intangible assets with finite lives
Gross Carrying Amount	2,254	2,240
Accumulated Amortization and Impairment	1,517	1,444
Net Carrying Amount	737	796
Tradenames
Intangible assets with finite lives
Gross Carrying Amount	1,028	1,027
Accumulated Amortization and Impairment	847	740
Net Carrying Amount	181	287
Technology and other
Intangible assets with finite lives
Gross Carrying Amount	385	391
Accumulated Amortization and Impairment	330	325
Net Carrying Amount	$ 55	$ 66

Debt - Narrative (Details)

Debt - Narrative (Details)	Jun. 30, 2019USD ($)credit_facility	Jun. 30, 2019EUR (€)credit_facility	May 02, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 03, 2018USD ($)	Mar. 08, 2018USD ($)	Mar. 08, 2018CAD ($)
Debt Instrument [Line Items]
Short-term debt and current portion of long-term debt	$ 844,000,000			$ 251,000,000
Number of credit facilities | credit_facility	2	2
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%	3.75%	3.75%
4.500% Senior Notes Due December 2028 | Senior Notes
Debt Instrument [Line Items]
Debt face value					$ 350,000,000
Debt interest rate percentage (as a percent)	4.50%	4.50%			4.50%
4.76% Senior Notes Due March 2018 | Senior Notes
Debt Instrument [Line Items]
Debt interest rate percentage (as a percent)						4.76%	4.76%
Short-term debt and current portion of long-term debt						$ 291,000,000	$ 375,000,000
Foreign Line of Credit | 2020 Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 900,000,000
Credit Facility Expiring October 2022
Debt Instrument [Line Items]
Borrowings	0
Credit Facility Expiring October 2022 | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	400,000,000
Commercial paper | Commercial Paper Programs
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	1,300,000,000
United States | Commercial paper | Commercial Paper Programs
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 600,000,000
Europe | Commercial paper | Commercial Paper Programs
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity | €		€ 525,000,000

Debt - Schedule of Commercial

Debt - Schedule of Commercial Paper (Details) - Commercial paper - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Commercial paper outstanding	$ 843		$ 843		$ 250
Weighted average commercial paper outstanding	$ 639	$ 744	$ 482	$ 437
Weighted average interest rate of commercial paper outstanding	0.70%	0.92%	0.63%	0.85%

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate	16.30%	165.50%	15.90%	(4.80%)

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($)	3 Months Ended				6 Months Ended		87 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Feb. 28, 2017	Nov. 30, 2014	Apr. 30, 2012
Common Stock Programs
Shares purchased (in shares)							124,600,000
Total cost of shares purchased	$ 1,056,000,000	$ 101,000,000	$ 402,000,000	$ 553,000,000			$ 12,200,000,000
Weighted average shares outstanding
Basic weighted average ordinary shares outstanding (in shares)	240,600,000		246,000,000		241,400,000	247,200,000
Dilutive effect of potentially issuable shares (in shares)	2,200,000		1,400,000		1,800,000	1,600,000
Diluted weighted average ordinary shares outstanding (in shares)	242,800,000		247,400,000		243,200,000	248,800,000
Number of shares excluded from the calculation of diluted earnings per share (in shares)	0		0		0	0
Share Repurchase Program of 2014
Common Stock Programs
Share repurchase authorization limit (up to)	$ 15,000,000,000				$ 15,000,000,000		15,000,000,000	$ 5,000,000,000	$ 5,000,000,000
Share repurchase, remaining authorization limit (in shares)	$ 2,800,000,000				$ 2,800,000,000		$ 2,800,000,000
2012 - Share Repurchase Program
Common Stock Programs
Share repurchase authorization limit (up to)										$ 5,000,000,000
Shares purchased (in shares)	5,800,000		2,800,000		6,400,000	6,700,000
Total cost of shares purchased	$ 1,050,000,000		$ 400,000,000		$ 1,150,000,000	$ 950,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended		87 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Class of Stock [Line Items]
Shares purchased (in shares)							124.6
Total repurchase cost	$ 1,056	$ 101	$ 402	$ 553			$ 12,200
2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)	5.8		2.8		6.4	6.7
Average price per share of stock repurchased (in dollars per share)	$ 183.23		$ 141.23		$ 181.07	$ 141.06
Total repurchase cost	$ 1,050		$ 400		$ 1,150	$ 950
Additional associated costs	6		2		7	5
Total repurchase and associated costs	$ 1,056		$ 402		$ 1,157	$ 955

Shareholders' Equity - Accumula

Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 4,862	$ 5,385	$ 4,219	$ 5,140
Other comprehensive income (loss) before reclassifications, net			25
Amounts reclassified from accumulated other comprehensive income:
Amounts reclassified from accumulated other comprehensive income			60
Tax expense			(13)
Amounts reclassified from accumulated other comprehensive income, net			47
Total other comprehensive income (loss) attributable to Aon shareholders	(97)	(333)	72	(27)
Ending Balance	3,913	$ 4,618	3,913	$ 4,618
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance			(3,909)
Amounts reclassified from accumulated other comprehensive income:
Ending Balance	(3,837)		(3,837)
Change in Fair Value of Financial Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance			(15)
Other comprehensive income (loss) before reclassifications, net			(8)
Amounts reclassified from accumulated other comprehensive income:
Amounts reclassified from accumulated other comprehensive income			8
Tax expense			(1)
Amounts reclassified from accumulated other comprehensive income, net			7
Total other comprehensive income (loss) attributable to Aon shareholders			(1)
Ending Balance	(16)		(16)
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance			(1,319)
Other comprehensive income (loss) before reclassifications, net			28
Amounts reclassified from accumulated other comprehensive income:
Amounts reclassified from accumulated other comprehensive income			0
Tax expense			0
Amounts reclassified from accumulated other comprehensive income, net			0
Total other comprehensive income (loss) attributable to Aon shareholders			28
Ending Balance	(1,291)		(1,291)
Postretirement Benefit Obligation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance			(2,575)
Other comprehensive income (loss) before reclassifications, net			5
Amounts reclassified from accumulated other comprehensive income:
Amounts reclassified from accumulated other comprehensive income			52
Tax expense			(12)
Amounts reclassified from accumulated other comprehensive income, net			40
Total other comprehensive income (loss) attributable to Aon shareholders			45
Ending Balance	$ (2,530)		$ (2,530)

Employee Benefits (Details)

Employee Benefits (Details) £ in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2018GBP (£)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018GBP (£)	Jun. 30, 2018USD ($)
U.K.
Defined Benefit Plan Disclosure
Service cost	$ 0		$ 0	$ 0		$ 0
Interest cost	27		29	55		58
Expected return on plan assets, net of administration expenses	(48)		(50)	(97)		(101)
Amortization of prior-service cost	0		0	1		0
Amortization of net actuarial loss	8		7	15		15
Net periodic (benefit) cost	(13)		(14)	(26)		(28)
Loss on pension settlement	0		16	0		23
Total net periodic (benefit) cost	(13)		2	(26)		(5)
Payment for settlement					£ 99	132
Benefit obligation period increase (decrease)		£ (87)	(115)
Benefit obligation, (increase) decrease for settlement		£ 12	16		£ 17	23
Estimate of contributions to defined benefit pension plans for the current fiscal year	80			80
Contributions made to defined benefit pension plans	23		25	46		48
U.S.
Defined Benefit Plan Disclosure
Service cost	0		0	0		0
Interest cost	27		25	54		50
Expected return on plan assets, net of administration expenses	(34)		(36)	(68)		(72)
Amortization of prior-service cost	0		1	1		1
Amortization of net actuarial loss	14		15	27		30
Net periodic (benefit) cost	7		5	14		9
Loss on pension settlement	0		0	0		0
Total net periodic (benefit) cost	7		5	14		9
Estimate of contributions to defined benefit pension plans for the current fiscal year	46			46
Contributions made to defined benefit pension plans	6		8	23		25
Other
Defined Benefit Plan Disclosure
Service cost	0		0	0		0
Interest cost	7		7	14		14
Expected return on plan assets, net of administration expenses	(10)		(11)	(20)		(23)
Amortization of prior-service cost	0		0	0		0
Amortization of net actuarial loss	3		3	6		6
Net periodic (benefit) cost	0		(1)	0		(3)
Loss on pension settlement	0		0	0		0
Total net periodic (benefit) cost	0		(1)	0		(3)
Estimate of contributions to defined benefit pension plans for the current fiscal year	19			19
Contributions made to defined benefit pension plans	$ 3		$ 3	$ 10		$ 11

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Share-based compensation expenses recognized (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 91	$ 70	$ 180	$ 147
Restricted share units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	50	46	113	104
Performance share awards (“PSAs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	39	23	62	39
Employee share purchase plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 2	$ 1	$ 5	$ 4

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	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Non-vested share awards (in shares)
Non-vested at beginning of period (in shares)	4,208	4,849	4,849
Granted (in shares)	1,178	1,352
Vested (in shares)	(1,451)	(1,664)
Forfeited (in shares)	(97)	(109)
Non-vested at end of period (in shares)	3,838	4,428	4,208
Weighted Average Fair value
Non-vested at beginning of period (in dollars per share)	$ 120	$ 104	$ 104
Granted (in dollars per share)	173	140
Vested (in dollars per share)	113	98
Forfeited (in dollars per share)	124	109
Non-vested at end of period (in dollars per share)	$ 139	$ 117	$ 120
Unamortized deferred compensation expense	$ 426
Remaining weighted-average amortization period (in years)	2 years 1 month 6 days
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	6 Months Ended
	Jun. 30, 2019
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	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target PSAs granted during period (in shares)	467	564	548
Weighted average fair value per share at date of grant (in dollars per share)	$ 164	$ 134	$ 114
Number of shares that would be issued based on current performance levels (in shares)	464	970	1,066
Unamortized expense, based on current performance levels	$ 69	$ 67	$ 20

Derivatives and Hedging - Forei

Derivatives and Hedging - Foreign Exchange Risk Management Narrative (Details)	6 Months Ended
	Jun. 30, 2019
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) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value
Notional Amount	$ 873	$ 915
Derivative Assets	19	18
Derivative Liabilities	$ 1	8
Term of derivative contract	30 days
Other Current Assets
Derivatives, Fair Value
Derivative Assets	$ 8	3
Other non-current assets
Derivatives, Fair Value
Derivative Assets	11	15
Other current liabilities
Derivatives, Fair Value
Derivative Liabilities	1	5
Other non-current liabilities
Derivatives, Fair Value
Derivative Liabilities		3
Derivatives accounted for as hedges | Gross foreign exchange contracts
Derivatives, Fair Value
Notional Amount	588	646
Derivative Assets	14	17
Derivative Liabilities	1	2
Not Designated as Hedging Instrument | Gross foreign exchange contracts
Derivatives, Fair Value
Notional Amount	285	269
Derivative Assets	5	1
Derivative Liabilities	$ 0	$ 6

Derivatives and Hedging - Sched

Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Gain (loss) recognized in Accumulated other comprehensive loss	$ (12)		$ (8)
Gain (loss) recognized in Accumulated other comprehensive loss		$ (25)		$ (11)
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(3)		(8)
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		(2)		(6)
Revenue
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(3)		(7)
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		0		0
Compensation and benefits
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	0		0
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		0		1
Other general expenses
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	0		0
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		(1)		(2)
Interest expense
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	0		(1)
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		0		(1)
Other income (expense) (1)
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	$ 0		$ 0
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		$ (1)		$ (4)

Derivatives and Hedging - Inter

Derivatives and Hedging - Interest Rate Management Risk Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
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 | Gross foreign exchange contracts
Derivative [Line Items]
Derivative gain (loss)	$ (9)	$ (20)	$ (4)	$ (11)

Derivatives and Hedging - For_2

Derivatives and Hedging - Foreign Hedge (Details) - 6 months ended Jun. 30, 2019 - Net Investment Hedging € in Millions, $ in Millions	USD ($)	EUR (€)
Derivatives, Fair Value
European denominated commercial paper	$ 568	€ 500
Effective portion of loss reclassified from Accumulated OCI	$ 16

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	Jun. 30, 2019	Dec. 31, 2018
Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	$ 2,356	$ 1,759
Government bonds
Assets
Other investments:	1	1
Equity investments
Assets
Other investments:	1	2
Gross foreign exchange contracts
Assets
Derivatives	21	21
Liabilities
Derivatives	3	12
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	2,356	1,759
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	2
Significant Other Observable Inputs (Level 2) | Gross foreign exchange contracts
Assets
Derivatives	21	21
Liabilities
Derivatives	3	12
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	Jun. 30, 2019	Dec. 31, 2018
Carrying Value
Fair value of financial instrument
Long-term debt	$ 6,740	$ 5,993
Fair Value | Fair Value, Inputs, Level 2
Fair value of financial instrument
Long-term debt	$ 7,356	$ 6,159

Claims, Lawsuits and Other Co_2

Claims, Lawsuits and Other Contingencies - Narrative (Details) £ in Millions, $ in Millions	Jun. 30, 2019USD ($)	Sep. 06, 2018USD ($)	Oct. 03, 2017NZD ($)	Dec. 20, 2016GBP (£)	Jun. 29, 2015NZD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Apr. 30, 2014GBP (£)
Legal, Guarantees and Indemnifications
Revenue						$ 2,606,000,000	$ 2,561,000,000	$ 5,749,000,000	$ 5,651,000,000
Maximum potential funding under commitments	$ 102,000,000					102,000,000		102,000,000			$ 103,000,000
Letters of credit outstanding	74,000,000					74,000,000		74,000,000			$ 83,000,000
Potential Claim for Pension Advisory Services
Legal, Guarantees and Indemnifications
Estimate of possible loss	57,000,000					57,000,000		57,000,000				£ 45
Pending Litigation | Trustees Of Gleeds Pension Fund 2016
Legal, Guarantees and Indemnifications
Estimate of possible loss	89,000,000					89,000,000		89,000,000
Damages sought | £				£ 70
Pending Litigation | Lyttleton Port Company Limited
Legal, Guarantees and Indemnifications
Damages sought	123,000,000				$ 184
Pending Litigation | Christchurch City Council
Legal, Guarantees and Indemnifications
Damages sought	353,000,000		$ 528
Minimum
Legal, Guarantees and Indemnifications
Estimate of possible loss	0					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		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
Guarantor obligations, current carrying value	15,000,000					15,000,000		15,000,000
Loss contingency accrual payments								0
Maximum potential funding under commitments	77,000,000					77,000,000		77,000,000
Discontinued Operations, Disposed of by Sale | Tempo Business | Performance Guarantee
Legal, Guarantees and Indemnifications
Guarantor obligations, current carrying value	1,000,000					1,000,000		1,000,000
Loss contingency accrual payments						0
Maximum potential funding under commitments	$ 170,000,000					$ 170,000,000		$ 170,000,000

Segment Information (Details)

Segment Information (Details)	6 Months Ended
	Jun. 30, 2019segmentrevenue_linemetric
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) - subsidiary	Jun. 30, 2019	May 02, 2019	Dec. 31, 2018	Dec. 03, 2018
Condensed Financial Statements, Captions [Line Items]
Number of subsidiaries			2
Aon plc
Condensed Financial Statements, Captions [Line Items]
Parent company's percentage ownership of guarantors	100.00%
5.00% Senior notes due September 2020
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	5.00%
8.205% Junior subordinated deferrable interest debentures due January 2027
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	8.205%
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% notes due May 2044
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.60%
4.75% Notes Due May 2045
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.75%
4.500% Senior Notes Due December 2028 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	4.50%			4.50%
3.75% Senior Notes Due May 2, 2029 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	3.75%	3.75%
2.80% Senior Notes Due 2021
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage (as a percent)	2.80%
3.875% due in 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				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue
Total revenue	$ 2,606		$ 2,561		$ 5,749	$ 5,651
Expenses
Compensation and benefits	1,501		1,494		3,085	3,110
Information technology	126		123		243	238
Premises	85		96		172	189
Depreciation of fixed assets	40		47		80	86
Amortization and impairment of intangible assets	97		282		194	392
Other general expenses	344		535		690	853
Total operating expenses	2,193		2,577		4,464	4,868
Operating income (loss)	413		(16)		1,285	783
Interest income	1		1		3	5
Interest expense	(77)		(69)		(149)	(139)
Intercompany interest income (expense)	0		0		0	0
Intercompany other income (expense)	0		0		0	0
Other income (expense)	6		(3)		6	(18)
Income (loss) from continuing operations before income taxes	343		(87)		1,145	631
Income tax expense (benefit)	56		(144)		182	(30)
Net income from continuing operations	287		57		963	661
Net income from discontinued operations	0		1		0	7
Net income (loss) before equity in earnings of subsidiaries	287		58		963	668
Equity in earnings of subsidiaries	0		0		0	0
Net income	287	$ 676	58	$ 610	963	668
Less: Net income attributable to noncontrolling interests	10		10		27	26
Net income attributable to Aon shareholders	277		48		936	642
Aon plc
Revenue
Total revenue	0		0		0	0
Expenses
Compensation and benefits	22		15		42	34
Information technology	0		0		0	0
Premises	0		0		0	0
Depreciation of fixed assets	0		0		0	0
Amortization and impairment of intangible assets	0		0		0	0
Other general expenses	3		2		3	3
Total operating expenses	25		17		45	37
Operating income (loss)	(25)		(17)		(45)	(37)
Interest income	0		0		0	0
Interest expense	(45)		(48)		(91)	(97)
Intercompany interest income (expense)	3		3		7	7
Intercompany other income (expense)	137		(93)		168	(146)
Other income (expense)	(11)		48		(6)	23
Income (loss) from continuing operations before income taxes	59		(107)		33	(250)
Income tax expense (benefit)	0		(3)		(5)	(19)
Net income from continuing operations	59		(104)		38	(231)
Net income from discontinued operations	0		0		0	0
Net income (loss) before equity in earnings of subsidiaries	59		(104)		38	(231)
Equity in earnings of subsidiaries	211		170		893	888
Net income	270		66		931	657
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	270		66		931	657
Aon Corporation
Revenue
Total revenue	0		0		0	0
Expenses
Compensation and benefits	4		1		12	2
Information technology	0		0		0	0
Premises	9		0		13	0
Depreciation of fixed assets	0		0		0	0
Amortization and impairment of intangible assets	0		0		0	0
Other general expenses	6		91		2	91
Total operating expenses	19		92		27	93
Operating income (loss)	(19)		(92)		(27)	(93)
Interest income	9		15		18	29
Interest expense	(34)		(25)		(62)	(49)
Intercompany interest income (expense)	(116)		(129)		(232)	(257)
Intercompany other income (expense)	(164)		10		(263)	5
Other income (expense)	(14)		(20)		(25)	(26)
Income (loss) from continuing operations before income taxes	(338)		(241)		(591)	(391)
Income tax expense (benefit)	(64)		(50)		(106)	(77)
Net income from continuing operations	(274)		(191)		(485)	(314)
Net income from discontinued operations	0		0		0	0
Net income (loss) before equity in earnings of subsidiaries	(274)		(191)		(485)	(314)
Equity in earnings of subsidiaries	301		207		1,025	912
Net income	27		16		540	598
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	27		16		540	598
Other Non-Guarantor Subsidiaries
Revenue
Total revenue	2,606		2,561		5,749	5,651
Expenses
Compensation and benefits	1,475		1,478		3,031	3,074
Information technology	126		123		243	238
Premises	76		96		159	189
Depreciation of fixed assets	40		47		80	86
Amortization and impairment of intangible assets	97		282		194	392
Other general expenses	335		442		685	759
Total operating expenses	2,149		2,468		4,392	4,738
Operating income (loss)	457		93		1,357	913
Interest income	0		0		0	0
Interest expense	(6)		(10)		(11)	(17)
Intercompany interest income (expense)	113		126		225	250
Intercompany other income (expense)	27		83		95	141
Other income (expense)	24		(13)		32	0
Income (loss) from continuing operations before income taxes	615		279		1,698	1,287
Income tax expense (benefit)	120		(91)		293	66
Net income from continuing operations	495		370		1,405	1,221
Net income from discontinued operations	0		1		0	7
Net income (loss) before equity in earnings of subsidiaries	495		371		1,405	1,228
Equity in earnings of subsidiaries	27		16		540	598
Net income	522		387		1,945	1,826
Less: Net income attributable to noncontrolling interests	10		10		27	26
Net income attributable to Aon shareholders	512		377		1,918	1,800
Consolidation Adjustments
Revenue
Total revenue	0		0		0	0
Expenses
Compensation and benefits	0		0		0	0
Information technology	0		0		0	0
Premises	0		0		0	0
Depreciation of fixed assets	0		0		0	0
Amortization and impairment of intangible assets	0		0		0	0
Other general expenses	0		0		0	0
Total operating expenses	0		0		0	0
Operating income (loss)	0		0		0	0
Interest income	(8)		(14)		(15)	(24)
Interest expense	8		14		15	24
Intercompany interest income (expense)	0		0		0	0
Intercompany other income (expense)	0		0		0	0
Other income (expense)	7		(18)		5	(15)
Income (loss) from continuing operations before income taxes	7		(18)		5	(15)
Income tax expense (benefit)	0		0		0	0
Net income from continuing operations	7		(18)		5	(15)
Net income from discontinued operations	0		0		0	0
Net income (loss) before equity in earnings of subsidiaries	7		(18)		5	(15)
Equity in earnings of subsidiaries	(539)		(393)		(2,458)	(2,398)
Net income	(532)		(411)		(2,453)	(2,413)
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	$ (532)		$ (411)		$ (2,453)	$ (2,413)

Guarantee of Registered Secur_5

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Net income	$ 287	$ 676	$ 58	$ 610	$ 963	$ 668
Less: Net income attributable to noncontrolling interests	10		10		27	26
Net income attributable to Aon shareholders	277		48		936	642
Change in fair value of financial instruments	(8)	7	(1)	14	(1)	13
Foreign currency translation adjustments	(103)	133	(460)	247	30	(213)
Postretirement benefit obligation	14	$ 31	122	$ 48	45	170
Total other comprehensive (loss) income	(97)		(339)		74	(30)
Equity in other comprehensive income (loss) of subsidiaries, net of tax	0		0		0	0
Less: Other comprehensive loss attributable to noncontrolling interests	0		(6)		2	(3)
Total other comprehensive income (loss) attributable to Aon shareholders	(97)		(333)		72	(27)
Comprehensive income (loss) attributable to Aon shareholders	180		(285)		1,008	615
Aon plc
Condensed Financial Statements, Captions [Line Items]
Net income	270		66		931	657
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	270		66		931	657
Change in fair value of financial instruments	0		0		0	0
Foreign currency translation adjustments	0		0		0	0
Postretirement benefit obligation	0		0		0	0
Total other comprehensive (loss) income	0		0		0	0
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(90)		(351)		77	(42)
Less: Other comprehensive loss attributable to noncontrolling interests	0		0		0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(90)		(351)		77	(42)
Comprehensive income (loss) attributable to Aon shareholders	180		(285)		1,008	615
Aon Corporation
Condensed Financial Statements, Captions [Line Items]
Net income	27		16		540	598
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	27		16		540	598
Change in fair value of financial instruments	0		(4)		2	(1)
Foreign currency translation adjustments	0		0		0	0
Postretirement benefit obligation	10		11		32	22
Total other comprehensive (loss) income	10		7		34	21
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(118)		(345)		(3)	(60)
Less: Other comprehensive loss attributable to noncontrolling interests	0		0		0	0
Total other comprehensive income (loss) attributable to Aon shareholders	(108)		(338)		31	(39)
Comprehensive income (loss) attributable to Aon shareholders	(81)		(322)		571	559
Other Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	522		387		1,945	1,826
Less: Net income attributable to noncontrolling interests	10		10		27	26
Net income attributable to Aon shareholders	512		377		1,918	1,800
Change in fair value of financial instruments	(8)		3		(3)	14
Foreign currency translation adjustments	(96)		(478)		35	(228)
Postretirement benefit obligation	4		111		13	148
Total other comprehensive (loss) income	(100)		(364)		45	(66)
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(108)		(338)		31	(39)
Less: Other comprehensive loss attributable to noncontrolling interests	0		(6)		2	(3)
Total other comprehensive income (loss) attributable to Aon shareholders	(208)		(696)		74	(102)
Comprehensive income (loss) attributable to Aon shareholders	304		(319)		1,992	1,698
Consolidation Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income	(532)		(411)		(2,453)	(2,413)
Less: Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to Aon shareholders	(532)		(411)		(2,453)	(2,413)
Change in fair value of financial instruments	0		0		0	0
Foreign currency translation adjustments	(7)		18		(5)	15
Postretirement benefit obligation	0		0		0	0
Total other comprehensive (loss) income	(7)		18		(5)	15
Equity in other comprehensive income (loss) of subsidiaries, net of tax	316		1,034		(105)	141
Less: Other comprehensive loss attributable to noncontrolling interests	0		0		0	0
Total other comprehensive income (loss) attributable to Aon shareholders	309		1,052		(110)	156
Comprehensive income (loss) attributable to Aon shareholders	$ (223)		$ 641		$ (2,563)	$ (2,257)

Guarantee of Registered Secur_6

Guarantee of Registered Securities - Condensed Consolidating Statement of Financial Position (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 581		$ 656
Short-term investments	235		172
Receivables, net	3,227		2,760
Fiduciary assets	12,071		10,166
Current intercompany receivables	0		0
Other current assets	631		618
Total current assets	16,745		14,372
Goodwill	8,198		8,171
Intangible assets, net	973		1,149
Fixed assets, net	599		588
Operating lease right-of-use assets	959
Deferred tax assets	599		561
Prepaid pension	1,213		1,133
Non-current intercompany receivables	0		0
Other non-current assets	521		448
Investment in subsidiary	0		0
Total assets	29,807		26,422
Current liabilities
Accounts payable and accrued liabilities	1,369		1,943
Short-term debt and current portion of long-term debt	844		251
Fiduciary liabilities	12,071		10,166
Current intercompany payables	0		0
Other current liabilities	1,197		936
Total current liabilities	15,481		13,296
Long-term debt	6,740		5,993
Non-current operating lease liabilities	962
Deferred tax liabilities	211		181
Pension, other postretirement, and postemployment liabilities	1,576		1,636
Non-current intercompany payables	0		0
Other non-current liabilities	924		1,097
Total liabilities	25,894		22,203
Total Aon shareholders’ equity	3,836		4,151
Noncontrolling interests	77		68
Total equity	3,913	$ 4,862	4,219	$ 4,618	$ 5,385	$ 5,140
Total liabilities and equity	29,807		26,422
Aon plc
Current assets
Cash and cash equivalents	0		0
Short-term investments	0		0
Receivables, net	0		0
Fiduciary assets	0		0
Current intercompany receivables	167		191
Other current assets	0		0
Total current assets	167		191
Goodwill	0		0
Intangible assets, net	0		0
Fixed assets, net	0		0
Operating lease right-of-use assets	0
Deferred tax assets	93		94
Prepaid pension	0		0
Non-current intercompany receivables	404		403
Other non-current assets	1		1
Investment in subsidiary	8,937		8,433
Total assets	9,602		9,122
Current liabilities
Accounts payable and accrued liabilities	582		274
Short-term debt and current portion of long-term debt	569		250
Fiduciary liabilities	0		0
Current intercompany payables	378		213
Other current liabilities	0		0
Total current liabilities	1,529		737
Long-term debt	4,234		4,231
Non-current operating lease liabilities	0
Deferred tax liabilities	0		0
Pension, other postretirement, and postemployment liabilities	0		0
Non-current intercompany payables	0		0
Other non-current liabilities	3		3
Total liabilities	5,766		4,971
Total Aon shareholders’ equity	3,836		4,151
Noncontrolling interests	0		0
Total equity	3,836		4,151
Total liabilities and equity	9,602		9,122
Aon Corporation
Current assets
Cash and cash equivalents	1,371		862
Short-term investments	125		56
Receivables, net	0		0
Fiduciary assets	0		0
Current intercompany receivables	3,421		897
Other current assets	10		16
Total current assets	4,927		1,831
Goodwill	0		0
Intangible assets, net	0		0
Fixed assets, net	0		0
Operating lease right-of-use assets	112
Deferred tax assets	498		467
Prepaid pension	5		5
Non-current intercompany receivables	261		261
Other non-current assets	28		30
Investment in subsidiary	20,147		19,132
Total assets	25,978		21,726
Current liabilities
Accounts payable and accrued liabilities	57		70
Short-term debt and current portion of long-term debt	275		0
Fiduciary liabilities	0		0
Current intercompany payables	14,633		11,875
Other current liabilities	78		69
Total current liabilities	15,043		12,014
Long-term debt	2,506		1,762
Non-current operating lease liabilities	149
Deferred tax liabilities	0		0
Pension, other postretirement, and postemployment liabilities	1,232		1,275
Non-current intercompany payables	7,366		7,390
Other non-current liabilities	106		167
Total liabilities	26,402		22,608
Total Aon shareholders’ equity	(424)		(882)
Noncontrolling interests	0		0
Total equity	(424)		(882)
Total liabilities and equity	25,978		21,726
Other Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	537		575
Short-term investments	110		116
Receivables, net	3,227		2,760
Fiduciary assets	12,071		10,166
Current intercompany receivables	12,843		11,634
Other current assets	621		602
Total current assets	29,409		25,853
Goodwill	8,198		8,171
Intangible assets, net	973		1,149
Fixed assets, net	599		588
Operating lease right-of-use assets	847
Deferred tax assets	150		144
Prepaid pension	1,208		1,128
Non-current intercompany receivables	7,200		7,225
Other non-current assets	492		417
Investment in subsidiary	(424)		(882)
Total assets	48,652		43,793
Current liabilities
Accounts payable and accrued liabilities	2,057		2,380
Short-term debt and current portion of long-term debt	0		1
Fiduciary liabilities	12,071		10,166
Current intercompany payables	1,420		634
Other current liabilities	1,119		867
Total current liabilities	16,667		14,048
Long-term debt	0		0
Non-current operating lease liabilities	813
Deferred tax liabilities	353		325
Pension, other postretirement, and postemployment liabilities	344		361
Non-current intercompany payables	499		499
Other non-current liabilities	815		927
Total liabilities	19,491		16,160
Total Aon shareholders’ equity	29,084		27,565
Noncontrolling interests	77		68
Total equity	29,161		27,633
Total liabilities and equity	48,652		43,793
Consolidation Adjustments
Current assets
Cash and cash equivalents	(1,327)		(781)
Short-term investments	0		0
Receivables, net	0		0
Fiduciary assets	0		0
Current intercompany receivables	(16,431)		(12,722)
Other current assets	0		0
Total current assets	(17,758)		(13,503)
Goodwill	0		0
Intangible assets, net	0		0
Fixed assets, net	0		0
Operating lease right-of-use assets	0
Deferred tax assets	(142)		(144)
Prepaid pension	0		0
Non-current intercompany receivables	(7,865)		(7,889)
Other non-current assets	0		0
Investment in subsidiary	(28,660)		(26,683)
Total assets	(54,425)		(48,219)
Current liabilities
Accounts payable and accrued liabilities	(1,327)		(781)
Short-term debt and current portion of long-term debt	0		0
Fiduciary liabilities	0		0
Current intercompany payables	(16,431)		(12,722)
Other current liabilities	0		0
Total current liabilities	(17,758)		(13,503)
Long-term debt	0		0
Non-current operating lease liabilities	0
Deferred tax liabilities	(142)		(144)
Pension, other postretirement, and postemployment liabilities	0		0
Non-current intercompany payables	(7,865)		(7,889)
Other non-current liabilities	0		0
Total liabilities	(25,765)		(21,536)
Total Aon shareholders’ equity	(28,660)		(26,683)
Noncontrolling interests	0		0
Total equity	(28,660)		(26,683)
Total liabilities and equity	$ (54,425)		$ (48,219)

Guarantee of Registered Secur_7

Guarantee of Registered Securities - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Cash provided by (used for) operating activities	$ 361	$ 413
Cash flows from investing activities
Proceeds from investments	14	23
Payments for investments	(60)	(36)
Net sales (purchases) of short-term investments - non-fiduciary	(62)	352
Acquisition of businesses, net of cash acquired	(15)	(50)
Sale of businesses, net of cash sold	7	1
Capital expenditures	(106)	(111)
Cash provided by (used for) investing activities	(222)	179
Cash flows from financing activities
Share repurchase	(1,155)	(971)
Advances from (to) affiliates	0	0
Issuance of shares for employee benefit plans	(144)	(150)
Issuance of debt	3,559	2,552
Repayment of debt	(2,228)	(2,027)
Cash dividends to shareholders	(203)	(187)
Noncontrolling interests and other financing activities	(61)	(15)
Cash used for financing activities	(232)	(798)
Effect of exchange rates on cash and cash equivalents	18	(63)
Net increase (decrease) in cash and cash equivalents	(75)	(269)
Cash and cash equivalents at beginning of period	656	756
Cash and cash equivalents at end of period	581	487
Aon plc
Cash flows from operating activities
Cash provided by (used for) operating activities	366	(126)
Cash flows from investing activities
Proceeds from investments	0	0
Payments for investments	0	(12)
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 provided by (used for) investing activities	0	(12)
Cash flows from financing activities
Share repurchase	(1,155)	(971)
Advances from (to) affiliates	823	965
Issuance of shares for employee benefit plans	(144)	(150)
Issuance of debt	1,219	752
Repayment of debt	(906)	(272)
Cash dividends to shareholders	(203)	(187)
Noncontrolling interests and other financing activities	0	0
Cash used for financing activities	(366)	137
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	0	(1)
Cash and cash equivalents at beginning of period	0	1
Cash and cash equivalents at end of period	0	0
Aon Corporation
Cash flows from operating activities
Cash provided by (used for) operating activities	(110)	582
Cash flows from investing activities
Proceeds from investments	9	13
Payments for investments	(19)	(17)
Net sales (purchases) of short-term investments - non-fiduciary	(69)	296
Acquisition of businesses, net of cash acquired	0	0
Sale of businesses, net of cash sold	0	0
Capital expenditures	0	0
Cash provided by (used for) investing activities	(79)	292
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(320)	(810)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	2,340	1,800
Repayment of debt	(1,322)	(1,461)
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash used for financing activities	698	(471)
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	509	403
Cash and cash equivalents at beginning of period	862	2,524
Cash and cash equivalents at end of period	1,371	2,927
Other Non-Guarantor Subsidiaries
Cash flows from operating activities
Cash provided by (used for) operating activities	690	759
Cash flows from investing activities
Proceeds from investments	5	10
Payments for investments	(41)	(19)
Net sales (purchases) of short-term investments - non-fiduciary	7	56
Acquisition of businesses, net of cash acquired	(15)	(50)
Sale of businesses, net of cash sold	7	1
Capital expenditures	(106)	(111)
Cash provided by (used for) investing activities	(143)	(113)
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(542)	(395)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	0
Repayment of debt	0	(294)
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	(61)	(15)
Cash used for financing activities	(603)	(704)
Effect of exchange rates on cash and cash equivalents	18	(63)
Net increase (decrease) in cash and cash equivalents	(38)	(121)
Cash and cash equivalents at beginning of period	575	793
Cash and cash equivalents at end of period	537	672
Consolidation Adjustments
Cash flows from operating activities
Cash provided by (used for) operating activities	(585)	(802)
Cash flows from investing activities
Proceeds from investments	0	0
Payments for investments	0	12
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 provided by (used for) investing activities	0	12
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	39	240
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 used for financing activities	39	240
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	(546)	(550)
Cash and cash equivalents at beginning of period	(781)	(2,562)
Cash and cash equivalents at end of period	$ (1,327)	$ (3,112)

Lease Commitments - Assets and

Lease Commitments - Assets and Liabilities of Lessee (Details) $ in Millions	Jun. 30, 2019USD ($)
Assets
Operating lease right-of-use assets	$ 959
Finance lease assets	65
Total lease assets	1,024
Current lease liabilities
Operating	199
Finance	27
Non-current lease liabilities
Operating	962
Finance	37
Total lease liabilities	$ 1,225

Lease Commitments - Lease Costs

Lease Commitments - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 65	$ 133
Finance lease costs
Amortization of leased assets	6	13
Interest on lease liabilities	0	1
Variable lease cost	12	18
Short-term lease cost	1	2
Sublease income	(8)	(16)
Net lease cost	$ 76	$ 151

Lease Commitments - Lease Matur

Lease Commitments - Lease Maturity (Details) $ in Millions	Jun. 30, 2019USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Remainder of 2019	$ 127
2020	248
2021	224
2022	198
2023	144
Thereafter	511
Total undiscounted future minimum lease payments	1,452
Imputed interest	(151)
Present value of lease liabilities	1,301
Finance Lease, Liability, Payment, Due [Abstract]
Remainder of 2019	14
2020	28
2021	22
2022	2
2023	0
Thereafter	0
Total undiscounted future minimum lease payments	66
Imputed interest	(1)
Present value of lease liabilities	65
Rentals from subleases
Remainder of 2019	(17)
2020	(34)
2021	(33)
2022	(34)
2023	(15)
Thereafter	(8)
Total undiscounted future minimum lease payments	(141)
Imputed interest	0
Present value of lease liabilities	(141)
Total
Remainder of 2019	124
2020	242
2021	213
2022	166
2023	129
Thereafter	503
Total undiscounted future minimum lease payments	1,377
Imputed interest	(152)
Present value of lease liabilities	$ 1,225

Lease Commitments - Lease Mat_2

Lease Commitments - Lease Maturity Prior to Topic 842 (Details) $ in Millions	Dec. 31, 2018USD ($)
Gross rental commitments
2019	$ 303
2020	253
2021	221
2022	182
2023	148
Thereafter	472
Total minimum payments required	1,579
Rentals from subleases
2019	(34)
2020	(30)
2021	(30)
2022	(30)
2023	(12)
Thereafter	(5)
Total minimum payments required	(141)
Operating Lease Payments Net Of Sublease Rental Income [Abstract]
2019	269
2020	223
2021	191
2022	152
2023	136
Thereafter	467
Total minimum payments required	$ 1,438

Lease Commitments - Lease Terms

Lease Commitments - Lease Terms and Assumptions (Details)	Jun. 30, 2019
Weighted average remaining lease term (years)
Operating leases	8 years
Finance leases	2 years 6 months
Weighted average discount rate
Operating leases	3.30%
Finance leases	2.40%

Lease Commitments - Cash Flow o

Lease Commitments - Cash Flow of Lessee (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 116
Non-cash related activities
ROU assets obtained in exchange for new operating lease liabilities	$ 50

Lease Commitments - Narrative (

Lease Commitments - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)
Leases [Abstract]
Non cash right-of-use asset lease expense	$ 68
Increase (decrease) in operating lease liabilities	$ (52)