Aon (AON) 10-Q 25 Oct 19 2019 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2019	Oct. 24, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 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		234,137,408
Entity Central Index Key	0000315293
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue
Total revenue	$ 2,379	$ 2,349	$ 8,128	$ 8,000
Expenses
Compensation and benefits	1,368	1,392	4,453	4,502
Information technology	120	125	363	363
Premises	76	94	248	283
Depreciation of fixed assets	44	40	124	126
Amortization and impairment of intangible assets	101	100	295	492
Other general expenses	310	336	1,000	1,189
Total operating expenses	2,019	2,087	6,483	6,955
Operating income (loss)	360	262	1,645	1,045
Interest income	1	0	4	5
Interest expense	(78)	(69)	(227)	(208)
Other income (expense)	2	1	8	(17)
Income (loss) from continuing operations before income taxes	285	194	1,430	825
Income tax expense (benefit)	56	39	238	9
Net income from continuing operations	229	155	1,192	816
Net income (loss) from discontinued operations	(1)	(2)	(1)	5
Net income	228	153	1,191	821
Less: Net income attributable to noncontrolling interests	6	6	33	32
Net income attributable to Aon shareholders	$ 222	$ 147	$ 1,158	$ 789
Basic net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	$ 0.94	$ 0.61	$ 4.83	$ 3.18
Discontinued operations (in dollars per share)	0	(0.01)	0	0.02
Net income (in dollars per share)	0.94	0.60	4.83	3.20
Diluted net income per share attributable to Aon shareholders
Continuing operations (in dollars per share)	0.93	0.61	4.79	3.17
Discontinued operations (in dollars per share)	0	(0.01)	0	0.02
Net income (in dollars per share)	$ 0.93	$ 0.60	$ 4.79	$ 3.19
Weighted average ordinary shares outstanding - basic (in shares)	236.9	244	239.9	246.2
Weighted average ordinary shares outstanding - diluted (in shares)	239.1	245.6	241.9	247.7

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 228	$ 153	$ 1,191	$ 821
Less: Net income attributable to noncontrolling interests	6	6	33	32
Net income attributable to Aon shareholders	222	147	1,158	789
Other comprehensive income (loss), net of tax:
Change in fair value of financial instruments	(2)	1	(3)	14
Foreign currency translation adjustments	(212)	(50)	(182)	(263)
Postretirement benefit obligation	17	(62)	62	108
Total other comprehensive loss	(197)	(111)	(123)	(141)
Less: Other comprehensive loss attributable to noncontrolling interests	(4)	(3)	(2)	(6)
Total other comprehensive loss attributable to Aon shareholders	(193)	(108)	(121)	(135)
Comprehensive income (loss) attributable to Aon shareholders	$ 29	$ 39	$ 1,037	$ 654

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Financial Position - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 602	$ 656
Short-term investments	177	172
Receivables, net	2,866	2,760
Fiduciary assets	11,041	10,166
Other current assets	631	618
Total current assets	15,317	14,372
Goodwill	8,071	8,171
Intangible assets, net	874	1,149
Fixed assets, net	606	588
Operating lease right-of-use assets	913
Deferred tax assets	611	561
Prepaid pension	1,213	1,133
Other non-current assets	562	448
Total assets	28,167	26,422
Current liabilities
Accounts payable and accrued liabilities	1,499	1,943
Short-term debt and current portion of long-term debt	1,148	251
Fiduciary liabilities	11,041	10,166
Other current liabilities	1,163	936
Total current liabilities	14,851	13,296
Long-term debt	6,120	5,993
Non-current operating lease liabilities	922
Deferred tax liabilities	209	181
Pension, other postretirement, and postemployment liabilities	1,551	1,636
Other non-current liabilities	953	1,097
Total liabilities	24,606	22,203
Equity
Ordinary shares - $0.01 nominal value Authorized: 750 shares (issued: 2019 - 234.1; 2018 - 240.1)	2	2
Additional paid-in capital	6,084	5,965
Retained earnings	1,436	2,093
Accumulated other comprehensive loss	(4,030)	(3,909)
Total Aon shareholders' equity	3,492	4,151
Noncontrolling interests	69	68
Total equity	3,561	4,219
Total liabilities and equity	$ 28,167	$ 26,422

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Financial Position (Parenthetical) - $ / shares	Sep. 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)	234,100,000	240,100,000

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Ordinary Shares and Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Tax	Non- controlling Interests
Beginning Balance (in shares) at Dec. 31, 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	821
Net change in fair value of financial instruments	14
Net foreign currency translation adjustments	(263)
Net postretirement benefit obligation	108
Ending Balance (in shares) at Sep. 30, 2018		241.2
Ending Balance at Sep. 30, 2018	4,328	$ 5,852	2,042	(3,632)	66
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
Increase (Decrease) in Shareholders' Equity
Net income	153		147		6
Shares issued - employee stock compensation plans (in shares)		0.3
Shares issued - employee stock compensation plans	10	$ 11	(1)
Shares purchased (in shares)		(2.1)
Shares purchased	(301)		(301)
Share-based compensation expense	67	$ 67
Dividends to shareholders	(98)		(98)
Net change in fair value of financial instruments	1			1
Net foreign currency translation adjustments	(50)			(47)	(3)
Net postretirement benefit obligation	(62)			(62)
Dividends paid to noncontrolling interests on subsidiary common stock	(10)				(10)
Ending Balance (in shares) at Sep. 30, 2018		241.2
Ending Balance at Sep. 30, 2018	$ 4,328	$ 5,852	2,042	(3,632)	66
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	1,191
Net change in fair value of financial instruments	(3)
Net foreign currency translation adjustments	(182)
Net postretirement benefit obligation	$ 62
Ending Balance (in shares) at Sep. 30, 2019	234.1	234.1
Ending Balance at Sep. 30, 2019	$ 3,561	$ 6,086	1,436	(4,030)	69
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
Ending Balance at Jun. 30, 2019	3,913	$ 6,004	1,669	(3,837)	77
Increase (Decrease) in Shareholders' Equity
Net income	228		222		6
Shares issued - employee stock compensation plans (in shares)		0.2
Shares issued - employee stock compensation plans	9	$ 10	(1)
Shares purchased (in shares)		(1.8)
Shares purchased	(350)		(350)
Share-based compensation expense	72	$ 72
Dividends to shareholders	(104)		(104)
Net change in fair value of financial instruments	(2)			(2)
Net foreign currency translation adjustments	(212)			(208)	(4)
Net postretirement benefit obligation	17			17
Dividends paid to noncontrolling interests on subsidiary common stock	$ (10)				(10)
Ending Balance (in shares) at Sep. 30, 2019	234.1	234.1
Ending Balance at Sep. 30, 2019	$ 3,561	$ 6,086	$ 1,436	$ (4,030)	$ 69

Condensed Consolidated Statem_6

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

Condensed Consolidated Statem_7

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net income	$ 1,191	$ 821
Net income (loss) from discontinued operations	(1)	5
Adjustments to reconcile net income to cash provided by operating activities:
(Gain) loss from sales of businesses, net	(8)	4
Depreciation of fixed assets	124	126
Amortization and impairment of intangible assets	295	492
Share-based compensation expense	252	214
Deferred income taxes	(44)	(128)
Change in assets and liabilities:
Fiduciary receivables	174	766
Short-term investments — funds held on behalf of clients	(1,285)	(731)
Fiduciary liabilities	1,111	(35)
Receivables, net	(167)	(11)
Accounts payable and accrued liabilities	(385)	(331)
Restructuring reserves	(62)	14
Current income taxes	3	(137)
Pension, other postretirement and postemployment liabilities	(127)	(223)
Other assets and liabilities	90	139
Cash provided by operating activities	1,163	975
Cash flows from investing activities
Proceeds from investments	33	30
Payments for investments	(94)	(65)
Net sales (purchases) of short-term investments — non-fiduciary	(7)	356
Acquisition of businesses, net of cash acquired	(39)	(50)
Sale of businesses, net of cash sold	43	(8)
Capital expenditures	(167)	(179)
Cash provided by (used for) investing activities	(231)	84
Cash flows from financing activities
Share repurchase	(1,507)	(1,272)
Issuance of shares for employee benefit plans	(133)	(139)
Issuance of debt	4,918	3,960
Repayment of debt	(3,858)	(3,498)
Cash dividends to shareholders	(307)	(285)
Noncontrolling interests and other financing activities	(81)	(21)
Cash used for financing activities	(968)	(1,255)
Effect of exchange rates on cash and cash equivalents	(18)	(76)
Net increase (decrease) in cash and cash equivalents	(54)	(272)
Cash and cash equivalents at beginning of period	656	756
Cash and cash equivalents at end of period	602	484
Supplemental disclosures:
Interest paid	196	172
Income taxes paid, net of refunds	$ 279	$ 274

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 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 United States 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 nine months ended September 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	9 Months Ended
	Sep. 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 Financial Accounting Standards Board (“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 nine months ended September 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 nine months ended September 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 as of September 30, 2019. 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 Statement 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 Cloud Computing Arrangements In August 2018, the FASB issued new accounting guidance on implementation costs incurred in a cloud computing arrangement that is a service contract. The new guidance aligns capitalization requirements for certain implementation costs incurred in cloud computing arrangements with existing requirements for capitalizing implementation costs for internal-use software. These costs will be deferred over the term of the hosting arrangement, including any optional renewal periods the entity is reasonably certain to exercise. An entity may apply the new guidance on either a prospective or retrospective basis. The new guidance is effective for Aon in the first quarter of 2020 with early adoption permitted. The Company does not expect there to be a significant impact on the Financial Statements and will adopt the new accounting guidance in the first quarter of 2020 on a prospective basis for all implementation costs incurred after the date of initial adoption. Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued new accounting guidance related to the disclosure requirements for employers that sponsor defined benefit pension and other postretirement benefit plans. The guidance requires sponsors of these plans to provide additional disclosures, including weighted average interest rates used in the entity’s cash balance pension plans and a narrative description of reasons for any significant gains or losses impacting the benefit obligation for the period, and eliminates certain previous disclosure requirements. The new guidance is effective for Aon in the first quarter of 2021 with early adoption permitted and will be applied retrospectively. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption. 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 does not expect there to be a significant impact on the Financial Statements and will adopt the new guidance in the first quarter of 2020. 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 does not expect there to be a significant impact 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	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Commercial Risk Solutions $ 1,057 $ 1,029 $ 3,342 $ 3,379 Reinsurance Solutions 291 279 1,499 1,401 Retirement Solutions 484 501 1,323 1,356 Health Solutions 279 278 1,082 1,038 Data & Analytic Services 271 263 893 834 Elimination (3 ) (1 ) (11 ) (8 ) Total revenue $ 2,379 $ 2,349 $ 8,128 $ 8,000 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 United States $ 1,209 $ 1,215 $ 3,516 $ 3,456 Americas other than United States 256 203 723 683 United Kingdom 358 264 1,210 1,161 Europe, Middle East, & Africa other than United Kingdom 283 399 1,793 1,871 Asia Pacific 273 268 886 829 Total revenue $ 2,379 $ 2,349 $ 8,128 $ 8,000 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 216 $ 216 $ 329 $ 298 Additions 326 332 1,008 1,043 Amortization (299 ) (305 ) (1,095 ) (1,090 ) Impairment — — — — Foreign currency translation and other (4 ) 5 (3 ) (3 ) Balance at end of period $ 239 $ 248 $ 239 $ 248 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 161 $ 144 $ 156 $ 145 Additions 14 16 40 37 Amortization (11 ) (9 ) (33 ) (30 ) Impairment — — — — Foreign currency translation and other (1 ) (1 ) — (2 ) Balance at end of period $ 163 $ 150 $ 163 $ 150

Cash and Cash Equivalents and S

Cash and Cash Equivalents and Short-term Investments	9 Months Ended
	Sep. 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 September 30, 2019 , Cash and cash equivalents and Short-term investments were $779 million compared to $828 million at December 31, 2018 , a decrease of $49 million . Of the total balances, $96 million and $91 million were restricted as to their use at September 30, 2019 and December 31, 2018 , respectively. Included within Short-term investments as of September 30, 2019 and December 31, 2018 were £42.7 million ( $52.6 million at September 30, 2019 exchange rates and $53.9 million at December 31, 2018 exchange rates) of operating funds required to be held by the Company in the United Kingdom (the “U.K.”) by the Financial Conduct Authority (the “FCA”), a U.K.-based regulator.

Other Financial Data

Other Financial Data	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Foreign currency remeasurement $ 17 $ 3 $ 17 $ 16 Disposal of businesses 1 (3 ) 8 (4 ) Pension and other postretirement 3 — 12 (5 ) Equity earnings 1 1 3 3 Financial instruments (20 ) — (32 ) (27 ) Total $ 2 $ 1 $ 8 $ (17 ) 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 65 $ 62 $ 64 $ 59 Provision charged to Other general expense 7 9 19 21 Accounts written off, net of recoveries (6 ) (8 ) (17 ) (17 ) Foreign currency translation and other 1 3 1 3 Balance at end of period $ 67 $ 66 $ 67 $ 66 Other Current Assets The components of Other current assets are as follows (in millions): As of September 30, December 31, Costs to fulfill contracts with customers (1) $ 239 $ 329 Prepaid expenses 123 97 Taxes receivable 177 113 Other (2) 92 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 September 30, December 31, Costs to obtain contracts with customers (1) $ 163 $ 156 Taxes receivable 100 100 Leases (2) 106 — Investments 52 54 Other 141 138 Total $ 562 $ 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 September 30, December 31, Deferred revenue (1) $ 256 $ 251 Leases (2) 218 — Taxes payable 152 83 Other 537 602 Total $ 1,163 $ 936 (1) During the three and nine months ended September 30, 2019 , $144 million and $385 million , respectively, was recognized in the Condensed Consolidated Statements of Income. During the three and nine months ended September 30, 2018 , $133 million and $348 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 September 30, December 31, Taxes payable (1) $ 578 $ 585 Leases 82 169 Deferred revenue 59 65 Compensation and benefits 48 56 Other 186 222 Total $ 953 $ 1,097 (1) Includes $218 million and $240 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of September 30, 2019 and December 31, 2018 , respectively.

Discontinued Operations

Discontinued Operations	9 Months Ended
	Sep. 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 nine months ended September 30, 2019 and 2018 are presented as Net income (loss) 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Expenses Total operating expenses $ 1 $ 4 $ 2 $ 7 Loss from discontinued operations before income taxes (1 ) (4 ) (2 ) (7 ) Income tax benefit — (2 ) (1 ) (3 ) Net loss from discontinued operations excluding gain (1 ) (2 ) (1 ) (4 ) Gain on sale of discontinued operations, net of tax — — — 9 Net income (loss) from discontinued operations $ (1 ) $ (2 ) $ (1 ) $ 5 There were no cash or cash equivalents of discontinued operations at September 30, 2019

Restructuring

Restructuring	9 Months Ended
	Sep. 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. The Company also estimates there to be 5,400 to 5,600 total role eliminations associated with the Restructuring Plan. 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 $550 million in workforce reduction, $125 million in technology rationalization costs, $80 million in lease consolidation costs, $50 million in non-cash asset impairments, and $545 million in other costs, including certain separation costs associated with the sale of the Divested Business. From the inception of the Restructuring Plan through September 30, 2019 , the Company has eliminated 5,353 positions and incurred total charges of $1,263 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 expense in the accompanying Condensed Consolidated Statements of Income. The following table summarizes restructuring and separation costs by type that have been incurred through September 30, 2019 and are estimated to be incurred through the end of the Restructuring Plan (in millions). Estimated costs by type have been revised based on updated assumptions: Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Inception to Date Estimated Remaining Costs Estimated Total Cost (1) Workforce reduction $ 9 $ 111 $ 525 $ 25 $ 550 Technology rationalization (2) 14 29 109 16 125 Lease consolidation (2) 3 17 53 27 80 Asset impairments 5 7 46 4 50 Other costs associated with restructuring and separation (2) (3) 32 117 530 15 545 Total restructuring and related expenses $ 63 $ 281 $ 1,263 $ 87 $ 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 for the three months ended September 30, 2019 were $9 million , $2 million , and $18 million ; for the nine months ended September 30, 2019 , were $12 million , $15 million , and $21 million ; and since inception of the Restructuring Plan, were $18 million , $48 million , and $109 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 $20 million , $80 million , and $116 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 September 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 201 Expensed 260 Cash payments (322 ) Foreign currency translation (1 ) Balance as of September 30, 2019 $ 138

Acquisitions and Dispositions o

Acquisitions and Dispositions of Businesses	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
Acquisitions and Dispositions of Businesses	Acquisitions and Dispositions of Businesses Completed Acquisitions The Company completed three acquisitions during the nine months ended September 30, 2019 and five acquisitions during the nine months ended September 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): Nine Months Ended September 30, 2019 Consideration Transferred $ 42 Deferred and contingent consideration 8 Aggregate consideration transferred $ 50 Assets acquired Cash and cash equivalents $ 4 Receivables, net 1 Goodwill 33 Intangible assets, net 22 Fixed assets, net 1 Other assets 13 Total assets acquired 74 Liabilities assumed Current liabilities 18 Other non-current liabilities 6 Total liabilities assumed 24 Net assets acquired $ 50 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 July 31, 2019, the Company completed the transaction to acquire Ovatio Courtage SAS, an insurance broker based in France. On July 31, 2019, the Company completed the transaction to acquire Zalba-Caldu Correduria de Seguros, S.A., a Spanish insurance broker. 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 two dispositions during the three months ended September 30, 2019 and six dispositions during the nine months ended September 30, 2019 . The Company completed two dispositions during the three months ended September 30, 2018 and three dispositions during the nine months ended September 30, 2018 . Total pretax gains recognized for the three and nine months ended September 30, 2019 were $1 million and $8 million , respectively. Total losses, net of gains, recognized for the three and nine months ended September 30, 2018 were $3 million and $4 million , respectively. 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	9 Months Ended
	Sep. 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 nine months ended September 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 8,171 Goodwill related to current year acquisitions 33 Goodwill related to disposals (10 ) Goodwill related to prior year acquisitions 2 Foreign currency translation and other (125 ) Balance as of September 30, 2019 $ 8,071 Other intangible assets by asset class are as follows (in millions): September 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 $ 2,229 $ 1,531 $ 698 $ 2,240 $ 1,444 $ 796 Tradenames 1,025 899 126 1,027 740 287 Technology and other 375 325 50 391 325 66 Total $ 3,629 $ 2,755 $ 874 $ 3,658 $ 2,509 $ 1,149 The estimated future amortization for finite lived intangible assets as of September 30, 2019 is as follows (in millions): Remainder of 2019 $ 96 2020 220 2021 126 2022 86 2023 76 2024 59 Thereafter 211 Total $ 874

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt	Debt Notes In September 2019, the Company’s $600 million 5.00% Senior Notes due September 2020 were classified as Short-term debt and current portion of long-term debt in the Condensed Consolidated Statement of Financial Position as the date of maturity is in less than one year. On May 2, 2019, Aon Corporation issued $750 million 3.75% Senior Notes due May 2029. The Company used the net proceeds of the offering to pay down a portion of outstanding commercial paper and for general corporate purposes. 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 September 30, 2019 , Aon plc had two primary committed credit facilities outstanding: its $900 million multi-currency 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”). On October 19, 2019, the Company extended the $400 million multi-currency U.S. credit facility expiring in October 2022 by one year, and it will now expire in October 2023. 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 September 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 September 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. 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 September 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 September 30, 2019 December 31, 2018 Commercial paper outstanding $ 546 $ 250 The weighted average commercial paper outstanding and its related interest rates are as follows (in millions, except percentages): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Weighted average commercial paper outstanding $ 656 $ 820 541 $ 566 Weighted average interest rate of commercial paper outstanding 0.15 % 0.79 % 0.43 % 0.83 %

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rates on net income from continuing operations were 19.6% and 16.6% for the three and nine months ended September 30, 2019 , respectively. The effective tax rates on net income from continuing operations were 20.1% and 1.1% for the three and nine months ended September 30, 2018 , respectively. For the three months ended September 30, 2019 , the tax rate was primarily driven by the geographical distribution of income, including restructuring charges, and certain discrete items. For the three months ended September 30, 2018 , the tax rate was primarily driven by the geographical distribution of income and certain discrete items including return to accrual adjustments and changes in the assertion for unremitted earnings. For the nine months ended September 30, 2019 , the tax rate was primarily driven by the geographical distribution of income, including restructuring charges, as well as certain favorable discrete items, primarily the impact of shared-based payments and changes in the assertion for unremitted earnings. For the nine months ended September 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 previously classified as held for sale. The tax rate was also impacted by certain discrete items including the net tax benefit associated with the sale of certain assets and liabilities previously classified as held for sale, the impact of share-based payments, and changes in the assertion for unremitted earnings.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 (1) 2018 2019 (1) 2018 Shares repurchased 1.8 2.1 8.2 8.8 Average price per share $ 190.83 $ 145.71 $ 183.26 $ 142.15 Costs recorded to retained earnings Total repurchase cost $ 350 $ 300 $ 1,500 $ 1,250 Additional associated costs — 1 7 6 Total costs recorded to retained earnings $ 350 $ 301 $ 1,507 $ 1,256 (1) Included in the 1.8 million and 8.2 million shares repurchased during the three and nine months ended September 30, 2019, respectively, were 25 thousand shares that did not settle until October 2019. These shares were settled at an average price per share of $193.91 and total cost of $4.8 million . At September 30, 2019 , the remaining authorized amount for share repurchase under the Repurchase Program was $2.5 billion . Under the Repurchase Program, the Company has repurchased a total of 126.5 million shares for an aggregate cost of approximately $12.5 billion . Net Income Per Share Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Basic weighted average ordinary shares outstanding 236.9 244.0 239.9 246.2 Dilutive effect of potentially issuable shares 2.2 1.6 2.0 1.5 Diluted weighted average ordinary shares outstanding 239.1 245.6 241.9 247.7 Potentially issuable shares are not included in the computation of diluted net income per share if their inclusion would be antidilutive. There were no shares excluded from the calculation for the three and nine months ended September 30, 2019 or September 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 (12 ) (180 ) 2 (190 ) Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 12 — 79 91 Tax expense (3 ) — (19 ) (22 ) Amounts reclassified from accumulated other comprehensive income, net 9 — 60 69 Net current period other comprehensive income (loss) (3 ) (180 ) 62 (121 ) Balance at September 30, 2019 $ (18 ) $ (1,499 ) $ (2,513 ) $ (4,030 ) (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	9 Months Ended
	Sep. 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 major pension plans, which are located in the Netherlands and Canada. Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): Three Months Ended September 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 26 26 27 24 6 6 Expected return on plan assets, net of administration expenses (46 ) (46 ) (34 ) (36 ) (9 ) (11 ) Amortization of prior-service cost — 1 1 — — — Amortization of net actuarial loss 7 6 13 15 3 3 Net periodic (benefit) cost (13 ) (13 ) 7 3 — (2 ) Loss on pension settlement — 9 — — — — Total net periodic (benefit) cost $ (13 ) $ (4 ) $ 7 $ 3 $ — $ (2 ) Nine Months Ended September 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 81 84 81 74 20 20 Expected return on plan assets, net of administration expenses (143 ) (147 ) (102 ) (108 ) (29 ) (34 ) Amortization of prior-service cost 1 1 2 1 — — Amortization of net actuarial loss 22 21 40 45 9 9 Net periodic (benefit) cost (39 ) (41 ) 21 12 — (5 ) Loss on pension settlement — 32 — — — — Total net periodic (benefit) cost $ (39 ) $ (9 ) $ 21 $ 12 $ — $ (5 ) 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 nine months ended September 30, 2018 , lump sum payments from plan assets of £125 million ( $164 million using September 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 third quarter of 2018, which in aggregate resulted in a reduction to the projected benefit obligation of £108 million ( $143 million using September 30, 2018 exchange rates), as well as a non-cash settlement charge of £7 million ( $9 million using average September 30, 2018 exchange rates) in the third quarter of 2018 and £24 million ( $32 million using average exchange rates) for the nine months ended September 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 major pension plans, respectively, during 2019. The following table summarizes contributions made to the Company’s significant pension plans (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Contributions to U.K. pension plans $ 19 $ 27 $ 65 $ 75 Contributions to U.S. pension plans (1) 7 108 30 133 Contributions to other major pension plans 3 3 13 14 Total contributions $ 29 $ 138 $ 108 $ 222 (1) Includes the Company’s contribution to the qualified U.S. pension plan of $100 million for the three and nine months ended September 30, 2018, which allowed the pension contribution tax deduction to be taken at the 2017 federal tax rate of 35%.

Share-Based Compensation Plans

Share-Based Compensation Plans	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Restricted share units (“RSUs”) $ 42 $ 41 $ 155 $ 145 Performance share awards (“PSAs”) 28 24 90 63 Employee share purchase plans 2 2 7 6 Total share-based compensation expense $ 72 $ 67 $ 252 $ 214 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): Nine Months Ended September 30, 2019 Nine Months Ended September 30, 2018 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 4,208 $ 120 4,849 $ 104 Granted 1,225 $ 174 1,409 $ 140 Vested (1,551 ) $ 112 (1,772 ) $ 97 Forfeited (164 ) $ 128 (158 ) $ 111 Non-vested at end of period 3,718 $ 141 4,328 $ 118 (1) Represents per share weighted average fair value of award at date of grant. Unamortized deferred compensation expense amounted to $384 million as of September 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 issuance of shares may range from 0 - 200% of the target number of PSAs granted, based on the terms of the plan and level of achievement of the related performance target. The grant date fair value of PSAs is based upon the market price of 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 nine months ended September 30, 2019 and the years ended December 31, 2018 and 2017 , respectively (shares in thousands and dollars in millions, except fair value): September 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 458 958 1,057 Unamortized expense, based on current performance levels $ 61 $ 54 $ 10

Derivatives and Hedging

Derivatives and Hedging	9 Months Ended
	Sep. 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) September 30, December 31, September 30, December 31, September 30, December 31, Foreign exchange contracts Accounted for as hedges $ 607 $ 646 $ 10 $ 17 $ 1 $ 2 Not accounted for as hedges (3) 313 269 — 1 1 6 Total $ 920 $ 915 $ 10 $ 18 $ 2 $ 8 (1) Included within Other current assets ( $3 million at September 30, 2019 and $3 million at December 31, 2018 ) or Other non-current assets ( $7 million at September 30, 2019 and $15 million at December 31, 2018 ). (2) Included within Other current liabilities ( $2 million at September 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Loss recognized in Accumulated other comprehensive loss $ (6 ) $ (3 ) $ (14 ) $ (14 ) 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Total revenue (1) $ (4 ) $ — $ (11 ) $ — Compensation and benefits — — — 1 Other general expense — — — (2 ) Interest expense — — (1 ) (1 ) Other income (expense) (1) — (3 ) — (7 ) Total $ (4 ) $ (3 ) $ (12 ) $ (9 ) (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 nine months ended September 30, 2019 , the Company recorded losses of $16 million and $20 million , respectively, in Other income (expense) for foreign exchange derivatives not accounted for as hedges. During the three and nine months ended September 30, 2018 , the Company recorded losses of $4 million and $15 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. The Company had €500 million ( $546 million at September 30, 2019 exchange rates) and € 220 million ( $250 million at December 31, 2018 exchange rates) of outstanding euro-denominated commercial paper at September 30, 2019 and December 31, 2018, respectively, designated as a hedge of the foreign currency exposure of its net investment in its European operations. The unrealized gain recognized in Accumulated other comprehensive loss related to the net investment non derivative hedging instrument was $38 million and $21 million , as of September 30, 2019 and December 31, 2018, respectively. The Company did not reclassify any deferred gains or losses related to net investment hedges from Accumulated other comprehensive loss to earnings during the three and nine months ended September 30, 2019

Fair Value Measurements and Fin

Fair Value Measurements and Financial Instruments	9 Months Ended
	Sep. 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 September 30, 2019 and December 31, 2018 (in millions): Fair Value Measurements Using Balance at September 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) $ 1,851 $ 1,851 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 12 $ — $ 12 $ — 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 0 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 nine months ended September 30, 2019 or 2018 . The Company recognized no realized or unrealized gains or losses in the Condensed Consolidated Statements of Income during either the nine months ended September 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): September 30, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value Current portion of long-term debt $ 599 $ 617 $ — $ — Long-term debt $ 6,120 $ 6,915 $ 5,993 $ 6,159

Claims, Lawsuits and Other Cont

Claims, Lawsuits and Other Contingencies	9 Months Ended
	Sep. 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 expense in the Condensed Consolidated Statements of Income to the extent that losses are deemed probable and are reasonably estimable. These amounts are adjusted from time to time as developments warrant. Matters that are not probable and reasonably estimable are not accrued for in the financial statements. The Company has included in the current matters described below certain matters in which (1) loss is probable, (2) loss is reasonably possible, that is, more than remote but not probable, or (3) there exists the reasonable possibility of loss greater than the accrued amount. In addition, the Company may from time to time disclose matters for which the probability of loss could be remote but the claim amounts associated with such matters are potentially significant. The reasonably possible range of loss for the matters described below for which loss is estimable, in excess of amounts that are deemed probable and estimable and therefore already accrued, is estimated to be between $0 and $0.1 billion , exclusive of any insurance coverage. These estimates are based on available information as of the date of this filing. As available information changes, the matters for which Aon is able to estimate 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 ( $55 million at September 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 ( $86 million at September 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 ( $333 million at September 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 ( $116 million at September 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 September 30, 2019 , the undiscounted maximum potential future payments under the lease guarantee is $74 million , with an estimated fair value of $14 million . No cash payments were made in connection to the lease commitments during the three and nine months ended September 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 September 30, 2019 , the undiscounted maximum potential future payments under the performance guarantees were $160 million , with an estimated fair value of $1 million . No cash payments were made in connection to the performance guarantees during the three and nine months ended September 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 $71 million at September 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 $83 million at September 30, 2019 compared to $103 million at December 31, 2018 .

Segment Information

Segment Information	9 Months Ended
	Sep. 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	9 Months Ended
	Sep. 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 December 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 May 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 September 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 nine months ended September 30, 2019 and 2018 , Condensed Consolidating Statements of Financial Position as of September 30, 2019 and December 31, 2018 , and Condensed Consolidating Statements of Cash Flows for the nine months ended September 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 September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,379 $ — $ 2,379 Expenses Compensation and benefits 12 2 1,354 — 1,368 Information technology — — 120 — 120 Premises — 4 72 — 76 Depreciation of fixed assets — — 44 — 44 Amortization and impairment of intangible assets — — 101 — 101 Other general expense (income) 2 1 307 — 310 Total operating expenses 14 7 1,998 — 2,019 Operating income (loss) (14 ) (7 ) 381 — 360 Interest income — 11 — (10 ) 1 Interest expense (47 ) (35 ) (6 ) 10 (78 ) Intercompany interest income (expense) 4 (116 ) 112 — — Intercompany other income (expense) (70 ) (9 ) 79 — — Other income (expense) 39 (22 ) 7 (22 ) 2 Income (loss) from continuing operations before income taxes (88 ) (178 ) 573 (22 ) 285 Income tax expense (benefit) (2 ) (35 ) 93 — 56 Net income (loss) from continuing operations (86 ) (143 ) 480 (22 ) 229 Net income (loss) from discontinued operations — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries (86 ) (143 ) 479 (22 ) 228 Equity in earnings of subsidiaries 330 107 (36 ) (401 ) — Net income (loss) 244 (36 ) 443 (423 ) 228 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders $ 244 $ (36 ) $ 437 $ (423 ) $ 222 Condensed Consolidating Statement of Income Three Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,349 $ — $ 2,349 Expenses Compensation and benefits 13 3 1,376 — 1,392 Information technology — — 125 — 125 Premises — — 94 — 94 Depreciation of fixed assets — — 40 — 40 Amortization and impairment of intangible assets — — 100 — 100 Other general expense (income) — (1 ) 337 — 336 Total operating expenses 13 2 2,072 — 2,087 Operating income (loss) (13 ) (2 ) 277 — 262 Interest income — 15 — (15 ) — Interest expense (52 ) (26 ) (6 ) 15 (69 ) Intercompany interest income (expense) 4 (128 ) 124 — — Intercompany other income (expense) 245 (245 ) — — — Other income (expense) (5 ) (3 ) 7 2 1 Income (loss) from continuing operations before income taxes 179 (389 ) 402 2 194 Income tax expense (benefit) (8 ) (67 ) 114 — 39 Net income (loss) from continuing operations 187 (322 ) 288 2 155 Net income (loss) from discontinued operations — — (2 ) — (2 ) Net income (loss) before equity in earnings of subsidiaries 187 (322 ) 286 2 153 Equity in earnings of subsidiaries (42 ) (42 ) (364 ) 448 — Net income (loss) 145 (364 ) (78 ) 450 153 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders $ 145 $ (364 ) $ (84 ) $ 450 $ 147 Condensed Consolidating Statement of Income Nine Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 8,128 $ — $ 8,128 Expenses Compensation and benefits 54 14 4,385 — 4,453 Information technology — — 363 — 363 Premises — 17 231 — 248 Depreciation of fixed assets — — 124 — 124 Amortization and impairment of intangible assets — — 295 — 295 Other general expense (income) 5 3 992 — 1,000 Total operating expenses 59 34 6,390 — 6,483 Operating income (loss) (59 ) (34 ) 1,738 — 1,645 Interest income — 29 — (25 ) 4 Interest expense (138 ) (97 ) (17 ) 25 (227 ) Intercompany interest income (expense) 11 (348 ) 337 — — Intercompany other income (expense) 98 (272 ) 174 — — Other income (expense) 33 (47 ) 39 (17 ) 8 Income (loss) from continuing operations before income taxes (55 ) (769 ) 2,271 (17 ) 1,430 Income tax expense (benefit) (7 ) (141 ) 386 — 238 Net income (loss) from continuing operations (48 ) (628 ) 1,885 (17 ) 1,192 Net income (loss) from discontinued operations — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries (48 ) (628 ) 1,884 (17 ) 1,191 Equity in earnings of subsidiaries 1,223 1,132 504 (2,859 ) — Net income (loss) 1,175 504 2,388 (2,876 ) 1,191 Less: Net income attributable to noncontrolling interests — — 33 — 33 Net income (loss) attributable to Aon shareholders $ 1,175 $ 504 $ 2,355 $ (2,876 ) $ 1,158 Condensed Consolidating Statement of Income Nine Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 8,000 $ — $ 8,000 Expenses Compensation and benefits 47 5 4,450 — 4,502 Information technology — — 363 — 363 Premises — — 283 — 283 Depreciation of fixed assets — — 126 — 126 Amortization and impairment of intangible assets — — 492 — 492 Other general expense (income) 3 90 1,096 — 1,189 Total operating expenses 50 95 6,810 — 6,955 Operating income (loss) (50 ) (95 ) 1,190 — 1,045 Interest income — 44 — (39 ) 5 Interest expense (149 ) (75 ) (23 ) 39 (208 ) Intercompany interest income (expense) 11 (385 ) 374 — — Intercompany other income (expense) 99 (240 ) 141 — — Other income (expense) 18 (29 ) 7 (13 ) (17 ) Income (loss) from continuing operations before income taxes (71 ) (780 ) 1,689 (13 ) 825 Income tax expense (benefit) (27 ) (144 ) 180 — 9 Net income (loss) from continuing operations (44 ) (636 ) 1,509 (13 ) 816 Net income (loss) from discontinued operations — — 5 — 5 Net income (loss) before equity in earnings of subsidiaries (44 ) (636 ) 1,514 (13 ) 821 Equity in earnings of subsidiaries 846 870 234 (1,950 ) — Net income (loss) 802 234 1,748 (1,963 ) 821 Less: Net income attributable to noncontrolling interests — — 32 — 32 Net income (loss) attributable to Aon shareholders $ 802 $ 234 $ 1,716 $ (1,963 ) $ 789 Condensed Consolidating Statement of Comprehensive Income Three Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 244 $ (36 ) $ 443 $ (423 ) $ 228 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders 244 (36 ) 437 (423 ) 222 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (2 ) — (2 ) Foreign currency translation adjustments — — (234 ) 22 (212 ) Postretirement benefit obligation — 10 7 — 17 Total other comprehensive income (loss) — 10 (229 ) 22 (197 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (215 ) (220 ) (210 ) 645 — Less: Other comprehensive loss attributable to noncontrolling interests — — (4 ) — (4 ) Total other comprehensive income (loss) attributable to Aon shareholders (215 ) (210 ) (435 ) 667 (193 ) Comprehensive income (loss) attributable to Aon shareholders $ 29 $ (246 ) $ 2 $ 244 $ 29 Condensed Consolidating Statement of Comprehensive Income Three Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 145 $ (364 ) $ (78 ) $ 450 $ 153 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders 145 (364 ) (84 ) 450 147 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (2 ) 3 — 1 Foreign currency translation adjustments — — (48 ) (2 ) (50 ) Postretirement benefit obligation — 12 (74 ) — (62 ) Total other comprehensive income (loss) — 10 (119 ) (2 ) (111 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (106 ) (134 ) (124 ) 364 — Less: Other comprehensive loss attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive income (loss) attributable to Aon shareholders (106 ) (124 ) (240 ) 362 (108 ) Comprehensive income (loss) attributable to Aon shareholders $ 39 $ (488 ) $ (324 ) $ 812 $ 39 Condensed Consolidating Statement of Comprehensive Income Nine Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 1,175 $ 504 $ 2,388 $ (2,876 ) $ 1,191 Less: Net income attributable to noncontrolling interests — — 33 — 33 Net income (loss) attributable to Aon shareholders 1,175 504 2,355 (2,876 ) 1,158 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — 2 (5 ) — (3 ) Foreign currency translation adjustments — — (199 ) 17 (182 ) Postretirement benefit obligation — 42 20 — 62 Total other comprehensive income (loss) — 44 (184 ) 17 (123 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (138 ) (223 ) (179 ) 540 — Less: Other comprehensive loss attributable to noncontrolling interests — — (2 ) — (2 ) Total other comprehensive income (loss) attributable to Aon shareholders (138 ) (179 ) (361 ) 557 (121 ) Comprehensive income (loss) attributable to Aon shareholders $ 1,037 $ 325 $ 1,994 $ (2,319 ) $ 1,037 Condensed Consolidating Statement of Comprehensive Income Nine Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 802 $ 234 $ 1,748 $ (1,963 ) $ 821 Less: Net income attributable to noncontrolling interests — — 32 — 32 Net income (loss) attributable to Aon shareholders 802 234 1,716 (1,963 ) 789 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (3 ) 17 — 14 Foreign currency translation adjustments — — (276 ) 13 (263 ) Postretirement benefit obligation — 34 74 — 108 Total other comprehensive income (loss) — 31 (185 ) 13 (141 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (148 ) (194 ) (163 ) 505 — Less: Other comprehensive loss attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive income (loss) attributable to Aon shareholders (148 ) (163 ) (342 ) 518 (135 ) Comprehensive income (loss) attributable to Aon shareholders $ 654 $ 71 $ 1,374 $ (1,445 ) $ 654 Condensed Consolidating Statement of Financial Position As of September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 1,530 $ 491 $ (1,419 ) $ 602 Short-term investments — 63 114 — 177 Receivables, net — — 2,866 — 2,866 Fiduciary assets — — 11,041 — 11,041 Current intercompany receivables 153 4,090 13,669 (17,912 ) — Other current assets — 6 625 — 631 Total current assets 153 5,689 28,806 (19,331 ) 15,317 Goodwill — — 8,071 — 8,071 Intangible assets, net — — 874 — 874 Fixed assets, net — — 606 — 606 Operating lease right-of-use assets — 109 804 — 913 Deferred tax assets 93 513 150 (145 ) 611 Prepaid pension — 5 1,208 — 1,213 Non-current intercompany receivables 394 261 7,198 (7,853 ) — Other non-current assets 2 35 525 — 562 Investment in subsidiary 9,052 20,085 (725 ) (28,412 ) — Total assets $ 9,694 $ 26,697 $ 47,517 $ (55,741 ) $ 28,167 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 1,171 $ 42 $ 1,705 $ (1,419 ) $ 1,499 Short-term debt and current portion of long-term debt 546 599 3 — 1,148 Fiduciary liabilities — — 11,041 — 11,041 Current intercompany payables 268 15,956 1,688 (17,912 ) — Other current liabilities — 79 1,084 — 1,163 Total current liabilities 1,985 16,676 15,521 (19,331 ) 14,851 Long-term debt 4,213 1,907 — — 6,120 Non-current operating lease liabilities — 146 776 — 922 Deferred tax liabilities 1 — 353 (145 ) 209 Pension, other postretirement, and postemployment liabilities — 1,222 329 — 1,551 Non-current intercompany payables — 7,364 489 (7,853 ) — Other non-current liabilities 3 107 843 — 953 Total liabilities 6,202 27,422 18,311 (27,329 ) 24,606 Equity Total Aon shareholders’ equity 3,492 (725 ) 29,137 (28,412 ) 3,492 Noncontrolling interests — — 69 — 69 Total equity 3,492 (725 ) 29,206 (28,412 ) 3,561 Total liabilities and equity $ 9,694 $ 26,697 $ 47,517 $ (55,741 ) $ 28,167 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 Nine Months Ended September 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 $ 356 $ (118 ) $ 1,578 $ (653 ) $ 1,163 Cash flows from investing activities Proceeds from investments 17 16 33 Payments for investments — (46 ) (49 ) 1 (94 ) Net sales (purchases) of short-term investments - non-fiduciary — (7 ) — — (7 ) Acquisition of businesses, net of cash acquired — — (39 ) — (39 ) Sale of businesses, net of cash sold — — 43 — 43 Capital expenditures — — (167 ) — (167 ) Cash provided by (used for) investing activities — (36 ) (196 ) 1 (231 ) Cash flows from financing activities Share repurchase (1,507 ) — — — (1,507 ) Advances from (to) affiliates 1,277 79 (1,370 ) 14 — Issuance of shares for employee benefit plans (133 ) — — — (133 ) Issuance of debt 2,099 2,816 3 4,918 Repayment of debt (1,785 ) (2,073 ) — — (3,858 ) Cash dividends to shareholders (307 ) — — — (307 ) Noncontrolling interests and other financing activities — — (81 ) — (81 ) Cash provided by (used for) financing activities (356 ) 822 (1,448 ) 14 (968 ) Effect of exchange rate changes on cash and cash equivalents — — (18 ) — (18 ) Net increase (decrease) in cash and cash equivalents — 668 (84 ) (638 ) (54 ) Cash and cash equivalents at beginning of period — 862 575 (781 ) 656 Cash and cash equivalents at end of period $ — $ 1,530 $ 491 $ (1,419 ) $ 602 Condensed Consolidating Statement of Cash Flows Nine Months Ended September 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 $ (143 ) $ 479 $ 2,258 $ (1,619 ) $ 975 Cash flows from investing activities Proceeds from investments — 16 14 — 30 Payments for investments (12 ) (36 ) (29 ) 12 (65 ) Net sales (purchases) of short-term investments - non-fiduciary — 308 48 — 356 Acquisition of businesses, net of cash acquired — — (50 ) — (50 ) Sale of businesses, net of cash sold — — (8 ) — (8 ) Capital expenditures — (179 ) — (179 ) Cash provided by (used for) investing activities (12 ) 288 (204 ) 12 84 Cash flows from financing activities Share repurchase (1,272 ) — — — (1,272 ) Advances from (to) affiliates 1,292 (1,564 ) (2,054 ) 2,326 — Issuance of shares for employee benefit plans (139 ) — — — (139 ) Issuance of debt 1,258 2,701 1 — 3,960 Repayment of debt (700 ) (2,501 ) (297 ) — (3,498 ) Cash dividends to shareholders (285 ) — — — (285 ) Noncontrolling interests and other financing activities — — (21 ) — (21 ) Cash provided by (used for) financing activities 154 (1,364 ) (2,371 ) 2,326 (1,255 ) Effect of exchange rate changes on cash and cash equivalents — — (76 ) — (76 ) Net increase (decrease) in cash and cash equivalents (1 ) (597 ) (393 ) 719 (272 ) Cash and cash equivalents at beginning of period 1 2,524 793 (2,562 ) 756 Cash and cash equivalents at end of period $ — $ 1,927 $ 400 $ (1,843 ) $ 484

Lease Commitments

Lease Commitments	9 Months Ended
	Sep. 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 September 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 913 Finance lease assets Other non-current assets 106 Total lease assets $ 1,019 Liabilities Current lease liabilities Operating Other current liabilities $ 194 Finance Other current liabilities 24 Non-current lease liabilities Operating Non-current operating lease liabilities 922 Finance Other non-current liabilities 82 Total lease liabilities $ 1,222 The components of lease costs are as follows (in millions): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost $ 43 $ 176 Finance lease costs Amortization of leased assets 7 20 Interest on lease liabilities — 1 Variable lease cost 31 49 Short-term lease cost (1) 1 3 Sublease income (8 ) (24 ) Net lease cost $ 74 $ 225 (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 September 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 4.6 Weighted average discount rate Operating leases 3.3 % Finance leases 2.0 % Other cash and non-cash related activities are as follows (in millions): Nine Months Ended September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 182 Financing cash flows from finance leases $ 11 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 95 ROU assets obtained in exchange for new finance lease liabilities $ 48 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 operating ROU asset lease expense was $87 million and the change in Non-current operating lease liabilities was a decrease of $92 million for the nine months ended September 30, 2019 . Maturity analysis of operating and finance leases as of September 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 61 $ 7 $ (9 ) $ 59 2020 246 26 (34 ) 238 2021 225 26 (33 ) 218 2022 199 19 (33 ) 185 2023 144 18 (14 ) 148 Thereafter 513 15 (6 ) 522 Total undiscounted future minimum lease payments 1,388 111 (129 ) 1,370 Less: Imputed interest (143 ) (5 ) — (148 ) Present value of lease liabilities $ 1,245 $ 106 $ (129 ) $ 1,222 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 September 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 913 Finance lease assets Other non-current assets 106 Total lease assets $ 1,019 Liabilities Current lease liabilities Operating Other current liabilities $ 194 Finance Other current liabilities 24 Non-current lease liabilities Operating Non-current operating lease liabilities 922 Finance Other non-current liabilities 82 Total lease liabilities $ 1,222 The components of lease costs are as follows (in millions): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost $ 43 $ 176 Finance lease costs Amortization of leased assets 7 20 Interest on lease liabilities — 1 Variable lease cost 31 49 Short-term lease cost (1) 1 3 Sublease income (8 ) (24 ) Net lease cost $ 74 $ 225 (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 September 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 4.6 Weighted average discount rate Operating leases 3.3 % Finance leases 2.0 % Other cash and non-cash related activities are as follows (in millions): Nine Months Ended September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 182 Financing cash flows from finance leases $ 11 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 95 ROU assets obtained in exchange for new finance lease liabilities $ 48 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 operating ROU asset lease expense was $87 million and the change in Non-current operating lease liabilities was a decrease of $92 million for the nine months ended September 30, 2019 . Maturity analysis of operating and finance leases as of September 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 61 $ 7 $ (9 ) $ 59 2020 246 26 (34 ) 238 2021 225 26 (33 ) 218 2022 199 19 (33 ) 185 2023 144 18 (14 ) 148 Thereafter 513 15 (6 ) 522 Total undiscounted future minimum lease payments 1,388 111 (129 ) 1,370 Less: Imputed interest (143 ) (5 ) — (148 ) Present value of lease liabilities $ 1,245 $ 106 $ (129 ) $ 1,222 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)	9 Months Ended
	Sep. 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 United States 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 Financial Accounting Standards Board (“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 nine months ended September 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 nine months ended September 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 as of September 30, 2019. 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 Statement 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 Cloud Computing Arrangements In August 2018, the FASB issued new accounting guidance on implementation costs incurred in a cloud computing arrangement that is a service contract. The new guidance aligns capitalization requirements for certain implementation costs incurred in cloud computing arrangements with existing requirements for capitalizing implementation costs for internal-use software. These costs will be deferred over the term of the hosting arrangement, including any optional renewal periods the entity is reasonably certain to exercise. An entity may apply the new guidance on either a prospective or retrospective basis. The new guidance is effective for Aon in the first quarter of 2020 with early adoption permitted. The Company does not expect there to be a significant impact on the Financial Statements and will adopt the new accounting guidance in the first quarter of 2020 on a prospective basis for all implementation costs incurred after the date of initial adoption. Changes to the Disclosure Requirements for Defined Benefit Plans In August 2018, the FASB issued new accounting guidance related to the disclosure requirements for employers that sponsor defined benefit pension and other postretirement benefit plans. The guidance requires sponsors of these plans to provide additional disclosures, including weighted average interest rates used in the entity’s cash balance pension plans and a narrative description of reasons for any significant gains or losses impacting the benefit obligation for the period, and eliminates certain previous disclosure requirements. The new guidance is effective for Aon in the first quarter of 2021 with early adoption permitted and will be applied retrospectively. The Company is currently evaluating the impact that the guidance will have on the Financial Statements and the period of adoption. 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 does not expect there to be a significant impact on the Financial Statements and will adopt the new guidance in the first quarter of 2020. 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 does not expect there to be a significant impact on the Financial Statements and will adopt the new accounting standard in the first quarter of 2020.
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)	9 Months Ended
	Sep. 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 Statement 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)	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Commercial Risk Solutions $ 1,057 $ 1,029 $ 3,342 $ 3,379 Reinsurance Solutions 291 279 1,499 1,401 Retirement Solutions 484 501 1,323 1,356 Health Solutions 279 278 1,082 1,038 Data & Analytic Services 271 263 893 834 Elimination (3 ) (1 ) (11 ) (8 ) Total revenue $ 2,379 $ 2,349 $ 8,128 $ 8,000 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 United States $ 1,209 $ 1,215 $ 3,516 $ 3,456 Americas other than United States 256 203 723 683 United Kingdom 358 264 1,210 1,161 Europe, Middle East, & Africa other than United Kingdom 283 399 1,793 1,871 Asia Pacific 273 268 886 829 Total revenue $ 2,379 $ 2,349 $ 8,128 $ 8,000
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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 216 $ 216 $ 329 $ 298 Additions 326 332 1,008 1,043 Amortization (299 ) (305 ) (1,095 ) (1,090 ) Impairment — — — — Foreign currency translation and other (4 ) 5 (3 ) (3 ) Balance at end of period $ 239 $ 248 $ 239 $ 248 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 161 $ 144 $ 156 $ 145 Additions 14 16 40 37 Amortization (11 ) (9 ) (33 ) (30 ) Impairment — — — — Foreign currency translation and other (1 ) (1 ) — (2 ) Balance at end of period $ 163 $ 150 $ 163 $ 150

Other Financial Data (Tables)

Other Financial Data (Tables)	9 Months Ended
	Sep. 30, 2019
Other Financial Data [Abstract]
Schedule of Other Income (Expense)	Other income (expense) consists of the following (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Foreign currency remeasurement $ 17 $ 3 $ 17 $ 16 Disposal of businesses 1 (3 ) 8 (4 ) Pension and other postretirement 3 — 12 (5 ) Equity earnings 1 1 3 3 Financial instruments (20 ) — (32 ) (27 ) Total $ 2 $ 1 $ 8 $ (17 )
Schedule of Allowance for Doubtful Accounts	An analysis of the allowance for doubtful accounts are as follows (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Balance at beginning of period $ 65 $ 62 $ 64 $ 59 Provision charged to Other general expense 7 9 19 21 Accounts written off, net of recoveries (6 ) (8 ) (17 ) (17 ) Foreign currency translation and other 1 3 1 3 Balance at end of period $ 67 $ 66 $ 67 $ 66
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions): As of September 30, December 31, Costs to fulfill contracts with customers (1) $ 239 $ 329 Prepaid expenses 123 97 Taxes receivable 177 113 Other (2) 92 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 September 30, December 31, Costs to obtain contracts with customers (1) $ 163 $ 156 Taxes receivable 100 100 Leases (2) 106 — Investments 52 54 Other 141 138 Total $ 562 $ 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 September 30, December 31, Deferred revenue (1) $ 256 $ 251 Leases (2) 218 — Taxes payable 152 83 Other 537 602 Total $ 1,163 $ 936 (1) During the three and nine months ended September 30, 2019 , $144 million and $385 million , respectively, was recognized in the Condensed Consolidated Statements of Income. During the three and nine months ended September 30, 2018 , $133 million and $348 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 September 30, December 31, Taxes payable (1) $ 578 $ 585 Leases 82 169 Deferred revenue 59 65 Compensation and benefits 48 56 Other 186 222 Total $ 953 $ 1,097 (1) Includes $218 million and $240 million for the non-current portion of the one-time mandatory transition tax on accumulated foreign earnings as of September 30, 2019 and December 31, 2018 , respectively.

Discontinued Operations (Tables

Discontinued Operations (Tables)	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Expenses Total operating expenses $ 1 $ 4 $ 2 $ 7 Loss from discontinued operations before income taxes (1 ) (4 ) (2 ) (7 ) Income tax benefit — (2 ) (1 ) (3 ) Net loss from discontinued operations excluding gain (1 ) (2 ) (1 ) (4 ) Gain on sale of discontinued operations, net of tax — — — 9 Net income (loss) from discontinued operations $ (1 ) $ (2 ) $ (1 ) $ 5

Restructuring (Tables)

Restructuring (Tables)	9 Months Ended
	Sep. 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 September 30, 2019 and are estimated to be incurred through the end of the Restructuring Plan (in millions). Estimated costs by type have been revised based on updated assumptions: Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Inception to Date Estimated Remaining Costs Estimated Total Cost (1) Workforce reduction $ 9 $ 111 $ 525 $ 25 $ 550 Technology rationalization (2) 14 29 109 16 125 Lease consolidation (2) 3 17 53 27 80 Asset impairments 5 7 46 4 50 Other costs associated with restructuring and separation (2) (3) 32 117 530 15 545 Total restructuring and related expenses $ 63 $ 281 $ 1,263 $ 87 $ 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 for the three months ended September 30, 2019 were $9 million , $2 million , and $18 million ; for the nine months ended September 30, 2019 , were $12 million , $15 million , and $21 million ; and since inception of the Restructuring Plan, were $18 million , $48 million , and $109 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 $20 million , $80 million , and $116 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 September 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 201 Expensed 260 Cash payments (322 ) Foreign currency translation (1 ) Balance as of September 30, 2019 $ 138

Acquisitions and Dispositions_2

Acquisitions and Dispositions of Businesses (Tables)	9 Months Ended
	Sep. 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): Nine Months Ended September 30, 2019 Consideration Transferred $ 42 Deferred and contingent consideration 8 Aggregate consideration transferred $ 50 Assets acquired Cash and cash equivalents $ 4 Receivables, net 1 Goodwill 33 Intangible assets, net 22 Fixed assets, net 1 Other assets 13 Total assets acquired 74 Liabilities assumed Current liabilities 18 Other non-current liabilities 6 Total liabilities assumed 24 Net assets acquired $ 50

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 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 nine months ended September 30, 2019 are as follows (in millions): Balance as of December 31, 2018 $ 8,171 Goodwill related to current year acquisitions 33 Goodwill related to disposals (10 ) Goodwill related to prior year acquisitions 2 Foreign currency translation and other (125 ) Balance as of September 30, 2019 $ 8,071
Schedule of Other Intangible Assets by Asset Class	Other intangible assets by asset class are as follows (in millions): September 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 $ 2,229 $ 1,531 $ 698 $ 2,240 $ 1,444 $ 796 Tradenames 1,025 899 126 1,027 740 287 Technology and other 375 325 50 391 325 66 Total $ 3,629 $ 2,755 $ 874 $ 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 September 30, 2019 is as follows (in millions): Remainder of 2019 $ 96 2020 220 2021 126 2022 86 2023 76 2024 59 Thereafter 211 Total $ 874

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Weighted average commercial paper outstanding $ 656 $ 820 541 $ 566 Weighted average interest rate of commercial paper outstanding 0.15 % 0.79 % 0.43 % 0.83 % 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 September 30, 2019 December 31, 2018 Commercial paper outstanding $ 546 $ 250

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Schedule of Share Repurchase Agreements	The following table summarizes the Company’s Share Repurchase activity (in millions, except per share data): Three Months Ended September 30 Nine Months Ended September 30 2019 (1) 2018 2019 (1) 2018 Shares repurchased 1.8 2.1 8.2 8.8 Average price per share $ 190.83 $ 145.71 $ 183.26 $ 142.15 Costs recorded to retained earnings Total repurchase cost $ 350 $ 300 $ 1,500 $ 1,250 Additional associated costs — 1 7 6 Total costs recorded to retained earnings $ 350 $ 301 $ 1,507 $ 1,256
Schedule of Components of Weighted Average Number of Shares	Weighted average ordinary shares outstanding are as follows (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Basic weighted average ordinary shares outstanding 236.9 244.0 239.9 246.2 Dilutive effect of potentially issuable shares 2.2 1.6 2.0 1.5 Diluted weighted average ordinary shares outstanding 239.1 245.6 241.9 247.7
Components of Accumulated Other Comprehensive Loss, Net of Related Tax	Changes in Accumulated other comprehensive loss by component, net of related tax, are as follows (in millions): Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Postretirement Benefit Obligation (2) Total Balance at December 31, 2018 $ (15 ) $ (1,319 ) $ (2,575 ) $ (3,909 ) Other comprehensive income (loss) before reclassifications, net (12 ) (180 ) 2 (190 ) Amounts reclassified from accumulated other comprehensive income Amounts reclassified from accumulated other comprehensive income 12 — 79 91 Tax expense (3 ) — (19 ) (22 ) Amounts reclassified from accumulated other comprehensive income, net 9 — 60 69 Net current period other comprehensive income (loss) (3 ) (180 ) 62 (121 ) Balance at September 30, 2019 $ (18 ) $ (1,499 ) $ (2,513 ) $ (4,030 ) (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)	9 Months Ended
	Sep. 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 major pension plans, which are located in the Netherlands and Canada. Service cost is reported in Compensation and benefits and all other components are reported in Other income (expense) as follows (in millions): Three Months Ended September 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 26 26 27 24 6 6 Expected return on plan assets, net of administration expenses (46 ) (46 ) (34 ) (36 ) (9 ) (11 ) Amortization of prior-service cost — 1 1 — — — Amortization of net actuarial loss 7 6 13 15 3 3 Net periodic (benefit) cost (13 ) (13 ) 7 3 — (2 ) Loss on pension settlement — 9 — — — — Total net periodic (benefit) cost $ (13 ) $ (4 ) $ 7 $ 3 $ — $ (2 ) Nine Months Ended September 30 U.K. U.S. Other 2019 2018 2019 2018 2019 2018 Service cost $ — $ — $ — $ — $ — $ — Interest cost 81 84 81 74 20 20 Expected return on plan assets, net of administration expenses (143 ) (147 ) (102 ) (108 ) (29 ) (34 ) Amortization of prior-service cost 1 1 2 1 — — Amortization of net actuarial loss 22 21 40 45 9 9 Net periodic (benefit) cost (39 ) (41 ) 21 12 — (5 ) Loss on pension settlement — 32 — — — — Total net periodic (benefit) cost $ (39 ) $ (9 ) $ 21 $ 12 $ — $ (5 )
Schedule of employer's contributions	The following table summarizes contributions made to the Company’s significant pension plans (in millions): Three Months Ended September 30 Nine Months Ended September 30 2019 2018 2019 2018 Contributions to U.K. pension plans $ 19 $ 27 $ 65 $ 75 Contributions to U.S. pension plans (1) 7 108 30 133 Contributions to other major pension plans 3 3 13 14 Total contributions $ 29 $ 138 $ 108 $ 222 (1) Includes the Company’s contribution to the qualified U.S. pension plan of $100 million for the three and nine months ended September 30, 2018, which allowed the pension contribution tax deduction to be taken at the 2017 federal tax rate of 35%.

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	9 Months Ended
	Sep. 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Restricted share units (“RSUs”) $ 42 $ 41 $ 155 $ 145 Performance share awards (“PSAs”) 28 24 90 63 Employee share purchase plans 2 2 7 6 Total share-based compensation expense $ 72 $ 67 $ 252 $ 214
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): Nine Months Ended September 30, 2019 Nine Months Ended September 30, 2018 Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of period 4,208 $ 120 4,849 $ 104 Granted 1,225 $ 174 1,409 $ 140 Vested (1,551 ) $ 112 (1,772 ) $ 97 Forfeited (164 ) $ 128 (158 ) $ 111 Non-vested at end of period 3,718 $ 141 4,328 $ 118 (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 nine months ended September 30, 2019 and the years ended December 31, 2018 and 2017 , respectively (shares in thousands and dollars in millions, except fair value): September 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 458 958 1,057 Unamortized expense, based on current performance levels $ 61 $ 54 $ 10

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	9 Months Ended
	Sep. 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) September 30, December 31, September 30, December 31, September 30, December 31, Foreign exchange contracts Accounted for as hedges $ 607 $ 646 $ 10 $ 17 $ 1 $ 2 Not accounted for as hedges (3) 313 269 — 1 1 6 Total $ 920 $ 915 $ 10 $ 18 $ 2 $ 8 (1) Included within Other current assets ( $3 million at September 30, 2019 and $3 million at December 31, 2018 ) or Other non-current assets ( $7 million at September 30, 2019 and $15 million at December 31, 2018 ). (2) Included within Other current liabilities ( $2 million at September 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Loss recognized in Accumulated other comprehensive loss $ (6 ) $ (3 ) $ (14 ) $ (14 ) 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 September 30 Nine Months Ended September 30 2019 2018 2019 2018 Total revenue (1) $ (4 ) $ — $ (11 ) $ — Compensation and benefits — — — 1 Other general expense — — — (2 ) Interest expense — — (1 ) (1 ) Other income (expense) (1) — (3 ) — (7 ) Total $ (4 ) $ (3 ) $ (12 ) $ (9 ) (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)	9 Months Ended
	Sep. 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 September 30, 2019 and December 31, 2018 (in millions): Fair Value Measurements Using Balance at September 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) $ 1,851 $ 1,851 $ — $ — Other investments Government bonds $ 1 $ — $ 1 $ — Equity investments $ 1 $ — $ 1 $ — Derivatives (2) Gross foreign exchange contracts $ 12 $ — $ 12 $ — 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 0 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): September 30, 2019 December 31, 2018 Carrying Value Fair Value Carrying Value Fair Value Current portion of long-term debt $ 599 $ 617 $ — $ — Long-term debt $ 6,120 $ 6,915 $ 5,993 $ 6,159

Guarantee of Registered Secur_2

Guarantee of Registered Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Guarantee of Registered Securities [Abstract]
Condensed Consolidating Statements of Income	Condensed Consolidating Statement of Income Three Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,379 $ — $ 2,379 Expenses Compensation and benefits 12 2 1,354 — 1,368 Information technology — — 120 — 120 Premises — 4 72 — 76 Depreciation of fixed assets — — 44 — 44 Amortization and impairment of intangible assets — — 101 — 101 Other general expense (income) 2 1 307 — 310 Total operating expenses 14 7 1,998 — 2,019 Operating income (loss) (14 ) (7 ) 381 — 360 Interest income — 11 — (10 ) 1 Interest expense (47 ) (35 ) (6 ) 10 (78 ) Intercompany interest income (expense) 4 (116 ) 112 — — Intercompany other income (expense) (70 ) (9 ) 79 — — Other income (expense) 39 (22 ) 7 (22 ) 2 Income (loss) from continuing operations before income taxes (88 ) (178 ) 573 (22 ) 285 Income tax expense (benefit) (2 ) (35 ) 93 — 56 Net income (loss) from continuing operations (86 ) (143 ) 480 (22 ) 229 Net income (loss) from discontinued operations — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries (86 ) (143 ) 479 (22 ) 228 Equity in earnings of subsidiaries 330 107 (36 ) (401 ) — Net income (loss) 244 (36 ) 443 (423 ) 228 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders $ 244 $ (36 ) $ 437 $ (423 ) $ 222 Condensed Consolidating Statement of Income Three Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 2,349 $ — $ 2,349 Expenses Compensation and benefits 13 3 1,376 — 1,392 Information technology — — 125 — 125 Premises — — 94 — 94 Depreciation of fixed assets — — 40 — 40 Amortization and impairment of intangible assets — — 100 — 100 Other general expense (income) — (1 ) 337 — 336 Total operating expenses 13 2 2,072 — 2,087 Operating income (loss) (13 ) (2 ) 277 — 262 Interest income — 15 — (15 ) — Interest expense (52 ) (26 ) (6 ) 15 (69 ) Intercompany interest income (expense) 4 (128 ) 124 — — Intercompany other income (expense) 245 (245 ) — — — Other income (expense) (5 ) (3 ) 7 2 1 Income (loss) from continuing operations before income taxes 179 (389 ) 402 2 194 Income tax expense (benefit) (8 ) (67 ) 114 — 39 Net income (loss) from continuing operations 187 (322 ) 288 2 155 Net income (loss) from discontinued operations — — (2 ) — (2 ) Net income (loss) before equity in earnings of subsidiaries 187 (322 ) 286 2 153 Equity in earnings of subsidiaries (42 ) (42 ) (364 ) 448 — Net income (loss) 145 (364 ) (78 ) 450 153 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders $ 145 $ (364 ) $ (84 ) $ 450 $ 147 Condensed Consolidating Statement of Income Nine Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 8,128 $ — $ 8,128 Expenses Compensation and benefits 54 14 4,385 — 4,453 Information technology — — 363 — 363 Premises — 17 231 — 248 Depreciation of fixed assets — — 124 — 124 Amortization and impairment of intangible assets — — 295 — 295 Other general expense (income) 5 3 992 — 1,000 Total operating expenses 59 34 6,390 — 6,483 Operating income (loss) (59 ) (34 ) 1,738 — 1,645 Interest income — 29 — (25 ) 4 Interest expense (138 ) (97 ) (17 ) 25 (227 ) Intercompany interest income (expense) 11 (348 ) 337 — — Intercompany other income (expense) 98 (272 ) 174 — — Other income (expense) 33 (47 ) 39 (17 ) 8 Income (loss) from continuing operations before income taxes (55 ) (769 ) 2,271 (17 ) 1,430 Income tax expense (benefit) (7 ) (141 ) 386 — 238 Net income (loss) from continuing operations (48 ) (628 ) 1,885 (17 ) 1,192 Net income (loss) from discontinued operations — — (1 ) — (1 ) Net income (loss) before equity in earnings of subsidiaries (48 ) (628 ) 1,884 (17 ) 1,191 Equity in earnings of subsidiaries 1,223 1,132 504 (2,859 ) — Net income (loss) 1,175 504 2,388 (2,876 ) 1,191 Less: Net income attributable to noncontrolling interests — — 33 — 33 Net income (loss) attributable to Aon shareholders $ 1,175 $ 504 $ 2,355 $ (2,876 ) $ 1,158 Condensed Consolidating Statement of Income Nine Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Total revenue $ — $ — $ 8,000 $ — $ 8,000 Expenses Compensation and benefits 47 5 4,450 — 4,502 Information technology — — 363 — 363 Premises — — 283 — 283 Depreciation of fixed assets — — 126 — 126 Amortization and impairment of intangible assets — — 492 — 492 Other general expense (income) 3 90 1,096 — 1,189 Total operating expenses 50 95 6,810 — 6,955 Operating income (loss) (50 ) (95 ) 1,190 — 1,045 Interest income — 44 — (39 ) 5 Interest expense (149 ) (75 ) (23 ) 39 (208 ) Intercompany interest income (expense) 11 (385 ) 374 — — Intercompany other income (expense) 99 (240 ) 141 — — Other income (expense) 18 (29 ) 7 (13 ) (17 ) Income (loss) from continuing operations before income taxes (71 ) (780 ) 1,689 (13 ) 825 Income tax expense (benefit) (27 ) (144 ) 180 — 9 Net income (loss) from continuing operations (44 ) (636 ) 1,509 (13 ) 816 Net income (loss) from discontinued operations — — 5 — 5 Net income (loss) before equity in earnings of subsidiaries (44 ) (636 ) 1,514 (13 ) 821 Equity in earnings of subsidiaries 846 870 234 (1,950 ) — Net income (loss) 802 234 1,748 (1,963 ) 821 Less: Net income attributable to noncontrolling interests — — 32 — 32 Net income (loss) attributable to Aon shareholders $ 802 $ 234 $ 1,716 $ (1,963 ) $ 789
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statement of Comprehensive Income Three Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 244 $ (36 ) $ 443 $ (423 ) $ 228 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders 244 (36 ) 437 (423 ) 222 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (2 ) — (2 ) Foreign currency translation adjustments — — (234 ) 22 (212 ) Postretirement benefit obligation — 10 7 — 17 Total other comprehensive income (loss) — 10 (229 ) 22 (197 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (215 ) (220 ) (210 ) 645 — Less: Other comprehensive loss attributable to noncontrolling interests — — (4 ) — (4 ) Total other comprehensive income (loss) attributable to Aon shareholders (215 ) (210 ) (435 ) 667 (193 ) Comprehensive income (loss) attributable to Aon shareholders $ 29 $ (246 ) $ 2 $ 244 $ 29 Condensed Consolidating Statement of Comprehensive Income Three Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 145 $ (364 ) $ (78 ) $ 450 $ 153 Less: Net income attributable to noncontrolling interests — — 6 — 6 Net income (loss) attributable to Aon shareholders 145 (364 ) (84 ) 450 147 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (2 ) 3 — 1 Foreign currency translation adjustments — — (48 ) (2 ) (50 ) Postretirement benefit obligation — 12 (74 ) — (62 ) Total other comprehensive income (loss) — 10 (119 ) (2 ) (111 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (106 ) (134 ) (124 ) 364 — Less: Other comprehensive loss attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive income (loss) attributable to Aon shareholders (106 ) (124 ) (240 ) 362 (108 ) Comprehensive income (loss) attributable to Aon shareholders $ 39 $ (488 ) $ (324 ) $ 812 $ 39 Condensed Consolidating Statement of Comprehensive Income Nine Months Ended September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 1,175 $ 504 $ 2,388 $ (2,876 ) $ 1,191 Less: Net income attributable to noncontrolling interests — — 33 — 33 Net income (loss) attributable to Aon shareholders 1,175 504 2,355 (2,876 ) 1,158 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — 2 (5 ) — (3 ) Foreign currency translation adjustments — — (199 ) 17 (182 ) Postretirement benefit obligation — 42 20 — 62 Total other comprehensive income (loss) — 44 (184 ) 17 (123 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (138 ) (223 ) (179 ) 540 — Less: Other comprehensive loss attributable to noncontrolling interests — — (2 ) — (2 ) Total other comprehensive income (loss) attributable to Aon shareholders (138 ) (179 ) (361 ) 557 (121 ) Comprehensive income (loss) attributable to Aon shareholders $ 1,037 $ 325 $ 1,994 $ (2,319 ) $ 1,037 Condensed Consolidating Statement of Comprehensive Income Nine Months Ended September 30, 2018 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income (loss) $ 802 $ 234 $ 1,748 $ (1,963 ) $ 821 Less: Net income attributable to noncontrolling interests — — 32 — 32 Net income (loss) attributable to Aon shareholders 802 234 1,716 (1,963 ) 789 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (3 ) 17 — 14 Foreign currency translation adjustments — — (276 ) 13 (263 ) Postretirement benefit obligation — 34 74 — 108 Total other comprehensive income (loss) — 31 (185 ) 13 (141 ) Equity in other comprehensive income (loss) of subsidiaries, net of tax (148 ) (194 ) (163 ) 505 — Less: Other comprehensive loss attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive income (loss) attributable to Aon shareholders (148 ) (163 ) (342 ) 518 (135 ) Comprehensive income (loss) attributable to Aon shareholders $ 654 $ 71 $ 1,374 $ (1,445 ) $ 654
Condensed Consolidating Statements of Financial Position	Condensed Consolidating Statement of Financial Position As of September 30, 2019 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Assets Current assets Cash and cash equivalents $ — $ 1,530 $ 491 $ (1,419 ) $ 602 Short-term investments — 63 114 — 177 Receivables, net — — 2,866 — 2,866 Fiduciary assets — — 11,041 — 11,041 Current intercompany receivables 153 4,090 13,669 (17,912 ) — Other current assets — 6 625 — 631 Total current assets 153 5,689 28,806 (19,331 ) 15,317 Goodwill — — 8,071 — 8,071 Intangible assets, net — — 874 — 874 Fixed assets, net — — 606 — 606 Operating lease right-of-use assets — 109 804 — 913 Deferred tax assets 93 513 150 (145 ) 611 Prepaid pension — 5 1,208 — 1,213 Non-current intercompany receivables 394 261 7,198 (7,853 ) — Other non-current assets 2 35 525 — 562 Investment in subsidiary 9,052 20,085 (725 ) (28,412 ) — Total assets $ 9,694 $ 26,697 $ 47,517 $ (55,741 ) $ 28,167 Liabilities and equity Liabilities Current liabilities Accounts payable and accrued liabilities $ 1,171 $ 42 $ 1,705 $ (1,419 ) $ 1,499 Short-term debt and current portion of long-term debt 546 599 3 — 1,148 Fiduciary liabilities — — 11,041 — 11,041 Current intercompany payables 268 15,956 1,688 (17,912 ) — Other current liabilities — 79 1,084 — 1,163 Total current liabilities 1,985 16,676 15,521 (19,331 ) 14,851 Long-term debt 4,213 1,907 — — 6,120 Non-current operating lease liabilities — 146 776 — 922 Deferred tax liabilities 1 — 353 (145 ) 209 Pension, other postretirement, and postemployment liabilities — 1,222 329 — 1,551 Non-current intercompany payables — 7,364 489 (7,853 ) — Other non-current liabilities 3 107 843 — 953 Total liabilities 6,202 27,422 18,311 (27,329 ) 24,606 Equity Total Aon shareholders’ equity 3,492 (725 ) 29,137 (28,412 ) 3,492 Noncontrolling interests — — 69 — 69 Total equity 3,492 (725 ) 29,206 (28,412 ) 3,561 Total liabilities and equity $ 9,694 $ 26,697 $ 47,517 $ (55,741 ) $ 28,167 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 Nine Months Ended September 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 $ 356 $ (118 ) $ 1,578 $ (653 ) $ 1,163 Cash flows from investing activities Proceeds from investments 17 16 33 Payments for investments — (46 ) (49 ) 1 (94 ) Net sales (purchases) of short-term investments - non-fiduciary — (7 ) — — (7 ) Acquisition of businesses, net of cash acquired — — (39 ) — (39 ) Sale of businesses, net of cash sold — — 43 — 43 Capital expenditures — — (167 ) — (167 ) Cash provided by (used for) investing activities — (36 ) (196 ) 1 (231 ) Cash flows from financing activities Share repurchase (1,507 ) — — — (1,507 ) Advances from (to) affiliates 1,277 79 (1,370 ) 14 — Issuance of shares for employee benefit plans (133 ) — — — (133 ) Issuance of debt 2,099 2,816 3 4,918 Repayment of debt (1,785 ) (2,073 ) — — (3,858 ) Cash dividends to shareholders (307 ) — — — (307 ) Noncontrolling interests and other financing activities — — (81 ) — (81 ) Cash provided by (used for) financing activities (356 ) 822 (1,448 ) 14 (968 ) Effect of exchange rate changes on cash and cash equivalents — — (18 ) — (18 ) Net increase (decrease) in cash and cash equivalents — 668 (84 ) (638 ) (54 ) Cash and cash equivalents at beginning of period — 862 575 (781 ) 656 Cash and cash equivalents at end of period $ — $ 1,530 $ 491 $ (1,419 ) $ 602 Condensed Consolidating Statement of Cash Flows Nine Months Ended September 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 $ (143 ) $ 479 $ 2,258 $ (1,619 ) $ 975 Cash flows from investing activities Proceeds from investments — 16 14 — 30 Payments for investments (12 ) (36 ) (29 ) 12 (65 ) Net sales (purchases) of short-term investments - non-fiduciary — 308 48 — 356 Acquisition of businesses, net of cash acquired — — (50 ) — (50 ) Sale of businesses, net of cash sold — — (8 ) — (8 ) Capital expenditures — (179 ) — (179 ) Cash provided by (used for) investing activities (12 ) 288 (204 ) 12 84 Cash flows from financing activities Share repurchase (1,272 ) — — — (1,272 ) Advances from (to) affiliates 1,292 (1,564 ) (2,054 ) 2,326 — Issuance of shares for employee benefit plans (139 ) — — — (139 ) Issuance of debt 1,258 2,701 1 — 3,960 Repayment of debt (700 ) (2,501 ) (297 ) — (3,498 ) Cash dividends to shareholders (285 ) — — — (285 ) Noncontrolling interests and other financing activities — — (21 ) — (21 ) Cash provided by (used for) financing activities 154 (1,364 ) (2,371 ) 2,326 (1,255 ) Effect of exchange rate changes on cash and cash equivalents — — (76 ) — (76 ) Net increase (decrease) in cash and cash equivalents (1 ) (597 ) (393 ) 719 (272 ) Cash and cash equivalents at beginning of period 1 2,524 793 (2,562 ) 756 Cash and cash equivalents at end of period $ — $ 1,927 $ 400 $ (1,843 ) $ 484

Lease Commitments - (Tables)

Lease Commitments - (Tables)	9 Months Ended
	Sep. 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 September 30, 2019 Assets Operating lease assets Operating lease right-of-use assets $ 913 Finance lease assets Other non-current assets 106 Total lease assets $ 1,019 Liabilities Current lease liabilities Operating Other current liabilities $ 194 Finance Other current liabilities 24 Non-current lease liabilities Operating Non-current operating lease liabilities 922 Finance Other non-current liabilities 82 Total lease liabilities $ 1,222
Lease, Cost	Weighted average remaining lease term and discount rate related to operating and finance leases are as follows: As of September 30, 2019 Weighted average remaining lease term (years) Operating leases 8.0 Finance leases 4.6 Weighted average discount rate Operating leases 3.3 % Finance leases 2.0 % Other cash and non-cash related activities are as follows (in millions): Nine Months Ended September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 182 Financing cash flows from finance leases $ 11 Non-cash related activities ROU assets obtained in exchange for new operating lease liabilities $ 95 ROU assets obtained in exchange for new finance lease liabilities $ 48 The components of lease costs are as follows (in millions): Three Months Ended September 30, 2019 Nine Months Ended September 30, 2019 Operating lease cost $ 43 $ 176 Finance lease costs Amortization of leased assets 7 20 Interest on lease liabilities — 1 Variable lease cost 31 49 Short-term lease cost (1) 1 3 Sublease income (8 ) (24 ) Net lease cost $ 74 $ 225 (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 September 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 61 $ 7 $ (9 ) $ 59 2020 246 26 (34 ) 238 2021 225 26 (33 ) 218 2022 199 19 (33 ) 185 2023 144 18 (14 ) 148 Thereafter 513 15 (6 ) 522 Total undiscounted future minimum lease payments 1,388 111 (129 ) 1,370 Less: Imputed interest (143 ) (5 ) — (148 ) Present value of lease liabilities $ 1,245 $ 106 $ (129 ) $ 1,222 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 September 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 61 $ 7 $ (9 ) $ 59 2020 246 26 (34 ) 238 2021 225 26 (33 ) 218 2022 199 19 (33 ) 185 2023 144 18 (14 ) 148 Thereafter 513 15 (6 ) 522 Total undiscounted future minimum lease payments 1,388 111 (129 ) 1,370 Less: Imputed interest (143 ) (5 ) — (148 ) Present value of lease liabilities $ 1,245 $ 106 $ (129 ) $ 1,222 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 September 30, 2019 are as follows (in millions): Operating Finance Less: Leases Leases Subleases Total Remainder of 2019 $ 61 $ 7 $ (9 ) $ 59 2020 246 26 (34 ) 238 2021 225 26 (33 ) 218 2022 199 19 (33 ) 185 2023 144 18 (14 ) 148 Thereafter 513 15 (6 ) 522 Total undiscounted future minimum lease payments 1,388 111 (129 ) 1,370 Less: Imputed interest (143 ) (5 ) — (148 ) Present value of lease liabilities $ 1,245 $ 106 $ (129 ) $ 1,222 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	Sep. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 913
Present value of lease liabilities	$ 1,245
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	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Operating lease right-of-use assets	$ 913
Other non-current assets	562		$ 448
Liabilities
Other current liabilities	1,163		936
Non-current operating lease liabilities	922
Other non-current liabilities	$ 953		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	448
Other non-current assets | Accounting Standards Update 2016-02
Assets
Other non-current assets		78
Other current liabilities
Liabilities
Other current liabilities		1,155	936
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	$ 1,097
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,379	$ 2,349	$ 8,128	$ 8,000
United States
Disaggregation of Revenue [Line Items]
Total revenue	1,209	1,215	3,516	3,456
Americas other than United States
Disaggregation of Revenue [Line Items]
Total revenue	256	203	723	683
United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	358	264	1,210	1,161
Europe, Middle East, & Africa other than United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	283	399	1,793	1,871
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	273	268	886	829
Operating Segments | Commercial Risk Solutions
Disaggregation of Revenue [Line Items]
Total revenue	1,057	1,029	3,342	3,379
Operating Segments | Reinsurance Solutions
Disaggregation of Revenue [Line Items]
Total revenue	291	279	1,499	1,401
Operating Segments | Retirement Solutions
Disaggregation of Revenue [Line Items]
Total revenue	484	501	1,323	1,356
Operating Segments | Health Solutions
Disaggregation of Revenue [Line Items]
Total revenue	279	278	1,082	1,038
Operating Segments | Data & Analytic Services
Disaggregation of Revenue [Line Items]
Total revenue	271	263	893	834
Elimination
Disaggregation of Revenue [Line Items]
Total revenue	$ (3)	$ (1)	$ (11)	$ (8)

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 216	$ 216	$ 329	$ 298
Additions	326	332	1,008	1,043
Amortization	(299)	(305)	(1,095)	(1,090)
Impairment	0	0	0	0
Foreign currency translation and other	(4)	5	(3)	(3)
Balance at end of period	239	248	239	248
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	161	144	156	145
Additions	14	16	40	37
Amortization	(11)	(9)	(33)	(30)
Impairment	0	0	0	0
Foreign currency translation and other	(1)	(1)	0	(2)
Balance at end of period	$ 163	$ 150	$ 163	$ 150

Cash and Cash Equivalents and_2

Cash and Cash Equivalents and Short-term Investments (Details) £ in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019GBP (£)	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents and short-term investments			$ 779	$ 828
Cash and cash equivalents and short term investments, period increase (decrease)	$ (49)
Restricted cash and investments			96	91
Operating funds in U.K.		£ 42.7	$ 52.6	$ 53.9

Other Financial Data - Schedule

Other Financial Data - Schedule of Other Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other (Expense) Income
Foreign currency remeasurement	$ 17	$ 3	$ 17	$ 16
Disposal of businesses	1	(3)	8	(4)
Pension and other postretirement	3	0	12	(5)
Equity earnings	1	1	3	3
Financial instruments	(20)	0	(32)	(27)
Total	$ 2	$ 1	$ 8	$ (17)

Other Financial Data - Schedu_2

Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 65	$ 62	$ 64	$ 59
Provision charged to Other general expenses	7	9	19	21
Accounts written off, net of recoveries	(6)	(8)	(17)	(17)
Foreign currency translation and other	1	3	1	3
Balance at end of period	$ 67	$ 66	$ 67	$ 66

Other Financial Data - Schedu_3

Other Financial Data - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Cost to fulfill contracts with customers	$ 239	$ 329
Prepaid expenses	123	97
Taxes receivable	177	113
Other	92	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	Sep. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Cost to obtain contracts with customers	$ 163	$ 156
Taxes receivable	100	100
Leases	106
Investments	52	54
Other	141	138
Total	$ 562	$ 448

Other Financial Data - Schedu_5

Other Financial Data - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Other Financial Data [Abstract]
Deferred revenue	$ 256		$ 256		$ 251
Leases	218		218
Taxes payable	152		152		83
Other	537		537		602
Total	1,163		1,163		$ 936
Revenue recognized from deferred revenue	$ 144	$ 133	$ 385	$ 348

Other Financial Data - Schedu_6

Other Financial Data - Schedule of Other Non-current Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Other Financial Data [Abstract]
Taxes payable	$ 578	$ 585
Leases	82	169
Deferred revenue	59	65
Compensation and benefits	48	56
Other	186	222
Total	953	1,097
Noncurrent portion of transition tax	$ 218	$ 240

Discontinued Operations (Detail

Discontinued Operations (Details) - Tempo Business	May 01, 2017USD ($)agreement	Sep. 30, 2019USD ($)
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Expenses
Net income (loss) from discontinued operations	$ (1)	$ (2)	$ (1)	$ 5
Tempo Business | Discontinued Operations, Disposed of by Sale
Expenses
Total operating expenses	1	4	2	7
Loss from discontinued operations before income taxes	(1)	(4)	(2)	(7)
Income tax benefit	0	(2)	(1)	(3)
Net loss from discontinued operations excluding gain	(1)	(2)	(1)	(4)
Gain on sale of discontinued operations, net of tax	0	0	0	9
Net income (loss) from discontinued operations	$ (1)	$ (2)	$ (1)	$ 5

Restructuring - Narrative (Det

Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	9 Months Ended	33 Months Ended
	Jun. 30, 2019USD ($)	Sep. 30, 2019USD ($)job_elimination	Sep. 30, 2019USD ($)job_elimination
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 125	$ 260	$ 1,263
Expected total cost		1,350	$ 1,350
Number of positions eliminated to date | job_elimination			5,353
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost		550	$ 550
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost		125	125
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost		80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost		50	50
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost		$ 545	$ 545
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,400
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		9 Months Ended	33 Months Ended
	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)job_elimination
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 63		$ 281
Expensed		$ 125	260	$ 1,263
Restructuring and Related Cost, Number of Positions Eliminated | job_elimination				5,353
Estimated Remaining Costs	87		87	$ 87
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	9		111	525
Estimated Remaining Costs	25		25	25
Expected total cost	550		550	550
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Costs incurred	14		29	109
Estimated Remaining Costs	16		16	16
Expected total cost	125		125	125
Contract termination costs incurred	9		12	18
Expected contract termination cost remaining	20		20	20
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Costs incurred	3		17	53
Estimated Remaining Costs	27		27	27
Expected total cost	80		80	80
Contract termination costs incurred	2		15	48
Expected contract termination cost remaining	80		80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Costs incurred	5		7	46
Estimated Remaining Costs	4		4	4
Expected total cost	50		50	50
Other costs associated with restructuring and separation
Restructuring Cost and Reserve [Line Items]
Costs incurred	32		117	530
Estimated Remaining Costs	15		15	15
Expected total cost	545		545	545
Contract termination costs incurred	18		21	109
Expected contract termination cost remaining	$ 116		$ 116	$ 116

Restructuring - Schedule of _2

Restructuring - Schedule of Restructuring Reserve (Details) - 2017 Plan - USD ($) $ in Millions	3 Months Ended	9 Months Ended	33 Months Ended
	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2019
Restructuring Plan
Balance as of December 31, 2018		$ 201
Expensed	$ 125	260	$ 1,263
Cash payments		(322)
Foreign currency translation		(1)
Balance as of September 30, 2019		$ 138	$ 138

Acquisitions and Dispositions_3

Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)acquisition	Sep. 30, 2018acquisition	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Number of business acquired under business combination | acquisition	3	5
Assets acquired
Goodwill	$ 8,071		$ 8,171
2019 Acquisitions
Business Combination, Consideration Transferred [Abstract]
Consideration Transferred	42
Deferred and contingent consideration	8
Aggregate consideration transferred	50
Assets acquired
Cash and cash equivalents	4
Receivables, net	1
Goodwill	33
Intangible assets, net	22
Fixed assets, net	1
Other assets	13
Total assets acquired	74
Liabilities assumed
Current liabilities	18
Other non-current liabilities	6
Total liabilities assumed	24
Net assets acquired	$ 50

Acquisitions and Dispositions_4

Acquisitions and Dispositions of Businesses - Dispositions (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)disposal	Sep. 30, 2018USD ($)disposal	Sep. 30, 2019USD ($)disposal	Sep. 30, 2018USD ($)disposal
Dispositions
Pretax gains (losses) recognized on disposal of businesses | $	$ 1	$ (3)	$ 8	$ (4)
Disposal Group, Not Discontinued Operations
Dispositions
Number of dispositions | disposal	2	2	6	3

- Goodwill and Other Intangible

- Goodwill and Other Intangible Assets Rollforward (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Changes in the net carrying amount of goodwill by operating segment
Beginning balance	$ 8,171
Goodwill related to current year acquisitions	33
Goodwill related to disposals	(10)
Goodwill related to prior year acquisitions	2
Foreign currency translation and other	(125)
Ending balance	$ 8,071

- Goodwill and Other Intangib_2

- Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Intangible assets with finite lives
Gross Carrying Amount	$ 3,629	$ 3,658
Accumulated Amortization and Impairment	2,755	2,509
Net Carrying Amount	874	1,149
Estimated amortization for intangible assets
Remainder of 2019	96
2020	220
2021	126
2022	86
2023	76
2024	59
Thereafter	211
Total	874
Customer related and contract based
Intangible assets with finite lives
Gross Carrying Amount	2,229	2,240
Accumulated Amortization and Impairment	1,531	1,444
Net Carrying Amount	698	796
Tradenames
Intangible assets with finite lives
Gross Carrying Amount	1,025	1,027
Accumulated Amortization and Impairment	899	740
Net Carrying Amount	126	287
Technology and other
Intangible assets with finite lives
Gross Carrying Amount	375	391
Accumulated Amortization and Impairment	325	325
Net Carrying Amount	$ 50	$ 66

Debt - Narrative (Details)

Debt - Narrative (Details)	Sep. 30, 2019USD ($)credit_facility	Sep. 30, 2019EUR (€)credit_facility	May 02, 2019USD ($)	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	$ 1,148,000,000			$ 251,000,000
Number of credit facilities | credit_facility	2	2
5.00% Senior Notes Due September 2020
Debt Instrument [Line Items]
Debt face value	$ 600,000,000
Debt interest rate percentage (as a percent)	5.00%	5.00%
3.75% Senior Notes Due May 2, 2029 | 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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Commercial paper outstanding	$ 546		$ 546		$ 250
Weighted average commercial paper outstanding	$ 656	$ 820	$ 541	$ 566
Weighted average interest rate of commercial paper outstanding	0.15%	0.79%	0.43%	0.83%

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate	19.60%	20.10%	16.60%	1.10%

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($)	3 Months Ended						9 Months Ended		90 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Feb. 28, 2017	Nov. 30, 2014	Apr. 30, 2012
Common Stock Programs
Total cost of shares purchased	$ 350,000,000	$ 1,056,000,000	$ 101,000,000	$ 301,000,000	$ 402,000,000	$ 553,000,000
Weighted average shares outstanding
Basic weighted average ordinary shares outstanding (in shares)	236,900,000			244,000,000			239,900,000	246,200,000
Dilutive effect of potentially issuable shares (in shares)	2,200,000			1,600,000			2,000,000	1,500,000
Diluted weighted average ordinary shares outstanding (in shares)	239,100,000			245,600,000			241,900,000	247,700,000
Number of shares excluded from the calculation of diluted earnings per share (in shares)	0			0			0	0
2012 - Share Repurchase Program
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	$ 5,000,000,000
Share repurchase, remaining authorization limit (in shares)	$ 2,500,000,000						$ 2,500,000,000		$ 2,500,000,000
Shares purchased (in shares)	1,800,000			2,100,000			8,200,000	8,800,000	126,500,000
Total cost of shares purchased	$ 350,000,000			$ 300,000,000			$ 1,500,000,000	$ 1,250,000,000	$ 12,500,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Stock Repurchases (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						4 Months Ended	9 Months Ended		90 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Oct. 25, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019
Class of Stock [Line Items]
Total repurchase cost	$ 350	$ 1,056	$ 101	$ 301	$ 402	$ 553
2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)	1,800			2,100				8,200	8,800	126,500
Average price per share of stock repurchased (in dollars per share)	$ 190.83			$ 145.71				$ 183.26	$ 142.15
Total repurchase cost	$ 350			$ 300				$ 1,500	$ 1,250	$ 12,500
Additional associated costs	0			1				7	6
Total costs recorded to retained earnings	$ 350			$ 301				$ 1,507	$ 1,256
Subsequent Event | 2012 - Share Repurchase Program
Class of Stock [Line Items]
Shares purchased (in shares)							25
Average price per share of stock repurchased (in dollars per share)							$ 193.91
Total repurchase cost							$ 4.8

Shareholders' Equity - Accumula

Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 3,913	$ 4,618	$ 4,219	$ 5,140
Other comprehensive income (loss) before reclassifications, net			(190)
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income			91
Tax expense			(22)
Amounts reclassified from accumulated other comprehensive income, net			69
Total other comprehensive loss attributable to Aon shareholders	(193)	(108)	(121)	(135)
Ending Balance	3,561	$ 4,328	3,561	$ 4,328
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	(4,030)		(4,030)
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			(12)
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income			12
Tax expense			(3)
Amounts reclassified from accumulated other comprehensive income, net			9
Total other comprehensive loss attributable to Aon shareholders			(3)
Ending Balance	(18)		(18)
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			(180)
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 loss attributable to Aon shareholders			(180)
Ending Balance	(1,499)		(1,499)
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			2
Amounts reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive income			79
Tax expense			(19)
Amounts reclassified from accumulated other comprehensive income, net			60
Total other comprehensive loss attributable to Aon shareholders			62
Ending Balance	$ (2,513)		$ (2,513)

Employee Benefits - Components

Employee Benefits - Components of Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	27	24	81	74
Expected return on plan assets, net of administration expenses	(34)	(36)	(102)	(108)
Amortization of prior-service cost	1	0	2	1
Amortization of net actuarial loss	13	15	40	45
Net periodic (benefit) cost	7	3	21	12
Loss on pension settlement	0	0	0	0
Total net periodic (benefit) cost	7	3	21	12
U.K.
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	26	26	81	84
Expected return on plan assets, net of administration expenses	(46)	(46)	(143)	(147)
Amortization of prior-service cost	0	1	1	1
Amortization of net actuarial loss	7	6	22	21
Net periodic (benefit) cost	(13)	(13)	(39)	(41)
Loss on pension settlement	0	9	0	32
Total net periodic (benefit) cost	(13)	(4)	(39)	(9)
Other
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	6	6	20	20
Expected return on plan assets, net of administration expenses	(9)	(11)	(29)	(34)
Amortization of prior-service cost	0	0	0	0
Amortization of net actuarial loss	3	3	9	9
Net periodic (benefit) cost	0	(2)	0	(5)
Loss on pension settlement	0	0	0	0
Total net periodic (benefit) cost	$ 0	$ (2)	$ 0	$ (5)

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) £ in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018GBP (£)	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Estimate of contributions to defined benefit pension plans for the current fiscal year					$ 46
U.K.
Defined Benefit Plan Disclosure [Line Items]
Payment for settlement			£ 125	$ 164
Benefit obligation period increase (decrease)	£ (108)	$ (143)
Benefit obligation, (increase) decrease for settlement	£ 7	$ 9	£ 24	$ 32
Estimate of contributions to defined benefit pension plans for the current fiscal year					80
Other
Defined Benefit Plan Disclosure [Line Items]
Estimate of contributions to defined benefit pension plans for the current fiscal year					$ 19

Employee Benefits - Summary of

Employee Benefits - Summary of Employer Contributions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 29	$ 138	$ 108	$ 222
U.S.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	7	108	30	133
U.K.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	19	27	65	75
Other
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 3	3	$ 13	14
Qualified Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans		$ 100		$ 100

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Share-based compensation expenses recognized (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 72	$ 67	$ 252	$ 214
Restricted share units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	42	41	155	145
Performance share awards (“PSAs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	28	24	90	63
Employee share purchase plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 2	$ 2	$ 7	$ 6

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	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 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)	1,225	1,409
Vested (in shares)	(1,551)	(1,772)
Forfeited (in shares)	(164)	(158)
Non-vested at end of period (in shares)	3,718	4,328	4,208
Weighted Average Fair value
Non-vested at beginning of period (in dollars per share)	$ 120	$ 104	$ 104
Granted (in dollars per share)	174	140
Vested (in dollars per share)	112	97
Forfeited (in dollars per share)	128	111
Non-vested at end of period (in dollars per share)	$ 141	$ 118	$ 120
Unamortized deferred compensation expense	$ 384
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	9 Months Ended
	Sep. 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	9 Months Ended	12 Months Ended
	Sep. 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)	458	958	1,057
Unamortized expense, based on current performance levels	$ 61	$ 54	$ 10

Derivatives and Hedging - Forei

Derivatives and Hedging - Foreign Exchange Risk Management Narrative (Details)	9 Months Ended
	Sep. 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	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value
Notional Amount	$ 920	$ 915
Derivative Assets	10	18
Derivative Liabilities	$ 2	8
Term of derivative contract	30 days
Other Current Assets
Derivatives, Fair Value
Derivative Assets	$ 3	3
Other non-current assets
Derivatives, Fair Value
Derivative Assets	7	15
Other current liabilities
Derivatives, Fair Value
Derivative Liabilities	2	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	607	646
Derivative Assets	10	17
Derivative Liabilities	1	2
Not Designated as Hedging Instrument | Gross foreign exchange contracts
Derivatives, Fair Value
Notional Amount	313	269
Derivative Assets	0	1
Derivative Liabilities	$ 1	$ 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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Gain (loss) recognized in Accumulated other comprehensive loss	$ (6)		$ (14)
Gain (loss) recognized in Accumulated other comprehensive loss		$ (3)		$ (14)
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(4)		(12)
Derivative gain (loss) reclassified from accumulated OCI into income, effective portion, net		(3)		(9)
Total revenue
Derivative [Line Items]
Derivative gains (losses) reclassified from accumulated other comprehensive loss	(4)		(11)
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		0		(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)
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		$ (3)		$ (7)

Derivatives and Hedging - Inter

Derivatives and Hedging - Interest Rate Management Risk Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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)	$ (16)	$ (4)	$ (20)	$ (15)

Derivatives and Hedging - For_2

Derivatives and Hedging - Foreign Hedge (Details) - Net Investment Hedging € in Millions, $ in Millions	Sep. 30, 2019USD ($)	Sep. 30, 2019EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)
Derivatives, Fair Value
European denominated commercial paper	$ 546	€ 500	$ 250	€ 220
Effective portion of loss reclassified from Accumulated OCI	$ 38		$ 21

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	Sep. 30, 2019	Dec. 31, 2018
Money market funds and highly liquid debt securities
Assets
Money market funds and highly liquid debt securities	$ 1,851	$ 1,759
Government bonds
Assets
Other investments	1	1
Equity investments
Assets
Other investments	1	2
Gross foreign exchange contracts
Assets
Derivatives	12	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	1,851	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	12	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	Sep. 30, 2019	Dec. 31, 2018
Carrying Value
Fair value of financial instrument
Current portion of long-term debt	$ 599	$ 0
Long-term debt	6,120	5,993
Fair Value | Fair Value, Inputs, Level 2
Fair value of financial instrument
Current portion of long-term debt	617	0
Long-term debt	$ 6,915	$ 6,159

Claims, Lawsuits and Other Co_2

Claims, Lawsuits and Other Contingencies - Narrative (Details) £ in Millions, $ in Millions	Sep. 30, 2019USD ($)	Sep. 06, 2018USD ($)	Oct. 03, 2017NZD ($)	Dec. 20, 2016GBP (£)	Jun. 29, 2015NZD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Apr. 30, 2014GBP (£)
Legal, Guarantees and Indemnifications
Revenue						$ 2,379,000,000	$ 2,349,000,000	$ 8,128,000,000	$ 8,000,000,000
Maximum potential funding under commitments	$ 83,000,000					83,000,000		83,000,000			$ 103,000,000
Letters of credit outstanding	71,000,000					71,000,000		71,000,000			$ 83,000,000
Potential Claim for Pension Advisory Services
Legal, Guarantees and Indemnifications
Estimate of possible loss	55,000,000					55,000,000		55,000,000				£ 45
Pending Litigation | Trustees Of Gleeds Pension Fund 2016
Legal, Guarantees and Indemnifications
Damages sought	86,000,000			£ 70
Pending Litigation | Lyttleton Port Company Limited
Legal, Guarantees and Indemnifications
Damages sought	116,000,000				$ 184
Pending Litigation | Christchurch City Council
Legal, Guarantees and Indemnifications
Damages sought	333,000,000		$ 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
Maximum potential funding under commitments	74,000,000					74,000,000		74,000,000
Guarantor obligations, current carrying value	14,000,000					14,000,000		14,000,000
Loss contingency accrual payments								0
Discontinued Operations, Disposed of by Sale | Tempo Business | Performance Guarantee
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	160,000,000					160,000,000		160,000,000
Guarantor obligations, current carrying value	$ 1,000,000					1,000,000		1,000,000
Loss contingency accrual payments						$ 0		$ 0

Segment Information (Details)

Segment Information (Details)	9 Months Ended
	Sep. 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	Sep. 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						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue
Total revenue	$ 2,379			$ 2,349			$ 8,128	$ 8,000
Expenses
Compensation and benefits	1,368			1,392			4,453	4,502
Information technology	120			125			363	363
Premises	76			94			248	283
Depreciation of fixed assets	44			40			124	126
Amortization and impairment of intangible assets	101			100			295	492
Other general expenses	310			336			1,000	1,189
Total operating expenses	2,019			2,087			6,483	6,955
Operating income (loss)	360			262			1,645	1,045
Interest income	1			0			4	5
Interest expense	(78)			(69)			(227)	(208)
Intercompany interest income (expense)	0			0			0	0
Intercompany other income (expense)	0			0			0	0
Other income (expense)	2			1			8	(17)
Income (loss) from continuing operations before income taxes	285			194			1,430	825
Income tax expense (benefit)	56			39			238	9
Net income from continuing operations	229			155			1,192	816
Net income (loss) from discontinued operations	(1)			(2)			(1)	5
Net income (loss) before equity in earnings of subsidiaries	228			153			1,191	821
Equity in earnings of subsidiaries	0			0			0	0
Net income	228	$ 287	$ 676	153	$ 58	$ 610	1,191	821
Less: Net income attributable to noncontrolling interests	6			6			33	32
Net income attributable to Aon shareholders	222			147			1,158	789
Aon plc
Revenue
Total revenue	0			0			0	0
Expenses
Compensation and benefits	12			13			54	47
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	2			0			5	3
Total operating expenses	14			13			59	50
Operating income (loss)	(14)			(13)			(59)	(50)
Interest income	0			0			0	0
Interest expense	(47)			(52)			(138)	(149)
Intercompany interest income (expense)	4			4			11	11
Intercompany other income (expense)	(70)			245			98	99
Other income (expense)	39			(5)			33	18
Income (loss) from continuing operations before income taxes	(88)			179			(55)	(71)
Income tax expense (benefit)	(2)			(8)			(7)	(27)
Net income from continuing operations	(86)			187			(48)	(44)
Net income (loss) from discontinued operations	0			0			0	0
Net income (loss) before equity in earnings of subsidiaries	(86)			187			(48)	(44)
Equity in earnings of subsidiaries	330			(42)			1,223	846
Net income	244			145			1,175	802
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	244			145			1,175	802
Aon Corporation
Revenue
Total revenue	0			0			0	0
Expenses
Compensation and benefits	2			3			14	5
Information technology	0			0			0	0
Premises	4			0			17	0
Depreciation of fixed assets	0			0			0	0
Amortization and impairment of intangible assets	0			0			0	0
Other general expenses	1			(1)			3	90
Total operating expenses	7			2			34	95
Operating income (loss)	(7)			(2)			(34)	(95)
Interest income	11			15			29	44
Interest expense	(35)			(26)			(97)	(75)
Intercompany interest income (expense)	(116)			(128)			(348)	(385)
Intercompany other income (expense)	(9)			(245)			(272)	(240)
Other income (expense)	(22)			(3)			(47)	(29)
Income (loss) from continuing operations before income taxes	(178)			(389)			(769)	(780)
Income tax expense (benefit)	(35)			(67)			(141)	(144)
Net income from continuing operations	(143)			(322)			(628)	(636)
Net income (loss) from discontinued operations	0			0			0	0
Net income (loss) before equity in earnings of subsidiaries	(143)			(322)			(628)	(636)
Equity in earnings of subsidiaries	107			(42)			1,132	870
Net income	(36)			(364)			504	234
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	(36)			(364)			504	234
Other Non-Guarantor Subsidiaries
Revenue
Total revenue	2,379			2,349			8,128	8,000
Expenses
Compensation and benefits	1,354			1,376			4,385	4,450
Information technology	120			125			363	363
Premises	72			94			231	283
Depreciation of fixed assets	44			40			124	126
Amortization and impairment of intangible assets	101			100			295	492
Other general expenses	307			337			992	1,096
Total operating expenses	1,998			2,072			6,390	6,810
Operating income (loss)	381			277			1,738	1,190
Interest income	0			0			0	0
Interest expense	(6)			(6)			(17)	(23)
Intercompany interest income (expense)	112			124			337	374
Intercompany other income (expense)	79			0			174	141
Other income (expense)	7			7			39	7
Income (loss) from continuing operations before income taxes	573			402			2,271	1,689
Income tax expense (benefit)	93			114			386	180
Net income from continuing operations	480			288			1,885	1,509
Net income (loss) from discontinued operations	(1)			(2)			(1)	5
Net income (loss) before equity in earnings of subsidiaries	479			286			1,884	1,514
Equity in earnings of subsidiaries	(36)			(364)			504	234
Net income	443			(78)			2,388	1,748
Less: Net income attributable to noncontrolling interests	6			6			33	32
Net income attributable to Aon shareholders	437			(84)			2,355	1,716
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	(10)			(15)			(25)	(39)
Interest expense	10			15			25	39
Intercompany interest income (expense)	0			0			0	0
Intercompany other income (expense)	0			0			0	0
Other income (expense)	(22)			2			(17)	(13)
Income (loss) from continuing operations before income taxes	(22)			2			(17)	(13)
Income tax expense (benefit)	0			0			0	0
Net income from continuing operations	(22)			2			(17)	(13)
Net income (loss) from discontinued operations	0			0			0	0
Net income (loss) before equity in earnings of subsidiaries	(22)			2			(17)	(13)
Equity in earnings of subsidiaries	(401)			448			(2,859)	(1,950)
Net income	(423)			450			(2,876)	(1,963)
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	$ (423)			$ 450			$ (2,876)	$ (1,963)

Guarantee of Registered Secur_5

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Net income	$ 228	$ 287	$ 676	$ 153	$ 58	$ 610	$ 1,191	$ 821
Less: Net income attributable to noncontrolling interests	6			6			33	32
Net income attributable to Aon shareholders	222			147			1,158	789
Change in fair value of financial instruments	(2)	(8)	7	1	(1)	14	(3)	14
Foreign currency translation adjustments	(212)	(103)	133	(50)	(460)	247	(182)	(263)
Postretirement benefit obligation	17	$ 14	$ 31	(62)	$ 122	$ 48	62	108
Net current period other comprehensive income (loss)	(197)			(111)			(123)	(141)
Equity in other comprehensive income (loss) of subsidiaries, net of tax	0			0			0	0
Less: Other comprehensive loss attributable to noncontrolling interests	(4)			(3)			(2)	(6)
Total other comprehensive loss attributable to Aon shareholders	(193)			(108)			(121)	(135)
Comprehensive income (loss) attributable to Aon shareholders	29			39			1,037	654
Aon plc
Condensed Financial Statements, Captions [Line Items]
Net income	244			145			1,175	802
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	244			145			1,175	802
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
Net current period other comprehensive income (loss)	0			0			0	0
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(215)			(106)			(138)	(148)
Less: Other comprehensive loss attributable to noncontrolling interests	0			0			0	0
Total other comprehensive loss attributable to Aon shareholders	(215)			(106)			(138)	(148)
Comprehensive income (loss) attributable to Aon shareholders	29			39			1,037	654
Aon Corporation
Condensed Financial Statements, Captions [Line Items]
Net income	(36)			(364)			504	234
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	(36)			(364)			504	234
Change in fair value of financial instruments	0			(2)			2	(3)
Foreign currency translation adjustments	0			0			0	0
Postretirement benefit obligation	10			12			42	34
Net current period other comprehensive income (loss)	10			10			44	31
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(220)			(134)			(223)	(194)
Less: Other comprehensive loss attributable to noncontrolling interests	0			0			0	0
Total other comprehensive loss attributable to Aon shareholders	(210)			(124)			(179)	(163)
Comprehensive income (loss) attributable to Aon shareholders	(246)			(488)			325	71
Other Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	443			(78)			2,388	1,748
Less: Net income attributable to noncontrolling interests	6			6			33	32
Net income attributable to Aon shareholders	437			(84)			2,355	1,716
Change in fair value of financial instruments	(2)			3			(5)	17
Foreign currency translation adjustments	(234)			(48)			(199)	(276)
Postretirement benefit obligation	7			(74)			20	74
Net current period other comprehensive income (loss)	(229)			(119)			(184)	(185)
Equity in other comprehensive income (loss) of subsidiaries, net of tax	(210)			(124)			(179)	(163)
Less: Other comprehensive loss attributable to noncontrolling interests	(4)			(3)			(2)	(6)
Total other comprehensive loss attributable to Aon shareholders	(435)			(240)			(361)	(342)
Comprehensive income (loss) attributable to Aon shareholders	2			(324)			1,994	1,374
Consolidation Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income	(423)			450			(2,876)	(1,963)
Less: Net income attributable to noncontrolling interests	0			0			0	0
Net income attributable to Aon shareholders	(423)			450			(2,876)	(1,963)
Change in fair value of financial instruments	0			0			0	0
Foreign currency translation adjustments	22			(2)			17	13
Postretirement benefit obligation	0			0			0	0
Net current period other comprehensive income (loss)	22			(2)			17	13
Equity in other comprehensive income (loss) of subsidiaries, net of tax	645			364			540	505
Less: Other comprehensive loss attributable to noncontrolling interests	0			0			0	0
Total other comprehensive loss attributable to Aon shareholders	667			362			557	518
Comprehensive income (loss) attributable to Aon shareholders	$ 244			$ 812			$ (2,319)	$ (1,445)

Guarantee of Registered Secur_6

Guarantee of Registered Securities - Condensed Consolidating Statement of Financial Position (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 602			$ 656
Short-term investments	177			172
Receivables, net	2,866			2,760
Fiduciary assets	11,041			10,166
Current intercompany receivables	0			0
Other current assets	631			618
Total current assets	15,317			14,372
Goodwill	8,071			8,171
Intangible assets, net	874			1,149
Fixed assets, net	606			588
Operating lease right-of-use assets	913
Deferred tax assets	611			561
Prepaid pension	1,213			1,133
Non-current intercompany receivables	0			0
Other non-current assets	562			448
Investment in subsidiary	0			0
Total assets	28,167			26,422
Current liabilities
Accounts payable and accrued liabilities	1,499			1,943
Short-term debt and current portion of long-term debt	1,148			251
Fiduciary liabilities	11,041			10,166
Current intercompany payables	0			0
Other current liabilities	1,163			936
Total current liabilities	14,851			13,296
Long-term debt	6,120			5,993
Non-current operating lease liabilities	922
Deferred tax liabilities	209			181
Pension, other postretirement, and postemployment liabilities	1,551			1,636
Non-current intercompany payables	0			0
Other non-current liabilities	953			1,097
Total liabilities	24,606			22,203
Total Aon shareholders’ equity	3,492			4,151
Noncontrolling interests	69			68
Total equity	3,561	$ 3,913	$ 4,862	4,219	$ 4,328	$ 4,618	$ 5,385	$ 5,140
Total liabilities and equity	28,167			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	153			191
Other current assets	0			0
Total current assets	153			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	394			403
Other non-current assets	2			1
Investment in subsidiary	9,052			8,433
Total assets	9,694			9,122
Current liabilities
Accounts payable and accrued liabilities	1,171			274
Short-term debt and current portion of long-term debt	546			250
Fiduciary liabilities	0			0
Current intercompany payables	268			213
Other current liabilities	0			0
Total current liabilities	1,985			737
Long-term debt	4,213			4,231
Non-current operating lease liabilities	0
Deferred tax liabilities	1			0
Pension, other postretirement, and postemployment liabilities	0			0
Non-current intercompany payables	0			0
Other non-current liabilities	3			3
Total liabilities	6,202			4,971
Total Aon shareholders’ equity	3,492			4,151
Noncontrolling interests	0			0
Total equity	3,492			4,151
Total liabilities and equity	9,694			9,122
Aon Corporation
Current assets
Cash and cash equivalents	1,530			862
Short-term investments	63			56
Receivables, net	0			0
Fiduciary assets	0			0
Current intercompany receivables	4,090			897
Other current assets	6			16
Total current assets	5,689			1,831
Goodwill	0			0
Intangible assets, net	0			0
Fixed assets, net	0			0
Operating lease right-of-use assets	109
Deferred tax assets	513			467
Prepaid pension	5			5
Non-current intercompany receivables	261			261
Other non-current assets	35			30
Investment in subsidiary	20,085			19,132
Total assets	26,697			21,726
Current liabilities
Accounts payable and accrued liabilities	42			70
Short-term debt and current portion of long-term debt	599			0
Fiduciary liabilities	0			0
Current intercompany payables	15,956			11,875
Other current liabilities	79			69
Total current liabilities	16,676			12,014
Long-term debt	1,907			1,762
Non-current operating lease liabilities	146
Deferred tax liabilities	0			0
Pension, other postretirement, and postemployment liabilities	1,222			1,275
Non-current intercompany payables	7,364			7,390
Other non-current liabilities	107			167
Total liabilities	27,422			22,608
Total Aon shareholders’ equity	(725)			(882)
Noncontrolling interests	0			0
Total equity	(725)			(882)
Total liabilities and equity	26,697			21,726
Other Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	491			575
Short-term investments	114			116
Receivables, net	2,866			2,760
Fiduciary assets	11,041			10,166
Current intercompany receivables	13,669			11,634
Other current assets	625			602
Total current assets	28,806			25,853
Goodwill	8,071			8,171
Intangible assets, net	874			1,149
Fixed assets, net	606			588
Operating lease right-of-use assets	804
Deferred tax assets	150			144
Prepaid pension	1,208			1,128
Non-current intercompany receivables	7,198			7,225
Other non-current assets	525			417
Investment in subsidiary	(725)			(882)
Total assets	47,517			43,793
Current liabilities
Accounts payable and accrued liabilities	1,705			2,380
Short-term debt and current portion of long-term debt	3			1
Fiduciary liabilities	11,041			10,166
Current intercompany payables	1,688			634
Other current liabilities	1,084			867
Total current liabilities	15,521			14,048
Long-term debt	0			0
Non-current operating lease liabilities	776
Deferred tax liabilities	353			325
Pension, other postretirement, and postemployment liabilities	329			361
Non-current intercompany payables	489			499
Other non-current liabilities	843			927
Total liabilities	18,311			16,160
Total Aon shareholders’ equity	29,137			27,565
Noncontrolling interests	69			68
Total equity	29,206			27,633
Total liabilities and equity	47,517			43,793
Consolidation Adjustments
Current assets
Cash and cash equivalents	(1,419)			(781)
Short-term investments	0			0
Receivables, net	0			0
Fiduciary assets	0			0
Current intercompany receivables	(17,912)			(12,722)
Other current assets	0			0
Total current assets	(19,331)			(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	(145)			(144)
Prepaid pension	0			0
Non-current intercompany receivables	(7,853)			(7,889)
Other non-current assets	0			0
Investment in subsidiary	(28,412)			(26,683)
Total assets	(55,741)			(48,219)
Current liabilities
Accounts payable and accrued liabilities	(1,419)			(781)
Short-term debt and current portion of long-term debt	0			0
Fiduciary liabilities	0			0
Current intercompany payables	(17,912)			(12,722)
Other current liabilities	0			0
Total current liabilities	(19,331)			(13,503)
Long-term debt	0			0
Non-current operating lease liabilities	0
Deferred tax liabilities	(145)			(144)
Pension, other postretirement, and postemployment liabilities	0			0
Non-current intercompany payables	(7,853)			(7,889)
Other non-current liabilities	0			0
Total liabilities	(27,329)			(21,536)
Total Aon shareholders’ equity	(28,412)			(26,683)
Noncontrolling interests	0			0
Total equity	(28,412)			(26,683)
Total liabilities and equity	$ (55,741)			$ (48,219)

Guarantee of Registered Secur_7

Guarantee of Registered Securities - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Cash provided by (used for) operating activities	$ 1,163	$ 975
Cash flows from investing activities
Proceeds from investments	33	30
Payments for investments	(94)	(65)
Net sales (purchases) of short-term investments - non-fiduciary	(7)	356
Acquisition of businesses, net of cash acquired	(39)	(50)
Sale of businesses, net of cash sold	43	(8)
Capital expenditures	(167)	(179)
Cash provided by (used for) investing activities	(231)	84
Cash flows from financing activities
Share repurchase	(1,507)	(1,272)
Advances from (to) affiliates	0	0
Issuance of shares for employee benefit plans	(133)	(139)
Issuance of debt	4,918	3,960
Repayment of debt	(3,858)	(3,498)
Cash dividends to shareholders	(307)	(285)
Noncontrolling interests and other financing activities	(81)	(21)
Cash used for financing activities	(968)	(1,255)
Effect of exchange rates on cash and cash equivalents	(18)	(76)
Net increase (decrease) in cash and cash equivalents	(54)	(272)
Cash and cash equivalents at beginning of period	656	756
Cash and cash equivalents at end of period	602	484
Aon plc
Cash flows from operating activities
Cash provided by (used for) operating activities	356	(143)
Cash flows from investing activities
Proceeds from investments		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
Cash provided by (used for) investing activities	0	(12)
Cash flows from financing activities
Share repurchase	(1,507)	(1,272)
Advances from (to) affiliates	1,277	1,292
Issuance of shares for employee benefit plans	(133)	(139)
Issuance of debt	2,099	1,258
Repayment of debt	(1,785)	(700)
Cash dividends to shareholders	(307)	(285)
Noncontrolling interests and other financing activities	0	0
Cash used for financing activities	(356)	154
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	(118)	479
Cash flows from investing activities
Proceeds from investments	17	16
Payments for investments	(46)	(36)
Net sales (purchases) of short-term investments - non-fiduciary	(7)	308
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	(36)	288
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	79	(1,564)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	2,816	2,701
Repayment of debt	(2,073)	(2,501)
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash used for financing activities	822	(1,364)
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	668	(597)
Cash and cash equivalents at beginning of period	862	2,524
Cash and cash equivalents at end of period	1,530	1,927
Other Non-Guarantor Subsidiaries
Cash flows from operating activities
Cash provided by (used for) operating activities	1,578	2,258
Cash flows from investing activities
Proceeds from investments	16	14
Payments for investments	(49)	(29)
Net sales (purchases) of short-term investments - non-fiduciary	0	48
Acquisition of businesses, net of cash acquired	(39)	(50)
Sale of businesses, net of cash sold	43	(8)
Capital expenditures	(167)	(179)
Cash provided by (used for) investing activities	(196)	(204)
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	(1,370)	(2,054)
Issuance of shares for employee benefit plans	0	0
Issuance of debt	3	1
Repayment of debt	0	(297)
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	(81)	(21)
Cash used for financing activities	(1,448)	(2,371)
Effect of exchange rates on cash and cash equivalents	(18)	(76)
Net increase (decrease) in cash and cash equivalents	(84)	(393)
Cash and cash equivalents at beginning of period	575	793
Cash and cash equivalents at end of period	491	400
Consolidation Adjustments
Cash flows from operating activities
Cash provided by (used for) operating activities	(653)	(1,619)
Cash flows from investing activities
Proceeds from investments		0
Payments for investments	1	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	1	12
Cash flows from financing activities
Share repurchase	0	0
Advances from (to) affiliates	14	2,326
Issuance of shares for employee benefit plans	0	0
Issuance of debt		0
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Noncontrolling interests and other financing activities	0	0
Cash used for financing activities	14	2,326
Effect of exchange rates on cash and cash equivalents	0	0
Net increase (decrease) in cash and cash equivalents	(638)	719
Cash and cash equivalents at beginning of period	(781)	(2,562)
Cash and cash equivalents at end of period	$ (1,419)	$ (1,843)

Lease Commitments - Assets and

Lease Commitments - Assets and Liabilities of Lessee (Details) $ in Millions	Sep. 30, 2019USD ($)
Assets
Operating lease right-of-use assets	$ 913
Finance lease assets	106
Total lease assets	1,019
Current lease liabilities
Operating	194
Finance	24
Non-current lease liabilities
Operating	922
Finance	82
Total lease liabilities	$ 1,222

Lease Commitments - Lease Costs

Lease Commitments - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 43	$ 176
Finance lease costs
Amortization of leased assets	7	20
Interest on lease liabilities	0	1
Variable lease cost	31	49
Short-term lease cost	1	3
Sublease income	(8)	(24)
Net lease cost	$ 74	$ 225

Lease Commitments - Lease Terms

Lease Commitments - Lease Terms and Assumptions (Details)	Sep. 30, 2019
Weighted average remaining lease term (years)
Operating leases	8 years
Finance leases	4 years 7 months 6 days
Weighted average discount rate
Operating leases	3.30%
Finance leases	2.00%

Lease Commitments - Cash Flow o

Lease Commitments - Cash Flow of Lessee (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 182
Financing cash flows from finance leases	11
Non-cash related activities
ROU assets obtained in exchange for new operating lease liabilities	95
ROU assets obtained in exchange for new finance lease liabilities	$ 48

Lease Commitments - Lease Matur

Lease Commitments - Lease Maturity (Details) $ in Millions	Sep. 30, 2019USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Remainder of 2019	$ 61
2020	246
2021	225
2022	199
2023	144
Thereafter	513
Total undiscounted future minimum lease payments	1,388
Imputed interest	(143)
Present value of lease liabilities	1,245
Finance Lease, Liability, Payment, Due [Abstract]
Remainder of 2019	7
2020	26
2021	26
2022	19
2023	18
Thereafter	15
Total undiscounted future minimum lease payments	111
Imputed interest	(5)
Present value of lease liabilities	106
Rentals from subleases
Remainder of 2019	(9)
2020	(34)
2021	(33)
2022	(33)
2023	(14)
Thereafter	(6)
Total undiscounted future minimum lease payments	(129)
Imputed interest	0
Present value of lease liabilities	(129)
Total
Remainder of 2019	59
2020	238
2021	218
2022	185
2023	148
Thereafter	522
Total undiscounted future minimum lease payments	1,370
Imputed interest	(148)
Present value of lease liabilities	$ 1,222

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 - Narrative (

Lease Commitments - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Leases [Abstract]
Non cash right-of-use asset lease expense	$ 87
Increase (decrease) in operating lease liabilities	$ 92