Aon (AON) 10-K 23 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 22, 2017	Jun. 30, 2016
Document and Entity Information
Entity Registrant Name	Aon plc
Entity Central Index Key	315,293
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		262,600,762
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Entity Public Float			$ 29,031,404,998

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue
Commissions, fees and other	$ 11,605	$ 11,661	$ 12,019
Fiduciary investment income	22	21	26
Total revenue	11,627	11,682	12,045
Expenses
Compensation and benefits	6,914	6,837	7,014
Other general expenses	2,807	2,997	3,065
Total operating expenses	9,721	9,834	10,079
Operating income	1,906	1,848	1,966
Interest income	9	14	10
Interest expense	(282)	(273)	(255)
Other income	36	100	44
Income before income taxes	1,669	1,689	1,765
Income taxes	239	267	334
Net income	1,430	1,422	1,431
Less: Net income attributable to noncontrolling interests	34	37	34
Net income attributable to Aon shareholders	$ 1,396	$ 1,385	$ 1,397
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ 5.21	$ 4.93	$ 4.73
Diluted net income per share attributable to Aon shareholders (in dollars per share)	5.16	4.88	4.66
Cash dividends per share paid on ordinary shares (in dollars per share)	$ 1.29	$ 1.15	$ 0.92
Weighted average ordinary shares outstanding - basic (in shares)	268.1	280.8	295.5
Weighted average ordinary shares outstanding - diluted (in shares)	270.3	283.8	299.6

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 459	$ 326	$ 308	$ 337	$ 540	$ 311	$ 214	$ 357	$ 645	$ 971	$ 1,430	$ 1,422	$ 1,431
Less: Net income attributable to noncontrolling interests	7	7	8	12	6	8	10	13			34	37	34
Net income attributable to Aon shareholders	$ 452	$ 319	$ 300	$ 325	$ 534	$ 303	$ 204	$ 344			1,396	1,385	1,397
Other comprehensive (loss) income, net of tax:
Change in fair value of financial instruments											(12)	(8)	4
Foreign currency translation adjustments											(495)	(442)	(507)
Post-retirement benefit obligation											16	155	(260)
Total other comprehensive loss											(491)	(295)	(763)
Less: Other comprehensive loss attributable to noncontrolling interests											(2)	(6)	(3)
Total other comprehensive loss attributable to Aon shareholders											(489)	(289)	(760)
Comprehensive income attributable to Aon shareholders											$ 907	$ 1,096	$ 637

Consolidated Statements of Fina

Consolidated Statements of Financial Position - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
CURRENT ASSETS
Cash and cash equivalents	$ 431	$ 384
Short-term investments	290	356
Receivables, net	2,589	2,564
Fiduciary assets	9,485	9,932
Other current assets	351	329
Total Current Assets	13,146	13,565
Goodwill	8,747	8,448
Intangible assets, net	2,223	2,180
Fixed assets, net	765	765
Deferred tax assets	322	300
Prepaid pension	858	1,033
Other non-current assets	554	592
TOTAL ASSETS	26,615	26,883
CURRENT LIABILITIES
Accounts payable and accrued liabilities	1,801	1,772
Short-term debt and current portion of long-term debt	336	562
Fiduciary liabilities	9,485	9,932
Other current liabilities	873	819
Total Current Liabilities	12,495	13,085
Long-term debt	5,869	5,138
Deferred tax liabilities	101	37
Pension, other post retirement, and post employment liabilities	1,774	1,795
Other non-current liabilities	844	769
TOTAL LIABILITIES	21,083	20,824
EQUITY
Ordinary shares - $0.01 nominal value Authorized: 750 shares (issued: 2016 - 262.0; 2015 - 269.8)	3	3
Additional paid-in capital	5,577	5,409
Retained earnings	3,807	4,013
Accumulated other comprehensive loss	(3,912)	(3,423)
TOTAL AON SHAREHOLDERS' EQUITY	5,475	6,002
Noncontrolling interests	57	57
TOTAL EQUITY	5,532	6,059
TOTAL LIABILITIES AND EQUITY	$ 26,615	$ 26,883

Consolidated Statements of Fin5

Consolidated Statements of Financial Position (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Ordinary shares, nominal or par value	$ 0.01	$ 0.01
Ordinary shares, Authorized shares	750,000,000	750,000,000
Ordinary shares, issued shares	262,000,000	269,800,000

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Ordinary Shares and Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, Net of Tax	Noncontrolling Interests
Balance (in shares) at Dec. 31, 2013		300.7
Balance at Dec. 31, 2013	$ 8,091	$ 4,788	$ 5,627	$ (2,374)	$ 50
Increase (Decrease) in Shareholders' Equity
Net income	1,431		1,397		34
Shares issued - employee benefit plan (in shares)		0.4
Shares issued — employee benefit plans	26	$ 26
Shares issued - employee compensation (in shares)		4.7
Shares issued — employee compensation	(131)	$ (131)
Shares purchased (in shares)		(25.8)
Shares purchased	(2,250)		(2,250)
Tax benefit — employee benefit plans	89	$ 89
Share-based compensation expense	328	328
Dividends to shareholders	(273)		(273)
Net change in fair value of financial instruments	4
Net change in fair value of financial instruments	4			4
Net foreign currency translation adjustments	(507)			(504)	(3)
Net post-retirement benefit obligation	(260)			(260)
Net sales of subsidiary shares to noncontrolling interests	3	$ 0			3
Dividends paid to noncontrolling interests on subsidiary common stock	(24)				(24)
Balance (in shares) at Dec. 31, 2014		280
Balance at Dec. 31, 2014	6,527	$ 5,100	4,501	(3,134)	60
Increase (Decrease) in Shareholders' Equity
Net income	1,422		1,385		37
Shares issued - employee benefit plan (in shares)		0.5
Shares issued — employee benefit plans	33	$ 33
Shares issued - employee compensation (in shares)		5.3
Shares issued — employee compensation	(188)	$ (188)
Shares purchased (in shares)		(16)
Shares purchased	(1,550)		(1,550)
Tax benefit — employee benefit plans	126	$ 126
Share-based compensation expense	340	340
Dividends to shareholders	(323)		(323)
Net change in fair value of financial instruments	(8)			(8)
Net foreign currency translation adjustments	(442)			(436)	(6)
Net post-retirement benefit obligation	155			155
Net purchases of shares from noncontrolling interests	(6)	$ 1			(7)
Dividends paid to noncontrolling interests on subsidiary common stock	$ (27)				(27)
Balance (in shares) at Dec. 31, 2015	269.8	269.8
Balance at Dec. 31, 2015	$ 6,059	$ 5,412	4,013	(3,423)	57
Increase (Decrease) in Shareholders' Equity
Net income	1,430		1,396		34
Shares issued - employee benefit plan (in shares)		0.7
Shares issued — employee benefit plans	49	$ 49
Shares issued - employee compensation (in shares)		3.6
Shares issued — employee compensation	(174)	$ (174)
Shares purchased (in shares)		(12.1)
Shares purchased	(1,257)		(1,257)
Tax benefit — employee benefit plans	(4)	$ (4)
Share-based compensation expense	331	331
Dividends to shareholders	(345)		(345)
Net change in fair value of financial instruments	(12)			(12)
Net foreign currency translation adjustments	(495)			(493)	(2)
Net post-retirement benefit obligation	16			16
Net purchases of shares from noncontrolling interests	(38)	$ (34)			(4)
Dividends paid to noncontrolling interests on subsidiary common stock	$ (28)				(28)
Balance (in shares) at Dec. 31, 2016	262	262
Balance at Dec. 31, 2016	$ 5,532	$ 5,580	$ 3,807	$ (3,912)	$ 57

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 1,430	$ 1,422	$ 1,431
Adjustments to reconcile net income to cash provided by operating activities:
Gain from sales of businesses and investments, net	(39)	(81)	(44)
Depreciation of fixed assets	232	229	242
Amortization of intangible assets	277	314	352
Share-based compensation expense	331	340	328
Deferred income taxes	(24)	(223)	(135)
Change in assets and liabilities:
Fiduciary receivables	594	599	(19)
Short-term investments — funds held on behalf of clients	(598)	350	(403)
Fiduciary liabilities	4	(949)	422
Receivables, net	(86)	(83)	(25)
Accounts payable and accrued liabilities	64	87	4
Current income taxes	49	116	42
Pension, other post-retirement and other post-employment liabilities	42	(230)	(340)
Other assets and liabilities	50	118	(43)
CASH PROVIDED BY OPERATING ACTIVITIES	2,326	2,009	1,812
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	43	220	52
Payments for investments	(64)	(266)	(20)
Net sales (purchases) of short-term investments — non-fiduciary	61	9	110
Acquisition of businesses, net of cash acquired	(879)	(16)	(479)
Proceeds from sale of businesses	107	205	48
Capital expenditures	(222)	(290)	(256)
CASH USED FOR INVESTING ACTIVITIES	(954)	(138)	(545)
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	(1,257)	(1,550)	(2,250)
Issuance of shares for employee benefit plans	(129)	(30)	(105)
Issuance of debt	3,467	5,351	5,239
Repayment of debt	(2,945)	(5,098)	(3,918)
Cash dividends to shareholders	(345)	(323)	(273)
Noncontrolling interests and other financing activities	(77)	(39)	4
CASH USED FOR FINANCING ACTIVITIES	(1,286)	(1,689)	(1,303)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(39)	(172)	(67)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	47	10	(103)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	384	374	477
CASH AND CASH EQUIVALENTS AT END OF YEAR	431	384	374
Supplemental disclosures:
Interest paid	272	254	245
Income taxes paid, net of refunds	$ 218	$ 249	$ 337

Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying Consolidated Financial Statements and Notes thereto have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). The Consolidated Financial Statements include the accounts of Aon plc and all of its controlled subsidiaries (“Aon” or the “Company”). All intercompany accounts and transactions have been eliminated. The Consolidated Financial Statements include, in the opinion of management, all adjustments necessary to present fairly the Company’s consolidated financial position, results of operations and cash flows for all periods presented. Revision of Previously Issued Financial Statements During the fourth quarter of 2016, the Company identified errors related to the recognition of revenue for certain brokerage fee arrangements, specifically the consideration for certain arrangements covering multiple insurance placements was not appropriately allocated to each individual placement. Based on an analysis of quantitative and qualitative factors in accordance with SEC Staff Accounting Bulletins 99 and 108, the Company concluded that these errors were immaterial, individually and in the aggregate, to the Consolidated Statements of Financial Position, Consolidated Statements of Income, or Consolidated Statements of Cash Flows as presented in the Company’s quarterly and annual financial statements previously filed in the Company’s Quarterly Reports on Form 10-Q and Annual Reports on Form 10-K. While Aon concluded that the errors were immaterial to each of the prior reporting periods affected, the Company further concluded that correcting the errors cumulatively in fiscal year 2016 would materially misstate the Consolidated Statement of Income for the year ended December 31, 2016. As a result, amendment of such reports is not required. In preparing the Company’s Consolidated Financial Statements for the year ended December 31, 2016, the Company made appropriate revisions to its financial statements for historical periods. Such changes are reflected for the years ended December 31, 2015 and 2014, included in these financial statements, and will also be reflected in the historical periods included in the Company’s subsequent quarterly and annual consolidated financial statements. The impact to the Consolidated Statements of Financial Position was a decrease of $170 million to Receivables, net, an increase of $66 million to Deferred tax assets, and a decrease of $104 million to Retained earnings in all periods presented. The impact to the full year Consolidated Statements of Income and Consolidated Statements of Comprehensive Income was de minimis in all periods presented. and therefore remains unchanged. There was no impact to the full year cash provided by operating activities in the Consolidated Statements of Cash Flows. The impact to the Consolidated Statements of Cash Flows previously filed in unaudited Quarterly Reports on Form 10-Q is as follows (in millions): Q1 2016 Q2 2016 Q3 2016 (Unaudited) As Reported Effect of Change (1) As Revised As Reported Effect of Change (1) As Revised As Reported Effect of Change (1) As Revised Net Income $ 327 $ 10 $ 337 $ 607 $ 38 $ 645 $ 921 $ 50 $ 971 Change in assets and liabilities: Receivables, net 110 (13 ) 97 175 (47 ) 128 289 (61 ) 228 Other assets and liabilities $ 69 $ 3 $ 72 $ 56 $ 9 $ 65 $ 83 $ 11 $ 94 (1) No net impact to Cash Provided by Operating Activities. Refer to Note 17 “Quarterly Financial Data” for the impact to the Company’s Condensed Consolidated Statements of Income previously filed in Quarterly Reports on Form 10-Q. Reclassification Certain amounts in prior years’ Consolidated Financial Statements and related notes have been reclassified to conform to the 2016 presentation. In prior periods, cash outflows from Restructuring activities were shown as a separate line item within Cash Flows From Operating Activities in the Consolidated Statements of Cash Flows. Beginning in 2016, these amounts are disclosed as a component of the change in Other assets and liabilities within Cash Flows From Operating Activities in the Consolidated Statements of Cash Flows. Cash outflows for Restructuring reserves were $31 million at December 31, 2015 and $83 million at December 31, 2014. Use of Estimates The preparation of the accompanying Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, 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, among other factors, 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.

Summary of Significant Accounti

Summary of Significant Accounting Principles and Practices	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Principles and Practices	Summary of Significant Accounting Principles and Practices Revenue Recognition Risk Solutions segment revenues primarily include insurance commissions and fees for services rendered and investment income on funds held on behalf of clients. Revenues are recognized when they are earned and realized or realizable. The Company considers revenues to be earned and realized or realizable when all of the following four conditions are met: (1) persuasive evidence of an arrangement exists, (2) the arrangement fee is fixed or determinable, (3) delivery or performance has occurred, and (4) collectability is reasonably assured. For brokerage commissions, revenue is typically recognized at the completion of the placement process, assuming all four criteria required to recognize revenue have been met. The placement process is typically considered complete on the effective date of the related policy. Commission revenues are recorded net of allowances for estimated policy cancellations, which are determined based on an evaluation of historical and current cancellation data. HR Solutions segment revenues consist primarily of fees paid by clients for consulting advice and outsourcing contracts. Fees paid by clients for consulting services are typically charged on an hourly, project or fixed-fee basis. Revenues from time-and-materials or cost-plus arrangements are recognized as services are performed, assuming all four criteria to recognize revenue have been met. Revenues from fixed-fee contracts are recognized as services are provided using a proportional-performance model or at the completion of a project based on facts and circumstances of the client arrangement. Revenues from health care exchange arrangements are typically recognized upon successful enrollment of participants, net of a reserve for estimated cancellations, assuming all four criteria to recognize revenue have been met. Reimbursements received for out-of-pocket expenses are recorded as a component of revenues. The Company’s outsourcing contracts typically have three -to- five year terms for both benefits services and human resources business process outsourcing (“HR BPO”) services. The Company recognizes revenues as services are performed, assuming all criteria to recognize revenue have been met. The Company may also receive implementation fees from clients either up-front or over the ongoing services period as a component of the fee per participant. Lump sum implementation fees received from a client are typically deferred and recognized ratably over the ongoing contract service period. If a client terminates an outsourcing service arrangement prior to the end of the contract, a loss on the contract may be recorded, if necessary, and any remaining deferred implementation revenues would typically be recognized over the remaining service period through the termination date. In connection with the Company’s long-term outsourcing service agreements, highly customized implementation efforts are often necessary to set up clients and their human resource or benefit programs on the Company’s systems and operating processes. Qualifying costs of implementation incurred prior to the services commencing are generally deferred and amortized over the period that the related ongoing services revenue is recognized. Deferred costs are assessed for recoverability on a periodic basis to the extent the deferred cost exceeds related deferred revenue. Share-Based Compensation Costs Share-based payments to employees, including grants of restricted share units and performance share awards, are measured based on estimated grant date fair value. The Company recognizes compensation expense over the requisite service period for awards expected to ultimately vest. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates. Pension and Other Post-Retirement Benefits The Company records net period cost relating to its pension and other post-retirement benefit plans based on calculations that include various actuarial assumptions, including discount rates, assumed rates of return on plan assets, inflation rates, mortality rates, compensation increases, and turnover rates. The Company reviews its actuarial assumptions on an annual basis and modifies these assumptions based on current rates and trends. The effects of gains, losses, and prior service costs and credits are amortized over future service periods or future estimated lives if the plans are frozen. The funded status of each plan, calculated as the fair value of plan assets less the benefit obligation, is reflected in the Company’s Consolidated Statements of Financial Position using a December 31 measurement date. Net Income per Share Basic net income per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, including participating securities, which consist of unvested share awards with non-forfeitable rights to dividends. Diluted net income per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, which have been adjusted for the dilutive effect of potentially issuable ordinary shares (excluding those that are considered participating securities), including certain contingently issuable shares. The diluted earnings per share calculation reflects the more dilutive effect of either (1) the two-class method that assumes that the participating securities have not been exercised, or (2) the treasury stock method. Potentially issuable shares are not included in the computation of diluted income per share if their inclusion would be antidilutive. Cash and Cash Equivalents and Short-term Investments Cash and cash equivalents include cash balances and all highly liquid investments with initial maturities of three months or less. Short-term investments consist of money market funds. The estimated fair value of cash and cash equivalents and short-term investments approximates their carrying values. At December 31, 2016 , Cash and cash equivalents and Short-term investments totaled $721 million compared to $740 million at December 31, 2015 . Of the total balance, $82 million and $105 million was restricted as to its use at December 31, 2016 and 2015 , respectively. Included within the December 31, 2016 and 2015 balances, respectively, were £43.3 million ( $53.2 million at December 31, 2016 exchanges rates) and £43.3 million ( $64.6 million at December 31, 2015 exchange rates) of operating funds required to be held by the Company in the U.K. by the Financial Conduct Authority, a U.K.-based regulator, which were included in Short-term investments. In addition, Cash and cash equivalents included restricted balances of $29 million and $40 million at December 31, 2016 and 2015 , respectively. Fiduciary Assets and Liabilities In its capacity as an insurance agent and broker, Aon collects premiums from insureds and, after deducting its commission, remits the premiums to the respective insurers. Aon also collects claims or refunds from insurers on behalf of insureds. Uncollected premiums from insureds and uncollected claims or refunds from insurers are recorded as Fiduciary assets in the Company’s Consolidated Statements of Financial Position. Unremitted insurance premiums and claims are held in a fiduciary capacity and the obligation to remit these funds is recorded as Fiduciary liabilities in the Company’s Consolidated Statements of Financial Position. Some of the Company’s outsourcing agreements also require it to hold funds to pay certain obligations on behalf of clients. These funds are also recorded as Fiduciary assets with the related obligation recorded as Fiduciary liabilities in the Company’s Consolidated Statements of Financial Position. Aon maintained premium trust balances for premiums collected from insureds but not yet remitted to insurance companies of $3.8 billion and $3.4 billion at December 31, 2016 and 2015 , respectively. These funds and a corresponding liability are included in Fiduciary assets and Fiduciary liabilities, respectively, in the accompanying Consolidated Statements of Financial Position. Allowance for Doubtful Accounts The Company’s allowance for doubtful accounts with respect to receivables is based on a combination of factors, including evaluation of historical write-offs, aging of balances, and other qualitative and quantitative analyses. Receivables, net included an allowance for doubtful accounts of $58 million at both December 31, 2016 and 2015 . Fixed Assets Fixed assets are stated at cost, less accumulated depreciation. Included in this category is internal use software, which is software that is acquired, internally developed or modified solely to meet internal needs, with no plan to market externally. Costs related to directly obtaining, developing or upgrading internal use software are capitalized. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Asset Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years Goodwill and Intangible Assets Goodwill represents the excess of acquisition cost over the fair value of the net assets in the acquisition of a business. Goodwill is allocated to various reporting units, which are one reporting level below the operating segment. Upon disposition of a business entity, goodwill is allocated to the disposed entity based on the fair value of that entity compared to the fair value of the reporting unit in which it was included. Goodwill is not amortized, but instead is tested for impairment at least annually. The goodwill impairment test is performed at the reporting unit level. The Company initially performs a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If such a determination is made, then the Company will perform a two-step quantitative analysis. First, the fair value of each reporting unit is compared to its carrying value. If the fair value of the reporting unit is less than its carrying value, the Company performs a hypothetical purchase price allocation based on the reporting unit’s fair value to determine the fair value of the reporting unit’s goodwill. Any resulting difference will be a charge to Other general expenses in the Consolidated Statements of Income in the period in which the determination is made. Fair value is determined using a combination of present value techniques and market prices of comparable businesses. Intangible assets are primarily comprised of tradenames and customer-related, contract-based, and technology assets. Tradenames are not amortized when such assets have been determined to have indefinite useful lives, and are tested at least annually for impairments using an analysis of expected future cash flows. Interim impairment testing may be performed when events or changes in circumstances indicate that the carrying amount of the intangible asset may not be recoverable. Customer related and contract based assets are amortized over periods ranging from 1 to 16 years, with a weighted average original life of 11 years. Technology assets are typically amortized over 7 years. Derivatives Derivative instruments are recognized in the Consolidated Statements of Financial Position at fair value. Where the Company has entered into master netting agreements with counterparties, the derivative positions are netted by counterparty and are reported accordingly in other assets or other liabilities. Changes in the fair value of derivative instruments are recognized in earnings each period, unless the derivative is designated and qualifies as a cash flow or net investment hedge. The Company has historically designated the following hedging relationships for certain transactions: (i) a hedge of the change in fair value of a recognized asset or liability or firm commitment (“fair value hedge”), (ii) a hedge of the variability in cash flows from a recognized variable-rate asset or liability or forecasted transaction (“cash flow hedge”), and (iii) a hedge of the net investment in a foreign operation (“net investment hedge”). In order for a derivative to qualify for hedge accounting, the derivative must be formally designated as a fair value, cash flow, or a net investment hedge by documenting the relationship between the derivative and the hedged item. The documentation must include a description of the hedging instrument, the hedged item, the risk being hedged, Aon’s risk management objective and strategy for undertaking the hedge, the method for assessing the effectiveness of the hedge, and the method for measuring hedge ineffectiveness. Additionally, the hedge relationship must be expected to be highly effective at offsetting changes in either the fair value or cash flows of the hedged item at both the inception of the hedge and on an ongoing basis. Aon assesses the ongoing effectiveness of its hedges and measures and records hedge ineffectiveness, if any, at the end of each quarter or more frequently if facts and circumstances require. For a derivative designated as a hedging instrument, the changes in the fair value of a recognized asset or liability or a firm commitment (a fair value hedge), the gain or loss is recognized in earnings in the period of change together with the offsetting loss or gain on the hedged item attributable to the risk being hedged. The effect is to reflect in earnings the extent to which the hedge is not effective in achieving offsetting changes in fair value. For a cash flow hedge that qualifies for hedge accounting, the effective portion of the change in fair value of a hedging instrument is recognized in Other Comprehensive Income (“OCI”) and subsequently reclassified to earnings in the same period the hedged item impacts earnings. The ineffective portion of the change in fair value is recognized immediately in earnings. For a net investment hedge, the effective portion of the change in fair value of the hedging instrument is recognized in OCI as part of the cumulative translation adjustment, while the ineffective portion is recognized immediately in earnings. Changes in the fair value of a derivative that is not designated as part of a hedging relationship (commonly referred to as an “economic hedge”) are recorded in Other income in the Consolidated Statements of Income. The Company discontinues hedge accounting prospectively when (1) the derivative expires or is sold, terminated, or exercised, (2) the qualifying criteria are no longer met, or (3) management removes the designation of the hedging relationship. Foreign Currency Certain of the Company’s non-US operations use their respective local currency as their functional currency. These operations that do not have the U.S. dollar as their functional currency translate their financial statements at the current rates of exchange in effect at the balance sheet date and revenues and expenses using rates that approximate those in effect during the period. The resulting translation adjustments are included in net foreign currency translation adjustments within the Consolidated Statements of Shareholders’ Equity. Gains and losses from the remeasurement of monetary assets and liabilities that are denominated in a non-functional currency are included in Other income within the Consolidated Statements of Income. The effect of foreign exchange gains and losses on the Consolidated Statements of Income were losses of $9 million , $11 million , and $1 million in 2016 , 2015 , and 2014 , respectively. Included in these amounts were hedging losses of $7 million in 2016 and hedging losses of $19 million in both 2015 and 2014 . Income Taxes Deferred income taxes are recognized for the effect of temporary differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted marginal tax rates and laws that are currently in effect. The effect on deferred tax assets and liabilities from a change in tax rates is recognized in the period when the rate change is enacted. Deferred tax assets are reduced by valuation allowances if, based on the consideration of all available evidence, it is more likely than not that some portion of the deferred tax asset will not be realized. Significant weight is given to evidence that can be objectively verified. Deferred tax assets are realized by having sufficient future taxable income to allow the related tax benefits to reduce taxes otherwise payable. The sources of taxable income that may be available to realize the benefit of deferred tax assets are future reversals of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences and carry-forwards, taxable income in carry-back years and tax planning strategies that are both prudent and feasible. The Company recognizes the effect of income tax positions only if sustaining those positions is more likely than not. Tax positions that meet the more likely than not recognition threshold but are not highly certain are initially and subsequently measured based on the largest amount of benefit that is greater than 50% likely of being realized upon settlement with the taxing authority. Only information that is available at the reporting date is considered in the Company’s recognition and measurement analysis, and events or changes in facts and circumstances are accounted for in the period in which the event or change in circumstance occurs. The Company records penalties and interest related to unrecognized tax benefits in Income taxes in the Company’s Consolidated Statements of Income. New Accounting Pronouncements Income Tax Consequences of Intercompany Transactions In October 2016, the Financial Accounting Standards Board (“FASB”) issued new accounting guidance on the income tax consequences of intra-entity asset transfers other than inventory. The guidance will require that the seller and buyer recognize the consolidated current and deferred income tax consequences of a transaction in the period the transaction occurs rather than deferring to a future period and recognizing those consequences when the asset has been sold to an outside party or otherwise recovered through use (i.e. depreciated, amortized, impaired). An entity will apply the new guidance on a modified retrospective basis with a cumulative effect adjustment to retained earnings as of the beginning of the period of adoption. The new guidance is effective for Aon in the first quarter of 2018, and the Company is currently evaluating the impact that the standard will have on its Consolidated Financial Statements. Statement of Cash Flows In August 2016, the FASB issued new accounting guidance on the classification of certain cash receipts and cash payments. Under the new guidance, an entity will no longer have discretion to choose the classification for a number of transactions, including contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, and distributions received from equity method investees. The new standard will be effective for the Company in the first quarter of 2018, with early application permitted. An entity will apply the new guidance through retrospective adjustment to all periods presented. The retrospective approach includes a practical expedient that entities may apply should retrospective application be impracticable; in this case, the amendments for these issues may be applied prospectively as of the earliest date practicable. The guidance will not have a material impact upon the Company’s Consolidated Statement of Cash Flows. Credit Losses In June 2016, the FASB issued new accounting guidance on the measurement of credit losses on financial instruments. The new guidance 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 guidance through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The guidance is effective for Aon in the first quarter of 2020 and early adoption is permitted beginning in the first quarter of 2019. Aon is currently evaluating the impact that the standard will have on its Consolidated Financial Statements, as well as the method of transition and period of adoption. Share-based Compensation In March 2016, the FASB issued new accounting guidance on several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The new guidance requires all excess tax benefits and tax deficiencies to be recognized as income tax expense or benefit in the income statement and treated as discrete items in the reporting period. Further, excess tax benefits are required to be classified along with other income tax cash flows as an operating activity. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements, forfeitures, and intrinsic value should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments related to the presentation of employee taxes paid on the statement of cash flows when an employer withholds shares to meet the minimum statutory withholding requirement should be applied retrospectively. Amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement and the practical expedient for estimating expected term should be applied prospectively. An entity may elect to apply the amendments related to the presentation of excess tax benefits on the statement of cash flows using either a prospective transition method or a retrospective transition method. The guidance is effective for Aon in the first quarter of 2017 and early adoption is permitted. Upon the adoption of this guidance on January 1, 2017, the Company expects to recognize an increase to Deferred tax assets of approximately $49 million through a cumulative-effect adjustment to Retained earnings for excess tax benefits not previously recognized. On a prospective basis, excess tax benefits will be recognized in the Consolidated Statements of Income each quarter as share-based payment awards vest, which could have a significant impact on Income tax expense in the Consolidated Statement of Income and Additional paid-in capital in the Consolidated Statements of Financial Position. The impact will be driven, in part, by the difference between the Company’s share price at the time share-based payment transactions vest or options are exercised in the future periods and the fair value of the awards at the date of grant. Amendments related to the presentation of excess tax benefits on the Consolidated Statement of Cash Flows, which will be applied prospectively, may have a significant impact on Cash Flows from Operating Activities and Cash Flows from Financing Activities in the Consolidated Statements of Cash Flows. The impact will also be driven by the Company’s share price at the time share-based payment transactions vest in future periods. The Company does not expect other elements of the guidance to have a material impact on its Consolidated Financial Statements. Leases In February 2016, the FASB issued new accounting guidance on leases, which requires lessees to recognize assets and liabilities for most leases. Under the new guidance, a lessee should recognize in the Consolidated Statement of Financial Position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from currently effective U.S. GAAP. The new standard will be effective for the Company in the first quarter of 2019, with early application permitted. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply. 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. Aon is currently evaluating the impact the standard will have on its Consolidated Financial Statements, as well as the method of transition and period of adoption. Financial Assets and Liabilities In January 2016, the FASB issued new accounting guidance on recognition and measurement of financial assets and financial liabilities. The amendments in the new guidance make targeted improvements, which include the requirement to measure equity investments with readily determinable fair values at fair value through net income, simplification of the impairment assessment for equity investments without readily determinable fair values, adjustments to existing and additional disclosure requirements, and additional tax considerations. An entity should apply the amendments by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. The amendments related to equity securities without readily determinable fair values (including disclosure requirements) should be applied prospectively to equity investments that exist as of the date of adoption of the guidance. The guidance is effective for the Company in the first quarter of 2018 and early adoption is permitted. Aon is currently evaluating the impact that the standard will have on the its Consolidated Financial Statements, as well as the method of transition and period of adoption. Presentation of Deferred Taxes In November 2015, the FASB issued new accounting guidance on the balance sheet presentation of deferred taxes, which requires that deferred tax liabilities and assets be classified as non-current. Aon early adopted this guidance in the second quarter of 2016 and retrospectively applied its requirements to all periods presented. For the year ended December 31, 2015, Aon reclassified its current deferred tax positions to non-current and netted the new balances by jurisdiction, which increased Deferred tax assets by $93 million and decreased Deferred tax liabilities by $139 million on the Consolidated Statement of Financial Position. Debt Issuance Costs In April 2015, the FASB issued new accounting guidance on the presentation of debt issuance costs, which requires debt issuance costs to be presented in the balance sheet as a direct deduction from the associated debt liability. Debt issuance costs related to its line-of-credit arrangements will be shown within Other non-current assets. This guidance was effective for Aon in the first quarter of 2016, which required retrospective application to prior year comparable periods. For the year ended December 31, 2015, Aon reclassified $4 million from Other current assets and $33 million from Other non-current assets to Long-term debt on the Consolidated Statement of Financial Position. Consolidations In February 2015, the FASB issued new accounting guidance on consolidations, which will eliminate the deferral granted to investment companies from applying the variable interest entities guidance and make targeted amendments to the current consolidation guidance. The new guidance applies to all entities involved with limited partnerships or similar entities and requires re-evaluation of these entities under the revised guidance, which could change previous consolidation conclusions. The guidance was effective for the Company in the first quarter of 2016. The adoption of this guidance did not have a material impact on the Company’s Consolidated Financial Statements. Revenue Recognition In May 2014, the FASB issued new accounting guidance on revenue from contracts with customers, which, when effective, will supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principal of the standard is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The standard is effective for Aon in the first quarter of 2018 and early adoption is permitted beginning the first quarter of 2017. Two methods of transition are permitted upon adoption: full retrospective and modified retrospective. Under the full retrospective method, prior periods would be restated under the new revenue standard, providing a comparable view across all periods presented. Under the modified retrospective method, prior periods would not be restated. Rather, revenues and other disclosures for pre-2018 periods would be provided in the notes to the financial statements as previously reported under the current revenue standard. The Company will adopt this standard in the first quarter of 2018 and is evaluating both methods of transition; however, it is currently anticipated that a modified retrospective adoption approach will be used. A preliminary assessment to determine the impacts of the new accounting standard has been performed. The Company is currently implementing accounting and operational processes which will be impacted by the new standard, but is unable to provide information on quantitative impacts at this time. However, the primary impacts of the new standard to the Company’s product and service lines are anticipated to be as follows: The Company currently recognizes revenue for certain brokerage activities within the Risk Solutions business over a period of time either due to the transfer of value to customers or as the remuneration becomes determinable. Under the new standard, this revenue will be recognized on the effective date of the associated policies when control of the policy transfers to the customer. As a result, revenue from these arrangements will be recognized in earlier periods under the new standard in comparison to the current guidance and will change the timing and amount of revenue recognized for annual and interim periods. Similarly, the Company is currently assessing the timing and measurement of revenue recognition under the new standard for outsourcing and consulting operations within the HR Solutions business. Additionally, the new standard provides guidance on accounting for certain revenue-related costs including when to capitalize costs associated with obtaining and fulfilling a contract. These costs are currently expensed as incurred under existing U.S. GAAP. These assets recognized for the costs to obtain and/or fulfill a contract will be amortized on a on a systematic basis that is consistent with the transfer of the services to which the asset relates. The Company is quantifying the nature and amount of costs that would qualify for capitalization and the amount of amortization that will be recognized in each period.

Other Financial Data

Other Financial Data	12 Months Ended
	Dec. 31, 2016
Other Financial Data [Abstract]
Other Financial Data	Other Financial Data Consolidated Statements of Income Information Other Income Other income consists of the following (in millions): Years ended December 31 2016 2015 2014 Equity earnings $ 13 $ 13 $ 12 Net gain on disposals of businesses 39 82 24 Foreign currency remeasurement (loss) gain (2 ) 30 18 (Loss) income on financial instruments (14 ) (24 ) (15 ) Other — (1 ) 5 Total $ 36 $ 100 $ 44 Consolidated Statements of Financial Position Information Allowance for Doubtful Accounts An analysis of the allowance for doubtful accounts is as follows (in millions): Years ended December 31 2016 2015 2014 Balance at January 1 $ 58 $ 74 $ 90 Provision charged to operations 11 13 12 Accounts written off, net of recoveries (14 ) (34 ) (33 ) Foreign currency translation 3 5 5 Balance at December 31 $ 58 $ 58 $ 74 Other Current Assets The components of Other current assets are as follows (in millions): As of December 31 2016 2015 Taxes receivable $ 100 $ 94 Prepaid expenses 125 130 Deferred project costs 87 92 Other 39 13 Total $ 351 $ 329 Fixed Assets, net The components of Fixed assets, net are as follows (in millions): As of December 31 2016 2015 Software $ 948 $ 1,095 Leasehold improvements 452 422 Computer equipment 417 358 Furniture, fixtures and equipment 300 315 Construction in progress 93 76 Other 115 115 Fixed assets, gross 2,325 2,381 Less: Accumulated depreciation 1,560 1,616 Fixed assets, net $ 765 $ 765 Depreciation expense, which includes software amortization, was $232 million , $229 million , and $242 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively. Other Non-Current Assets The components of Other non-current assets are as follows (in millions): As of December 31 2016 2015 Deferred project costs $ 183 $ 210 Investments 119 135 Taxes receivable 82 82 Other 170 165 Total $ 554 $ 592 Other Current Liabilities The components of Other current liabilities are as follows (in millions): As of December 31 2016 2015 Deferred revenue $ 393 $ 394 Taxes payable 78 94 Other 402 331 Total $ 873 $ 819 Other Non-Current Liabilities The components of Other non-current liabilities are as follows (in millions): As of December 31 2016 2015 Taxes payable $ 288 $ 223 Leases 169 166 Deferred revenue 140 159 Compensation and benefits 56 59 Other 191 162 Total $ 844 $ 769

Acquisitions and Dispositions o

Acquisitions and Dispositions of Businesses	12 Months Ended
	Dec. 31, 2016
Business Combinations and Discontinued Operations and Disposal Groups [Abstract]
Acquisitions and Dispositions of Businesses	Acquisitions and Dispositions of Businesses Acquisitions The number of acquisitions completed within each reportable segment is as follows: Years ended December 31 2016 2015 Risk Solutions 5 4 HR Solutions 3 3 Total 8 7 2016 Acquisitions On January 1, 2016, the Company completed the transaction to acquire Globe Events Management, an insurance, retirement, and investment consulting business company based in Australia. On February 1, 2016, the Company completed the transaction to acquire Modern Survey, an employee survey and talent analytics solutions provider based in Minneapolis. On April 11, 2016, the Company completed the transaction to acquire Nexus Insurance Brokers Limited and Bayfair Insurance Centre Limited, insurance brokerage firms located in New Zealand. On June 1, 2016, the Company completed the transaction to acquire Univers Workplace Solutions, a leading elective benefit enrollment and communication services firm based in New Jersey. On August 19, 2016, the Company completed the transaction to acquire Cammack Health LLC, a leading health and benefits consulting firm that serves large health care organizations in the Eastern region of the U.S., including health plans, health systems and employers. On October 31, 2016, the Company completed the transaction to acquire Stroz, Friedberg, Inc., a leading global cyber risk management firm based in New York City, with offices across the U.S. and in London, Zurich, Dubai and Hong Kong. On November 11, 2016 the Company completed the transaction to acquire CoCubes, a leading hiring assessment company based in India. On December 26, 2016, the Company completed the transaction to acquire Admix, a leading health and benefits brokerage and solutions firm based in Brazil. The following table includes the preliminary fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Year ended December 31 2016 Cash $ 891 Deferred and contingent consideration 43 Aggregate consideration transferred 934 Assets acquired: Cash and cash equivalents 12 Receivables, net 52 Goodwill 642 Intangible assets, net 366 Fixed assets, net 30 Other assets 2 Total assets acquired 1,104 Liabilities assumed: Current liabilities 163 Other liabilities 7 Total liabilities assumed 170 Net assets acquired $ 934 Intangible assets are primarily customer-related and contract-based assets; those acquired as part of a business acquisition in 2016 had a weighted average useful economic life of 13 years . Acquisition related costs incurred and recognized within Other general expenses for the year ended December 31, 2016 were $8 million . Total revenue for these acquisitions included in the Company’s Consolidated Statement of Income for the year ended December 31, 2016 was $68 million . The results of operations of these acquisitions are included in the Consolidated Financial Statements as of the acquisition date. The results of operations of the Company would not have been materially different if these acquisitions had been reported from the beginning of the period in which they were acquired. 2015 Acquisitions The following table includes the preliminary fair values of consideration transferred and intangible assets acquired as a result of the Company’s acquisitions (in millions): Year ended December 31 2015 Consideration $ 27 Intangible assets: Goodwill $ 18 Other intangible assets 6 Total intangible assets $ 24 The results of operations of these acquisitions are included in the Consolidated Financial Statements as of the acquisition date. The results of operations of the Company would not have been materially different if these acquisitions had been reported from the beginning of the period in which they were acquired. Dispositions The number of dispositions completed within each reportable segment is as follows: Years ended December 31 2016 2015 2014 Risk Solutions 4 4 2 HR Solutions 1 3 0 Total 5 7 2 Total pretax gains, net of losses, recognized were $39 million , $82 million , and $24 million , respectively, for the years ended December 31, 2016 , 2015 , and 2014 . Gains and losses recognized as a result of a disposition are included in Other income in the Consolidated Statements of Income.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2016
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 by reportable segment for the years ended December 31, 2016 and 2015 , respectively, are as follows (in millions): Risk Solutions HR Solutions Total Balance as of January 1, 2015 $ 5,911 $ 2,949 $ 8,860 Goodwill related to current year acquisitions 2 16 18 Goodwill related to disposals (1 ) (76 ) (77 ) Goodwill related to prior year acquisitions — — — Foreign currency translation (319 ) (34 ) (353 ) Balance as of December 31, 2015 $ 5,593 $ 2,855 $ 8,448 Goodwill related to current year acquisitions 632 10 642 Goodwill related to disposals (8 ) (26 ) (34 ) Goodwill related to prior year acquisitions 4 — 4 Foreign currency translation (268 ) (45 ) (313 ) Balance as of December 31, 2016 $ 5,953 $ 2,794 $ 8,747 Other intangible assets by asset class are as follows (in millions): As of December 31 2016 2015 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Intangible assets with indefinite lives: Tradenames $ 998 $ — $ 998 $ 1,019 $ — $ 1,019 Intangible assets with finite lives: Customer related and contract based 3,108 1,971 1,137 2,886 1,809 1,077 Technology and other 574 486 88 541 457 84 Total $ 4,680 $ 2,457 $ 2,223 $ 4,446 $ 2,266 $ 2,180 Amortization expense from finite-lived intangible assets was $277 million , $314 million and $352 million during 2016 , 2015 and 2014 , respectively. The estimated future amortization for finite-lived intangible assets as of December 31, 2016 is as follows (in millions): Risk Solutions HR Solutions Total 2017 $ 123 $ 136 $ 259 2018 118 91 209 2019 107 73 180 2020 97 61 158 2021 66 53 119 Thereafter 239 61 300 Total $ 750 $ 475 $ 1,225

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt	Debt The following is a summary of outstanding debt (in millions): As of December 31 2016 2015 (1) 3.875% Senior Notes due December 2025 $ 744 $ — 5.00% Senior Notes due September 2020 598 597 4.75% Senior Notes due May 2045 592 591 3.50% Senior Notes due June 2024 594 593 4.60% Senior Notes due June 2044 543 543 2.875% Senior Notes due May 2026 (EUR 500M) 516 541 8.205% Junior Subordinated Notes due January 2027 521 521 3.125% Senior Notes due May 2016 — 500 2.80% Senior Notes due March 2021 397 396 4.00% Senior Notes due November 2023 347 347 6.25% Senior Notes due September 2040 295 295 4.76% Senior Notes due March 2018 (CAD 375M) 277 270 4.45% Senior Notes due May 2043 246 246 4.25% Senior Notes due December 2042 197 195 Commercial paper 329 50 Other 9 15 Total debt 6,205 5,700 Less short-term and current portion of long-term debt 336 562 Total long-term debt $ 5,869 $ 5,138 (1) Amended to reflect the adoption of new guidance related to the presentation of debt issuance costs as described in Note 2 “Summary of Significant Accounting Principles and Practices.” On May 27, 2016, $500 million of 3.125% Senior Notes due May 2016 issued by Aon Corporation matured and were repaid in full. On March 1, 2016, Aon plc issued $750 million of 3.875% Senior Notes due December 2025. The Company used the proceeds of the issuance for general corporate purposes. On November 13, 2015, Aon plc issued $400 million of 2.80% Senior Notes due March 2021. The Company used the proceeds of the issuance for general corporate purposes. On September 30, 2015, $600 million of 3.50% Senior Notes issued by Aon Corporation matured and were repaid in full. On May 20, 2015, Aon plc issued $600 million of 4.750% Senior Notes due May 2045. The Company used the proceeds of the issuance for general corporate purposes. Each of the notes issued by Aon plc and described above is fully and unconditionally guaranteed by Aon Corporation. The 4.76% Senior Notes due March 2018 identified in the table above were issued by a Canadian subsidiary of Aon Corporation and are fully and unconditionally guaranteed by Aon plc and Aon Corporation. Refer to Note 16 “Guarantee of Registered Securities” for additional information regarding guarantees of outstanding debt securities. Each of the notes described above and identified in the table above contains customary representations, warranties and covenants, and the Company was in compliance with all such covenants as of December 31, 2016 . Repayments of total debt are as follows (in millions): 2017 $ 336 2018 278 2019 — 2020 600 2021 400 Thereafter 4,700 Total Repayments 6,314 Unamortized discount, premium, and debt issuance cost (109 ) Total Debt $ 6,205 Revolving Credit Facilities As of December 31, 2016 , Aon plc had two primary committed credit facilities outstanding: its $400 million U.S. credit facility expiring in March 2017 (the “2017 Facility”) and its $900 million multi-currency U.S. credit facility expiring in February 2021 (the “2021 Facility”). The Company plans to let the 2017 facility expire but may evaluate obtaining additional committed credit in the future. Each of these facilities includes customary representations, warranties and covenants, including financial covenants that require Aon plc to maintain specified ratios of adjusted consolidated EBITDA to consolidated interest expense and consolidated debt to adjusted consolidated EBITDA, in each case, tested quarterly. At December 31, 2016 , Aon plc did not have borrowings under either the 2017 Facility or the 2021 Facility, and was in compliance with all covenants contained therein during the twelve months ended December 31, 2016 . Commercial Paper Aon Corporation, a wholly-owned subsidiary of Aon plc, has established a U.S. commercial paper program, which provides for commercial paper to be issued in an aggregate principal amount of up to $900 million , and Aon plc has established a European multi-currency commercial paper program that provides for commercial paper to be issued in an aggregate principal amount of up to €300 million . The U.S. commercial paper program is fully and unconditionally guaranteed by Aon plc and the European commercial paper program is fully and unconditionally guaranteed by Aon Corporation. In the aggregate, the Company had $329.2 million and $50.0 million of commercial paper outstanding at December 31, 2016 and 2015 , respectively, which was included in Short-term debt and current portion of long-term debt in the Company’s Consolidated Statements of Financial Position. The weighted average commercial paper outstanding for 2016 and 2015 was $265.0 million and $402.0 million , respectively. The weighted average interest rate of the commercial paper outstanding during 2016 and 2015 was 0.22% and 0.50% , respectively.

Lease Commitments

Lease Commitments	12 Months Ended
	Dec. 31, 2016
Leases, Operating [Abstract]
Lease Commitments	Lease Commitments The Company leases office facilities, equipment, and automobiles under non-cancelable operating leases. These leases expire at various dates and may contain renewal and expansion options. In addition to base rental costs, occupancy lease agreements generally provide for rent escalations resulting from increased assessments for real estate taxes and other charges. The Company’s lease obligations are primarily for the use of office space. Rental expenses (including amounts applicable to taxes, insurance and maintenance) for operating leases are as follows (in millions): Years ended December 31 2016 2015 2014 Rental expense $ 400 $ 454 $ 455 Less: Sub lease rental income (64 ) (83 ) (75 ) Net rental expense $ 336 $ 371 $ 380 At December 31, 2016 , 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): Years ended December 31, 2016 Gross rental commitments Rentals from subleases Net rental commitments 2017 $ 355 $ (55 ) $ 300 2018 317 (44 ) 273 2019 283 (38 ) 245 2020 237 (34 ) 203 2021 214 (33 ) 181 Thereafter 696 (47 ) 649 Total minimum payments required $ 2,102 $ (251 ) $ 1,851

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income before income tax and the provision for income tax consist of the following (in millions): Years ended December 31 2016 2015 2014 Income before income taxes: U.K. $ (202 ) $ 149 $ 347 U.S. (104 ) (51 ) (55 ) Other 1,975 1,591 1,473 Total $ 1,669 $ 1,689 $ 1,765 Income tax expense (benefit): Current: U.K. $ (54 ) $ 43 $ 1 U.S. federal 94 137 156 U.S. state and local — 54 75 Other 223 256 236 Total current tax expense $ 263 $ 490 $ 468 Deferred tax expense (benefit): U.K. $ 59 $ (39 ) $ 38 U.S. federal (47 ) (140 ) (133 ) U.S. state and local 6 (14 ) (24 ) Other (42 ) (30 ) (15 ) Total deferred tax benefit $ (24 ) $ (223 ) $ (134 ) Total income tax expense $ 239 $ 267 $ 334 Income before income taxes shown above is based on the location of the business unit to which such earnings are attributable for tax purposes. In addition, because the earnings shown above may in some cases be subject to taxation in more than one country, the income tax provision shown above as U.K., U.S. or Other may not correspond to the geographic attribution of the earnings. The Company performs a reconciliation of the income tax provisions based on its domicile and statutory rate at each reporting period. The 2016 , 2015 , and 2014 reconciliations are based on the U.K. statutory corporate tax rate of 20.0% , 20.3% , and 21.5% , respectively. The reconciliation to the provisions reflected in the Consolidated Financial Statements is as follows: Years ended December 31 2016 2015 2014 Statutory tax rate 20.0% 20.3% 21.5% U.S. state income taxes, net of U.S. federal benefit 0.7 0.5 1.5 Taxes on international operations (1) (8.5) (6.0) (8.9) Nondeductible expenses 1.2 2.2 1.7 Adjustments to prior year tax requirements (1.0) (1.3) 0.9 Adjustments to valuation allowances (1.8) (1.2) 0.6 Change in uncertain tax positions 3.0 1.4 1.7 Other — net 0.7 (0.1) (0.1) Effective tax rate 14.3% 15.8% 18.9% (1) The Company determines the adjustment for taxes on international operations based on the difference between the statutory tax rate applicable to earnings in each foreign jurisdiction and the enacted rate of 20.0% , 20.3% and 21.5% at December 31, 2016 , 2015 , and 2014 , respectively. The benefit to the Company’s effective income tax rate from taxes on international operations relates to benefits from lower-taxed global operations, primarily due to the use of global funding structures. The components of the Company’s deferred tax assets and liabilities are as follows (in millions): As of December 31 2016 2015 Deferred tax assets: Employee benefit plans $ 661 $ 635 Net operating/capital loss and tax credit carryforwards 399 336 Accrued interest 166 293 Other accrued expenses 102 98 Brokerage fee arrangements (1) 66 66 Deferred revenue 57 65 Investment basis differences 48 56 Other 60 57 Total 1,559 1,606 Valuation allowance on deferred tax assets (130 ) (162 ) Total $ 1,429 $ 1,444 Deferred tax liabilities: Intangibles and property, plant and equipment $ (982 ) $ (961 ) Other accrued expenses (101 ) (99 ) Deferred costs (20 ) (30 ) Unrealized foreign exchange gains (26 ) (29 ) Unremitted earnings (29 ) (18 ) Other (50 ) (44 ) Total $ (1,208 ) $ (1,181 ) Net deferred tax asset $ 221 $ 263 (1) Refer to Note 1 “Basis of Presentation” for details regarding the Revision of Previously Issued Financial Statements. Deferred income taxes (assets and liabilities have been netted by jurisdiction) have been classified in the Consolidated Statements of Financial Position as follows (in millions): As of December 31 2016 2015 Deferred tax assets — non-current (2) $ 322 $ 300 Deferred tax liabilities — non-current (2) (101 ) (37 ) Net deferred tax asset $ 221 $ 263 (2) For the year ended December 31, 2015, Aon reclassified its current deferred tax positions to non-current and netted the new balances by jurisdiction. Refer to Note 2 “Summary of Significant Accounting Principles and Practices” for additional details. Valuation allowances have been established primarily with regard to the tax benefits of certain net operating loss, capital loss and interest expense carryforwards. Valuation allowances decreased by $32 million as of December 31, 2016 , when compared to December 31, 2015 , primarily attributable to the reversal of a valuation allowance and the impact of foreign currency translation. The Company recognized, as an adjustment to additional paid-in-capital, income tax benefits attributable to employee stock compensation of $(4) million , $126 million and $89 million in 2016 , 2015 , and 2014 , respectively. The year-over-year change is primarily attributable to excess tax benefits not recorded in 2016 because the deduction did not decrease income taxes payable. Deferred income taxes of $11 million were accrued in 2016 on undistributed earnings that are not permanently reinvested. Undistributed earnings of non-U.S. entities were approximately $2.3 billion at December 31, 2016 . U.S. income taxes have not been provided on these undistributed earnings because they are considered to be permanently reinvested in those subsidiaries. It is not practicable to estimate the amount of unrecognized deferred tax liabilities, if any, for these undistributed foreign earnings. The Company had the following operating and capital loss carryforwards (in millions): As of December 31 2016 2015 UK Operating loss carryforwards $ 325 $ 449 Capital loss carryforwards 294 360 US Federal operating loss carryforwards $ 196 $ 8 State operating loss carryforwards 474 443 Other Non-US Operating loss carryforwards $ 350 $ 245 Capital loss carryforwards 218 206 As of December 31, 2016, the Company had $126 million of federal operating loss carryforwards and $110 million of state operating loss carryforwards for which a benefit will be recorded in APIC when realized. The U.K. operating losses and capital losses have an indefinite carryforward. The federal operating loss carryforwards as of December 31, 2016 expire at various dates from 2020 to 2036 and the state operating losses as of December 31, 2016 expire at various dates from 2017 to 2036. Operating and capital losses in other non-US jurisdictions have various carryforward periods and will begin to expire in 2019. During 2012, the Company was granted a tax holiday for the period from October 1, 2012 through September 30, 2022, with respect to withholding taxes and certain income derived from services in Singapore. This tax holiday and reduced withholding tax rate may be extended when certain conditions are met or may be terminated early if certain conditions are not met. The benefit realized was approximately $46 million , $23 million , and $7 million during the years ended December 31, 2016 , 2015 , and 2014 , respectively. The impact of this tax holiday on diluted earnings per share was $0.17 , $0.08 , and $0.02 during the years ended December 31, 2016, 2015, and 2014, respectively. Uncertain Tax Positions The following is a reconciliation of the Company’s beginning and ending amount of uncertain tax positions (in millions): 2016 2015 Balance at January 1 $ 238 $ 211 Additions based on tax positions related to the current year 36 31 Additions for tax positions of prior years 20 53 Reductions for tax positions of prior years (12 ) (18 ) Settlements — (32 ) Business combinations 2 — Lapse of statute of limitations (5 ) (5 ) Foreign currency translation (1 ) (2 ) Balance at December 31 $ 278 $ 238 The Company’s liability for uncertain tax positions as of December 31, 2016 , 2015 , and 2014 , includes $240 million , $200 million , and $174 million , respectively, related to amounts that would impact the effective tax rate if recognized. It is possible that the amount of unrecognized tax benefits may change in the next twelve months; however, the Company does not expect the change to have a significant impact on its consolidated statements of income or consolidated balance sheets. These changes may be the result of settlements of ongoing audits. At this time, an estimate of the range of the reasonably possible outcomes within the twelve months cannot be made. The Company recognizes interest and penalties related to uncertain tax positions in its provision for income taxes. The Company accrued potential interest and penalties of $15 million , $2 million , and $4 million in 2016 , 2015 , and 2014 , respectively. The Company recorded a liability for interest and penalties of $48 million , $33 million , and $31 million as of December 31, 2016 , 2015 , and 2014 , respectively. The Company and its subsidiaries file income tax returns in their respective jurisdictions. The Company has substantially concluded all U.S. federal income tax matters for years through 2007. Material U.S. state and local income tax jurisdiction examinations have been concluded for years through 2005. The Company has concluded income tax examinations in its primary non-U.S. jurisdictions through 2005.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity Distributable Reserves As a U.K. incorporated company, the Company is required under U.K. law to have available “distributable reserves” to make share repurchases or pay dividends to shareholders. Distributable reserves may be created through the earnings of the U.K. parent company and, amongst other methods, through a reduction in share capital approved by the English Companies Court. Distributable reserves are not linked to a U.S. GAAP reported amount (e.g., retained earnings). As of December 31, 2016 and 2015 , the Company had distributable reserves in excess of $1.6 billion and $2.1 billion , respectively. Ordinary Shares In April 2012, the Company’s Board of Directors authorized a share repurchase program under which up to $5.0 billion of Class A Ordinary Shares may be repurchased (“2012 Share Repurchase Program”). In November 2014, the Company’s Board of Directors authorized a new $5.0 billion share repurchase program in addition to the existing program (“2014 Share Repurchase Program” and, together with the 2012 Share Repurchase Program, the “Repurchase Programs”). Subsequent to the close of the fourth quarter 2016, the Board of Directors authorized a $5.0 billion increase to the existing remaining authorization under its share repurchase program. Under each program, 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. During 2016 , the Company repurchased 12.2 million shares at an average price per share of $102.66 for a total cost of $1.3 billion under the 2014 Share Repurchase Program. The Company recorded an additional $6 million of transaction costs associated with the repurchase to retained earnings during 2016. During 2015 , the Company repurchased 16.0 million shares at an average price per share of $97.04 for a total cost of $1.6 billion under the Repurchase Programs. In August 2015, the $5 billion of Class A Ordinary Shares authorized under the 2012 Share Repurchase Program was exhausted. At December 31, 2016, the remaining authorized amount for share repurchase under the 2014 Share Repurchase Program is $2.8 billion . Under the Repurchase Programs, the Company has repurchased a total of 90.2 million shares for an aggregate cost of $7.2 billion . Net Income Per Share Weighted average shares outstanding are as follows (in millions): Year ended December 31, 2016 2015 2014 Basic weighted-average ordinary shares outstanding 268.1 280.8 295.5 Dilutive effect of potentially issuable shares 2.2 3.0 4.1 Diluted weighted-average ordinary shares outstanding 270.3 283.8 299.6 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 in 2016 , 2015 , or 2014 . Dividends During 2016 , 2015 , and 2014 , the Company paid dividends on its Class A Ordinary Shares of $345.0 million , $323.0 million , and $273.0 million , respectively. Dividends paid per Class A Ordinary Share were $1.29 , $1.15 and $0.92 for the years ended December 31, 2016 , 2015 , and 2014 respectively. Accumulated Other Comprehensive Loss Changes in Accumulated other comprehensive loss by component, net of related tax, are as follows (in millions): Change in Fair Value of Financial Instruments (1) Foreign Currency Translation Adjustments Post-Retirement Benefit Obligation (2) Total Balance at January 1, 2014 $ (21 ) $ 169 $ (2,522 ) $ (2,374 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (13 ) (492 ) (563 ) (1,068 ) Tax benefit 4 (12 ) 229 221 Other comprehensive loss before reclassifications, net (9 ) (504 ) (334 ) (847 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 20 — 106 126 Tax benefit (7 ) — (32 ) (39 ) Amounts reclassified from accumulated other comprehensive loss, net 13 — 74 87 Net current period other comprehensive (loss) income 4 (504 ) (260 ) (760 ) Balance at December 31, 2014 (17 ) (335 ) (2,782 ) (3,134 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (4 ) (467 ) 82 (389 ) Tax benefit 1 31 (9 ) 23 Other comprehensive loss before reclassifications, net (3 ) (436 ) 73 (366 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 11 — 117 128 Tax benefit (16 ) — (35 ) (51 ) Amounts reclassified from accumulated other comprehensive loss, net (5 ) — 82 77 Net current period other comprehensive (loss) income (8 ) (436 ) 155 (289 ) Balance at December 31, 2015 (25 ) (771 ) (2,627 ) (3,423 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (25 ) (490 ) (276 ) (791 ) Tax benefit 6 (3 ) 74 77 Other comprehensive loss before reclassifications, net (19 ) (493 ) (202 ) (714 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 10 — 322 332 Tax benefit (3 ) — (104 ) (107 ) Amounts reclassified from accumulated other comprehensive loss, net 7 — 218 225 Net current period other comprehensive (loss) income (12 ) (493 ) 16 (489 ) Balance at December 31, 2016 $ (37 ) $ (1,264 ) $ (2,611 ) $ (3,912 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Other income (2) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Compensation and benefits

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Employee Benefits	Employee Benefits Defined Contribution Savings Plans Aon maintains defined contribution savings plans for the benefit of its U.S., U.K., Netherlands and Canada employees. The expense recognized for these plans is included in Compensation and benefits in the Consolidated Statements of Income, as follows (in millions): Years ended December 31 2016 2015 2014 U.S. $ 142 $ 133 $ 123 U.K. 43 42 42 Netherlands and Canada 27 25 30 Total $ 212 $ 200 $ 195 Pension and Other Post-retirement Benefits The Company sponsors defined benefit pension and post-retirement health and welfare plans that provide retirement, medical, and life insurance benefits. The post-retirement healthcare plans are contributory, with retiree contributions adjusted annually, and the life insurance and pension plans are generally noncontributory. The significant U.S., U.K., Netherlands and Canadian pension plans are closed to new entrants. Pension Plans The following tables provide a reconciliation of the changes in the projected benefit obligations and fair value of assets for the years ended December 31, 2016 and 2015 and a statement of the funded status as of December 31, 2016 and 2015 , for the material U.K. plans, U.S. plans and other major plans, which are located in the Netherlands and Canada. These plans represent approximately 92% of the Company’s projected benefit obligations. U.K. U.S. Other (millions) 2016 2015 2016 2015 2016 2015 Change in projected benefit obligation At January 1 $ 4,985 $ 5,529 $ 3,160 $ 3,350 $ 1,177 $ 1,399 Service cost — 1 — — — — Interest cost 158 198 111 131 29 33 Plan amendment (20 ) 27 — — — (10 ) Settlements (159 ) — (281 ) — — — Plan transfer and acquisitions — (2 ) — (18 ) — — Actuarial loss (gain) 32 (83 ) (43 ) (25 ) (7 ) 24 Benefit payments (242 ) (217 ) (139 ) (133 ) (39 ) (38 ) Change in discount rate 1,079 (247 ) 100 (145 ) 100 (66 ) Foreign currency impact (959 ) (221 ) — — (33 ) (165 ) At December 31 $ 4,874 $ 4,985 $ 2,908 $ 3,160 $ 1,227 $ 1,177 Accumulated benefit obligation at end of year $ 4,874 $ 4,985 $ 2,908 $ 3,160 $ 1,191 $ 1,135 Change in fair value of plan assets At January 1 $ 5,903 $ 6,224 $ 1,951 $ 2,036 $ 1,019 $ 1,161 Actual return on plan assets 1,233 91 116 (60 ) 111 8 Employer contributions 67 65 36 108 20 21 Settlements (159 ) — (281 ) — — — Plan transfer and acquisitions — (3 ) — — — — Benefit payments (242 ) (217 ) (139 ) (133 ) (39 ) (38 ) Foreign currency impact (1,127 ) (257 ) — — (35 ) (133 ) At December 31 $ 5,675 $ 5,903 $ 1,683 $ 1,951 $ 1,076 $ 1,019 Market related value at end of year $ 5,675 $ 5,903 $ 1,819 $ 2,064 $ 1,076 $ 1,019 Amount recognized in Statement of Financial Position at December 31 Funded status $ 801 $ 918 $ (1,225 ) $ (1,209 ) $ (151 ) $ (158 ) Unrecognized prior-service cost 19 46 6 9 (6 ) (7 ) Unrecognized loss 1,237 1,465 1,612 1,723 400 389 Net amount recognized $ 2,057 $ 2,429 $ 393 $ 523 $ 243 $ 224 In March 2016, the Company entered into an insurance contract that covers a portion of the assets within select U.K. pension schemes. The transaction resulted in a decrease in Prepaid pension assets and Accumulated other comprehensive income of $267 million . Amounts recognized in the Consolidated Statements of Financial Position consist of (in millions): U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Prepaid benefit cost (1) $ 836 $ 1,012 $ — $ — $ — $ — Accrued benefit liability (2) (35 ) (94 ) (1,225 ) (1,209 ) (151 ) (158 ) Accumulated other comprehensive loss 1,256 1,511 1,618 1,732 394 382 Net amount recognized $ 2,057 $ 2,429 $ 393 $ 523 $ 243 $ 224 (1) Included in Prepaid pension (2) Included in Other current liabilities and Pension, other post retirement, and post employment liabilities Amounts recognized in Accumulated other comprehensive loss (income) that have not yet been recognized as components of net periodic benefit cost at December 31, 2016 and 2015 consist of (in millions): U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Net loss $ 1,237 $ 1,465 $ 1,612 $ 1,723 $ 400 $ 389 Prior service cost (income) 19 46 6 9 (6 ) (7 ) Total $ 1,256 $ 1,511 $ 1,618 $ 1,732 $ 394 $ 382 In 2016 , U.S. plans with a projected benefit obligation (“PBO”) and an accumulated benefit obligation (“ABO”) in excess of the fair value of plan assets had a PBO of $2.9 billion , an ABO of $2.9 billion , and plan assets with a fair value of $1.7 billion . U.K. plans with a PBO in excess of the fair value of plan assets had a PBO of $1.2 billion and plan assets with a fair value of $1.1 billion , and plans with an ABO in excess of the fair value of plan assets had an ABO of $1.2 billion and plan assets with a fair value of $1.1 billion . Other plans with a PBO in excess of the fair value of plan assets had a PBO of $1.2 billion and plan assets with a fair value of $1.0 billion , and plans with an ABO in excess of the fair value of plan assets had an ABO of $1.1 billion and plan assets with a fair value of $1.0 billion . In 2015 , U.S. plans with a PBO and an ABO in excess of the fair value of plan assets had a PBO of $3.2 billion , an ABO of $3.2 billion , and plan assets of $2.0 billion . U.K. plans with a PBO in excess of the fair value of plan assets had a PBO of $1.2 billion and plan assets with a fair value of $1.1 billion , and plans with an ABO in excess of the fair value of plan assets had an ABO of $1.2 billion and plan assets with a fair value of $1.1 billion . Other plans with a PBO in excess of the fair value of plan assets had a PBO of $1.2 billion and plan assets with a fair value of $1.0 billion , and plans with an ABO in excess of the fair value of plan assets had an ABO of $1.1 billion and plan assets with a fair value of $1.0 billion . The following table provides the components of net periodic benefit (income) cost for the plans (in millions): U.K. U.S. Other 2016 2015 2014 2016 2015 2014 2016 2015 2014 Service cost $ — $ 1 $ 1 $ — $ — $ 2 $ — $ — $ — Interest cost 158 198 230 111 131 129 29 33 47 Expected return on plan assets, net of administration expenses (243 ) (307 ) (326 ) (156 ) (154 ) (157 ) (48 ) (50 ) (59 ) Amortization of prior-service cost 2 1 1 2 2 2 — — — Amortization of net actuarial loss 31 41 52 50 54 42 10 11 10 Net periodic benefit (income) cost (52 ) (66 ) (42 ) 7 33 18 (9 ) (6 ) (2 ) Settlement expense 61 — — 158 — — — — — Curtailment gain and other — — — — — — — — (2 ) Total net periodic benefit cost (income) $ 9 $ (66 ) $ (42 ) $ 165 $ 33 $ 18 $ (9 ) $ (6 ) $ (4 ) Beginning in 2016, the Company has elected to utilize a full yield curve approach in the estimation of the service and interest cost components of net periodic pension and post-retirement benefit cost for its major pension and other post-retirement benefit plans by applying the specific spot rates along the yield curve used in the determination of the benefit obligation to the relevant projected cash flows. In 2015 and prior years, the Company estimated these components of net periodic pension and post-retirement benefit cost by applying a single weighted-average discount rate, derived from the yield curve used to measure the benefit obligation at the beginning of the period. In March 2016, the Company announced a plan to offer a voluntary one-time lump sum payment option to certain eligible former employees under one 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 the second quarter of 2016. In total, lump sum payments from plan assets of £116 million ( $159 million using June 30, 2016 exchange rates) were paid. As a result of this settlement, the Company remeasured the assets and liabilities of the U.K. pension plan during the second quarter of 2016, which in aggregate resulted in a reduction to the projected benefit obligation of £103 million ( $141 million using June 30, 2016 Exchange rates) as well as a non-cash settlement charge of £42 million ( $61 million using average June 2016 exchange rate) in the second quarter of 2016. In August 2016, the Company announced a plan to offer a voluntary one-time lump sum payment option to certain eligible former employees under one of the Company’s U.S. pension plans, that if accepted, would settle the Company’s pension obligations to them. The lump sum cash payment offer closed during the fourth quarter of 2016. In total, lump sum payments from plan assets of $281 million were paid. As a result of this settlement, the Company remeasured the assets and liabilities of the U.S. pension plan during the fourth quarter of 2016, which in aggregate resulted in a reduction to the projected benefit obligation of $325 million as well as a non-cash settlement charge of $158 million in the fourth quarter of 2016. The weighted-average assumptions used to determine benefit obligations are as follows: U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Discount rate 2.77% 3.96% 3.53-4.11% 3.69-4.43% 1.85-3.81% 2.43-3.96% Rate of compensation increase 3.70 - 4.20% 3.63-4.13% N/A N/A 1.00-3.50% 2.00-3.50% Underlying price inflation 1.83% 1.88% N/A N/A 2.00-2.50% 2.00-2.50% The weighted-average assumptions used to determine the net periodic benefit cost are as follows: U.K. U.S. Other 2016 2015 2014 2016 2015 2014 2016 2015 2014 Discount rate 3.96% 3.70% 4.55% 3.69 - 4.43% 3.37 - 4.08% 3.97 - 4.87% 2.43 - 3.96% 2.03 - 3.91% 3.60 - 4.71% Expected return on plan assets, net of administration expenses 4.55% 5.09% 6.00% 7.81% 7.96% 8.80% 3.47 - 4.95% 3.99 - 5.21% 4.70 - 6.50% Rate of compensation increase 3.63 - 4.13% 3.55 - 4.05% 3.70 - 4.40% N/A N/A N/A 2.00 - 3.50% 2.25 - 3.50% 2.25 - 3.50% The amounts in Accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost during 2017 are $52 million in the U.S. and $41 million outside the U.S. Expected Return on Plan Assets To determine the expected long-term rate of return on plan assets, the historical performance, investment community forecasts and current market conditions are analyzed to develop expected returns for each asset class used by the plans. The expected returns for each asset class are weighted by the target allocations of the plans. The expected return on plan assets in the U.S. of 7.81% reflects a portfolio that is seeking asset growth through a higher equity allocation while maintaining prudent risk levels. The portfolio contains certain assets that have historically resulted in higher returns and other financial instruments to minimize downside risk. No plan assets are expected to be returned to the Company during 2017 . Fair value of plan assets The Company determined the fair value of plan assets through numerous procedures based on the asset class and available information. Refer to Note 13 “Fair Value Measurements and Financial Instruments” for a description of the procedures performed to determine the fair value of the plan assets. The fair values of the Company’s U.S. pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Asset Category Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 100 $ 100 $ — $ — Equity investments: Large cap domestic 268 268 — — Small cap domestic 15 15 — — International 64 64 — — Equity derivatives 81 78 3 — Pooled funds: International (2) 196 — — — Small cap domestic (2) 52 — — — Fixed income investments: (3) Corporate bonds 105 — 105 — Government and agency bonds 132 76 56 — Asset-backed securities — — — — Fixed income derivatives 65 65 — — Pooled funds: Corporate bonds (2) 255 — — — Other investments: Commodity derivatives (4) 22 — 22 — Real estate and REITS (5) 61 61 — — Alternative investments (2) (6) 267 — — — Total $ 1,683 $ 727 $ 186 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of corporate and government bonds, asset-backed securities, and fixed income derivatives. (4) Consists of long-dated options and swaps on a commodity index. (5) Consists of exchange traded real estate investment trusts (“REITS”). (6) Consists of limited partnerships, private equity and hedge funds. Fair Value Measurements Using Asset Category Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 33 $ 33 $ — $ — Equity investments: Large cap domestic 299 299 — — Small cap domestic 30 30 — — International 52 52 — — Equity derivatives 203 170 33 — Pooled funds: International (2) 210 — — — Small cap domestic (2) 58 — — — Fixed income investments: (3) Corporate bonds 148 — 148 — Government and agency bonds 128 52 76 — Asset-backed securities — — — — Fixed income derivatives 69 47 22 — Pooled funds: Corporate bonds (2) 336 — — — Other investments: Commodity derivatives (4) 13 — 13 — Real estate and REITS (5) 67 67 — — Alternative investments (2) (6) 305 — — — Total $ 1,951 $ 750 $ 292 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of corporate and government bonds, asset-backed securities, and fixed income derivatives. (4) Consists of long-dated options on a commodity index. (5) Consists of exchange traded REITS. (6) Consists of limited partnerships, private equity and hedge funds. The fair values of the Company’s major U.K. pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 86 $ 86 $ — $ — Equity investments: Global 135 135 — — Pooled funds: Global (2) 365 — — — Europe (2) 18 — — — Fixed income investments: (3) Derivatives (4) 10 — 10 — Fixed income securities (5) 2,129 1,726 403 — Annuities 1,773 — — 1,773 Pooled funds: Derivatives (2) 62 — — — Fixed income securities (2) 223 — — — Other investments: Real estate (2) (6) 101 — — — Alternative investments (2) (7) 773 — — — Total $ 5,675 $ 1,947 $ 413 $ 1,773 (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of various equity, fixed income, commodity, and real estate mutual fund type investment vehicles. (4) Consists of equity securities and equity derivatives. (5) Consists of corporate and government bonds and fixed income derivatives. (6) Consists of property funds and trusts holding direct real estate investments. (7) Consists of limited partnerships, private equity and hedge funds. Fair Value Measurements Using Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 159 $ 159 $ — $ — Equity investments: Derivatives 66 — 66 — Global 133 133 — — Pooled funds: Global (2) 360 — — — Europe (2) 17 — — — Fixed income investments: (3) Derivatives (4) 111 — 111 — Fixed income securities (5) 3,145 2,268 877 — Annuities 827 — — 827 Pooled funds: Fixed income securities (2) 283 — — — Other investments: Real estate (2) (6) 85 — — — Alternative investments (2) (7) 717 — — — Total $ 5,903 $ 2,560 $ 1,054 $ 827 (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of various equity, fixed income, commodity, and real estate mutual fund type investment vehicles. (4) Consists of equity securities and equity derivatives. (5) Consists of corporate and government bonds and fixed income derivatives. (6) Consists of property funds and trusts holding direct real estate investments. (7) Consists of limited partnerships, private equity and hedge funds. The following table presents the changes in the Level 3 fair-value category in the Company’s U.K. pension plans for the years ended December 31, 2016 and December 31, 2015 (in millions): Fair Value Measurements Using Level 3 Inputs Annuities Balance at January 1, 2015 $ 836 Actual return on plan assets: Relating to assets still held at December 31, 2015 (32 ) Purchases, sales and settlements—net 58 Foreign exchange (35 ) Balance at December 31, 2015 827 Actual return on plan assets: Relating to assets still held at December 31, 2016 7 Purchases, sales and settlements—net 1,248 Foreign exchange (309 ) Balance at December 31, 2016 $ 1,773 The fair values of the Company’s other major pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 11 $ 11 $ — $ — Equity investments: Pooled funds: Global (1) 322 — — — North America (1) 36 — — — Derivatives (1) 20 — — — Fixed income investments: Fixed income securities (2) 166 — 166 — Derivatives (2) 37 — 37 — Pooled funds: Fixed income securities (1) 469 — — — Other investments: Alternative investments (1) (3) 9 — — — Pooled funds: REITS (1) (4) 6 — — — Total $ 1,076 $ 11 $ 203 $ — (1) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (2) Consists of corporate and government bonds and fixed income derivatives. (3) Consists of limited partnerships, private equity and hedge funds. (4) Consists of property funds and trusts holding direct real estate investments. Fair Value Measurements Using Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 11 $ 11 $ — $ — Equity investments: Pooled funds: Global (1) 270 — — — North America (1) 37 — — — Derivatives (1) 21 — — — Fixed income investments: Fixed income securities (2) 30 — 30 — Derivatives (2) 48 — 48 — Pooled funds: Fixed income securities (1) 576 — — — Derivatives (1) 12 — — — Other investments: Alternative investments (1) (3) 9 — — — Pooled funds: Commodities (1) 2 — — — REITS (1) (4) 3 — — — Total $ 1,019 $ 11 $ 78 $ — (1) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (2) Consists of corporate and government bonds and fixed income derivatives. (3) Consists of limited partnerships, private equity and hedge funds. (4) Consists of property funds and trusts holding direct real estate investments. Investment Policy and Strategy The U.S. investment policy, as established by the Aon Retirement Plan Governance and Investment Committee (“RPGIC”), seeks reasonable asset growth at prudent risk levels within target allocations, which are 41% equity investments, 30% fixed income investments, and 29% other investments. Aon believes that plan assets are well-diversified and are of appropriate quality. The investment portfolio asset allocation is reviewed quarterly and re-balanced to be within policy target allocations. The investment policy is reviewed at least annually and revised, as deemed appropriate by the RPGIC. The investment policies for international plans are generally established by the local pension plan trustees and seek to maintain the plans’ ability to meet liabilities and to comply with local minimum funding requirements. Plan assets are invested in diversified portfolios that provide adequate levels of return at an acceptable level of risk. The investment policies are reviewed at least annually and revised, as deemed appropriate to ensure that the objectives are being met. At December 31, 2016 , the weighted average targeted allocation for the U.K. and non-U.S. plans was 14% for equity investments, 77% for fixed income investments, and 9% for other investments. Cash Flows Contributions Based on current assumptions, in 2017 , the Company expects to contribute approximately $80 million , $87 million , and $18 million to its U.K., U.S. and other significant international pension plans, respectively. Estimated Future Benefit Payments Estimated future benefit payments for plans are as follows at December 31, 2016 (in millions): U.K. U.S. Other 2017 $ 124 $ 168 $ 39 2018 130 180 40 2019 140 187 40 2020 148 191 41 2021 156 185 42 2022 – 2026 892 893 228 U.S. and Canadian Other Post-Retirement Benefits The following table provides an overview of the accumulated projected benefit obligation, fair value of plan assets, funded status and net amount recognized as of December 31, 2016 and 2015 for the Company’s other significant post-retirement benefit plans located in the U.S. and Canada (in millions): 2016 2015 Accumulated projected benefit obligation $ 110 $ 105 Fair value of plan assets 18 18 Funded status (92 ) (87 ) Unrecognized prior-service credit (3 ) (3 ) Unrecognized loss 10 7 Net amount recognized $ (85 ) $ (83 ) Other information related to the Company’s other post-retirement benefit plans are as follows: 2016 2015 2014 Net periodic benefit cost recognized (millions) $5 $6 $3 Weighted-average discount rate used to determine future benefit obligations 3.71-4.15% 3.99-4.33% 3.83 - 4.08 Weighted-average discount rate used to determine net periodic benefit costs 3.99-4.33% 3.83-4.08% 4.44 - 4.95 Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized as components of net periodic benefit cost at December 31, 2016 are $10 million and $3 million of net loss and prior service credit, respectively. The amount in Accumulated other comprehensive income expected to be recognized as a component of net periodic benefit cost during 2017 is $0.2 million and $0.3 million of net gain and prior service credit, respectively. Based on current assumptions, the Company expects: • To contribute $4 million to fund significant other post-retirement benefit plans during 2017 . • Estimated future benefit payments will be approximately $6 million each year for 2017 through 2021, and $30 million in aggregate for 2022-2026. The accumulated post-retirement benefit obligation is increased by $7 million and decreased by $6 million by a respective 1% increase or decrease to the assumed healthcare trend rate. The service cost and interest cost components of net periodic benefits cost is increased by $0.6 million and decreased by $0.5 million by a respective 1% increase or decrease to the assumed healthcare trend rate. For most of the participants in the U.S. plan, Aon’s liability for future plan cost increases for pre-65 and Medical Supplement plan coverage is limited to 5% per annum. Although the net employer trend rates range from 4% to 8.5% per year, because of this cap, these plans are effectively limited to 5% per year in the future.

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The following table summarizes share-based compensation expense recognized in the Consolidated Statements of Income in Compensation and benefits (in millions): Years ended December 31 2016 2015 2014 Restricted share units (“RSUs”) $ 194 $ 201 $ 187 Performance share awards ("PSAs") 125 127 132 Employee share purchase plans 12 11 9 Total share-based compensation expense 331 339 328 Tax benefit 94 95 94 Share-based compensation expense, net of tax $ 237 $ 244 $ 234 Restricted Share Units RSUs generally vest between three and five years. The fair value of RSUs is based upon the market value of Aon 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. A summary of the status of the Company’s RSUs is as follows (shares in thousands): Years ended December 31 2016 2015 2014 Shares Fair Value (1) Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of year 7,167 $ 77 8,381 $ 63 9,759 $ 51 Granted 2,252 101 2,459 97 2,844 84 Vested (2,845 ) 70 (3,385 ) 58 (3,732 ) 49 Forfeited (379 ) 82 (288 ) 71 (490 ) 58 Non-vested at end of year 6,195 89 7,167 77 8,381 63 (1) Represents per share weighted average fair value of award at date of grant. The fair value of RSUs that vested during 2016 , 2015 and 2014 was $200 million , $196 million and $183 million , respectively. Unamortized deferred compensation expense amounted to $382 million as of December 31, 2016, 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 performance over a three -year period. The actual issue of shares may range from 0 - 200% of the target number of PSAs granted, based on the terms of the plan and level of achievement of the related performance target. The grant date fair value of PSAs is based upon the market price of an Aon ordinary share 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 expense, if necessary. Dividend equivalents are not paid on PSAs. Information regarding the Company’s target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the years ended December 31, 2016 , 2015 , and 2014 , respectively, is as follows (shares in thousands, dollars in millions, except fair value): 2016 2015 2014 Target PSAs granted per share 783 993 816 Weighted average fair value per share at date of grant $ 100 $ 96 $ 81 Number of shares that would be issued based on current performance levels 777 1,437 1,540 Unamortized expense, based on current performance levels $ 57 $ 48 $ — During 2016 , the Company issued approximately 1.3 million shares in connection with performance achievements related to the 2013-2015 Leadership Performance Plan (“LPP”) cycle. During 2015, the Company issued approximately 1.6 million shares in connection with performance achievements related to the 2012-2014 LPP cycle. During 2014, the Company issued approximately 0.8 million shares in connection with performance achievements related to the 2011-2013 LPP cycle and 0.2 million shares related to other performance plans.

Derivatives and Hedging

Derivatives and Hedging	12 Months Ended
	Dec. 31, 2016
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 denominated in a currency that differs from its functional currency, or enters into other transactions that are denominated in a currency other than its functional currency. The Company uses foreign exchange derivatives, typically forward contracts, options and cross-currency swaps, to reduce its overall exposure to the effects of currency fluctuations on cash flows. These exposures are hedged, on average, for less than two years. These derivatives are accounted for as hedges, and changes in fair value are recorded each period in Other comprehensive income (loss) in the Consolidated Statements of Comprehensive Income. The Company also uses foreign exchange derivatives, typically forward contracts and options to economically hedge the currency exposure of the Company’s global liquidity profile, including monetary assets or liabilities that are denominated in a non-functional currency of an entity, typically on a rolling 30-day basis, but may be for up to one year in the future. These derivatives are not accounted for as hedges, and changes in fair value are recorded each period in Other income in the Consolidated Statements of Income. The notional and fair values of derivative instruments are as follows (in millions): Notional Amount Derivative Assets (1) Derivative Liabilities (2) As of December 31 2016 2015 2016 2015 2016 2015 Foreign exchange contracts: Accounted for as hedges $ 758 $ 778 $ 14 $ 32 $ 13 $ 18 Not accounted for as hedges (3) 189 280 1 — 1 — Total $ 947 $ 1,058 $ 15 $ 32 $ 14 $ 18 (1) Included within Other current assets ( $6 million in 2016 and $15 million in 2015 , respectively) or Other non-current assets ( $9 million in 2016 and $17 million in 2015 , respectively) (2) Included within Other current liabilities ( $7 million in 2016 and $13 million in 2015 , respectively) or Other non-current liabilities ( $7 million in 2016 and $5 million in 2015 , respectively) (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. Offsetting of financial assets and derivatives assets are as follows (in millions): Gross Amounts of Recognized Assets Gross Amounts Offset in the Statement of Financial Position Net Amounts of Assets Presented in the Statement of Financial Position (1) Derivatives accounted for as hedges: 2016 2015 2016 2015 2016 2015 Foreign exchange contracts $ 14 $ 32 $ (1 ) $ (13 ) $ 13 $ 19 (1) Included within Other current assets ( $4 million in 2016 and $6 million in 2015 , respectively) or Other non-current assets ( $9 million in 2016 and $13 million in 2015 , respectively) Offsetting of financial liabilities and derivative liabilities are as follows (in millions): Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Statement of Financial Position Net Amounts of Liabilities Presented in the Statement of Financial Position (1) Derivatives accounted for as hedges: 2016 2015 2016 2015 2016 2015 Foreign exchange contracts $ 13 $ 18 $ (1 ) $ (13 ) $ 12 $ 5 (1) Included within Other current liabilities ( $5 million in 2016 and $4 million in 2015 , respectively) or Other non-current liabilities ( $7 million in 2016 and $1 million in 2015 , respectively) The amounts of derivative gains (losses) recognized in the Consolidated Financial Statements are as follows (in millions): Cash Flow Hedge - Foreign Exchange Contracts Location of future reclassification from Accumulated Other Comprehensive Loss Gain (Loss) Recognized in Accumulated Other Comprehensive Loss: Compensation and Benefits Other General Expenses Interest Expense Other Income (Expense) Total 2016 $ 8 $ (13 ) $ — $ (20 ) $ (25 ) 2015 4 (3 ) — (10 ) (9 ) 2014 11 (3 ) — (10 ) (2 ) Cash Flow Hedge - Foreign Exchange Contracts Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion): Compensation and Benefits Other General Expenses Interest Expense Other Income Total 2016 $ 2 $ (4 ) $ (1 ) $ (7 ) $ (10 ) 2015 4 (1 ) (9 ) (11 ) (17 ) 2014 (5 ) 3 (10 ) (2 ) (14 ) The Company recognized no gain (loss) in Interest expense for fair value hedges related to fixed rate debt for 2016 and 2015. There was a gain of $9 million recognized in 2014. The Company estimates that approximately $12 million of pretax losses currently included within Accumulated other comprehensive loss will be reclassified in to earnings in the next twelve months. The amount of gain (loss) recognized in income on the ineffective portion of derivatives for 2016 , 2015 , and 2014 was immaterial. The Company recorded a loss of $0.2 million for 2016 and a loss of $8 million and $18 million in Other income for foreign exchange derivatives not designated or qualifying as hedges for 2015 and 2014 , respectively. Net Investments in Foreign Operations Risk Management The Company uses non-derivative financial instruments to protect the value of its investments in a number of foreign subsidiaries. In 2016, the Company designated a portion of its Euro-denominated commercial paper issuances as a non-derivative economic hedge of the foreign currency exposure of a net investment in its European operations. The change in fair value of the designated portion of the Euro-denominated commercial paper due to changes in foreign currency exchange rates is recorded in Foreign currency translation adjustment, a component of Accumulated other comprehensive income (loss), to the extent it is effective as a hedge. The foreign currency translation adjustment of the hedged net investments that is also recorded in Accumulated other comprehensive income (loss). Ineffective portions of net investment hedges, if any, are reclassified from Accumulated other comprehensive income (loss) into earnings during the period of change. As of December 31, 2016 , the Company has € 217 million ($ 227 million at December 31, 2016 exchange rates) of outstanding Euro-denominated commercial paper designated as a hedge of the foreign currency exposure of its net investment in its European operations. As of December 31, 2016 , the unrealized gain recognized in Accumulated other comprehensive income (loss) related to the net investment non derivative hedging instrument was $18 million . The Company did not reclassify any deferred gains or losses related to net investment hedges from Accumulated other comprehensive income (loss) to earnings during the twelve months ended December 31, 2016 . In addition, the Company did not incur any ineffectiveness related to net investment hedges during the twelve months ended December 31, 2016 .

Fair Value Measurements and Fin

Fair Value Measurements and Financial Instruments	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements and Financial Instruments	Fair Value Measurements and Financial Instruments Accounting standards establish a three tier fair value hierarchy that prioritizes the inputs used in measuring fair values as follows: • Level 1 — observable inputs such as quoted prices for identical assets in active markets; • Level 2 — inputs other than quoted prices for identical assets in active markets, that are observable either directly or indirectly; and • Level 3 — unobservable inputs in which there is little or no market data which requires the use of valuation techniques and the development of assumptions. The following methods and assumptions are used to estimate the fair values of the Company’s financial instruments, including pension assets (refer to Note 10 “Employee Benefits”): Money market funds consist of institutional prime, treasury, and government money market funds. The Company reviews these funds to obtain reasonable assurance that the fund net asset value is $1 per share. Cash and cash equivalents consist of cash and institutional short-term investment funds. The Company reviews the short-term investment funds to obtain reasonable assurance that the fund net asset value is $1 per share. Equity investments consist of 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 Consolidated Financial Statements. Pooled funds consist of various equity, fixed income, commodity, and real estate mutual fund type investment vehicles. Pooled investment funds fair value is estimated based on the proportionate share ownership in the underlying net assets of the investment, which is based on the fair value of the underlying securities that trade on a national securities exchange. The Company gains an understanding of the investment guidelines and valuation policies of the fund and discusses fund performance with pooled fund managers. The Company obtains audited fund manager financial statements, when available. If the pooled fund is designed to replicate a publicly traded index, the Company compares the performance of the fund to the index to assess the reasonableness of the fair value measurement. Alternative investments consist of limited partnerships, private equity, and hedge funds. Alternative investment fair value is generally estimated based on the proportionate share ownership in the underlying net assets of the investment as determined by the general partner or investment manager. The valuations are based on various factors depending on investment strategy, proprietary models, and specific financial data or projections. The Company obtains audited fund manager financial statements, when available. The Company obtains a detailed understanding of the models, inputs, and assumptions used in developing prices provided by the investment managers (or appropriate party) through regular discussions. The Company also obtains the investment manger’s valuation policies and assesses the assumptions used for reasonableness based on relevant market conditions and internal Company guidelines. If an assumption is deemed unreasonable, based on the Company’s guidelines, it is then reviewed by management and the fair value estimate provided by the vendor is adjusted, if deemed appropriate. These adjustments do not occur frequently and historically are not material to the fair value estimates in the Consolidated Financial Statements. Derivatives are carried at fair value, based upon industry standard valuation techniques that use, where possible, current market-based or independently sourced pricing inputs, such as interest rates, currency exchange rates, or implied volatilities. Annuity contracts consist of insurance group annuity contracts purchased to match the pension benefit payment stream owed to certain selected plan participant demographics within a few major U.K. defined benefit plans. Annuity contracts are valued using a discounted cash flow model utilizing assumptions such as discount rate, mortality, and inflation. Real estate and REITs consist of publicly traded real estate investment trusts (“REITs”) and direct real estate investments. Level 1 REITs are valued using the closing stock price on a national securities exchange. Non Level 1 values are based on the proportionate share of ownership in the underlying net asset value as determined by the investment manager. The Company independently reviews the listing of Level 1 REIT securities in the portfolio and agrees the closing stock prices to a national securities exchange. The Company gains an understanding of the investment guidelines and valuation policies of the non Level 1 real estate funds and discusses performance with the fund managers. The Company obtains audited fund manager financial statements, when available. See the description of “Alternative investments” for further detail on valuation procedures surrounding non Level 1 REITs. Debt is carried at outstanding principal balance, less any unamortized 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 December 31, 2016 and December 31, 2015 , respectively (in millions): Fair Value Measurements Using Balance at December 31, 2016 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) $ 1,371 $ 1,371 $ — $ — Other investments: Government bonds 1 — 1 — Equity investments 9 6 3 — Derivatives (2): Foreign exchange contracts 15 — 15 — Liabilities: Derivatives: Foreign exchange contracts 14 — 14 — (1) Included within Fiduciary assets, Short-term investments or Cash and cash equivalents in the Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 12 “Derivatives and Hedging” for additional information regarding the Company’s derivatives and hedging activity. Fair Value Measurements Using Balance at December 31, 2015 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) $ 1,396 $ 1,396 $ — $ — Other investments: Government bonds 1 — 1 — Equity investments 10 6 4 — Derivatives (2): Foreign exchange contracts 32 — 32 — Liabilities: Derivatives: Foreign exchange contracts 18 — 18 — (1) Included within Fiduciary assets, Short-term investments or Cash and cash equivalents in the Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 12 “Derivatives and Hedging” for additional information regarding the Company’s derivatives and hedging activity. There were no transfers of assets or liabilities between fair value hierarchy levels during 2016 or 2015 . The Company recognized no realized or unrealized gains or losses in the Consolidated Statements of Income related to assets and liabilities measured at fair value using unobservable inputs in 2016, 2015, or 2014. The fair value of Long-term debt is classified as Level 2 of the fair value hierarchy. The following table discloses the Company’s financial instruments where the carrying amounts and fair values differ (in millions): 2016 2015 As of December 31 Carrying Value Fair Value Carrying Value Fair Value Long-term debt $ 5,869 $ 6,264 $ 5,138 $ 5,386

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and 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 Consolidated Statements of Financial Position and have been recognized in Other general expenses in the Consolidated Statements of Income to the extent that losses are deemed probable and are reasonably estimable. These amounts are adjusted from time to time as developments warrant. Matters that are not probable and reasonably estimable are not accrued for in the financial statements. The Company 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, in excess of amounts that are deemed probable and estimable and therefore already accrued, is estimated to be between $0 and $0.2 billion , exclusive of any insurance coverage. These estimates are based on currently available information. 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 retail insurance brokerage subsidiary of Aon was sued on September 14, 2010 in the Chancery Court for Davidson County, Tennessee Twentieth Judicial District, at Nashville by a client, Opry Mills Mall Limited Partnership (“Opry Mills”) that sustained flood damage to its property in May 2010. The lawsuit seeks $200 million in coverage from numerous insurers with whom this Aon subsidiary placed the client’s property insurance coverage. The insurers contend that only $50 million in coverage (which has already been paid) is available for the loss because the flood event occurred on property in a high hazard flood zone. Opry Mills is seeking full coverage from the insurers for the loss and has sued this Aon subsidiary in the alternative for the same $150 million difference on various theories of professional liability if the court determines there is not full coverage. In addition, Opry Mills seeks prejudgment interest, attorneys’ fees and enhanced damages which could substantially increase Aon’s exposure. In March 2015, the trial court granted partial summary judgment in favor of plaintiffs and against the insurers, holding generally that the plaintiffs are entitled to $200 million in coverage under the language of the policies. In August 2015, a jury returned a verdict in favor of Opry Mills and against the insurers in the amount of $ 204 million . The insurers have appealed both of these trial court decisions. Aon believes it has meritorious defenses and intends to vigorously defend itself against these claims. On June 1, 2007, the International Road Transport Union (“IRU”) sued Aon in the Geneva Tribunal of First Instance in Switzerland. IRU alleges, among other things, that, between 1995 and 2004, a business acquired by Aon and, later, an Aon subsidiary (1) accepted commissions for certain insurance placements that violated a fee agreement entered between the parties and (2) negligently failed to ask certain insurance carriers to contribute to the IRU’s risk management costs. IRU sought damages of approximately CHF 46 million ( $45 million at December 31, 2016 exchange rates) and $3 million , plus legal fees and interest of approximately $30 million . On December 2, 2014, the Geneva Tribunal of First Instance entered a judgment that accepted some, and rejected other, of IRU’s claims. The judgment awarded IRU CHF 16.8 million ( $16 million at December 31, 2016 exchange rates) and $3 million , plus interest and adverse costs. The entire amount of the judgment, including interest through December 31, 2014, totaled CHF 27.9 million ( $27 million at December 31, 2016 exchange rates) and $5 million . On January 26, 2015, in return for IRU agreeing not to appeal the bulk of its dismissed claims, the Aon subsidiary agreed not to appeal a part of the judgment and to pay IRU CHF 12.8 million ( $14 million at January 31, 2015 exchange rates) and $4.7 million without Aon admitting liability. The Aon subsidiary appealed those aspects of the judgment it retained the right to appeal. IRU did not appeal. The Geneva Appellate Court affirmed the judgment of the Geneva Tribunal of First Instance. The Aon subsidiary filed an appeal (which is now under submission) to the Swiss Supreme Court. The Aon subsidiary’s maximum liability on appeal is limited to CHF 8.7 million ( $8 million at December 31, 2016 exchange rates) and $115,000 (plus interest and costs) beyond what the subsidiary has already paid. 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 December 31, 2016 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 December 31, 2016 exchange rates). Aon believes that it has meritorious defenses and intends to vigorously defend itself against this potential claim. 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 contends that acts and omissions by Aon caused LPC to recover less than it otherwise would have from insurers for losses suffered in the 2010/2011 Canterbury Earthquakes. LPC claims damages of approximately NZD $184 million ( $127 million at December 31, 2016 exchange rates) plus interest and costs. Aon believes that it has meritorious defenses and intends to vigorously defend itself against these claims. Settled/Closed Matters A pensions consulting and administration subsidiary of Hewitt before its acquisition by Aon provided advisory services to the trustees of the Philips UK pension fund and the relevant employer of fund beneficiaries. On January 2, 2014, Philips Pension Trustees Limited and Philips Electronics UK Limited (together, “Philips”) sued Aon in the High Court, Chancery Division, London alleging negligence and breach of duty. The proceedings assert Philips’ right to claim damages related to Philips’ use of a credit default swap hedging strategy pursuant to the supply of the advisory services, which is said to have resulted in substantial damages to Philips. Philips sought approximately £189 million ( $232 million at December 31, 2016 exchange rates), plus interest and costs. In June 2015, the High Court ordered Philips to clarify several aspects of its claim. In its clarification, Philips increased the amount of its claim to £290 million ( $356 million at December 31, 2016 exchange rates), plus interest and costs. In October 2016, all parties reached an agreement to settle this case, and the settlement is now concluded. The terms of this settlement did not have a material impact on Aon’s results of operations or financial condition. Guarantees and Indemnifications In connection with the redomicile of Aon’s headquarters (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), (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), and (4) First Supplemental Indenture, dated as of April 2, 2012, among Aon Finance N.S. 1, ULC, as issuer, Aon Corporation, as guarantor, Aon plc, as guarantor, and Computershare Trust Company of Canada, as trustee. 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 Consolidated 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. 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 a letter of credit (“LOCs”). The Company had total LOCs outstanding of approximately $90 million at December 31, 2016 , compared to $58 million at December 31, 2015 . These letters of credit 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 $95 million at December 31, 2016 compared to $104 million at December 31, 2015 .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has two reportable segments: Risk Solutions and HR Solutions. Unallocated income and expenses, when combined with the reportable segments and after the elimination of intersegment revenues and expenses, equal the amounts in the Consolidated Financial Statements. The accounting policies of the reportable segments are the same as those described in Note 2 “Summary of Significant Accounting Principles and Practices.” Reportable operating segments have been determined using a management approach, which is consistent with the basis and manner in which Aon’s chief operating decision maker (“CODM”) uses financial information for the purposes of allocating resources and evaluating performance. The CODM assesses performance based on a number of factors including revenue growth, expense discipline, return on invested capital, and other factors. The Company does not present net assets by reportable segment as this information is not reviewed by the CODM. Risk Solutions acts as an advisor and insurance and reinsurance broker, helping clients manage their risks, via consultation, as well as negotiation and placement of insurance risk with insurance carriers through Aon’s global distribution network. HR Solutions partners with organizations to solve their most complex benefits, talent and related financial challenges, and improve business performance by designing, implementing, communicating, and administering a wide range of human capital, retirement, investment management, health care, compensation, and talent management strategies. Aon’s total revenue is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 7,485 $ 7,426 $ 7,834 HR Solutions 4,183 4,303 4,264 Intersegment eliminations (41 ) (47 ) (53 ) Total revenue $ 11,627 $ 11,682 $ 12,045 Commissions, fees and other revenues by product are as follows (in millions): Years ended December 31 2016 2015 2014 Retail brokerage $ 6,096 $ 6,044 $ 6,334 Reinsurance brokerage 1,367 1,361 1,474 Total Risk Solutions Segment 7,463 7,405 7,808 Consulting services 1,662 1,686 1,700 Outsourcing 2,557 2,658 2,607 Intrasegment (36 ) (41 ) (43 ) Total HR Solutions Segment 4,183 4,303 4,264 Intersegment (41 ) (47 ) (53 ) Total commissions, fees and other revenue $ 11,605 $ 11,661 $ 12,019 Fiduciary investment income by segment is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 22 $ 21 $ 26 HR Solutions — — — Total fiduciary investment income $ 22 $ 21 $ 26 A reconciliation of segment operating income before tax to income before income taxes is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 1,587 $ 1,506 $ 1,648 HR Solutions 557 536 485 Segment income before income taxes 2,144 2,042 2,133 Unallocated expenses (238 ) (194 ) (167 ) Interest income 9 14 10 Interest expense (282 ) (273 ) (255 ) Other income 36 100 44 Income before income taxes $ 1,669 $ 1,689 $ 1,765 Unallocated expenses include administrative or other costs not attributable to the operating segments, such as corporate governance costs. Interest income represents income earned on Cash and cash equivalents and Short-term investments. Interest expense represents the cost of debt obligations. Other income consists of equity earnings, realized gains or losses on the sale of investments, gains or losses on the disposal of businesses, gains or losses on derivatives, and gains or losses on foreign currency remeasurement. Revenues are generally attributed to geographic areas based on the location of the resources producing the revenues. Intercompany revenues and expenses are eliminated in consolidated results. Consolidated Revenue by geographic area, which is attributed on the basis of where the services are performed, is as follows (in millions): Years ended December 31 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific 2016 11,627 $ 6,078 $ 995 $ 1,378 $ 1,760 $ 1,416 2015 11,682 6,063 1,053 1,527 1,909 1,130 2014 12,045 5,824 1,176 1,623 2,189 1,233 Consolidated Non-current assets by geographic area are as follows (in millions): As of December 31, 2016 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific Fixed assets, net 765 $ 443 $ 62 $ 65 $ 85 $ 110 Goodwill, intangible assets and other 12,382 6,947 887 2,091 2,054 403 Total 13,147 7,390 949 2,156 2,139 513 As of December 31, 2015 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific Fixed assets, net 765 $ 432 $ 48 $ 89 $ 89 $ 107 Goodwill, intangible assets and other 12,253 6,635 368 2,606 2,181 463 Total 13,018 7,067 416 2,695 2,270 570

Guarantee of Registered Securit

Guarantee of Registered Securities	12 Months Ended
	Dec. 31, 2016
Guarantee of Registered Securities
Guarantee of Registered Securities	Guarantee of Registered Securities As described in Note 14 “Commitments and 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 Corp Notes”). 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 Corp Notes. In addition, Aon Corporation entered into an agreement pursuant to which it agreed to guarantee the obligations of Aon plc arising under the 4.250% Notes due 2042 exchanged for Aon Corporation’s outstanding 8.205% Notes due January 2027 and also agreed to guarantee the obligations of Aon plc arising under the 4.45% Notes due 2043, the 4.00% Notes due November 2023, the 2.875% Notes due May 2026, the 3.50% Notes due June 2024, the 4.60% Notes due June 2044, the 4.75% Notes due May 2045, the 2.80% Notes due March 2021, and the 3.875% Notes due December 2025 (collectively, the “Aon plc Notes”). In each case, the guarantee of Aon Corporation is full and unconditional. There are no subsidiaries of Aon plc, other than Aon Corporation, that are guarantors of the Aon plc Notes. As a result of the existence of these guarantees, the Company has elected to present the financial information set forth in this footnote in accordance with Rule 3-10 of Regulation S-X. The following tables set forth Condensed Consolidating Statements of Income and Condensed Consolidating Statements of Comprehensive Income for the years ended December 31, 2016 , 2015 , and 2014 , Condensed Consolidating Statements of Financial Position as of December 31, 2016 and December 31, 2015 , and Condensed Consolidating Statements of Cash Flows for the years ended December 31, 2016 , 2015 , and 2014 , 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 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. In January 2015, Aon plc transferred its ownership of all of its directly held subsidiaries to Aon Global Holdings Limited, an intermediate holding company. The financial results of Aon Global Holdings Limited are included in the Other Non-Guarantor Subsidiaries column of the Condensed Consolidating Financial Statements. The Company has reflected the transfer of Aon Corporation from Aon plc to Aon Global Holdings Limited below for all periods presented. Certain amounts in prior year’s consolidating statements of income have been reclassified and adjusted to conform to the 2016 presentation. In prior periods, other income (expense) from intercompany transactions were recognized in Compensation and benefits and Other general expenses. These amounts are now included in Intercompany other income (expense) in the Condensed Consolidating Statements of Income. The Company believes this provides greater clarity into the income generated from operations and intercompany transactions. Condensed Consolidating Statement of Income Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Commissions, fees and other $ — $ — $ 11,605 $ — $ 11,605 Fiduciary investment income — — 22 — 22 Total revenue — — 11,627 — 11,627 Expenses Compensation and benefits 130 171 6,613 — 6,914 Other general expenses — 2 2,805 — 2,807 Total operating expenses 130 173 9,418 — 9,721 Operating (loss) income (130 ) (173 ) 2,209 — 1,906 Interest income — 16 22 (29 ) 9 Interest expense (196 ) (101 ) (14 ) 29 (282 ) Intercompany interest income (expense) 14 (541 ) 527 — — Intercompany other income (expense) 274 (361 ) 87 — — Other income (expense) 15 (5 ) 44 (18 ) 36 Income (loss) before taxes (23 ) (1,165 ) 2,875 (18 ) 1,669 Income tax expense (benefit) (55 ) (325 ) 619 — 239 Income (loss) before equity in earnings of subsidiaries 32 (840 ) 2,256 (18 ) 1,430 Equity in earnings of subsidiaries, net of tax 1,382 1,219 379 (2,980 ) — Net income 1,414 379 2,635 (2,998 ) 1,430 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,414 $ 379 $ 2,601 $ (2,998 ) $ 1,396 Condensed Consolidating Statement of Income Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Commissions, fees and other $ — $ — $ 11,661 $ — $ 11,661 Fiduciary investment income — — 21 — 21 Total revenue — — 11,682 — 11,682 Expenses Compensation and benefits 136 32 6,669 — 6,837 Other general expenses 8 7 2,982 — 2,997 Total operating expenses 144 39 9,651 — 9,834 Operating (loss) income (144 ) (39 ) 2,031 — 1,848 Interest income — 14 19 (19 ) 14 Interest expense (140 ) (130 ) (22 ) 19 (273 ) Intercompany interest income (expense) 429 (479 ) 50 — — Intercompany other income (expense) 302 (422 ) 120 — — Other income (expense) (1 ) — 101 — 100 Income (loss) before taxes 446 (1,056 ) 2,299 — 1,689 Income tax expense (benefit) 45 (262 ) 484 — 267 Income (loss) before equity in earnings of subsidiaries 401 (794 ) 1,815 — 1,422 Equity in earnings of subsidiaries, net of tax 984 1,290 496 (2,770 ) — Net income 1,385 496 2,311 (2,770 ) 1,422 Less: Net income attributable to noncontrolling interests — — 37 — 37 Net income attributable to Aon shareholders $ 1,385 $ 496 $ 2,274 $ (2,770 ) $ 1,385 Condensed Consolidating Statement of Income Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustment Consolidated Revenue Commissions, fees and other $ — $ — $ 12,019 $ — $ 12,019 Fiduciary investment income — — 26 — 26 Total revenue — — 12,045 — 12,045 Expenses Compensation and benefits 140 16 6,858 — 7,014 Other general expenses 3 5 3,057 — 3,065 Total operating expenses 143 21 9,915 — 10,079 Operating (loss) income (143 ) (21 ) 2,130 — 1,966 Interest income — 2 17 (9 ) 10 Interest expense (84 ) (139 ) (41 ) 9 (255 ) Intercompany interest (expense) income 449 (298 ) (151 ) — — Intercompany other (expense) income 342 (390 ) 48 — — Other income 2 5 37 — 44 Income (loss) before taxes 566 (841 ) 2,040 — 1,765 Income tax (benefit) expense 74 (192 ) 452 — 334 Income (loss) before equity in earnings of subsidiaries 492 (649 ) 1,588 — 1,431 Equity in earnings of subsidiaries, net of tax 905 1,195 546 (2,646 ) — Net income 1,397 546 2,134 (2,646 ) 1,431 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,397 $ 546 $ 2,100 $ (2,646 ) $ 1,397 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,414 $ 379 $ 2,635 $ (2,998 ) $ 1,430 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,414 $ 379 $ 2,601 $ (2,998 ) $ 1,396 Other comprehensive (loss) income, net of tax: Change in fair value of financial instruments — (1 ) (11 ) — (12 ) Foreign currency translation adjustments (2 ) 21 (532 ) 18 (495 ) Post-retirement benefit obligation — 68 (52 ) — 16 Total other comprehensive income (loss) (2 ) 88 (595 ) 18 (491 ) Equity in other comprehensive loss of subsidiaries, net of tax (505 ) (547 ) (459 ) 1,511 — Less: Other comprehensive loss attributable to noncontrolling interests — — (2 ) — (2 ) Total other comprehensive loss attributable to Aon shareholders (507 ) (459 ) (1,052 ) 1,529 (489 ) Comprehensive income (loss) attributable to Aon shareholders $ 907 $ (80 ) $ 1,549 $ (1,469 ) $ 907 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,385 $ 496 $ 2,311 $ (2,770 ) $ 1,422 Less: Net income attributable to noncontrolling interests — — 37 — 37 Net income attributable to Aon shareholders $ 1,385 $ 496 $ 2,274 $ (2,770 ) $ 1,385 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (8 ) — (8 ) Foreign currency translation adjustments — (47 ) (395 ) — (442 ) Post-retirement benefit obligation — 12 143 — 155 Total other comprehensive loss — (35 ) (260 ) — (295 ) Equity in other comprehensive loss of subsidiaries, net of tax (289 ) (259 ) (294 ) 842 — Less: Other comprehensive loss attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive loss attributable to Aon shareholders (289 ) (294 ) (548 ) 842 (289 ) Comprehensive income attributable to Aon shareholders $ 1,096 $ 202 $ 1,726 $ (1,928 ) $ 1,096 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,397 $ 546 $ 2,134 $ (2,646 ) $ 1,431 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,397 $ 546 $ 2,100 $ (2,646 ) $ 1,397 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (3 ) 7 — 4 Foreign currency translation adjustments — (31 ) (476 ) — (507 ) Post-retirement benefit obligation — (315 ) 55 — (260 ) Total other comprehensive loss — (349 ) (414 ) — (763 ) Equity in other comprehensive loss of subsidiaries, net of tax (760 ) (409 ) (758 ) 1,927 — Less: Other comprehensive loss attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive loss attributable to Aon shareholders (760 ) (758 ) (1,169 ) 1,927 (760 ) Comprehensive income (loss) attributable to Aon shareholders $ 637 $ (212 ) $ 931 $ (719 ) $ 637 Condensed Consolidating Statement of Financial Position As of December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated ASSETS Cash and cash equivalents $ — $ 1,633 $ 660 $ (1,862 ) $ 431 Short-term investments — 140 150 — 290 Receivables, net — 3 2,586 — 2,589 Fiduciary assets — — 9,485 — 9,485 Intercompany receivables 105 1,880 9,825 (11,810 ) — Other current assets — 25 326 — 351 Total Current Assets 105 3,681 23,032 (13,672 ) 13,146 Goodwill — — 8,747 — 8,747 Intangible assets, net — — 2,223 — 2,223 Fixed assets, net — — 765 — 765 Deferred tax assets 134 726 168 (706 ) 322 Intercompany receivables 366 261 8,711 (9,338 ) — Prepaid Pension — 5 853 — 858 Other non-current assets 2 119 433 — 554 Investment in subsidiary 10,107 17,137 (350 ) (26,894 ) — TOTAL ASSETS $ 10,714 $ 21,929 $ 44,582 $ (50,610 ) $ 26,615 LIABILITIES AND EQUITY Accounts payable and accrued liabilities $ 585 $ 44 $ 3,034 $ (1,862 ) $ 1,801 Short-term debt and current portion of long-term debt 279 50 7 — 336 Fiduciary Liabilities — — 9,485 — 9,485 Intercompany payables 142 10,399 1,269 (11,810 ) — Other current liabilities — 63 810 — 873 Total Current Liabilities 1,006 10,556 14,605 (13,672 ) 12,495 Long-term debt 4,177 1,413 279 — 5,869 Deferred tax liabilities — — 759 (658 ) 101 Pension, other post-retirement and other post-employment liabilities — 1,356 418 — 1,774 Intercompany payables — 8,877 461 (9,338 ) — Other non-current liabilities 8 77 759 — 844 TOTAL LIABILITIES 5,191 22,279 17,281 (23,668 ) 21,083 TOTAL AON SHAREHOLDERS’ EQUITY 5,523 (350 ) 27,244 (26,942 ) 5,475 Noncontrolling interests — — 57 — 57 TOTAL EQUITY 5,523 (350 ) 27,301 (26,942 ) 5,532 TOTAL LIABILITIES AND EQUITY $ 10,714 $ 21,929 $ 44,582 $ (50,610 ) $ 26,615 Condensed Consolidating Statement of Financial Position As of December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated ASSETS Cash and cash equivalents $ — $ 2,083 $ 1,242 $ (2,941 ) $ 384 Short-term investments — 209 147 — 356 Receivables, net 1 — 2,563 — 2,564 Fiduciary assets — — 9,932 — 9,932 Intercompany receivables 432 1,950 7,957 (10,339 ) — Other current assets — 19 310 — 329 Total Current Assets 433 4,261 22,151 (13,280 ) 13,565 Goodwill — — 8,448 — 8,448 Intangible assets, net — — 2,180 — 2,180 Fixed assets, net — — 765 — 765 Deferred tax assets 154 756 207 (817 ) 300 Intercompany receivables 375 526 8,633 (9,534 ) — Prepaid Pension — 6 1,027 — 1,033 Other non-current assets — 119 557 (84 ) 592 Investment in subsidiary 11,700 16,042 (123 ) (27,619 ) — TOTAL ASSETS $ 12,662 $ 21,710 $ 43,845 $ (51,334 ) $ 26,883 LIABILITIES AND EQUITY Accounts payable and accrued liabilities $ 2,988 $ 45 $ 1,680 $ (2,941 ) $ 1,772 Short-term debt and current portion of long-term debt — 550 12 — 562 Fiduciary Liabilities — — 9,932 — 9,932 Intercompany payables 167 9,518 654 (10,339 ) — Other current liabilities 47 56 716 — 819 Total Current Liabilities 3,202 10,169 12,994 (13,280 ) 13,085 Long-term debt 3,451 1,412 275 — 5,138 Deferred tax liabilities — — 855 (818 ) 37 Pension, other post-retirement and other post-employment liabilities — 1,313 482 — 1,795 Intercompany payables — 8,799 735 (9,534 ) — Other non-current liabilities 7 140 705 (83 ) 769 TOTAL LIABILITIES 6,660 21,833 16,046 (23,715 ) 20,824 TOTAL AON SHAREHOLDERS’ EQUITY 6,002 (123 ) 27,742 (27,619 ) 6,002 Noncontrolling interests — — 57 — 57 TOTAL EQUITY 6,002 (123 ) 27,799 (27,619 ) 6,059 TOTAL LIABILITIES AND EQUITY $ 12,662 $ 21,710 $ 43,845 $ (51,334 ) $ 26,883 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES $ 2,705 $ (536 ) $ 3,265 $ (3,108 ) $ 2,326 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 316 15 (288 ) 43 Payments for investments — (35 ) (29 ) — (64 ) Net (purchases) sales of short-term investments - non-fiduciary — 70 (9 ) — 61 Acquisition of businesses, net of cash acquired — (335 ) (608 ) 64 (879 ) Proceeds from sale of businesses — — 171 (64 ) 107 Capital expenditures — — (222 ) — (222 ) CASH USED FOR INVESTING ACTIVITIES — 16 (682 ) (288 ) (954 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (1,257 ) — — — (1,257 ) Advances from (to) affiliates and other (1) (2,008 ) 570 (3,037 ) 4,475 — Issuance of shares for employee benefit plans (129 ) — — — (129 ) Issuance of debt 1,879 1,588 — — 3,467 Repayment of debt (845 ) (2,088 ) (12 ) — (2,945 ) Cash dividends to shareholders (345 ) — — — (345 ) Noncontrolling interests and other financing activities — (77 ) — (77 ) CASH (USED FOR) PROVIDED BY FINANCING ACTIVITIES (2,705 ) 70 (3,126 ) 4,475 (1,286 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (39 ) — (39 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS — (450 ) (582 ) 1,079 47 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 2,083 1,242 (2,941 ) 384 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 1,633 $ 660 $ (1,862 ) $ 431 (1) Advances from (to) affiliates and other includes activity related to the Company’s intercompany and cash pooling arrangements. Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY OPERATING ACTIVITIES $ 695 $ 464 $ 2,523 $ (1,673 ) $ 2,009 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 27 193 — 220 Payments for investments (13 ) (47 ) (219 ) 13 (266 ) Net purchases of short-term investments - non-fiduciary — (42 ) 51 — 9 Acquisition of businesses, net of cash acquired — — (16 ) — (16 ) Proceeds from sale of businesses — — 205 — 205 Capital expenditures — — (290 ) — (290 ) CASH USED FOR INVESTING ACTIVITIES (13 ) (62 ) (76 ) 13 (138 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (1,550 ) — — — (1,550 ) Advances from (to) affiliates and other (1) 232 (326 ) (2,339 ) 2,433 — Issuance of shares for employee benefit plans (29 ) — (1 ) — (30 ) Issuance of debt 1,318 4,026 7 — 5,351 Repayment of debt (330 ) (4,746 ) (22 ) — (5,098 ) Cash dividends to shareholders (323 ) — — — (323 ) Noncontrolling interests and other financing activities — — (39 ) — (39 ) CASH USED FOR FINANCING ACTIVITIES (682 ) (1,046 ) (2,394 ) 2,433 (1,689 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (172 ) — (172 ) NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS — (644 ) (119 ) 773 10 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 2,727 1,361 (3,714 ) 374 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 2,083 $ 1,242 $ (2,941 ) $ 384 (1) Advances from (to) affiliates and other includes activity related to the Company’s intercompany and cash pooling arrangements. Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES $ 769 $ (927 ) $ 1,970 $ — $ 1,812 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 39 13 — 52 Payments for investments — (20 ) — — (20 ) Net sales of short-term investments - non-fiduciary — (3 ) 113 — 110 Acquisition of businesses, net of cash acquired — — (479 ) — (479 ) Proceeds from sale of businesses — — 48 — 48 Capital expenditures — — (256 ) — (256 ) CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES — 16 (561 ) — (545 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (2,250 ) — — — (2,250 ) Advances from (to) affiliates 19 3,215 (536 ) (2,698 ) — Issuance of shares for employee benefit plans (105 ) — — — (105 ) Issuance of debt 2,908 2,326 5 — 5,239 Repayment of debt (1,068 ) (2,150 ) (700 ) — (3,918 ) Cash dividends to shareholders (273 ) — — — (273 ) Noncontrolling interests and other financing activities — — 4 — 4 CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES (769 ) 3,391 (1,227 ) (2,698 ) (1,303 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (67 ) — (67 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS — 2,480 115 (2,698 ) (103 ) CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 247 1,246 (1,016 ) 477 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 2,727 $ 1,361 $ (3,714 ) $ 374

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	Quarterly Financial Data (Unaudited) As discussed in Note 1 “Basis of Presentation,” the Company has identified certain accounting errors that affected consolidated financial amounts that were previously presented in its earlier Forms 10-Q and 10-K for the periods below. Selected quarterly financial data for the years ended December 31, 2016 and 2015 as reported, the effect of the change, and selected quarterly financial data for the years ended December 31, 2016 and 2015 as revised, are as follows (in millions, except per share data): (As reported) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,787 $ 2,761 $ 2,740 $ 3,317 $ 11,605 Fiduciary investment income 5 5 6 6 22 Total revenue 2,792 2,766 2,746 3,323 11,627 Operating income 450 405 422 629 1,906 Net income 327 280 314 509 1,430 Less: Net income attributable to noncontrolling interests 12 8 7 7 34 Net income attributable to Aon shareholders $ 315 $ 272 $ 307 $ 502 $ 1,396 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.16 $ 1.01 $ 1.15 $ 1.89 $ 5.21 Diluted net income per share attributable to Aon shareholders $ 1.15 $ 1.01 $ 1.14 $ 1.87 $ 5.16 (Effect of change) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 13 $ 34 $ 14 $ (61 ) $ — Fiduciary investment income — — — — — Total revenue 13 34 14 (61 ) — Operating income 13 34 14 (61 ) — Net income 10 28 12 (50 ) — Less: Net income attributable to noncontrolling interests — — — — — Net income attributable to Aon shareholders $ 10 $ 28 $ 12 $ (50 ) $ — PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 0.04 $ 0.11 $ 0.04 $ (0.19 ) $ — Diluted net income per share attributable to Aon shareholders $ 0.04 $ 0.10 $ 0.04 $ (0.19 ) $ — (As revised) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,800 $ 2,795 $ 2,754 $ 3,256 $ 11,605 Fiduciary investment income 5 5 6 6 22 Total revenue 2,805 2,800 2,760 3,262 11,627 Operating income 463 439 436 568 1,906 Net income 337 308 326 459 1,430 Less: Net income attributable to noncontrolling interests 12 8 7 7 34 Net income attributable to Aon shareholders $ 325 $ 300 $ 319 $ 452 $ 1,396 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.20 $ 1.12 $ 1.19 $ 1.70 $ 5.21 Diluted net income per share attributable to Aon shareholders $ 1.19 $ 1.11 $ 1.18 $ 1.68 $ 5.16 (As reported) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,842 $ 2,800 $ 2,736 $ 3,283 $ 11,661 Fiduciary investment income 5 5 6 5 21 Total revenue 2,847 2,805 2,742 3,288 11,682 Operating income 441 277 413 717 1,848 Net income 341 188 303 590 1,422 Less: Net income attributable to noncontrolling interests 13 10 8 6 37 Net income attributable to Aon shareholders $ 328 $ 178 $ 295 $ 584 $ 1,385 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.15 $ 0.63 $ 1.05 $ 2.12 $ 4.93 Diluted net income per share attributable to Aon shareholders $ 1.14 $ 0.62 $ 1.04 $ 2.09 $ 4.88 (Effect of change) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 20 $ 31 $ 10 $ (61 ) $ — Fiduciary investment income — — — — — Total revenue 20 31 10 (61 ) — Operating income 20 31 10 (61 ) — Net income 16 26 8 (50 ) — Less: Net income attributable to noncontrolling interests — — — — — Net income attributable to Aon shareholders $ 16 $ 26 $ 8 $ (50 ) $ — PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 0.06 $ 0.09 $ 0.03 $ (0.18 ) $ — Diluted net income per share attributable to Aon shareholders $ 0.06 $ 0.09 $ 0.03 $ (0.18 ) $ — (As revised) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,862 $ 2,831 $ 2,746 $ 3,222 $ 11,661 Fiduciary investment income 5 5 6 5 21 Total revenue 2,867 2,836 2,752 3,227 11,682 Operating income 461 308 423 656 1,848 Net income 357 214 311 540 1,422 Less: Net income attributable to noncontrolling interests 13 10 8 6 37 Net income attributable to Aon shareholders $ 344 $ 204 $ 303 $ 534 $ 1,385 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.21 $ 0.72 $ 1.08 $ 1.94 $ 4.93 Diluted net income per share attributable to Aon shareholders $ 1.20 $ 0.71 $ 1.07 $ 1.91 $ 4.88

Subsequent Event - Disposition

Subsequent Event - Disposition of Benefits Administration and Business Process Outsourcing (Notes)	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Event - Disposition of Benefits Administration and Business Process Outsourcing	Subsequent Event - Disposition of Benefits Administration and Business Process Outsourcing On February 9, 2017, Aon entered into a Purchase Agreement (the “Purchase Agreement”) with Tempo Acquisition, LLC (the “Buyer”). Pursuant to the Purchase Agreement, Aon has agreed to sell its benefits administration and business process outsourcing business (the “Tempo Business”) to the Buyer, an entity formed and controlled by affiliates of The Blackstone Group L.P. (the “Sponsor”), and certain designated purchasers that are direct or indirect subsidiaries of the Buyer. The Tempo Business develops and implements software and services solutions, and provides to clients, health and welfare and retirement benefits administration services, hosted and cloud-based human resources business process outsourcing administration and implementation services, and other related communications consulting services. Subject to the terms and conditions of the Purchase Agreement, the Buyer has agreed to purchase all of the outstanding equity interests of the Tempo Business, plus certain related assets, for a purchase price of (i) $4.3 billion in cash payable at closing, subject to customary adjustments set forth in the Purchase Agreement, and (ii) deferred consideration of up to $500 million , plus the assumption of certain liabilities (the “Transaction”). Under the Purchase Agreement, the deferred consideration is payable in cash in an amount equal to 20% of the incremental cash proceeds realized by the affiliates of the Sponsor and certain other equityholders of the Buyer from a liquidity event if (i) total realized cash proceeds to the Sponsor and such other equityholders over the life of their respective investments upon the closing of the Transaction (inclusive of all interim distributions) exceeds 2.25 times the amount of their equity investments in the Buyer at the closing of the Transaction and (ii) the internal rate of return over the life of their respective investments (inclusive of all interim distributions) exceeds 15% . The completion of the Transaction is subject to customary closing conditions, including, among others: (i) the expiration or termination of the waiting period under the Hart-Scott Rodino Antitrust Improvements Act of 1976, as amended; and (ii) the receipt of all approvals and the filing of all applicable filings under any relevant foreign jurisdictions that are required to be made or obtained as set forth in the Purchase Agreement. The Buyer’s obligations under the Purchase Agreement are not conditioned on receipt of financing; however, the Buyer is not required to complete the Transaction until after the completion of a customary fifteen days consecutive business-day marketing period to commence after the Company has provided required financial information to the Buyer. The Buyer has obtained an equity commitment (“Equity Commitment”) from affiliates of the Sponsor and debt financing commitments (“Debt Commitments”) from BofA Merrill Lynch, Barclays, Credit Suisse, Citigroup, Macquarie, Deutsche Bank, and Morgan Stanley, together with certain of their respective affiliates. The aggregate proceeds of the Equity Commitment and the Debt Commitments will be used by the Buyer (i) to pay the Purchase Price, and (ii) to pay fees and expenses incurred by the Buyer in connection with the Transaction. The Purchase Agreement provides that the Buyer will be required to pay to Aon a $215 million termination fee, together with the reimbursement of certain expenses, if the Purchase Agreement is terminated under certain circumstances. Both Aon and the Buyer have the right to terminate the Purchase Agreement if the closing has not occurred on or before August 9, 2017. An affiliate of the Sponsor has guaranteed the payment of the termination fee to the Company, if and when due, under the Purchase Agreement, together with certain other reimbursement obligations of the Buyer under the Purchase Agreement. Both Aon and the Buyer have agreed to indemnify each other for losses arising from certain breaches of the Purchase Agreement and for certain other liabilities, subject to certain limitations. Aon and the Buyer have made representations and warranties and have agreed to covenants related to the Tempo Business and the Transaction. Between the date of the Purchase Agreement and the closing of the Transaction, Aon has agreed to operate the Tempo Business in the ordinary course substantially as operated immediately prior to the date of the Purchase Agreement and to preserve the goodwill of the suppliers, contractors, licensors, employees, customers, and distributors of, and others having business relations with the Tempo Business. Aon and the Buyer have agreed to enter into certain Transaction-related agreements at the closing, including two commercial agreements, a transition services agreement, certain intellectual property license agreements, sub-leases and other customary agreements. Aon will continue to be a significant client of the Tempo Business and the Tempo Business has agreed to use Aon for its broking and other services. In connection with the Transaction, the Company expects to implement a cost reduction program.

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of the accompanying Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, 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, among other factors, 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.

Summary of Significant Accoun27

Summary of Significant Accounting Principles and Practices (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition Risk Solutions segment revenues primarily include insurance commissions and fees for services rendered and investment income on funds held on behalf of clients. Revenues are recognized when they are earned and realized or realizable. The Company considers revenues to be earned and realized or realizable when all of the following four conditions are met: (1) persuasive evidence of an arrangement exists, (2) the arrangement fee is fixed or determinable, (3) delivery or performance has occurred, and (4) collectability is reasonably assured. For brokerage commissions, revenue is typically recognized at the completion of the placement process, assuming all four criteria required to recognize revenue have been met. The placement process is typically considered complete on the effective date of the related policy. Commission revenues are recorded net of allowances for estimated policy cancellations, which are determined based on an evaluation of historical and current cancellation data. HR Solutions segment revenues consist primarily of fees paid by clients for consulting advice and outsourcing contracts. Fees paid by clients for consulting services are typically charged on an hourly, project or fixed-fee basis. Revenues from time-and-materials or cost-plus arrangements are recognized as services are performed, assuming all four criteria to recognize revenue have been met. Revenues from fixed-fee contracts are recognized as services are provided using a proportional-performance model or at the completion of a project based on facts and circumstances of the client arrangement. Revenues from health care exchange arrangements are typically recognized upon successful enrollment of participants, net of a reserve for estimated cancellations, assuming all four criteria to recognize revenue have been met. Reimbursements received for out-of-pocket expenses are recorded as a component of revenues. The Company’s outsourcing contracts typically have three -to- five year terms for both benefits services and human resources business process outsourcing (“HR BPO”) services. The Company recognizes revenues as services are performed, assuming all criteria to recognize revenue have been met. The Company may also receive implementation fees from clients either up-front or over the ongoing services period as a component of the fee per participant. Lump sum implementation fees received from a client are typically deferred and recognized ratably over the ongoing contract service period. If a client terminates an outsourcing service arrangement prior to the end of the contract, a loss on the contract may be recorded, if necessary, and any remaining deferred implementation revenues would typically be recognized over the remaining service period through the termination date. In connection with the Company’s long-term outsourcing service agreements, highly customized implementation efforts are often necessary to set up clients and their human resource or benefit programs on the Company’s systems and operating processes. Qualifying costs of implementation incurred prior to the services commencing are generally deferred and amortized over the period that the related ongoing services revenue is recognized. Deferred costs are assessed for recoverability on a periodic basis to the extent the deferred cost exceeds related deferred revenue.
Share-Based Compensation Costs	Share-Based Compensation Costs Share-based payments to employees, including grants of restricted share units and performance share awards, are measured based on estimated grant date fair value. The Company recognizes compensation expense over the requisite service period for awards expected to ultimately vest. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates.
Pension and Other Post-Retirement Benefits	Pension and Other Post-Retirement Benefits The Company records net period cost relating to its pension and other post-retirement benefit plans based on calculations that include various actuarial assumptions, including discount rates, assumed rates of return on plan assets, inflation rates, mortality rates, compensation increases, and turnover rates. The Company reviews its actuarial assumptions on an annual basis and modifies these assumptions based on current rates and trends. The effects of gains, losses, and prior service costs and credits are amortized over future service periods or future estimated lives if the plans are frozen. The funded status of each plan, calculated as the fair value of plan assets less the benefit obligation, is reflected in the Company’s Consolidated Statements of Financial Position using a December 31 measurement date.
Net Income per Share	Net Income per Share Basic net income per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, including participating securities, which consist of unvested share awards with non-forfeitable rights to dividends. Diluted net income per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding, which have been adjusted for the dilutive effect of potentially issuable ordinary shares (excluding those that are considered participating securities), including certain contingently issuable shares. The diluted earnings per share calculation reflects the more dilutive effect of either (1) the two-class method that assumes that the participating securities have not been exercised, or (2) the treasury stock method. Potentially issuable shares are not included in the computation of diluted income per share if their inclusion would be antidilutive.
Cash and Cash Equivalents and Short-term Investments	Cash and Cash Equivalents and Short-term Investments Cash and cash equivalents include cash balances and all highly liquid investments with initial maturities of three months or less. Short-term investments consist of money market funds
Fiduciary Assets and Liabilities	Fiduciary Assets and Liabilities In its capacity as an insurance agent and broker, Aon collects premiums from insureds and, after deducting its commission, remits the premiums to the respective insurers. Aon also collects claims or refunds from insurers on behalf of insureds. Uncollected premiums from insureds and uncollected claims or refunds from insurers are recorded as Fiduciary assets in the Company’s Consolidated Statements of Financial Position. Unremitted insurance premiums and claims are held in a fiduciary capacity and the obligation to remit these funds is recorded as Fiduciary liabilities in the Company’s Consolidated Statements of Financial Position. Some of the Company’s outsourcing agreements also require it to hold funds to pay certain obligations on behalf of clients. These funds are also recorded as Fiduciary assets with the related obligation recorded as Fiduciary liabilities in the Company’s Consolidated Statements of Financial Position.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company’s allowance for doubtful accounts with respect to receivables is based on a combination of factors, including evaluation of historical write-offs, aging of balances, and other qualitative and quantitative analyses.
Fixed Assets	Fixed Assets Fixed assets are stated at cost, less accumulated depreciation. Included in this category is internal use software, which is software that is acquired, internally developed or modified solely to meet internal needs, with no plan to market externally. Costs related to directly obtaining, developing or upgrading internal use software are capitalized. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Asset Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill represents the excess of acquisition cost over the fair value of the net assets in the acquisition of a business. Goodwill is allocated to various reporting units, which are one reporting level below the operating segment. Upon disposition of a business entity, goodwill is allocated to the disposed entity based on the fair value of that entity compared to the fair value of the reporting unit in which it was included. Goodwill is not amortized, but instead is tested for impairment at least annually. The goodwill impairment test is performed at the reporting unit level. The Company initially performs a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If such a determination is made, then the Company will perform a two-step quantitative analysis. First, the fair value of each reporting unit is compared to its carrying value. If the fair value of the reporting unit is less than its carrying value, the Company performs a hypothetical purchase price allocation based on the reporting unit’s fair value to determine the fair value of the reporting unit’s goodwill. Any resulting difference will be a charge to Other general expenses in the Consolidated Statements of Income in the period in which the determination is made. Fair value is determined using a combination of present value techniques and market prices of comparable businesses. Intangible assets are primarily comprised of tradenames and customer-related, contract-based, and technology assets. Tradenames are not amortized when such assets have been determined to have indefinite useful lives, and are tested at least annually for impairments using an analysis of expected future cash flows. Interim impairment testing may be performed when events or changes in circumstances indicate that the carrying amount of the intangible asset may not be recoverable. Customer related and contract based assets are amortized over periods ranging from 1 to 16 years, with a weighted average original life of 11 years. Technology assets are typically amortized over 7 years.
Derivatives	Derivatives Derivative instruments are recognized in the Consolidated Statements of Financial Position at fair value. Where the Company has entered into master netting agreements with counterparties, the derivative positions are netted by counterparty and are reported accordingly in other assets or other liabilities. Changes in the fair value of derivative instruments are recognized in earnings each period, unless the derivative is designated and qualifies as a cash flow or net investment hedge. The Company has historically designated the following hedging relationships for certain transactions: (i) a hedge of the change in fair value of a recognized asset or liability or firm commitment (“fair value hedge”), (ii) a hedge of the variability in cash flows from a recognized variable-rate asset or liability or forecasted transaction (“cash flow hedge”), and (iii) a hedge of the net investment in a foreign operation (“net investment hedge”). In order for a derivative to qualify for hedge accounting, the derivative must be formally designated as a fair value, cash flow, or a net investment hedge by documenting the relationship between the derivative and the hedged item. The documentation must include a description of the hedging instrument, the hedged item, the risk being hedged, Aon’s risk management objective and strategy for undertaking the hedge, the method for assessing the effectiveness of the hedge, and the method for measuring hedge ineffectiveness. Additionally, the hedge relationship must be expected to be highly effective at offsetting changes in either the fair value or cash flows of the hedged item at both the inception of the hedge and on an ongoing basis. Aon assesses the ongoing effectiveness of its hedges and measures and records hedge ineffectiveness, if any, at the end of each quarter or more frequently if facts and circumstances require. For a derivative designated as a hedging instrument, the changes in the fair value of a recognized asset or liability or a firm commitment (a fair value hedge), the gain or loss is recognized in earnings in the period of change together with the offsetting loss or gain on the hedged item attributable to the risk being hedged. The effect is to reflect in earnings the extent to which the hedge is not effective in achieving offsetting changes in fair value. For a cash flow hedge that qualifies for hedge accounting, the effective portion of the change in fair value of a hedging instrument is recognized in Other Comprehensive Income (“OCI”) and subsequently reclassified to earnings in the same period the hedged item impacts earnings. The ineffective portion of the change in fair value is recognized immediately in earnings. For a net investment hedge, the effective portion of the change in fair value of the hedging instrument is recognized in OCI as part of the cumulative translation adjustment, while the ineffective portion is recognized immediately in earnings. Changes in the fair value of a derivative that is not designated as part of a hedging relationship (commonly referred to as an “economic hedge”) are recorded in Other income in the Consolidated Statements of Income. The Company discontinues hedge accounting prospectively when (1) the derivative expires or is sold, terminated, or exercised, (2) the qualifying criteria are no longer met, or (3) management removes the designation of the hedging relationship.
Foreign Currency	Foreign Currency Certain of the Company’s non-US operations use their respective local currency as their functional currency. These operations that do not have the U.S. dollar as their functional currency translate their financial statements at the current rates of exchange in effect at the balance sheet date and revenues and expenses using rates that approximate those in effect during the period. The resulting translation adjustments are included in net foreign currency translation adjustments within the Consolidated Statements of Shareholders’ Equity. Gains and losses from the remeasurement of monetary assets and liabilities that are denominated in a non-functional currency are included in Other income within the Consolidated Statements of Income.
Income Taxes	Income Taxes Deferred income taxes are recognized for the effect of temporary differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted marginal tax rates and laws that are currently in effect. The effect on deferred tax assets and liabilities from a change in tax rates is recognized in the period when the rate change is enacted. Deferred tax assets are reduced by valuation allowances if, based on the consideration of all available evidence, it is more likely than not that some portion of the deferred tax asset will not be realized. Significant weight is given to evidence that can be objectively verified. Deferred tax assets are realized by having sufficient future taxable income to allow the related tax benefits to reduce taxes otherwise payable. The sources of taxable income that may be available to realize the benefit of deferred tax assets are future reversals of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences and carry-forwards, taxable income in carry-back years and tax planning strategies that are both prudent and feasible. The Company recognizes the effect of income tax positions only if sustaining those positions is more likely than not. Tax positions that meet the more likely than not recognition threshold but are not highly certain are initially and subsequently measured based on the largest amount of benefit that is greater than 50% likely of being realized upon settlement with the taxing authority. Only information that is available at the reporting date is considered in the Company’s recognition and measurement analysis, and events or changes in facts and circumstances are accounted for in the period in which the event or change in circumstance occurs. The Company records penalties and interest related to unrecognized tax benefits in Income taxes in the Company’s Consolidated Statements of Income.
New Accounting Pronouncements	New Accounting Pronouncements Income Tax Consequences of Intercompany Transactions In October 2016, the Financial Accounting Standards Board (“FASB”) issued new accounting guidance on the income tax consequences of intra-entity asset transfers other than inventory. The guidance will require that the seller and buyer recognize the consolidated current and deferred income tax consequences of a transaction in the period the transaction occurs rather than deferring to a future period and recognizing those consequences when the asset has been sold to an outside party or otherwise recovered through use (i.e. depreciated, amortized, impaired). An entity will apply the new guidance on a modified retrospective basis with a cumulative effect adjustment to retained earnings as of the beginning of the period of adoption. The new guidance is effective for Aon in the first quarter of 2018, and the Company is currently evaluating the impact that the standard will have on its Consolidated Financial Statements. Statement of Cash Flows In August 2016, the FASB issued new accounting guidance on the classification of certain cash receipts and cash payments. Under the new guidance, an entity will no longer have discretion to choose the classification for a number of transactions, including contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies, and distributions received from equity method investees. The new standard will be effective for the Company in the first quarter of 2018, with early application permitted. An entity will apply the new guidance through retrospective adjustment to all periods presented. The retrospective approach includes a practical expedient that entities may apply should retrospective application be impracticable; in this case, the amendments for these issues may be applied prospectively as of the earliest date practicable. The guidance will not have a material impact upon the Company’s Consolidated Statement of Cash Flows. Credit Losses In June 2016, the FASB issued new accounting guidance on the measurement of credit losses on financial instruments. The new guidance 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 guidance through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The guidance is effective for Aon in the first quarter of 2020 and early adoption is permitted beginning in the first quarter of 2019. Aon is currently evaluating the impact that the standard will have on its Consolidated Financial Statements, as well as the method of transition and period of adoption. Share-based Compensation In March 2016, the FASB issued new accounting guidance on several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The new guidance requires all excess tax benefits and tax deficiencies to be recognized as income tax expense or benefit in the income statement and treated as discrete items in the reporting period. Further, excess tax benefits are required to be classified along with other income tax cash flows as an operating activity. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements, forfeitures, and intrinsic value should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments related to the presentation of employee taxes paid on the statement of cash flows when an employer withholds shares to meet the minimum statutory withholding requirement should be applied retrospectively. Amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement and the practical expedient for estimating expected term should be applied prospectively. An entity may elect to apply the amendments related to the presentation of excess tax benefits on the statement of cash flows using either a prospective transition method or a retrospective transition method. The guidance is effective for Aon in the first quarter of 2017 and early adoption is permitted. Upon the adoption of this guidance on January 1, 2017, the Company expects to recognize an increase to Deferred tax assets of approximately $49 million through a cumulative-effect adjustment to Retained earnings for excess tax benefits not previously recognized. On a prospective basis, excess tax benefits will be recognized in the Consolidated Statements of Income each quarter as share-based payment awards vest, which could have a significant impact on Income tax expense in the Consolidated Statement of Income and Additional paid-in capital in the Consolidated Statements of Financial Position. The impact will be driven, in part, by the difference between the Company’s share price at the time share-based payment transactions vest or options are exercised in the future periods and the fair value of the awards at the date of grant. Amendments related to the presentation of excess tax benefits on the Consolidated Statement of Cash Flows, which will be applied prospectively, may have a significant impact on Cash Flows from Operating Activities and Cash Flows from Financing Activities in the Consolidated Statements of Cash Flows. The impact will also be driven by the Company’s share price at the time share-based payment transactions vest in future periods. The Company does not expect other elements of the guidance to have a material impact on its Consolidated Financial Statements. Leases In February 2016, the FASB issued new accounting guidance on leases, which requires lessees to recognize assets and liabilities for most leases. Under the new guidance, a lessee should recognize in the Consolidated Statement of Financial Position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from currently effective U.S. GAAP. The new standard will be effective for the Company in the first quarter of 2019, with early application permitted. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply. 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. Aon is currently evaluating the impact the standard will have on its Consolidated Financial Statements, as well as the method of transition and period of adoption. Financial Assets and Liabilities In January 2016, the FASB issued new accounting guidance on recognition and measurement of financial assets and financial liabilities. The amendments in the new guidance make targeted improvements, which include the requirement to measure equity investments with readily determinable fair values at fair value through net income, simplification of the impairment assessment for equity investments without readily determinable fair values, adjustments to existing and additional disclosure requirements, and additional tax considerations. An entity should apply the amendments by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. The amendments related to equity securities without readily determinable fair values (including disclosure requirements) should be applied prospectively to equity investments that exist as of the date of adoption of the guidance. The guidance is effective for the Company in the first quarter of 2018 and early adoption is permitted. Aon is currently evaluating the impact that the standard will have on the its Consolidated Financial Statements, as well as the method of transition and period of adoption. Presentation of Deferred Taxes In November 2015, the FASB issued new accounting guidance on the balance sheet presentation of deferred taxes, which requires that deferred tax liabilities and assets be classified as non-current. Aon early adopted this guidance in the second quarter of 2016 and retrospectively applied its requirements to all periods presented. For the year ended December 31, 2015, Aon reclassified its current deferred tax positions to non-current and netted the new balances by jurisdiction, which increased Deferred tax assets by $93 million and decreased Deferred tax liabilities by $139 million on the Consolidated Statement of Financial Position. Debt Issuance Costs In April 2015, the FASB issued new accounting guidance on the presentation of debt issuance costs, which requires debt issuance costs to be presented in the balance sheet as a direct deduction from the associated debt liability. Debt issuance costs related to its line-of-credit arrangements will be shown within Other non-current assets. This guidance was effective for Aon in the first quarter of 2016, which required retrospective application to prior year comparable periods. For the year ended December 31, 2015, Aon reclassified $4 million from Other current assets and $33 million from Other non-current assets to Long-term debt on the Consolidated Statement of Financial Position. Consolidations In February 2015, the FASB issued new accounting guidance on consolidations, which will eliminate the deferral granted to investment companies from applying the variable interest entities guidance and make targeted amendments to the current consolidation guidance. The new guidance applies to all entities involved with limited partnerships or similar entities and requires re-evaluation of these entities under the revised guidance, which could change previous consolidation conclusions. The guidance was effective for the Company in the first quarter of 2016. The adoption of this guidance did not have a material impact on the Company’s Consolidated Financial Statements. Revenue Recognition In May 2014, the FASB issued new accounting guidance on revenue from contracts with customers, which, when effective, will supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principal of the standard is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. The standard is effective for Aon in the first quarter of 2018 and early adoption is permitted beginning the first quarter of 2017. Two methods of transition are permitted upon adoption: full retrospective and modified retrospective. Under the full retrospective method, prior periods would be restated under the new revenue standard, providing a comparable view across all periods presented. Under the modified retrospective method, prior periods would not be restated. Rather, revenues and other disclosures for pre-2018 periods would be provided in the notes to the financial statements as previously reported under the current revenue standard. The Company will adopt this standard in the first quarter of 2018 and is evaluating both methods of transition; however, it is currently anticipated that a modified retrospective adoption approach will be used. A preliminary assessment to determine the impacts of the new accounting standard has been performed. The Company is currently implementing accounting and operational processes which will be impacted by the new standard, but is unable to provide information on quantitative impacts at this time. However, the primary impacts of the new standard to the Company’s product and service lines are anticipated to be as follows: The Company currently recognizes revenue for certain brokerage activities within the Risk Solutions business over a period of time either due to the transfer of value to customers or as the remuneration becomes determinable. Under the new standard, this revenue will be recognized on the effective date of the associated policies when control of the policy transfers to the customer. As a result, revenue from these arrangements will be recognized in earlier periods under the new standard in comparison to the current guidance and will change the timing and amount of revenue recognized for annual and interim periods. Similarly, the Company is currently assessing the timing and measurement of revenue recognition under the new standard for outsourcing and consulting operations within the HR Solutions business. Additionally, the new standard provides guidance on accounting for certain revenue-related costs including when to capitalize costs associated with obtaining and fulfilling a contract. These costs are currently expensed as incurred under existing U.S. GAAP. These assets recognized for the costs to obtain and/or fulfill a contract will be amortized on a on a systematic basis that is consistent with the transfer of the services to which the asset relates. The Company is quantifying the nature and amount of costs that would qualify for capitalization and the amount of amortization that will be recognized in each period.

Basis of Presentation (Tables)

Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Prior Period Adjustments	The impact to the Consolidated Statements of Cash Flows previously filed in unaudited Quarterly Reports on Form 10-Q is as follows (in millions): Q1 2016 Q2 2016 Q3 2016 (Unaudited) As Reported Effect of Change (1) As Revised As Reported Effect of Change (1) As Revised As Reported Effect of Change (1) As Revised Net Income $ 327 $ 10 $ 337 $ 607 $ 38 $ 645 $ 921 $ 50 $ 971 Change in assets and liabilities: Receivables, net 110 (13 ) 97 175 (47 ) 128 289 (61 ) 228 Other assets and liabilities $ 69 $ 3 $ 72 $ 56 $ 9 $ 65 $ 83 $ 11 $ 94 (1) No net impact to Cash Provided by Operating Activities.

Summary of Significant Accoun29

Summary of Significant Accounting Principles and Practices (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of estimated useful lives of assets	Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets, which are generally as follows: Asset Description Asset Life Software Lesser of the life of an associated license, or 4 to 7 years Leasehold improvements Lesser of estimated useful life or lease term, not to exceed 10 years Furniture, fixtures and equipment 4 to 10 years Computer equipment 4 to 6 years Buildings 35 years Automobiles 6 years

Other Financial Data (Tables)

Other Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Other Financial Data [Abstract]
Other income (Expense)	Other income consists of the following (in millions): Years ended December 31 2016 2015 2014 Equity earnings $ 13 $ 13 $ 12 Net gain on disposals of businesses 39 82 24 Foreign currency remeasurement (loss) gain (2 ) 30 18 (Loss) income on financial instruments (14 ) (24 ) (15 ) Other — (1 ) 5 Total $ 36 $ 100 $ 44
Schedule of Allowance for Doubtful Accounts	An analysis of the allowance for doubtful accounts is as follows (in millions): Years ended December 31 2016 2015 2014 Balance at January 1 $ 58 $ 74 $ 90 Provision charged to operations 11 13 12 Accounts written off, net of recoveries (14 ) (34 ) (33 ) Foreign currency translation 3 5 5 Balance at December 31 $ 58 $ 58 $ 74
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions): As of December 31 2016 2015 Taxes receivable $ 100 $ 94 Prepaid expenses 125 130 Deferred project costs 87 92 Other 39 13 Total $ 351 $ 329
Components of Fixed assets, net	The components of Fixed assets, net are as follows (in millions): As of December 31 2016 2015 Software $ 948 $ 1,095 Leasehold improvements 452 422 Computer equipment 417 358 Furniture, fixtures and equipment 300 315 Construction in progress 93 76 Other 115 115 Fixed assets, gross 2,325 2,381 Less: Accumulated depreciation 1,560 1,616 Fixed assets, net $ 765 $ 765
Schedule of Other Non-current Assets	The components of Other non-current assets are as follows (in millions): As of December 31 2016 2015 Deferred project costs $ 183 $ 210 Investments 119 135 Taxes receivable 82 82 Other 170 165 Total $ 554 $ 592
Schedule of Other Current Liabilities	The components of Other current liabilities are as follows (in millions): As of December 31 2016 2015 Deferred revenue $ 393 $ 394 Taxes payable 78 94 Other 402 331 Total $ 873 $ 819
Schedule of Other Non-current Liabilities	The components of Other non-current liabilities are as follows (in millions): As of December 31 2016 2015 Taxes payable $ 288 $ 223 Leases 169 166 Deferred revenue 140 159 Compensation and benefits 56 59 Other 191 162 Total $ 844 $ 769

Acquisitions and Dispositions31

Acquisitions and Dispositions of Businesses (Tables)	12 Months Ended
	Dec. 31, 2016
Business Combinations and Discontinued Operations and Disposal Groups [Abstract]
Schedule of number of acquisitions	The number of acquisitions completed within each reportable segment is as follows: Years ended December 31 2016 2015 Risk Solutions 5 4 HR Solutions 3 3 Total 8 7
Consideration transferred and preliminary value of intangible assets	The following table includes the preliminary fair values of consideration transferred and intangible assets acquired as a result of the Company’s acquisitions (in millions): Year ended December 31 2015 Consideration $ 27 Intangible assets: Goodwill $ 18 Other intangible assets 6 Total intangible assets $ 24 The following table includes the preliminary fair values of consideration transferred, assets acquired, and liabilities assumed as a result of the Company’s acquisitions (in millions): Year ended December 31 2016 Cash $ 891 Deferred and contingent consideration 43 Aggregate consideration transferred 934 Assets acquired: Cash and cash equivalents 12 Receivables, net 52 Goodwill 642 Intangible assets, net 366 Fixed assets, net 30 Other assets 2 Total assets acquired 1,104 Liabilities assumed: Current liabilities 163 Other liabilities 7 Total liabilities assumed 170 Net assets acquired $ 934
Schedule of number of disposals	The number of dispositions completed within each reportable segment is as follows: Years ended December 31 2016 2015 2014 Risk Solutions 4 4 2 HR Solutions 1 3 0 Total 5 7 2

Goodwill and Other Intangible32

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
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 by reportable segment for the years ended December 31, 2016 and 2015 , respectively, are as follows (in millions): Risk Solutions HR Solutions Total Balance as of January 1, 2015 $ 5,911 $ 2,949 $ 8,860 Goodwill related to current year acquisitions 2 16 18 Goodwill related to disposals (1 ) (76 ) (77 ) Goodwill related to prior year acquisitions — — — Foreign currency translation (319 ) (34 ) (353 ) Balance as of December 31, 2015 $ 5,593 $ 2,855 $ 8,448 Goodwill related to current year acquisitions 632 10 642 Goodwill related to disposals (8 ) (26 ) (34 ) Goodwill related to prior year acquisitions 4 — 4 Foreign currency translation (268 ) (45 ) (313 ) Balance as of December 31, 2016 $ 5,953 $ 2,794 $ 8,747
Schedule of other intangible assets by asset class	Other intangible assets by asset class are as follows (in millions): As of December 31 2016 2015 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Intangible assets with indefinite lives: Tradenames $ 998 $ — $ 998 $ 1,019 $ — $ 1,019 Intangible assets with finite lives: Customer related and contract based 3,108 1,971 1,137 2,886 1,809 1,077 Technology and other 574 486 88 541 457 84 Total $ 4,680 $ 2,457 $ 2,223 $ 4,446 $ 2,266 $ 2,180
Schedule of estimated future amortization expense on intangible assets	The estimated future amortization for finite-lived intangible assets as of December 31, 2016 is as follows (in millions): Risk Solutions HR Solutions Total 2017 $ 123 $ 136 $ 259 2018 118 91 209 2019 107 73 180 2020 97 61 158 2021 66 53 119 Thereafter 239 61 300 Total $ 750 $ 475 $ 1,225

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Summary of outstanding debt	The following is a summary of outstanding debt (in millions): As of December 31 2016 2015 (1) 3.875% Senior Notes due December 2025 $ 744 $ — 5.00% Senior Notes due September 2020 598 597 4.75% Senior Notes due May 2045 592 591 3.50% Senior Notes due June 2024 594 593 4.60% Senior Notes due June 2044 543 543 2.875% Senior Notes due May 2026 (EUR 500M) 516 541 8.205% Junior Subordinated Notes due January 2027 521 521 3.125% Senior Notes due May 2016 — 500 2.80% Senior Notes due March 2021 397 396 4.00% Senior Notes due November 2023 347 347 6.25% Senior Notes due September 2040 295 295 4.76% Senior Notes due March 2018 (CAD 375M) 277 270 4.45% Senior Notes due May 2043 246 246 4.25% Senior Notes due December 2042 197 195 Commercial paper 329 50 Other 9 15 Total debt 6,205 5,700 Less short-term and current portion of long-term debt 336 562 Total long-term debt $ 5,869 $ 5,138 (1) Amended to reflect the adoption of new guidance related to the presentation of debt issuance costs as described in Note 2 “Summary of Significant Accounting Principles and Practices.”
Repayments of long-term debt	Repayments of total debt are as follows (in millions): 2017 $ 336 2018 278 2019 — 2020 600 2021 400 Thereafter 4,700 Total Repayments 6,314 Unamortized discount, premium, and debt issuance cost (109 ) Total Debt $ 6,205

Lease Commitments (Tables)

Lease Commitments (Tables)	12 Months Ended
	Dec. 31, 2016
Leases, Operating [Abstract]
Rental expenses for operating leases	Rental expenses (including amounts applicable to taxes, insurance and maintenance) for operating leases are as follows (in millions): Years ended December 31 2016 2015 2014 Rental expense $ 400 $ 454 $ 455 Less: Sub lease rental income (64 ) (83 ) (75 ) Net rental expense $ 336 $ 371 $ 380
Future minimum rental payments under operating leases for continuing operations that have initial or remaining noncancelable lease terms in excess of one year, net of sublease rental income	At December 31, 2016 , 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): Years ended December 31, 2016 Gross rental commitments Rentals from subleases Net rental commitments 2017 $ 355 $ (55 ) $ 300 2018 317 (44 ) 273 2019 283 (38 ) 245 2020 237 (34 ) 203 2021 214 (33 ) 181 Thereafter 696 (47 ) 649 Total minimum payments required $ 2,102 $ (251 ) $ 1,851

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income from continuing operations before income tax	Income before income tax and the provision for income tax consist of the following (in millions): Years ended December 31 2016 2015 2014 Income before income taxes: U.K. $ (202 ) $ 149 $ 347 U.S. (104 ) (51 ) (55 ) Other 1,975 1,591 1,473 Total $ 1,669 $ 1,689 $ 1,765 Income tax expense (benefit): Current: U.K. $ (54 ) $ 43 $ 1 U.S. federal 94 137 156 U.S. state and local — 54 75 Other 223 256 236 Total current tax expense $ 263 $ 490 $ 468 Deferred tax expense (benefit): U.K. $ 59 $ (39 ) $ 38 U.S. federal (47 ) (140 ) (133 ) U.S. state and local 6 (14 ) (24 ) Other (42 ) (30 ) (15 ) Total deferred tax benefit $ (24 ) $ (223 ) $ (134 ) Total income tax expense $ 239 $ 267 $ 334
Reconciliation of the income tax provisions based on the U.S. statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements	The reconciliation to the provisions reflected in the Consolidated Financial Statements is as follows: Years ended December 31 2016 2015 2014 Statutory tax rate 20.0% 20.3% 21.5% U.S. state income taxes, net of U.S. federal benefit 0.7 0.5 1.5 Taxes on international operations (1) (8.5) (6.0) (8.9) Nondeductible expenses 1.2 2.2 1.7 Adjustments to prior year tax requirements (1.0) (1.3) 0.9 Adjustments to valuation allowances (1.8) (1.2) 0.6 Change in uncertain tax positions 3.0 1.4 1.7 Other — net 0.7 (0.1) (0.1) Effective tax rate 14.3% 15.8% 18.9% (1) The Company determines the adjustment for taxes on international operations based on the difference between the statutory tax rate applicable to earnings in each foreign jurisdiction and the enacted rate of 20.0% , 20.3% and 21.5% at December 31, 2016 , 2015 , and 2014 , respectively. The benefit to the Company’s effective income tax rate from taxes on international operations relates to benefits from lower-taxed global operations, primarily due to the use of global funding structures.
Components of Aon's deferred tax assets and liabilities	The components of the Company’s deferred tax assets and liabilities are as follows (in millions): As of December 31 2016 2015 Deferred tax assets: Employee benefit plans $ 661 $ 635 Net operating/capital loss and tax credit carryforwards 399 336 Accrued interest 166 293 Other accrued expenses 102 98 Brokerage fee arrangements (1) 66 66 Deferred revenue 57 65 Investment basis differences 48 56 Other 60 57 Total 1,559 1,606 Valuation allowance on deferred tax assets (130 ) (162 ) Total $ 1,429 $ 1,444 Deferred tax liabilities: Intangibles and property, plant and equipment $ (982 ) $ (961 ) Other accrued expenses (101 ) (99 ) Deferred costs (20 ) (30 ) Unrealized foreign exchange gains (26 ) (29 ) Unremitted earnings (29 ) (18 ) Other (50 ) (44 ) Total $ (1,208 ) $ (1,181 ) Net deferred tax asset $ 221 $ 263 (1) Refer to Note 1 “Basis of Presentation” for details regarding the Revision of Previously Issued Financial Statements.
Deferred income taxes (assets and liabilities netted by jurisdiction) as classified in the Consolidated Statements of Financial Position	Deferred income taxes (assets and liabilities have been netted by jurisdiction) have been classified in the Consolidated Statements of Financial Position as follows (in millions): As of December 31 2016 2015 Deferred tax assets — non-current (2) $ 322 $ 300 Deferred tax liabilities — non-current (2) (101 ) (37 ) Net deferred tax asset $ 221 $ 263 (2) For the year ended December 31, 2015, Aon reclassified its current deferred tax positions to non-current and netted the new balances by jurisdiction. Refer to Note 2 “Summary of Significant Accounting Principles and Practices” for additional details.
Summary of operating and capital loss carryforwards	The Company had the following operating and capital loss carryforwards (in millions): As of December 31 2016 2015 UK Operating loss carryforwards $ 325 $ 449 Capital loss carryforwards 294 360 US Federal operating loss carryforwards $ 196 $ 8 State operating loss carryforwards 474 443 Other Non-US Operating loss carryforwards $ 350 $ 245 Capital loss carryforwards 218 206
Reconciliation of the beginning and ending amount of unrecognized tax benefits	The following is a reconciliation of the Company’s beginning and ending amount of uncertain tax positions (in millions): 2016 2015 Balance at January 1 $ 238 $ 211 Additions based on tax positions related to the current year 36 31 Additions for tax positions of prior years 20 53 Reductions for tax positions of prior years (12 ) (18 ) Settlements — (32 ) Business combinations 2 — Lapse of statute of limitations (5 ) (5 ) Foreign currency translation (1 ) (2 ) Balance at December 31 $ 278 $ 238

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of components of weighted average number of shares outstanding	Weighted average shares outstanding are as follows (in millions): Year ended December 31, 2016 2015 2014 Basic weighted-average ordinary shares outstanding 268.1 280.8 295.5 Dilutive effect of potentially issuable shares 2.2 3.0 4.1 Diluted weighted-average ordinary shares outstanding 270.3 283.8 299.6
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 Post-Retirement Benefit Obligation (2) Total Balance at January 1, 2014 $ (21 ) $ 169 $ (2,522 ) $ (2,374 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (13 ) (492 ) (563 ) (1,068 ) Tax benefit 4 (12 ) 229 221 Other comprehensive loss before reclassifications, net (9 ) (504 ) (334 ) (847 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 20 — 106 126 Tax benefit (7 ) — (32 ) (39 ) Amounts reclassified from accumulated other comprehensive loss, net 13 — 74 87 Net current period other comprehensive (loss) income 4 (504 ) (260 ) (760 ) Balance at December 31, 2014 (17 ) (335 ) (2,782 ) (3,134 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (4 ) (467 ) 82 (389 ) Tax benefit 1 31 (9 ) 23 Other comprehensive loss before reclassifications, net (3 ) (436 ) 73 (366 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 11 — 117 128 Tax benefit (16 ) — (35 ) (51 ) Amounts reclassified from accumulated other comprehensive loss, net (5 ) — 82 77 Net current period other comprehensive (loss) income (8 ) (436 ) 155 (289 ) Balance at December 31, 2015 (25 ) (771 ) (2,627 ) (3,423 ) Other comprehensive loss before reclassifications: Other comprehensive loss before reclassifications (25 ) (490 ) (276 ) (791 ) Tax benefit 6 (3 ) 74 77 Other comprehensive loss before reclassifications, net (19 ) (493 ) (202 ) (714 ) Amounts reclassified from accumulated other comprehensive loss: Amounts reclassified from accumulated other comprehensive loss 10 — 322 332 Tax benefit (3 ) — (104 ) (107 ) Amounts reclassified from accumulated other comprehensive loss, net 7 — 218 225 Net current period other comprehensive (loss) income (12 ) (493 ) 16 (489 ) Balance at December 31, 2016 $ (37 ) $ (1,264 ) $ (2,611 ) $ (3,912 ) (1) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Other income (2) Reclassifications from this category included in Accumulated other comprehensive loss are recorded in Compensation and benefits

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Expense recognized for defined contribution savings plans, included in compensation and benefits and discontinued operations in the consolidated statements of income	The expense recognized for these plans is included in Compensation and benefits in the Consolidated Statements of Income, as follows (in millions): Years ended December 31 2016 2015 2014 U.S. $ 142 $ 133 $ 123 U.K. 43 42 42 Netherlands and Canada 27 25 30 Total $ 212 $ 200 $ 195
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status	The following tables provide a reconciliation of the changes in the projected benefit obligations and fair value of assets for the years ended December 31, 2016 and 2015 and a statement of the funded status as of December 31, 2016 and 2015 , for the material U.K. plans, U.S. plans and other major plans, which are located in the Netherlands and Canada. These plans represent approximately 92% of the Company’s projected benefit obligations. U.K. U.S. Other (millions) 2016 2015 2016 2015 2016 2015 Change in projected benefit obligation At January 1 $ 4,985 $ 5,529 $ 3,160 $ 3,350 $ 1,177 $ 1,399 Service cost — 1 — — — — Interest cost 158 198 111 131 29 33 Plan amendment (20 ) 27 — — — (10 ) Settlements (159 ) — (281 ) — — — Plan transfer and acquisitions — (2 ) — (18 ) — — Actuarial loss (gain) 32 (83 ) (43 ) (25 ) (7 ) 24 Benefit payments (242 ) (217 ) (139 ) (133 ) (39 ) (38 ) Change in discount rate 1,079 (247 ) 100 (145 ) 100 (66 ) Foreign currency impact (959 ) (221 ) — — (33 ) (165 ) At December 31 $ 4,874 $ 4,985 $ 2,908 $ 3,160 $ 1,227 $ 1,177 Accumulated benefit obligation at end of year $ 4,874 $ 4,985 $ 2,908 $ 3,160 $ 1,191 $ 1,135 Change in fair value of plan assets At January 1 $ 5,903 $ 6,224 $ 1,951 $ 2,036 $ 1,019 $ 1,161 Actual return on plan assets 1,233 91 116 (60 ) 111 8 Employer contributions 67 65 36 108 20 21 Settlements (159 ) — (281 ) — — — Plan transfer and acquisitions — (3 ) — — — — Benefit payments (242 ) (217 ) (139 ) (133 ) (39 ) (38 ) Foreign currency impact (1,127 ) (257 ) — — (35 ) (133 ) At December 31 $ 5,675 $ 5,903 $ 1,683 $ 1,951 $ 1,076 $ 1,019 Market related value at end of year $ 5,675 $ 5,903 $ 1,819 $ 2,064 $ 1,076 $ 1,019 Amount recognized in Statement of Financial Position at December 31 Funded status $ 801 $ 918 $ (1,225 ) $ (1,209 ) $ (151 ) $ (158 ) Unrecognized prior-service cost 19 46 6 9 (6 ) (7 ) Unrecognized loss 1,237 1,465 1,612 1,723 400 389 Net amount recognized $ 2,057 $ 2,429 $ 393 $ 523 $ 243 $ 224
Amounts recognized in the Consolidated Statements of Financial Position	Amounts recognized in the Consolidated Statements of Financial Position consist of (in millions): U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Prepaid benefit cost (1) $ 836 $ 1,012 $ — $ — $ — $ — Accrued benefit liability (2) (35 ) (94 ) (1,225 ) (1,209 ) (151 ) (158 ) Accumulated other comprehensive loss 1,256 1,511 1,618 1,732 394 382 Net amount recognized $ 2,057 $ 2,429 $ 393 $ 523 $ 243 $ 224 (1) Included in Prepaid pension (2) Included in Other current liabilities and Pension, other post retirement, and post employment liabilities
Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized as components of net periodic benefit cost	Amounts recognized in Accumulated other comprehensive loss (income) that have not yet been recognized as components of net periodic benefit cost at December 31, 2016 and 2015 consist of (in millions): U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Net loss $ 1,237 $ 1,465 $ 1,612 $ 1,723 $ 400 $ 389 Prior service cost (income) 19 46 6 9 (6 ) (7 ) Total $ 1,256 $ 1,511 $ 1,618 $ 1,732 $ 394 $ 382
Components of net periodic benefit cost for the pension plans	The following table provides the components of net periodic benefit (income) cost for the plans (in millions): U.K. U.S. Other 2016 2015 2014 2016 2015 2014 2016 2015 2014 Service cost $ — $ 1 $ 1 $ — $ — $ 2 $ — $ — $ — Interest cost 158 198 230 111 131 129 29 33 47 Expected return on plan assets, net of administration expenses (243 ) (307 ) (326 ) (156 ) (154 ) (157 ) (48 ) (50 ) (59 ) Amortization of prior-service cost 2 1 1 2 2 2 — — — Amortization of net actuarial loss 31 41 52 50 54 42 10 11 10 Net periodic benefit (income) cost (52 ) (66 ) (42 ) 7 33 18 (9 ) (6 ) (2 ) Settlement expense 61 — — 158 — — — — — Curtailment gain and other — — — — — — — — (2 ) Total net periodic benefit cost (income) $ 9 $ (66 ) $ (42 ) $ 165 $ 33 $ 18 $ (9 ) $ (6 ) $ (4 )
Weighted-average assumptions used to determine future benefit obligations and net periodic benefit cost	The weighted-average assumptions used to determine benefit obligations are as follows: U.K. U.S. Other 2016 2015 2016 2015 2016 2015 Discount rate 2.77% 3.96% 3.53-4.11% 3.69-4.43% 1.85-3.81% 2.43-3.96% Rate of compensation increase 3.70 - 4.20% 3.63-4.13% N/A N/A 1.00-3.50% 2.00-3.50% Underlying price inflation 1.83% 1.88% N/A N/A 2.00-2.50% 2.00-2.50% The weighted-average assumptions used to determine the net periodic benefit cost are as follows: U.K. U.S. Other 2016 2015 2014 2016 2015 2014 2016 2015 2014 Discount rate 3.96% 3.70% 4.55% 3.69 - 4.43% 3.37 - 4.08% 3.97 - 4.87% 2.43 - 3.96% 2.03 - 3.91% 3.60 - 4.71% Expected return on plan assets, net of administration expenses 4.55% 5.09% 6.00% 7.81% 7.96% 8.80% 3.47 - 4.95% 3.99 - 5.21% 4.70 - 6.50% Rate of compensation increase 3.63 - 4.13% 3.55 - 4.05% 3.70 - 4.40% N/A N/A N/A 2.00 - 3.50% 2.25 - 3.50% 2.25 - 3.50%
Estimated Future Benefit Payments	Estimated future benefit payments for plans are as follows at December 31, 2016 (in millions): U.K. U.S. Other 2017 $ 124 $ 168 $ 39 2018 130 180 40 2019 140 187 40 2020 148 191 41 2021 156 185 42 2022 – 2026 892 893 228
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	The fair values of the Company’s U.S. pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Asset Category Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 100 $ 100 $ — $ — Equity investments: Large cap domestic 268 268 — — Small cap domestic 15 15 — — International 64 64 — — Equity derivatives 81 78 3 — Pooled funds: International (2) 196 — — — Small cap domestic (2) 52 — — — Fixed income investments: (3) Corporate bonds 105 — 105 — Government and agency bonds 132 76 56 — Asset-backed securities — — — — Fixed income derivatives 65 65 — — Pooled funds: Corporate bonds (2) 255 — — — Other investments: Commodity derivatives (4) 22 — 22 — Real estate and REITS (5) 61 61 — — Alternative investments (2) (6) 267 — — — Total $ 1,683 $ 727 $ 186 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of corporate and government bonds, asset-backed securities, and fixed income derivatives. (4) Consists of long-dated options and swaps on a commodity index. (5) Consists of exchange traded real estate investment trusts (“REITS”). (6) Consists of limited partnerships, private equity and hedge funds. Fair Value Measurements Using Asset Category Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 33 $ 33 $ — $ — Equity investments: Large cap domestic 299 299 — — Small cap domestic 30 30 — — International 52 52 — — Equity derivatives 203 170 33 — Pooled funds: International (2) 210 — — — Small cap domestic (2) 58 — — — Fixed income investments: (3) Corporate bonds 148 — 148 — Government and agency bonds 128 52 76 — Asset-backed securities — — — — Fixed income derivatives 69 47 22 — Pooled funds: Corporate bonds (2) 336 — — — Other investments: Commodity derivatives (4) 13 — 13 — Real estate and REITS (5) 67 67 — — Alternative investments (2) (6) 305 — — — Total $ 1,951 $ 750 $ 292 $ — (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of corporate and government bonds, asset-backed securities, and fixed income derivatives. (4) Consists of long-dated options on a commodity index. (5) Consists of exchange traded REITS. (6) Consists of limited partnerships, private equity and hedge funds.
U.K.
Defined Benefit Plan Disclosure [Line Items]
Fair values of pension plan assets	The fair values of the Company’s major U.K. pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 86 $ 86 $ — $ — Equity investments: Global 135 135 — — Pooled funds: Global (2) 365 — — — Europe (2) 18 — — — Fixed income investments: (3) Derivatives (4) 10 — 10 — Fixed income securities (5) 2,129 1,726 403 — Annuities 1,773 — — 1,773 Pooled funds: Derivatives (2) 62 — — — Fixed income securities (2) 223 — — — Other investments: Real estate (2) (6) 101 — — — Alternative investments (2) (7) 773 — — — Total $ 5,675 $ 1,947 $ 413 $ 1,773 (1) Consists of cash and institutional short-term investment funds. (2) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (3) Consists of various equity, fixed income, commodity, and real estate mutual fund type investment vehicles. (4) Consists of equity securities and equity derivatives. (5) Consists of corporate and government bonds and fixed income derivatives. (6) Consists of property funds and trusts holding direct real estate investments. (7) Consists of limited partnerships, private equity and hedge funds. Fair Value Measurements Using Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents (1) $ 159 $ 159 $ — $ — Equity investments: Derivatives 66 — 66 — Global 133 133 — — Pooled funds: Global (2) 360 — — — Europe (2) 17 — — — Fixed income investments: (3) Derivatives (4) 111 — 111 — Fixed income securities (5) 3,145 2,268 877 — Annuities 827 — — 827 Pooled funds: Fixed income securities (2) 283 — — — Other investments: Real estate (2) (6) 85 — — — Alternative investments (2) (7) 717 — — — Total $ 5,903 $ 2,560 $ 1,054 $ 827
Changes in the Level 3 fair-value category	The following table presents the changes in the Level 3 fair-value category in the Company’s U.K. pension plans for the years ended December 31, 2016 and December 31, 2015 (in millions): Fair Value Measurements Using Level 3 Inputs Annuities Balance at January 1, 2015 $ 836 Actual return on plan assets: Relating to assets still held at December 31, 2015 (32 ) Purchases, sales and settlements—net 58 Foreign exchange (35 ) Balance at December 31, 2015 827 Actual return on plan assets: Relating to assets still held at December 31, 2016 7 Purchases, sales and settlements—net 1,248 Foreign exchange (309 ) Balance at December 31, 2016 $ 1,773
U.S. and Canadian Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status	The following table provides an overview of the accumulated projected benefit obligation, fair value of plan assets, funded status and net amount recognized as of December 31, 2016 and 2015 for the Company’s other significant post-retirement benefit plans located in the U.S. and Canada (in millions): 2016 2015 Accumulated projected benefit obligation $ 110 $ 105 Fair value of plan assets 18 18 Funded status (92 ) (87 ) Unrecognized prior-service credit (3 ) (3 ) Unrecognized loss 10 7 Net amount recognized $ (85 ) $ (83 )
Fair values of pension plan assets	The fair values of the Company’s other major pension plan assets at December 31, 2016 and December 31, 2015 , by asset category, are as follows (in millions): Fair Value Measurements Using Balance at December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 11 $ 11 $ — $ — Equity investments: Pooled funds: Global (1) 322 — — — North America (1) 36 — — — Derivatives (1) 20 — — — Fixed income investments: Fixed income securities (2) 166 — 166 — Derivatives (2) 37 — 37 — Pooled funds: Fixed income securities (1) 469 — — — Other investments: Alternative investments (1) (3) 9 — — — Pooled funds: REITS (1) (4) 6 — — — Total $ 1,076 $ 11 $ 203 $ — (1) Certain investments that are measured at fair value using the net asset value per share practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in the above table are intended to permit reconciliation of the fair values to the amounts presented in the plan assets contained in this Note. (2) Consists of corporate and government bonds and fixed income derivatives. (3) Consists of limited partnerships, private equity and hedge funds. (4) Consists of property funds and trusts holding direct real estate investments. Fair Value Measurements Using Balance at December 31, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 11 $ 11 $ — $ — Equity investments: Pooled funds: Global (1) 270 — — — North America (1) 37 — — — Derivatives (1) 21 — — — Fixed income investments: Fixed income securities (2) 30 — 30 — Derivatives (2) 48 — 48 — Pooled funds: Fixed income securities (1) 576 — — — Derivatives (1) 12 — — — Other investments: Alternative investments (1) (3) 9 — — — Pooled funds: Commodities (1) 2 — — — REITS (1) (4) 3 — — — Total $ 1,019 $ 11 $ 78 $ —
Other information related to the Company's other post-retirement benefit plans	Other information related to the Company’s other post-retirement benefit plans are as follows: 2016 2015 2014 Net periodic benefit cost recognized (millions) $5 $6 $3 Weighted-average discount rate used to determine future benefit obligations 3.71-4.15% 3.99-4.33% 3.83 - 4.08 Weighted-average discount rate used to determine net periodic benefit costs 3.99-4.33% 3.83-4.08% 4.44 - 4.95

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based compensation expense recognized in continuing operations	The following table summarizes share-based compensation expense recognized in the Consolidated Statements of Income in Compensation and benefits (in millions): Years ended December 31 2016 2015 2014 Restricted share units (“RSUs”) $ 194 $ 201 $ 187 Performance share awards ("PSAs") 125 127 132 Employee share purchase plans 12 11 9 Total share-based compensation expense 331 339 328 Tax benefit 94 95 94 Share-based compensation expense, net of tax $ 237 $ 244 $ 234
Restricted share unit activity	A summary of the status of the Company’s RSUs is as follows (shares in thousands): Years ended December 31 2016 2015 2014 Shares Fair Value (1) Shares Fair Value (1) Shares Fair Value (1) Non-vested at beginning of year 7,167 $ 77 8,381 $ 63 9,759 $ 51 Granted 2,252 101 2,459 97 2,844 84 Vested (2,845 ) 70 (3,385 ) 58 (3,732 ) 49 Forfeited (379 ) 82 (288 ) 71 (490 ) 58 Non-vested at end of year 6,195 89 7,167 77 8,381 63 (1) Represents per share weighted average fair value of award at date of grant.
Performance-based plans	Information regarding the Company’s target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the years ended December 31, 2016 , 2015 , and 2014 , respectively, is as follows (shares in thousands, dollars in millions, except fair value): 2016 2015 2014 Target PSAs granted per share 783 993 816 Weighted average fair value per share at date of grant $ 100 $ 96 $ 81 Number of shares that would be issued based on current performance levels 777 1,437 1,540 Unamortized expense, based on current performance levels $ 57 $ 48 $ —

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2016
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 Derivative Assets (1) Derivative Liabilities (2) As of December 31 2016 2015 2016 2015 2016 2015 Foreign exchange contracts: Accounted for as hedges $ 758 $ 778 $ 14 $ 32 $ 13 $ 18 Not accounted for as hedges (3) 189 280 1 — 1 — Total $ 947 $ 1,058 $ 15 $ 32 $ 14 $ 18 (1) Included within Other current assets ( $6 million in 2016 and $15 million in 2015 , respectively) or Other non-current assets ( $9 million in 2016 and $17 million in 2015 , respectively) (2) Included within Other current liabilities ( $7 million in 2016 and $13 million in 2015 , respectively) or Other non-current liabilities ( $7 million in 2016 and $5 million in 2015 , respectively) (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. Offsetting of financial assets and derivatives assets are as follows (in millions): Gross Amounts of Recognized Assets Gross Amounts Offset in the Statement of Financial Position Net Amounts of Assets Presented in the Statement of Financial Position (1) Derivatives accounted for as hedges: 2016 2015 2016 2015 2016 2015 Foreign exchange contracts $ 14 $ 32 $ (1 ) $ (13 ) $ 13 $ 19 (1) Included within Other current assets ( $4 million in 2016 and $6 million in 2015 , respectively) or Other non-current assets ( $9 million in 2016 and $13 million in 2015 , respectively) Offsetting of financial liabilities and derivative liabilities are as follows (in millions): Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Statement of Financial Position Net Amounts of Liabilities Presented in the Statement of Financial Position (1) Derivatives accounted for as hedges: 2016 2015 2016 2015 2016 2015 Foreign exchange contracts $ 13 $ 18 $ (1 ) $ (13 ) $ 12 $ 5 (1) Included within Other current liabilities ( $5 million in 2016 and $4 million in 2015 , respectively) or Other non-current liabilities ( $7 million in 2016 and $1 million in 2015 , respectively)
Derivative gains (losses)	The amounts of derivative gains (losses) recognized in the Consolidated Financial Statements are as follows (in millions): Cash Flow Hedge - Foreign Exchange Contracts Location of future reclassification from Accumulated Other Comprehensive Loss Gain (Loss) Recognized in Accumulated Other Comprehensive Loss: Compensation and Benefits Other General Expenses Interest Expense Other Income (Expense) Total 2016 $ 8 $ (13 ) $ — $ (20 ) $ (25 ) 2015 4 (3 ) — (10 ) (9 ) 2014 11 (3 ) — (10 ) (2 ) Cash Flow Hedge - Foreign Exchange Contracts Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion): Compensation and Benefits Other General Expenses Interest Expense Other Income Total 2016 $ 2 $ (4 ) $ (1 ) $ (7 ) $ (10 ) 2015 4 (1 ) (9 ) (11 ) (17 ) 2014 (5 ) 3 (10 ) (2 ) (14 )

Fair Value Measurements and F40

Fair Value Measurements and Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of assets and liabilities that are measured at fair value on a recurring basis	The following tables present the categorization of the Company’s assets and liabilities that are measured at fair value on a recurring basis at December 31, 2016 and December 31, 2015 , respectively (in millions): Fair Value Measurements Using Balance at December 31, 2016 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) $ 1,371 $ 1,371 $ — $ — Other investments: Government bonds 1 — 1 — Equity investments 9 6 3 — Derivatives (2): Foreign exchange contracts 15 — 15 — Liabilities: Derivatives: Foreign exchange contracts 14 — 14 — (1) Included within Fiduciary assets, Short-term investments or Cash and cash equivalents in the Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 12 “Derivatives and Hedging” for additional information regarding the Company’s derivatives and hedging activity. Fair Value Measurements Using Balance at December 31, 2015 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) $ 1,396 $ 1,396 $ — $ — Other investments: Government bonds 1 — 1 — Equity investments 10 6 4 — Derivatives (2): Foreign exchange contracts 32 — 32 — Liabilities: Derivatives: Foreign exchange contracts 18 — 18 — (1) Included within Fiduciary assets, Short-term investments or Cash and cash equivalents in the Consolidated Statements of Financial Position, depending on their nature and initial maturity. (2) Refer to Note 12 “Derivatives and Hedging” for additional information regarding the Company’s derivatives and hedging activity.
Schedule of financial instruments where the carrying amounts and fair values differ	The fair value of Long-term debt is classified as Level 2 of the fair value hierarchy. The following table discloses the Company’s financial instruments where the carrying amounts and fair values differ (in millions): 2016 2015 As of December 31 Carrying Value Fair Value Carrying Value Fair Value Long-term debt $ 5,869 $ 6,264 $ 5,138 $ 5,386

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Aon’s total revenue is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 7,485 $ 7,426 $ 7,834 HR Solutions 4,183 4,303 4,264 Intersegment eliminations (41 ) (47 ) (53 ) Total revenue $ 11,627 $ 11,682 $ 12,045 Fiduciary investment income by segment is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 22 $ 21 $ 26 HR Solutions — — — Total fiduciary investment income $ 22 $ 21 $ 26
Revenue from External Customers by Products and Services	Commissions, fees and other revenues by product are as follows (in millions): Years ended December 31 2016 2015 2014 Retail brokerage $ 6,096 $ 6,044 $ 6,334 Reinsurance brokerage 1,367 1,361 1,474 Total Risk Solutions Segment 7,463 7,405 7,808 Consulting services 1,662 1,686 1,700 Outsourcing 2,557 2,658 2,607 Intrasegment (36 ) (41 ) (43 ) Total HR Solutions Segment 4,183 4,303 4,264 Intersegment (41 ) (47 ) (53 ) Total commissions, fees and other revenue $ 11,605 $ 11,661 $ 12,019
Schedule of reconciliation of segment income before tax to income from continuing operations before income taxes	A reconciliation of segment operating income before tax to income before income taxes is as follows (in millions): Years ended December 31 2016 2015 2014 Risk Solutions $ 1,587 $ 1,506 $ 1,648 HR Solutions 557 536 485 Segment income before income taxes 2,144 2,042 2,133 Unallocated expenses (238 ) (194 ) (167 ) Interest income 9 14 10 Interest expense (282 ) (273 ) (255 ) Other income 36 100 44 Income before income taxes $ 1,669 $ 1,689 $ 1,765
Schedule of consolidated revenue by geographic area	Consolidated Revenue by geographic area, which is attributed on the basis of where the services are performed, is as follows (in millions): Years ended December 31 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific 2016 11,627 $ 6,078 $ 995 $ 1,378 $ 1,760 $ 1,416 2015 11,682 6,063 1,053 1,527 1,909 1,130 2014 12,045 5,824 1,176 1,623 2,189 1,233
Schedule of consolidated non-current assets by geographic area	Consolidated Non-current assets by geographic area are as follows (in millions): As of December 31, 2016 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific Fixed assets, net 765 $ 443 $ 62 $ 65 $ 85 $ 110 Goodwill, intangible assets and other 12,382 6,947 887 2,091 2,054 403 Total 13,147 7,390 949 2,156 2,139 513 As of December 31, 2015 Total United States Americas other than U.S. United Kingdom Europe, Middle East, & Africa Asia Pacific Fixed assets, net 765 $ 432 $ 48 $ 89 $ 89 $ 107 Goodwill, intangible assets and other 12,253 6,635 368 2,606 2,181 463 Total 13,018 7,067 416 2,695 2,270 570

Guarantee of Registered Secur42

Guarantee of Registered Securities (Tables)	12 Months Ended
	Dec. 31, 2016
Guarantee of Registered Securities
Condensed Consolidating Statement of Income	Condensed Consolidating Statement of Income Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Commissions, fees and other $ — $ — $ 11,605 $ — $ 11,605 Fiduciary investment income — — 22 — 22 Total revenue — — 11,627 — 11,627 Expenses Compensation and benefits 130 171 6,613 — 6,914 Other general expenses — 2 2,805 — 2,807 Total operating expenses 130 173 9,418 — 9,721 Operating (loss) income (130 ) (173 ) 2,209 — 1,906 Interest income — 16 22 (29 ) 9 Interest expense (196 ) (101 ) (14 ) 29 (282 ) Intercompany interest income (expense) 14 (541 ) 527 — — Intercompany other income (expense) 274 (361 ) 87 — — Other income (expense) 15 (5 ) 44 (18 ) 36 Income (loss) before taxes (23 ) (1,165 ) 2,875 (18 ) 1,669 Income tax expense (benefit) (55 ) (325 ) 619 — 239 Income (loss) before equity in earnings of subsidiaries 32 (840 ) 2,256 (18 ) 1,430 Equity in earnings of subsidiaries, net of tax 1,382 1,219 379 (2,980 ) — Net income 1,414 379 2,635 (2,998 ) 1,430 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,414 $ 379 $ 2,601 $ (2,998 ) $ 1,396 Condensed Consolidating Statement of Income Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Revenue Commissions, fees and other $ — $ — $ 11,661 $ — $ 11,661 Fiduciary investment income — — 21 — 21 Total revenue — — 11,682 — 11,682 Expenses Compensation and benefits 136 32 6,669 — 6,837 Other general expenses 8 7 2,982 — 2,997 Total operating expenses 144 39 9,651 — 9,834 Operating (loss) income (144 ) (39 ) 2,031 — 1,848 Interest income — 14 19 (19 ) 14 Interest expense (140 ) (130 ) (22 ) 19 (273 ) Intercompany interest income (expense) 429 (479 ) 50 — — Intercompany other income (expense) 302 (422 ) 120 — — Other income (expense) (1 ) — 101 — 100 Income (loss) before taxes 446 (1,056 ) 2,299 — 1,689 Income tax expense (benefit) 45 (262 ) 484 — 267 Income (loss) before equity in earnings of subsidiaries 401 (794 ) 1,815 — 1,422 Equity in earnings of subsidiaries, net of tax 984 1,290 496 (2,770 ) — Net income 1,385 496 2,311 (2,770 ) 1,422 Less: Net income attributable to noncontrolling interests — — 37 — 37 Net income attributable to Aon shareholders $ 1,385 $ 496 $ 2,274 $ (2,770 ) $ 1,385 Condensed Consolidating Statement of Income Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustment Consolidated Revenue Commissions, fees and other $ — $ — $ 12,019 $ — $ 12,019 Fiduciary investment income — — 26 — 26 Total revenue — — 12,045 — 12,045 Expenses Compensation and benefits 140 16 6,858 — 7,014 Other general expenses 3 5 3,057 — 3,065 Total operating expenses 143 21 9,915 — 10,079 Operating (loss) income (143 ) (21 ) 2,130 — 1,966 Interest income — 2 17 (9 ) 10 Interest expense (84 ) (139 ) (41 ) 9 (255 ) Intercompany interest (expense) income 449 (298 ) (151 ) — — Intercompany other (expense) income 342 (390 ) 48 — — Other income 2 5 37 — 44 Income (loss) before taxes 566 (841 ) 2,040 — 1,765 Income tax (benefit) expense 74 (192 ) 452 — 334 Income (loss) before equity in earnings of subsidiaries 492 (649 ) 1,588 — 1,431 Equity in earnings of subsidiaries, net of tax 905 1,195 546 (2,646 ) — Net income 1,397 546 2,134 (2,646 ) 1,431 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,397 $ 546 $ 2,100 $ (2,646 ) $ 1,397
Condensed Consolidating Statement of Comprehensive Income	Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,414 $ 379 $ 2,635 $ (2,998 ) $ 1,430 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,414 $ 379 $ 2,601 $ (2,998 ) $ 1,396 Other comprehensive (loss) income, net of tax: Change in fair value of financial instruments — (1 ) (11 ) — (12 ) Foreign currency translation adjustments (2 ) 21 (532 ) 18 (495 ) Post-retirement benefit obligation — 68 (52 ) — 16 Total other comprehensive income (loss) (2 ) 88 (595 ) 18 (491 ) Equity in other comprehensive loss of subsidiaries, net of tax (505 ) (547 ) (459 ) 1,511 — Less: Other comprehensive loss attributable to noncontrolling interests — — (2 ) — (2 ) Total other comprehensive loss attributable to Aon shareholders (507 ) (459 ) (1,052 ) 1,529 (489 ) Comprehensive income (loss) attributable to Aon shareholders $ 907 $ (80 ) $ 1,549 $ (1,469 ) $ 907 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,385 $ 496 $ 2,311 $ (2,770 ) $ 1,422 Less: Net income attributable to noncontrolling interests — — 37 — 37 Net income attributable to Aon shareholders $ 1,385 $ 496 $ 2,274 $ (2,770 ) $ 1,385 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — — (8 ) — (8 ) Foreign currency translation adjustments — (47 ) (395 ) — (442 ) Post-retirement benefit obligation — 12 143 — 155 Total other comprehensive loss — (35 ) (260 ) — (295 ) Equity in other comprehensive loss of subsidiaries, net of tax (289 ) (259 ) (294 ) 842 — Less: Other comprehensive loss attributable to noncontrolling interests — — (6 ) — (6 ) Total other comprehensive loss attributable to Aon shareholders (289 ) (294 ) (548 ) 842 (289 ) Comprehensive income attributable to Aon shareholders $ 1,096 $ 202 $ 1,726 $ (1,928 ) $ 1,096 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated Net income $ 1,397 $ 546 $ 2,134 $ (2,646 ) $ 1,431 Less: Net income attributable to noncontrolling interests — — 34 — 34 Net income attributable to Aon shareholders $ 1,397 $ 546 $ 2,100 $ (2,646 ) $ 1,397 Other comprehensive income (loss), net of tax: Change in fair value of financial instruments — (3 ) 7 — 4 Foreign currency translation adjustments — (31 ) (476 ) — (507 ) Post-retirement benefit obligation — (315 ) 55 — (260 ) Total other comprehensive loss — (349 ) (414 ) — (763 ) Equity in other comprehensive loss of subsidiaries, net of tax (760 ) (409 ) (758 ) 1,927 — Less: Other comprehensive loss attributable to noncontrolling interests — — (3 ) — (3 ) Total other comprehensive loss attributable to Aon shareholders (760 ) (758 ) (1,169 ) 1,927 (760 ) Comprehensive income (loss) attributable to Aon shareholders $ 637 $ (212 ) $ 931 $ (719 ) $ 637
Condensed Consolidating Statement of Financial Position	Condensed Consolidating Statement of Financial Position As of December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated ASSETS Cash and cash equivalents $ — $ 1,633 $ 660 $ (1,862 ) $ 431 Short-term investments — 140 150 — 290 Receivables, net — 3 2,586 — 2,589 Fiduciary assets — — 9,485 — 9,485 Intercompany receivables 105 1,880 9,825 (11,810 ) — Other current assets — 25 326 — 351 Total Current Assets 105 3,681 23,032 (13,672 ) 13,146 Goodwill — — 8,747 — 8,747 Intangible assets, net — — 2,223 — 2,223 Fixed assets, net — — 765 — 765 Deferred tax assets 134 726 168 (706 ) 322 Intercompany receivables 366 261 8,711 (9,338 ) — Prepaid Pension — 5 853 — 858 Other non-current assets 2 119 433 — 554 Investment in subsidiary 10,107 17,137 (350 ) (26,894 ) — TOTAL ASSETS $ 10,714 $ 21,929 $ 44,582 $ (50,610 ) $ 26,615 LIABILITIES AND EQUITY Accounts payable and accrued liabilities $ 585 $ 44 $ 3,034 $ (1,862 ) $ 1,801 Short-term debt and current portion of long-term debt 279 50 7 — 336 Fiduciary Liabilities — — 9,485 — 9,485 Intercompany payables 142 10,399 1,269 (11,810 ) — Other current liabilities — 63 810 — 873 Total Current Liabilities 1,006 10,556 14,605 (13,672 ) 12,495 Long-term debt 4,177 1,413 279 — 5,869 Deferred tax liabilities — — 759 (658 ) 101 Pension, other post-retirement and other post-employment liabilities — 1,356 418 — 1,774 Intercompany payables — 8,877 461 (9,338 ) — Other non-current liabilities 8 77 759 — 844 TOTAL LIABILITIES 5,191 22,279 17,281 (23,668 ) 21,083 TOTAL AON SHAREHOLDERS’ EQUITY 5,523 (350 ) 27,244 (26,942 ) 5,475 Noncontrolling interests — — 57 — 57 TOTAL EQUITY 5,523 (350 ) 27,301 (26,942 ) 5,532 TOTAL LIABILITIES AND EQUITY $ 10,714 $ 21,929 $ 44,582 $ (50,610 ) $ 26,615 Condensed Consolidating Statement of Financial Position As of December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated ASSETS Cash and cash equivalents $ — $ 2,083 $ 1,242 $ (2,941 ) $ 384 Short-term investments — 209 147 — 356 Receivables, net 1 — 2,563 — 2,564 Fiduciary assets — — 9,932 — 9,932 Intercompany receivables 432 1,950 7,957 (10,339 ) — Other current assets — 19 310 — 329 Total Current Assets 433 4,261 22,151 (13,280 ) 13,565 Goodwill — — 8,448 — 8,448 Intangible assets, net — — 2,180 — 2,180 Fixed assets, net — — 765 — 765 Deferred tax assets 154 756 207 (817 ) 300 Intercompany receivables 375 526 8,633 (9,534 ) — Prepaid Pension — 6 1,027 — 1,033 Other non-current assets — 119 557 (84 ) 592 Investment in subsidiary 11,700 16,042 (123 ) (27,619 ) — TOTAL ASSETS $ 12,662 $ 21,710 $ 43,845 $ (51,334 ) $ 26,883 LIABILITIES AND EQUITY Accounts payable and accrued liabilities $ 2,988 $ 45 $ 1,680 $ (2,941 ) $ 1,772 Short-term debt and current portion of long-term debt — 550 12 — 562 Fiduciary Liabilities — — 9,932 — 9,932 Intercompany payables 167 9,518 654 (10,339 ) — Other current liabilities 47 56 716 — 819 Total Current Liabilities 3,202 10,169 12,994 (13,280 ) 13,085 Long-term debt 3,451 1,412 275 — 5,138 Deferred tax liabilities — — 855 (818 ) 37 Pension, other post-retirement and other post-employment liabilities — 1,313 482 — 1,795 Intercompany payables — 8,799 735 (9,534 ) — Other non-current liabilities 7 140 705 (83 ) 769 TOTAL LIABILITIES 6,660 21,833 16,046 (23,715 ) 20,824 TOTAL AON SHAREHOLDERS’ EQUITY 6,002 (123 ) 27,742 (27,619 ) 6,002 Noncontrolling interests — — 57 — 57 TOTAL EQUITY 6,002 (123 ) 27,799 (27,619 ) 6,059 TOTAL LIABILITIES AND EQUITY $ 12,662 $ 21,710 $ 43,845 $ (51,334 ) $ 26,883
Condensed Consolidating Statement of Cash Flows	Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2016 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES $ 2,705 $ (536 ) $ 3,265 $ (3,108 ) $ 2,326 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 316 15 (288 ) 43 Payments for investments — (35 ) (29 ) — (64 ) Net (purchases) sales of short-term investments - non-fiduciary — 70 (9 ) — 61 Acquisition of businesses, net of cash acquired — (335 ) (608 ) 64 (879 ) Proceeds from sale of businesses — — 171 (64 ) 107 Capital expenditures — — (222 ) — (222 ) CASH USED FOR INVESTING ACTIVITIES — 16 (682 ) (288 ) (954 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (1,257 ) — — — (1,257 ) Advances from (to) affiliates and other (1) (2,008 ) 570 (3,037 ) 4,475 — Issuance of shares for employee benefit plans (129 ) — — — (129 ) Issuance of debt 1,879 1,588 — — 3,467 Repayment of debt (845 ) (2,088 ) (12 ) — (2,945 ) Cash dividends to shareholders (345 ) — — — (345 ) Noncontrolling interests and other financing activities — (77 ) — (77 ) CASH (USED FOR) PROVIDED BY FINANCING ACTIVITIES (2,705 ) 70 (3,126 ) 4,475 (1,286 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (39 ) — (39 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS — (450 ) (582 ) 1,079 47 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 2,083 1,242 (2,941 ) 384 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 1,633 $ 660 $ (1,862 ) $ 431 (1) Advances from (to) affiliates and other includes activity related to the Company’s intercompany and cash pooling arrangements. Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2015 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY OPERATING ACTIVITIES $ 695 $ 464 $ 2,523 $ (1,673 ) $ 2,009 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 27 193 — 220 Payments for investments (13 ) (47 ) (219 ) 13 (266 ) Net purchases of short-term investments - non-fiduciary — (42 ) 51 — 9 Acquisition of businesses, net of cash acquired — — (16 ) — (16 ) Proceeds from sale of businesses — — 205 — 205 Capital expenditures — — (290 ) — (290 ) CASH USED FOR INVESTING ACTIVITIES (13 ) (62 ) (76 ) 13 (138 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (1,550 ) — — — (1,550 ) Advances from (to) affiliates and other (1) 232 (326 ) (2,339 ) 2,433 — Issuance of shares for employee benefit plans (29 ) — (1 ) — (30 ) Issuance of debt 1,318 4,026 7 — 5,351 Repayment of debt (330 ) (4,746 ) (22 ) — (5,098 ) Cash dividends to shareholders (323 ) — — — (323 ) Noncontrolling interests and other financing activities — — (39 ) — (39 ) CASH USED FOR FINANCING ACTIVITIES (682 ) (1,046 ) (2,394 ) 2,433 (1,689 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (172 ) — (172 ) NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS — (644 ) (119 ) 773 10 CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 2,727 1,361 (3,714 ) 374 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 2,083 $ 1,242 $ (2,941 ) $ 384 (1) Advances from (to) affiliates and other includes activity related to the Company’s intercompany and cash pooling arrangements. Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2014 (millions) Aon plc Aon Corporation Other Non-Guarantor Subsidiaries Consolidating Adjustments Consolidated CASH FLOWS FROM OPERATING ACTIVITIES CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES $ 769 $ (927 ) $ 1,970 $ — $ 1,812 CASH FLOWS FROM INVESTING ACTIVITIES Proceeds from investments — 39 13 — 52 Payments for investments — (20 ) — — (20 ) Net sales of short-term investments - non-fiduciary — (3 ) 113 — 110 Acquisition of businesses, net of cash acquired — — (479 ) — (479 ) Proceeds from sale of businesses — — 48 — 48 Capital expenditures — — (256 ) — (256 ) CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES — 16 (561 ) — (545 ) CASH FLOWS FROM FINANCING ACTIVITIES Share repurchase (2,250 ) — — — (2,250 ) Advances from (to) affiliates 19 3,215 (536 ) (2,698 ) — Issuance of shares for employee benefit plans (105 ) — — — (105 ) Issuance of debt 2,908 2,326 5 — 5,239 Repayment of debt (1,068 ) (2,150 ) (700 ) — (3,918 ) Cash dividends to shareholders (273 ) — — — (273 ) Noncontrolling interests and other financing activities — — 4 — 4 CASH PROVIDED BY (USED FOR) FINANCING ACTIVITIES (769 ) 3,391 (1,227 ) (2,698 ) (1,303 ) EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS — — (67 ) — (67 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS — 2,480 115 (2,698 ) (103 ) CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR — 247 1,246 (1,016 ) 477 CASH AND CASH EQUIVALENTS AT END OF PERIOD $ — $ 2,727 $ 1,361 $ (3,714 ) $ 374

Quarterly Financial Data (Una43

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	Selected quarterly financial data for the years ended December 31, 2016 and 2015 as reported, the effect of the change, and selected quarterly financial data for the years ended December 31, 2016 and 2015 as revised, are as follows (in millions, except per share data): (As reported) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,787 $ 2,761 $ 2,740 $ 3,317 $ 11,605 Fiduciary investment income 5 5 6 6 22 Total revenue 2,792 2,766 2,746 3,323 11,627 Operating income 450 405 422 629 1,906 Net income 327 280 314 509 1,430 Less: Net income attributable to noncontrolling interests 12 8 7 7 34 Net income attributable to Aon shareholders $ 315 $ 272 $ 307 $ 502 $ 1,396 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.16 $ 1.01 $ 1.15 $ 1.89 $ 5.21 Diluted net income per share attributable to Aon shareholders $ 1.15 $ 1.01 $ 1.14 $ 1.87 $ 5.16 (Effect of change) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 13 $ 34 $ 14 $ (61 ) $ — Fiduciary investment income — — — — — Total revenue 13 34 14 (61 ) — Operating income 13 34 14 (61 ) — Net income 10 28 12 (50 ) — Less: Net income attributable to noncontrolling interests — — — — — Net income attributable to Aon shareholders $ 10 $ 28 $ 12 $ (50 ) $ — PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 0.04 $ 0.11 $ 0.04 $ (0.19 ) $ — Diluted net income per share attributable to Aon shareholders $ 0.04 $ 0.10 $ 0.04 $ (0.19 ) $ — (As revised) 1Q 2Q 3Q 4Q 2016 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,800 $ 2,795 $ 2,754 $ 3,256 $ 11,605 Fiduciary investment income 5 5 6 6 22 Total revenue 2,805 2,800 2,760 3,262 11,627 Operating income 463 439 436 568 1,906 Net income 337 308 326 459 1,430 Less: Net income attributable to noncontrolling interests 12 8 7 7 34 Net income attributable to Aon shareholders $ 325 $ 300 $ 319 $ 452 $ 1,396 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.20 $ 1.12 $ 1.19 $ 1.70 $ 5.21 Diluted net income per share attributable to Aon shareholders $ 1.19 $ 1.11 $ 1.18 $ 1.68 $ 5.16 (As reported) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,842 $ 2,800 $ 2,736 $ 3,283 $ 11,661 Fiduciary investment income 5 5 6 5 21 Total revenue 2,847 2,805 2,742 3,288 11,682 Operating income 441 277 413 717 1,848 Net income 341 188 303 590 1,422 Less: Net income attributable to noncontrolling interests 13 10 8 6 37 Net income attributable to Aon shareholders $ 328 $ 178 $ 295 $ 584 $ 1,385 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.15 $ 0.63 $ 1.05 $ 2.12 $ 4.93 Diluted net income per share attributable to Aon shareholders $ 1.14 $ 0.62 $ 1.04 $ 2.09 $ 4.88 (Effect of change) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 20 $ 31 $ 10 $ (61 ) $ — Fiduciary investment income — — — — — Total revenue 20 31 10 (61 ) — Operating income 20 31 10 (61 ) — Net income 16 26 8 (50 ) — Less: Net income attributable to noncontrolling interests — — — — — Net income attributable to Aon shareholders $ 16 $ 26 $ 8 $ (50 ) $ — PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 0.06 $ 0.09 $ 0.03 $ (0.18 ) $ — Diluted net income per share attributable to Aon shareholders $ 0.06 $ 0.09 $ 0.03 $ (0.18 ) $ — (As revised) 1Q 2Q 3Q 4Q 2015 INCOME STATEMENT DATA Commissions, fees and other revenue $ 2,862 $ 2,831 $ 2,746 $ 3,222 $ 11,661 Fiduciary investment income 5 5 6 5 21 Total revenue 2,867 2,836 2,752 3,227 11,682 Operating income 461 308 423 656 1,848 Net income 357 214 311 540 1,422 Less: Net income attributable to noncontrolling interests 13 10 8 6 37 Net income attributable to Aon shareholders $ 344 $ 204 $ 303 $ 534 $ 1,385 PER SHARE DATA Basic net income per share attributable to Aon shareholders $ 1.21 $ 0.72 $ 1.08 $ 1.94 $ 4.93 Diluted net income per share attributable to Aon shareholders $ 1.20 $ 0.71 $ 1.07 $ 1.91 $ 4.88

Basis of Presentation (Reclassi

Basis of Presentation (Reclassification) (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Reclassification From Prior Period [Line Items]
Net income	$ 459	$ 326	$ 308	$ 337	$ 540	$ 311	$ 214	$ 357	$ 645	$ 971	$ 1,430	$ 1,422	$ 1,431
Investments	119				135						119	135
Purchases of shares from noncontrolling interests											(77)	(39)	4
Receivables, net				97					128	228	(86)	(83)	(25)
Other assets and liabilities				72					65	94	50	118	(43)
Increase (decrease) in restructuring reserve												31	83
Accounts Receivable
Summary of Reclassification From Prior Period [Line Items]
Reclassification adjustment											170	170	170
Non-current Deferred Tax Asset
Summary of Reclassification From Prior Period [Line Items]
Reclassification adjustment											(66)	(66)	(66)
Retained Earnings
Summary of Reclassification From Prior Period [Line Items]
Reclassification adjustment											(104)	(104)	$ (104)
Scenario, Previously Reported
Summary of Reclassification From Prior Period [Line Items]
Net income	509	314	280	327	590	303	188	341	607	921	1,430	1,422
Receivables, net				110					175	289
Other assets and liabilities				69					56	83
Restatement Adjustment
Summary of Reclassification From Prior Period [Line Items]
Net income	$ (50)	$ 12	$ 28	10	$ (50)	$ 8	$ 26	$ 16			$ 0	$ 0
Adjustments for New Accounting Pronouncement | Restatement Adjustment
Summary of Reclassification From Prior Period [Line Items]
Net income				10					38	50
Receivables, net				(13)					(47)	(61)
Other assets and liabilities				$ 3					$ 9	$ 11

Summary of Significant Accoun45

Summary of Significant Accounting Principles and Practices (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Jan. 01, 2017USD ($)	Dec. 31, 2016GBP (£)	Dec. 31, 2016USD ($)	Dec. 31, 2015GBP (£)	Dec. 31, 2015USD ($)	Dec. 31, 2013USD ($)
Cash and Cash Equivalents
Cash and cash equivalents and short-term investments						$ 721		$ 740
Restricted cash and investments, current						82		105
Operating funds in U.K.					£ 43.3	53.2	£ 43.3	64.6
Cash and cash equivalents, restricted						29		40
Fiduciary Assets and Liabilities
Premium trust balances						3,800		3,400
Allowance for Doubtful Accounts
Allowance for doubtful accounts			$ 74			58		58	$ 90
Foreign Currency
Effect of foreign exchange gains (losses) on the consolidated statements of income	$ 9	$ 11	1
Loss on hedging activity	$ 7	$ 19	$ 19
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Deferred tax assets, net						322		300
Deferred tax liabilities, net, current						$ 101		37
Technology equipment
Fixed Assets
Fixed assets, original life, weighted-average	7 years
Buildings
Fixed Assets
Fixed assets, original life, weighted-average	35 years
Automobiles
Fixed Assets
Fixed assets, original life, weighted-average	6 years
Minimum
Revenue Recognition
Term of outsourcing contracts for benefit services	3 years
Goodwill and Intangible Assets
Useful life of finite-lived intangible assets	1 year
Minimum | Software
Fixed Assets
Fixed assets, original life, weighted-average	4 years
Minimum | Furniture, fixtures and equipment
Fixed Assets
Fixed assets, original life, weighted-average	4 years
Minimum | Computer equipment
Fixed Assets
Fixed assets, original life, weighted-average	4 years
Maximum
Revenue Recognition
Term of outsourcing contracts for benefit services	5 years
Goodwill and Intangible Assets
Useful life of finite-lived intangible assets	16 years
Maximum | Software
Fixed Assets
Fixed assets, original life, weighted-average	7 years
Maximum | Leasehold improvements
Fixed Assets
Fixed assets, original life, weighted-average	10 years
Maximum | Furniture, fixtures and equipment
Fixed Assets
Fixed assets, original life, weighted-average	10 years
Maximum | Computer equipment
Fixed Assets
Fixed assets, original life, weighted-average	6 years
Weighted average
Goodwill and Intangible Assets
Useful life of finite-lived intangible assets	11 years
Other Current Assets | Accounting Standard Update 2015-03
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Debt issuance costs, net								4
Other Noncurrent Assets | Accounting Standard Update 2015-03
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Debt issuance costs, net								33
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2015-07
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Deferred tax assets, net								(93)
Deferred tax liabilities, net, current								$ (139)
Retained Earnings | Subsequent Event | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Adjustments to retained earnings for deferred tax asset changes due to share-based compensation changes				$ 49

Other Financial Data - Schedule

Other Financial Data - Schedule of Other Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Financial Data [Abstract]
Equity earnings	$ 13	$ 13	$ 12
Net gain on disposals of businesses	39	82	24
Foreign currency remeasurement (loss) gain	(2)	30	18
(Loss) income on financial instruments	(14)	(24)	(15)
Other	0	(1)	5
Other income	$ 36	$ 100	$ 44

Other Financial Data - Schedu47

Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at January 1	$ 58	$ 74	$ 90
Provision charged to operations	11	13	12
Accounts written off, net of recoveries	(14)	(34)	(33)
Foreign currency translation	3	5	5
Balance at December 31	$ 58	$ 58	$ 74

Other Financial Data - Schedu48

Other Financial Data - Schedule of Other Current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Financial Data [Abstract]
Taxes receivable	$ 100	$ 94
Prepaid expenses	125	130
Deferred project costs	87	92
Other	39	13
Total Other Current Assets	$ 351	$ 329

Other Financial Data - Componen

Other Financial Data - Components of Fixed Assets, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fixed Assets, net
Fixed assets, gross	$ 2,325	$ 2,381
Less: Accumulated depreciation	1,560	1,616
Fixed assets, net	765	765
Depreciation expense including software amortization	232	229	$ 242
Software
Fixed Assets, net
Fixed assets, gross	948	1,095
Leasehold improvements
Fixed Assets, net
Fixed assets, gross	452	422
Computer equipment
Fixed Assets, net
Fixed assets, gross	417	358
Furniture, fixtures and equipment
Fixed Assets, net
Fixed assets, gross	300	315
Construction in progress
Fixed Assets, net
Fixed assets, gross	93	76
Other
Fixed Assets, net
Fixed assets, gross	$ 115	$ 115

Other Financial Data - Schedu50

Other Financial Data - Schedule of Other Non-current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Financial Data [Abstract]
Deferred project costs	$ 183	$ 210
Investments	119	135
Taxes receivable	82	82
Other	170	165
Total Other Non-Current Assets	$ 554	$ 592

Other Financial Data - Schedu51

Other Financial Data - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Financial Data [Abstract]
Deferred revenue	$ 393	$ 394
Taxes payable	78	94
Other	402	331
Total Other Current Liabilities	$ 873	$ 819

Other Financial Data - Schedu52

Other Financial Data - Schedule of Other Non-Current Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Financial Data [Abstract]
Taxes payable	$ 288	$ 223
Leases	169	166
Deferred revenue	140	159
Compensation and benefits	56	59
Other	191	162
Total Other Non-Current Liabilities	$ 844	$ 769

Acquisitions and Dispositions53

Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)acquisition	Dec. 31, 2015USD ($)acquisition	Dec. 31, 2014USD ($)
Business Acquisition
Number of business acquired under business combination | acquisition	8	7
Goodwill	$ 8,747	$ 8,448	$ 8,860
Risk Solutions
Business Acquisition
Number of business acquired under business combination | acquisition	5	4
Goodwill	$ 5,953	$ 5,593	5,911
HR Solutions
Business Acquisition
Number of business acquired under business combination | acquisition	3	3
Goodwill	$ 2,794	$ 2,855	$ 2,949
2016 Acquisitions
Business Acquisition
Cash	891
Deferred and contingent consideration	43
Aggregate consideration transferred	934
Cash and cash equivalents	12
Receivables, net	52
Goodwill	642
Intangible assets, net	366
Fixed assets, net	30
Other assets	2
Total assets acquired	1,104
Current liabilities	163
Other liabilities	7
Total liabilities assumed	170
Net assets acquired	$ 934
Acquired intangible assets, weighted average useful life (in years)	13 years
Acquisition costs	$ 8
Revenue	$ 68
2015 Acquisitions
Business Acquisition
Aggregate consideration transferred		27
Goodwill		18
Intangible assets, net		6
Total intangible assets		$ 24

Acquisitions and Dispositions54

Acquisitions and Dispositions of Businesses - Dispositions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)disposal	Dec. 31, 2015USD ($)disposal	Dec. 31, 2014USD ($)disposal
Dispositions
Net gain on disposals of businesses | $	$ 39	$ 82	$ 24
Disposal Group, Not Discontinued Operations
Dispositions
Number of dispositions	5	7	2
Disposal Group, Not Discontinued Operations | Risk Solutions
Dispositions
Number of dispositions	4	4	2
Disposal Group, Not Discontinued Operations | HR Solutions
Dispositions
Number of dispositions	1	3	0

Goodwill and Other Intangible55

Goodwill and Other Intangible Assets - Schedule of changes in the net carrying amount of goodwill by operating segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	$ 8,448	$ 8,860
Goodwill related to current year acquisitions	642	18
Goodwill related to disposals	(34)	(77)
Goodwill related to prior year acquisitions	4	0
Foreign currency translation	(313)	(353)
Balance at the end of the period	8,747	8,448
Risk Solutions
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	5,593	5,911
Goodwill related to current year acquisitions	632	2
Goodwill related to disposals	(8)	(1)
Goodwill related to prior year acquisitions	4	0
Foreign currency translation	(268)	(319)
Balance at the end of the period	5,953	5,593
HR Solutions
Changes in the net carrying amount of goodwill by operating segment (in millions)
Balance at the beginning of the period	2,855	2,949
Goodwill related to current year acquisitions	10	16
Goodwill related to disposals	(26)	(76)
Goodwill related to prior year acquisitions	0	0
Foreign currency translation	(45)	(34)
Balance at the end of the period	$ 2,794	$ 2,855

Goodwill and Other Intangible56

Goodwill and Other Intangible Assets - Schedule of other intangible assets by asset class (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Intangible assets with finite lives, gross carrying amount	$ 4,680	$ 4,446
Intangible assets with finite lives, accumulated amortization	2,457	2,266
Intangible assets, net	2,223	2,180
Amortization expense on intangible assets	277	314	$ 352
Tradenames
Finite-Lived Intangible Assets [Line Items]
Intangible assets with finite lives, gross carrying amount	998	1,019
Intangible assets with finite lives, accumulated amortization	0	0
Intangible assets, net	998	1,019
Customer related and contract based
Finite-Lived Intangible Assets [Line Items]
Intangible assets with finite lives, gross carrying amount	3,108	2,886
Intangible assets with finite lives, accumulated amortization	1,971	1,809
Intangible assets, net	1,137	1,077
Technology and other
Finite-Lived Intangible Assets [Line Items]
Intangible assets with finite lives, gross carrying amount	574	541
Intangible assets with finite lives, accumulated amortization	486	457
Intangible assets, net	$ 88	$ 84

Goodwill and Other Intangible57

Goodwill and Other Intangible Assets - Schedule of estimated future amortization expense on intangible assets (Details) $ in Millions	Dec. 31, 2016USD ($)
Finite-Lived Intangible Assets [Line Items]
2,017	$ 259
2,018	209
2,019	180
2,020	158
2,021	119
Thereafter	300
Total future amortization of intangible assets	1,225
Risk Solutions
Finite-Lived Intangible Assets [Line Items]
2,017	123
2,018	118
2,019	107
2,020	97
2,021	66
Thereafter	239
Total future amortization of intangible assets	750
HR Solutions
Finite-Lived Intangible Assets [Line Items]
2,017	136
2,018	91
2,019	73
2,020	61
2,021	53
Thereafter	61
Total future amortization of intangible assets	$ 475

Debt - Summary of outstanding d

Debt - Summary of outstanding debt (Details) € in Millions, CAD in Millions	Dec. 31, 2016USD ($)	Dec. 31, 2016CAD	Dec. 31, 2016EUR (€)	May 27, 2016USD ($)	Mar. 01, 2016USD ($)	Dec. 31, 2015USD ($)	Nov. 13, 2015USD ($)	May 20, 2015USD ($)
Debt Instrument [Line Items]
Total debt	$ 6,205,000,000					$ 5,700,000,000
Less short-term and current portion of long-term debt	336,000,000					562,000,000
Long-term debt	5,869,000,000					5,138,000,000
Commercial Paper
Debt Instrument [Line Items]
Total debt	329,000,000					50,000,000
Other
Debt Instrument [Line Items]
Total debt	9,000,000					15,000,000
3.875% Senior Notes due December 2025 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 744,000,000					0
Interest rate on debt	3.875%	3.875%	3.875%
Debt face value					$ 750,000,000
5.00% Senior Notes due September 2020 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 598,000,000					597,000,000
Interest rate on debt	5.00%	5.00%	5.00%
4.75% Senior Notes due May 2045 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 592,000,000					591,000,000
Interest rate on debt	4.75%	4.75%	4.75%
Debt face value								$ 600,000,000
3.50% Senior Notes due June 2024 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 594,000,000					593,000,000
Interest rate on debt	3.50%	3.50%	3.50%
4.60% Senior Notes due June 2044 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 543,000,000					543,000,000
Interest rate on debt	4.60%	4.60%	4.60%
2.875% Senior Notes due May 2026 (EUR 500M) | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 516,000,000					541,000,000
Interest rate on debt	2.875%	2.875%	2.875%
Debt face value | €			€ 500
8.205% Junior Subordinated Notes due January 2027 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 521,000,000					521,000,000
Interest rate on debt	8.205%	8.205%	8.205%
3.125% Senior Notes due May 2016 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 0					500,000,000
Interest rate on debt	3.125%	3.125%	3.125%
Debt face value				$ 500,000,000
2.80% Senior Notes due March 2021 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 397,000,000					396,000,000
Interest rate on debt	2.80%	2.80%	2.80%
Debt face value							$ 400,000,000
4.00% Senior Notes due November 2023 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 347,000,000					347,000,000
Interest rate on debt	4.00%	4.00%	4.00%
6.25% Senior Notes due September 2040 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 295,000,000					295,000,000
Interest rate on debt	6.25%	6.25%	6.25%
4.76% Senior Notes due March 2018 (CAD 375M) | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 277,000,000					270,000,000
Interest rate on debt	4.76%	4.76%	4.76%
Debt face value | CAD		CAD 375
4.45% Senior Notes due May 2043 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 246,000,000					246,000,000
Interest rate on debt	4.45%	4.45%	4.45%
4.25% Senior Notes due December 2042 | Senior Notes
Debt Instrument [Line Items]
Total debt	$ 197,000,000					$ 195,000,000
Interest rate on debt	4.25%	4.25%	4.25%

Debt - Repayments of long-term

Debt - Repayments of long-term debt (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Debt Disclosure [Abstract]
2,017	$ 336
2,018	278
2,019	0
2,020	600
2,021	400
Thereafter	4,700
Total Repayments	6,314
Unamortized discount, premium, and debt issuance cost	(109)
Long-term Debt	$ 6,205

Debt - Narrative (Details)

Debt - Narrative (Details) CAD in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)credit_facility	Dec. 31, 2015USD ($)	Dec. 31, 2016CAD	Dec. 31, 2016EUR (€)	May 27, 2016USD ($)	Mar. 01, 2016USD ($)	Nov. 13, 2015USD ($)	May 20, 2015USD ($)
Debt Instrument [Line Items]
Number of committed credit facilities | credit_facility		2
Weighted average commercial paper outstanding		$ 265,000,000	$ 402,000,000
Senior Notes | 3.125% Senior Notes due May 2016
Debt Instrument [Line Items]
Debt face value						$ 500,000,000
Interest rate on debt		3.125%		3.125%	3.125%
Senior Notes | 3.875% Senior Notes due December 2025
Debt Instrument [Line Items]
Debt face value							$ 750,000,000
Interest rate on debt		3.875%		3.875%	3.875%
Senior Notes | 2.80% Senior Notes due March 2021
Debt Instrument [Line Items]
Debt face value								$ 400,000,000
Interest rate on debt		2.80%		2.80%	2.80%
Senior Notes | 4.75% Senior Notes due May 2045
Debt Instrument [Line Items]
Debt face value									$ 600,000,000
Interest rate on debt		4.75%		4.75%	4.75%
Senior Notes | 4.76% Senior Notes due March 2018 (CAD 375M)
Debt Instrument [Line Items]
Debt face value | CAD				CAD 375
Interest rate on debt		4.76%		4.76%	4.76%
Unsecured Debt | 4.76% Senior Notes due March 2018 (CAD 375M)
Debt Instrument [Line Items]
Interest rate on debt		4.76%		4.76%	4.76%
Commercial Paper
Debt Instrument [Line Items]
Weighted-average interest rates		0.22%	0.50%
Senior Notes | 3.50% Senior Notes due September 2015
Debt Instrument [Line Items]
Interest rate on debt	3.50%
Extinguishment of debt	$ 600,000,000
Credit Facility Expiring March 2017
Debt Instrument [Line Items]
New credit and loan facility		$ 400,000,000
Long-term commercial paper		0
Credit Facility Expiring February 2021
Debt Instrument [Line Items]
New credit and loan facility		900,000,000
Long-term commercial paper		0
Commercial Paper | Line of Credit
Debt Instrument [Line Items]
Long-term commercial paper		329,200,000	$ 50,000,000
Commercial Paper | US Commercial Paper Program
Debt Instrument [Line Items]
New credit and loan facility		$ 900,000,000
Commercial Paper | European Multi-Currency Commercial Paper Program
Debt Instrument [Line Items]
New credit and loan facility | €					€ 300,000,000

Lease Commitments (Details)

Lease Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Rental expenses for operating leases
Rental expense	$ 400	$ 454	$ 455
Less: Sub lease rental income	(64)	(83)	(75)
Net rental expense	336	$ 371	$ 380
Future minimum rental payments under operating leases
Gross rental commitment 2017	355
Gross rental commitment 2018	317
Gross rental commitment 2019	283
Gross rental commitment 2020	237
Gross rental commitment 2021	214
Gross rental commitment thereafter	696
Total gross rental commitments	2,102
Sublease income 2017	(55)
Sublease income 2018	(44)
Sublease income 2019	(38)
Sublease income 2020	(34)
Sublease income 2021	(33)
Sublease income thereafter	(47)
Total future sublease income	(251)
Net rental commitment 2017	300
Net rental commitment 2018	273
Net rental commitment 2019	245
Net rental commitment 2020	203
Net rental commitment 2021	181
Net rental commitment thereafter	649
Total minimum payments required	$ 1,851

Income Taxes - Income from cont

Income Taxes - Income from continuing operations before income tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income before income taxes:
Income from continuing operations before income taxes	$ 1,669	$ 1,689	$ 1,765
Current:
Total current	263	490	468
Deferred tax expense (benefit):
Total deferred	(24)	(223)	(134)
Total income taxes expenses	239	267	334
UK
Income before income taxes:
Income from continuing operations before income taxes	(202)	149	347
Current:
Total current	(54)	43	1
Deferred tax expense (benefit):
Total deferred	59	(39)	38
U.S. federal
Income before income taxes:
Income from continuing operations before income taxes	(104)	(51)	(55)
Current:
Total current	94	137	156
Deferred tax expense (benefit):
Total deferred	(47)	(140)	(133)
U.S. state and local
Current:
Total current	0	54	75
Deferred tax expense (benefit):
Total deferred	6	(14)	(24)
Other
Income before income taxes:
Income from continuing operations before income taxes	1,975	1,591	1,473
Current:
Total current	223	256	236
Deferred tax expense (benefit):
Total deferred	$ (42)	$ (30)	$ (15)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the income tax provisions based on the U.S. statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of the income tax provisions based on the statutory corporate tax rate to the provisions reflected in the Consolidated Financial Statements
Statutory tax rate	20.00%	20.30%	21.50%
U.S. state income taxes, net of U.S. federal benefit	0.70%	0.50%	1.50%
Taxes on international operations	(8.50%)	(6.00%)	(8.90%)
Nondeductible expenses	1.20%	2.20%	1.70%
Adjustments to prior year tax requirements	(1.00%)	(1.30%)	0.90%
Adjustments to valuation allowances	(1.80%)	(1.20%)	0.60%
Change in uncertain tax positions	3.00%	1.40%	1.70%
Other — net	0.70%	(0.10%)	(0.10%)
Effective tax rate	14.30%	15.80%	18.90%

Income Taxes - Components of Ao

Income Taxes - Components of Aon's deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Employee benefit plans	$ 661	$ 635
Net operating/capital loss and tax credit carryforwards	399	336
Accrued interest	166	293
Other accrued expenses	102	98
Brokerage fee arrangements (1)	66	66
Deferred revenue	57	65
Investment basis differences	48	56
Other	60	57
Total	1,559	1,606
Valuation allowance on deferred tax assets	(130)	(162)
Total	1,429	1,444
Deferred tax liabilities:
Intangibles and property, plant and equipment	(982)	(961)
Other accrued expenses	(101)	(99)
Deferred costs	(20)	(30)
Unrealized foreign exchange gains	(26)	(29)
Unremitted earnings	(29)	(18)
Other	(50)	(44)
Total	(1,208)	(1,181)
Net deferred tax asset	$ 221	$ 263

Income Taxes - Deferred income

Income Taxes - Deferred income taxes (assets and liabilities netted by jurisdiction) as classified in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred income taxes
Deferred tax assets — non-current (2)	$ 322	$ 300
Deferred tax liabilities — non-current (2)	(101)	(37)
Net deferred tax asset	$ 221	$ 263

Income Taxes - Reconciliation66

Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the Company's beginning and ending amount of unrecognized tax benefits
Balance at the beginning of the period	$ 238	$ 211
Additions based on tax positions related to the current year	36	31
Additions for tax positions of prior years	20	53
Reductions for tax positions of prior years	(12)	(18)
Settlements	0	(32)
Business combinations	2	0
Lapse of statute of limitations	(5)	(5)
Foreign currency translation	(1)	(2)
Balance at the end of the period	$ 278	$ 238

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance	$ 32
Adjustment to additional paid-in-capital for income tax benefits attributable to employee stock compensation	4	$ (126)	$ (89)
Deferred tax liabilities from undistributed foreign earnings	11
Undistributed foreign earnings	2,300
Benefit realized from tax holiday granted	$ 46	$ 23	$ 7
Earnings per share impact of tax holiday	$ 0.17	$ 0.08	$ 0.02
Unrecognized tax benefits that would impact effective tax rate	$ 240	$ 200	$ 174
Accrued potential interest and penalties	15	2	4
Liability recorded for interest and penalties	48	$ 33	$ 31
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	126
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 110

Income Taxes Operating Loss Car

Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
UK
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 325	$ 449
Capital Loss Carryforwards	294	360
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	196	8
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	474	443
Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	350	245
Capital Loss Carryforwards	$ 218	$ 206

Shareholders' Equity - Redomest

Shareholders' Equity - Redomestication Narrative (Details) - USD ($)	Feb. 23, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2015	Nov. 30, 2014
Subsequent Event [Line Items]
Distributable reserves available amount		$ 1,600,000,000	$ 2,100,000,000
Share Repurchase Program of 2014
Subsequent Event [Line Items]
Share repurchase authorization limit				$ 5,000,000,000	$ 5,000,000,000
Share Repurchase Program of 2014 | Subsequent Event
Subsequent Event [Line Items]
Share repurchase authorization limit	$ 5,000,000,000

Shareholders' Equity - Ordinary

Shareholders' Equity - Ordinary Shares (Details) - USD ($) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 31, 2015	Nov. 30, 2014	Apr. 30, 2012
Common Stock Programs
Cost of shares repurchased	$ 1,257,000,000	$ 1,550,000,000	$ 2,250,000,000
Treasury Stock, Acquired, Additional Transaction Costs	$ 6,000,000
Share Repurchase Program
Common Stock Programs
Number of shares repurchased (in shares)	12.2	16
Average price per share of shares purchased under share repurchase program (in dollars per share)	$ 102.66	$ 97.04
Cost of shares repurchased	$ 1,300,000,000	$ 1,600,000,000
Share Repurchase Programs of 2012 and 2014
Common Stock Programs
Share repurchase, remaining authorization limit	$ 2,800,000,000
Share Repurchase Program of 2012
Common Stock Programs
Share repurchase authorization limit						$ 5,000,000,000
Number of shares repurchased (in shares)	90.2
Cost of shares repurchased	$ 7,200,000,000
Share Repurchase Program of 2014
Common Stock Programs
Share repurchase authorization limit				$ 5,000,000,000	$ 5,000,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of weighted average shares outstanding (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Basic weighted-average ordinary shares outstanding	268.1	280.8	295.5
Dilutive effect of potentially issuable shares	2.2	3	4.1
Diluted weighted-average ordinary shares outstanding	270.3	283.8	299.6

Shareholders' Equity - Dividend

Shareholders' Equity - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Cash dividends to shareholders	$ 345	$ 323	$ 273
Dividends paid per share (in dollars per share)	$ 1.29	$ 1.15	$ 0.92

Shareholders' Equity - Componen

Shareholders' Equity - Components of Accumulated other comprehensive loss, net of related tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ 6,059	$ 6,527	$ 8,091
Other comprehensive loss before reclassifications	(791)	(389)	(1,068)
Tax benefit	77	23	221
Other comprehensive loss before reclassifications, net	(714)	(366)	(847)
Amounts reclassified from accumulated other comprehensive loss	332	128	126
Tax benefit	(107)	(51)	(39)
Amounts reclassified from accumulated other comprehensive loss, net	225	77	87
Total other comprehensive loss attributable to Aon shareholders	(489)	(289)	(760)
Balance	5,532	6,059	6,527
Change in Fair Value of Investments
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(25)	(17)	(21)
Other comprehensive loss before reclassifications	(25)	(4)	(13)
Tax benefit	6	1	4
Other comprehensive loss before reclassifications, net	(19)	(3)	(9)
Amounts reclassified from accumulated other comprehensive loss	10	11	20
Tax benefit	(3)	(16)	(7)
Amounts reclassified from accumulated other comprehensive loss, net	7	(5)	13
Total other comprehensive loss attributable to Aon shareholders	(12)	(8)	4
Balance	(37)	(25)	(17)
Foreign Currency Translation Adjustments
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(771)	(335)	169
Other comprehensive loss before reclassifications	(490)	(467)	(492)
Tax benefit	(3)	31	(12)
Other comprehensive loss before reclassifications, net	(493)	(436)	(504)
Amounts reclassified from accumulated other comprehensive loss	0	0	0
Tax benefit	0	0	0
Amounts reclassified from accumulated other comprehensive loss, net	0	0	0
Total other comprehensive loss attributable to Aon shareholders	(493)	(436)	(504)
Balance	(1,264)	(771)	(335)
Post-retirement Benefit Obligations
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(2,627)	(2,782)	(2,522)
Other comprehensive loss before reclassifications	(276)	82	(563)
Tax benefit	74	(9)	229
Other comprehensive loss before reclassifications, net	(202)	73	(334)
Amounts reclassified from accumulated other comprehensive loss	322	117	106
Tax benefit	(104)	(35)	(32)
Amounts reclassified from accumulated other comprehensive loss, net	218	82	74
Total other comprehensive loss attributable to Aon shareholders	16	155	(260)
Balance	(2,611)	(2,627)	(2,782)
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(3,423)	(3,134)	(2,374)
Balance	$ (3,912)	$ (3,423)	$ (3,134)

Employee Benefits - Schedule of

Employee Benefits - Schedule of expense recognized in Compensation and benefit in the Consolidated Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Savings Plans
U.S.	$ 142	$ 133	$ 123
U.K.	43	42	42
Other	27	25	30
Expense recognized for defined contribution savings plans	$ 212	$ 200	$ 195

Employee Benefits - Pension Pla

Employee Benefits - Pension Plans Narrative (Details) £ in Millions, $ in Millions	1 Months Ended	3 Months Ended			12 Months Ended
	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016GBP (£)	Jun. 30, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of the Company's projected benefit obligation		92.00%			92.00%
U.S. Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plans with PBO in excess of the fair value of plan assets, PBO		$ 2,900			$ 2,900	$ 3,200
Plans with ABO in excess of the fair value of plan assets, ABO		2,900			2,900	3,200
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets		1,700			1,700	2,000
Defined benefit plan, benefits paid		281			139	133
Defined benefit plan, benefit obligation, period increase (decrease)		325
Defined benefit plan, settlements, benefit obligation		158			281	0
Future amortization of loss					52
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plans with PBO in excess of the fair value of plan assets, PBO		1,200			1,200	1,200
Plans with ABO in excess of the fair value of plan assets, ABO		1,200			1,200	1,200
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets		1,100			1,100	1,100
Plans with PBO in excess of the fair value of plan assets		1,100			1,100	1,100
Defined benefit plan, benefits paid			£ 116	$ 159	242	217
Defined benefit plan, benefit obligation, period increase (decrease)			103	141
Defined benefit plan, settlements, benefit obligation			£ 42	$ 61	159	0
Future amortization of loss					41
Effect of UK Plan insurance contract	$ 267
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plans with PBO in excess of the fair value of plan assets, PBO		1,200			1,200	1,200
Plans with ABO in excess of the fair value of plan assets, ABO		1,100			1,100	1,100
Plans with ABO in excess of the fair value of plan assets, fair value of plan assets		1,000			1,000	1,000
Plans with PBO in excess of the fair value of plan assets		$ 1,000			1,000	1,000
Defined benefit plan, benefits paid					39	38
Defined benefit plan, settlements, benefit obligation					$ 0	$ 0

Employee Benefits - Reconciliat

Employee Benefits - Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status (Details) £ in Millions, $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2016USD ($)	Jun. 30, 2016GBP (£)	Jun. 30, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
U.K.
Change in projected benefit obligation
Balance at the beginning of the Period				$ 4,985	$ 5,529
Service cost				0	1	$ 1
Interest cost				158	198	230
Plan amendment				(20)	27
Settlements		£ (42)	$ (61)	(159)	0
Plan transfer and acquisitions				0	(2)
Actuarial loss (gain)				32	(83)
Benefit payments		(116)	(159)	(242)	(217)
Change in discount rate				1,079	(247)
Foreign currency impact				(959)	(221)
Balance at the end of the period	$ 4,874			4,874	4,985	5,529
Accumulated benefit obligation at end of year	4,874			4,874	4,985
Change in fair value of plan assets
Balance at the beginning of the period				5,903	6,224
Actual return on plan assets				1,233	91
Employer contributions				67	65
Settlements				(159)	0
Plan transfer and acquisitions				0	(3)
Benefit payments		£ (116)	$ (159)	(242)	(217)
Foreign currency impact				(1,127)	(257)
Balance at the end of the period	5,675			5,675	5,903	6,224
Market related value at end of year	5,675			5,675	5,903
Funded status	801			801	918
Unrecognized prior-service cost	19			19	46
Unrecognized loss	1,237			1,237	1,465
Net amount recognized	2,057			2,057	2,429
U.S.
Change in projected benefit obligation
Balance at the beginning of the Period				3,160	3,350
Service cost				0	0	2
Interest cost				111	131	129
Plan amendment				0	0
Settlements	(158)			(281)	0
Plan transfer and acquisitions				0	(18)
Actuarial loss (gain)				(43)	(25)
Benefit payments	(281)			(139)	(133)
Change in discount rate				100	(145)
Foreign currency impact				0	0
Balance at the end of the period	2,908			2,908	3,160	3,350
Accumulated benefit obligation at end of year	2,908			2,908	3,160
Change in fair value of plan assets
Balance at the beginning of the period				1,951	2,036
Actual return on plan assets				116	(60)
Employer contributions				36	108
Settlements				(281)	0
Plan transfer and acquisitions				0	0
Benefit payments	(281)			(139)	(133)
Foreign currency impact				0	0
Balance at the end of the period	1,683			1,683	1,951	2,036
Market related value at end of year	1,819			1,819	2,064
Funded status	(1,225)			(1,225)	(1,209)
Unrecognized prior-service cost	6			6	9
Unrecognized loss	1,612			1,612	1,723
Net amount recognized	393			393	523
Other
Change in projected benefit obligation
Balance at the beginning of the Period				1,177	1,399
Service cost				0	0	0
Interest cost				29	33	47
Plan amendment				0	(10)
Settlements				0	0
Plan transfer and acquisitions				0	0
Actuarial loss (gain)				(7)	24
Benefit payments				(39)	(38)
Change in discount rate				100	(66)
Foreign currency impact				(33)	(165)
Balance at the end of the period	1,227			1,227	1,177	1,399
Accumulated benefit obligation at end of year	1,191			1,191	1,135
Change in fair value of plan assets
Balance at the beginning of the period				1,019	1,161
Actual return on plan assets				111	8
Employer contributions				20	21
Settlements				0	0
Plan transfer and acquisitions				0	0
Benefit payments				(39)	(38)
Foreign currency impact				(35)	(133)
Balance at the end of the period	1,076			1,076	1,019	$ 1,161
Market related value at end of year	1,076			1,076	1,019
Funded status	(151)			(151)	(158)
Unrecognized prior-service cost	(6)			(6)	(7)
Unrecognized loss	400			400	389
Net amount recognized	$ 243			$ 243	$ 224

Employee Benefits - Amounts rec

Employee Benefits - Amounts recognized in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	$ 836	$ 1,012
Accrued benefit liability	(35)	(94)
Accumulated other comprehensive loss	1,256	1,511
Net amount recognized	2,057	2,429
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	0
Accrued benefit liability	(1,225)	(1,209)
Accumulated other comprehensive loss	1,618	1,732
Net amount recognized	393	523
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	0
Accrued benefit liability	(151)	(158)
Accumulated other comprehensive loss	394	382
Net amount recognized	$ 243	$ 224

Employee Benefits - Amounts r78

Employee Benefits - Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized (Details 3) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
U.K.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	$ 1,237	$ 1,465
Prior service cost (income)	19	46
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	1,256	1,511
U.S.
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	1,612	1,723
Prior service cost (income)	6	9
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	1,618	1,732
Other
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	400	389
Prior service cost (income)	(6)	(7)
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	$ 394	$ 382

Employee Benefits - Components

Employee Benefits - Components of net periodic benefit cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 1	$ 1
Interest cost	158	198	230
Expected return on plan assets, net of administration expenses	(243)	(307)	(326)
Amortization of prior-service cost	2	1	1
Amortization of net actuarial loss	31	41	52
Net periodic benefit (income) cost	(52)	(66)	(42)
Settlement expense	61	0	0
Curtailment gain and other	0	0	0
Total net periodic benefit cost (income)	9	(66)	(42)
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	2
Interest cost	111	131	129
Expected return on plan assets, net of administration expenses	(156)	(154)	(157)
Amortization of prior-service cost	2	2	2
Amortization of net actuarial loss	50	54	42
Net periodic benefit (income) cost	7	33	18
Settlement expense	158	0	0
Curtailment gain and other	0	0	0
Total net periodic benefit cost (income)	165	33	18
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0
Interest cost	29	33	47
Expected return on plan assets, net of administration expenses	(48)	(50)	(59)
Amortization of prior-service cost	0	0	0
Amortization of net actuarial loss	10	11	10
Net periodic benefit (income) cost	(9)	(6)	(2)
Settlement expense	0	0
Curtailment gain and other	0	0	(2)
Total net periodic benefit cost (income)	$ (9)	$ (6)	$ (4)

Employee Benefits - Weighted-av

Employee Benefits - Weighted-average assumptions used to determine future benefit obligations (Details)	Dec. 31, 2016	Dec. 31, 2015
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.77%	3.96%
Underlying price inflation	1.83%	1.88%
U.K. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.70%	3.63%
U.K. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.20%	4.13%
U.S. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.53%	3.69%
U.S. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.11%	4.43%
Other | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	1.85%	2.43%
Rate of compensation increase	1.00%	2.00%
Underlying price inflation	2.00%	2.00%
Other | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.81%	3.96%
Rate of compensation increase	3.50%	3.50%
Underlying price inflation	2.50%	2.50%

Employee Benefits - Weighted-81

Employee Benefits - Weighted-average assumptions used to determine the net periodic benefit cost (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.96%	3.70%	4.55%
Expected return on plan assets, net of administration expenses	4.55%	5.09%	6.00%
U.K. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	3.63%	3.55%	3.70%
U.K. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate of compensation increase	4.13%	4.05%	4.40%
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets, net of administration expenses	7.81%	7.96%	8.80%
U.S. | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.69%	3.37%	3.97%
U.S. | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.43%	4.08%	4.87%
Other | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.43%	2.03%	3.60%
Expected return on plan assets, net of administration expenses	3.47%	3.99%	4.70%
Rate of compensation increase	2.00%	2.25%	2.25%
Other | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.96%	3.91%	4.71%
Expected return on plan assets, net of administration expenses	4.95%	5.21%	6.50%
Rate of compensation increase	3.50%	3.50%	3.50%

Employee Benefits - Expected Re

Employee Benefits - Expected Return on Plan Assets Narrative (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets, net of administration expenses	7.81%	7.96%	8.80%

Employee Benefits - Schedule 83

Employee Benefits - Schedule of Fair Value of U.S Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.K. and Non-U.S. Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total	$ 5,675	$ 5,903	$ 6,224
U.K. and Non-U.S. Pension Plan | Pooled Funds, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total	101	85
U.K. and Non-U.S. Pension Plan | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	86	159
U.K. and Non-U.S. Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	62	66
U.K. and Non-U.S. Pension Plan | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	10	111
U.K. and Non-U.S. Pension Plan | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	773	717
U.K. and Non-U.S. Pension Plan | Segment Geographical Groups of Countries Group Three [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	135	133
U.K. and Non-U.S. Pension Plan | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	2,129	3,145
U.K. and Non-U.S. Pension Plan | Pooled funds - Global
Defined Benefit Plan Disclosure [Line Items]
Total	365	360
U.K. and Non-U.S. Pension Plan | Pooled funds - Europe
Defined Benefit Plan Disclosure [Line Items]
Total	18	17
U.K. and Non-U.S. Pension Plan | Annuities
Defined Benefit Plan Disclosure [Line Items]
Total	1,773	827
U.K. and Non-U.S. Pension Plan | Pooled funds - Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	223	283
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total	1,947	2,560
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled Funds, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	86	159
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Segment Geographical Groups of Countries Group Three [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	135	133
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	1,726	2,268
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Global
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Europe
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Annuities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total	413	1,054
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Pooled Funds, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	66
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	10	111
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Segment Geographical Groups of Countries Group Three [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	403	877
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Pooled funds - Global
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Pooled funds - Europe
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Annuities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Pooled funds - Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total	1,773	827
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Pooled Funds, Real Estate
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Segment Geographical Groups of Countries Group Three [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Pooled funds - Global
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Pooled funds - Europe
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Annuities
Defined Benefit Plan Disclosure [Line Items]
Total	1,773	827	836
U.K. and Non-U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total	1,683	1,951	$ 2,036
U.S. Pension Plan | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	100	33
U.S. Pension Plan | Large cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	268	299
U.S. Pension Plan | Small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	15	30
U.S. Pension Plan | Large cap international
Defined Benefit Plan Disclosure [Line Items]
Total	64	52
U.S. Pension Plan | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	81	203
U.S. Pension Plan | International pooled funds
Defined Benefit Plan Disclosure [Line Items]
Total	196	210
U.S. Pension Plan | Pooled funds small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	52	58
U.S. Pension Plan | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total	105	148
U.S. Pension Plan | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Total	132	128
U.S. Pension Plan | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Fixed income derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	65	69
U.S. Pension Plan | Corporate Bonds And Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total	255	336
U.S. Pension Plan | Commodity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	22	13
U.S. Pension Plan | Real estate and REITS
Defined Benefit Plan Disclosure [Line Items]
Total	61	67
U.S. Pension Plan | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	267	305
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total	727	750
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	100	33
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Large cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	268	299
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	15	30
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Large cap international
Defined Benefit Plan Disclosure [Line Items]
Total	64	52
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	78	170
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | International pooled funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Total	76	52
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	65	47
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Bonds And Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate and REITS
Defined Benefit Plan Disclosure [Line Items]
Total	61	67
U.S. Pension Plan | Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total	186	292
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Large cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Large cap international
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	3	33
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | International pooled funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Pooled funds small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total	105	148
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Total	56	76
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Fixed income derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	22
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Corporate Bonds And Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Commodity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	22	13
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Real estate and REITS
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Other Observable Inputs (Level 2) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Large cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Large cap international
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Equity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | International pooled funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Pooled funds small cap domestic
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Government and agency bonds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Fixed income derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Corporate Bonds And Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Commodity derivatives
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Real estate and REITS
Defined Benefit Plan Disclosure [Line Items]
Total	0	0
U.S. Pension Plan | Significant Unobservable Inputs (Level 3) | Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Total	$ 0	$ 0

Employee Benefits - Schedule 84

Employee Benefits - Schedule of changes in Level 3 fair value for U.S. Pension Plans (Details) - U.S. - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Actual return on plan assets:
Balance at the beginning of the period	$ 1,951	$ 2,036
Balance at the end of the period	1,683	1,951
Significant Unobservable Inputs (Level 3)
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	$ 0	$ 0

Employee Benefits - Schedule 85

Employee Benefits - Schedule of Fair Value of U.K. Plan Assets (Details) - U.K. - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 5,675	$ 5,903	$ 6,224
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	86	159
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	62	66
Equity securities - global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	135	133
Pooled funds - Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	365	360
Pooled funds - Europe
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	18	17
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	10	111
Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	2,129	3,145
Annuities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,773	827
Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	223	283
Pooled Funds, Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	101	85
Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	773	717
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,947	2,560
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	86	159
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities - global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	135	133
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Europe
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,726	2,268
Quoted Prices in Active Markets for Identical Assets (Level 1) | Annuities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled Funds, Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	413	1,054
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	66
Significant Other Observable Inputs (Level 2) | Equity securities - global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Europe
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	10	111
Significant Other Observable Inputs (Level 2) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	403	877
Significant Other Observable Inputs (Level 2) | Annuities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled Funds, Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,773	827
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Equity securities - global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Europe
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Annuities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,773	827	$ 836
Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled Funds, Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 0	$ 0

Employee Benefits - Schedule 86

Employee Benefits - Schedule of changes in Level 3 fair value for U.K. Pension Plans (Details) - U.K. - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Actual return on plan assets:
Balance at the beginning of the period	$ 5,903	$ 6,224
Foreign exchange	(1,127)	(257)
Balance at the end of the period	5,675	5,903
Global
Actual return on plan assets:
Balance at the beginning of the period	360
Balance at the end of the period	365	360
Annuities
Actual return on plan assets:
Balance at the beginning of the period	827
Balance at the end of the period	1,773	827
Alternative investments
Actual return on plan assets:
Balance at the beginning of the period	717
Balance at the end of the period	773	717
Pooled funds - Fixed income securities
Actual return on plan assets:
Balance at the beginning of the period	283
Balance at the end of the period	223	283
Significant Unobservable Inputs (Level 3)
Actual return on plan assets:
Balance at the beginning of the period	827
Balance at the end of the period	1,773	827
Significant Unobservable Inputs (Level 3) | Global
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	0	0
Significant Unobservable Inputs (Level 3) | Annuities
Actual return on plan assets:
Balance at the beginning of the period	827	836
Relating to assets still held at the end of the year	7	(32)
Purchases, sales and settlements—net	1,248	58
Foreign exchange	(309)	(35)
Balance at the end of the period	1,773	827
Significant Unobservable Inputs (Level 3) | Alternative investments
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	$ 0	$ 0

Employee Benefits - Schedule 87

Employee Benefits - Schedule of Fair Value of Other Plan Assets (Details) - Other - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 1,076	$ 1,019	$ 1,161
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	11	11
Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	322	270
Pooled funds - North America
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	36	37
Pooled funds - Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	20	21
Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	166	30
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	37	48
Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	469	576
Pooled Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		12
Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	9	9
Commodity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		2
Pooled funds - REITS
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	6	3
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	11	11
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	11	11
Quoted Prices in Active Markets for Identical Assets (Level 1) | Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - North America
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - REITS
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	203	78
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - North America
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	166	30
Significant Other Observable Inputs (Level 2) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	37	48
Significant Other Observable Inputs (Level 2) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Other Observable Inputs (Level 2) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Commodity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Other Observable Inputs (Level 2) | Pooled funds - REITS
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Global
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - North America
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Unobservable Inputs (Level 3) | Alternative investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Commodity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Unobservable Inputs (Level 3) | Pooled funds - REITS
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 0	$ 0

Employee Benefits - Schedule 88

Employee Benefits - Schedule of changes in level 3 fair value for Other Plans (Details) - Other - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Actual return on plan assets:
Balance at the beginning of the period	$ 1,019	$ 1,161
Foreign currency impact	(35)	(133)
Balance at the end of the period	1,076	1,019
Alternative investments
Actual return on plan assets:
Balance at the beginning of the period	9
Balance at the end of the period	9	9
Significant Unobservable Inputs (Level 3)
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	0	0
Significant Unobservable Inputs (Level 3) | Alternative investments
Actual return on plan assets:
Balance at the beginning of the period	0
Balance at the end of the period	$ 0	$ 0

Employee Benefits - Investment

Employee Benefits - Investment Policy and Strategy Narrative (Details)	12 Months Ended
	Dec. 31, 2016
U.S. Pension Plan | Equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	41.00%
U.S. Pension Plan | Fixed income investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	30.00%
U.S. Pension Plan | Other Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage	29.00%
U.K. and Non-U.S. Pension Plan | Equity investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	14.00%
U.K. and Non-U.S. Pension Plan | Fixed income investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	77.00%
U.K. and Non-U.S. Pension Plan | Other Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual allocation percentage	9.00%

Employee Benefits - Cash Flows

Employee Benefits - Cash Flows Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
U.S. Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	$ 80
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	87
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions during next fiscal year	$ 18

Employee Benefits - Estimated F

Employee Benefits - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2016USD ($)
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	$ 124
2,018	130
2,019	140
2,020	148
2,021	156
2022 - 2025	892
U.S. Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	168
2,018	180
2,019	187
2,020	191
2,021	185
2022 - 2025	893
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,017	39
2,018	40
2,019	40
2,020	41
2,021	42
2022 - 2025	$ 228

Employee Benefits - Overview of

Employee Benefits - Overview of the accumulated benefit obligation, fair value of plan assets, funded status and net amount recognized for U.S. and Canadian Other Post-Retirement Benefits (Details) - U.S. and Canadian Other Post-Retirement Benefits - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated projected benefit obligation	$ 110	$ 105
Fair value of plan assets	18	18
Funded status	(92)	(87)
Unrecognized prior-service credit	(3)	(3)
Unrecognized loss	10	7
Net amount recognized	$ (85)	$ (83)

Employee Benefits - Schedule 93

Employee Benefits - Schedule of Other information related to Company's other post-retirement plan's (Details) - U.S. and Canadian Other Post-Retirement Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost recognized (millions)	$ 5	$ 6	$ 3
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average discount rate used to determine future benefit obligations	3.71%	3.99%	3.83%
Weighted-average discount rate used to determine net periodic benefit costs	3.99%	3.83%	4.44%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average discount rate used to determine future benefit obligations	4.15%	4.33%	4.08%
Weighted-average discount rate used to determine net periodic benefit costs	4.33%	4.08%	4.95%

Employee Benefits - U.S. and Ca

Employee Benefits - U.S. and Canadian Other Post-Retirement Benefits Narrative (Details) - U.S. and Canadian Other Post-Retirement Benefits $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized loss	$ (10)
Prior service cost	3
Future amortization of gain	0.2
Future amortization of prior service credit	0.3
Expected employer contributions during next fiscal year	4
Defined benefit plan, expected future benefit payments, next twelve months	6
Defined benefit plan, expected future benefit payments, five fiscal years thereafter	30
Effect of one percentage point increase on accumulated postretirement benefit obligation	7
Effect of one percentage point decrease on accumulated postretirement benefit obligation	6
Effect of one percentage point increase on service cost and interest cost components of net periodic benefit cost	0.6
Effect of one percentage point decrease on service cost and interest cost components of net periodic benefit cost	$ 0.5
Maximum percentage of liability for future plan cost increases for pre-65 and medical supplement plan coverage	5.00%
Maximum percentage of medical supplement plan into future periods	5.00%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Maximum percentage of liability for future plan cost increases for pre-65 and medical supplement plan coverage	8.50%
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Maximum percentage of liability for future plan cost increases for pre-65 and medical supplement plan coverage	4.00%

Share-Based Compensation Plan95

Share-Based Compensation Plans - Share-based compensation expense recognized in continuing operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 331	$ 339	$ 328
Tax benefit	94	95	94
Share-based compensation expense, net of tax	237	244	234
Employee share purchase plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	12	11	9
Restricted share units (“RSUs”)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	194	201	187
Performance share awards (PSAs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 125	$ 127	$ 132

Share-Based Compensation Plan96

Share-Based Compensation Plans - Restricted Share Units Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining amortization period (in years)	2 years 1 month 6 days
Restricted share units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of RSUs vested during the period	$ 200	$ 196	$ 183
Unamortized deferred compensation	$ 382
Restricted share units (RSUs) | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Restricted share units (RSUs) | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years

Share-Based Compensation Plan97

Share-Based Compensation Plans - Summary of the status of the Company's RSUs (Details) - Restricted share units (“RSUs”) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Non-vested share awards
Non-vested at beginning of period (in shares)	7,167	8,381	9,759
Granted (in shares)	2,252	2,459	2,844
Vested (in shares)	(2,845)	(3,385)	(3,732)
Forfeited (in shares)	(379)	(288)	(490)
Non-vested at end of period (in shares)	6,195	7,167	8,381
Weighted Average Fair value
Non-vested at beginning of period (in dollars per share)	$ 77	$ 63	$ 51
Granted (in dollars per share)	101	97	84
Vested (in dollars per share)	70	58	49
Forfeited (in dollars per share)	82	71	58
Non-vested at end of period (in dollars per share)	$ 89	$ 77	$ 63

Share-Based Compensation Plan98

Share-Based Compensation Plans - Performance Share Awards Narrative (Details) - Performance-based Awards - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, vesting conditions period (in years)	3 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, actual shares issued, percent	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSA, actual shares issued, percent	200.00%
2010 Leadership Performance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)	1.3
2009 Leadership Performance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)		1.6
2008 Leadership Performance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)			0.8
2006 Performance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued (in shares)			0.2

Share-Based Compensation Plan99

Share-Based Compensation Plans - Schedule of Performance-based plans (Details) - Performance-based Awards - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target PSAs granted (in shares)	783	993	816
Fair value (in dollars per share)	$ 100	$ 96	$ 81
Number of shares that would be issued based on current performance levels (in shares)	777	1,437	1,540
Unamortized expense, based on current performance levels	$ 57	$ 48	$ 0

Share-Based Compensation Pla100

Share-Based Compensation Plans - Employee Share Purchase Plan Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 331	$ 339	$ 328

Derivatives and Hedging - Forei

Derivatives and Hedging - Foreign Exchange Risk Management Narrative (Details) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016EUR (€)
Derivative [Line Items]
(Loss) income on financial instruments	$ (14)	$ (24)	$ (15)
Derivatives designated as a hedge of the foreign currency exposure	$ 227			€ 217
Cash Flow Hedging
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period ( in years)	2 years
Not Designated as Hedging Instrument
Derivative [Line Items]
Maximum length of time hedged in foreign currency undesignated hedge (in years)	1 year
Foreign exchange contracts | Not Designated as Hedging Instrument
Derivative [Line Items]
(Loss) income on financial instruments	$ 0.2	$ 8	$ 18

Derivatives and Hedging - Inter

Derivatives and Hedging - Interest Rate Risk Management (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	$ 0	$ 0	$ 9,000,000
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	12,000,000
(Loss) income on financial instruments	(14,000,000)	(24,000,000)	(15,000,000)
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
(Loss) income on financial instruments	$ 200,000	$ 8,000,000	$ 18,000,000

Derivatives and Hedging - Notio

Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets
Derivative [Line Items]
Derivative assets	$ 6	$ 15
Other Noncurrent Assets
Derivative [Line Items]
Derivative assets	9	17
Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	7	13
Other Noncurrent Liabilities
Derivative [Line Items]
Derivative liabilities	7	5
Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Notional amount	758	778
Derivative assets	14	32
Derivative liabilities	13	18
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	947	1,058
Derivative assets	15	32
Derivative liabilities	14	18
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Notional amount	189	280
Derivative assets	1	0
Derivative liabilities	$ 1	$ 0
Term of contract ( in days)	30 days

Derivatives and Hedging - Offse

Derivatives and Hedging - Offsetting of financial assets and derivatives assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 6	$ 15
Net amounts of assets presented in the statement of financial position	4	6
Other Noncurrent Assets
Derivative [Line Items]
Gross Amounts of Recognized Assets	9	17
Net amounts of assets presented in the statement of financial position	9	13
Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Gross Amounts of Recognized Assets	14	32
Gross Amounts Offset in the Statement of Financial Position	(1)	(13)
Net amounts of assets presented in the statement of financial position	13	19
Not Designated as Hedging Instrument
Derivative [Line Items]
Gross Amounts of Recognized Assets	15	32
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 1	$ 0

Derivatives and Hedging - Of105

Derivatives and Hedging - Offsetting of financial liabilities and derivative liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Current Liabilities
Derivative [Line Items]
Gross Amounts of Recognized Liabilities	$ 7	$ 13
Net Amounts of Liabilities Presented in the Statement of Financial Position (1)	5	4
Other Noncurrent Liabilities
Derivative [Line Items]
Gross Amounts of Recognized Liabilities	7	5
Net Amounts of Liabilities Presented in the Statement of Financial Position (1)	7	1
Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Gross Amounts of Recognized Liabilities	13	18
Gross Amounts Offset in the Statement of Financial Position	(1)	(13)
Net Amounts of Liabilities Presented in the Statement of Financial Position (1)	12	5
Not Designated as Hedging Instrument
Derivative [Line Items]
Gross Amounts of Recognized Liabilities	14	18
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
Gross Amounts of Recognized Liabilities	$ 1	$ 0

Derivatives and Hedging - Sched

Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	$ 0	$ 0	$ 9,000,000
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	12,000,000
(Loss) income on financial instruments	(14,000,000)	(24,000,000)	(15,000,000)
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
(Loss) income on financial instruments	200,000	8,000,000	18,000,000
Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
(Loss) income on financial instruments	18,000,000
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	(25,000,000)	(9,000,000)	(2,000,000)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(10,000,000)	(17,000,000)	(14,000,000)
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts | Compensation and Benefits
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	8,000,000	4,000,000	11,000,000
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	2,000,000	4,000,000	(5,000,000)
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts | Other General Expenses
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	(13,000,000)	(3,000,000)	(3,000,000)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(4,000,000)	(1,000,000)	3,000,000
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts | Interest Expense
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0	0
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(1,000,000)	(9,000,000)	(10,000,000)
Designated as Hedging Instrument | Cash Flow Hedging | Foreign exchange contracts | Other Income
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	(20,000,000)	(10,000,000)	(10,000,000)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	$ (7,000,000)	$ (11,000,000)	$ (2,000,000)

Derivatives and Hedging - Sc107

Derivatives and Hedging - Schedule of the amount of gain (loss) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
(Loss) income on financial instruments	$ (14)	$ (24)	$ (15)
Not Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
(Loss) income on financial instruments	0.2	$ 8	$ 18
Designated as Hedging Instrument | Foreign exchange contracts
Derivative [Line Items]
(Loss) income on financial instruments	$ 18

Fair Value Measurements and 108

Fair Value Measurements and Financial Instruments - Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Money market funds
Assets:
Money market funds	$ 1,371	$ 1,396
Government bonds
Assets:
Other investments:	1	1
Equity investments
Assets:
Other investments:	9	10
Foreign exchange contracts
Assets:
Derivatives	15	32
Liabilities:
Derivatives:	14	18
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Money market funds	1,371	1,396
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:	6	6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives:	0	0
Significant Other Observable Inputs (Level 2) | Money market funds
Assets:
Money market funds	0	0
Significant Other Observable Inputs (Level 2) | Government bonds
Assets:
Other investments:	1	1
Significant Other Observable Inputs (Level 2) | Equity investments
Assets:
Other investments:	3	4
Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets:
Derivatives	15	32
Liabilities:
Derivatives:	14	18
Significant Unobservable Inputs (Level 3) | Money market funds
Assets:
Money market funds	0	0
Significant Unobservable Inputs (Level 3) | Government bonds
Assets:
Other investments:	0	0
Significant Unobservable Inputs (Level 3) | Equity investments
Assets:
Other investments:	0	0
Significant Unobservable Inputs (Level 3) | Foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives:	$ 0	$ 0

Fair Value Measurements and 109

Fair Value Measurements and Financial Instruments - Schedule of financial instruments where the carrying amounts and fair values differ (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair value of financial instrument
Total long-term debt	$ 5,869	$ 5,138
Fair value of total debt	$ 6,264	$ 5,386

Fair Value Measurements and 110

Fair Value Measurements and Financial Instruments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Unrealized gain (loss)	$ 0	$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Legal Narrative (Details) £ in Millions, SFr in Millions, NZD in Millions

Dec. 31, 2016USD ($)

Jun. 29, 2015NZD

Jan. 26, 2015USD ($)

Jan. 26, 2015CHF (SFr)

Dec. 02, 2014USD ($)

Dec. 02, 2014CHF (SFr)

Jun. 01, 2007USD ($)

Jun. 01, 2007CHF (SFr)

Aug. 31, 2015USD ($)

Jun. 30, 2015GBP (£)

Mar. 31, 2015USD ($)

May 31, 2010USD ($)

Dec. 31, 2016GBP (£)

Dec. 31, 2016USD ($)

Dec. 20, 2016GBP (£)

Apr. 30, 2014GBP (£)

Potential Claim for Pension Advisory Services

Loss Contingencies [Line Items]

Estimate of possible loss

$ 55,000,000

$ 55,000,000

£ 45

Opry Mills Mall Limited Partnership

Loss Contingencies [Line Items]

Value of damages sought

$ 200,000,000

Amount of coverage for damages contended by the insurers

50,000,000

Difference amount of damages sought by the client

$ 150,000,000

Opry Mills Mall Limited Partnership

Loss Contingencies [Line Items]

Damages awarded

$ 204,000,000

$ 200,000,000

International Road Transport Union | Litigation Foreign Currency Denominated Award

Loss Contingencies [Line Items]

Value of damages sought

SFr 46

45,000,000

Damages awarded excluding interest and costs

SFr 16.8

16,000,000

Damages awarded

SFr 27.9

27,000,000

Litigation settlement

$ 14,000,000

SFr 12.8

Settlement agreement terms maximum liability

8,000,000

SFr 8.7

International Road Transport Union | Litigation USD Denominated Award

Loss Contingencies [Line Items]

Value of damages sought

$ 3,000,000

Damages awarded excluding interest and costs

$ 3,000,000

Damages awarded

$ 5,000,000

Litigation settlement

4,700,000

Settlement agreement terms maximum liability

$ 115,000

International Road Transport Union | Litigation Expenses and Interest

Loss Contingencies [Line Items]

Value of damages sought

$ 30,000,000

Trustees of Gleeds Pension Fund 2016 | Potential Claim for Pension Advisory Services

Loss Contingencies [Line Items]

Estimate of possible loss

86,000,000

86,000,000

£ 70

Philips

Loss Contingencies [Line Items]

Value of damages sought

£ 189

232,000,000

Philips 2,015

Loss Contingencies [Line Items]

Value of damages sought

£ 290

356,000,000

Pending Litigation | Lyttleton Port Company Limited

Loss Contingencies [Line Items]

Value of damages sought

NZD 184

127,000,000

Minimum

Loss Contingencies [Line Items]

Estimate of possible loss

0

0

Maximum

Loss Contingencies [Line Items]

Estimate of possible loss

$ 200,000,000

$ 200,000,000

Commitments and Contingencie112

Commitments and Contingencies - Guarantees and Indemnifications Narrative (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Maximum potential funding under commitments	$ 95,000,000	$ 104,000,000

Commitments and Contingencie113

Commitments and Contingencies - Letters of Credit Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 90	$ 58

Commitments and Contingencie114

Commitments and Contingencies - Commitments Narrative (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Maximum potential funding under commitments	$ 95,000,000	$ 104,000,000

Commitments and Contingencie115

Commitments and Contingencies - Premium Payments (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Maximum potential funding under commitments	$ 95,000,000	$ 104,000,000

Segment Information - Narrative

Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2016segment
Segment Reporting [Abstract]
Number of reportable segments	2

Segment Information - Schedule

Segment Information - Schedule of total revenue by business segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 3,262	$ 2,760	$ 2,800	$ 2,805	$ 3,227	$ 2,752	$ 2,836	$ 2,867	$ 11,627	$ 11,682	$ 12,045
Commissions, fees and other	$ 3,256	$ 2,754	$ 2,795	$ 2,800	$ 3,222	$ 2,746	$ 2,831	$ 2,862	11,605	11,661	12,019
Operating Segments | Risk Solutions
Segment Reporting Information [Line Items]
Revenue									7,485	7,426	7,834
Commissions, fees and other									7,463	7,405	7,808
Operating Segments | HR Solutions
Segment Reporting Information [Line Items]
Revenue									4,183	4,303	4,264
Commissions, fees and other									4,183	4,303	4,264
Intersegment elimination
Segment Reporting Information [Line Items]
Revenue									(41)	(47)	(53)
Commissions, fees and other									$ (41)	$ (47)	$ (53)

Segment Information - Schedu118

Segment Information - Schedule of commissions, fees, and other revenue by products (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Commissions, fees and other	$ 3,256	$ 2,754	$ 2,795	$ 2,800	$ 3,222	$ 2,746	$ 2,831	$ 2,862	$ 11,605	$ 11,661	$ 12,019
Operating Segments | Risk Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									7,463	7,405	7,808
Operating Segments | HR Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									4,183	4,303	4,264
Operating Segments | Reportable Subsegments | Retail Brokerage Revenues | Risk Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									6,096	6,044	6,334
Operating Segments | Reportable Subsegments | Reinsurance Brokerage Revenues | Risk Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									1,367	1,361	1,474
Operating Segments | Reportable Subsegments | Consulting Services Revenues | HR Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									1,662	1,686	1,700
Operating Segments | Reportable Subsegments | Outsourcing Revenues | HR Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									2,557	2,658	2,607
Operating Segments | Intersubsegment Eliminations | HR Solutions
Segment Reporting Information [Line Items]
Commissions, fees and other									(36)	(41)	(43)
Intersegment elimination
Segment Reporting Information [Line Items]
Commissions, fees and other									$ (41)	$ (47)	$ (53)

Segment Information - Schedu119

Segment Information - Schedule of fiduciary investment income by business segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Fiduciary investment income	$ 6	$ 6	$ 5	$ 5	$ 5	$ 6	$ 5	$ 5	$ 22	$ 21	$ 26
HR Solutions
Segment Reporting Information [Line Items]
Fiduciary investment income									0	0	0
Risk Solutions
Segment Reporting Information [Line Items]
Fiduciary investment income									$ 22	$ 21	$ 26

Segment Information - Schedu120

Segment Information - Schedule of reconciliation of segment income before tax to income from continuing operations before income taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes	$ 568	$ 436	$ 439	$ 463	$ 656	$ 423	$ 308	$ 461	$ 1,906	$ 1,848	$ 1,966
Interest income									9	14	10
Interest expense									(282)	(273)	(255)
Other income									36	100	44
Income before income taxes									1,669	1,689	1,765
Operating Segments
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									2,144	2,042	2,133
Operating Segments | Risk Solutions
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									1,587	1,506	1,648
Operating Segments | HR Solutions
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									557	536	485
Segment Reconciling Items
Segment Reporting Information [Line Items]
Operating income from continuing operations before income taxes									$ (238)	$ (194)	$ (167)

Segment Information - Schedu121

Segment Information - Schedule of consolidated revenue by geographic area (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 3,262	$ 2,760	$ 2,800	$ 2,805	$ 3,227	$ 2,752	$ 2,836	$ 2,867	$ 11,627	$ 11,682	$ 12,045
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									6,078	6,063	5,824
Americas other than U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									995	1,053	1,176
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,378	1,527	1,623
Europe, Middle East and Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,760	1,909	2,189
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 1,416	$ 1,130	$ 1,233

Segment Information - Schedu122

Segment Information - Schedule of consolidated non-current assets by geographic area (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	$ 765	$ 765
Goodwill, intangible assets and other	12,382	12,253
Total	13,147	13,018
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	443	432
Goodwill, intangible assets and other	6,947	6,635
Total	7,390	7,067
Americas other than U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	62	48
Goodwill, intangible assets and other	887	368
Total	949	416
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	65	89
Goodwill, intangible assets and other	2,091	2,606
Total	2,156	2,695
Europe, Middle East and Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	85	89
Goodwill, intangible assets and other	2,054	2,181
Total	2,139	2,270
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Fixed assets, net	110	107
Goodwill, intangible assets and other	403	463
Total	$ 513	$ 570

Guarantee of Registered Secu123

Guarantee of Registered Securities - Narrative (Details)	Dec. 31, 2016
5.00% Senior Notes due September 2020
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	5.00%
8.205% Junior Subordinated Deferrable Interest Debentures Percent Due 2027
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	8.205%
6.25% Senior Notes due September 2040
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	6.25%
4.250% Notes Due 2042
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	4.25%
4.45% Senior Notes due May 2043
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	4.45%
4.00% Senior Notes due November 2023
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	4.00%
2.875% Senior Notes due May 2026 (EUR 500M)
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	2.875%
3.50% Senior Notes due June 2024
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	3.50%
4.60% notes due May 2044
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	4.60%
4.75% Senior Notes due May 2045 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	4.75%
2.80% Senior Notes due March 2021 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	2.80%
3.875% Senior Notes due December 2025 | Senior Notes
Condensed Financial Statements, Captions [Line Items]
Interest rate on debt	3.875%

Guarantee of Registered Secu124

Guarantee of Registered Securities - Condensed Consolidating Statement of Income (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Deferred tax assets	$ 322				$ 300						$ 322	$ 300
Revenue
Commissions, fees and other	3,256	$ 2,754	$ 2,795	$ 2,800	3,222	$ 2,746	$ 2,831	$ 2,862			11,605	11,661	$ 12,019
Fiduciary investment income	6	6	5	5	5	6	5	5			22	21	26
Total revenue	3,262	2,760	2,800	2,805	3,227	2,752	2,836	2,867			11,627	11,682	12,045
Expenses
Compensation and benefits											6,914	6,837	7,014
Other general expenses											2,807	2,997	3,065
Total operating expenses											9,721	9,834	10,079
Operating income	568	436	439	463	656	423	308	461			1,906	1,848	1,966
Interest income											9	14	10
Interest expense											(282)	(273)	(255)
Intercompany interest income (expense)											0	0	0
Intercompany other income (expense)											0	0	0
Other income											36	100	44
Income before income taxes											1,669	1,689	1,765
Income tax expense (benefit)											239	267	334
Income (loss) before equity in earnings of subsidiaries											1,430	1,422	1,431
Equity in earnings of subsidiaries, net of tax											0	0	0
Net income	459	326	308	337	540	311	214	357	$ 645	$ 971	1,430	1,422	1,431
Less: Net income attributable to noncontrolling interests	7	7	8	12	6	8	10	13			34	37	34
Net income attributable to Aon shareholders	452	$ 319	$ 300	$ 325	534	$ 303	$ 204	$ 344			1,396	1,385	1,397
Aon plc
Condensed Financial Statements, Captions [Line Items]
Deferred tax assets	134				154						134	154
Revenue
Commissions, fees and other											0	0	0
Fiduciary investment income											0	0	0
Total revenue											0	0	0
Expenses
Compensation and benefits											130	136	140
Other general expenses											0	8	3
Total operating expenses											130	144	143
Operating income											(130)	(144)	(143)
Interest income											0	0	0
Interest expense											(196)	(140)	(84)
Intercompany interest income (expense)											14	429	449
Intercompany other income (expense)											274	302	342
Other income											15	(1)	2
Income before income taxes											(23)	446	566
Income tax expense (benefit)											(55)	45	74
Income (loss) before equity in earnings of subsidiaries											32	401	492
Equity in earnings of subsidiaries, net of tax											1,382	984	905
Net income											1,414	1,385	1,397
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											1,414	1,385	1,397
Aon Corporation
Condensed Financial Statements, Captions [Line Items]
Deferred tax assets	726				756						726	756
Revenue
Commissions, fees and other											0	0	0
Fiduciary investment income											0	0	0
Total revenue											0	0	0
Expenses
Compensation and benefits											171	32	16
Other general expenses											2	7	5
Total operating expenses											173	39	21
Operating income											(173)	(39)	(21)
Interest income											16	14	2
Interest expense											(101)	(130)	(139)
Intercompany interest income (expense)											(541)	(479)	(298)
Intercompany other income (expense)											(361)	(422)	(390)
Other income											(5)	0	5
Income before income taxes											(1,165)	(1,056)	(841)
Income tax expense (benefit)											(325)	(262)	(192)
Income (loss) before equity in earnings of subsidiaries											(840)	(794)	(649)
Equity in earnings of subsidiaries, net of tax											1,219	1,290	1,195
Net income											379	496	546
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											379	496	546
Other Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Deferred tax assets	168				207						168	207
Revenue
Commissions, fees and other											11,605	11,661	12,019
Fiduciary investment income											22	21	26
Total revenue											11,627	11,682	12,045
Expenses
Compensation and benefits											6,613	6,669	6,858
Other general expenses											2,805	2,982	3,057
Total operating expenses											9,418	9,651	9,915
Operating income											2,209	2,031	2,130
Interest income											22	19	17
Interest expense											(14)	(22)	(41)
Intercompany interest income (expense)											527	50	(151)
Intercompany other income (expense)											87	120	48
Other income											44	101	37
Income before income taxes											2,875	2,299	2,040
Income tax expense (benefit)											619	484	452
Income (loss) before equity in earnings of subsidiaries											2,256	1,815	1,588
Equity in earnings of subsidiaries, net of tax											379	496	546
Net income											2,635	2,311	2,134
Less: Net income attributable to noncontrolling interests											34	37	34
Net income attributable to Aon shareholders											2,601	2,274	2,100
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Deferred tax assets	$ (706)				$ (817)						(706)	(817)
Revenue
Commissions, fees and other											0	0	0
Fiduciary investment income											0	0	0
Total revenue											0	0	0
Expenses
Compensation and benefits											0	0	0
Other general expenses											0	0	0
Total operating expenses											0	0	0
Operating income											0	0	0
Interest income											(29)	(19)	(9)
Interest expense											29	19	9
Intercompany interest income (expense)											0	0	0
Intercompany other income (expense)											0	0	0
Other income											(18)	0	0
Income before income taxes											(18)	0	0
Income tax expense (benefit)											0	0	0
Income (loss) before equity in earnings of subsidiaries											(18)	0	0
Equity in earnings of subsidiaries, net of tax											(2,980)	(2,770)	(2,646)
Net income											(2,998)	(2,770)	(2,646)
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											$ (2,998)	$ (2,770)	$ (2,646)

Guarantee of Registered Secu125

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$ 459	$ 326	$ 308	$ 337	$ 540	$ 311	$ 214	$ 357	$ 645	$ 971	$ 1,430	$ 1,422	$ 1,431
Less: Net income attributable to noncontrolling interests	7	7	8	12	6	8	10	13			34	37	34
Net income attributable to Aon shareholders	$ 452	$ 319	$ 300	$ 325	$ 534	$ 303	$ 204	$ 344			1,396	1,385	1,397
Change in fair value of financial instruments													4
Net change in fair value of financial instruments											(12)	(8)	4
Foreign currency translation adjustments											(495)	(442)	(507)
Post-retirement benefit obligation											16	155	(260)
Total other comprehensive loss											(491)	(295)	(763)
Equity in other comprehensive loss of subsidiaries, net of tax											0	0	0
Less: Other comprehensive loss attributable to noncontrolling interests											(2)	(6)	(3)
Total other comprehensive loss attributable to Aon shareholders											(489)	(289)	(760)
Comprehensive income attributable to Aon shareholders											907	1,096	637
Aon plc
Condensed Financial Statements, Captions [Line Items]
Net income											1,414	1,385	1,397
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											1,414	1,385	1,397
Change in fair value of financial instruments													0
Net change in fair value of financial instruments											0	0
Foreign currency translation adjustments											(2)	0	0
Post-retirement benefit obligation											0	0	0
Total other comprehensive loss											(2)	0	0
Equity in other comprehensive loss of subsidiaries, net of tax											(505)	(289)	(760)
Less: Other comprehensive loss attributable to noncontrolling interests											0	0	0
Total other comprehensive loss attributable to Aon shareholders											(507)	(289)	(760)
Comprehensive income attributable to Aon shareholders											907	1,096	637
Aon Corporation
Condensed Financial Statements, Captions [Line Items]
Net income											379	496	546
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											379	496	546
Change in fair value of financial instruments													(3)
Net change in fair value of financial instruments											(1)	0
Foreign currency translation adjustments											21	(47)	(31)
Post-retirement benefit obligation											68	12	(315)
Total other comprehensive loss											88	(35)	(349)
Equity in other comprehensive loss of subsidiaries, net of tax											(547)	(259)	(409)
Less: Other comprehensive loss attributable to noncontrolling interests											0	0	0
Total other comprehensive loss attributable to Aon shareholders											(459)	(294)	(758)
Comprehensive income attributable to Aon shareholders											(80)	202	(212)
Other Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income											2,635	2,311	2,134
Less: Net income attributable to noncontrolling interests											34	37	34
Net income attributable to Aon shareholders											2,601	2,274	2,100
Change in fair value of financial instruments													7
Net change in fair value of financial instruments											(11)	(8)
Foreign currency translation adjustments											(532)	(395)	(476)
Post-retirement benefit obligation											(52)	143	55
Total other comprehensive loss											(595)	(260)	(414)
Equity in other comprehensive loss of subsidiaries, net of tax											(459)	(294)	(758)
Less: Other comprehensive loss attributable to noncontrolling interests											(2)	(6)	(3)
Total other comprehensive loss attributable to Aon shareholders											(1,052)	(548)	(1,169)
Comprehensive income attributable to Aon shareholders											1,549	1,726	931
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income											(2,998)	(2,770)	(2,646)
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to Aon shareholders											(2,998)	(2,770)	(2,646)
Change in fair value of financial instruments													0
Net change in fair value of financial instruments											0	0
Foreign currency translation adjustments											18	0	0
Post-retirement benefit obligation											0	0	0
Total other comprehensive loss											18	0	0
Equity in other comprehensive loss of subsidiaries, net of tax											1,511	842	1,927
Less: Other comprehensive loss attributable to noncontrolling interests											0	0	0
Total other comprehensive loss attributable to Aon shareholders											1,529	842	1,927
Comprehensive income attributable to Aon shareholders											$ (1,469)	$ (1,928)	$ (719)

Guarantee of Registered Secu126

Guarantee of Registered Securities - Condensed Consolidating Statement of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Total Current Assets
Cash and cash equivalents	$ 431	$ 384	$ 374	$ 477
Short-term investments	290	356
Receivables, net	2,589	2,564
Fiduciary assets	9,485	9,932
Intercompany receivables	0	0
Other current assets	351	329
Total Current Assets	13,146	13,565
Goodwill	8,747	8,448	8,860
Intangible assets, net	2,223	2,180
Fixed assets, net	765	765
Deferred tax assets	322	300
Intercompany receivables	0	0
Prepaid pension	858	1,033
Other non-current assets	554	592
Investment in subsidiary	0	0
TOTAL ASSETS	26,615	26,883
CURRENT LIABILITIES
Accounts payable and accrued liabilities	1,801	1,772
Short-term debt and current portion of long-term debt	336	562
Fiduciary liabilities	9,485	9,932
Intercompany payables	0	0
Other current liabilities	873	819
Total Current Liabilities	12,495	13,085
Long-term debt	5,869	5,138
Deferred tax liabilities	101	37
Pension, other post-retirement and other post-employment liabilities	1,774	1,795
Intercompany payables	0	0
Other non-current liabilities	844	769
TOTAL LIABILITIES	21,083	20,824
TOTAL AON SHAREHOLDERS’ EQUITY	5,475	6,002
Noncontrolling interests	57	57
TOTAL EQUITY	5,532	6,059	6,527	8,091
TOTAL LIABILITIES AND EQUITY	26,615	26,883
Aon plc
Total Current Assets
Cash and cash equivalents	0	0	0	0
Short-term investments	0	0
Receivables, net	0	1
Fiduciary assets	0	0
Intercompany receivables	105	432
Other current assets	0	0
Total Current Assets	105	433
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Deferred tax assets	134	154
Intercompany receivables	366	375
Prepaid pension	0	0
Other non-current assets	2	0
Investment in subsidiary	10,107	11,700
TOTAL ASSETS	10,714	12,662
CURRENT LIABILITIES
Accounts payable and accrued liabilities	585	2,988
Short-term debt and current portion of long-term debt	279	0
Fiduciary liabilities	0	0
Intercompany payables	142	167
Other current liabilities	0	47
Total Current Liabilities	1,006	3,202
Long-term debt	4,177	3,451
Deferred tax liabilities	0	0
Pension, other post-retirement and other post-employment liabilities	0	0
Intercompany payables	0	0
Other non-current liabilities	8	7
TOTAL LIABILITIES	5,191	6,660
TOTAL AON SHAREHOLDERS’ EQUITY	5,523	6,002
Noncontrolling interests	0	0
TOTAL EQUITY	5,523	6,002
TOTAL LIABILITIES AND EQUITY	10,714	12,662
Aon Corporation
Total Current Assets
Cash and cash equivalents	1,633	2,083	2,727	247
Short-term investments	140	209
Receivables, net	3	0
Fiduciary assets	0	0
Intercompany receivables	1,880	1,950
Other current assets	25	19
Total Current Assets	3,681	4,261
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Deferred tax assets	726	756
Intercompany receivables	261	526
Prepaid pension	5	6
Other non-current assets	119	119
Investment in subsidiary	17,137	16,042
TOTAL ASSETS	21,929	21,710
CURRENT LIABILITIES
Accounts payable and accrued liabilities	44	45
Short-term debt and current portion of long-term debt	50	550
Fiduciary liabilities	0	0
Intercompany payables	10,399	9,518
Other current liabilities	63	56
Total Current Liabilities	10,556	10,169
Long-term debt	1,413	1,412
Deferred tax liabilities	0	0
Pension, other post-retirement and other post-employment liabilities	1,356	1,313
Intercompany payables	8,877	8,799
Other non-current liabilities	77	140
TOTAL LIABILITIES	22,279	21,833
TOTAL AON SHAREHOLDERS’ EQUITY	(350)	(123)
Noncontrolling interests	0	0
TOTAL EQUITY	(350)	(123)
TOTAL LIABILITIES AND EQUITY	21,929	21,710
Other Non-Guarantor Subsidiaries
Total Current Assets
Cash and cash equivalents	660	1,242	1,361	1,246
Short-term investments	150	147
Receivables, net	2,586	2,563
Fiduciary assets	9,485	9,932
Intercompany receivables	9,825	7,957
Other current assets	326	310
Total Current Assets	23,032	22,151
Goodwill	8,747	8,448
Intangible assets, net	2,223	2,180
Fixed assets, net	765	765
Deferred tax assets	168	207
Intercompany receivables	8,711	8,633
Prepaid pension	853	1,027
Other non-current assets	433	557
Investment in subsidiary	(350)	(123)
TOTAL ASSETS	44,582	43,845
CURRENT LIABILITIES
Accounts payable and accrued liabilities	3,034	1,680
Short-term debt and current portion of long-term debt	7	12
Fiduciary liabilities	9,485	9,932
Intercompany payables	1,269	654
Other current liabilities	810	716
Total Current Liabilities	14,605	12,994
Long-term debt	279	275
Deferred tax liabilities	759	855
Pension, other post-retirement and other post-employment liabilities	418	482
Intercompany payables	461	735
Other non-current liabilities	759	705
TOTAL LIABILITIES	17,281	16,046
TOTAL AON SHAREHOLDERS’ EQUITY	27,244	27,742
Noncontrolling interests	57	57
TOTAL EQUITY	27,301	27,799
TOTAL LIABILITIES AND EQUITY	44,582	43,845
Consolidating Adjustments
Total Current Assets
Cash and cash equivalents	(1,862)	(2,941)	$ (3,714)	$ (1,016)
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Intercompany receivables	(11,810)	(10,339)
Other current assets	0	0
Total Current Assets	(13,672)	(13,280)
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Deferred tax assets	(706)	(817)
Intercompany receivables	(9,338)	(9,534)
Prepaid pension	0	0
Other non-current assets	0	(84)
Investment in subsidiary	(26,894)	(27,619)
TOTAL ASSETS	(50,610)	(51,334)
CURRENT LIABILITIES
Accounts payable and accrued liabilities	(1,862)	(2,941)
Short-term debt and current portion of long-term debt	0	0
Fiduciary liabilities	0	0
Intercompany payables	(11,810)	(10,339)
Other current liabilities	0	0
Total Current Liabilities	(13,672)	(13,280)
Long-term debt	0	0
Deferred tax liabilities	(658)	(818)
Pension, other post-retirement and other post-employment liabilities	0	0
Intercompany payables	(9,338)	(9,534)
Other non-current liabilities	0	(83)
TOTAL LIABILITIES	(23,668)	(23,715)
TOTAL AON SHAREHOLDERS’ EQUITY	(26,942)	(27,619)
Noncontrolling interests	0	0
TOTAL EQUITY	(26,942)	(27,619)
TOTAL LIABILITIES AND EQUITY	$ (50,610)	$ (51,334)

Guarantee of Registered Secu127

Guarantee of Registered Securities - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$ 2,326	$ 2,009	$ 1,812
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	43	220	52
Payments for investments	(64)	(266)	(20)
Net (purchases) sales of short-term investments - non-fiduciary	61	9	110
Acquisition of businesses, net of cash acquired	(879)	(16)	(479)
Proceeds from sale of businesses	107	205	48
Capital expenditures	(222)	(290)	(256)
CASH USED FOR INVESTING ACTIVITIES	(954)	(138)	(545)
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	(1,257)	(1,550)	(2,250)
Advances from (to) affiliates and other (1)	0	0	0
Issuance of shares for employee benefit plans	(129)	(30)	(105)
Issuance of debt	3,467	5,351	5,239
Repayment of debt	(2,945)	(5,098)	(3,918)
Cash dividends to shareholders	(345)	(323)	(273)
Noncontrolling interests and other financing activities	(77)	(39)	4
CASH USED FOR FINANCING ACTIVITIES	(1,286)	(1,689)	(1,303)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(39)	(172)	(67)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	47	10	(103)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	384	374	477
CASH AND CASH EQUIVALENTS AT END OF YEAR	431	384	374
Aon plc
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	2,705	695	769
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	0	0	0
Payments for investments	0	(13)	0
Net (purchases) sales of short-term investments - non-fiduciary	0	0	0
Acquisition of businesses, net of cash acquired	0	0	0
Proceeds from sale of businesses	0	0	0
Capital expenditures	0	0	0
CASH USED FOR INVESTING ACTIVITIES	0	(13)	0
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	(1,257)	(1,550)	(2,250)
Advances from (to) affiliates and other (1)	(2,008)	232	19
Issuance of shares for employee benefit plans	(129)	(29)	(105)
Issuance of debt	1,879	1,318	2,908
Repayment of debt	(845)	(330)	(1,068)
Cash dividends to shareholders	(345)	(323)	(273)
Noncontrolling interests and other financing activities		0	0
CASH USED FOR FINANCING ACTIVITIES	(2,705)	(682)	(769)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	0	0	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	0	0	0
CASH AND CASH EQUIVALENTS AT END OF YEAR	0	0	0
Aon Corporation
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	(536)	464	(927)
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	316	27	39
Payments for investments	(35)	(47)	(20)
Net (purchases) sales of short-term investments - non-fiduciary	70	(42)	(3)
Acquisition of businesses, net of cash acquired	(335)	0	0
Proceeds from sale of businesses	0	0	0
Capital expenditures	0	0	0
CASH USED FOR INVESTING ACTIVITIES	16	(62)	16
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0	0
Advances from (to) affiliates and other (1)	570	(326)	3,215
Issuance of shares for employee benefit plans	0	0	0
Issuance of debt	1,588	4,026	2,326
Repayment of debt	(2,088)	(4,746)	(2,150)
Cash dividends to shareholders	0	0	0
Noncontrolling interests and other financing activities	0	0	0
CASH USED FOR FINANCING ACTIVITIES	70	(1,046)	3,391
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(450)	(644)	2,480
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	2,083	2,727	247
CASH AND CASH EQUIVALENTS AT END OF YEAR	1,633	2,083	2,727
Other Non-Guarantor Subsidiaries
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	3,265	2,523	1,970
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	15	193	13
Payments for investments	(29)	(219)	0
Net (purchases) sales of short-term investments - non-fiduciary	(9)	51	113
Acquisition of businesses, net of cash acquired	(608)	(16)	(479)
Proceeds from sale of businesses	171	205	48
Capital expenditures	(222)	(290)	(256)
CASH USED FOR INVESTING ACTIVITIES	(682)	(76)	(561)
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0	0
Advances from (to) affiliates and other (1)	(3,037)	(2,339)	(536)
Issuance of shares for employee benefit plans	0	(1)	0
Issuance of debt	0	7	5
Repayment of debt	(12)	(22)	(700)
Cash dividends to shareholders	0	0	0
Noncontrolling interests and other financing activities	(77)	(39)	4
CASH USED FOR FINANCING ACTIVITIES	(3,126)	(2,394)	(1,227)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	(39)	(172)	(67)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(582)	(119)	115
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	1,242	1,361	1,246
CASH AND CASH EQUIVALENTS AT END OF YEAR	660	1,242	1,361
Consolidating Adjustments
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	(3,108)	(1,673)	0
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from investments	(288)	0	0
Payments for investments	0	13	0
Net (purchases) sales of short-term investments - non-fiduciary	0	0	0
Acquisition of businesses, net of cash acquired	64	0	0
Proceeds from sale of businesses	(64)	0	0
Capital expenditures	0	0	0
CASH USED FOR INVESTING ACTIVITIES	(288)	13	0
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0	0
Advances from (to) affiliates and other (1)	4,475	2,433	(2,698)
Issuance of shares for employee benefit plans	0	0	0
Issuance of debt	0	0	0
Repayment of debt	0	0	0
Cash dividends to shareholders	0	0	0
Noncontrolling interests and other financing activities	0	0	0
CASH USED FOR FINANCING ACTIVITIES	4,475	2,433	(2,698)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0	0
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	1,079	773	(2,698)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	(2,941)	(3,714)	(1,016)
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ (1,862)	$ (2,941)	$ (3,714)

Quarterly Financial Data (Un128

Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Commissions, fees and other revenue	$ 3,256	$ 2,754	$ 2,795	$ 2,800	$ 3,222	$ 2,746	$ 2,831	$ 2,862			$ 11,605	$ 11,661	$ 12,019
Fiduciary investment income	6	6	5	5	5	6	5	5			22	21	26
Total revenue	3,262	2,760	2,800	2,805	3,227	2,752	2,836	2,867			11,627	11,682	12,045
Operating income	568	436	439	463	656	423	308	461			1,906	1,848	1,966
Net income	459	326	308	337	540	311	214	357	$ 645	$ 971	1,430	1,422	1,431
Less: Net income attributable to noncontrolling interests	7	7	8	12	6	8	10	13			34	37	34
Net income attributable to Aon shareholders	$ 452	$ 319	$ 300	$ 325	$ 534	$ 303	$ 204	$ 344			$ 1,396	$ 1,385	$ 1,397
PER SHARE DATA
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ 1.70	$ 1.19	$ 1.12	$ 1.20	$ 1.94	$ 1.08	$ 0.72	$ 1.21			$ 5.21	$ 4.93
Diluted net income per share attributable to Aon shareholders (in dollars per share)	$ 1.68	$ 1.18	$ 1.11	$ 1.19	$ 1.91	$ 1.07	$ 0.71	$ 1.20			$ 5.16	$ 4.88
Scenario, Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Commissions, fees and other revenue	$ 3,317	$ 2,740	$ 2,761	$ 2,787	$ 3,283	$ 2,736	$ 2,800	$ 2,842			$ 11,605	$ 11,661
Fiduciary investment income	6	6	5	5	5	6	5	5			22	21
Total revenue	3,323	2,746	2,766	2,792	3,288	2,742	2,805	2,847			11,627	11,682
Operating income	629	422	405	450	717	413	277	441			1,906	1,848
Net income	509	314	280	327	590	303	188	341	$ 607	$ 921	1,430	1,422
Less: Net income attributable to noncontrolling interests	7	7	8	12	6	8	10	13			34	37
Net income attributable to Aon shareholders	$ 502	$ 307	$ 272	$ 315	$ 584	$ 295	$ 178	$ 328			$ 1,396	$ 1,385
PER SHARE DATA
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ 1.89	$ 1.15	$ 1.01	$ 1.16	$ 2.12	$ 1.05	$ 0.63	$ 1.15			$ 5.21	$ 4.93
Diluted net income per share attributable to Aon shareholders (in dollars per share)	$ 1.87	$ 1.14	$ 1.01	$ 1.15	$ 2.09	$ 1.04	$ 0.62	$ 1.14			$ 5.16	$ 4.88
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Commissions, fees and other revenue	$ (61)	$ 14	$ 34	$ 13	$ (61)	$ 10	$ 31	$ 20			$ 0	$ 0
Fiduciary investment income	0	0	0	0	0	0	0	0			0	0
Total revenue	(61)	14	34	13	(61)	10	31	20			0	0
Operating income	(61)	14	34	13	(61)	10	31	20			0	0
Net income	(50)	12	28	10	(50)	8	26	16			0	0
Less: Net income attributable to noncontrolling interests	0	0	0	0	0	0	0	0			0	0
Net income attributable to Aon shareholders	$ (50)	$ 12	$ 28	$ 10	$ (50)	$ 8	$ 26	$ 16			$ 0	$ 0
PER SHARE DATA
Basic net income per share attributable to Aon shareholders (in dollars per share)	$ (0.19)	$ 0.04	$ 0.11	$ 0.04	$ (0.18)	$ 0.03	$ 0.09	$ 0.06			$ 0	$ 0
Diluted net income per share attributable to Aon shareholders (in dollars per share)	$ (0.19)	$ 0.04	$ 0.10	$ 0.04	$ (0.18)	$ 0.03	$ 0.09	$ 0.06			$ 0	$ 0

Subsequent Event - Dispositi129

Subsequent Event - Disposition of Benefits Administration and Business Process Outsourcing (Details) - Tempo Business - Subsequent Event $ in Millions	Feb. 09, 2017USD ($)agreement
Subsequent Event [Line Items]
Number Of Commercial Agreements | agreement	2
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Subsequent Event [Line Items]
Purchase price	$ 4,300
Deferred consideration	$ 500
Deferred consideration payment installments	20.00%
Buyer required IRR to pay deferred consideration	15.00%
Sponsor required return on cash proceeds	225.00%
Customary transaction marketing period before close	15 days
Agreement termination fee due	$ 215