Aon (AON) 10-Q 1 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015
Document and Entity Information
Entity Registrant Name	Aon plc
Entity Central Index Key	315293
Document Type	10-Q
Document Period End Date	31-Mar-15
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	281,733,504
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Income (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Revenue
Commissions, fees and other	$2,842		$2,941
Fiduciary investment income	5		6
Total revenue	2,847		2,947
Expenses
Compensation and benefits	1,683		1,751
Other general expenses	723		727
Total operating expenses	2,406		2,478
Operating income	441		469
Interest income	3		2
Interest expense	-65		-58
Other income	42		1
Income before income taxes	421		414
Income taxes	80		78
Net income	341		336
Less: Net income attributable to noncontrolling interests	13		11
Net income attributable to Aon shareholders	$328		$325
Basic net income per share attributable to Aon shareholders	$1.15		$1.07
Diluted net income per share attributable to Aon shareholders	$1.14		$1.06
Cash dividends per share paid on ordinary shares	$0.25		$0.18
Weighted average ordinary shares outstanding - basic (in shares)	284.2	[1]	303.5	[1]
Weighted average ordinary shares outstanding - diluted (in shares)	287.1		307.2
[1]	Includes 2.5 million and 3.4 million of participating securities for the three months ended March 31, 2015 and 2014, respectively.

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$341	$336
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	328	325
Other comprehensive (loss) income, net of tax:
Change in fair value of investments	-1	1
Change in fair value of derivatives	6	9
Foreign currency translation adjustments	-322	16
Post-retirement benefit obligation	23	26
Total other comprehensive (loss) income	-294	52
Less: Other comprehensive (loss) income attributable to noncontrolling interests	-1	-2
Total other comprehensive (loss) income attributable to Aon shareholders	-293	54
Comprehensive income attributable to Aon shareholders	$35	$379

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Financial Position (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
CURRENT ASSETS
Cash and cash equivalents	$378	$374
Short-term investments	343	394
Receivables, net	2,672	2,815
Fiduciary assets	10,894	11,638
Other current assets	712	602
Total Current Assets	14,999	15,823
Goodwill	8,548	8,860
Intangible assets, net	2,410	2,520
Fixed assets, net	754	765
Other non-current assets	1,678	1,804
TOTAL ASSETS	28,389	29,772
CURRENT LIABILITIES
Fiduciary liabilities	10,894	11,638
Short-term debt and current portion of long-term debt	966	783
Accounts payable and accrued liabilities	1,391	1,805
Other current liabilities	865	788
Total Current Liabilities	14,116	15,014
Long-term debt	4,710	4,799
Pension, other post-retirement and post-employment liabilities	2,001	2,141
Other non-current liabilities	1,131	1,187
TOTAL LIABILITIES	21,958	23,141
EQUITY
Ordinary shares - $0.01 nominal value Authorized: 750 shares (issued: 2015 - 281.7; 2014 - 280.0)	3	3
Additional paid-in capital	5,177	5,097
Retained earnings	4,612	4,605
Accumulated other comprehensive loss	-3,427	-3,134
TOTAL AON SHAREHOLDERS' EQUITY	6,365	6,571
Noncontrolling interests	66	60
TOTAL EQUITY	6,431	6,631
TOTAL LIABILITIES AND EQUITY	$28,389	$29,772

Condensed_Consolidated_Stateme3

Condensed Consolidated Statements of Financial Position (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, except Per Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Common stock, nominal or par value (in dollars per share)	$0.01	$0.01
Common stock, Authorized shares	750	750
Common stock, issued shares	281.7	280

Condensed_Consolidated_Stateme4

Condensed Consolidated Statement of Shareholders' Equity (USD $)	Total	Ordinary Shares and Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income, Net of Tax [Member]	Non-controlling Interests [Member]
In Millions, unless otherwise specified
Beginning Balance at Dec. 31, 2014	$6,631	$5,100	$4,605	($3,134)	$60
Beginning Balance (in shares) at Dec. 31, 2014	280	280
Increase (Decrease) in Shareholders' Equity
Net income	341	0	328	0	13
Shares issued - employee benefit plans (in shares)		0.2
Shares issued - employee benefit plans	15	15	0	0	0
Shares issued - employee compensation (in shares)		4
Shares issued - employee compensation	-128	-128	0	0	0
Shares purchased (in shares)		-2.5
Shares purchased	-250	0	-250	0	0
Tax benefit - employee benefit plans	102	102	0	0	0
Share-based compensation expense	90	90	0	0	0
Dividends to shareholders	-71	0	-71	0	0
Net change in fair value of investments	-1	0	0	-1	0
Net change in fair value of derivatives	6	0	0	6	0
Net foreign currency translation adjustments	-322	0	0	-321	-1
Net post-retirement benefit obligation	23	0	0	23	0
Purchases of shares from noncontrolling interests	-4	1	0	0	-5
Dividends paid to noncontrolling interests on subsidiary common stock	-1	0	0	0	-1
Ending Balance at Mar. 31, 2015	$6,431	$5,180	$4,612	($3,427)	$66
Ending Balance (in shares) at Mar. 31, 2015	281.7	281.7

Condensed_Consolidated_Stateme5

Condensed Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$341	$336
Adjustments to reconcile net income to cash provided by (used for) operating activities:
Gain from sales of businesses and investments, net	-19	-5
Depreciation of fixed assets	56	60
Amortization of intangible assets	80	86
Share-based compensation expense	90	102
Deferred income taxes	7	10
Change in assets and liabilities:
Fiduciary receivables	173	165
Short-term investments b funds held on behalf of clients	63	-271
Fiduciary liabilities	-236	106
Receivables, net	49	13
Accounts payable and accrued liabilities	-466	-468
Restructuring reserves	-13	-40
Current income taxes	27	2
Pension, other post-retirement and other post-employment liabilities	-66	-128
Other assets and liabilities	50	21
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	136	-11
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	3	42
Purchases of long-term investments	-1	-10
Net sales of short-term investments b non-fiduciary	42	183
Acquisition of businesses, net of cash acquired	-21	-5
Proceeds from sale of businesses	41	1
Capital expenditures	-62	-55
CASH PROVIDED BY INVESTING ACTIVITIES	2	156
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	-250	-600
Issuance of shares for employee benefit plans	48	26
Issuance of debt	870	1,195
Repayment of debt	-686	-829
Cash dividends to shareholders	-71	-53
(Purchases) sales of shares (from) to noncontrolling interests	-5	1
Dividends paid to noncontrolling interests	1	0
CASH USED FOR FINANCING ACTIVITIES	-95	-260
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	-39	-24
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	4	-139
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	374	477
CASH AND CASH EQUIVALENTS AT END OF PERIOD	378	338
Supplemental disclosures:
Interest paid	63	64
Income taxes paid, net of refunds	$46	$66

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation
	The accompanying unaudited Condensed Consolidated Financial Statements and Notes thereto have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP").  The Condensed 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 Condensed Consolidated Financial Statements include, in the opinion of management, all adjustments (consisting of normal recurring adjustments and reclassifications) necessary to present fairly the Company's consolidated financial position, results of operations and cash flows for all periods presented.
	Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted.  These Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2014.  The results for the three months ended March 31, 2015 are not necessarily indicative of operating results that may be expected for the full year ending December 31, 2015.
	Reclassification
	Certain amounts in prior years' Condensed Consolidated Financial Statements and related notes have been reclassified to conform to the 2015 presentation. In prior periods, long-term investments were included in Investments in the Condensed Consolidated Statement of Financial Position. These amounts are now included in Other non-current assets in the Condensed Consolidated Statement of Financial Position, as shown in Note 4 to these Condensed Consolidated Financial Statements. Long-term investments were $143 million at both March 31, 2015 and December 31, 2014.
	Use of Estimates
	The preparation of the accompanying Condensed 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 movements increase the uncertainty inherent in such estimates and assumptions.  As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates.  Changes in estimates resulting from continuing changes in the economic environment will be reflected in the financial statements in future periods.

Accounting_Principles_and_Prac

Accounting Principles and Practices	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Accounting Principles and Practices	Accounting Principles and Practices
	New Accounting Pronouncements
	Debt Issuance Costs
	In April 2015, the Financial Accounting Standards Board ("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. The new guidance will be applied on a retrospective basis and is effective for the Company in the first quarter of 2016. The adoption of this guidance is not expected to have a material impact on the Company's Condensed Consolidated Financial Statements.
	Consolidations
	In February 2015, the FASB issued new accounting guidance on consolidations, which eliminates the deferral granted to investment companies from applying the variable interest entities ("VIEs") guidance and makes targeted amendments to the current consolidation guidance. The new guidance applies to all entities involved with limited partnerships or similar entities and will require re-evaluation of these entities under the revised guidance, which could change previous consolidation conclusions. The guidance is effective for the Company in the first quarter of 2016. The impact from the adoption of this guidance on the Company's Condensed Consolidated Financial Statements cannot be determined at this time.
	Revenue Recognition
	In May 2014, the FASB issued new accounting guidance on revenue from contracts with customers, which will supersede nearly all existing revenue recognition guidance under U.S. GAAP.  The core principal of the guidance 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 guidance 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 guidance is effective for Aon in the first quarter of 2017 and early adoption is not permitted. The guidance permits two methods of transition 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-2017 periods would be provided in the notes to the financial statements as previously reported under the current revenue standard. The impact from the adoption of this guidance on the Company's Condensed Consolidated Financial Statements cannot be determined at this time. The Company is also determining the appropriate method of transition to the guidance.
	Discontinued Operations
	In April 2014, the FASB issued new accounting guidance that increased the threshold for a disposal to qualify as a discontinued operation and requires new disclosures of both discontinued operations and certain other disposals that do not meet the definition of a discontinued operation. The guidance was effective for Aon in the first quarter of 2015. The adoption of this guidance did not have a material impact on the Company's Condensed Consolidated Financial Statements.

Cash_and_Cash_Equivalents_and_

Cash and Cash Equivalents and Short-term Investments	3 Months Ended
	Mar. 31, 2015
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and Cash Equivalents and Short-term Investments	Cash and Cash Equivalents and Short-term Investments
	Cash and cash equivalents include cash balances and all highly liquid investments with initial maturities of three months or less.  Short-term investments include certificates of deposit, money market funds and highly liquid debt instruments purchased with initial maturities in excess of three months but less than one year and are carried at amortized cost, which approximates fair value.
	At March 31, 2015, Cash and cash equivalents and Short-term investments were $721 million compared to $768 million at December 31, 2014. Of the total balance, $127 million and $169 million was restricted as to its use at March 31, 2015 and December 31, 2014, respectively. Included within that amount, the Company is required to hold £40.5 million of operating funds in the U.K. by the Financial Conduct Authority, a U.K.-based regulator, which were included in Short-term investments.  These operating funds, when translated to U.S. dollars, were equal to $60 million and $63 million at March 31, 2015 and December 31, 2014, respectively. In addition, Cash and cash equivalents included additional restricted balances of $67 million and $106 million at March 31, 2015 and December 31, 2014, respectively. The restricted balances primarily relate to cash required to be held as collateral.

Other_Financial_Data

Other Financial Data	3 Months Ended
	Mar. 31, 2015
Other Financial Data [Abstract]
Other Financial Data	Other Financial Data
	Condensed Consolidated Statements of Income Information
	Other Income
	Other income consists of the following (in millions):
		Three months ended March 31,
		2015			2014
	Foreign currency remeasurement gain	$	24		$	19
	Gain on disposal of business	19			—
	Equity earnings	2			5
	Loss on investments	(2		)	(1		)
	Derivative loss	(1		)	(23		)
	Other	—			1
	Total	$	42		$	1
	Condensed Consolidated Statements of Financial Position Information
	Allowance for Doubtful Accounts
	An analysis of the allowance for doubtful accounts is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Balance at beginning of period	$	74		$	90
	Provision charged to operations	8			4
	Accounts written off, net of recoveries	(9		)	(5		)
	Foreign currency translation	(3		)	—
	Balance at end of period	$	70		$	89
	Other Current Assets
	The components of Other current assets are as follows (in millions):
		March 31, 2015			December 31, 2014
	Taxes receivable	$	218		$	99
	Deferred tax assets	206			212
	Prepaid expenses	158			164
	Deferred project costs	108			102
	Other	22			25
	Total	$	712		$	602
	Other Non-Current Assets
	The components of Other non-current assets are as follows (in millions):
		March 31, 2015			December 31, 2014
	Prepaid pension	$	897		$	933
	Deferred project costs	237			250
	Deferred tax assets	146			144
	Investments	143			143
	Taxes receivable	57			101
	Other	198			233
	Total	$	1,678		$	1,804
	Other Current Liabilities
	The components of Other current liabilities are as follows (in millions):
		March 31, 2015			December 31, 2014
	Deferred revenue	$	410		$	408
	Taxes payable	89			64
	Deferred tax liabilities	2			2
	Other	364			314
	Total	$	865		$	788
	Other Non-Current Liabilities
	The components of Other non-current liabilities are as follows (in millions):
		March 31, 2015			December 31, 2014
	Deferred tax liabilities	$	307		$	313
	Taxes payable	201			210
	Deferred revenue	186			167
	Leases	172			184
	Compensation and benefits	55			57
	Other	210			256
	Total	$	1,131		$	1,187

Acquisitions_and_Dispositions

Acquisitions and Dispositions	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions
	Acquisitions
	During the three months ended March 31, 2015, the Company completed the acquisition of one business in the Risk Solutions segment and one business in the HR Solutions segment. During the three months ended March 31, 2014, the Company completed the acquisition of one business in the Risk Solutions segment and one business in the HR Solutions segment.
	The following table includes the aggregate consideration transferred and the preliminary value of intangible assets recorded as a result of the Company's acquisitions (in millions):
		Three months ended March 31,
		2015		2014
	Consideration	$	21	$	5
	Intangible assets:
	Goodwill	$	16	$	4
	Other intangible assets	1		4
	Total	$	17	$	8
	The results of operations of these acquisitions are included in the Condensed 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
	During the three months ended March 31, 2015, the Company completed the disposition of one business in the Risk Solutions segment and one business in the HR Solutions segment. A pretax gain of $19 million was recognized on these dispositions in the three months ended March 31, 2015, which is included in Other income in the Condensed Consolidated Statements of Income. During the three months ended March 31, 2014, the Company completed the disposition of one business in the Risk Solutions segment.  A pretax gain of $1 million was recognized on this disposition in the three months ended March 31, 2014, which is included in Other income in the Condensed Consolidated Statements of Income.

Goodwill_and_Other_Intangible_

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2015
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 three months ended March 31, 2015 are as follows (in millions):
		Risk			HR			Total
		Solutions			Solutions
	Balance as of January 1, 2015	$	5,911		$	2,949		$	8,860
	Goodwill related to current year acquisitions	1			15			16
	Goodwill related to disposals	—			(13		)	(13		)
	Foreign currency translation	(284		)	(31		)	(315		)
	Balance as of March 31, 2015	$	5,628		$	2,920		$	8,548
	Other intangible assets by asset class are as follows (in millions):
		March 31, 2015									December 31, 2014
		Gross Carrying Amount			Accumulated			Net Carrying Amount			Gross Carrying Amount		Accumulated		Net Carrying Amount
					Amortization								Amortization
	Intangible assets with indefinite lives:
	Tradenames	$	1,019		$	—		$	1,019		$	1,019	$	—	$	1,019
	Intangible assets with finite lives:
	Customer related and contract based	2,894			1,616			1,278			2,952		1,579		1,373
	Technology and other	548			435			113			571		443		128
	Total	$	4,461		$	2,051		$	2,410		$	4,542	$	2,022	$	2,520
	Amortization expense from finite lived intangible assets was $80 million and $86 million for the three months ended March 31, 2015 and 2014, respectively.
	The estimated future amortization for finite lived intangible assets as of March 31, 2015 is as follows (in millions):
		Risk Solutions			HR Solutions			Total
	Remainder of 2015	$	80		$	154		$	234
	2016	99			172			271
	2017	90			137			227
	2018	78			91			169
	2019	69			73			142
	Thereafter	185			163			348
	Total	$	601		$	790		$	1,391

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt	Debt
	Revolving Credit Facilities
	As of December 31, 2014, 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 €650 million ($707 million based on exchange rates at March 31, 2015) European credit facility expiring in October 2015 (the "2015 Facility"). Aon Corporation entered into the 2015 Facility on October 15, 2010 (Aon plc became a borrower under such facility on April 29, 2013) and Aon plc entered into the 2017 Facility on March 20, 2012. On February 2, 2015, Aon plc replaced the 2015 Facility with a new $900 million multi-currency U.S. credit facility expiring in February 2020 (the "2020 Facility"). Each of these facilities included 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 March 31, 2015, Aon plc had no borrowings under, and was in compliance with these financial covenants and all other covenants contained in, the 2017 Facility and 2020 Facility during the three months ended March 31, 2015.
	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 $355 million and $168 million of commercial paper outstanding at March 31, 2015 and December 31, 2014, respectively, which was included in Short-term debt and current portion of long-term debt in the Company's Condensed Consolidated Statements of Financial Position. The weighted average commercial paper outstanding for the three months ended March 31, 2015 was $317 million. The weighted average interest rate of the commercial paper outstanding for the three months ended March 31, 2015 was 0.50%.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The effective tax rate on net income was 19.1% and 18.9% for the three months ended March 31, 2015, and 2014, respectively. The effective tax rate in the first quarter of 2015 was unfavorably impacted by a change in the geographical distribution of income, partially offset by the impact of certain discrete items.
	During the three months ended March 31, 2015, the Company's uncertain tax positions decreased by $19 million, excluding interest and penalties, as compared to the year ended December 31, 2014. The decrease in uncertain tax positions was primarily related to the settlement of certain issues related to the IRS audit for tax years 2008-2011. As of March 31, 2015, the Company's liability for uncertain tax positions was $186 million, which was included in Other non-current liabilities in the Condensed Consolidated Statement of Financial Position, including interest and penalties of $25 million and net of $11 million of tax attributes.
	The Company's liability for uncertain tax positions as of March 31, 2015 includes $133 million related to amounts that would impact the effective tax rate if recognized.

Shareholders_Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Shareholders' Equity	Shareholders' Equity
	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"). 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.
	In the three months ended March 31, 2015, the Company repurchased 2.5 million shares at an average price per share of $100.15 for a total cost of approximately $250 million under the 2012 Share Repurchase Program. In the three months ended March 31, 2014, the Company repurchased 7.2 million shares at an average price per share of $83.45 for a total cost of $600 million under the 2012 Share Repurchase Program. The remaining authorized amount for share repurchase under the 2012 Share Repurchase Program and 2014 Share Repurchase Program is $5.4 billion. Since the program's inception in 2012, the Company repurchased a total of 64.6 million shares for an aggregate cost of $4.6 billion.
	Net Income Per Share
	Unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents, whether paid or unpaid, are participating securities, as defined, and therefore, should be included in computing basic and diluted earnings per share using the two class method.  Certain of the Company's restricted share awards allow the holder to receive a non-forfeitable dividend equivalent.
	Net income, attributable to participating securities was $2 million and $3 million in the three months ended March 31, 2015 and 2014, respectively.
	Weighted average shares outstanding are as follows (in millions):
		Three months ended March 31,
		2015			2014
	Shares for basic earnings per share (1)	284.2			303.5
	Common stock equivalents	2.9			3.7
	Shares for diluted earnings per share	287.1			307.2
	______________________________________________
	(1) Includes 2.5 million and 3.4 million of participating securities for the three months ended March 31, 2015 and 2014, respectively.
	Certain ordinary share equivalents may be excluded from the computation of diluted net income per share if their inclusion would be antidilutive. There were no shares excluded from the calculation for the three months ended March 31, 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 Investments (1)				Change in Fair Value of Derivatives (1)			Foreign Currency Translation Adjustments			Post-Retirement Benefit Obligation (2)			Total
	Balance at December 31, 2014	$	—			$	(17	)	$	(335	)	$	(2,782	)	$	(3,134	)
	Other comprehensive (loss) income before reclassifications, net	(1		)		(1		)	(321		)	3			(320		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amounts reclassified from accumulated other comprehensive loss	—				11			—			29			40
	Tax benefit	—				(4		)	—			(9		)	(13		)
	Amounts reclassified from accumulated other comprehensive loss, net	—				7			—			20			27
	Net current period other comprehensive (loss) income	(1		)		6			(321		)	23			(293		)
	Balance at March 31, 2015	$	(1	)		$	(11	)	$	(656	)	$	(2,759	)	$	(3,427	)
	______________________________________________
	(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	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefits	Employee Benefits
	The following table provides the components of the net periodic benefit cost recognized in the Condensed Consolidated Statements of Income in Compensation and benefits for Aon's material U.K., U.S., and other significant international pension plans located in the Netherlands and Canada (in millions):
		Three months ended March 31,
		U.K.						U.S.						Other
		2015			2014			2015			2014			2015			2014
	Service cost	$	—		$	—		$	1		$	—		$	—		$	—
	Interest cost	49			58			33			32			8			12
	Expected return on plan assets	(75		)	(82		)	(39		)	(39		)	(12		)	(15		)
	Amortization of net actuarial loss	10			13			14			10			3			2
	Net periodic (benefit) cost	(16		)	(11		)	9			3			(1		)	(1		)
	Curtailment loss (gain) and other	—			—			(1		)	1			—			(3		)
	Total net periodic (benefit) cost	$	(16	)	$	(11	)	$	8		$	4		$	(1	)	$	(4	)
	Based on current assumptions, in 2015, the Company expects to contribute approximately $65 million, $132 million, and $23 million to its U.K., U.S. and other significant international pension plans, respectively. During the three months ended March 31, 2015, contributions of $19 million, $34 million, and $4 million were made to the Company's U.K., U.S. and other significant international pension plans, respectively. During the three months ended March 31, 2014, contributions of $65 million, $40 million, and $12 million were made to the Company's U.K., U.S. and other significant international pension plans, respectively.

ShareBased_Compensation_Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 31, 2015
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 Condensed Consolidated Statements of Income in Compensation and benefits (in millions):
		Three months ended March 31,
		2015			2014
	Restricted share units ("RSUs")	$	65		$	60
	Performance share awards ("PSAs")	21			39
	Share options	—			—
	Employee share purchase plans	4			3
	Total share-based compensation expense	$	90		$	102
	Restricted Share Units
	A summary of the status of the Company's RSUs is as follows (shares in thousands):
		Three months ended March 31,
		2015					2014
		Shares		Fair Value (1)			Shares			Fair Value (1)
	Non-vested at beginning of period	8,381		$	63		9,759			$	51
	Granted	957		97			1,146			83
	Vested	(1,714	)	59			(1,950	)		51
	Forfeited	(49	)	64			(125	)		50
	Non-vested at end of period	7,575		69			8,830			56
	______________________________________________
	-1	Represents per share weighted average fair value of award at date of grant.
	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 performance conditions are not considered in the determination of the grant date fair value for these awards. The fair value of PSAs is based upon the market price of an Aon ordinary share at the date of grant. Compensation expense is recognized over the performance period based on management's estimate of the number of units expected to vest. Compensation expense is adjusted to reflect the actual number of shares issued at the end of the programs. 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. Dividend equivalents are not paid on PSAs.
	Information as of March 31, 2015 regarding the Company's target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the three months ended March 31, 2015 and the years ended December 31, 2014 and 2013, respectively, is as follows (shares in thousands, dollars in millions, except fair value):
		2015			2014			2013
	Target PSAs granted during period	978			816			1,135
	Weighted average fair value per share at date of grant	$	96		$	81		$	58
	Number of shares that would be issued based on current performance levels	978			1,201			2,197
	Unamortized expense, based on current performance levels	$	93		$	61		$	34
	Share Options
	The Company did not grant any share options during either the three months ended March 31, 2015 or 2014.
	A summary of the status of the Company's share options and related information is as follows (shares in thousands):
		Three months ended March 31,
		2015					2014
		Shares		Weighted- Average			Shares			Weighted- Average
				Exercise Price						Exercise Price
	Beginning outstanding	2,300		$	32		3,462			$	32
	Granted	—		—			—			—
	Exercised	(1,293	)	26			(416	)		33
	Forfeited and expired	(9	)	36			(2	)		36
	Outstanding at end of period	998		39			3,044			32
	Exercisable at end of period	998		39			2,928			32
	The weighted average remaining contractual life, in years, of outstanding options was 2.7 years and 2.0 years at March 31, 2015 and 2014, respectively.
	The aggregate intrinsic value represents the total pretax intrinsic value, based on options with an exercise price less than the Company's closing share price of $96.12 as of March 31, 2015, which would have been received by the option holders had those option holders exercised their options as of that date.  At March 31, 2015, the aggregate intrinsic value of options outstanding was $57 million, all of which were exercisable.
	Other information related to the Company's share options is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Aggregate intrinsic value of stock options exercised	$	94		$	21
	Cash received from the exercise of stock options	34			14
	Tax benefit realized from the exercise of stock options	34			6
	Unamortized deferred compensation expense, which includes both options and awards, amounted to $267 million as of March 31, 2015, with a remaining weighted-average amortization period of approximately 1.8 years.

Derivatives_and_Hedging

Derivatives and Hedging	3 Months Ended
	Mar. 31, 2015
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, or enters into monetary intercompany transfers denominated in a currency that differs from its functional currency, or 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 Condensed Consolidated Statements of Comprehensive Income.
	The Company also uses foreign exchange derivatives, typically forward contracts and options to economically hedge the currency exposure of the Company's global liquidity profile, including monetary assets or liabilities that are denominated in a non-functional currency of an entity, typically in 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 Condensed Consolidated Statements of Income.
	Interest Rate Risk Management
	The Company holds variable-rate short-term brokerage and other operating deposits. The Company uses interest rate derivatives, typically swaps, to reduce its exposure to the effects of interest rate fluctuations on the forecasted interest receipts from these deposits for up to two years in the future.
	Certain derivatives also give rise to credit risks from the possible non-performance by counterparties.  The credit risk at the balance sheet date is generally limited to the fair value of those contracts that are favorable to the Company.  The Company has reduced its credit risk by (1) using International Swaps and Derivatives Association master agreements, collateral and credit support arrangements, (2) entering into non-exchange-traded derivatives with highly-rated major financial institutions and (3) using exchange-traded instruments.  The Company monitors the creditworthiness of, and exposure to, its counterparties.  As of March 31, 2015, all net derivative positions were free of credit risk contingent features.  The Company had not received or pledged any collateral related to derivative arrangements as of March 31, 2015.
	The notional and fair values of derivative instruments are as follows (in millions):
		Notional Amount								Derivative Assets (1)								Derivative Liabilities (2)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	919				1,200				59				46				79				58
	Total	919				1,200				59				46				79				58
	Derivatives not accounted for as hedges:
	Foreign exchange contracts (3)	181				165				—				—				—				—
	Total	$	1,100			$	1,365			$	59			$	46			$	79			$	58
	______________________________________________
	-1	Included within Other current assets ($38 million at March 31, 2015 and $24 million at December 31, 2014) or Other non-current assets ($21 million at March 31, 2015 and $22 million at December 31, 2014).
	-2	Included within Other current liabilities ($66 million at March 31, 2015 and $52 million at December 31, 2014) or Other non-current liabilities ($13 million at March 31, 2015 and $6 million at December 31, 2014).
	-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)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	59				46				(32		)		(14		)		27				32
	Total	59				46				(32		)		(14		)		27				32
	Derivatives not accounted for as hedges:
	Foreign exchange contracts	—				—				—				—				—				—
	Total	$	59			$	46			$	(32	)		$	(14	)		$	27			$	32
	______________________________________________
	(1) Included within Other current assets ($15 million at March 31, 2015 and $12 million at December 31, 2014) or Other non-current assets ($12 million at March 31, 2015 and $20 million at December 31, 2014).
	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)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	79				58				(32		)		(14		)		47				44
	Total	79				58				(32		)		(14		)		47				44
	Derivatives not accounted for as hedges:
	Foreign exchange contracts	—				—				—				—				—				—
	Total	$	79			$	58			$	(32	)		$	(14	)		$	47			$	44
	______________________________________________
	(1) Included within Other current liabilities ($42 million at March 31, 2015 and $40 million at December 31, 2014) or Other non-current liabilities ($5 million at March 31, 2015 and $4 million at December 31, 2014).
	The amounts of derivative gains (losses) recognized in the Condensed Consolidated Financial Statements for the three months ended March 31, 2015 and 2014 are as follows (in millions):
	Three Months Ended March 31, 2015
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		5				(2		)		—				(4		)		(1		)
	Total		$	5			$	(2	)		$	—			$	(4	)		$	(1	)
	Three Months Ended March 31, 2014
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		11				—				—				(19		)		(8		)
	Total		$	11			$	—			$	—			$	(19	)		$	(8	)
Three Months Ended March 31, 2015
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
Cash flow hedges:
Interest rate contracts		$	—			$	—			$	(1	)		$	—			$	(1	)
Foreign exchange contracts		—				—				(2		)		(8		)		(10		)
Total		$	—			$	—			$	(3	)		$	(8	)		$	(11	)
Three Months Ended March 31, 2014
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
Cash flow hedges:
Interest rate contracts		$	—			$	—			$	—			$	—			$	—
Foreign exchange contracts		(3		)		—				—				(18		)		(21		)
Total		$	(3	)		$	—			$	—			$	(18	)		$	(21	)
The Company estimates that approximately $4 million of pretax losses currently included within Accumulated other comprehensive loss will be reclassified into earnings in the next twelve months.
The amount of gain (loss) recognized in income on the ineffective portion of derivatives for the three months ended March 31, 2015 and 2014 was not material.
During the three months ended March 31, 2015 and 2014, the Company recorded a gain of $7 million and a loss of $5 million, respectively, in Other income for foreign exchange derivatives not designated or qualifying as hedges.

Fair_Value_Measurements_and_Fi

Fair Value Measurements and Financial Instruments	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements and Financial Instruments	Fair Value Measurements and Financial Instruments
	Accounting standards establish a three tier fair value hierarchy that prioritizes the inputs used in measuring fair values as follows:
	•	Level 1 — observable inputs such as quoted prices for identical assets in active markets;
	•	Level 2 — inputs other than quoted prices for identical assets in active markets, that are observable either directly or indirectly; and
	•	Level 3 — unobservable inputs in which there is little or no market data which requires the use of valuation techniques and the development of assumptions.
	The following methods and assumptions are used to estimate the fair values of the Company's financial instruments:
	Money market funds and highly liquid debt securities are carried at cost and amortized cost, respectively, as an approximation of fair value. Based on market convention, the Company considers cost a practical and expedient measure of fair value.
	Equity investments consist of domestic and international equity securities valued using the closing stock price on a national securities exchange. 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 on a sample basis, independently verifies the observable inputs for Level 2 equity securities.
	Fixed income investments consist of corporate and government bonds. Corporate and government 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. The Company obtains a detailed understanding of the models, inputs, and assumptions used in developing prices provided by its vendors. This understanding includes discussions with valuation resources at the vendor. During these discussions, the Company uses a fair value measurement questionnaire, which is part of the Company's internal controls over financial reporting, to obtain the information necessary to assert the model, inputs and assumptions used to comply with U.S. GAAP, including disclosure requirements. The Company also obtains observable inputs from the pricing vendor and 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 have historically not been material to the fair value estimates used in the Condensed 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.
	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 March 31, 2015 and December 31, 2014 (in millions):
				Fair Value Measurements Using
		Balance at March 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 and highly liquid debt securities (1)	$	1,787	$	1,787	$	—	$	—
	Other investments:
	Corporate bonds	1		—		—		1
	Government bonds	6		—		6		—
	Equity investments	10		6		4		—
	Derivatives:
	Interest rate contracts	—		—		—		—
	Foreign exchange contracts	59		—		59		—
	Liabilities:
	Derivatives:
	Foreign exchange contracts	79		—		79		—
	______________________________________________
	(1) Includes $1,787 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.
				Fair Value Measurements Using
		Balance at December 31, 2014		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 and highly liquid debt securities (1)	$	1,850	$	1,850	$	—	$	—
	Other investments:
	Corporate bonds	1		—		—		1
	Government bonds	6		—		6		—
	Equity investments	11		6		5		—
	Derivatives:
	Interest rate contracts	—		—		—		—
	Foreign exchange contracts	46		—		46		—
	Liabilities:
	Derivatives:
	Foreign exchange contracts	58		—		58		—
	______________________________________________
	(1)  Includes $1,850 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.
	There were no transfers of assets or liabilities between fair value hierarchy levels in either the three months ended March 31, 2015 or 2014. The Company recognized no realized or unrealized gains or losses in the Condensed Consolidated Statements of Income during either the three months ended March 31, 2015 or 2014, related to assets and liabilities measured at fair value using unobservable inputs.
	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):
		March 31, 2015				December 31, 2014
		Carrying Value		Fair Value		Carrying Value		Fair Value
	Long-term debt	$	4,710	$	5,259	$	4,799	$	5,268

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
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. Aon has historically purchased E&O insurance and other insurance to provide protection against certain losses that arise in such matters. Aon has exhausted or materially depleted its coverage under some of the policies that protect the Company and, consequently, is self-insured or materially self-insured for some claims. Accruals for these exposures, and related insurance receivables, when applicable, are included in the Condensed Consolidated Statements of Financial Position and have been recognized in Other general expenses in the Condensed Consolidated Statements of Income to the extent that losses are deemed probable and are reasonably estimable. These amounts are adjusted from time to time as developments warrant. Matters that are not probable and estimable are not accrued for in the financial statements. Included in the matters described below are 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. 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 $0.6 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 will change, and the estimates themselves will 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.
	A predecessor of a retail insurance brokerage subsidiary of Aon provided insurance brokerage services to Northrop Grumman Corporation ("Northrop"). This subsidiary placed Northrop's property insurance program for the period covering 2005. Northrop suffered a substantial loss in August 2005 when Hurricane Katrina damaged Northrop's shipbuilding facilities in the Gulf States. Northrop's excess insurance carrier, Factory Mutual Insurance Company ("Factory Mutual"), denied coverage for storm surge damage pursuant to a flood exclusion in the excess policy. Northrop sued Factory Mutual in the United States District Court for the Central District of California. The district court granted summary judgment in Northrop's favor in August 2007. In August 2008, the United State Court of Appeals for the Ninth Circuit reversed the district court's ruling and held that the flood exclusion applied to storm surge damage. Northrop thereafter sought to join Aon's subsidiary as a defendant in the action against Factory Mutual, asserting that if Northrop's policy with Factory Mutual does not cover the Northrop storm surge losses, then the Aon subsidiary will be responsible for Northrop's losses. In August 2010, the court granted in large part Factory Mutual's motion for partial summary judgment regarding the applicability of the flood exclusion and denied Northrop's motion to add the Aon subsidiary as a defendant in the federal lawsuit. On January 27, 2011, Northrop filed suit against the Aon subsidiary in the Superior Court of the State of California, County of Los Angeles, asserting claims for negligence, breach of contract and negligent misrepresentation. Northrop later settled its claims with Factory Mutual. In January 2014, Northrop filed an amended complaint, adding additional claims against the Aon subsidiary for intentional misrepresentation and concealment. Northrop seeks compensatory damages of approximately $340 million, which includes prejudgment interest and attorneys' fees, and punitive damages that are a multiple of the compensatory damages sought. Aon asserts several defenses (which it believes to be meritorious), including, but not limited to, that it committed no error or omission in placing the Factory Mutual excess policy for Northrop and that Northrop did not suffer any damages as a result of Aon's conduct. Aon intends to vigorously defend itself against these claims.
	Another 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. Aon understands that the insurers intend to appeal this trial court decision. Aon believes it has meritorious defenses and intends to vigorously defend itself against these claims.
	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 is seeking approximately £189 million ($281 million at March 31, 2015 exchange rates), plus interest and costs. Aon believes that it has meritorious defenses and intends to vigorously defend itself against these allegations.
	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 predecessor of 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 seeks damages of approximately CHF 46 million ($48 million at March 31, 2015 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 ($17 million at March 31, 2015 exchange rates) and $3.1 million, plus interest and adverse costs. The entire amount of the judgment, including interest through December 31, 2014, totals CHF 27.9 million ($29 million at March 31, 2015 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 ($13 million at March 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 Aon subsidiary's maximum liability on appeal is limited to CHF 8.7 million ($9 million at March 31, 2015 exchange rates) and $115,000 (plus interest and costs) beyond what the subsidiary has already paid.
	On December 27, 2012, AXA Versicherung Aktiengesellschaft ("AXA") started arbitral proceedings in Hamburg, Germany against an insurance and reinsurance brokerage subsidiary of Aon in Germany.  Predecessors of AXA granted predecessors of the Aon subsidiary a mandate to underwrite non-proportional reinsurance business from 1975 through 1999. AXA alleges, among other things, that the Aon-related entities intentionally exceeded their mandate and that, if AXA had known of this intention, it would not have granted a mandate.  AXA seeks damages of approximately €183 million ($199 million at March 31, 2015 exchange rates). The arbitrators heard testimony over the course of four days in September and December 2014, and the evidentiary portion of the arbitration proceeding has now closed. The matter is now under submission. Aon believes that it has meritorious defenses and intends to vigorously defend itself against these claims.
	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 has been filed, although a tolling agreement has been 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 ($67 million at March 31, 2015 exchange rates). In December 2014, the Court of Appeal granted the employer leave to appeal the High Court decision. The Court of Appeal hearing is set for October 2015. Aon believes that it has meritorious defenses and intends to vigorously defend itself against this potential claim.
	From time to time, Aon's clients may bring claims and take legal action pertaining to the performance of fiduciary responsibilities. Whether client claims and legal action related to the Company's performance of fiduciary responsibilities are founded or unfounded, if such claims and legal actions are resolved in a manner unfavorable to the Company, they may adversely affect Aon's financial results and materially impair the market perception of the Company and that of its products and services.
	Guarantees and Indemnifications
	In connection with the redomicile of Aon's headquarters (the "Redomestication"), the Company on April 2, 2012 entered 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 Condensed 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
	The Company had total letters of credit ("LOCs") outstanding of approximately $68 million at March 31, 2015, compared to $95 million at December 31, 2014. 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 issued LOCs to cover contingent payments for taxes and other business obligations to third parties, and other guarantees for miscellaneous purposes at its international subsidiaries.
	Commitments
	The Company has provided commitments to fund certain limited partnerships in which it has an interest in the event that the general partners request funding. Some of these commitments have specific expiration dates and the maximum potential funding under these commitments was $12 million at March 31, 2015 compared to $14 million at December 31, 2014. During the three months ended March 31, 2015, the Company funded $2 million of these commitments.
	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 $77 million at March 31, 2015 compared to $112 million at December 31, 2014.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
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 operating segments and after the elimination of intersegment revenues and expenses, equal the amounts in the Condensed Consolidated Financial Statements.
	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 operating income and generally accounts for inter-segment revenue as if the revenue were from third parties and at what management believes are current market prices.  The Company does not present net assets by 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):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	1,895		$	1,994
	HR Solutions	970			965
	Intersegment eliminations	(18		)	(12		)
	Total revenue	$	2,847		$	2,947
	Commissions, fees and other revenues by product are as follows (in millions):
		Three months ended March 31,
		2015			2014
	Retail brokerage	$	1,513		$	1,579
	Reinsurance brokerage	377			409
	Total Risk Solutions Segment	1,890			1,988
	Consulting services	371			384
	Outsourcing	604			589
	Intrasegment	(5		)	(8		)
	Total HR Solutions Segment	970			965
	Intersegment	(18		)	(12		)
	Total commissions, fees and other revenue	$	2,842		$	2,941
	Fiduciary investment income by segment is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	5		$	6
	HR Solutions	—			—
	Total fiduciary investment income	$	5		$	6
	A reconciliation of segment operating income before tax to income before income taxes is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	412		$	445
	HR Solutions	76			67
	Segment income before income taxes	488			512
	Unallocated expenses	(47		)	(43		)
	Interest income	3			2
	Interest expense	(65		)	(58		)
	Other income	42			1
	Income before income taxes	$	421		$	414
	Unallocated expenses include administrative or other costs not attributable to the operating segments, such as corporate governance costs. Interest income represents income earned primarily on operating cash balances and certain income producing securities. 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 transactions.

Guarantee_of_Registered_Securi

Guarantee of Registered Securities	3 Months Ended
	Mar. 31, 2015
Guarantee of Registered Securities [Abstract]
Guarantee of Registered Securities	Guarantee of Registered Securities
	As described in Note 14, 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. Aon Corporation is a 100% indirectly owned subsidiary of Aon plc. The debt securities that are subject to Rule 3-10 of Regulation S-X are the 3.50% Notes due September 2015, the 3.125% Notes due May 2016, the 5.00% Notes due September 2020, the 8.205% Notes due January 2027 and the 6.25% Notes due September 2040. All guarantees of Aon plc are full and unconditional. There are no other subsidiaries of Aon plc that are guarantors of the debt.
	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. Those Notes are subject to Rule 3-10 of Regulation S-X. Aon Corporation 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, and the 4.60% Notes due June 2044. 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 4.250% Notes due 2042, the 4.45% Notes due 2043, the 4.00% Notes due 2023, the 2.875% Notes due 2026, the 3.50% Notes due 2024 or the 4.60% Notes due 2044.
	The following tables set forth condensed consolidating statements of income for the three months ended March 31, 2015 and 2014, condensed consolidating statements of comprehensive income for the three months ended March 31, 2015 and 2014, condensed consolidating statements of financial position as of March 31, 2015 and December 31, 2014, and condensed consolidating statements of cash flows for the three months ended March 31, 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, with Aon plc presented as the parent company in all periods prior and subsequent to the Redomestication. 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 condensed consolidating statements of income have been reclassified and adjusted to conform to the 2015 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
		Three months ended March 31, 2015
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Revenue
	Commissions, fees and other	$	—		$	—		$	2,842		$	—		$	2,842
	Fiduciary investment income	—			—			5			—			5
	Total revenue	—			—			2,847			—			2,847
	Expenses
	Compensation and benefits	52			11			1,620			—			1,683
	Other general expenses	13			2			708			—			723
	Total operating expenses	65			13			2,328			—			2,406
	Operating (loss) income	(65		)	(13		)	519			—			441
	Interest income	(5		)	3			5			—			3
	Interest expense	(25		)	(34		)	(6		)	—			(65		)
	Intercompany interest income (expense)	119			(105		)	(14		)	—			—
	Intercompany other (expense) income	(50		)	(8		)	58			—			—
	Other income	2			8			32			—			42
	(Loss) income before taxes	(24		)	(149		)	594			—			421
	Income tax (benefit) expense	(5		)	(50		)	135			—			80
	(Loss) income before equity in earnings of subsidiaries	(19		)	(99		)	459			—			341
	Equity in earnings of subsidiaries, net of tax	347			403			304			(1,054		)	—
	Net income	328			304			763			(1,054		)	341
	Less: Net income attributable to noncontrolling interests	—			—			13			—			13
	Net income attributable to Aon shareholders	$	328		$	304		$	750		$	(1,054	)	$	328
	Condensed Consolidating Statement of Income
		Three months ended March 31, 2014
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Revenue
	Commissions, fees and other	$	1		$	—		$	2,940		$	—		$	2,941
	Fiduciary investment income	—			—			6			—			6
	Total revenue	1			—			2,946			—			2,947
	Expenses
	Compensation and benefits	66			7			1,678			—			1,751
	Other general expenses	4			3			720			—			727
	Total operating expenses	70			10			2,398			—			2,478
	Operating (loss) income	(69		)	(10		)	548			—			469
	Interest income	(2		)	—			4			—			2
	Interest expense	(9		)	(31		)	(18		)	—			(58		)
	Intercompany interest income (expense)	111			(74		)	(37		)	—			—
	Intercompany other (expense) income	(19		)	(15		)	34			—			—
	Other income	—			—			1			—			1
	Income (loss) before taxes	12			(130		)	532			—			414
	Income tax expense (benefit)	3			(50		)	125			—			78
	Income (loss) before equity in earnings of subsidiaries	9			(80		)	407			—			336
	Equity in earnings of subsidiaries, net of tax	316			333			253			(902		)	—
	Net income	325			253			660			(902		)	336
	Less: Net income attributable to noncontrolling interests	—			—			11			—			11
	Net income attributable to Aon shareholders	$	325		$	253		$	649		$	(902	)	$	325
	Condensed Consolidating Statement of Comprehensive Income
		Three months ended March 31, 2015
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Net income	$	328		$	304		$	763		$	(1,054	)	$	341
Less: Net income attributable to noncontrolling interests	—			—			13			—			13
Net income attributable to Aon shareholders	$	328		$	304		$	750		$	(1,054	)	$	328
Other comprehensive (loss) income, net of tax:
Change in fair value of investments	—			—			(1		)	—			(1		)
Change in fair value of derivatives	—			(1		)	7			—			6
Foreign currency translation adjustments	—			(23		)	(299		)	—			(322		)
Post-retirement benefit obligation	—			8			15			—			23
Total other comprehensive loss	—			(16		)	(278		)	—			(294		)
Equity in other comprehensive loss of subsidiaries, net of tax	(293		)	(267		)	(283		)	843			—
Less: Other comprehensive income attributable to noncontrolling interests	—			—			(1		)	—			(1		)
Total other comprehensive loss attributable to Aon shareholders	(293		)	(283		)	(560		)	843			(293		)
Comprehensive income attributable to Aon shareholders	$	35		$	21		$	190		$	(211	)	$	35
Condensed Consolidating Statement of Comprehensive Income
	Three months ended March 31, 2014
							Other
	Aon			Aon			Non-Guarantor			Consolidating
(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
Net income	$	325		$	253		$	660		$	(902	)	$	336
Less: Net income attributable to noncontrolling interests	—			—			11			—			11
Net income attributable to Aon shareholders	$	325		$	253		$	649		$	(902	)	$	325
Other comprehensive income (loss), net of tax:
Change in fair value of investments	—			—			1			—			1
Change in fair value of derivatives	—			1			8			—			9
Foreign currency translation adjustments	—			(17		)	33			—			16
Post-retirement benefit obligation	—			6			20			—			26
Total other comprehensive (loss) income	—			(10		)	62			—			52
Equity in other comprehensive income of subsidiaries, net of tax	54			69			59			(182		)	—
Less: Other comprehensive income attributable to noncontrolling interests	—			—			(2		)	—			(2		)
Total other comprehensive income attributable to Aon shareholders	54			59			123			(182		)	54
Comprehensive income attributable to Aon Shareholders	$	379		$	312		$	772		$	(1,084	)	$	379
Condensed Consolidating Statement of Financial Position
	As of March 31, 2015
							Other
	Aon			Aon			Non-Guarantor			Consolidating
(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
ASSETS
Cash and cash equivalents	$	—		$	2,230		$	650		$	(2,502	)	$	378
Short-term investments	—			166			177			—			343
Receivables, net	—			—			2,672			—			2,672
Fiduciary assets	—			—			10,894			—			10,894
Intercompany receivables	125			3,581			9,681			(13,387		)	—
Other current assets	2			207			536			(33		)	712
Total Current Assets	127			6,184			24,610			(15,922		)	14,999
Goodwill	—			—			8,548			—			8,548
Intangible assets, net	—			—			2,410			—			2,410
Fixed assets, net	—			—			754			—			754
Intercompany receivables	7,374			577			121			(8,072		)	—
Other non-current assets	181			701			1,589			(793		)	1,678
Investment in subsidiary	4,121			15,391			1,868			(21,380		)	—
TOTAL ASSETS	$	11,803		$	22,853		$	39,900		$	(46,167	)	$	28,389
LIABILITIES AND EQUITY
Fiduciary liabilities	$	—		$	—		$	10,894		$	—		$	10,894
Short-term debt and current portion of long-term debt	109			846			11			—			966
Accounts payable and accrued liabilities	2,597			31			1,265			(2,502		)	1,391
Intercompany payables	246			9,382			3,759			(13,387		)	—
Other current liabilities	—			49			849			(33		)	865
Total Current Liabilities	2,952			10,308			16,778			(15,922		)	14,116
Long-term debt	2,480			1,917			313			—			4,710
Pension, other post-retirement and other post-employment liabilities	—			1,366			635			—			2,001
Intercompany payables	—			7,287			785			(8,072		)	—
Other non-current liabilities	6			107			1,811			(793		)	1,131
TOTAL LIABILITIES	5,438			20,985			20,322			(24,787		)	21,958
TOTAL AON SHAREHOLDERS' EQUITY	6,365			1,868			19,512			(21,380		)	6,365
Noncontrolling interests	—			—			66			—			66
TOTAL EQUITY	6,365			1,868			19,578			(21,380		)	6,431
TOTAL LIABILITIES AND EQUITY	$	11,803		$	22,853		$	39,900		$	(46,167	)	$	28,389
Condensed Consolidating Statement of Financial Position
	As of December 31, 2014
							Other
	Aon			Aon			Non-Guarantor			Consolidating
(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
ASSETS
Cash and cash equivalents	$	—		$	2,727		$	1,361		$	(3,714	)	$	374
Short-term investments	—			165			229			—			394
Receivables, net	—			—			2,815			—			2,815
Fiduciary assets	—			—			11,638			—			11,638
Intercompany receivables	455			2,814			9,156			(12,425		)	—
Other current assets	2			226			407			(33		)	602
Total Current Assets	457			5,932			25,606			(16,172		)	15,823
Goodwill	—			—			8,860			—			8,860
Intangible assets, net	—			—			2,520			—			2,520
Fixed assets, net	—			—			765			—			765
Intercompany receivables	7,399			600			111			(8,110		)	—
Other non-current assets	179			697			1,718			(790		)	1,804
Investment in subsidiary	4,962			15,200			1,880			(22,042		)	—
TOTAL ASSETS	$	12,997		$	22,429		$	41,460		$	(47,114	)	$	29,772
LIABILITIES AND EQUITY
Fiduciary liabilities	$	—		$	—		$	11,638		$	—		$	11,638
Short-term debt and current portion of long-term debt	—			767			16			—			783
Accounts payable and accrued liabilities	3,755			58			1,706			(3,714		)	1,805
Intercompany payables	122			8,960			3,343			(12,425		)	—
Other current liabilities	—			49			772			(33		)	788
Total Current Liabilities	3,877			9,834			17,475			(16,172		)	15,014
Long-term debt	2,544			1,917			338			—			4,799
Pension, other post-retirement and other post-employment liabilities	—			1,396			745			—			2,141
Intercompany payables	—			7,277			833			(8,110		)	—
Other non-current liabilities	5			125			1,847			(790		)	1,187
TOTAL LIABILITIES	6,426			20,549			21,238			(25,072		)	23,141
TOTAL AON SHAREHOLDERS' EQUITY	6,571			1,880			20,162			(22,042		)	6,571
Noncontrolling interests	—			—			60			—			60
TOTAL EQUITY	6,571			1,880			20,222			(22,042		)	6,631
TOTAL LIABILITIES AND EQUITY	$	12,997		$	22,429		$	41,460		$	(47,114	)	$	29,772
Condensed Consolidating Statement of Cash Flows
	Three months ended March 31, 2015
	Aon			Aon			Other			Consolidating
							Non-Guarantor
(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$	2		$	(188	)	$	322		$	—		$	136
CASH FLOWS FROM INVESTING ACTIVITIES
Sales of long-term investments	—			—			3			—			3
Purchase of long-term investments	—			(1		)	—			—			(1		)
Net sales of short-term investments - non-fiduciary	—			(1		)	43			—			42
Acquisition of businesses, net of cash acquired	—			—			(21		)	—			(21		)
Proceeds from sale of businesses	—			—			41			—			41
Capital expenditures	—			—			(62		)	—			(62		)
CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	—			(2		)	4			—			2
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	(250		)	—			—			—			(250		)
Advances from (to) affiliates	157			(385		)	(984		)	1,212			—
Issuance of shares for employee benefit plans	48			—			—			—			48
Issuance of debt	114			756			—			—			870
Repayment of debt	—			(678		)	(8		)	—			(686		)
Cash dividends to shareholders	(71		)	—			—			—			(71		)
Purchase of shares from noncontrolling interests	—			—			(5		)	—			(5		)
Dividends paid to noncontrolling interests	—			—			(1		)	—			(1		)
Proceeds from sale-leaseback	—			—			—			—			—
CASH (USED FOR) PROVIDED BY FINANCING ACTIVITIES	(2		)	(307		)	(998		)	1,212			(95		)
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	—			—			(39		)	—			(39		)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	—			(497		)	(711		)	1,212			4
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	—			2,727			1,361			(3,714		)	374
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	—		$	2,230		$	650		$	(2,502	)	$	378
Condensed Consolidating Statement of Cash Flows
	Three months ended March 31, 2014
							Other
	Aon			Aon			Non-Guarantor			Consolidating
(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$	89		$	(123	)	$	23		$	—		$	(11	)
CASH FLOWS FROM INVESTING ACTIVITIES
Sales of long-term investments	—			37			5			—			42
Purchase of long-term investments	—			(10		)	—			—			(10		)
Net sales of short-term investments - non-fiduciary	—			62			121			—			183
Acquisition of businesses, net of cash acquired	—			—			(5		)	—			(5		)
Proceeds from sale of businesses	—			—			1			—			1
Capital expenditures	—			—			(55		)	—			(55		)
CASH PROVIDED BY INVESTING ACTIVITIES	—			89			67			—			156
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	(600		)	—			—			—			(600		)
Advances from (to) affiliates	313			(206		)	65			(172		)	—
Issuance of shares for employee benefit plans	26			—			—			—			26
Issuance of debt	293			902			—			—			1,195
Repayment of debt	(68		)	(755		)	(6		)	—			(829		)
Cash dividends to shareholders	(53		)	—			—			—			(53		)
Purchase of shares from noncontrolling interests	—			—			1			—			1
CASH (USED FOR) PROVIDED BY	(89		)	(59		)	60			(172		)	(260		)
FINANCING ACTIVITIES
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	—			—			(24		)	—			(24		)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	—			(93		)	126			(172		)	(139		)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	—			247			1,246			(1,016		)	477
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	—		$	154		$	1,372		$	(1,188	)	$	338

Other_Financial_Data_Tables

Other Financial Data (Tables)	3 Months Ended
	Mar. 31, 2015
Other Financial Data [Abstract]
Schedule of Other Income	Other income consists of the following (in millions):
		Three months ended March 31,
		2015			2014
	Foreign currency remeasurement gain	$	24		$	19
	Gain on disposal of business	19			—
	Equity earnings	2			5
	Loss on investments	(2		)	(1		)
	Derivative loss	(1		)	(23		)
	Other	—			1
	Total	$	42		$	1
Schedule of Allowance for Doubtful Accounts	An analysis of the allowance for doubtful accounts is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Balance at beginning of period	$	74		$	90
	Provision charged to operations	8			4
	Accounts written off, net of recoveries	(9		)	(5		)
	Foreign currency translation	(3		)	—
	Balance at end of period	$	70		$	89
Schedule of Other Current Assets	The components of Other current assets are as follows (in millions):
		March 31, 2015			December 31, 2014
	Taxes receivable	$	218		$	99
	Deferred tax assets	206			212
	Prepaid expenses	158			164
	Deferred project costs	108			102
	Other	22			25
	Total	$	712		$	602
Schedule of Other Non-current Assets	The components of Other non-current assets are as follows (in millions):
		March 31, 2015			December 31, 2014
	Prepaid pension	$	897		$	933
	Deferred project costs	237			250
	Deferred tax assets	146			144
	Investments	143			143
	Taxes receivable	57			101
	Other	198			233
	Total	$	1,678		$	1,804
Schedule of Other Current Liabilities	The components of Other current liabilities are as follows (in millions):
		March 31, 2015			December 31, 2014
	Deferred revenue	$	410		$	408
	Taxes payable	89			64
	Deferred tax liabilities	2			2
	Other	364			314
	Total	$	865		$	788
Schedule of Other Non-current Liabilities	The components of Other non-current liabilities are as follows (in millions):
		March 31, 2015			December 31, 2014
	Deferred tax liabilities	$	307		$	313
	Taxes payable	201			210
	Deferred revenue	186			167
	Leases	172			184
	Compensation and benefits	55			57
	Other	210			256
	Total	$	1,131		$	1,187

Acquisitions_and_Dispositions_

Acquisitions and Dispositions (Tables)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Consideration transferred and preliminary value of intangible assets	The following table includes the aggregate consideration transferred and the preliminary value of intangible assets recorded as a result of the Company's acquisitions (in millions):
		Three months ended March 31,
		2015		2014
	Consideration	$	21	$	5
	Intangible assets:
	Goodwill	$	16	$	4
	Other intangible assets	1		4
	Total	$	17	$	8

Goodwill_and_Other_Intangible_1

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2015
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 three months ended March 31, 2015 are as follows (in millions):
		Risk			HR			Total
		Solutions			Solutions
	Balance as of January 1, 2015	$	5,911		$	2,949		$	8,860
	Goodwill related to current year acquisitions	1			15			16
	Goodwill related to disposals	—			(13		)	(13		)
	Foreign currency translation	(284		)	(31		)	(315		)
	Balance as of March 31, 2015	$	5,628		$	2,920		$	8,548
Schedule of other intangible assets by asset class	Other intangible assets by asset class are as follows (in millions):
		March 31, 2015									December 31, 2014
		Gross Carrying Amount			Accumulated			Net Carrying Amount			Gross Carrying Amount		Accumulated		Net Carrying Amount
					Amortization								Amortization
	Intangible assets with indefinite lives:
	Tradenames	$	1,019		$	—		$	1,019		$	1,019	$	—	$	1,019
	Intangible assets with finite lives:
	Customer related and contract based	2,894			1,616			1,278			2,952		1,579		1,373
	Technology and other	548			435			113			571		443		128
	Total	$	4,461		$	2,051		$	2,410		$	4,542	$	2,022	$	2,520
Schedule of estimated future amortization expense on intangible assets	The estimated future amortization for finite lived intangible assets as of March 31, 2015 is as follows (in millions):
		Risk Solutions			HR Solutions			Total
	Remainder of 2015	$	80		$	154		$	234
	2016	99			172			271
	2017	90			137			227
	2018	78			91			169
	2019	69			73			142
	Thereafter	185			163			348
	Total	$	601		$	790		$	1,391

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Schedule of components of weighted average number of shares	Weighted average shares outstanding are as follows (in millions):
		Three months ended March 31,
		2015			2014
	Shares for basic earnings per share (1)	284.2			303.5
	Common stock equivalents	2.9			3.7
	Shares for diluted earnings per share	287.1			307.2
	______________________________________________
	(1) Includes 2.5 million and 3.4 million of participating securities for the three months ended March 31, 2015 and 2014, respectively.
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 Investments (1)				Change in Fair Value of Derivatives (1)			Foreign Currency Translation Adjustments			Post-Retirement Benefit Obligation (2)			Total
	Balance at December 31, 2014	$	—			$	(17	)	$	(335	)	$	(2,782	)	$	(3,134	)
	Other comprehensive (loss) income before reclassifications, net	(1		)		(1		)	(321		)	3			(320		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amounts reclassified from accumulated other comprehensive loss	—				11			—			29			40
	Tax benefit	—				(4		)	—			(9		)	(13		)
	Amounts reclassified from accumulated other comprehensive loss, net	—				7			—			20			27
	Net current period other comprehensive (loss) income	(1		)		6			(321		)	23			(293		)
	Balance at March 31, 2015	$	(1	)		$	(11	)	$	(656	)	$	(2,759	)	$	(3,427	)
	______________________________________________
	(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)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Components of net periodic benefit cost for the pension plans	The following table provides the components of the net periodic benefit cost recognized in the Condensed Consolidated Statements of Income in Compensation and benefits for Aon's material U.K., U.S., and other significant international pension plans located in the Netherlands and Canada (in millions):
		Three months ended March 31,
		U.K.						U.S.						Other
		2015			2014			2015			2014			2015			2014
	Service cost	$	—		$	—		$	1		$	—		$	—		$	—
	Interest cost	49			58			33			32			8			12
	Expected return on plan assets	(75		)	(82		)	(39		)	(39		)	(12		)	(15		)
	Amortization of net actuarial loss	10			13			14			10			3			2
	Net periodic (benefit) cost	(16		)	(11		)	9			3			(1		)	(1		)
	Curtailment loss (gain) and other	—			—			(1		)	1			—			(3		)
	Total net periodic (benefit) cost	$	(16	)	$	(11	)	$	8		$	4		$	(1	)	$	(4	)

ShareBased_Compensation_Plans_

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2015
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 Condensed Consolidated Statements of Income in Compensation and benefits (in millions):
		Three months ended March 31,
		2015			2014
	Restricted share units ("RSUs")	$	65		$	60
	Performance share awards ("PSAs")	21			39
	Share options	—			—
	Employee share purchase plans	4			3
	Total share-based compensation expense	$	90		$	102
Restricted share unit activity	A summary of the status of the Company's RSUs is as follows (shares in thousands):
		Three months ended March 31,
		2015					2014
		Shares		Fair Value (1)			Shares			Fair Value (1)
	Non-vested at beginning of period	8,381		$	63		9,759			$	51
	Granted	957		97			1,146			83
	Vested	(1,714	)	59			(1,950	)		51
	Forfeited	(49	)	64			(125	)		50
	Non-vested at end of period	7,575		69			8,830			56
	______________________________________________
	-1	Represents per share weighted average fair value of award at date of grant.
Performance-based plans	Information as of March 31, 2015 regarding the Company's target PSAs granted and shares that would be issued at current performance levels for PSAs granted during the three months ended March 31, 2015 and the years ended December 31, 2014 and 2013, respectively, is as follows (shares in thousands, dollars in millions, except fair value):
		2015			2014			2013
	Target PSAs granted during period	978			816			1,135
	Weighted average fair value per share at date of grant	$	96		$	81		$	58
	Number of shares that would be issued based on current performance levels	978			1,201			2,197
	Unamortized expense, based on current performance levels	$	93		$	61		$	34
Share options and related information	A summary of the status of the Company's share options and related information is as follows (shares in thousands):
		Three months ended March 31,
		2015					2014
		Shares		Weighted- Average			Shares			Weighted- Average
				Exercise Price						Exercise Price
	Beginning outstanding	2,300		$	32		3,462			$	32
	Granted	—		—			—			—
	Exercised	(1,293	)	26			(416	)		33
	Forfeited and expired	(9	)	36			(2	)		36
	Outstanding at end of period	998		39			3,044			32
	Exercisable at end of period	998		39			2,928			32
Other information related to the company's share options	Other information related to the Company's share options is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Aggregate intrinsic value of stock options exercised	$	94		$	21
	Cash received from the exercise of stock options	34			14
	Tax benefit realized from the exercise of stock options	34			6

Derivatives_and_Hedging_Tables

Derivatives and Hedging (Tables)	3 Months Ended
	Mar. 31, 2015
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)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	919				1,200				59				46				79				58
	Total	919				1,200				59				46				79				58
	Derivatives not accounted for as hedges:
	Foreign exchange contracts (3)	181				165				—				—				—				—
	Total	$	1,100			$	1,365			$	59			$	46			$	79			$	58
	______________________________________________
	-1	Included within Other current assets ($38 million at March 31, 2015 and $24 million at December 31, 2014) or Other non-current assets ($21 million at March 31, 2015 and $22 million at December 31, 2014).
	-2	Included within Other current liabilities ($66 million at March 31, 2015 and $52 million at December 31, 2014) or Other non-current liabilities ($13 million at March 31, 2015 and $6 million at December 31, 2014).
	-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)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	59				46				(32		)		(14		)		27				32
	Total	59				46				(32		)		(14		)		27				32
	Derivatives not accounted for as hedges:
	Foreign exchange contracts	—				—				—				—				—				—
	Total	$	59			$	46			$	(32	)		$	(14	)		$	27			$	32
	______________________________________________
	(1) Included within Other current assets ($15 million at March 31, 2015 and $12 million at December 31, 2014) or Other non-current assets ($12 million at March 31, 2015 and $20 million at December 31, 2014).
	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)
		March 31,				December 31,				March 31,				December 31,				March 31,				December 31,
		2015				2014				2015				2014				2015				2014
	Derivatives accounted for as hedges:
	Interest rate contracts	$	—			$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts	79				58				(32		)		(14		)		47				44
	Total	79				58				(32		)		(14		)		47				44
	Derivatives not accounted for as hedges:
	Foreign exchange contracts	—				—				—				—				—				—
	Total	$	79			$	58			$	(32	)		$	(14	)		$	47			$	44
	______________________________________________
	(1) Included within Other current liabilities ($42 million at March 31, 2015 and $40 million at December 31, 2014) or Other non-current liabilities ($5 million at March 31, 2015 and $4 million at December 31, 2014)
Derivative gains (losses)	The amounts of derivative gains (losses) recognized in the Condensed Consolidated Financial Statements for the three months ended March 31, 2015 and 2014 are as follows (in millions):
	Three Months Ended March 31, 2015
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		5				(2		)		—				(4		)		(1		)
	Total		$	5			$	(2	)		$	—			$	(4	)		$	(1	)
	Three Months Ended March 31, 2014
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		11				—				—				(19		)		(8		)
	Total		$	11			$	—			$	—			$	(19	)		$	(8	)
	Three Months Ended March 31, 2015
	Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	(1	)		$	—			$	(1	)
	Foreign exchange contracts		—				—				(2		)		(8		)		(10		)
	Total		$	—			$	—			$	(3	)		$	(8	)		$	(11	)
	Three Months Ended March 31, 2014
	Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		(3		)		—				—				(18		)		(21		)
	Total		$	(3	)		$	—			$	—			$	(18	)		$	(21	)
	The amounts of derivative gains (losses) recognized in the Condensed Consolidated Financial Statements for the three months ended March 31, 2015 and 2014 are as follows (in millions):
	Three Months Ended March 31, 2015
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		5				(2		)		—				(4		)		(1		)
	Total		$	5			$	(2	)		$	—			$	(4	)		$	(1	)
	Three Months Ended March 31, 2014
			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
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		11				—				—				(19		)		(8		)
	Total		$	11			$	—			$	—			$	(19	)		$	(8	)
	Three Months Ended March 31, 2015
	Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	(1	)		$	—			$	(1	)
	Foreign exchange contracts		—				—				(2		)		(8		)		(10		)
	Total		$	—			$	—			$	(3	)		$	(8	)		$	(11	)
	Three Months Ended March 31, 2014
	Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):		Compensation and Benefits				Other General Expenses				Interest Expense				Other Income (Expense)				Total
	Cash flow hedges:
	Interest rate contracts		$	—			$	—			$	—			$	—			$	—
	Foreign exchange contracts		(3		)		—				—				(18		)		(21		)
	Total		$	(3	)		$	—			$	—			$	(18	)		$	(21	)

Fair_Value_Measurements_and_Fi1

Fair Value Measurements and Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of assets and liabilities that are measured at fair value on a recurring basis	The following tables present the categorization of the Company's assets and liabilities that are measured at fair value on a recurring basis at March 31, 2015 and December 31, 2014 (in millions):
				Fair Value Measurements Using
		Balance at March 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 and highly liquid debt securities (1)	$	1,787	$	1,787	$	—	$	—
	Other investments:
	Corporate bonds	1		—		—		1
	Government bonds	6		—		6		—
	Equity investments	10		6		4		—
	Derivatives:
	Interest rate contracts	—		—		—		—
	Foreign exchange contracts	59		—		59		—
	Liabilities:
	Derivatives:
	Foreign exchange contracts	79		—		79		—
	______________________________________________
	(1) Includes $1,787 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.
				Fair Value Measurements Using
		Balance at December 31, 2014		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 and highly liquid debt securities (1)	$	1,850	$	1,850	$	—	$	—
	Other investments:
	Corporate bonds	1		—		—		1
	Government bonds	6		—		6		—
	Equity investments	11		6		5		—
	Derivatives:
	Interest rate contracts	—		—		—		—
	Foreign exchange contracts	46		—		46		—
	Liabilities:
	Derivatives:
	Foreign exchange contracts	58		—		58		—
	______________________________________________
	(1)  Includes $1,850 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.
Schedule of financial instruments where the carrying amounts and fair values differ	The fair value of 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):
		March 31, 2015				December 31, 2014
		Carrying Value		Fair Value		Carrying Value		Fair Value
	Long-term debt	$	4,710	$	5,259	$	4,799	$	5,268

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Schedule of total revenue by business segments	Aon's total revenue is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	1,895		$	1,994
	HR Solutions	970			965
	Intersegment eliminations	(18		)	(12		)
	Total revenue	$	2,847		$	2,947
Schedule of commissions, fees and other revenues by products	Commissions, fees and other revenues by product are as follows (in millions):
		Three months ended March 31,
		2015			2014
	Retail brokerage	$	1,513		$	1,579
	Reinsurance brokerage	377			409
	Total Risk Solutions Segment	1,890			1,988
	Consulting services	371			384
	Outsourcing	604			589
	Intrasegment	(5		)	(8		)
	Total HR Solutions Segment	970			965
	Intersegment	(18		)	(12		)
	Total commissions, fees and other revenue	$	2,842		$	2,941
Schedule of fiduciary investment income by business segments	Fiduciary investment income by segment is as follows (in millions):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	5		$	6
	HR Solutions	—			—
	Total fiduciary investment income	$	5		$	6
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):
		Three months ended March 31,
		2015			2014
	Risk Solutions	$	412		$	445
	HR Solutions	76			67
	Segment income before income taxes	488			512
	Unallocated expenses	(47		)	(43		)
	Interest income	3			2
	Interest expense	(65		)	(58		)
	Other income	42			1
	Income before income taxes	$	421		$	414

Guarantee_of_Registered_Securi1

Guarantee of Registered Securities (Tables)	3 Months Ended
	Mar. 31, 2015
Guarantee of Registered Securities [Abstract]
Condensed Consolidating Statements of Income	Condensed Consolidating Statement of Income
		Three months ended March 31, 2015
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Revenue
	Commissions, fees and other	$	—		$	—		$	2,842		$	—		$	2,842
	Fiduciary investment income	—			—			5			—			5
	Total revenue	—			—			2,847			—			2,847
	Expenses
	Compensation and benefits	52			11			1,620			—			1,683
	Other general expenses	13			2			708			—			723
	Total operating expenses	65			13			2,328			—			2,406
	Operating (loss) income	(65		)	(13		)	519			—			441
	Interest income	(5		)	3			5			—			3
	Interest expense	(25		)	(34		)	(6		)	—			(65		)
	Intercompany interest income (expense)	119			(105		)	(14		)	—			—
	Intercompany other (expense) income	(50		)	(8		)	58			—			—
	Other income	2			8			32			—			42
	(Loss) income before taxes	(24		)	(149		)	594			—			421
	Income tax (benefit) expense	(5		)	(50		)	135			—			80
	(Loss) income before equity in earnings of subsidiaries	(19		)	(99		)	459			—			341
	Equity in earnings of subsidiaries, net of tax	347			403			304			(1,054		)	—
	Net income	328			304			763			(1,054		)	341
	Less: Net income attributable to noncontrolling interests	—			—			13			—			13
	Net income attributable to Aon shareholders	$	328		$	304		$	750		$	(1,054	)	$	328
	Condensed Consolidating Statement of Income
		Three months ended March 31, 2014
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Revenue
	Commissions, fees and other	$	1		$	—		$	2,940		$	—		$	2,941
	Fiduciary investment income	—			—			6			—			6
	Total revenue	1			—			2,946			—			2,947
	Expenses
	Compensation and benefits	66			7			1,678			—			1,751
	Other general expenses	4			3			720			—			727
	Total operating expenses	70			10			2,398			—			2,478
	Operating (loss) income	(69		)	(10		)	548			—			469
	Interest income	(2		)	—			4			—			2
	Interest expense	(9		)	(31		)	(18		)	—			(58		)
	Intercompany interest income (expense)	111			(74		)	(37		)	—			—
	Intercompany other (expense) income	(19		)	(15		)	34			—			—
	Other income	—			—			1			—			1
	Income (loss) before taxes	12			(130		)	532			—			414
	Income tax expense (benefit)	3			(50		)	125			—			78
	Income (loss) before equity in earnings of subsidiaries	9			(80		)	407			—			336
	Equity in earnings of subsidiaries, net of tax	316			333			253			(902		)	—
	Net income	325			253			660			(902		)	336
	Less: Net income attributable to noncontrolling interests	—			—			11			—			11
	Net income attributable to Aon shareholders	$	325		$	253		$	649		$	(902	)	$	325
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statement of Comprehensive Income
		Three months ended March 31, 2015
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Net income	$	328		$	304		$	763		$	(1,054	)	$	341
	Less: Net income attributable to noncontrolling interests	—			—			13			—			13
	Net income attributable to Aon shareholders	$	328		$	304		$	750		$	(1,054	)	$	328
	Other comprehensive (loss) income, net of tax:
	Change in fair value of investments	—			—			(1		)	—			(1		)
	Change in fair value of derivatives	—			(1		)	7			—			6
	Foreign currency translation adjustments	—			(23		)	(299		)	—			(322		)
	Post-retirement benefit obligation	—			8			15			—			23
	Total other comprehensive loss	—			(16		)	(278		)	—			(294		)
	Equity in other comprehensive loss of subsidiaries, net of tax	(293		)	(267		)	(283		)	843			—
	Less: Other comprehensive income attributable to noncontrolling interests	—			—			(1		)	—			(1		)
	Total other comprehensive loss attributable to Aon shareholders	(293		)	(283		)	(560		)	843			(293		)
	Comprehensive income attributable to Aon shareholders	$	35		$	21		$	190		$	(211	)	$	35
	Condensed Consolidating Statement of Comprehensive Income
		Three months ended March 31, 2014
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	Net income	$	325		$	253		$	660		$	(902	)	$	336
	Less: Net income attributable to noncontrolling interests	—			—			11			—			11
	Net income attributable to Aon shareholders	$	325		$	253		$	649		$	(902	)	$	325
	Other comprehensive income (loss), net of tax:
	Change in fair value of investments	—			—			1			—			1
	Change in fair value of derivatives	—			1			8			—			9
	Foreign currency translation adjustments	—			(17		)	33			—			16
	Post-retirement benefit obligation	—			6			20			—			26
	Total other comprehensive (loss) income	—			(10		)	62			—			52
	Equity in other comprehensive income of subsidiaries, net of tax	54			69			59			(182		)	—
	Less: Other comprehensive income attributable to noncontrolling interests	—			—			(2		)	—			(2		)
	Total other comprehensive income attributable to Aon shareholders	54			59			123			(182		)	54
	Comprehensive income attributable to Aon Shareholders	$	379		$	312		$	772		$	(1,084	)	$	379
Condensed Consolidating Statements of Financial Position	Condensed Consolidating Statement of Financial Position
		As of March 31, 2015
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	ASSETS
	Cash and cash equivalents	$	—		$	2,230		$	650		$	(2,502	)	$	378
	Short-term investments	—			166			177			—			343
	Receivables, net	—			—			2,672			—			2,672
	Fiduciary assets	—			—			10,894			—			10,894
	Intercompany receivables	125			3,581			9,681			(13,387		)	—
	Other current assets	2			207			536			(33		)	712
	Total Current Assets	127			6,184			24,610			(15,922		)	14,999
	Goodwill	—			—			8,548			—			8,548
	Intangible assets, net	—			—			2,410			—			2,410
	Fixed assets, net	—			—			754			—			754
	Intercompany receivables	7,374			577			121			(8,072		)	—
	Other non-current assets	181			701			1,589			(793		)	1,678
	Investment in subsidiary	4,121			15,391			1,868			(21,380		)	—
	TOTAL ASSETS	$	11,803		$	22,853		$	39,900		$	(46,167	)	$	28,389
	LIABILITIES AND EQUITY
	Fiduciary liabilities	$	—		$	—		$	10,894		$	—		$	10,894
	Short-term debt and current portion of long-term debt	109			846			11			—			966
	Accounts payable and accrued liabilities	2,597			31			1,265			(2,502		)	1,391
	Intercompany payables	246			9,382			3,759			(13,387		)	—
	Other current liabilities	—			49			849			(33		)	865
	Total Current Liabilities	2,952			10,308			16,778			(15,922		)	14,116
	Long-term debt	2,480			1,917			313			—			4,710
	Pension, other post-retirement and other post-employment liabilities	—			1,366			635			—			2,001
	Intercompany payables	—			7,287			785			(8,072		)	—
	Other non-current liabilities	6			107			1,811			(793		)	1,131
	TOTAL LIABILITIES	5,438			20,985			20,322			(24,787		)	21,958
	TOTAL AON SHAREHOLDERS' EQUITY	6,365			1,868			19,512			(21,380		)	6,365
	Noncontrolling interests	—			—			66			—			66
	TOTAL EQUITY	6,365			1,868			19,578			(21,380		)	6,431
	TOTAL LIABILITIES AND EQUITY	$	11,803		$	22,853		$	39,900		$	(46,167	)	$	28,389
	Condensed Consolidating Statement of Financial Position
		As of December 31, 2014
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	ASSETS
	Cash and cash equivalents	$	—		$	2,727		$	1,361		$	(3,714	)	$	374
	Short-term investments	—			165			229			—			394
	Receivables, net	—			—			2,815			—			2,815
	Fiduciary assets	—			—			11,638			—			11,638
	Intercompany receivables	455			2,814			9,156			(12,425		)	—
	Other current assets	2			226			407			(33		)	602
	Total Current Assets	457			5,932			25,606			(16,172		)	15,823
	Goodwill	—			—			8,860			—			8,860
	Intangible assets, net	—			—			2,520			—			2,520
	Fixed assets, net	—			—			765			—			765
	Intercompany receivables	7,399			600			111			(8,110		)	—
	Other non-current assets	179			697			1,718			(790		)	1,804
	Investment in subsidiary	4,962			15,200			1,880			(22,042		)	—
	TOTAL ASSETS	$	12,997		$	22,429		$	41,460		$	(47,114	)	$	29,772
	LIABILITIES AND EQUITY
	Fiduciary liabilities	$	—		$	—		$	11,638		$	—		$	11,638
	Short-term debt and current portion of long-term debt	—			767			16			—			783
	Accounts payable and accrued liabilities	3,755			58			1,706			(3,714		)	1,805
	Intercompany payables	122			8,960			3,343			(12,425		)	—
	Other current liabilities	—			49			772			(33		)	788
	Total Current Liabilities	3,877			9,834			17,475			(16,172		)	15,014
	Long-term debt	2,544			1,917			338			—			4,799
Pension, other post-retirement and other post-employment liabilities	—			1,396			745			—			2,141
Intercompany payables	—			7,277			833			(8,110		)	—
Other non-current liabilities	5			125			1,847			(790		)	1,187
TOTAL LIABILITIES	6,426			20,549			21,238			(25,072		)	23,141
TOTAL AON SHAREHOLDERS' EQUITY	6,571			1,880			20,162			(22,042		)	6,571
Noncontrolling interests	—			—			60			—			60
TOTAL EQUITY	6,571			1,880			20,222			(22,042		)	6,631
TOTAL LIABILITIES AND EQUITY	$	12,997		$	22,429		$	41,460		$	(47,114	)	$	29,772
Condensed Consolidating Statements of Cash Flows	Condensed Consolidating Statement of Cash Flows
		Three months ended March 31, 2015
		Aon			Aon			Other			Consolidating
								Non-Guarantor
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	CASH FLOWS FROM OPERATING ACTIVITIES
	CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$	2		$	(188	)	$	322		$	—		$	136
	CASH FLOWS FROM INVESTING ACTIVITIES
	Sales of long-term investments	—			—			3			—			3
	Purchase of long-term investments	—			(1		)	—			—			(1		)
	Net sales of short-term investments - non-fiduciary	—			(1		)	43			—			42
	Acquisition of businesses, net of cash acquired	—			—			(21		)	—			(21		)
	Proceeds from sale of businesses	—			—			41			—			41
	Capital expenditures	—			—			(62		)	—			(62		)
	CASH PROVIDED BY (USED FOR) INVESTING ACTIVITIES	—			(2		)	4			—			2
	CASH FLOWS FROM FINANCING ACTIVITIES
	Share repurchase	(250		)	—			—			—			(250		)
	Advances from (to) affiliates	157			(385		)	(984		)	1,212			—
	Issuance of shares for employee benefit plans	48			—			—			—			48
	Issuance of debt	114			756			—			—			870
	Repayment of debt	—			(678		)	(8		)	—			(686		)
	Cash dividends to shareholders	(71		)	—			—			—			(71		)
	Purchase of shares from noncontrolling interests	—			—			(5		)	—			(5		)
	Dividends paid to noncontrolling interests	—			—			(1		)	—			(1		)
	Proceeds from sale-leaseback	—			—			—			—			—
	CASH (USED FOR) PROVIDED BY FINANCING ACTIVITIES	(2		)	(307		)	(998		)	1,212			(95		)
	EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	—			—			(39		)	—			(39		)
	NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	—			(497		)	(711		)	1,212			4
	CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	—			2,727			1,361			(3,714		)	374
	CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	—		$	2,230		$	650		$	(2,502	)	$	378
	Condensed Consolidating Statement of Cash Flows
		Three months ended March 31, 2014
								Other
		Aon			Aon			Non-Guarantor			Consolidating
	(millions)	plc			Corporation			Subsidiaries			Adjustments			Consolidated
	CASH FLOWS FROM OPERATING ACTIVITIES
	CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$	89		$	(123	)	$	23		$	—		$	(11	)
	CASH FLOWS FROM INVESTING ACTIVITIES
	Sales of long-term investments	—			37			5			—			42
	Purchase of long-term investments	—			(10		)	—			—			(10		)
	Net sales of short-term investments - non-fiduciary	—			62			121			—			183
	Acquisition of businesses, net of cash acquired	—			—			(5		)	—			(5		)
	Proceeds from sale of businesses	—			—			1			—			1
	Capital expenditures	—			—			(55		)	—			(55		)
	CASH PROVIDED BY INVESTING ACTIVITIES	—			89			67			—			156
	CASH FLOWS FROM FINANCING ACTIVITIES
	Share repurchase	(600		)	—			—			—			(600		)
	Advances from (to) affiliates	313			(206		)	65			(172		)	—
	Issuance of shares for employee benefit plans	26			—			—			—			26
	Issuance of debt	293			902			—			—			1,195
	Repayment of debt	(68		)	(755		)	(6		)	—			(829		)
	Cash dividends to shareholders	(53		)	—			—			—			(53		)
	Purchase of shares from noncontrolling interests	—			—			1			—			1
	CASH (USED FOR) PROVIDED BY	(89		)	(59		)	60			(172		)	(260		)
	FINANCING ACTIVITIES
	EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	—			—			(24		)	—			(24		)
	NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	—			(93		)	126			(172		)	(139		)
	CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	—			247			1,246			(1,016		)	477
	CASH AND CASH EQUIVALENTS AT END OF PERIOD	$	—		$	154		$	1,372		$	(1,188	)	$	338

Basis_of_Presentation_Basis_of

Basis of Presentation Basis of Presentation (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Investments	$143	$143

Cash_and_Cash_Equivalents_Deta

Cash and Cash Equivalents (Details)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
	USD ($)	GBP (£)	USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Short-term investment, minimum maturity period	3 months	3 months
Short-term investment, maximum maturity period	1 year	1 year
Cash and Cash Equivalents and Short-Term Investments	$721		$768
Restricted Cash and Investments, Current	127		169
Operating funds in U.K.	60	40.5	63
Cash and cash equivalents, restricted	$67		$106

Other_Financial_Data_Schedule_

Other Financial Data - Schedule of Other Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Other (Expense) Income
Foreign currency remeasurement gain	$24	$19
Gain on disposal of business	19	0
Equity earnings	2	5
Loss on investments	-2	-1
Derivative loss	-1	-23
Other	0	1
Total	$42	$1

Other_Financial_Data_Schedule_1

Other Financial Data Schedule of Allowance for Doubtful Accounts (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period	$74	$90
Provision charged to operations	8	4
Accounts written off, net of recoveries	-9	-5
Foreign currency translation	-3	0
Balance at end of period	$70	$89

Other_Financial_Data_Schedule_2

Other Financial Data Schedule of Other Current Assets (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Other Financial Data [Abstract]
Taxes receivable	$218	$99
Deferred tax assets	206	212
Prepaid expenses	158	164
Deferred project costs	108	102
Other	22	25
Total	$712	$602

Other_Financial_Data_Schedule_3

Other Financial Data Schedule of Non-current Assets (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Other Financial Data [Abstract]
Prepaid pension	$897	$933
Deferred project costs	237	250
Deferred tax assets	146	144
Investments	143	143
Taxes receivable	57	101
Other	198	233
Total	$1,678	$1,804

Other_Financial_Data_Schedule_4

Other Financial Data Schedule of Other Current Liabilities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Other Financial Data [Abstract]
Deferred revenue	$410	$408
Taxes payable	89	64
Deferred tax liabilities	2	2
Other	364	314
Total	$865	$788

Other_Financial_Data_Schedule_5

Other Financial Data Schedule of Other Non-current Liabilities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Other Financial Data [Abstract]
Deferred tax liabilities	$307	$313
Taxes payable	201	210
Deferred revenue	186	167
Leases	172	184
Compensation and benefits	55	57
Other	210	256
Total	$1,131	$1,187

Acquisitions_and_Dispositions_1

Acquisitions and Dispositions - Acquisitions (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	business	business
Intangible assets:
Goodwill	$8,548		$8,860
Business Acquisition 1 [Member]
Business Acquisition
Consideration	21	5
Intangible assets:
Goodwill	16	4
Other intangible assets	1	4
Total	17	8
Risk Solutions [Member]
Business Acquisition
Number of business acquired under business combination	1	1
Intangible assets:
Goodwill	5,628		5,911
HR Solutions [Member]
Business Acquisition
Number of business acquired under business combination	1	1
Intangible assets:
Goodwill	$2,920		$2,949

Acquisitions_and_Dispositions_2

Acquisitions and Dispositions - Dispositions (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Dispositions
Gain on disposal of business	$19	$0
Risk Solutions [Member]
Dispositions
Number of dispositions	1	1
Gain on disposal of business		$1
HR Solutions [Member]
Dispositions
Number of dispositions	1

Goodwill_and_Other_Intangible_2

Goodwill and Other Intangible Assets (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Changes in the net carrying amount of goodwill by operating segment (in millions)
Beginning balance	$8,860
Goodwill related to current year acquisitions	16
Goodwill related to disposals	-13
Foreign currency translation	-315
Ending balance	8,548
Risk Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Beginning balance	5,911
Goodwill related to current year acquisitions	1
Goodwill related to disposals	0
Foreign currency translation	-284
Ending balance	5,628
HR Solutions [Member]
Changes in the net carrying amount of goodwill by operating segment (in millions)
Beginning balance	2,949
Goodwill related to current year acquisitions	15
Goodwill related to disposals	-13
Foreign currency translation	-31
Ending balance	$2,920

Goodwill_and_Other_Intangible_3

Goodwill and Other Intangible Assets (Details 2) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Intangible assets with indefinite lives
Tradenames	$1,019		$1,019
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	4,461		4,542
Intangible assets with finite lives, Accumulated Amortization	2,051		2,022
Intangible assets, Net Carrying Amount	2,410		2,520
Amortization expense on intangible assets	80	86
Estimated amortization for intangible assets
Remainder of 2015	234
2016	271
2017	227
2018	169
2019	142
Thereafter	348
Total	1,391
Risk Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	80
2016	99
2017	90
2018	78
2019	69
Thereafter	185
Total	601
HR Solutions [Member]
Estimated amortization for intangible assets
Remainder of 2015	154
2016	172
2017	137
2018	91
2019	73
Thereafter	163
Total	790
Customer related and contract based [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	2,894		2,952
Intangible assets with finite lives, Accumulated Amortization	1,616		1,579
Intangible assets, Net Carrying Amount	1,278		1,373
Marketing, technology and other [Member]
Intangible assets with finite lives
Intangible assets with finite lives, Gross Carrying Amount	548		571
Intangible assets with finite lives, Accumulated Amortization	435		443
Intangible assets, Net Carrying Amount	$113		$128

Debt_Details

Debt (Details)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2014	Mar. 31, 2015	Dec. 31, 2014	Feb. 02, 2015	Mar. 31, 2015	Mar. 31, 2015
	Commercial paper [Member]	Commercial paper [Member]	Domestic Line of Credit [Member]	Foreign Line of Credit [Member]	Foreign Line of Credit [Member]	Foreign Line of Credit [Member]	Commercial paper [Member]	Commercial paper [Member]
	USD ($)	USD ($)	2017 Facility [Member]	2015 Facility [Member]	2015 Facility [Member]	2020 Facility [Member]	US Commercial Paper Program [Member]	European Multi Currency Paper Program [Member]
			Line of Credit [Member]	Line of Credit [Member]	Line of Credit [Member]	Line of Credit [Member]	USD ($)	EUR (€)
			USD ($)	USD ($)	EUR (€)	USD ($)
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$400,000,000	$707,000,000	€ 650,000,000	$900,000,000	$900,000,000	€ 300,000,000
Total debt	355,000,000	168,000,000
Weighted average commercial paper outstanding	$317,000,000
Weighted-average interest rates (as a percent)	0.50%

Income_Taxes_Income_Taxes_Deta

Income Taxes Income Taxes (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Income Tax Contingency [Line Items]
Effective income tax rate	19.10%	18.90%
Decrease in uncertain tax positions	$19
Amount of liability for uncertain tax positions that would impact the effective tax rate if recognized	133
Other Noncurrent Liabilities [Member]
Income Tax Contingency [Line Items]
Liability for uncertain tax positions, noncurrent	186
Liability for uncertain tax positions, interest	25
Liability for uncertain tax positions, penalties	$11

Shareholders_Equity_Details

Shareholders' Equity (Details) (USD $)	3 Months Ended				36 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2015	Apr. 30, 2012	Nov. 30, 2014
Common Stock Programs
Total cost of shares purchased	$250,000,000
Weighted average shares outstanding
Shares for basic earnings per share (in shares)	284,200,000	[1]	303,500,000	[1]
Common stock equivalents (in shares)	2,900,000		3,700,000
Shares for diluted earnings per share (in shares)	287,100,000		307,200,000
Net income, attributable to participating securities	2,000,000		3,000,000
Number of participating securities (in shares)	2,500,000		3,400,000
Number of shares excluded from the calculation of diluted earnings per share	0		0
2012 - Share Repurchase Program [Member]
Common Stock Programs
Share repurchase authorization limit						5,000,000,000
Shares purchased (in shares)	2,500,000		7,200,000		64,600,000
Average price per share of stock repurchased	$100.15		$83.45
Total cost of shares purchased	250,000,000		600,000,000		4,600,000,000
Share repurchase, remaining authorization limit	5,400,000,000				5,400,000,000
Share Repurchase Program of 2014 [Member]
Common Stock Programs
Share repurchase authorization limit							$5,000,000,000
[1]	Includes 2.5 million and 3.4 million of participating securities for the three months ended MarchB 31, 2015 and 2014, respectively.

Shareholders_Equity_Details_2

Shareholders' Equity (Details 2) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	($3,134)
Other comprehensive (loss) income before reclassifications, net	-320
Amounts reclassified from accumulated other comprehensive loss:
Amounts reclassified from accumulated other comprehensive loss	40
Tax benefit	-13
Amounts reclassified from accumulated other comprehensive loss, net	27
Net current period other comprehensive (loss) income	-293
Ending balance	-3,427
Change in Fair Value of Investments [Member]
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	0	[1]
Other comprehensive (loss) income before reclassifications, net	-1	[1]
Amounts reclassified from accumulated other comprehensive loss:
Amounts reclassified from accumulated other comprehensive loss	0	[1]
Tax benefit	0	[1]
Amounts reclassified from accumulated other comprehensive loss, net	0	[1]
Net current period other comprehensive (loss) income	-1	[1]
Ending balance	-1	[1]
Change in Fair Value of Derivatives [Member]
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	-17	[1]
Other comprehensive (loss) income before reclassifications, net	-1	[1]
Amounts reclassified from accumulated other comprehensive loss:
Amounts reclassified from accumulated other comprehensive loss	11	[1]
Tax benefit	-4	[1]
Amounts reclassified from accumulated other comprehensive loss, net	7	[1]
Net current period other comprehensive (loss) income	6	[1]
Ending balance	-11	[1]
Foreign Currency Translation Adjustments [Member]
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	-335
Other comprehensive (loss) income before reclassifications, net	-321
Amounts reclassified from accumulated other comprehensive loss:
Amounts reclassified from accumulated other comprehensive loss	0
Tax benefit	0
Amounts reclassified from accumulated other comprehensive loss, net	0
Net current period other comprehensive (loss) income	-321
Ending balance	-656
Post-Retirement Benefit Obligation [Member]
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	-2,782	[2]
Other comprehensive (loss) income before reclassifications, net	3	[2]
Amounts reclassified from accumulated other comprehensive loss:
Amounts reclassified from accumulated other comprehensive loss	29	[2]
Tax benefit	-9	[2]
Amounts reclassified from accumulated other comprehensive loss, net	20	[2]
Net current period other comprehensive (loss) income	23	[2]
Ending balance	($2,759)	[2]
[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_Details

Employee Benefits (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
U.K. [Member]
Defined Benefit Plan Disclosure
Service cost	$0	$0
Interest cost	49	58
Expected return on plan assets	-75	-82
Amortization of net actuarial loss	10	13
Net periodic (benefit) cost	-16	-11
Curtailment loss (gain) and other	0	0
Total net periodic (benefit) cost	-16	-11
Estimate of contributions to defined benefit pension plans for the current fiscal year	65
Contributions made to defined benefit pension plans	19	65
U.S. [Member]
Defined Benefit Plan Disclosure
Service cost	1	0
Interest cost	33	32
Expected return on plan assets	-39	-39
Amortization of net actuarial loss	14	10
Net periodic (benefit) cost	9	3
Curtailment loss (gain) and other	-1	1
Total net periodic (benefit) cost	8	4
Estimate of contributions to defined benefit pension plans for the current fiscal year	132
Contributions made to defined benefit pension plans	34	40
Other [Member]
Defined Benefit Plan Disclosure
Service cost	0	0
Interest cost	8	12
Expected return on plan assets	-12	-15
Amortization of net actuarial loss	3	2
Net periodic (benefit) cost	-1	-1
Curtailment loss (gain) and other	0	-3
Total net periodic (benefit) cost	-1	-4
Estimate of contributions to defined benefit pension plans for the current fiscal year	23
Contributions made to defined benefit pension plans	$4	$12

ShareBased_Compensation_Plans_1

Share-Based Compensation Plans Share-based compensation expenses recognized (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$90	$102
Restricted share units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	65	60
Performance share awards (bPSAsb) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	21	39
Share options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	0	0
Employee share purchase plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$4	$3

ShareBased_Compensation_Plans_2

Share-Based Compensation Plans Restricted share unit activity (Details) (Restricted share units (RSUs) [Member], USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Restricted share units (RSUs) [Member]
Non-vested share awards (in shares)
Non-vested at beginning of period	8,381		9,759
Granted	957		1,146
Vested	-1,714		-1,950
Forfeited	-49		-125
Non-vested at end of period	7,575		8,830
Weighted Average Fair value (in dollars per share)
Non-vested at beginning of period	$63	[1]	$51	[1]
Granted	$97	[1]	$83	[1]
Vested	$59	[1]	$51	[1]
Forfeited	$64	[1]	$50	[1]
Non-vested at end of period	$69	[1]	$56	[1]
[1]	Represents per share weighted average fair value of award at date of grant.

ShareBased_Compensation_Plans_3

Share-Based Compensation Plans Performance Share Awards Narrative (Details) (Performance Shares [Member])	3 Months Ended
	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting conditions period	3 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, percent	0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued, percent	200.00%

ShareBased_Compensation_Plans_4

Share-Based Compensation Plans Schedule of Performance-based plans (Details) (Performance Shares [Member], USD $)	3 Months Ended	12 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target PSAs granted during period	978	816	1,135
Weighted average fair value per share at date of grant	$96	$81	$58
Number of shares that would be issued based on current performance levels	978	1,201	2,197
Unamortized expense, based on current performance levels	$93	$61	$34

ShareBased_Compensation_Plans_5

Share-Based Compensation Plans Share options activity (Details) (Share options [Member], USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share options [Member]
Share Options (in shares)
Beginning outstanding	2,300	3,462
Granted	0	0
Exercised	-1,293	-416
Forfeited and expired	-9	-2
Outstanding at end of period	998	3,044
Exercisable at end of period	998	2,928
Weighted-Average Exercise Price (in dollars per share)
Beginning outstanding	$32	$32
Granted	$0	$0
Exercised	$26	$33
Forfeited and expired	$36	$36
Outstanding at end of period	$39	$32
Exercisable at end of period	$39	$32

ShareBased_Compensation_Plans_6

Share-Based Compensation Plans Stock Option Narrative (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Closing share price (in dollars per share)	96.12
Aggregate intrinsic value of options outstanding	57
Unamortized deferred compensation expense	267
Remaining weighted-average amortization period	1 year 9 months 6 days
Share options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual life	2 years 8 months 6 days	2 years

ShareBased_Compensation_Plans_7

Share-Based Compensation Plans Other information related to the company's share options (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Aggregate intrinsic value of stock options exercised	$94	$21
Cash received from the exercise of stock options	34	14
Tax benefit realized from the exercise of stock options	$34	$6

Derivatives_and_Hedging_Foreig

Derivatives and Hedging Foreign Exchange Risk Management Narrative (Details)	3 Months Ended
	Mar. 31, 2015
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Foreign currency exposures, maximum hedging period	1 year
Cash Flow Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum average hedging period	2 years
Net Investment Hedging [Member]
Derivative [Line Items]
Foreign currency exposures, maximum hedging period	2 years

Derivatives_and_Hedging_Intere

Derivatives and Hedging Interest Rate Management Risk Narrative (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	$4
Derivative gain (loss)	-1	-23
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Derivative gain (loss)	$7	($5)
Cash Flow Hedging [Member]
Derivative [Line Items]
Interest rate fluctuations, maximum hedging period	2 years

Derivatives_and_Hedging_Notion

Derivatives and Hedging Notional and fair values of derivative instruments (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Derivatives, Fair Value
Notional Amount	$1,100		$1,365
Derivative Assets	59	[1]	46	[1]
Derivative Liabilities	79	[2]	58	[2]
Term of derivative contract	30 days
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Assets Presented in the Statement of Financial Position	27	[3]	32	[3]
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Liabilities Presented in the Statement of Financial Position	47	[4]	44	[4]
Other Current Assets [Member]
Derivatives, Fair Value
Derivative Assets	38		24
Net Amounts of Assets Presented in the Statement of Financial Position	15		12
Other Noncurrent Assets [Member]
Derivatives, Fair Value
Derivative Assets	21		22
Net Amounts of Assets Presented in the Statement of Financial Position	12		20
Other Current Liabilities [Member]
Derivatives, Fair Value
Derivative Liabilities	66		52
Net Amounts of Liabilities Presented in the Statement of Financial Position	42		40
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value
Derivative Liabilities	13		6
Net Amounts of Liabilities Presented in the Statement of Financial Position	5		4
Derivatives accounted for as hedges [Member]
Derivatives, Fair Value
Notional Amount	919		1,200
Derivative Assets	59	[1]	46	[1]
Derivative Liabilities	79	[2]	58	[2]
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Assets Presented in the Statement of Financial Position	27	[3]	32	[3]
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Liabilities Presented in the Statement of Financial Position	47	[4]	44	[4]
Derivatives accounted for as hedges [Member] | Interest rate contracts [Member]
Derivatives, Fair Value
Notional Amount	0		0
Derivative Assets	0		0
Derivative Liabilities	0		0
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	0	[3]	0	[3]
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Liabilities Presented in the Statement of Financial Position	0	[4]	0	[4]
Derivatives accounted for as hedges [Member] | Foreign exchange contracts [Member]
Derivatives, Fair Value
Notional Amount	919		1,200
Derivative Assets	59		46
Derivative Liabilities	79		58
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Assets Presented in the Statement of Financial Position	27	[3]	32	[3]
Gross Amounts Offset in the Statement of Financial Position	-32		-14
Net Amounts of Liabilities Presented in the Statement of Financial Position	47	[4]	44	[4]
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivatives, Fair Value
Notional Amount	181	[5]	165	[5]
Derivative Assets	0		0
Derivative Liabilities	0		0
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	0	[3]	0	[3]
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Liabilities Presented in the Statement of Financial Position	$0	[4]	$0	[4]
[1]	Included within Other current assets ($38 million at March 31, 2015 and $24 millionB at DecemberB 31, 2014) or Other non-current assets ($21 million at March 31, 2015 and $22 millionB at DecemberB 31, 2014).
[2]	Included within Other current liabilities ($66 million at March 31, 2015 and $52 millionB at DecemberB 31, 2014) or Other non-current liabilities ($13 million at March 31, 2015 and $6 millionB at DecemberB 31, 2014).
[3]	Included within Other current assets ($15 million at March 31, 2015 and $12 millionB at DecemberB 31, 2014) or Other non-current assets ($12 million at March 31, 2015 and $20 millionB at DecemberB 31, 2014).
[4]	Included within Other current liabilities ($42 million at March 31, 2015 and $40 millionB at DecemberB 31, 2014) or Other non-current liabilities ($5 million at March 31, 2015 and $4 millionB at DecemberB 31, 2014).
[5]	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.

Derivatives_and_Hedging_Schedu

Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) (Cash Flow Hedging [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	($1)	($8)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-11	-21
Interest rate contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-1	0
Foreign exchange contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	-1	-8
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-10	-21
Compensation and Benefits [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	5	11
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	-3
Compensation and Benefits [Member] | Interest rate contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	0
Compensation and Benefits [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	5	11
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	-3
Other General Expenses [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	-2	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	0
Other General Expenses [Member] | Interest rate contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	0
Other General Expenses [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	-2	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	0
Interest Expense [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-3	0
Interest Expense [Member] | Interest rate contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-1	0
Interest Expense [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-2	0
Other Income [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	-4	-19
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	-8	-18
Other Income [Member] | Interest rate contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	0	0
Other Income [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	-4	-19
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion):	($8)	($18)

Fair_Value_Measurements_and_Fi2

Fair Value Measurements and Financial Instruments Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details) (Recurring [Member], USD $)	Mar. 31, 2015		Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value [Member] | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	$1,787	[1]	$1,850	[2]
Fair Value [Member] | Money market funds [Member]
Assets:
Money market funds and highly liquid debt securities	1,787		1,850
Fair Value [Member] | Corporate bonds [Member]
Assets:
Other investments	1		1
Fair Value [Member] | Government bonds [Member]
Assets:
Other investments	6		6
Fair Value [Member] | Equity investments [Member]
Assets:
Other investments	10		11
Fair Value [Member] | Interest rate contracts [Member]
Assets:
Derivatives	0		0
Fair Value [Member] | Foreign exchange contracts [Member]
Assets:
Derivatives	59		46
Liabilities:
Derivatives	79		58
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	1,787	[1]	1,850	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Assets:
Other investments	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government bonds [Member]
Assets:
Other investments	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity investments [Member]
Assets:
Other investments	6		6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest rate contracts [Member]
Assets:
Derivatives	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign exchange contracts [Member]
Assets:
Derivatives	0		0
Liabilities:
Derivatives	0		0
Significant Other Observable Inputs (Level 2) [Member] | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	0	[1]	0	[2]
Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Assets:
Other investments	0		0
Significant Other Observable Inputs (Level 2) [Member] | Government bonds [Member]
Assets:
Other investments	6		6
Significant Other Observable Inputs (Level 2) [Member] | Equity investments [Member]
Assets:
Other investments	4		5
Significant Other Observable Inputs (Level 2) [Member] | Interest rate contracts [Member]
Assets:
Derivatives	0		0
Significant Other Observable Inputs (Level 2) [Member] | Foreign exchange contracts [Member]
Assets:
Derivatives	59		46
Liabilities:
Derivatives	79		58
Significant Unobservable Inputs (Level 3) [Member] | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	0	[1]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Assets:
Other investments	1		1
Significant Unobservable Inputs (Level 3) [Member] | Government bonds [Member]
Assets:
Other investments	0		0
Significant Unobservable Inputs (Level 3) [Member] | Equity investments [Member]
Assets:
Other investments	0		0
Significant Unobservable Inputs (Level 3) [Member] | Interest rate contracts [Member]
Assets:
Derivatives	0		0
Significant Unobservable Inputs (Level 3) [Member] | Foreign exchange contracts [Member]
Assets:
Derivatives	0		0
Liabilities:
Derivatives	$0		$0
[1]	Includes $1,787 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.
[2]	Includes $1,850 million of money market funds that are classified as Fiduciary assets, Short-term investments or Cash and cash equivalents in the Condensed Consolidated Statements of Financial Position, depending on their nature and initial maturity.

Fair_Value_Measurements_and_Fi3

Fair Value Measurements and Financial Instruments Schedule of financial instruments where the carrying amounts and fair values differ (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Fair value of financial instrument
Carrying value of total debt	$4,710	$4,799
Fair value of total debt	$5,259	$5,268

Commitments_and_Contingencies_

Commitments and Contingencies (Details)

Mar. 31, 2015

Dec. 31, 2014

Mar. 31, 2015

Apr. 30, 2014

Mar. 31, 2015

Dec. 31, 2014

Jan. 31, 2014

Sep. 14, 2010

Mar. 31, 2015

Mar. 31, 2015

Jan. 02, 2014

Mar. 31, 2015

Jan. 26, 2015

Dec. 02, 2014

Jun. 01, 2007

Dec. 31, 2014

Jan. 26, 2015

Dec. 02, 2014

Jun. 01, 2007

Dec. 31, 2014

Jun. 01, 2007

Mar. 31, 2015

Dec. 27, 2012

USD ($)

USD ($)

Potential Claim for Pension Advisory Services [Member]

Potential Claim for Pension Advisory Services [Member]

Commitments to fund certain limited partnerships or subsidiaries [Member]

Commitments to fund certain limited partnerships or subsidiaries [Member]

Northrop Grumman Corporation [Member]

Opry Mills Mall Limited Partnership [Member]

Opry Mills Mall Limited Partnership [Member]

Philips [Member]

Philips [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

International Road Transport Union [Member]

Versicherung Aktiengesellschaft [Member]

Versicherung Aktiengesellschaft [Member]

USD ($)

GBP (£)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

GBP (£)

Litigation Award [Member]

Litigation Award [Member]

Litigation Award [Member]

Litigation Award [Member]

Litigation Award [Member]

Litigation USD Denominated Award [Member]

Litigation USD Denominated Award [Member]

Litigation USD Denominated Award [Member]

Litigation USD Denominated Award [Member]

Litigation Expenses and Interest [Member]

Litigation Award [Member]

Litigation Award [Member]

USD ($)

CHF

CHF

CHF

CHF

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

EUR (€)

Legal, Guarantees and Indemnifications

Range of possible loss, minimum

$0

Range of possible loss, maximum

600,000,000

Damages sought

340,000,000

200,000,000

281,000,000

189,000,000

48,000,000

46,000,000

3,000,000

30,000,000

199,000,000

183,000,000

Amount of coverage for damages contended by the insurers

50,000,000

Difference amount of damages sought by the client

150,000,000

Damages awarded excluding interest and costs

17,000,000

16,800,000

3,100,000

Damages awarded

200,000,000

29,000,000

27,900,000

5,000,000

Case settlement amount

13,000,000

12,800,000

4,700,000

Settlement, maximum liability

9,000,000

8,700,000

115,000

Estimate of possible loss

67,000,000

45,000,000

Maximum potential funding under commitments

77,000,000

112,000,000

12,000,000

14,000,000

Letters of credit outstanding

68,000,000

95,000,000

Commitments funded

$2,000,000

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	segment
Segment Reporting Information
Number of reportable segments	2
Total revenue	$2,847	$2,947
Total commissions, fees and other revenue	2,842	2,941
Total fiduciary investment income	5	6
Operating income before income tax	441	469
Interest income	3	2
Interest expense	-65	-58
Other income	42	1
Income before income taxes	421	414
Total operating segments [Member]
Segment Reporting Information
Operating income before income tax	488	512
Risk Solutions [Member]
Segment Reporting Information
Total revenue	1,895	1,994
Total commissions, fees and other revenue	1,890	1,988
Total fiduciary investment income	5	6
Operating income before income tax	412	445
Retail brokerage [Member]
Segment Reporting Information
Total commissions, fees and other revenue	1,513	1,579
Reinsurance brokerage [Member]
Segment Reporting Information
Total commissions, fees and other revenue	377	409
HR Solutions [Member]
Segment Reporting Information
Total revenue	970	965
Total commissions, fees and other revenue	970	965
Total fiduciary investment income	0	0
Operating income before income tax	76	67
Consulting services [Member]
Segment Reporting Information
Total commissions, fees and other revenue	371	384
Outsourcing [Member]
Segment Reporting Information
Total commissions, fees and other revenue	604	589
Intrasegment [Member]
Segment Reporting Information
Total commissions, fees and other revenue	-5	-8
Intersegment elimination [Member]
Segment Reporting Information
Total revenue	-18	-12
Total commissions, fees and other revenue	-18	-12
Unallocated Expense [Member]
Segment Reporting Information
Operating income before income tax	($47)	($43)

Guarantee_of_Registered_Securi2

Guarantee of Registered Securities (Narrative) (Details)	Mar. 31, 2015
Aon plc [Member]
Condensed Financial Statements, Captions [Line Items]
Parent company's percentage ownership of guarantors	100.00%
3.50% senior notes due September 2015 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	3.50%
3.125% Senior notes due 2016 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	3.13%
5.00% Senior notes due September 2020 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	5.00%
8.205% Junior subordinated deferrable interest debentures due January 2027 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	8.21%
6.25% Senior notes due September 2040 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	6.25%
4.250% Senior notes due 2042 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	4.25%
4.45% notes due 2043 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	4.45%
4.00% notes due 2023 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	4.00%
2.875% notes due 2026 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	2.88%
3.50% Notes due June 2024 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	3.50%
4.60% notes due May 2044 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	4.60%
3.50% notes due 2024 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	3.50%
4.60% notes due 2044 [Member]
Condensed Financial Statements, Captions [Line Items]
Debt interest rate percentage	4.60%

Guarantee_of_Registered_Securi3

Guarantee of Registered Securities - Condensed Consolidating Statement of Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenue
Commissions, fees and other	$2,842	$2,941
Fiduciary investment income	5	6
Total revenue	2,847	2,947
Expenses
Compensation and benefits	1,683	1,751
Other general expenses	723	727
Total operating expenses	2,406	2,478
Operating income	441	469
Interest income	3	2
Interest expense	-65	-58
Intercompany interest income (expense)	0	0
Intercompany other (expense) income	0	0
Other income	42	1
Income before income taxes	421	414
Income tax (benefit) expense	80	78
(Loss) income before equity in earnings of subsidiaries	341	336
Equity in earnings of subsidiaries, net of tax	0	0
Net income	341	336
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	328	325
Aon plc [Member]
Revenue
Commissions, fees and other	0	1
Fiduciary investment income	0	0
Total revenue	0	1
Expenses
Compensation and benefits	52	66
Other general expenses	13	4
Total operating expenses	65	70
Operating income	-65	-69
Interest income	-5	-2
Interest expense	-25	-9
Intercompany interest income (expense)	119	111
Intercompany other (expense) income	-50	-19
Other income	2	0
Income before income taxes	-24	12
Income tax (benefit) expense	-5	3
(Loss) income before equity in earnings of subsidiaries	-19	9
Equity in earnings of subsidiaries, net of tax	347	316
Net income	328	325
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	328	325
Aon Corporation [Member]
Revenue
Commissions, fees and other	0	0
Fiduciary investment income	0	0
Total revenue	0	0
Expenses
Compensation and benefits	11	7
Other general expenses	2	3
Total operating expenses	13	10
Operating income	-13	-10
Interest income	3	0
Interest expense	-34	-31
Intercompany interest income (expense)	-105	-74
Intercompany other (expense) income	-8	-15
Other income	8	0
Income before income taxes	-149	-130
Income tax (benefit) expense	-50	-50
(Loss) income before equity in earnings of subsidiaries	-99	-80
Equity in earnings of subsidiaries, net of tax	403	333
Net income	304	253
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	304	253
Other Non-Guarantor Subsidiaries [Member]
Revenue
Commissions, fees and other	2,842	2,940
Fiduciary investment income	5	6
Total revenue	2,847	2,946
Expenses
Compensation and benefits	1,620	1,678
Other general expenses	708	720
Total operating expenses	2,328	2,398
Operating income	519	548
Interest income	5	4
Interest expense	-6	-18
Intercompany interest income (expense)	-14	-37
Intercompany other (expense) income	58	34
Other income	32	1
Income before income taxes	594	532
Income tax (benefit) expense	135	125
(Loss) income before equity in earnings of subsidiaries	459	407
Equity in earnings of subsidiaries, net of tax	304	253
Net income	763	660
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	750	649
Consolidating Adjustments [Member]
Revenue
Commissions, fees and other	0	0
Fiduciary investment income	0	0
Total revenue	0	0
Expenses
Compensation and benefits	0	0
Other general expenses	0	0
Total operating expenses	0	0
Operating income	0	0
Interest income	0	0
Interest expense	0	0
Intercompany interest income (expense)	0	0
Intercompany other (expense) income	0	0
Other income	0	0
Income before income taxes	0	0
Income tax (benefit) expense	0	0
(Loss) income before equity in earnings of subsidiaries	0	0
Equity in earnings of subsidiaries, net of tax	-1,054	-902
Net income	-1,054	-902
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	($1,054)	($902)

Guarantee_of_Registered_Securi4

Guarantee of Registered Securities - Condensed Consolidating Statement of Comprehensive Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$341	$336
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	328	325
Change in fair value of investments	-1	1
Change in fair value of derivatives	6	9
Foreign currency translation adjustments	-322	16
Post-retirement benefit obligation	23	26
Total other comprehensive (loss) income	-294	52
Equity in other comprehensive loss of subsidiaries, net of tax	0	0
Less: Other comprehensive (loss) income attributable to noncontrolling interests	-1	-2
Total other comprehensive (loss) income attributable to Aon shareholders	-293	54
Comprehensive income attributable to Aon shareholders	35	379
Aon plc [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	328	325
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	328	325
Change in fair value of investments	0	0
Change in fair value of derivatives	0	0
Foreign currency translation adjustments	0	0
Post-retirement benefit obligation	0	0
Total other comprehensive (loss) income	0	0
Equity in other comprehensive loss of subsidiaries, net of tax	-293	54
Less: Other comprehensive (loss) income attributable to noncontrolling interests	0	0
Total other comprehensive (loss) income attributable to Aon shareholders	-293	54
Comprehensive income attributable to Aon shareholders	35	379
Aon Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	304	253
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	304	253
Change in fair value of investments	0	0
Change in fair value of derivatives	-1	1
Foreign currency translation adjustments	-23	-17
Post-retirement benefit obligation	8	6
Total other comprehensive (loss) income	-16	-10
Equity in other comprehensive loss of subsidiaries, net of tax	-267	69
Less: Other comprehensive (loss) income attributable to noncontrolling interests	0	0
Total other comprehensive (loss) income attributable to Aon shareholders	-283	59
Comprehensive income attributable to Aon shareholders	21	312
Other Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	763	660
Less: Net income attributable to noncontrolling interests	13	11
Net income attributable to Aon shareholders	750	649
Change in fair value of investments	-1	1
Change in fair value of derivatives	7	8
Foreign currency translation adjustments	-299	33
Post-retirement benefit obligation	15	20
Total other comprehensive (loss) income	-278	62
Equity in other comprehensive loss of subsidiaries, net of tax	-283	59
Less: Other comprehensive (loss) income attributable to noncontrolling interests	-1	-2
Total other comprehensive (loss) income attributable to Aon shareholders	-560	123
Comprehensive income attributable to Aon shareholders	190	772
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	-1,054	-902
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to Aon shareholders	-1,054	-902
Change in fair value of investments	0	0
Change in fair value of derivatives	0	0
Foreign currency translation adjustments	0	0
Post-retirement benefit obligation	0	0
Total other comprehensive (loss) income	0	0
Equity in other comprehensive loss of subsidiaries, net of tax	843	-182
Less: Other comprehensive (loss) income attributable to noncontrolling interests	0	0
Total other comprehensive (loss) income attributable to Aon shareholders	843	-182
Comprehensive income attributable to Aon shareholders	($211)	($1,084)

Guarantee_of_Registered_Securi5

Guarantee of Registered Securities - Condensed Consolidating Statement of Financial Position (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
CURRENT ASSETS :
Cash and cash equivalents	$378	$374	$338	$477
Short-term investments	343	394
Receivables, net	2,672	2,815
Fiduciary assets	10,894	11,638
Intercompany receivables	0	0
Other current assets	712	602
Total Current Assets	14,999	15,823
Goodwill	8,548	8,860
Intangible assets, net	2,410	2,520
Fixed assets, net	754	765
Intercompany receivables	0	0
Other non-current assets	1,678	1,804
Investment in subsidiary	0	0
TOTAL ASSETS	28,389	29,772
CURRENT LIABILITIES
Fiduciary liabilities	10,894	11,638
Short-term debt and current portion of long-term debt	966	783
Accounts payable and accrued liabilities	1,391	1,805
Intercompany payables	0	0
Other current liabilities	865	788
Total Current Liabilities	14,116	15,014
Long-term debt	4,710	4,799
Pension, other post-retirement and post-employment liabilities	2,001	2,141
Intercompany payables	0	0
Other non-current liabilities	1,131	1,187
TOTAL LIABILITIES	21,958	23,141
TOTAL AON SHAREHOLDERS' EQUITY	6,365	6,571
Noncontrolling interests	66	60
TOTAL EQUITY	6,431	6,631
TOTAL LIABILITIES AND EQUITY	28,389	29,772
Aon plc [Member]
CURRENT ASSETS :
Cash and cash equivalents	0	0	0	0
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Intercompany receivables	125	455
Other current assets	2	2
Total Current Assets	127	457
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Intercompany receivables	7,374	7,399
Other non-current assets	181	179
Investment in subsidiary	4,121	4,962
TOTAL ASSETS	11,803	12,997
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	109	0
Accounts payable and accrued liabilities	2,597	3,755
Intercompany payables	246	122
Other current liabilities	0	0
Total Current Liabilities	2,952	3,877
Long-term debt	2,480	2,544
Pension, other post-retirement and post-employment liabilities	0	0
Intercompany payables	0	0
Other non-current liabilities	6	5
TOTAL LIABILITIES	5,438	6,426
TOTAL AON SHAREHOLDERS' EQUITY	6,365	6,571
Noncontrolling interests	0	0
TOTAL EQUITY	6,365	6,571
TOTAL LIABILITIES AND EQUITY	11,803	12,997
Aon Corporation [Member]
CURRENT ASSETS :
Cash and cash equivalents	2,230	2,727	154	247
Short-term investments	166	165
Receivables, net	0	0
Fiduciary assets	0	0
Intercompany receivables	3,581	2,814
Other current assets	207	226
Total Current Assets	6,184	5,932
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Intercompany receivables	577	600
Other non-current assets	701	697
Investment in subsidiary	15,391	15,200
TOTAL ASSETS	22,853	22,429
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	846	767
Accounts payable and accrued liabilities	31	58
Intercompany payables	9,382	8,960
Other current liabilities	49	49
Total Current Liabilities	10,308	9,834
Long-term debt	1,917	1,917
Pension, other post-retirement and post-employment liabilities	1,366	1,396
Intercompany payables	7,287	7,277
Other non-current liabilities	107	125
TOTAL LIABILITIES	20,985	20,549
TOTAL AON SHAREHOLDERS' EQUITY	1,868	1,880
Noncontrolling interests	0	0
TOTAL EQUITY	1,868	1,880
TOTAL LIABILITIES AND EQUITY	22,853	22,429
Other Non-Guarantor Subsidiaries [Member]
CURRENT ASSETS :
Cash and cash equivalents	650	1,361	1,372	1,246
Short-term investments	177	229
Receivables, net	2,672	2,815
Fiduciary assets	10,894	11,638
Intercompany receivables	9,681	9,156
Other current assets	536	407
Total Current Assets	24,610	25,606
Goodwill	8,548	8,860
Intangible assets, net	2,410	2,520
Fixed assets, net	754	765
Intercompany receivables	121	111
Other non-current assets	1,589	1,718
Investment in subsidiary	1,868	1,880
TOTAL ASSETS	39,900	41,460
CURRENT LIABILITIES
Fiduciary liabilities	10,894	11,638
Short-term debt and current portion of long-term debt	11	16
Accounts payable and accrued liabilities	1,265	1,706
Intercompany payables	3,759	3,343
Other current liabilities	849	772
Total Current Liabilities	16,778	17,475
Long-term debt	313	338
Pension, other post-retirement and post-employment liabilities	635	745
Intercompany payables	785	833
Other non-current liabilities	1,811	1,847
TOTAL LIABILITIES	20,322	21,238
TOTAL AON SHAREHOLDERS' EQUITY	19,512	20,162
Noncontrolling interests	66	60
TOTAL EQUITY	19,578	20,222
TOTAL LIABILITIES AND EQUITY	39,900	41,460
Consolidating Adjustments [Member]
CURRENT ASSETS :
Cash and cash equivalents	-2,502	-3,714	-1,188	-1,016
Short-term investments	0	0
Receivables, net	0	0
Fiduciary assets	0	0
Intercompany receivables	-13,387	-12,425
Other current assets	-33	-33
Total Current Assets	-15,922	-16,172
Goodwill	0	0
Intangible assets, net	0	0
Fixed assets, net	0	0
Intercompany receivables	-8,072	-8,110
Other non-current assets	-793	-790
Investment in subsidiary	-21,380	-22,042
TOTAL ASSETS	-46,167	-47,114
CURRENT LIABILITIES
Fiduciary liabilities	0	0
Short-term debt and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	-2,502	-3,714
Intercompany payables	-13,387	-12,425
Other current liabilities	-33	-33
Total Current Liabilities	-15,922	-16,172
Long-term debt	0	0
Pension, other post-retirement and post-employment liabilities	0	0
Intercompany payables	-8,072	-8,110
Other non-current liabilities	-793	-790
TOTAL LIABILITIES	-24,787	-25,072
TOTAL AON SHAREHOLDERS' EQUITY	-21,380	-22,042
Noncontrolling interests	0	0
TOTAL EQUITY	-21,380	-22,042
TOTAL LIABILITIES AND EQUITY	($46,167)	($47,114)

Guarantee_of_Registered_Securi6

Guarantee of Registered Securities - Condensed Consolidating Statement of Cash Flows (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	$136	($11)
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	3	42
Purchases of long-term investments	-1	-10
Net sales of short-term investments - non-fiduciary	42	183
Acquisition of businesses, net of cash acquired	-21	-5
Proceeds from sale of businesses	41	1
Capital expenditures	-62	-55
CASH PROVIDED BY INVESTING ACTIVITIES	2	156
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	-250	-600
Advances from (to) affiliates	0	0
Issuance of shares for employee benefit plans	48	26
Issuance of debt	870	1,195
Repayment of debt	-686	-829
Cash dividends to shareholders	-71	-53
Purchase of shares from noncontrolling interests	-5	1
Dividends paid to noncontrolling interests	-1	0
Proceeds from sale-leaseback	0
CASH USED FOR FINANCING ACTIVITIES	-95	-260
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	-39	-24
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	4	-139
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	374	477
CASH AND CASH EQUIVALENTS AT END OF PERIOD	378	338
Aon plc [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	2	89
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	0	0
Purchases of long-term investments	0	0
Net sales of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Proceeds from sale of businesses	0	0
Capital expenditures	0	0
CASH PROVIDED BY INVESTING ACTIVITIES	0	0
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	-250	-600
Advances from (to) affiliates	157	313
Issuance of shares for employee benefit plans	48	26
Issuance of debt	114	293
Repayment of debt	0	-68
Cash dividends to shareholders	-71	-53
Purchase of shares from noncontrolling interests	0	0
Dividends paid to noncontrolling interests	0
Proceeds from sale-leaseback	0
CASH USED FOR FINANCING ACTIVITIES	-2	-89
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	0	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	0	0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	0	0
Aon Corporation [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	-188	-123
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	0	37
Purchases of long-term investments	-1	-10
Net sales of short-term investments - non-fiduciary	-1	62
Acquisition of businesses, net of cash acquired	0	0
Proceeds from sale of businesses	0	0
Capital expenditures	0	0
CASH PROVIDED BY INVESTING ACTIVITIES	-2	89
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0
Advances from (to) affiliates	-385	-206
Issuance of shares for employee benefit plans	0	0
Issuance of debt	756	902
Repayment of debt	-678	-755
Cash dividends to shareholders	0	0
Purchase of shares from noncontrolling interests	0	0
Dividends paid to noncontrolling interests	0
Proceeds from sale-leaseback	0
CASH USED FOR FINANCING ACTIVITIES	-307	-59
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-497	-93
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	2,727	247
CASH AND CASH EQUIVALENTS AT END OF PERIOD	2,230	154
Other Non-Guarantor Subsidiaries [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	322	23
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	3	5
Purchases of long-term investments	0	0
Net sales of short-term investments - non-fiduciary	43	121
Acquisition of businesses, net of cash acquired	-21	-5
Proceeds from sale of businesses	41	1
Capital expenditures	-62	-55
CASH PROVIDED BY INVESTING ACTIVITIES	4	67
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0
Advances from (to) affiliates	-984	65
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	0
Repayment of debt	-8	-6
Cash dividends to shareholders	0	0
Purchase of shares from noncontrolling interests	-5	1
Dividends paid to noncontrolling interests	-1
Proceeds from sale-leaseback	0
CASH USED FOR FINANCING ACTIVITIES	-998	60
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	-39	-24
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-711	126
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	1,361	1,246
CASH AND CASH EQUIVALENTS AT END OF PERIOD	650	1,372
Consolidating Adjustments [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
CASH PROVIDED BY (USED FOR) OPERATING ACTIVITIES	0	0
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of long-term investments	0	0
Purchases of long-term investments	0	0
Net sales of short-term investments - non-fiduciary	0	0
Acquisition of businesses, net of cash acquired	0	0
Proceeds from sale of businesses	0	0
Capital expenditures	0	0
CASH PROVIDED BY INVESTING ACTIVITIES	0	0
CASH FLOWS FROM FINANCING ACTIVITIES
Share repurchase	0	0
Advances from (to) affiliates	1,212	-172
Issuance of shares for employee benefit plans	0	0
Issuance of debt	0	0
Repayment of debt	0	0
Cash dividends to shareholders	0	0
Purchase of shares from noncontrolling interests	0	0
Dividends paid to noncontrolling interests	0
Proceeds from sale-leaseback	0
CASH USED FOR FINANCING ACTIVITIES	1,212	-172
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS	0	0
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	1,212	-172
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	-3,714	-1,016
CASH AND CASH EQUIVALENTS AT END OF PERIOD	($2,502)	($1,188)