Arthur J. Gallagher & Co. (AJG) 10-Q 29 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014
Document And Entity Information [Abstract]	'
Document Type	'10-Q
Amendment Flag	'false
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
Trading Symbol	'AJG
Entity Registrant Name	'GALLAGHER ARTHUR J & CO
Entity Central Index Key	'0000354190
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Large Accelerated Filer
Entity Common Stock, Shares Outstanding	161,374,000

Consolidated_Statement_of_Earn

Consolidated Statement of Earnings (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Commissions	$572.50	$399.10	$1,523.50	$1,126.80
Fees	337.7	270	912.3	778.6
Supplemental commissions	24.2	17.8	77.5	53.4
Contingent commissions	14.4	6.5	68.4	43.5
Investment income	18.4	2.6	23.1	5.5
Gains on books of business sales	0.9	0	2.6	3.3
Revenues from clean coal activities	321.2	134.9	750.4	264.1
Other net (losses) revenues	-2.5	4.9	23.3	14.2
Total revenues	1,286.80	835.8	3,381.10	2,289.40
Compensation	564.6	412.5	1,560.90	1,211.90
Operating	205	133.1	546.2	404.7
Cost of revenues from clean coal activities	326.2	146.9	767.7	281.6
Interest	25.9	13.1	63.3	36.2
Depreciation	18.6	14.3	50	38.2
Amortization	54.3	30.8	135.3	90.1
Change in estimated acquisition earnout payables	4.5	-0.4	16.6	1.5
Total expenses	1,199.10	750.3	3,140	2,064.20
Earnings before income taxes	87.7	85.5	241.1	225.2
Provision (benefit) for income taxes	-5.9	10.9	-10.8	16.6
Net earnings	$93.60	$74.60	$251.90	$208.60
Basic net earnings per share	$0.58	$0.57	$1.68	$1.63
Diluted net earnings per share	$0.58	$0.57	$1.67	$1.61
Dividends declared per common share	$0.36	$0.35	$1.08	$1.05

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Earnings (Unaudited) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'	'
Net earnings	$93.60	$74.60	$251.90	$208.60
Change in pension liability, net of taxes	0.5	0.2	1.4	0.4
Foreign currency translation	-136.5	29.1	-82	-9.9
Change in fair value of derivative investments, net of taxes	-1.9	1.5	-0.5	0.5
Comprehensive earnings (loss)	($44.30)	$105.40	$170.80	$199.60

Consolidated_Balance_Sheet

Consolidated Balance Sheet (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Cash and cash equivalents	$290.50	$298.10
Restricted cash	1,342.10	1,027.40
Premiums and fees receivable	1,669	1,288.80
Other current assets	670.8	261.3
Total current assets	3,972.40	2,875.60
Fixed assets - net	196.6	160.4
Deferred income taxes	352.7	279.8
Other noncurrent assets	399	320.7
Goodwill - net	3,296.20	2,145.20
Amortizable intangible assets - net	1,771.10	1,078.80
Total assets	9,988	6,860.50
Premiums payable to insurance and reinsurance companies	2,755.40	2,154.70
Accrued compensation and other accrued liabilities	560.9	370.6
Unearned fees	98.7	84.5
Other current liabilities	58.6	44.5
Premium financing debt	149.2	0
Corporate related borrowings - current	147	630.5
Total current liabilities	3,769.80	3,284.80
Corporate related borrowings - noncurrent	2,125	825
Other noncurrent liabilities	837.2	665.2
Total liabilities	6,732	4,775
Stockholders' equity:	'	'
Common stock - issued and outstanding 161.4 shares in 2014 and 133.6 shares in 2013	161.4	133.6
Capital in excess of par value	2,494.60	1,358.10
Retained earnings	683.7	596.4
Accumulated other comprehensive loss	-83.7	-2.6
Total stockholders' equity	3,256	2,085.50
Total liabilities and stockholders' equity	$9,988	$6,860.50

Consolidated_Balance_Sheet_Par

Consolidated Balance Sheet (Parenthetical)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Common stock - issued shares	161.4	133.6
Common stock - outstanding shares	161.4	133.6

Consolidated_Statement_of_Cash

Consolidated Statement of Cash Flows (Unaudited) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:	'	'
Net earnings	$251.90	$208.60
Adjustments to reconcile net earnings to net cash provided by operating activities:	'	'
Net gain on investments and other	-23.2	-17.6
Depreciation and amortization	185.3	128.3
Change in estimated acquisition earnout payables	16.6	1.5
Amortization of deferred compensation and restricted stock	17.3	10.6
Stock-based and other noncash compensation expense	7.8	5.4
Effect of changes in foreign exchange rates	-0.7	0
Net change in restricted cash	2.7	-29.3
Net change in premiums receivable	-50.1	62.3
Net change in premiums payable	39	-7.2
Net change in other current assets	-123.5	-71.5
Net change in accrued compensation and other accrued liabilities	111.4	50.1
Net change in fees receivable/unearned fees	-23.8	-11.3
Net change in income taxes payable	5.9	9.5
Net change in deferred income taxes	-75.5	-36.6
Net change in other noncurrent assets and liabilities	-107.9	-24.2
Net cash provided by operating activities	233.2	278.6
Cash flows from investing activities:	'	'
Net additions to fixed assets	-59.7	-69.8
Cash paid for acquisitions, net of cash acquired	-1,834.60	-333
Net proceeds from sales of operations/books of business	3.1	3.3
Net funding of investment transactions	-19.5	-31
Net cash used by investing activities	-1,910.70	-430.5
Cash flows from financing activities:	'	'
Proceeds from issuance of common stock	960.6	64.5
Tax impact from issuance of common stock	6.7	6.3
Dividends paid	-164.3	-136
Net borrowings on premium financing debt facility	36.3	'
Borrowings on line of credit facility	1,017.40	445.5
Repayments on line of credit facility	-1,400.90	-439
Net borrowings of corporate related long-term debt	1,200	200
Net cash provided by financing activities	1,655.80	141.3
Effect of changes in foreign exchange rates on cash and cash equivalents	14.1	-4.6
Net decrease in cash and cash equivalents	-7.6	-15.2
Cash and cash equivalents at beginning of period	298.1	302.1
Cash and cash equivalents at end of period	290.5	286.9
Supplemental disclosures of cash flow information:	'	'
Interest paid	59.7	40.4
Income taxes paid	$51.60	$37.10

Consolidated_Statement_of_Stoc

Consolidated Statement of Stockholders' Equity (Unaudited) (USD $)	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Earnings (Loss) [Member]
In Millions, unless otherwise specified
Beginning Balance at Dec. 31, 2013	$2,085.50	$133.60	$1,358.10	$596.40	($2.60)
Beginning Balance, Shares at Dec. 31, 2013	'	133.6	'	'	'
Net earnings	251.9	'	'	251.9	0
Change in pension liability, net of taxes of $0.9 million	1.4	'	'	'	1.4
Foreign currency translation	-82	'	'	'	-82
Change in fair value of derivative instruments, net of taxes of ($0.3) million	-0.5	'	'	'	-0.5
Compensation expense related to stock option plan grants	6.7	'	6.7	'	'
Tax impact from issuance of common stock	6.7	'	6.7	'	'
Common stock issued in:	'	'	'	'	'
Thirty-eight purchase transactions	186.3	4.1	182.2	'	'
Thirty-eight purchase transaction, in shares	'	4.1	'	'	'
Stock option plans	39.3	1.5	37.8	'	'
Stock option plans (in shares)	1.5	1.5	'	'	'
Employee stock purchase plan	9.9	0.2	9.7	'	'
Employee stock purchase plan (in shares)	'	0.2	'	'	'
Deferred compensation and restricted stock	2.9	0.1	2.8	'	'
Deferred compensation and restricted stock (in shares)	'	0.1	'	'	'
Stock issuance from public offering	911.4	21.9	889.5	'	'
Stock issuance from public offering (in shares)	21.9	21.9	'	'	'
Other compensation expense	1.1	'	1.1	'	'
Cash dividends declared on common stock	-164.6	'	'	-164.6	'
Ending Balance at Sep. 30, 2014	$3,256	$161.40	$2,494.60	$683.70	($83.70)
Ending Balance, Shares at Sep. 30, 2014	'	161.4	'	'	'

Consolidated_Statement_of_Stoc1

Consolidated Statement of Stockholders' Equity (Unaudited) (Parenthetical) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Statement of Stockholders' Equity [Abstract]	'
Tax effect on net change in pension liability	$0.90
Net change in fair value of derivative instruments, tax	($0.30)

Nature_of_Operations_and_Basis

Nature of Operations and Basis of Presentation	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Nature of Operations and Basis of Presentation	'
	1. Nature of Operations and Basis of Presentation
	Arthur J. Gallagher & Co. and its subsidiaries, collectively referred to herein as we, our, us or the company, provide insurance brokerage and risk management services to a wide variety of commercial, industrial, institutional and governmental organizations through three reportable operating segments. Commission and fee revenue generated by the brokerage segment is primarily related to the negotiation and placement of insurance for our clients. Fee revenue generated by the risk management segment is primarily related to claims management, information management, risk control consulting (loss control) services and appraisals in the property/casualty market. Investment income and other revenue are generated from our investment portfolio, which includes invested cash and restricted funds, as well as clean energy and other investments. We are headquartered in Itasca, Illinois, have operations in 30 countries and offer client-service capabilities in more than 140 countries globally through a network of correspondent insurance brokers and consultants.
	We have prepared the accompanying unaudited consolidated financial statements pursuant to the rules and regulations of the Securities and Exchange Commission. Certain information and footnote disclosures normally included in annual financial statements have been omitted pursuant to such rules and regulations. The unaudited consolidated financial statements included herein are, in the opinion of management, prepared on a basis consistent with our audited consolidated financial statements for the year ended December 31, 2013 and include all normal recurring adjustments necessary for a fair presentation of the information set forth. The quarterly results of operations are not necessarily indicative of the results of operations to be reported for subsequent quarters or the full year. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2013. In the preparation of our unaudited consolidated financial statements as of September 30, 2014, management evaluated all material subsequent events or transactions that occurred after the balance sheet date through the date on which the financial statements were issued, for potential recognition or disclosure therein.

Effect_of_New_Accounting_Prono

Effect of New Accounting Pronouncements	9 Months Ended
	Sep. 30, 2014
Accounting Changes and Error Corrections [Abstract]	'
Effect of New Accounting Pronouncements	'
	2. Effect of New Accounting Pronouncements
	Revenue Recognition
	In May 2014, the Financial Accounting Standards Board (which we refer to as 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 new 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. This new guidance is effective for 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. Management is currently reviewing the guidance, and the impact from its adoption on our consolidated financial statements cannot be determined at this time.
	Presentation of Unrecognized Tax Benefits
	In July 2013, the FASB issued ASU 2013-11, “Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists,” which provides explicit guidance on the presentation of certain unrecognized tax benefits in the financial statements that did not previously exist. The guidance provides that a liability related to an unrecognized tax benefit would be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. In that case, the liability associated with the unrecognized tax benefit is presented in the financial statements as a reduction to the related deferred tax asset. In situations in which a net operating loss carryforward, a similar tax loss or a tax credit carryforward is not available at the reporting date under the tax law of the jurisdiction or the tax law of the jurisdiction does not require, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit will be presented in the financial statements as a liability and will not be combined with deferred tax assets. This new guidance was effective in first quarter 2014. We adopted the new guidance effective January 1, 2014. The impact of the new guidance upon adoption was not material to our 2014 unaudited consolidated financial statements.

Business_Combinations

Business Combinations	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Business Combinations	'
	3. Business Combinations
	During the nine-month period ended September 30, 2014, we acquired substantially all of the net assets of the following firms in exchange for our common stock and/or cash. These acquisitions have been accounted for using the acquisition method for recording business combinations (in millions except share data):
	Name and Effective	Common		Common		Cash		Accrued		Escrow		Recorded		Total		Maximum
	Date of Acquisition	Shares		Share		Paid		Liability		Deposited		Earnout		Recorded		Potential
		Issued		Value								Payable		Purchase		Earnout
														Price		Payable
		(000s)
	Benefit Development Group, Inc. February 1, 2014		46	$	2	$	0.7	$	—	$	0.1	$	0.6	$	3.4	$	2
	Kent, Kent & Tingle February 1, 2014		229		9.1		3.5		—		1.4		3.5		17.5		7.8
	L&R Benefits, LLC March 1, 2014		115		5.3		1.8		—		0.1		1		8.2		6
	Spataro Insurance Agency, Inc. March 1, 2014		47		2		—		—		0.2		0.4		2.6		0.6
	Tudor Risk Services, LLC March 1, 2014		—		—		2.1		—		0.2		0.1		2.4		1.3
	American Wholesalers Underwriting Ltd April 1, 2014		133		6		5.7		—		0.5		—		12.2		—
	Mike Henry Insurance Brokers Limited April 1, 2014		—		—		9.6		—		1.7		4.2		15.5		6.8
	Oval Group of Companies (OGC) April 1, 2014		—		—		338.4		—		11.8		—		350.2		—
	Heritage Insurance Management Limited (HIM) May 1, 2014		—		—		33.9		—		3.8		—		37.7		—
	MGA Insurance Group (MGA) May 1, 2014		547		25.1		26.8		—		2.5		11.9		66.3		20
	Shilling Limited May 1, 2014		198		8.9		1.7		—		1.2		1		12.8		8.4
	Sunderland Insurance Services, Inc. May 1, 2014		204		9.2		2.4		—		0.6		—		12.2		—
	Plus Companies, Inc. June 1, 2014		221		9.3		3.4		—		0.8		—		13.5		—
	Tri-State General Insurance Agency, Inc. June 1, 2014		47		2.2		0.6		—		0.1		—		2.9		—
	Crombie/OAMPS (CO) June 16, 2014		—		—		951.5		—		—		—		951.5		—
	Foundation Strategies, Inc. July 1, 2014		46		2		0.7		—		0.1		0.4		3.2		3
	Insurance Point, LLC (IPL) July 1, 2014		255		11.2		3.9		—		0.5		2.5		18.1		24.4
	Trip Mate, Inc. (TMI) July 1, 2014		209		8.4		3.9		—		1		5.9		19.2		12.5
	Noraxis Capital Corporation (NCC) July 2, 2014		—		—		413.3		—		1.9		—		415.2		—
	Cowles & Connell (CC) August 1, 2014		331		14.8		4.2		—		0.8		—		19.8		—
	Denman Consulting Services August 1, 2014		40		1.7		0.6		—		0.1		0.3		2.7		1.6
	Minvielle & Chastanet Insurance Brokers August 8, 2014		—		—		5		—		—		3		8		5
	Baker Tilly Financial Management Limited August 29, 2014		185		8.7		2.3		—		0.7		4.6		16.3		5.4
	Benfield Group September 1, 2014		82		3.8		1.1		—		0.1		0.9		5.9		3.5
	Everett James, Inc. September 1, 2014		52		2.4		0.7		—		0.1		0.8		4		4
	Hagedorn & Company September 1, 2014		281		11.5		—		—		1.3		—		12.8		—
	Parmia Pty Ltd. September 1, 2014		—		—		1.7		—		—		1.2		2.9		1.2
	Eighteen other acquisitions completed in 2014		305		13.2		17.4		—		0.9		9.8		41.3		19
			3,573	$	156.8	$	1,836.90	$	—	$	32.5	$	52.1	$	2,078.30	$	132.5
	On April 1, 2014, we closed on an agreement to acquire the Oval Group of Companies (which we refer to as Oval). Under the agreement, we agreed to purchase all of the outstanding equity of Oval for net cash consideration of approximately $338.0 million. Oval was an independent commercial insurance broker operating out of 24 offices throughout the U.K., with over 1,000 employees.
	On April 16, 2014, we closed on a secondary public offering of our common stock whereby 21.85 million shares of our stock were issued for net proceeds, after underwriting discounts and other expenses related to this offering, of $911.4 million. We used the net proceeds of the offering to fund acquisitions.
	On June 16, 2014, we closed on an agreement to acquire the Wesfarmers Insurance Brokerage operations (which we refer to as Crombie/OAMPS). The Crombie/OAMPS transaction, which includes the OAMPS businesses in Australia and the U.K., Crombie in New Zealand and the associated premium funding operations. Under the agreement, we agreed to purchase all of the outstanding shares of these three operating companies for net cash consideration of approximately $952.0 million, plus any adjustments required based on a final net current assets amount acquired. The Crombie/OAMPS operations have approximately 1,700 employees operating out of more than 50 offices across Australia, New Zealand and the U.K. We entered into a AU$400.0 million foreign currency derivative investment contract that we executed on April 16, 2014 in connection with the signing of the agreement to acquire the Crombie/OAMPS operations. The derivative investment contract was exercised on June 16, 2014 and we recorded a pretax gain of $1.9 million related to this derivative investment contract. Per the terms of the purchase agreement for the Crombie/OAMPS transaction, on October 14, 2014, we paid the sellers an additional $35.3 million related to a true-up of the excess of net current assets over target amount as defined in the agreement based on the final acquisition date balance sheet. That amount has not been recorded in the consolidated balance sheet as of September 30, 2014 or reflected in the table above.
	On July 2, 2014, we closed on an agreement to acquire Noraxis Capital Corporation (which we refer to as Noraxis), paying cash consideration of approximately $420.0 million for approximately 89% of the equity of Noraxis. The remaining equity is held by various management employees of Noraxis. Noraxis generated nearly CN$125.0 million in revenue for the year ended December 31, 2013, and has more than 650 employees in offices across Alberta, Manitoba, New Brunswick, Nova Scotia and Ontario.
	Common shares issued in connection with acquisitions are valued at closing market prices as of the effective date of the applicable acquisition. We record escrow deposits that are returned to us as a result of adjustments to net assets acquired as reductions of goodwill when the escrows are settled. The maximum potential earnout payables disclosed in the foregoing table represent the maximum amount of additional consideration that could be paid pursuant to the terms of the purchase agreement for the applicable acquisition. The amounts recorded as earnout payables, which are primarily based upon the estimated future operating results of the acquired entities over a two- to three-year period subsequent to the acquisition date, are measured at fair value as of the acquisition date and are included on that basis in the recorded purchase price consideration in the foregoing table. We will record subsequent changes in these estimated earnout obligations, including the accretion of discount, in our consolidated statement of earnings when incurred.
	The fair value of these earnout obligations is based on the present value of the expected future payments to be made to the sellers of the acquired entities in accordance with the provisions outlined in the respective purchase agreements, which is a Level 3 fair value measurement. In determining fair value, we estimated the acquired entity’s future performance using financial projections developed by management for the acquired entity and market participant assumptions that were derived for revenue growth and/or profitability. Revenue growth rates generally ranged from 5.0% to 10.0% for our 2014 acquisitions. We estimated future payments using the earnout formula and performance targets specified in each purchase agreement and these financial projections. We then discounted these payments to present value using a risk-adjusted rate that takes into consideration market-based rates of return that reflect the ability of the acquired entity to achieve the targets. These discount rates generally ranged from 8.5% to 9.5% for all of our 2014 acquisitions. Changes in financial projections, market participant assumptions for revenue growth and/or profitability, or the risk-adjusted discount rate, would result in a change in the fair value of recorded earnout obligations.
	During the three-month periods ended September 30, 2014 and 2013, we recognized $3.9 million and $2.9 million, respectively, of expense in our consolidated statement of earnings related to the accretion of the discount recorded for earnout obligations in connection with our acquisitions. During the nine-month periods ended September 30, 2014 and 2013, we recognized $10.6 million and $8.7 million, respectively, of expense in our consolidated statement of earnings related to the accretion of the discount recorded for earnout obligations in connection with our acquisitions. In addition, during the three-month periods ended September 30, 2014 and 2013, we recognized $0.6 million of expense and $3.3 million of income, respectively, related to net adjustments in the estimated fair value of earnout obligations in connection with revised projections of future performance for 17 and 20 acquisitions, respectively. During the nine-month periods ended September 30, 2014 and 2013, we recognized $6.0 million of expense and $7.2 million of income, respectively, related to net adjustments in the estimated fair value of earnout obligations in connection with revised projections of future performance for 49 and 53 acquisitions, respectively. The aggregate amount of maximum earnout obligations related to acquisitions made in 2009 and subsequent years was $517.9 million as of September 30, 2014, of which $185.4 million was recorded in our consolidated balance sheet as of September 30, 2014, based on the estimated fair value of the expected future payments to be made.
	The following is a summary of the estimated fair values of the net assets acquired at the date of each acquisition made in the nine-month period ended September 30, 2014 (in millions):
		OGC		HIM		MGA		CO		IPL		TMI		NCC		CC		Thirty-Seven		Total
																		Other
																		Acquisitions
	Cash	$	23.1	$	2.9	$	0.2	$	26.6	$	2.7	$	—	$	10.2	$	0.6	$	1.2	$	67.5
	Other current assets		129.6		4.9		8.9		695.5		0.4		7		73		9.1		25.3		953.7
	Fixed assets		2.1		0.3		0.8		17.1		—		1.9		4.9		0.1		1.6		28.8
	Noncurrent assets		—		—		—		7		—		—		3.5		—		4.1		14.6
	Goodwill		245.7		14.8		27		535.9		2.5		5.9		291		7.8		92.7		1,223.30
	Expiration lists		129.9		20.3		33.2		325.3		15.3		10.3		139.7		11.2		105.5		790.7
	Non-compete agreements		1		1.3		0.3		4.2		0.2		0.1		4		—		0.9		12
	Trade names		0.6		—		—		4.2		—		—		4		0.4		0.8		10
	Total assets acquired		532		44.5		70.4		1,615.80		21.1		25.2		530.3		29.2		232.1		3,100.60
	Current liabilities		129.5		6.8		4.1		490		2.9		5.8		72.5		9.4		25.6		746.6
	Noncurrent liabilities		52.3		—		—		174.3		0.1		0.2		42.6		—		6.2		275.7
	Total liabilities assumed		181.8		6.8		4.1		664.3		3		6		115.1		9.4		31.8		1,022.30
	Total net assets acquired	$	350.2	$	37.7	$	66.3	$	951.5	$	18.1	$	19.2	$	415.2	$	19.8	$	200.3	$	2,078.30
	Among other benefits, these acquisitions allow us to expand into desirable geographic locations, further extend our presence in the retail and wholesale insurance brokerage services and risk management industries and increase the volume of general services currently provided. The excess of the purchase price over the estimated fair value of the tangible net assets acquired at the acquisition date was allocated to goodwill, expiration lists, non-compete agreements and trade names in the amounts of $1,223.3 million, $790.7 million, $12.0 million and $10.0 million, respectively, within the brokerage segment.
	Provisional estimates of fair value are established at the time of each acquisition and are subsequently reviewed within the first year of operations subsequent to the acquisition date to determine the necessity for adjustments. The fair value of the tangible assets and liabilities for each applicable acquisition at the acquisition date approximated their carrying values. The fair value of expiration lists was established using the excess earnings method, which is an income approach based on estimated financial projections developed by management for each acquired entity using market participant assumptions. Revenue growth and attrition rates generally ranged from 2.0% to 3.0% and 5.0% to 11.5%, respectively, for our 2014 and 2013 acquisitions, for which a valuation was performed in the nine-month period ended September 30, 2014. We estimate the fair value as the present value of the benefits anticipated from ownership of the subject customer list in excess of returns required on the investment in contributory assets necessary to realize those benefits. The rate used to discount the net benefits was based on a risk-adjusted rate that takes into consideration market-based rates of return and reflects the risk of the asset relative to the acquired business. These discount rates generally ranged from 12.5% to 14.5% for our 2014 and 2013 acquisitions, for which a valuation was performed in the nine-month period ended September 30, 2014. The fair value of non-compete agreements was established using the profit differential method, which is an income approach based on estimated financial projections developed by management for the acquired company using market participant assumptions and various non-compete scenarios.
	Expiration lists, non-compete agreements and trade names related to our acquisitions are amortized using the straight-line method over their estimated useful lives (three to fifteen years for expiration lists, one to five years for non-compete agreements and three to fifteen years for trade names), while goodwill is not subject to amortization. We use the straight-line method to amortize these intangible assets because the pattern of their economic benefits cannot be reasonably determined with any certainty. We review all of our intangible assets for impairment periodically (at least annually) and whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. In reviewing intangible assets, if the fair value is less than the carrying amount of the respective (or underlying) asset, an indicator of impairment would exist and further analysis would be required to determine whether or not a loss would need to be charged against current period earnings. Based on the results of impairment reviews during the three-month and nine-month periods ended September 30, 2014, we wrote off $0.6 million and $1.2 million, respectively, of amortizable intangible assets related to the brokerage segment. Based on the results of impairment reviews during the nine-month period ended September 30, 2013, we wrote off $2.2 million, respectively, of amortizable intangible assets related to the brokerage segment.
Of the $790.7 million of expiration lists, $12.0 million of non-compete agreements and $10.0 million of trade names related to our acquisitions made during the nine-month period ended September 30, 2014, $602.8 million, $10.5 million and $8.9 million, respectively, is not expected to be deductible for income tax purposes. Accordingly, we recorded a deferred tax liability of $109.0 million, and a corresponding amount of goodwill, in the nine-month period ended September 30, 2014 related to nondeductible amortizable intangible assets.
Our consolidated financial statements for the nine-month period ended September 30, 2014 include the operations of the acquired entities from their respective acquisition dates. The following is a summary of the unaudited pro forma historical results, as if these entities had been acquired at January 1, 2013 (in millions, except per share data):
	Three-month period ended				Nine-month period ended
	September 30,				September 30,
	2014		2013		2014		2013
Total revenues	$	1,293.00	$	1,004.60	$	3,681.00	$	2,833.40
Net earnings		94.2		87		271.1		256.8
Basic net earnings per share		0.59		0.56		1.69		1.68
Diluted net earnings per share		0.58		0.56		1.68		1.66
The unaudited pro forma results above have been prepared for comparative purposes only and do not purport to be indicative of the results of operations which actually would have resulted had these acquisitions occurred at January 1, 2013, nor are they necessarily indicative of future operating results. Annualized revenues of the businesses acquired during the nine-month period ended September 30, 2014 totaled approximately $693.6 million. For the nine-month period ended September 30, 2014, total revenues and net earnings recorded in our unaudited consolidated statement of earnings related to our acquisitions made during the nine-month period ended September 30, 2014 in the aggregate, were $245.7 million and $27.3 million, respectively.

Intangible_Assets

Intangible Assets	9 Months Ended
	Sep. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Intangible Assets	'
	4. Intangible Assets
	The carrying amount of goodwill at September 30, 2014 and December 31, 2013 allocated by domestic and foreign operations is as follows (in millions):
		Brokerage			Risk			Corporate		Total
					Management
	At September 30, 2014
	United States	$	1,572.00		$	20.2		$	—	$	1,592.20
	United Kingdom		831.2			2.2			—		833.4
	Canada		307.6			—			—		307.6
	Australia		271.4			—			—		271.4
	Other foreign, principally New Zealand		291.6			—			—		291.6
	Total goodwill - net	$	3,273.80		$	22.4		$	—	$	3,296.20
	At December 31, 2013
	United States	$	1,449.60		$	20.2		$	—	$	1,469.80
	United Kingdom		582.8			2.1			—		584.9
	Canada		26.8			—			—		26.8
	Australia		37.1			—			—		37.1
	Other foreign, principally New Zealand		26.6			—			—		26.6
	Total goodwill - net	$	2,122.90		$	22.3		$	—	$	2,145.20
	The changes in the carrying amount of goodwill for the nine-month period ended September 30, 2014 are as follows (in millions):
		Brokerage			Risk			Corporate		Total
					Management
	Balance as of December 31, 2013	$	2,122.90		$	22.3		$	—	$	2,145.20
	Goodwill acquired during the period		1,223.30			—			—		1,223.30
	Goodwill adjustments due to appraisals and other acquisition adjustments		(27.7	)		—			—		(27.7	)
	Goodwill written-off related to sales of business		(0.6	)		—			—		(0.6	)
	Foreign currency translation adjustments during the period		(44.1	)		0.1			—		(44.0	)
	Balance as of September 30, 2014	$	3,273.80		$	22.4		$	—	$	3,296.20
	Major classes of amortizable intangible assets at September 30, 2014 and December 31, 2013 consist of the following (in millions):
		September 30,			December 31,
		2014			2013
	Expiration lists	$	2,409.00		$	1,563.50
	Accumulated amortization - expiration lists		(675.9	)		(511.3	)
			1,733.10			1,052.20
	Non-compete agreements		44			37.3
	Accumulated amortization - non-compete agreements		(28.4	)		(25.9	)
			15.6			11.4
	Trade names		31.8			22.1
	Accumulated amortization - trade names		(9.4	)		(6.9	)
			22.4			15.2
	Net amortizable assets	$	1,771.10		$	1,078.80
	Estimated aggregate amortization expense for each of the next five years is as follows:
	2014 (remaining three months)	$	53.2
	2015		208.8
	2016		203.1
	2017		193.1
	2018		180.3
	Total	$	838.5

Credit_and_Other_Debt_Agreemen

Credit and Other Debt Agreements	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Credit and Other Debt Agreements	'
	5. Credit and Other Debt Agreements
	Note Purchase Agreements - We are a party to an amended and restated note purchase agreement dated December 19, 2007, with certain accredited institutional investors, pursuant to which we issued and sold $300.0 million in aggregate principal amount of our 6.44% Senior Notes, Series B, due August 3, 2017, in a private placement. These notes require semi-annual payments of interest that are due in February and August of each year.
	We are a party to a note purchase agreement dated November 30, 2009, with certain accredited institutional investors, pursuant to which we issued and sold $150.0 million in aggregate principal amount of our 5.85% Senior Notes, Series C, due in three equal installments on November 30, 2016, November 30, 2018 and November 30, 2019, in a private placement. These notes require semi-annual payments of interest that are due in May and November of each year.
	We are a party to a note purchase agreement dated February 10, 2011, with certain accredited institutional investors, pursuant to which we issued and sold $75.0 million in aggregate principal amount of our 5.18% Senior Notes, Series D, due February 10, 2021 and $50.0 million in aggregate principal amount of our 5.49% Senior Notes, Series E, due February 10, 2023, in a private placement. These notes require semi-annual payments of interest that are due in February and August of each year.
	We are a party to a note purchase agreement dated July 10, 2012, with certain accredited institutional investors, pursuant to which we issued and sold $50.0 million in aggregate principal amount of our 3.99% Senior Notes, Series F, due July 10, 2020, in a private placement. These notes require semi-annual payments of interest that are due in January and July of each year.
	We are a party to a note purchase agreement dated June 14, 2013, with certain accredited institutional investors, pursuant to which we issued and sold $200.0 million in aggregate principal amount of our 3.69% Senior Notes, Series G, due June 14, 2022, in a private placement. These notes require semi-annual payments of interest that are due in June and December of each year.
	We are a party to a note purchase agreement dated December 20, 2013, with certain accredited institutional investors, pursuant to which we issued and sold $325.0 million in aggregate principal amount of our 4.58% Senior Notes, Series H, due February 27, 2024, $175.0 million in aggregate principal amount of our 4.73% Senior Notes, Series I, due February 27, 2026 and $100.0 million in aggregate principal amount of our 4.98% Senior Notes, Series J, due February 27, 2029. These notes require semi-annual payments of interest that are due in February and August of each year. The funding of this note purchase agreement occurred on February 27, 2014. We incurred approximately $1.4 million of debt acquisition costs that was capitalized and will be amortized on a pro rata basis over the life of the debt.
	We are a party to a note purchase agreement dated June 24, 2014, with certain accredited institutional investors, pursuant to which we issued and sold $50.0 million in aggregate principal amount of our 2.80% Senior Notes, Series K, due 2018, $50.0 million in aggregate principal amount of our 3.20% Senior Notes, Series L, due 2019, $50.0 million in aggregate principal amount of our 3.48% Senior Notes, Series M, due 2020, $200.0 million in aggregate principal amount of our 4.13% Senior Notes, Series N, due 2023, $200.0 million in aggregate principal amount of our 4.31% Senior Notes, Series O, due 2025 and $150.0 million in aggregate principal amount of our 4.36% Senior Notes, Series P, due 2026. These notes require semi-annual payments of interest that are due in June and December of each year. We incurred approximately $2.6 million of debt acquisition costs that was capitalized and will be amortized on a pro rata basis over the life of the debt.
	Under the terms of the note purchase agreements described above, we may redeem the notes at any time, in whole or in part, at 100% of the principal amount of such notes being redeemed, together with accrued and unpaid interest and a “make-whole amount.” The “make-whole amount” is derived from a net present value computation of the remaining scheduled payments of principal and interest using a discount rate based on U.S. Treasury yields plus 0.5% and is designed to compensate the purchasers of the notes for their investment risk in the event prevailing interest rates at the time of prepayment are less favorable than the interest rates under the notes. We do not currently intend to prepay any of the notes.
	The note purchase agreements described above contain customary provisions for transactions of this type, including representations and warranties regarding us and our subsidiaries and various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of September 30, 2014. The note purchase agreements also provide customary events of default, generally with corresponding grace periods, including, without limitation, payment defaults with respect to the notes, covenant defaults, cross-defaults to other agreements evidencing our or our subsidiaries’ indebtedness, certain judgments against us or our subsidiaries and events of bankruptcy involving us or our material subsidiaries.
	The notes issued under the note purchase agreements are senior unsecured obligations of ours and rank equal in right of payment with our Credit Agreement discussed below.
	Credit Agreement - On September 19, 2013, we entered into a $600.0 million unsecured multicurrency credit agreement (which we refer to as the Credit Agreement), which expires on September 19, 2018, with a group of fifteen financial institutions. The Credit Agreement provides for a revolving credit commitment of up to $600.0 million, of which up to $75.0 million may be used for issuances of standby or commercial letters of credit and up to $50.0 million may be used for the making of swing loans, as defined in the Credit Agreement. We may from time to time request, subject to certain conditions, an increase in the revolving credit commitment up to a maximum aggregate revolving credit commitment of $850.0 million.
	The Credit Agreement provides that we may elect that each borrowing in U.S. dollars be either base rate loans or Eurocurrency loans, as defined in the Credit Agreement. All loans denominated in currencies other than U.S. dollars will be Eurocurrency loans. Interest rates on base rate loans and outstanding drawings on letters of credit in U.S. dollars under the Credit Agreement are based on the base rate, as defined in the Credit Agreement. Interest rates on Eurocurrency loans or outstanding drawings on letters of credit in currencies other than U.S. dollars are based on an adjusted London Interbank Offered Rate (which we refer to as LIBOR), as defined in the Credit Agreement, plus a margin of 0.85%, 0.95%, 1.05%, 1.25% or 1.45%, depending on the financial leverage ratio we maintain. Interest rates on swing loans are based, at our election, on either the base rate, as defined in the Credit Agreement, or such alternate rate as may be quoted by the lead lender. The annual facility fee related to the Credit Agreement is 0.15%, 0.175%, 0.20%, 0.25% or 0.30% of the used and unused portions of the revolving credit commitment, depending on the financial leverage ratio we maintain. In connection with entering into the Credit Agreement, we incurred approximately $2.1 million of debt acquisition costs that were capitalized and will be amortized on a pro rata basis over the term of the Credit Agreement.
	The terms of the Credit Agreement include various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of September 30, 2014. The Credit Agreement also includes customary provisions for transactions of this type, including events of default, with corresponding grace periods and cross-defaults to other agreements evidencing our indebtedness.
	At September 30, 2014, $20.6 million of letters of credit (for which we had $9.3 million of liabilities recorded at September 30, 2014) were outstanding under the Credit Agreement. There were $147.0 million of borrowings outstanding under the Credit Agreement at September 30, 2014. Accordingly, as of September 30, 2014, $432.4 million remained available for potential borrowings under the Credit Agreement, of which $54.4 million was available for additional letters of credit.
	Premium Financing Debt Facility - On June 16, 2014 we entered into a Syndicated Facility Agreement, revolving loan facility, which we refer to as the Premium Financing Debt Facility, that provides funding for the three acquired Australian (AU) and New Zealand (NZ) premium finance subsidiaries. See Note 3 “Business Combinations.” The Premium Financing Debt Facility is comprised of: (i) Facility B is separate AU$150.0 million and NZ$35.0 million tranches, (ii) Facility C is an AU$25.0 million equivalent multi-currency overdraft tranche and (iii) Facility D is a NZ$15.0 million equivalent multi-currency overdraft tranche. The Premium Financing Debt Facility expires June 15, 2016.
	The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.65%. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.85%. The annual fee for Facility B is 0.7425% of the undrawn commitments for the two tranches of the facility. The annual fee for Facilities C and D is 0.80% of the total commitments of the facilities. In connection with entering into the Premium Financing Debt Facility, we incurred an upfront fee of 0.30% of the principal amount of the committed facilities.
	The terms of our Premium Financing Debt Facility include various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of September 30, 2014. The Premium Financing Debt Facility also includes customary provisions for transactions of this type, including events of default, with corresponding grace periods and cross-defaults to other agreements evidencing our indebtedness. Facilities B, C and D are secured by the premium finance receivables of the Australian and New Zealand premium finance subsidiaries.
	At September 30, 2014, AU$133.0 million and NZ$22.0 million of borrowings were outstanding under Facility B, AU$5.2 million of borrowings were outstanding under Facility C and NZ$11.5 million of borrowings were outstanding under Facility D. Accordingly, as of September 30, 2014, AU$17.0 million and NZ$13.0 million remained available for potential borrowing under Facility B, and AU$19.8 million and NZ$3.5 million under Facilities C and D, respectively.
	See Note 12 to these unaudited consolidated financial statements for additional discussion on our contractual obligations and commitments as of September 30, 2014.
	The following is a summary of our corporate and other debt (in millions):
		September 30,		December 31,
		2014		2013
	Note Purchase Agreements:
	Semi-annual payments of interest, fixed rate of 6.26%, balloon due 2014	$	—	$	100
	Semi-annual payments of interest, fixed rate of 6.44%, balloon due 2017		300		300
	Semi-annual payments of interest, fixed rate of 2.80%, balloon due 2018		50		—
	Semi-annual payments of interest, fixed rate of 3.20%, balloon due 2019		50		—
	Semi-annual payments of interest, fixed rate of 5.85%, $50 million due in 2016, 2018 and 2019		150		150
	Semi-annual payments of interest, fixed rate of 3.99%, balloon due 2020		50		50
	Semi-annual payments of interest, fixed rate of 3.48%, balloon due 2020		50		—
	Semi-annual payments of interest, fixed rate of 5.18%, balloon due 2021		75		75
	Semi-annual payments of interest, fixed rate of 3.69%, balloon due 2022		200		200
	Semi-annual payments of interest, fixed rate of 5.49%, balloon due 2023		50		50
	Semi-annual payments of interest, fixed rate of 4.13%, balloon due 2023		200		—
	Semi-annual payments of interest, fixed rate of 4.58%, balloon due 2024		325		—
	Semi-annual payments of interest, fixed rate of 4.31%, balloon due 2025		200		—
	Semi-annual payments of interest, fixed rate of 4.73%, balloon due 2026		175		—
	Semi-annual payments of interest, fixed rate of 4.36%, balloon due 2026		150		—
	Semi-annual payments of interest, fixed rate of 4.98%, balloon due 2029		100		—
	Total Note Purchase Agreements		2,125.00		925
	Credit Agreement:
	Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires September 19, 2018		147		530.5
	Premium Financing Debt Facility - expires June 15, 2016:
	Periodic payments of interest and principal, Interbank rates plus 1.65% for Facility B; plus 0.85% for Facilities C and D
	Facility B
	AUD denominated tranche		117.7		—
	NZD denominated tranche		17.7		—
	Facility C and D
	AUD denominated tranche		4.6		—
	NZD denominated tranche		9.2		—
	Total Premium Financing Debt Facility		149.2		—
	Total corporate and other debt	$	2,421.20	$	1,455.50
	The fair value of the $2,125.0 million in debt under the note purchase agreements at September 30, 2014 was $2,253.5 million due to the long-term duration and fixed interest rates associated with these debt obligations. No active or observable market exists for our private placement long-term debt. Therefore, the estimated fair value of this debt is based on discounted future cash flows, which is a Level 3 fair value measurement, using current interest rates available for debt with similar terms and remaining maturities. See Note 1, Fair Value of Financial Instruments, to our consolidated financial statements included in Item 8 of our Annual Report on Form 10-K for the year ended December 31, 2013. To estimate an all-in interest rate for discounting, we obtain market quotes for notes with the same terms as ours, which we have deemed to be the closest approximation of current market rates. The estimated fair value of the $147.0 million of borrowings outstanding under our Credit Agreement approximates their carrying value due to their short-term duration and variable interest rates. The estimated fair value of the $149.2 million of borrowings outstanding under our Premium Financing Debt Facility approximates their carrying value due to their short-term duration and variable interest rates.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	6. Earnings Per Share
	The following table sets forth the computation of basic and diluted net earnings per share (in millions, except per share data):
		Three-month period ended				Nine-month period ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net earnings	$	93.6	$	74.6	$	251.9	$	208.6
	Weighted average number of common shares outstanding		160.2		129.8		149.6		127.7
	Dilutive effect of stock options using the treasury stock method		1.3		1.5		1.4		1.6
	Weighted average number of common and common equivalent shares outstanding		161.5		131.3		151		129.3
	Basic net earnings per share	$	0.58	$	0.57	$	1.68	$	1.63
	Diluted net earnings per share	$	0.58	$	0.57	$	1.67	$	1.61
	Options to purchase 1.9 million and 1.7 million shares of common stock were outstanding at September 30, 2014 and 2013, respectively, but were not included in the computation of the dilutive effect of stock options for the three-month periods then ended. Options to purchase 1.4 million and 1.2 million shares of common stock were outstanding at September 30, 2014 and 2013, respectively, but were not included in the computation of the dilutive effect of stock options for the nine-month periods then ended. These stock options were excluded from the computation because the options’ exercise prices were greater than the average market price of our common shares during the respective period, and therefore would be anti-dilutive to earnings per share under the treasury stock method.

Stock_Option_Plans

Stock Option Plans	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Stock Option Plans	'
	7. Stock Option Plans
	Long-Term Incentive Plan
	On May 13, 2014, our stockholders approved the Arthur J. Gallagher 2014 Long-Term Incentive Plan (which we refer to as the LTIP), which replaced our previous stockholder-approved Arthur J. Gallagher & Co. 2011 Long-Term Incentive Plan (which we refer to as the 2011 LTIP). The LTIP term began May 13, 2014 and terminates on the date of the annual meeting of stockholders in 2021, unless terminated earlier by our board of directors. All of our officers, employees and non-employee directors are eligible to receive awards under the LTIP. The compensation committee of our board of directors determines the participants under the LTIP. The LTIP provides for non-qualified and incentive stock options, stock appreciation rights, restricted stock, restricted stock units and performance units, any or all of which may be made contingent upon the achievement of performance criteria. A stock appreciation right entitles the holder to receive, upon exercise and subject to withholding taxes, cash or shares of our common stock (which may be restricted stock) with a value equal to the difference between the fair market value of our common stock on the exercise date and the base price of the stock appreciation right. Subject to the LTIP limits, the compensation committee has the discretionary authority to determine the size of an award.
	Shares of our common stock available for issuance under the LTIP include authorized and unissued shares of common stock or authorized and issued shares of common stock reacquired and held as treasury shares or otherwise, or a combination thereof. The number of available shares is reduced by the aggregate number of shares that become subject to outstanding awards granted under the LTIP. To the extent that shares subject to an outstanding award granted under either the LTIP or the 2011 LTIP are not issued or delivered by reason of the expiration, termination, cancellation or forfeiture of such award or by reason of the settlement of such award in cash, then such shares will again be available for grant under the LTIP. Shares withheld to satisfy tax withholding requirements upon the vesting of awards other than stock options and stock appreciation rights will also be available for grant under the LTIP. Shares that are subject to a stock appreciation right and were not issued upon the net settlement or net exercise of such stock appreciation right, shares that are used to pay the exercise price of an option, shares delivered to or withheld by us to pay withholding taxes related to stock options or stock appreciation rights, and shares that are purchased on the open market with the proceeds of an option exercise, may not again be made available for issuance.
	The maximum number of shares available under the LTIP for restricted stock, restricted stock unit awards and performance unit awards settled with stock (i.e., all awards other than stock options and stock appreciation rights) is 2.0 million at September 30, 2014. To the extent necessary to be qualified performance-based compensation under Section 162(m) of the Internal Revenue Code (which we refer to as the IRC): (i) the maximum number of shares with respect to which options or stock appreciation rights or a combination thereof that may be granted during any fiscal year to any person is 200,000; (ii) the maximum number of shares with respect to which performance-based restricted stock or restricted stock units that may be granted during any fiscal year to any person is 100,000; (iii) the maximum amount that may be payable with respect to cash-settled performance units granted during any fiscal year to any person is $5.0 million; and (iv) the maximum number of shares with respect to which stock-settled performance units may be granted during any fiscal year to any person is 100,000.
	The LTIP provides for the grant of stock options, which may be either tax-qualified incentive stock options or non-qualified options and stock appreciation rights. The compensation committee determines the period for the exercise of a non-qualified stock option, tax-qualified incentive stock option or stock appreciation right, provided that no option can be exercised later than seven years after its date of grant. The exercise price of a non-qualified stock option or tax-qualified incentive stock option and the base price of a stock appreciation right cannot be less than 100% of the fair market value of a share of our common stock on the date of grant, provided that the base price of a stock appreciation right granted in tandem with an option will be the exercise price of the related option.
	Upon exercise, the option exercise price may be paid in cash, by the delivery of previously owned shares of our common stock, through a net-exercise arrangement, or through a broker-assisted cashless exercise arrangement. The compensation committee determines all of the terms relating to the exercise, cancellation or other disposition of an option or stock appreciation right upon a termination of employment, whether by reason of disability, retirement, death or any other reason. Stock option and stock appreciation right awards under the LTIP are non-transferable.
	On March 12, 2014, the compensation committee granted 1,923,000 options under the 2011 LTIP to our officers and key employees that become exercisable at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2017, 2018 and 2019, respectively. On March 13, 2013, the compensation committee granted 1,665,000 options under the 2011 LTIP to our officers and key employees that become exercisable at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2016, 2017 and 2018, respectively. The 2014 and 2013 options expire seven years from the date of grant, or earlier in the event of certain terminations of employment. For certain of our executive officers age 55 or older, stock options awarded in 2014 and 2013 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant.
	Other Information
	All of our stock option plans provide for the immediate vesting of all outstanding stock option grants in the event of a change in control of our company, as defined in the applicable plan documents.
	During the three-month periods ended September 30, 2014 and 2013, we recognized $2.7 million and $2.2 million, respectively, of compensation expense related to our stock option grants. During the nine-month periods ended September 30, 2014 and 2013, we recognized $6.7 million and $5.4 million, respectively, of compensation expense related to our stock option grants.
	For purposes of expense recognition, the estimated fair values of the stock option grants are amortized to expense over the options’ vesting period. We estimated the fair value of stock options at the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:
		2014				2013
	Expected dividend yield		3	%			3.5	%
	Expected risk-free interest rate		1.8	%			1.2	%
	Volatility		28.9	%			29.6	%
	Expected life (in years)		5.5				6
	Option valuation models require the input of highly subjective assumptions including the expected stock price volatility. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options which have no vesting restrictions and are fully transferable. Because our employee and director stock options have characteristics significantly different from those of traded options, and because changes in the selective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models do not necessarily provide a reliable single measure of the fair value of our employee and non-employee director stock options. The weighted average fair value per option for all options granted during the nine-month periods ended September 30, 2014 and 2013, as determined on the grant date using the Black-Scholes option pricing model, was $9.66 and $7.51, respectively.
	The following is a summary of our stock option activity and related information for 2014 (in millions, except exercise price and year data):
		Nine-month period ended September 30, 2014
		Shares				Weighted				Weighted				Aggregate
		Under				Average				Average				Intrinsic
		Option				Exercise				Remaining				Value
						Price				Contractual
										Term
										(in years)
	Beginning balance		8.3			$	31.35
	Granted		1.9				46.86
	Exercised		(1.5	)			28.94
	Forfeited or canceled		(0.1	)			28.56
	Ending balance		8.6			$	35.31				4.15			$	89.3
	Exercisable at end of period		2.8			$	26.96				2.08			$	51.8
	Ending vested and expected to vest		8.4			$	35.18				4.12			$	88.7
	Options with respect to 9.2 million shares (less any shares of restricted stock issued under the LTIP - see Note 9 to these unaudited consolidated financial statements) were available for grant under the LTIP at September 30, 2014.
	The total intrinsic value of options exercised during the nine-month periods ended September 30, 2014 and 2013 was $26.6 million and $28.8 million, respectively. As of September 30, 2014, we had approximately $31.6 million of total unrecognized compensation expense related to nonvested options. We expect to recognize that expense over a weighted average period of approximately four years.
	Other information regarding stock options outstanding and exercisable at September 30, 2014 is summarized as follows (in millions, except exercise price and year data):
				Options Outstanding												Options Exercisable
	Range of Exercise Prices			Number				Weighted				Weighted				Number		Weighted
				Outstanding				Average				Average				Exercisable		Average
								Remaining				Exercise						Exercise
								Contractual				Price						Price
								Term
								(in years)
	$    21.28   -  $   27.25				2.4				1.82			$	25.81				2	$	25.8
	27.35   -        35.71				2.6				3.76				33.04				0.8		29.86
	35.95   -        39.17				1.7				5.45				39.15				—		—
	46.16   -        46.87				1.9				6.45				46.87				—		—
	$    21.28   -  $   46.87				8.6				4.15			$	35.31				2.8	$	26.96

Deferred_Compensation

Deferred Compensation	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Deferred Compensation	'
	8. Deferred Compensation
	We have a Deferred Equity Participation Plan (which we refer to as the Age 62 Plan), which is a non-qualified plan that generally provides for distributions to certain of our key executives when they reach age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement. Under the provisions of the Age 62 Plan, we typically contribute cash in an amount approved by compensation committee to the rabbi trust on behalf of the executives participating in the Age 62 Plan, and instruct the trustee to acquire a specified number of shares of our common stock on the open market or in privately negotiated transactions based on participant elections. Distributions under the Age 62 Plan may not normally be made until the participant reaches age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) and are subject to forfeiture in the event of voluntary termination of employment prior to then. All contributions to the plan deemed to be invested in shares of our common stock are distributed in the form of our common stock and all other distributions are paid in cash.
	Our common stock that is issued to or purchased by the rabbi trust as a contribution under the Age 62 Plan is valued at historical cost, which equals its fair market value at the date of grant or date of purchase. When common stock is issued or purchased, we record an unearned deferred compensation obligation as a reduction of capital in excess of par value in the accompanying consolidated balance sheet, which is amortized to compensation expense ratably over the vesting period of the participants. Future changes in the fair market value of our common stock owed to the participants do not have any impact on the amounts recorded in our consolidated financial statements.
	In the first quarter of each of 2014 and 2013, the compensation committee approved $9.2 million and $8.0 million, respectively, of awards in the aggregate to certain key executives under the Age 62 Plan that were contributed to the rabbi trust in first quarter 2014 and second quarter 2013, respectively. We contributed cash to the rabbi trust and instructed the trustee to acquire a specified number of shares of our common stock on the open market to fund these 2014 and 2013 awards. During the three-month periods ended September 30, 2014 and 2013, we charged $2.4 million and $2.0 million, respectively, to compensation expense related to these awards. During the nine-month periods ended September 30, 2014 and 2013, we charged $5.6 million and $5.3 million, respectively, to compensation expense related to these awards.
	At September 30, 2014 and December 31, 2013, we recorded $30.7 million (related to 2.3 million shares) and $26.3 million (related to 2.1 million shares), respectively, of unearned deferred compensation as a reduction of capital in excess of par value in the accompanying consolidated balance sheet. The total intrinsic value of our unvested equity based awards under the plan at September 30, 2014 and December 31, 2013 was $102.5 million and $96.4 million, respectively. During the nine-month periods ended September 30, 2014 and 2013, cash and equity awards with an aggregate fair value of $1.3 million and $0.7 million, respectively, were vested and distributed to executives under the Age 62 Plan.
	We have a Deferred Cash Participation Plan (which we refer to as the DCPP), which is a non-qualified deferred compensation plan for certain key employees, other than executive officers, that generally provides for distributions no sooner than five years from the date of awards, with full vesting after thirteen months from the date of awards. Under the provisions of the DCPP, we typically contribute cash in an amount approved by compensation committee to the rabbi trust on behalf of the executives participating in the DCPP, and instruct the trustee to acquire a specified number of shares of our common stock on the open market or in privately negotiated transactions based on participant elections. In the first quarter of each of 2014 and 2013, the compensation committee approved $2.9 million and $2.7 million, respectively, of awards in the aggregate to certain key executives under the DCPP that were contributed to the rabbi trust in first quarter 2014 and second quarter 2013, respectively. During the three-month periods ended September 30, 2014 and 2013, we charged $0.7 million and $0.7 million, respectively, to compensation expense related to these awards. During the nine-month periods ended September 30, 2014 and 2013, we charged $2.2 million and $1.5 million, respectively, to compensation expense related to these awards. During the nine-month period ended September 30, 2014, cash and equity awards with an aggregate fair value of $0.1 million were vested and distributed to executives under the DCPP.

Restricted_Stock_Performance_S

Restricted Stock, Performance Share and Cash Awards	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Restricted Stock, Performance Share and Cash Awards	'
	9. Restricted Stock, Performance Share and Cash Awards
	Restricted Stock Awards
	As discussed in Note 7 to these unaudited consolidated financial statements, on May 13, 2014, our stockholders approved the LTIP, which replaced our previous stockholder-approved 2011 LTIP. The LTIP provides for the grant of a stock award either as restricted stock or as restricted stock units. In either case, the compensation committee may determine that the award will be subject to the attainment of performance measures over an established performance period. Stock awards and the related dividend equivalents are non-transferable and subject to forfeiture if the holder does not remain continuously employed with us during the applicable restriction period or, in the case of a performance-based award, if applicable performance measures are not attained. The compensation committee will determine all of the terms relating to the satisfaction of performance measures and the termination of a restriction period, or the forfeiture and cancellation of a restricted stock award upon a termination of employment, whether by reason of disability, retirement, death or any other reason. The compensation committee may grant unrestricted shares of common stock or units representing the right to receive shares of common stock to employees who have attained age 62.
	The agreements awarding restricted stock units under the LTIP will specify whether such awards may be settled in shares of our common stock, cash or a combination of shares and cash and whether the holder will be entitled to receive dividend equivalents, on a current or deferred basis, with respect to such award. Prior to the settlement of a restricted stock unit, the holder of a restricted stock unit will have no rights as a stockholder of the company. The maximum number of shares available under the LTIP for restricted stock, restricted stock units and performance unit awards settled with stock (i.e., all awards other than stock options and stock appreciation rights) is 2.0 million. At September 30, 2014, 2.0 million shares were available for grant under the LTIP for such awards.
	In the first quarter of each of 2014 and 2013, we granted 323,600 and 345,000 restricted stock units, respectively, to employees under the LTIP, with an aggregate fair value of $15.2 million and $13.5 million, respectively, at the date of grant. These 2014 and 2013 awards of restricted stock units vest as follows: 323,600 units granted in first quarter 2014 and 345,000 units granted in first quarter 2013, vest in full based on continued employment through March 12, 2018 and March 13, 2017, respectively. In the second quarter of each of 2014 and 2013, we granted 19,250 and 17,000 restricted stock units, respectively, to employees under the LTIP, with an aggregate fair value of $0.9 million and $0.8 million, respectively, at the date of grant. These grants vest in full one year from the date of grant. In the third quarter of 2014, we granted 33,741 restricted stock units to employees with an aggregate fair value of $1.5 million at the date of grant. These grants vest at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2015, 2016 and 2017, respectively from the date of grant. For certain of our executive officers age 55 or older, restricted stock units awarded in 2014 and 2013 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant.
	We account for restricted stock awards at historical cost, which equals its fair market value at the date of grant, which is amortized to compensation expense ratably over the vesting period of the participants. Future changes in the fair value of our common stock that is owed to the participants do not have any impact on the amounts recorded in our consolidated financial statements. During the three-month periods ended September 30, 2014 and 2013, we charged $3.1 million and $2.3 million, respectively, to compensation expense related to restricted stock unit awards granted in 2006 through 2014. During the nine-month periods ended September 30, 2014 and 2013, we charged $9.6 million and $7.4 million, respectively, to compensation expense related to restricted stock unit awards granted in 2006 through 2014. The total intrinsic value of unvested restricted stock units at September 30, 2014 and 2013 was $55.0 million and $46.4 million, respectively. During the nine-month periods ended September 30, 2014 and 2013, equity awards (including accrued dividends) with an aggregate fair value of $9.7 million and $8.4 million were vested and distributed to employees under this plan.
	Performance Share Awards
	On March 12, 2014, pursuant to the LTIP, the compensation committee approved 48,800 provisional performance unit awards, with an aggregate fair value of $2.3 million, for future grants to our officers. Each performance unit award was equivalent to the value of one share of our common stock on the date such provisional award was approved. These awards are subject to a one-year performance period based on our financial performance and a two-year vesting period. At the discretion of the compensation committee and determined based on our performance, the eligible officer will be granted a percentage of the provisional performance unit award that equates to the EBITAC growth achieved (as specified in the applicable grant agreement). At the end of the performance period, eligible participants will be granted a number of units based on achievement of the performance goal and subject to approval by the compensation committee. Granted units for the 2014 provisional award will fully vest based on continuous employment through January 1, 2017, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable in 2017. For certain of our executive officers age 55 or older, awards granted in 2014 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. If an eligible employee leaves us prior to the vesting date, the entire award will be forfeited.
	Cash Awards
	On March 12, 2014, pursuant to our Performance Unit Program (which we refer to as the Program), the compensation committee approved provisional cash awards of $10.8 million in the aggregate for future grants to our officers and key employees that are denominated in units (229,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. The Program consists of a one-year performance period based on our financial performance and a two-year vesting period. At the discretion of the compensation committee and determined based on our performance, the eligible officer or key employee will be granted a percentage of the provisional cash award units that equates to the EBITAC growth achieved (as defined in the Program). At the end of the performance period, eligible participants will be granted a number of units based on achievement of the performance goal and subject to approval by the compensation committee. Granted units for the 2014 provisional award will fully vest based on continuous employment through January 1, 2017. For certain of our executive officers age 55 or older, awards granted under the Program in 2014 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of the provisional award. The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2016, multiplied by the number of units subject to the award, but limited to between 0.5 and 1.5 times the original value of the units determined as of the grant date. The fair value of the awarded units will be paid out in cash as soon as practicable in 2017. If an eligible employee leaves us prior to the vesting date, the entire award will be forfeited. We did not recognize any compensation expense during the nine-month period ended September 30, 2014 related to the 2014 provisional award under the Program.
	On March 13, 2013, pursuant to the Program, the compensation committee approved provisional cash awards of $10.5 million in the aggregate for future grant to our officers and key employees that are denominated in units (269,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2013 provisional awards were similar to the terms of the 2014 provisional awards. Based on our performance for 2013, we granted 263,000 units under the Program in first quarter 2014 that will fully vest on January 1, 2016. During the three-month period ended September 30, 2014, we charged $1.5 million to compensation expense related to these awards. During the nine-month period ended September 30, 2014, we charged $4.5 million to compensation expense related to these awards. We did not recognize any compensation expense during 2013 related to the 2013 awards.
	On March 16, 2012, pursuant to the Program, the compensation committee approved provisional cash awards of $13.1 million in the aggregate for future grant to our officers and key employees that are denominated in units (368,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2012 provisional awards were similar to the terms of the 2014 provisional awards. Based on our performance for 2012, we granted 365,000 units under the Program in first quarter 2013 that will fully vest on January 1, 2015. During the three-month periods ended September 30, 2014 and 2013, we charged $1.8 million and $2.0 million, respectively, to compensation expense related to the 2012 awards. During the nine-month periods ended September 30, 2014 and 2013, we charged $6.3 million and $5.4 million, respectively, to compensation expense related to the 2012 awards.
	On March 8, 2011, pursuant to the Program, the compensation committee approved provisional cash awards of $14.4 million in the aggregate for future grant to our officers and key employees that are denominated in units (464,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2011 provisional awards were similar to the terms of the 2014 provisional awards. Based on our performance for 2011, we granted 432,000 units under the Program in first quarter 2012 that fully vested on January 1, 2014. During the three-month period ended September 30, 2013, we charged $2.6 million to compensation expense related to these awards. During the nine-month period ended September 30, 2013, we charged $6.9 million to compensation expense related to these awards. We did not recognize any compensation expense during 2014 related to the 2011 awards.
	During the nine-month period ended September 30, 2014, cash awards related to the 2011 provisional award with an aggregate fair value of $17.6 million (0.4 million units in the aggregate) were vested and distributed to employees under the Program.

Retirement_Plans

Retirement Plans	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Retirement Plans	'
	10. Retirement Plans
	We have a noncontributory defined benefit pension plan that, prior to July 1, 2005, covered substantially all of our domestic employees who had attained a specified age and one year of employment. Benefits under the plan were based on years of service and salary history. In 2005, we amended our defined benefit pension plan to freeze the accrual of future benefits for all U.S. employees, effective on July 1, 2005. In the table below, the service cost component represents plan administration costs that are incurred directly by the plan.
	The components of the net periodic pension benefit cost for the plan consists of the following (in millions):
		Three-month period ended						Nine-month period ended
		September 30,						September 30,
		2014			2013			2014			2013
	Service cost	$	0.1		$	0.2		$	0.3		$	0.4
	Interest cost on benefit obligation		3.2			2.9			9.6			8.8
	Expected return on plan assets		(4.7	)		(4.2	)		(14.1	)		(12.8	)
	Amortization of net actuarial loss		0.6			2			1.8			5.9
	Net periodic benefit (earnings) cost	$	(0.8	)	$	0.9		$	(2.4	)	$	2.3
	We are not required under the IRC to make any minimum contributions to the plan for the 2014 plan year nor were we required to make any minimum contributions to the plan for the 2013 plan year. This level of required funding is based on the plan being frozen and the aggregate amount of our historical funding. During the nine-month period ended September 30, 2013, we made discretionary contributions of $6.3 million to the plan. We did not make any discretionary contributions to the plan during the nine-month period ended September 30, 2014.
	In August 2014, we decided to pursue a pension de-risking strategy to reduce the size of our pension obligations and the volatility in our overall financial condition. On September 12, 2014, the fiduciaries of the plan began offering certain former employees who are participants in the plan, the option of receiving the value of their pension benefit in a lump sum payment or as an accelerated reduced annuity, in lieu of monthly annuity payments when they retire. The voluntary offer is being made to approximately 2,200 terminated, vested participants in the plan whose employment terminated with the company prior to August 1, 2014 and who have not commenced benefit payments as of November 1, 2014. Eligible participants have from September 12, 2014 to November 12, 2014 to accept the offer, and the lump-sum payments will be made in November and December of 2014, and the accelerated reduced annuity payments will begin as of December 1, 2014. All payouts related to this offer will be made using assets from the plan and could aggregate to approximately $73.0 million.
	We expect to record a non-cash settlement charge in the fourth quarter of 2014 once we know the number of participants accepting the lump sum payment option, the actual return on plan assets and various actuarial assumptions, including discount rate, long-term rate of return on assets, retirement age and mortality at the remeasurement date.

Investments

Investments	9 Months Ended
	Sep. 30, 2014
Equity Method Investments and Joint Ventures [Abstract]	'
Investments	'
	11. Investments
	The following is a summary of our investments and the related funding commitments (in millions):
			September 30, 2014				December 31,
					Funding		2013
			Assets		Commitments		Assets
	Chem-Mod LLC		$	4	$	—	$	4
	Chem-Mod International LLC			2		—		2
	C-Quest Technologies LLC and C-Quest Technologies International LLC			—		—		2
	Clean-coal investments
	Controlling interest in five limited liability companies that own fourteen 2009 Era Clean Coal Plants			23.2		—		18.3
	Non-controlling interest in one limited liability company that owns one 2011 Era Clean Coal Plant			1		—		1.1
	Controlling interest in thirteen limited liability companies that own nineteen 2011 Era Clean Coal Plants			57.2		—		59.3
	Other investments			3.2		2.9		3.7
	Total investments		$	90.6	$	2.9	$	90.4
	Chem-Mod LLC - At September 30, 2014, we held a 46.54% controlling interest in Chem-Mod. Chem-Mod possesses the exclusive marketing rights, in the U.S. and Canada, for technologies used to reduce emissions created during the combustion of coal. The refined coal production plants discussed below, as well as those owned by other unrelated parties, license and use Chem-Mod’s proprietary technologies, The Chem-Mod™ Solution, in the production of refined coal. The Chem-Mod™ Solution uses a dual injection sorbent system to reduce mercury, sulfur dioxide and other emissions at coal-fired power plants.
	We believe that the application of The Chem-Mod™ Solution qualifies for refined coal tax credits under IRC Section 45 when used with refined coal production plants placed in service by December 31, 2011 or 2009. Chem-Mod has been marketing its technologies principally to coal-fired power plants owned by utility companies, including those utilities that are operating with the IRC Section 45 refined coal production plants in which we hold an investment.
	Chem-Mod is determined to be a variable interest entity (which we refer to as a VIE). We are the controlling manager of Chem-Mod and therefore consolidate its operations into our consolidated financial statements. At September 30, 2014, total assets and total liabilities of this VIE included in our consolidated balance sheet were $11.0 million and $1.0 million, respectively. For the nine-month period ended September 30, 2014, total revenues and expenses were $52.5 million and $29.1 million (including non-controlling interest of $26.9 million), respectively. We are under no obligation to fund Chem-Mod’s operations in the future.
	Chem-Mod International LLC - At September 30, 2014, we held a 31.52% non-controlling ownership interest in Chem-Mod International. Chem-Mod International has the rights to market The Chem-Mod™ Solution in countries other than the U.S. and Canada. Such marketing activity has been limited to date.
	C-Quest Technologies LLC and C-Quest Technologies International LLC (together, C-Quest) - At September 30, 2014, we held a non-controlling 12% interest in C-Quest’s global entities, which is an increase of 4% resulting from the transaction described below. C-Quest possesses rights, information and technology for the reduction of carbon dioxide emissions created by burning fossil fuels. Thus far, C-Quest’s operations have been limited to laboratory testing. C-Quest is determined to be a VIE, but due to our lack of control over the operation of C-Quest, we do not consolidate this investment into our consolidated financial statements. Prior to August 1, 2013, we had an option to acquire an additional 19% interest in C-Quest’s global entities for $9.5 million at any time on or prior to August 1, 2016. On August 1, 2013, we loaned the majority owner $2.0 million at a 2% interest rate, which was to mature on May 15, 2014. Also on August 1, 2013, the option to acquire the 19% interests was extended to August 15, 2016. The loan was to be repaid in cash or by delivery of an additional 4% ownership interest in C-Quest’s global entities. On March 31, 2014, we accepted payment of the loan by delivery of the additional 4% ownership interest, therefore our remaining option was reduced to 15% and the remaining purchase price was reduced to $7.5 million.
	Clean Coal Investments -
		•		We have investments in limited liability companies that own 34 refined coal production plants which produce refined coal using propriety technologies owned by Chem-Mod. We believe the production and sale of refined coal at these plants is qualified to receive refined coal tax credits under IRC Section 45. The fourteen plants placed in service prior to December 31, 2009 (which we refer to as the 2009 Era Plants) are eligible to receive tax credits through 2019 and the twenty plants placed in service prior to December 31, 2011 (which we refer to as the 2011 Era Plants) are eligible to receive tax credits through 2021.
		•		On March 1, 2013, we purchased an additional ownership interest in twelve of the 2009 Era Plants from a co-investor. For nine of the plants, our ownership increased from 24.5% to 49.5%. For the other three of the plants, our ownership increased from 25.0% to 60.0%. Our investment in these plants had been accounted for under the equity method of accounting. As of March 1, 2013, we consolidated the operations of the limited liability company that owns these three plants. Total revenues and expenses recorded in our unaudited consolidated statement of earnings for the nine-month period ended September 30, 2014 related to this acquisition, were $191.2 million and $197.7 million, respectively.
		•		Our purchase price for the additional ownership interests in these twelve plants was the assumption of the promissory note that we received as consideration for the co-investor’s purchase of ownership interests in three of the 2009 Era Plants on March 1, 2010, which had a carrying value, including accrued interest, of $8.0 million at March 1, 2013, plus the payment of cash and other consideration of $5.0 million. We recognized a gain of $11.4 million as a component of other net revenues in the accompanying unaudited consolidated statement of earnings, which included the increase in fair value of our prior 25% equity interest in the limited liability company upon the acquisition of the additional 35% equity interest, and recorded $26.3 million of fixed and other amortizable intangible assets and $6.8 million of other assets in connection with this transaction. The carrying value of our prior non-controlling interest in the limited liability company was $4.8 million as of the acquisition date. The fair value of our prior non-controlling interest in the limited liability company was determined by allocating, on a pro rata basis, the fair value of the limited liability company as adjusted for our lack of control in our prior ownership position. We determined the fair value of the limited liability company using similar valuation techniques to those discussed in Note 3 to these unaudited consolidated financial statements.
		•		On September 1, 2013, we purchased a 99% interest in a limited liability company that has ownership interests in four limited liability companies that own five 2011 Era Plants. The purchase price was $4.0 million in cash plus a $10.0 million note with 3% interest due in installments through December 19, 2021. Total revenues and expenses recorded in our unaudited consolidated statement of earnings for the nine-month period ended September 30, 2014 related to this acquisition, were $60.5 million and $67.2 million, respectively.
		•		On March 1, 2014, we purchased an additional ownership interest in seven of the 2009 Era Plants and five of the 2011 Era Plants from a co-investor. For all seven of the 2009 Era plants, our ownership increased from 49.5% to 100.0%. For the 2011 Era plants, our ownership increased from 48.8% to 90.0% for one of the plants, from 49.0% to 100.0% for three of the plants and from 98.0% to 100.0% for one of the plants. Our investments in the plants where our ownership was less than 50% had been accounted for under the equity method of accounting. As of March 1, 2014 we consolidated the operations of the limited liability companies that own these plants. Total revenues and expenses recorded in our unaudited consolidated statement of earnings for the nine-month period ended September 30, 2014 related to this acquisition were $131.5 million and $138.0 million, respectively.
		•		We received $0.5 million from our co-investor as part of the 2014 acquisition transaction in addition to receiving the additional ownership interests. We recognized a gain of $25.6 million as a component of other net revenues in the accompanying unaudited consolidated statement of earnings, which resulted from the increase in fair value of our prior equity interests in the limited liability companies upon the acquisition of the additional equity interests, and recorded $26.3 million of fixed and other amortizable intangible assets, $3.3 million of other assets and other liabilities of $4.5 million in connection with this transaction. The carrying value of our prior non-controlling interest in the limited liability companies was $15.5 million as of the acquisition date. The fair value of our prior non-controlling interest in the limited liability company was determined by allocating, on a pro rata basis, the fair value of the limited liability company as adjusted for our lack of control in our prior ownership position. We determined the fair value of the limited liability company using similar valuation techniques to those discussed in Note 3 to these consolidated financial statements.
		•		As of September 30, 2014:
		•		Twenty-seven of the plants have long-term production contracts.
		•		The remaining seven plants are in various stages of seeking and negotiating long-term production contracts.
		•		We have a non-controlling interest in one plant, which is owned by a limited liability company (which we refer to as a LLC). We have determined that this LLC is a VIE, for which we are not the primary beneficiary. At September 30, 2014, total assets and total liabilities of this VIE were $4.4 million and $1.3 million, respectively. For the nine-month period ended September 30, 2014, total revenues and expenses of this VIE were $28.9 million and $35.4 million, respectively.
		•		We may sell ownership interests in some or all of the plants to co-investors and relinquish control of the plants, thereby becoming a non-controlling, minority investor. In any limited liability company where we are a non-controlling, minority investor, the membership agreement for the operations contains provisions that preclude an individual member from being able to make major decisions that would denote control. As of any date we become a non-controlling, minority investor, we deconsolidate the entity and subsequently account for the investment using equity method accounting.
		•		For all plants that are not under long-term production contracts, we estimate that we will invest, on average, an additional $5.0 million per plant to connect and house each of them. For those plants that will have majority ownership co-investors, the average additional investment is estimated to be $2.5 million. We currently have no commitments related to our refined coal plants. We further estimate that we will invest an additional $30.0 million to $40.0 million to redeploy the remainder of the refined coal plants in 2015, before anyco-investor contributions.
		•		We and our co-investors each fund our portion of the on-going operations of the limited liability companies in proportion to our investment ownership percentages. Other than our portion of the on-going operational funding, there are no additional amounts that we are committed to related to funding these investments.
		•		We are aware that some of the coal-fired power plants that purchase the refined coal are considering burning natural gas rather than coal, or shutting down completely for economic reasons. The entities that own such plants are prepared to move the refined coal plants to other, generally higher volume, coal-fired power plants. If these potential developments were to occur, we estimate those plants will not operate for 12 to 18 months during their movement and redeployment, which could have a material impact on the amount of tax credits that are generated by these plants.
	Other Investments - At September 30, 2014, we owned a non-controlling, minority interest in four venture capital funds totaling $2.7 million, a 20% non-controlling interest in an investment management company totaling $0.5 million, twelve certified low-income housing developments with zero carrying value and two real estate entities with zero carrying value. The low-income housing developments and real estate entities have been determined to be VIEs, but are not required to be consolidated due to our lack of control over their respective operations. At September 30, 2014, total assets and total debt of these VIEs were approximately $60.0 million and $20.0 million, respectively.

Commitments_Contingencies_and_

Commitments, Contingencies and Off-Balance Sheet Arrangements	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments, Contingencies and Off-Balance Sheet Arrangements	'
	12. Commitments, Contingencies and Off-Balance Sheet Arrangements
	In connection with our investing and operating activities, we have entered into certain contractual obligations and commitments. See Notes 5 and 11 to these unaudited consolidated financial statements for additional discussion of these obligations and commitments. Our future minimum cash payments, including interest, associated with our contractual obligations pursuant to the note purchase agreements, Credit Agreement, Premium Financing Debt Facility, operating leases and purchase commitments at September 30, 2014 were as follows (in millions):
		Payments Due by Period
	Contractual Obligations	2014			2015			2016			2017			2018			Thereafter		Total
	Note purchase agreements	$	—		$	—		$	50		$	300		$	100		$	1,675.00	$	2,125.00
	Credit Agreement		147			—			—			—			—			—		147
	Premium Financing Debt Facility		149.2			—			—			—			—			—		149.2
	Interest on debt		33.2			100.4			100.4			97.5			77.5			397.1		806.1
	Total debt obligations		329.4			100.4			150.4			397.5			177.5			2,072.10		3,227.30
	Operating lease obligations		29.4			104.5			88.5			72.8			55.1			242.4		592.7
	Less sublease arrangements		(2.3	)		(1.4	)		(0.7	)		(0.4	)		(0.1	)		—		(4.9	)
	Outstanding purchase obligations		9.5			21.1			3.2			1			0.4			—		35.2
	Total contractual obligations	$	366		$	224.6		$	241.4		$	470.9		$	232.9		$	2,314.50	$	3,850.30
	The amounts presented in the table above may not necessarily reflect our actual future cash funding requirements, because the actual timing of future payments may vary from the stated contractual obligation.
	Note Purchase Agreements, Credit Agreement and Premium Financing Debt Facility - See Note 5 to these unaudited consolidated financial statements for a discussion of the terms of the note purchase agreements, the Credit Agreement and Premium Financing Debt Facility.
	Operating Lease Obligations - Our corporate segment’s executive offices and certain subsidiary and branch facilities of our brokerage and risk management segments are located at Two Pierce Place, Itasca, Illinois, where we lease approximately 306,000 square feet of space, or approximately 60% of the building. The lease commitment on this property expires February 28, 2018.
	We generally operate in leased premises at our other locations. Certain of these leases have options permitting renewals for additional periods. In addition to minimum fixed rentals, a number of leases contain annual escalation clauses which are generally related to increases in an inflation index.
	We have leased certain office space to several non-affiliated tenants under operating sublease arrangements. In the normal course of business, we expect that certain of these leases will not be renewed or replaced. We adjust charges for real estate taxes and common area maintenance annually based on actual expenses, and we recognize the related revenues in the year in which the expenses are incurred. These amounts are not included in the minimum future rentals to be received in the contractual obligations table above.
	Outstanding Purchase Obligations - We typically do not have a material amount of outstanding purchase obligations at any point in time. The amount disclosed in the contractual obligations table above represents the aggregate amount of unrecorded purchase obligations that we had outstanding at September 30, 2014. These obligations represent agreements to purchase goods or services that were executed in the normal course of business.
	Off-Balance Sheet Commitments - Our total unrecorded commitments associated with outstanding letters of credit, financial guarantees and funding commitments as of September 30, 2014 were as follows (in millions):
																			Total
		Amount of Commitment Expiration by Period																	Amounts
	Off-Balance Sheet Commitments	2014			2015			2016			2017			2018			Thereafter		Committed
	Letters of credit	$	—		$	—		$	—		$	—		$	—		$	20.6	$	20.6
	Financial guarantees		—			—			—			—			—			21.1		21.1
	Funding commitments		—			—			—			—			—			2.9		2.9
	Payment related to acquisition of Crombie/OAMPS (see Note 3)		35.3			—			—			—			—			—		35.3
	Total commitments	$	35.3		$	—		$	—		$	—		$	—		$	44.6	$	79.9
	Since commitments may expire unused, the amounts presented in the table above do not necessarily reflect our actual future cash funding requirements. See Note 11 to these unaudited consolidated financial statements for a discussion of our funding commitments related to our corporate segment and the Off-Balance Sheet Debt section below for a discussion of our letters of credit. All of the letters of credit represent multiple year commitments that have annual, automatic renewing provisions and are classified by the latest commitment date.
	Since January 1, 2002, we have acquired 333 companies, all of which were accounted for using the acquisition method for recording business combinations. Substantially all of the purchase agreements related to these acquisitions contain provisions for potential earnout obligations. For all of our acquisitions made in the period from 2011 to 2014 that contain potential earnout obligations, such obligations are measured at fair value as of the acquisition date and are included on that basis in the recorded purchase price consideration for the respective acquisition. The amounts recorded as earnout payables are primarily based upon estimated future operating results of the acquired entities over a two- to three-year period subsequent to the acquisition date. The aggregate amount of the maximum earnout obligations related to these acquisitions was $517.9 million, of which $185.4 million was recorded in our consolidated balance sheet as of September 30, 2014 based on the estimated fair value of the expected future payments to be made. See Note 3 to these unaudited consolidated financial statements for a discussion of our funding commitments related to a large acquisition we signed in April 2014 and completed in July 2014.
	Off-Balance Sheet Debt - Our unconsolidated investment portfolio includes investments in enterprises where our ownership interest is between 1% and 50%, in which management has determined that our level of influence and economic interest is not sufficient to require consolidation. As a result, these investments are accounted for under the equity method. None of these unconsolidated investments had any outstanding debt at September 30, 2014 or December 31, 2013 that was recourse to us.
	At September 30, 2014, we had posted two letters of credit totaling $9.3 million, in the aggregate, related to our self-insurance deductibles, for which we had a recorded liability of $9.3 million. We have an equity investment in a rent-a-captive facility, which we use as a placement facility for certain of our insurance brokerage operations. At September 30, 2014, we had posted seven letters of credit totaling $6.3 million to allow certain of our captive operations to meet minimum statutory surplus requirements and for additional collateral related to premium and claim funds held in a fiduciary capacity. At September 30, 2014, we had posted one letter of credit totaling $5.0 million to support our potential obligation under a client’s insurance program. These letters of credit have never been drawn upon.
	Litigation, Regulatory and Taxation Matters - We are a defendant in various legal actions incidental to the nature of our business including but not limited to matters related to employment practices, alleged breaches of non-compete or other restrictive covenants, theft of trade secrets, breaches of fiduciary duties and related causes of action. We are also periodically the subject of inquiries and investigations by regulatory and taxing authorities into various matters related to our business. Neither the outcomes of these matters nor their effect upon our business, financial condition or results of operations can be determined at this time.
	Our micro-captive advisory services are the subject of an investigation by the Internal Revenue Service (IRS). Additionally, the IRS has initiated audits for the 2012 tax year of over 100 of the micro-captive insurance companies organized and/or managed by us. Among other matters, the IRS is investigating whether we have been acting as a tax shelter promoter in connection with these operations. While the IRS has not made any specific allegations relating to our operations, if the IRS were to successfully assert that the micro-captives organized and/or managed by us do not meet the requirements of IRC Section 831(b), we could be subject to monetary claims by the IRS and/or our micro-captive clients, and our future earnings from our micro-captive operations could be materially adversely affected, any of which could negatively impact the overall captive business and adversely affect our consolidated results of operations and financial condition. Due to the early stage of the investigation and the fact that the IRS has not made any allegation against us at this time, we are not able to reasonably estimate the amount of any potential loss in connection with this investigation.
	In July 2014, Gallagher was named in a lawsuit that asserts Gallagher, its subsidiary, Gallagher Clean Energy, LLC, and Chem-Mod LLC are liable for infringement of a patent held by Nalco Company. The complaint seeks a judgment of infringement, damages, costs and attorneys’ fees, and injunctive relief. We and the other defendants dispute the allegations contained in the complaint and intend to defend this matter vigorously. On September 30, 2014, we filed a motion to dismiss the complaint on behalf of all defendants. We believe that the probability of a material loss is remote. However, litigation is inherently uncertain and it is not possible to predict the ultimate disposition of this proceeding.
	Contingent Liabilities - We purchase insurance to provide protection from errors and omissions (which we refer to as E&O) claims that may arise during the ordinary course of business. We currently retain the first $5.0 million of each and every E&O claim. Our E&O insurance provides aggregate coverage for E&O losses up to $175.0 million in excess of our retained amounts. We have historically maintained self-insurance reserves for the portion of our E&O exposure that is not insured. We periodically determine a range of possible reserve levels using actuarial techniques that rely heavily on projecting historical claim data into the future. Our E&O reserve in the September 30, 2014 unaudited consolidated balance sheet is above the lower end of the most recently determined actuarial range by $1.4 million and below the upper end of the actuarial range by $5.4 million. We can make no assurances that the historical claim data used to project the current reserve levels will be indicative of future claim activity. Thus, the E&O reserve level and corresponding actuarial range could change in the future as more information becomes known, which could materially impact the amounts reported and disclosed herein.
	Tax-advantaged Investments No Longer Held - Between 1996 and 2007, we developed and then sold portions of our ownership in various energy related investments, many of which qualified for tax credits under IRC Section 29. In connection with the sales to other investors, we provided various indemnities. At September 30, 2014, the maximum potential amount of future payments that we could be required to make under these indemnification provisions totaled approximately $32.0 million, net of the applicable income tax benefit. In addition, we recorded tax benefits in connection with our ownership in these investments. At September 30, 2014, we had exposure on $117.0 million of previously earned tax credits. In 2004, 2007 and 2009, the IRS examined several of these investments and all examinations were closed without any changes being proposed by the IRS. However, any future adverse tax audits, administrative rulings or judicial decisions could disallow previously claimed tax credits or cause us to be subject to liability under our indemnification obligations. Because of the contingent nature of these exposures, no liabilities have been recorded in our September 30, 2014 consolidated balance sheet related to these indemnification obligations.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Earnings (Loss)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Accumulated Other Comprehensive Earnings (Loss)	'
	The after-tax components of our accumulated other comprehensive earnings (loss) consist of the following:
		Pension			Foreign			Fair Value of			Accumulated
		Liability			Currency			Derivative			Comprehensive
					Translation			Investments			Earnings (Loss)
	Balance as of December 31, 2013	$	(25.6	)	$	22.1		$	0.9		$	(2.6	)
	Net change in period		1.4			(82.0	)		(0.5	)		(81.1	)
	Balance as of September 30, 2014	$	(24.2	)	$	(59.9	)	$	0.4		$	(83.7	)
	The foreign currency translation during the nine-month period ended September 30, 2014 primarily relates to the net impact of changes in the value of the local currencies relative to the U.S. dollar for our operations in Australia, Canada, the Caribbean, India, New Zealand, Singapore and the U.K.
	During the nine-month periods ended September 30, 2014 and 2013, $1.8 million and $5.9 million, respectively, of expense related to the pension liability was reclassified from accumulated other comprehensive earnings (loss) to compensation expense in the statement of earnings. During the nine-month periods ended September 30, 2014 and 2013, $0.5 million and $0.6 million, respectively, of expense related to the fair value of derivative investments was reclassified from accumulated other comprehensive earnings (loss) to the statement of earnings. During the nine-month periods ended September 30, 2014 and 2013, no amounts related to foreign currency translation were reclassified from accumulated other comprehensive earnings (loss) to the statement of earnings.

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	14. Segment Information
	We have three reportable segments: brokerage, risk management and corporate.
	The brokerage segment is primarily comprised of our retail and wholesale insurance brokerage operations. The brokerage segment generates revenues through commissions paid by insurance underwriters and through fees charged to our clients. Our brokers, agents and administrators act as intermediaries between insurers and their customers and we do not assume underwriting risks.
	The risk management segment provides contract claim settlement and administration services for enterprises that choose to self-insure some or all of their property/casualty coverages and for insurance companies that choose to outsource some or all of their property/casualty claims departments. These operations also provide claims management, loss control consulting and insurance property appraisal services. Revenues are principally generated on a negotiated per-claim or per-service fee basis.
	The corporate segment manages our clean energy and other investments. This segment also holds all of our corporate debt.
	Allocations of investment income and certain expenses are based on reasonable assumptions and estimates primarily using revenue, headcount and other information. We allocate the provision for income taxes to the brokerage and risk management segments using the local country statutory rates. Reported operating results by segment would change if different methods were applied.
	Financial information relating to our segments for the three-month and nine-month periods ended September 30, 2014 and 2013 is as follows (in millions):
		Three-month period						Nine-month period
		ended September  30,						ended September  30,
		2014			2013			2014			2013
	Brokerage
	Total revenues	$	799.8		$	546.3		$	2,111.00		$	1,551.60
	Earnings before income taxes	$	124.2		$	97.3		$	311.1		$	250.5
	Identifiable assets at September 30, 2014 and 2013							$	8,404.20		$	4,661.90
	Risk Management
	Total revenues	$	168.3		$	149.7		$	496.4		$	459.5
	Earnings before income taxes	$	20.2		$	17.9		$	59.8		$	59.6
	Identifiable assets at September 30, 2014 and 2013							$	593.9		$	546.2
	Corporate
	Total revenues	$	318.7		$	139.8		$	773.7		$	278.3
	Loss before income taxes	$	(56.7	)	$	(29.7	)	$	(129.8	)	$	(84.9	)
	Identifiable assets at September 30, 2014 and 2013							$	989.9		$	762.1

Effect_of_New_Accounting_Prono1

Effect of New Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Changes and Error Corrections [Abstract]	'
Revenue Recognition	'
	Revenue Recognition
	In May 2014, the Financial Accounting Standards Board (which we refer to as 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 new 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. This new guidance is effective for 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. Management is currently reviewing the guidance, and the impact from its adoption on our consolidated financial statements cannot be determined at this time.
Presentation of Unrecognized Tax Benefits	'
	Presentation of Unrecognized Tax Benefits
	In July 2013, the FASB issued ASU 2013-11, “Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists,” which provides explicit guidance on the presentation of certain unrecognized tax benefits in the financial statements that did not previously exist. The guidance provides that a liability related to an unrecognized tax benefit would be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. In that case, the liability associated with the unrecognized tax benefit is presented in the financial statements as a reduction to the related deferred tax asset. In situations in which a net operating loss carryforward, a similar tax loss or a tax credit carryforward is not available at the reporting date under the tax law of the jurisdiction or the tax law of the jurisdiction does not require, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit will be presented in the financial statements as a liability and will not be combined with deferred tax assets. This new guidance was effective in first quarter 2014. We adopted the new guidance effective January 1, 2014. The impact of the new guidance upon adoption was not material to our 2014 unaudited consolidated financial statements.

Business_Combinations_Tables

Business Combinations (Tables)	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Acquisition Method for Recording Business Combinations	'
	During the nine-month period ended September 30, 2014, we acquired substantially all of the net assets of the following firms in exchange for our common stock and/or cash. These acquisitions have been accounted for using the acquisition method for recording business combinations (in millions except share data):
	Name and Effective	Common		Common		Cash		Accrued		Escrow		Recorded		Total		Maximum
	Date of Acquisition	Shares		Share		Paid		Liability		Deposited		Earnout		Recorded		Potential
		Issued		Value								Payable		Purchase		Earnout
														Price		Payable
		(000s)
	Benefit Development Group, Inc. February 1, 2014		46	$	2	$	0.7	$	—	$	0.1	$	0.6	$	3.4	$	2
	Kent, Kent & Tingle February 1, 2014		229		9.1		3.5		—		1.4		3.5		17.5		7.8
	L&R Benefits, LLC March 1, 2014		115		5.3		1.8		—		0.1		1		8.2		6
	Spataro Insurance Agency, Inc. March 1, 2014		47		2		—		—		0.2		0.4		2.6		0.6
	Tudor Risk Services, LLC March 1, 2014		—		—		2.1		—		0.2		0.1		2.4		1.3
	American Wholesalers Underwriting Ltd April 1, 2014		133		6		5.7		—		0.5		—		12.2		—
	Mike Henry Insurance Brokers Limited April 1, 2014		—		—		9.6		—		1.7		4.2		15.5		6.8
	Oval Group of Companies (OGC) April 1, 2014		—		—		338.4		—		11.8		—		350.2		—
	Heritage Insurance Management Limited (HIM) May 1, 2014		—		—		33.9		—		3.8		—		37.7		—
	MGA Insurance Group (MGA) May 1, 2014		547		25.1		26.8		—		2.5		11.9		66.3		20
	Shilling Limited May 1, 2014		198		8.9		1.7		—		1.2		1		12.8		8.4
	Sunderland Insurance Services, Inc. May 1, 2014		204		9.2		2.4		—		0.6		—		12.2		—
	Plus Companies, Inc. June 1, 2014		221		9.3		3.4		—		0.8		—		13.5		—
	Tri-State General Insurance Agency, Inc. June 1, 2014		47		2.2		0.6		—		0.1		—		2.9		—
	Crombie/OAMPS (CO) June 16, 2014		—		—		951.5		—		—		—		951.5		—
	Foundation Strategies, Inc. July 1, 2014		46		2		0.7		—		0.1		0.4		3.2		3
	Insurance Point, LLC (IPL) July 1, 2014		255		11.2		3.9		—		0.5		2.5		18.1		24.4
	Trip Mate, Inc. (TMI) July 1, 2014		209		8.4		3.9		—		1		5.9		19.2		12.5
	Noraxis Capital Corporation (NCC) July 2, 2014		—		—		413.3		—		1.9		—		415.2		—
	Cowles & Connell (CC) August 1, 2014		331		14.8		4.2		—		0.8		—		19.8		—
	Denman Consulting Services August 1, 2014		40		1.7		0.6		—		0.1		0.3		2.7		1.6
	Minvielle & Chastanet Insurance Brokers August 8, 2014		—		—		5		—		—		3		8		5
	Baker Tilly Financial Management Limited August 29, 2014		185		8.7		2.3		—		0.7		4.6		16.3		5.4
	Benfield Group September 1, 2014		82		3.8		1.1		—		0.1		0.9		5.9		3.5
	Everett James, Inc. September 1, 2014		52		2.4		0.7		—		0.1		0.8		4		4
	Hagedorn & Company September 1, 2014		281		11.5		—		—		1.3		—		12.8		—
	Parmia Pty Ltd. September 1, 2014		—		—		1.7		—		—		1.2		2.9		1.2
	Eighteen other acquisitions completed in 2014		305		13.2		17.4		—		0.9		9.8		41.3		19
			3,573	$	156.8	$	1,836.90	$	—	$	32.5	$	52.1	$	2,078.30	$	132.5
Summary of Estimated Fair Values of Net Assets Acquired	'
	The following is a summary of the estimated fair values of the net assets acquired at the date of each acquisition made in the nine-month period ended September 30, 2014 (in millions):
		OGC		HIM		MGA		CO		IPL		TMI		NCC		CC		Thirty-Seven		Total
																		Other
																		Acquisitions
	Cash	$	23.1	$	2.9	$	0.2	$	26.6	$	2.7	$	—	$	10.2	$	0.6	$	1.2	$	67.5
	Other current assets		129.6		4.9		8.9		695.5		0.4		7		73		9.1		25.3		953.7
	Fixed assets		2.1		0.3		0.8		17.1		—		1.9		4.9		0.1		1.6		28.8
	Noncurrent assets		—		—		—		7		—		—		3.5		—		4.1		14.6
	Goodwill		245.7		14.8		27		535.9		2.5		5.9		291		7.8		92.7		1,223.30
	Expiration lists		129.9		20.3		33.2		325.3		15.3		10.3		139.7		11.2		105.5		790.7
	Non-compete agreements		1		1.3		0.3		4.2		0.2		0.1		4		—		0.9		12
	Trade names		0.6		—		—		4.2		—		—		4		0.4		0.8		10
	Total assets acquired		532		44.5		70.4		1,615.80		21.1		25.2		530.3		29.2		232.1		3,100.60
	Current liabilities		129.5		6.8		4.1		490		2.9		5.8		72.5		9.4		25.6		746.6
	Noncurrent liabilities		52.3		—		—		174.3		0.1		0.2		42.6		—		6.2		275.7
	Total liabilities assumed		181.8		6.8		4.1		664.3		3		6		115.1		9.4		31.8		1,022.30
	Total net assets acquired	$	350.2	$	37.7	$	66.3	$	951.5	$	18.1	$	19.2	$	415.2	$	19.8	$	200.3	$	2,078.30
Summary of Unaudited Pro Forma Historical Results	'
	The following is a summary of the unaudited pro forma historical results, as if these entities had been acquired at January 1, 2013 (in millions, except per share data):
		Three-month period ended				Nine-month period ended
		September 30,				September 30,
		2014		2013		2014		2013
	Total revenues	$	1,293.00	$	1,004.60	$	3,681.00	$	2,833.40
	Net earnings		94.2		87		271.1		256.8
	Basic net earnings per share		0.59		0.56		1.69		1.68
	Diluted net earnings per share		0.58		0.56		1.68		1.66

Intangible_Assets_Tables

Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations	'
	The carrying amount of goodwill at September 30, 2014 and December 31, 2013 allocated by domestic and foreign operations is as follows (in millions):
		Brokerage			Risk			Corporate		Total
					Management
	At September 30, 2014
	United States	$	1,572.00		$	20.2		$	—	$	1,592.20
	United Kingdom		831.2			2.2			—		833.4
	Canada		307.6			—			—		307.6
	Australia		271.4			—			—		271.4
	Other foreign, principally New Zealand		291.6			—			—		291.6
	Total goodwill - net	$	3,273.80		$	22.4		$	—	$	3,296.20
	At December 31, 2013
	United States	$	1,449.60		$	20.2		$	—	$	1,469.80
	United Kingdom		582.8			2.1			—		584.9
	Canada		26.8			—			—		26.8
	Australia		37.1			—			—		37.1
	Other foreign, principally New Zealand		26.6			—			—		26.6
	Total goodwill - net	$	2,122.90		$	22.3		$	—	$	2,145.20
Changes in Carrying Amount of Goodwill	'
	The changes in the carrying amount of goodwill for the nine-month period ended September 30, 2014 are as follows (in millions):
		Brokerage			Risk			Corporate		Total
					Management
	Balance as of December 31, 2013	$	2,122.90		$	22.3		$	—	$	2,145.20
	Goodwill acquired during the period		1,223.30			—			—		1,223.30
	Goodwill adjustments due to appraisals and other acquisition adjustments		(27.7	)		—			—		(27.7	)
	Goodwill written-off related to sales of business		(0.6	)		—			—		(0.6	)
	Foreign currency translation adjustments during the period		(44.1	)		0.1			—		(44.0	)
	Balance as of September 30, 2014	$	3,273.80		$	22.4		$	—	$	3,296.20
Major Classes of Amortizable Intangible Assets	'
	Major classes of amortizable intangible assets at September 30, 2014 and December 31, 2013 consist of the following (in millions):
		September 30,			December 31,
		2014			2013
	Expiration lists	$	2,409.00		$	1,563.50
	Accumulated amortization - expiration lists		(675.9	)		(511.3	)
			1,733.10			1,052.20
	Non-compete agreements		44			37.3
	Accumulated amortization - non-compete agreements		(28.4	)		(25.9	)
			15.6			11.4
	Trade names		31.8			22.1
	Accumulated amortization - trade names		(9.4	)		(6.9	)
			22.4			15.2
	Net amortizable assets	$	1,771.10		$	1,078.80
Estimated Aggregate Amortization Expense	'
	Estimated aggregate amortization expense for each of the next five years is as follows:
	2014 (remaining three months)	$	53.2
	2015		208.8
	2016		203.1
	2017		193.1
	2018		180.3
	Total	$	838.5

Credit_and_Other_Debt_Agreemen1

Credit and Other Debt Agreements (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Summary of Corporate and Other Debt	'
	The following is a summary of our corporate and other debt (in millions):
		September 30,		December 31,
		2014		2013
	Note Purchase Agreements:
	Semi-annual payments of interest, fixed rate of 6.26%, balloon due 2014	$	—	$	100
	Semi-annual payments of interest, fixed rate of 6.44%, balloon due 2017		300		300
	Semi-annual payments of interest, fixed rate of 2.80%, balloon due 2018		50		—
	Semi-annual payments of interest, fixed rate of 3.20%, balloon due 2019		50		—
	Semi-annual payments of interest, fixed rate of 5.85%, $50 million due in 2016, 2018 and 2019		150		150
	Semi-annual payments of interest, fixed rate of 3.99%, balloon due 2020		50		50
	Semi-annual payments of interest, fixed rate of 3.48%, balloon due 2020		50		—
	Semi-annual payments of interest, fixed rate of 5.18%, balloon due 2021		75		75
	Semi-annual payments of interest, fixed rate of 3.69%, balloon due 2022		200		200
	Semi-annual payments of interest, fixed rate of 5.49%, balloon due 2023		50		50
	Semi-annual payments of interest, fixed rate of 4.13%, balloon due 2023		200		—
	Semi-annual payments of interest, fixed rate of 4.58%, balloon due 2024		325		—
	Semi-annual payments of interest, fixed rate of 4.31%, balloon due 2025		200		—
	Semi-annual payments of interest, fixed rate of 4.73%, balloon due 2026		175		—
	Semi-annual payments of interest, fixed rate of 4.36%, balloon due 2026		150		—
	Semi-annual payments of interest, fixed rate of 4.98%, balloon due 2029		100		—
	Total Note Purchase Agreements		2,125.00		925
	Credit Agreement:
	Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires September 19, 2018		147		530.5
	Premium Financing Debt Facility - expires June 15, 2016:
	Periodic payments of interest and principal, Interbank rates plus 1.65% for Facility B; plus 0.85% for Facilities C and D
	Facility B
	AUD denominated tranche		117.7		—
	NZD denominated tranche		17.7		—
	Facility C and D
	AUD denominated tranche		4.6		—
	NZD denominated tranche		9.2		—
	Total Premium Financing Debt Facility		149.2		—
	Total corporate and other debt	$	2,421.20	$	1,455.50

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Computation of Basic and Diluted Net EPS	'
	The following table sets forth the computation of basic and diluted net earnings per share (in millions, except per share data):
		Three-month period ended				Nine-month period ended
		September 30,				September 30,
		2014		2013		2014		2013
	Net earnings	$	93.6	$	74.6	$	251.9	$	208.6
	Weighted average number of common shares outstanding		160.2		129.8		149.6		127.7
	Dilutive effect of stock options using the treasury stock method		1.3		1.5		1.4		1.6
	Weighted average number of common and common equivalent shares outstanding		161.5		131.3		151		129.3
	Basic net earnings per share	$	0.58	$	0.57	$	1.68	$	1.63
	Diluted net earnings per share	$	0.58	$	0.57	$	1.67	$	1.61

Stock_Option_Plans_Tables

Stock Option Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Black-Scholes Option Pricing Model with Weighted Average	'
	For purposes of expense recognition, the estimated fair values of the stock option grants are amortized to expense over the options’ vesting period. We estimated the fair value of stock options at the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:
		2014				2013
	Expected dividend yield		3	%			3.5	%
	Expected risk-free interest rate		1.8	%			1.2	%
	Volatility		28.9	%			29.6	%
	Expected life (in years)		5.5				6
Stock Option Activity and Related Information	'
	The following is a summary of our stock option activity and related information for 2014 (in millions, except exercise price and year data):
		Nine-month period ended September 30, 2014
		Shares				Weighted				Weighted				Aggregate
		Under				Average				Average				Intrinsic
		Option				Exercise				Remaining				Value
						Price				Contractual
										Term
										(in years)
	Beginning balance		8.3			$	31.35
	Granted		1.9				46.86
	Exercised		(1.5	)			28.94
	Forfeited or canceled		(0.1	)			28.56
	Ending balance		8.6			$	35.31				4.15			$	89.3
	Exercisable at end of period		2.8			$	26.96				2.08			$	51.8
	Ending vested and expected to vest		8.4			$	35.18				4.12			$	88.7
Other Information Regarding Stock Options Outstanding and Exercisable	'
	Other information regarding stock options outstanding and exercisable at September 30, 2014 is summarized as follows (in millions, except exercise price and year data):
				Options Outstanding												Options Exercisable
	Range of Exercise Prices			Number				Weighted				Weighted				Number		Weighted
				Outstanding				Average				Average				Exercisable		Average
								Remaining				Exercise						Exercise
								Contractual				Price						Price
								Term
								(in years)
	$    21.28   -  $   27.25				2.4				1.82			$	25.81				2	$	25.8
	27.35   -        35.71				2.6				3.76				33.04				0.8		29.86
	35.95   -        39.17				1.7				5.45				39.15				—		—
	46.16   -        46.87				1.9				6.45				46.87				—		—
	$    21.28   -  $   46.87				8.6				4.15			$	35.31				2.8	$	26.96

Retirement_Plans_Tables

Retirement Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Components of Net Periodic Pension Benefit Cost	'
	The components of the net periodic pension benefit cost for the plan consists of the following (in millions):
		Three-month period ended						Nine-month period ended
		September 30,						September 30,
		2014			2013			2014			2013
	Service cost	$	0.1		$	0.2		$	0.3		$	0.4
	Interest cost on benefit obligation		3.2			2.9			9.6			8.8
	Expected return on plan assets		(4.7	)		(4.2	)		(14.1	)		(12.8	)
	Amortization of net actuarial loss		0.6			2			1.8			5.9
	Net periodic benefit (earnings) cost	$	(0.8	)	$	0.9		$	(2.4	)	$	2.3

Investments_Tables

Investments (Tables)	9 Months Ended
	Sep. 30, 2014
Equity Method Investments and Joint Ventures [Abstract]	'
Investments Reported in Other Current and Non-Current Assets	'
	The following is a summary of our investments and the related funding commitments (in millions):
		September 30, 2014				December 31,
				Funding		2013
		Assets		Commitments		Assets
	Chem-Mod LLC	$	4	$	—	$	4
	Chem-Mod International LLC		2		—		2
	C-Quest Technologies LLC and C-Quest Technologies International LLC		—		—		2
	Clean-coal investments
	Controlling interest in five limited liability companies that own fourteen 2009 Era Clean Coal Plants		23.2		—		18.3
	Non-controlling interest in one limited liability company that owns one 2011 Era Clean Coal Plant		1		—		1.1
	Controlling interest in thirteen limited liability companies that own nineteen 2011 Era Clean Coal Plants		57.2		—		59.3
	Other investments		3.2		2.9		3.7
	Total investments	$	90.6	$	2.9	$	90.4

Commitments_Contingencies_and_1

Commitments, Contingencies and Off-Balance Sheet Arrangements (Tables)	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Contractual Obligations	'
	Our future minimum cash payments, including interest, associated with our contractual obligations pursuant to the note purchase agreements, Credit Agreement, Premium Financing Debt Facility, operating leases and purchase commitments at September 30, 2014 were as follows (in millions):
		Payments Due by Period
	Contractual Obligations	2014			2015			2016			2017			2018			Thereafter		Total
	Note purchase agreements	$	—		$	—		$	50		$	300		$	100		$	1,675.00	$	2,125.00
	Credit Agreement		147			—			—			—			—			—		147
	Premium Financing Debt Facility		149.2			—			—			—			—			—		149.2
	Interest on debt		33.2			100.4			100.4			97.5			77.5			397.1		806.1
	Total debt obligations		329.4			100.4			150.4			397.5			177.5			2,072.10		3,227.30
	Operating lease obligations		29.4			104.5			88.5			72.8			55.1			242.4		592.7
	Less sublease arrangements		(2.3	)		(1.4	)		(0.7	)		(0.4	)		(0.1	)		—		(4.9	)
	Outstanding purchase obligations		9.5			21.1			3.2			1			0.4			—		35.2
	Total contractual obligations	$	366		$	224.6		$	241.4		$	470.9		$	232.9		$	2,314.50	$	3,850.30
Off-Balance Sheet Commitments	'
	Off-Balance Sheet Commitments - Our total unrecorded commitments associated with outstanding letters of credit, financial guarantees and funding commitments as of September 30, 2014 were as follows (in millions):
																			Total
		Amount of Commitment Expiration by Period																	Amounts
	Off-Balance Sheet Commitments	2014			2015			2016			2017			2018			Thereafter		Committed
	Letters of credit	$	—		$	—		$	—		$	—		$	—		$	20.6	$	20.6
	Financial guarantees		—			—			—			—			—			21.1		21.1
	Funding commitments		—			—			—			—			—			2.9		2.9
	Payment related to acquisition of Crombie/OAMPS (see Note 3)		35.3			—			—			—			—			—		35.3
	Total commitments	$	35.3		$	—		$	—		$	—		$	—		$	44.6	$	79.9

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Earnings (Loss) (Tables)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Schedule of Accumulated Other Comprehensive Earnings (Loss)	'
	The after-tax components of our accumulated other comprehensive earnings (loss) consist of the following:
		Pension			Foreign			Fair Value of			Accumulated
		Liability			Currency			Derivative			Comprehensive
					Translation			Investments			Earnings (Loss)
	Balance as of December 31, 2013	$	(25.6	)	$	22.1		$	0.9		$	(2.6	)
	Net change in period		1.4			(82.0	)		(0.5	)		(81.1	)
	Balance as of September 30, 2014	$	(24.2	)	$	(59.9	)	$	0.4		$	(83.7	)

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting [Abstract]	'
Schedule of Segment Reporting Information by Segment	'
	Financial information relating to our segments for the three-month and nine-month periods ended September 30, 2014 and 2013 is as follows (in millions):
		Three-month period						Nine-month period
		ended September  30,						ended September  30,
		2014			2013			2014			2013
	Brokerage
	Total revenues	$	799.8		$	546.3		$	2,111.00		$	1,551.60
	Earnings before income taxes	$	124.2		$	97.3		$	311.1		$	250.5
	Identifiable assets at September 30, 2014 and 2013							$	8,404.20		$	4,661.90
	Risk Management
	Total revenues	$	168.3		$	149.7		$	496.4		$	459.5
	Earnings before income taxes	$	20.2		$	17.9		$	59.8		$	59.6
	Identifiable assets at September 30, 2014 and 2013							$	593.9		$	546.2
	Corporate
	Total revenues	$	318.7		$	139.8		$	773.7		$	278.3
	Loss before income taxes	$	(56.7	)	$	(29.7	)	$	(129.8	)	$	(84.9	)
	Identifiable assets at September 30, 2014 and 2013							$	989.9		$	762.1

Nature_of_Operations_and_Basis1

Nature of Operations and Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2014
	Segment
	Country
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Number of countries in which the company has operations	30
Number of countries in which the company does business through a network of correspondent brokers and consultants	140
Number of reportable segments	3

Business_Combinations_Acquisit

Business Combinations - Acquisition Method for Recording Business Combinations (Detail) (USD $)	9 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Sep. 30, 2014
Business Acquisition [Line Items]	'
Common Shares Issued	3,573
Common Share Value	$156.80
Cash Paid	1,836.90
Accrued Liability	0
Escrow Deposited	32.5
Recorded Earnout Payable	52.1
Total Recorded Purchase Price	2,078.30
Maximum Potential Earnout Payable	132.5
Benefit Development Group, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	46
Common Share Value	2
Cash Paid	0.7
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0.6
Total Recorded Purchase Price	3.4
Maximum Potential Earnout Payable	2
Kent, Kent & Tingle [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	229
Common Share Value	9.1
Cash Paid	3.5
Accrued Liability	0
Escrow Deposited	1.4
Recorded Earnout Payable	3.5
Total Recorded Purchase Price	17.5
Maximum Potential Earnout Payable	7.8
L&R Benefits, LLC [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	115
Common Share Value	5.3
Cash Paid	1.8
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	1
Total Recorded Purchase Price	8.2
Maximum Potential Earnout Payable	6
Spataro Insurance Agency, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	47
Common Share Value	2
Cash Paid	0
Accrued Liability	0
Escrow Deposited	0.2
Recorded Earnout Payable	0.4
Total Recorded Purchase Price	2.6
Maximum Potential Earnout Payable	0.6
Tudor Risk Services, LLC [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	2.1
Accrued Liability	0
Escrow Deposited	0.2
Recorded Earnout Payable	0.1
Total Recorded Purchase Price	2.4
Maximum Potential Earnout Payable	1.3
American Wholesalers Underwriting Ltd [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	133
Common Share Value	6
Cash Paid	5.7
Accrued Liability	0
Escrow Deposited	0.5
Recorded Earnout Payable	0
Total Recorded Purchase Price	12.2
Maximum Potential Earnout Payable	0
Mike Henry Insurance Brokers Limited [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	9.6
Accrued Liability	0
Escrow Deposited	1.7
Recorded Earnout Payable	4.2
Total Recorded Purchase Price	15.5
Maximum Potential Earnout Payable	6.8
Oval Group of Companies (OGC) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	338.4
Accrued Liability	0
Escrow Deposited	11.8
Recorded Earnout Payable	0
Total Recorded Purchase Price	350.2
Maximum Potential Earnout Payable	0
Heritage Insurance Management Limited (HIM) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	33.9
Accrued Liability	0
Escrow Deposited	3.8
Recorded Earnout Payable	0
Total Recorded Purchase Price	37.7
Maximum Potential Earnout Payable	0
MGA Insurance Group (MGA) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	547
Common Share Value	25.1
Cash Paid	26.8
Accrued Liability	0
Escrow Deposited	2.5
Recorded Earnout Payable	11.9
Total Recorded Purchase Price	66.3
Maximum Potential Earnout Payable	20
Shilling Limited [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	198
Common Share Value	8.9
Cash Paid	1.7
Accrued Liability	0
Escrow Deposited	1.2
Recorded Earnout Payable	1
Total Recorded Purchase Price	12.8
Maximum Potential Earnout Payable	8.4
Sunderland Insurance Services, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	204
Common Share Value	9.2
Cash Paid	2.4
Accrued Liability	0
Escrow Deposited	0.6
Recorded Earnout Payable	0
Total Recorded Purchase Price	12.2
Maximum Potential Earnout Payable	0
Plus Companies, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	221
Common Share Value	9.3
Cash Paid	3.4
Accrued Liability	0
Escrow Deposited	0.8
Recorded Earnout Payable	0
Total Recorded Purchase Price	13.5
Maximum Potential Earnout Payable	0
Tri-State General Insurance Agency, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	47
Common Share Value	2.2
Cash Paid	0.6
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0
Total Recorded Purchase Price	2.9
Maximum Potential Earnout Payable	0
Crombie/OAMPS (CO) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	951.5
Accrued Liability	0
Escrow Deposited	0
Recorded Earnout Payable	0
Total Recorded Purchase Price	951.5
Maximum Potential Earnout Payable	0
Foundation Strategies, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	46
Common Share Value	2
Cash Paid	0.7
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0.4
Total Recorded Purchase Price	3.2
Maximum Potential Earnout Payable	3
Insurance Point, LLC (IPL) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	255
Common Share Value	11.2
Cash Paid	3.9
Accrued Liability	0
Escrow Deposited	0.5
Recorded Earnout Payable	2.5
Total Recorded Purchase Price	18.1
Maximum Potential Earnout Payable	24.4
Trip Mate, Inc. (TMI) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	209
Common Share Value	8.4
Cash Paid	3.9
Accrued Liability	0
Escrow Deposited	1
Recorded Earnout Payable	5.9
Total Recorded Purchase Price	19.2
Maximum Potential Earnout Payable	12.5
Noraxis Capital Corporation (NCC) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	413.3
Accrued Liability	0
Escrow Deposited	1.9
Recorded Earnout Payable	0
Total Recorded Purchase Price	415.2
Maximum Potential Earnout Payable	0
Cowles & Connell (CC) [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	331
Common Share Value	14.8
Cash Paid	4.2
Accrued Liability	0
Escrow Deposited	0.8
Recorded Earnout Payable	0
Total Recorded Purchase Price	19.8
Maximum Potential Earnout Payable	0
Denman Consulting Services [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	40
Common Share Value	1.7
Cash Paid	0.6
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0.3
Total Recorded Purchase Price	2.7
Maximum Potential Earnout Payable	1.6
Minvielle & Chastanet Insurance Brokers [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	5
Accrued Liability	0
Escrow Deposited	0
Recorded Earnout Payable	3
Total Recorded Purchase Price	8
Maximum Potential Earnout Payable	5
Baker Tilly Financial Management Limited [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	185
Common Share Value	8.7
Cash Paid	2.3
Accrued Liability	0
Escrow Deposited	0.7
Recorded Earnout Payable	4.6
Total Recorded Purchase Price	16.3
Maximum Potential Earnout Payable	5.4
Benfield Group [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	82
Common Share Value	3.8
Cash Paid	1.1
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0.9
Total Recorded Purchase Price	5.9
Maximum Potential Earnout Payable	3.5
Everett James, Inc. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	52
Common Share Value	2.4
Cash Paid	0.7
Accrued Liability	0
Escrow Deposited	0.1
Recorded Earnout Payable	0.8
Total Recorded Purchase Price	4
Maximum Potential Earnout Payable	4
Hagedorn & Company [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	281
Common Share Value	11.5
Cash Paid	0
Accrued Liability	0
Escrow Deposited	1.3
Recorded Earnout Payable	0
Total Recorded Purchase Price	12.8
Maximum Potential Earnout Payable	0
Parmia Pty Ltd. [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	0
Common Share Value	0
Cash Paid	1.7
Accrued Liability	0
Escrow Deposited	0
Recorded Earnout Payable	1.2
Total Recorded Purchase Price	2.9
Maximum Potential Earnout Payable	1.2
Eighteen Other Acquisitions [Member]	'
Business Acquisition [Line Items]	'
Common Shares Issued	305
Common Share Value	13.2
Cash Paid	17.4
Accrued Liability	0
Escrow Deposited	0.9
Recorded Earnout Payable	9.8
Total Recorded Purchase Price	41.3
Maximum Potential Earnout Payable	$19

Business_Combinations_Acquisit1

Business Combinations - Acquisition Method for Recording Business Combinations (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2014
Benefit Development Group, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Feb-14
Kent, Kent & Tingle [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Feb-14
L&R Benefits, LLC [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Mar-14
Spataro Insurance Agency, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Mar-14
Tudor Risk Services, LLC [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Mar-14
American Wholesalers Underwriting Ltd [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Apr-14
Mike Henry Insurance Brokers Limited [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Apr-14
Oval Group of Companies (OGC) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Apr-14
Heritage Insurance Management Limited (HIM) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-May-14
MGA Insurance Group (MGA) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-May-14
Shilling Limited [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-May-14
Sunderland Insurance Services, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-May-14
Plus Companies, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Jun-14
Tri-State General Insurance Agency, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Jun-14
Crombie/OAMPS (CO) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	16-Jun-14
Foundation Strategies, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Jul-14
Insurance Point, LLC (IPL) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Jul-14
Trip Mate, Inc. (TMI) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Jul-14
Noraxis Capital Corporation (NCC) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	2-Jul-14
Cowles & Connell (CC) [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Aug-14
Denman Consulting Services [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Aug-14
Minvielle & Chastanet Insurance Brokers [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	8-Aug-14
Baker Tilly Financial Management Limited [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	29-Aug-14
Benfield Group [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Sep-14
Everett James, Inc. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Sep-14
Hagedorn & Company [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Sep-14
Parmia Pty Ltd. [Member]	'
Business Acquisition [Line Items]	'
Effective Date of Acquisition	1-Sep-14

Business_Combinations_Addition

Business Combinations - Additional Information (Detail)

3 Months Ended

9 Months Ended

153 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Oct. 14, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Brokerage [Member]

Brokerage [Member]

2014 Acquisitions [Member]

2014 Acquisitions [Member]

Oval Group of Companies (OGC) [Member]

Crombie Lockwood Oamps [Member]

Crombie Lockwood Oamps [Member]

Crombie Lockwood Oamps [Member]

Noraxis Capital Corporation (NCC) [Member]

Noraxis Capital Corporation (NCC) [Member]

2013 Acquisitions [Member]

2013 Acquisitions [Member]

Business Acquisition [Member]

Business Acquisition [Member]

Business Acquisition [Member]

Business Acquisition [Member]

Business Acquisition [Member]

Entity

Entity

Entity

Entity

Entity

USD ($)

USD ($)

Market Approach Valuation Technique [Member]

Market Approach Valuation Technique [Member]

USD ($)

USD ($)

AUD

Subsequent Event [Member]

USD ($)

CAD

Income Approach Valuation Technique [Member]

Income Approach Valuation Technique [Member]

USD ($)

Brokerage [Member]

Brokerage [Member]

Brokerage [Member]

Brokerage [Member]

Minimum [Member]

Maximum [Member]

Employee

Employees

USD ($)

Employees

Minimum [Member]

Maximum [Member]

USD ($)

Expiration Lists [Member]

Non-Compete Agreements [Member]

Trade Names [Member]

Office

Office

USD ($)

USD ($)

USD ($)

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash paid for acquisition of equity interest

'

'

$1,836.90

'

'

'

'

'

'

$338.40

$952

'

'

$413.30

'

'

'

'

'

'

'

'

Acquisition agreement date

'

'

'

'

'

'

'

'

'

1-Apr-14

16-Apr-14

'

'

2-Jul-14

2-Jul-14

'

'

'

'

'

'

'

Number of employees at offices of acquired entity

'

'

'

'

'

'

'

'

'

1,000

1,700

'

'

650

650

'

'

'

'

'

'

'

Number of offices in which acquiree entity operates

'

'

'

'

'

'

'

'

'

24

50

'

'

'

'

'

'

'

'

'

'

'

Common stock issued for net proceeds

'

'

21.9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Underwriting discount

'

'

911.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Foreign currency derivative investment contract amount

'

'

'

'

'

'

'

'

'

'

'

400

'

'

'

'

'

'

'

'

'

'

Unrealized fair value, pretax gain

'

'

'

'

'

'

'

'

'

'

1.9

'

'

'

'

'

'

'

'

'

'

'

Payment for excess of net current assets

'

'

'

'

'

'

'

'

'

'

'

'

35.3

'

'

'

'

'

'

'

'

'

Percentage of equity on which cash consideration paid

'

'

'

'

'

'

'

'

'

'

'

'

'

89.00%

89.00%

'

'

'

'

'

'

'

Revenue generated by Noraxis

'

'

'

'

'

'

'

'

'

'

'

'

'

'

125

'

'

'

'

'

'

'

Revenue growth rate

'

'

'

'

'

'

'

5.00%

10.00%

'

'

'

'

'

'

2.00%

3.00%

'

'

'

'

'

Discount rate

'

'

'

'

'

'

'

8.50%

9.50%

'

'

'

'

'

'

12.50%

14.50%

'

'

'

'

'

Accretion of the discount on acquisition

3.9

2.9

10.6

8.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Income related to net adjustments

0.6

3.3

6

7.2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of companies acquired

17

20

49

53

333

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate amount of maximum earnout obligations related to acquisitions

'

'

517.9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet

'

'

185.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill

1,223.30

'

1,223.30

'

1,223.30

1,223.30

1,223.30

'

'

245.7

'

'

'

291

'

'

'

'

'

'

'

'

Expiration lists

790.7

'

790.7

'

790.7

790.7

790.7

'

'

129.9

'

'

'

139.7

'

'

'

'

790.7

'

'

'

Non-compete agreements

12

'

12

'

12

12

12

'

'

1

'

'

'

4

'

'

'

'

12

'

'

'

Trade name

10

'

10

'

10

10

10

'

'

0.6

'

'

'

4

'

'

'

'

10

'

'

'

Attrition rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.00%

11.50%

'

'

'

'

'

Expiration lists, amortization period, minimum, years

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expiration lists, amortization period, maximum, years

'

'

'

'

'

'

'15 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non-compete agreements, amortization period, minimum, years

'

'

'

'

'

'

'1 year

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non-compete agreements, amortization period, maximum, years

'

'

'

'

'

'

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Trade names, amortization period, minimum ,years

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Trade names, amortization period, maximum, years

'

'

'

'

'

'

'15 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization of intangible assets related to brokerage segment

'

'

'

2.2

'

0.6

1.2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Business acquisition not deductible for income tax purposes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

602.8

10.5

8.9

Deferred tax liability

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

109

'

'

'

Goodwill related to nondeductible amortizable intangible assets

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

109

'

'

'

Annualized revenue of business acquisitions during 9 month period ended September 30, 2014

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

693.6

'

'

'

'

Total revenues related to acquisitions in the aggregate

1,293

1,004.60

3,681

2,833.40

'

'

'

'

'

'

'

'

'

'

'

'

'

245.7

'

'

'

'

Net earnings

$94.20

$87

$271.10

$256.80

'

'

'

'

'

'

'

'

'

'

'

'

'

$27.30

'

'

'

'

Business_Combinations_Summary_

Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	$67.50
Other current assets	953.7
Fixed assets	28.8
Noncurrent assets	14.6
Goodwill	1,223.30
Expiration lists	790.7
Non-compete agreements	12
Trade names	10
Total assets acquired	3,100.60
Current liabilities	746.6
Noncurrent liabilities	275.7
Total liabilities assumed	1,022.30
Total net assets acquired	2,078.30
Oval Group of Companies (OGC) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	23.1
Other current assets	129.6
Fixed assets	2.1
Noncurrent assets	0
Goodwill	245.7
Expiration lists	129.9
Non-compete agreements	1
Trade names	0.6
Total assets acquired	532
Current liabilities	129.5
Noncurrent liabilities	52.3
Total liabilities assumed	181.8
Total net assets acquired	350.2
Heritage Insurance Management Limited (HIM) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	2.9
Other current assets	4.9
Fixed assets	0.3
Noncurrent assets	0
Goodwill	14.8
Expiration lists	20.3
Non-compete agreements	1.3
Trade names	0
Total assets acquired	44.5
Current liabilities	6.8
Noncurrent liabilities	0
Total liabilities assumed	6.8
Total net assets acquired	37.7
MGA Insurance Group (MGA) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	0.2
Other current assets	8.9
Fixed assets	0.8
Noncurrent assets	0
Goodwill	27
Expiration lists	33.2
Non-compete agreements	0.3
Trade names	0
Total assets acquired	70.4
Current liabilities	4.1
Noncurrent liabilities	0
Total liabilities assumed	4.1
Total net assets acquired	66.3
Crombie/OAMPS (CO) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	26.6
Other current assets	695.5
Fixed assets	17.1
Noncurrent assets	7
Goodwill	535.9
Expiration lists	325.3
Non-compete agreements	4.2
Trade names	4.2
Total assets acquired	1,615.80
Current liabilities	490
Noncurrent liabilities	174.3
Total liabilities assumed	664.3
Total net assets acquired	951.5
Insurance Point, LLC (IPL) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	2.7
Other current assets	0.4
Fixed assets	0
Noncurrent assets	0
Goodwill	2.5
Expiration lists	15.3
Non-compete agreements	0.2
Trade names	0
Total assets acquired	21.1
Current liabilities	2.9
Noncurrent liabilities	0.1
Total liabilities assumed	3
Total net assets acquired	18.1
Trip Mate, Inc. (TMI) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	0
Other current assets	7
Fixed assets	1.9
Noncurrent assets	0
Goodwill	5.9
Expiration lists	10.3
Non-compete agreements	0.1
Trade names	0
Total assets acquired	25.2
Current liabilities	5.8
Noncurrent liabilities	0.2
Total liabilities assumed	6
Total net assets acquired	19.2
Noraxis Capital Corporation (NCC) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	10.2
Other current assets	73
Fixed assets	4.9
Noncurrent assets	3.5
Goodwill	291
Expiration lists	139.7
Non-compete agreements	4
Trade names	4
Total assets acquired	530.3
Current liabilities	72.5
Noncurrent liabilities	42.6
Total liabilities assumed	115.1
Total net assets acquired	415.2
Cowles & Connell (CC) [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	0.6
Other current assets	9.1
Fixed assets	0.1
Noncurrent assets	0
Goodwill	7.8
Expiration lists	11.2
Non-compete agreements	0
Trade names	0.4
Total assets acquired	29.2
Current liabilities	9.4
Noncurrent liabilities	0
Total liabilities assumed	9.4
Total net assets acquired	19.8
Thirty-Seven Other Acquisitions [Member]	'
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]	'
Cash	1.2
Other current assets	25.3
Fixed assets	1.6
Noncurrent assets	4.1
Goodwill	92.7
Expiration lists	105.5
Non-compete agreements	0.9
Trade names	0.8
Total assets acquired	232.1
Current liabilities	25.6
Noncurrent liabilities	6.2
Total liabilities assumed	31.8
Total net assets acquired	$200.30

Business_Combinations_Summary_1

Business Combinations - Summary of Unaudited Pro Forma Historical Results (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Business Combinations [Abstract]	'	'	'	'
Total revenues	$1,293	$1,004.60	$3,681	$2,833.40
Net earnings	$94.20	$87	$271.10	$256.80
Basic net earnings per share	$0.59	$0.56	$1.69	$1.68
Diluted net earnings per share	$0.58	$0.56	$1.68	$1.66

Intangible_Assets_Carrying_Amo

Intangible Assets - Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill [Line Items]	'	'
Total goodwill - net	$3,296.20	$2,145.20
Unites States [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	1,592.20	1,469.80
United Kingdom [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	833.4	584.9
Canada [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	307.6	26.8
Australia [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	271.4	37.1
Other Foreign, Principally New Zealand [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	291.6	26.6
Brokerage [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	3,273.80	2,122.90
Brokerage [Member] | Unites States [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	1,572	1,449.60
Brokerage [Member] | United Kingdom [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	831.2	582.8
Brokerage [Member] | Canada [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	307.6	26.8
Brokerage [Member] | Australia [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	271.4	37.1
Brokerage [Member] | Other Foreign, Principally New Zealand [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	291.6	26.6
Risk Management [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	22.4	22.3
Risk Management [Member] | Unites States [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	20.2	20.2
Risk Management [Member] | United Kingdom [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	2.2	2.1
Risk Management [Member] | Canada [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Risk Management [Member] | Australia [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Risk Management [Member] | Other Foreign, Principally New Zealand [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member] | Unites States [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member] | United Kingdom [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member] | Canada [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member] | Australia [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	0	0
Corporate [Member] | Other Foreign, Principally New Zealand [Member]	'	'
Goodwill [Line Items]	'	'
Total goodwill - net	$0	$0

Intangible_Assets_Changes_in_C

Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Goodwill [Line Items]	'
Beginning Balance	$2,145.20
Goodwill acquired during the period	1,223.30
Goodwill adjustments due to appraisals and other acquisition adjustments	-27.7
Goodwill written-off related to sales of business	-0.6
Foreign currency translation adjustments during the period	-44
Ending Balance	3,296.20
Brokerage [Member]	'
Goodwill [Line Items]	'
Beginning Balance	2,122.90
Goodwill acquired during the period	1,223.30
Goodwill adjustments due to appraisals and other acquisition adjustments	-27.7
Goodwill written-off related to sales of business	-0.6
Foreign currency translation adjustments during the period	-44.1
Ending Balance	3,273.80
Risk Management [Member]	'
Goodwill [Line Items]	'
Beginning Balance	22.3
Goodwill acquired during the period	0
Goodwill adjustments due to appraisals and other acquisition adjustments	0
Goodwill written-off related to sales of business	0
Foreign currency translation adjustments during the period	0.1
Ending Balance	22.4
Corporate [Member]	'
Goodwill [Line Items]	'
Beginning Balance	0
Goodwill acquired during the period	0
Goodwill adjustments due to appraisals and other acquisition adjustments	0
Goodwill written-off related to sales of business	0
Foreign currency translation adjustments during the period	0
Ending Balance	$0

Intangible_Assets_Major_Classe

Intangible Assets - Major Classes of Amortizable Intangible Assets (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]	'	'
Amortizable intangible assets, net	$1,771.10	$1,078.80
Expiration Lists [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Amortizable intangible assets, gross	2,409	1,563.50
Accumulated amortization	-675.9	-511.3
Amortizable intangible assets, net	1,733.10	1,052.20
Non-Compete Agreements [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Amortizable intangible assets, gross	44	37.3
Accumulated amortization	-28.4	-25.9
Amortizable intangible assets, net	15.6	11.4
Trade Names [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Amortizable intangible assets, gross	31.8	22.1
Accumulated amortization	-9.4	-6.9
Amortizable intangible assets, net	$22.40	$15.20

Intangible_Assets_Estimated_Ag

Intangible Assets - Estimated Aggregate Amortization Expense (Detail) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'
2014 (remaining six months)	$53.20
2015	208.8
2016	203.1
2017	193.1
2018	180.3
Total	$838.50

Credit_and_Other_Debt_Agreemen2

Credit and Other Debt Agreements - Note Purchase Agreements - Additional information (Detail) (Note Purchase Agreements [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Debt Instrument [Line Items]	'
Amount payable to redeem the notes, percent of the principal amount	100.00%
Discount rate used to compute the remaining scheduled payments of principal and interest	'U.S. Treasury yields plus 0.5%
6.44% Senior Notes, Series B [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	300
Note payable, semi-annual payments of interest, fixed rate	6.44%
Debt instrument, maturity date	3-Aug-17
5.85% Senior Notes, Series C [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	150
Note payable, semi-annual payments of interest, fixed rate	5.85%
5.85% Senior Notes, Series C [Member] | First Installment [Member]	'
Debt Instrument [Line Items]	'
Debt instrument, maturity date	30-Nov-16
5.85% Senior Notes, Series C [Member] | Second Installment [Member]	'
Debt Instrument [Line Items]	'
Debt instrument, maturity date	30-Nov-18
5.85% Senior Notes, Series C [Member] | Third Installment [Member]	'
Debt Instrument [Line Items]	'
Debt instrument, maturity date	30-Nov-19
5.18% Senior Notes, Series D [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	75
Note payable, semi-annual payments of interest, fixed rate	5.18%
Debt instrument, maturity date	10-Feb-21
5.49% Senior Notes, Series E [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	50
Note payable, semi-annual payments of interest, fixed rate	5.49%
Debt instrument, maturity date	10-Feb-23
3.99% Senior Notes, Series F [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	50
Note payable, semi-annual payments of interest, fixed rate	3.99%
Debt instrument, maturity date	10-Jul-20
3.69% Senior Notes Series G [Member] | Private Placement [Member]	'
Debt Instrument [Line Items]	'
Debt instrument, maturity date	14-Jun-22
Private placement debt, additional amount committed to borrow	200
Interest rate	3.69%
4.58% Senior Notes, Series H [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	325
Note payable, semi-annual payments of interest, fixed rate	4.58%
Debt instrument, maturity date	27-Feb-24
4.73% Senior Notes, Series I [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	175
Note payable, semi-annual payments of interest, fixed rate	4.73%
Debt instrument, maturity date	27-Feb-26
4.98% Senior Notes, Series J [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	100
Note payable, semi-annual payments of interest, fixed rate	4.98%
Debt instrument, maturity date	27-Feb-29
Senior Notes Series H, I & J [Member]	'
Debt Instrument [Line Items]	'
Debt acquisition costs	1.4
2.80% Senior Notes, Series K [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	50
Note payable, semi-annual payments of interest, fixed rate	2.80%
Debt instrument, maturity period	'2018
3.20% Senior Notes, Series L [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	50
Note payable, semi-annual payments of interest, fixed rate	3.20%
Debt instrument, maturity period	'2019
3.48% Senior Notes, Series M [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	50
Note payable, semi-annual payments of interest, fixed rate	3.48%
Debt instrument, maturity period	'2020
4.13% Senior Notes, Series N [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	200
Note payable, semi-annual payments of interest, fixed rate	4.13%
Debt instrument, maturity period	'2023
4.31% Senior Notes, Series O [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	200
Note payable, semi-annual payments of interest, fixed rate	4.31%
Debt instrument, maturity period	'2025
4.36% Senior Notes, Series P [Member]	'
Debt Instrument [Line Items]	'
Notes issued and sold	150
Note payable, semi-annual payments of interest, fixed rate	4.36%
Debt instrument, maturity period	'2026
Senior Notes Series K, L, M, N, O & P [Member]	'
Debt Instrument [Line Items]	'
Debt acquisition costs	2.6

Credit_and_Other_Debt_Agreemen3

Credit and Other Debt Agreements - Credit Agreement - Additional information (Detail)

9 Months Ended

9 Months Ended

9 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

USD ($)

USD ($)

USD ($)

Revolving Credit Facility [Member]

Credit Agreement [Member]

Credit Agreement [Member]

Credit Agreement [Member]

Credit Facility Two [Member]

Credit Facility Two [Member]

Credit Facility Three [Member]

Credit Facility Three [Member]

Credit Facility Four [Member]

Credit Facility Four [Member]

Note Purchase Agreements [Member]

USD ($)

USD ($)

Swing Loan [Member]

Standby Letters of Credit [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Level 3 [Member]

Institution

USD ($)

USD ($)

AUD

NZD

AUD

NZD

NZD

AUD

USD ($)

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility, maximum borrowing capacity

'

'

'

'

$600,000,000

'

'

'

'

'

'

'

'

'

Number of financial institutions entered in unsecured multicurrency credit agreement

'

'

'

'

15

'

'

'

'

'

'

'

'

'

Debt instrument, maturity date

'

'

'

'

19-Sep-18

'

'

'

'

'

'

'

'

'

Long-term debt, gross

'

'

'

'

'

50,000,000

75,000,000

'

'

'

'

'

'

'

Line of credit facility, maximum amount outstanding during period

'

'

'

'

850,000,000

'

'

'

'

'

'

'

'

'

Fixed rate (alternative one) over LIBOR

'

'

'

'

0.85%

'

'

'

'

'

'

'

'

'

Fixed rate (alternative two) over LIBOR

'

'

'

'

0.95%

'

'

'

'

'

'

'

'

'

Fixed rate (alternative three) over LIBOR

'

'

'

'

1.05%

'

'

'

'

'

'

'

'

'

Fixed rate (alternative four) over LIBOR

'

'

'

'

1.25%

'

'

'

'

'

'

'

'

'

Fixed rate (alternative five) over LIBOR

'

'

'

'

1.45%

'

'

'

'

'

'

'

'

'

Annual facility fee of revolving credit facility (alternative one)

'

'

'

'

0.15%

'

'

'

'

'

'

'

'

'

Annual facility fee of revolving credit facility (alternative two)

'

'

'

'

0.18%

'

'

'

'

'

'

'

'

'

Annual facility fee of revolving credit facility (alternative three)

'

'

'

'

0.20%

'

'

'

'

'

'

'

'

'

Annual facility fee of revolving credit facility (alternative four)

'

'

'

'

0.25%

'

'

'

'

'

'

'

'

'

Annual facility fee of revolving credit facility (alternative five)

'

'

'

'

0.30%

'

'

'

'

'

'

'

'

'

Debt acquisition costs

'

'

'

'

2,100,000

'

'

'

'

'

'

'

'

'

Line of credit facility, amount outstanding

'

'

'

'

'

'

20,600,000

133,000,000

22,000,000

'

5,200,000

11,500,000

'

'

Liabilities

6,732,000,000

'

4,775,000,000

'

'

'

9,300,000

'

'

'

'

'

'

'

Line of credit facility, fair value of amount outstanding

'

'

'

'

'

'

147,000,000

'

'

'

'

'

'

2,253,500,000

Line of credit facility, remaining borrowing capacity

'

'

'

'

'

'

432,400,000

17,000,000

13,000,000

19,800,000

3,500,000

3,500,000

19,800,000

'

Line of credit facility, increase in additional borrowings

1,017,400,000

445,500,000

'

'

'

'

54,400,000

'

'

'

'

'

'

'

Net borrowings on premium financing debt facility

36,300,000

'

'

'

'

'

'

150,000,000

35,000,000

25,000,000

'

15,000,000

'

'

Date of expire

'

'

'

15-Jun-16

'

'

'

'

'

'

'

'

'

'

Interest rate for facility

'

'

'

'The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.65%. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.85%.B The annual fee for Facility B is 0.7425% of the undrawn commitments for the two tranches of the facility.B The annual fee for Facilities C and D is 0.80% of the total commitments of the facilities.B In connection with entering into the Premium Financing Debt Facility, we incurred an upfront fee of 0.30% of the principal amount of the committed facilities.

'

'

'

'

'

'

'

'

'

'

Interest rate on debt percentage

'

'

'

'

'

'

'

1.65%

1.65%

0.85%

'

0.85%

'

'

Annual fee percentage

'

'

'

'

'

'

'

0.74%

0.74%

0.80%

'

0.80%

'

'

Up front fee Percentage

'

'

'

0.30%

'

'

'

'

'

'

'

'

'

'

Long-term debt

'

'

'

'

'

'

'

'

'

'

'

'

'

2,125,000,000

Estimated fair value of outstanding borrowings

'

'

'

'

147,000,000

'

'

'

'

'

'

'

'

'

Debt instrument fair value amount

'

'

'

$149,200,000

'

'

'

'

'

'

'

'

'

'

Credit_and_Other_Debt_Agreemen4

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	$2,421.20	$1,455.50
Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	149.2	0
Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	2,125	925
Fixed Rate of 6.26%, Balloon Due 2014 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	'	100
Fixed Rate of 6.44%, Balloon Due 2017 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	300	300
Fixed Rate of 2.80%, Balloon Due 2018 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	50	'
Fixed Rate of 3.20%, Balloon Due 2019 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	50	'
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	150	150
Fixed Rate of 3.99%, Balloon Due 2020 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	50	50
Fixed Rate of 3.48%, Balloon Due 2020 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	50	'
Fixed Rate of 5.18%, Balloon Due 2021 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	75	75
Fixed rate of 3.69%, Balloon Due 2022 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	200	200
Fixed Rate of 5.49%, Balloon Due 2023 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	50	50
Fixed Rate of 4.13%, Balloon Due 2023 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	200	'
Fixed Rate of 4.58% Balloon Due 2024 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	325	'
Fixed Rate of 4.31%, Balloon Due 2025 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	200	'
Fixed Rate of 4.73% Balloon Due 2026 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	175	'
Fixed Rate of 4.36%, Balloon Due 2026 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	150	'
Fixed Rate of 4.98% Balloon Due 2029 [Member] | Note Purchase Agreements [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	100	0
Prime or LIBOR plus up to 1.45%, expires September 19, 2018 [Member] | Credit Agreement [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	147	530.5
Interbank rates plus 1.65%, Expires June 15, 2016 [Member] | AUD denominated tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	117.7	0
Interbank rates plus 1.65%, Expires June 15, 2016 [Member] | NZD denominated tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	17.7	0
Interbank rates plus 0.85%, Expires June 15, 2016 [Member] | AUD denominated tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	4.6	0
Interbank rates plus 0.85%, Expires June 15, 2016 [Member] | NZD denominated tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Semi-annual payments of interest	$9.20	$0

Credit_and_Other_Debt_Agreemen5

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fixed Rate of 6.26%, Balloon Due 2014 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	6.26%	6.26%
Principal payments, year due	'2014	'2014
Fixed Rate of 6.44%, Balloon Due 2017 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	6.44%	6.44%
Principal payments, year due	'2017	'2017
Fixed Rate of 2.80%, Balloon Due 2018 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	2.80%	2.80%
Principal payments, year due	'2018	'2018
Fixed Rate of 3.20%, Balloon Due 2019 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	3.20%	3.20%
Principal payments, year due	'2019	'2019
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	5.85%	5.85%
Long-Term debt maturities repayments in 2016	50	50
Long-Term debt maturities repayments in 2018	50	50
Long-Term debt maturities repayments in 2019	50	50
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member] | First Installment [Member]	'	'
Debt Instrument [Line Items]	'	'
Principal payments, year due	'2016	'2016
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member] | Second Installment [Member]	'	'
Debt Instrument [Line Items]	'	'
Principal payments, year due	'2018	'2018
Fixed Rate of 5.85%, $50.0 Million Due in 2016, 2018 and 2019 [Member] | Third Installment [Member]	'	'
Debt Instrument [Line Items]	'	'
Principal payments, year due	'2019	'2019
Fixed Rate of 3.99%, Balloon Due 2020 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	3.99%	3.99%
Principal payments, year due	'2020	'2020
Fixed Rate of 3.48%, Balloon Due 2020 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	3.48%	3.48%
Principal payments, year due	'2020	'2020
Fixed Rate of 5.18%, Balloon Due 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	5.18%	5.18%
Principal payments, year due	'2021	'2021
Fixed rate of 3.69%, Balloon Due 2022 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	3.69%	3.69%
Principal payments, year due	'2022	'2022
Fixed Rate of 5.49%, Balloon Due 2023 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	5.49%	5.49%
Principal payments, year due	'2023	'2023
Fixed Rate of 4.13%, Balloon Due 2023 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.13%	4.13%
Principal payments, year due	'2023	'2023
Fixed Rate of 4.58% Balloon Due 2024 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.58%	4.58%
Principal payments, year due	'2024	'2024
Fixed Rate of 4.31%, Balloon Due 2025 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.31%	4.31%
Principal payments, year due	'2025	'2025
Fixed Rate of 4.73% Balloon Due 2026 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.73%	4.73%
Principal payments, year due	'2026	'2026
Fixed Rate of 4.36%, Balloon Due 2026 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.36%	4.36%
Principal payments, year due	'2026	'2026
Fixed Rate of 4.98% Balloon Due 2029 [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	4.98%	4.98%
Principal payments, year due	'2029	'2029
Prime or LIBOR plus up to 1.45%, expires September 19, 2018 [Member] | Credit Agreement [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	1.45%	1.45%
Periodic payments of interest and principal, expiry date	19-Sep-18	19-Sep-18
Premium Financing Debt Facility [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic payments of interest and principal, expiry date	15-Jun-16	15-Jun-16
Premium Financing Debt Facility [Member] | Interbank rates plus 1.65%, Expires June 15, 2016 [Member] | Facility B [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	1.65%	1.65%
Premium Financing Debt Facility [Member] | Interbank rates plus 0.85%, Expires June 15, 2016 [Member] | Facility C and D [Member]	'	'
Debt Instrument [Line Items]	'	'
Periodic Payment of Interest	0.85%	0.85%

Earnings_Per_Share_Computation

Earnings Per Share - Computation of Basic and Diluted Net EPS (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]	'	'	'	'
Net earnings	$93.60	$74.60	$251.90	$208.60
Weighted average number of common shares outstanding	160.2	129.8	149.6	127.7
Dilutive effect of stock options using the treasury stock method	1.3	1.5	1.4	1.6
Weighted average number of common and common equivalent shares outstanding	161.5	131.3	151	129.3
Basic net earnings per share	$0.58	$0.57	$1.68	$1.63
Diluted net earnings per share	$0.58	$0.57	$1.67	$1.61

Earnings_Per_Share_Additional_

Earnings Per Share - Additional information (Detail)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]	'	'	'	'
Options to purchase common stock shares outstanding	1.9	1.7	1.4	1.2

Stock_Option_Plans_Additional_

Stock Option Plans - Additional information (Detail) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

0 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Mar. 12, 2014

Mar. 13, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Minimum [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Executive Officer [Member]

Long Term Incentive Plan [Member]

Performance-Based Restricted Stock [Member]

Cash Settled Performance Shares [Member]

Stock Settled Performance Shares [Member]

Black-Scholes Option Pricing Model [Member]

Black-Scholes Option Pricing Model [Member]

Performance-Based Restricted Stock [Member]

Performance-Based Restricted Stock [Member]

Stock Option Plans [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum number of shares available

'

'

'

'

'

'

'

'

'

2,000,000

'

'

'

'

'

Maximum number of shares granted during any fiscal year to any person

'

'

200,000

'

'

'

'

'

'

'

100,000

'

100,000

'

'

Maximum amount payable for the shares granted during any fiscal year to any person

'

'

'

'

'

'

'

'

'

'

'

$5,000,000

'

'

'

Maximum period for the exercise of stock options, years

'

'

'7 years

'

'

'

'

'

'

'

'

'

'

'

'

Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

Shares available for grant

'

'

'

'

'

'

1,923,000

1,665,000

'

9,200,000

'

'

'

'

'

Stock options granted, exercise percentage, on the anniversary date of the grant in 2017

'

'

'

'

'

'

34.00%

34.00%

'

'

'

'

'

'

'

Stock options granted, exercise percentage, on the anniversary date of the grant in 2018

'

'

'

'

'

'

33.00%

33.00%

'

'

'

'

'

'

'

Stock options granted, exercise percentage, on the anniversary date of the grant in 2019

'

'

'

'

'

'

33.00%

33.00%

'

'

'

'

'

'

'

Number of years options expire, maximum

'

'

'7 years

'

'7 years

'

'

'

'

'

'

'

'

'

'

Minimum age of employee with not subject to award forfeiture on condition compliance

'

'

'

'

'

'

'

'

'55 years

'

'

'

'

'

'

Period of Service from Grant Date Stock Options Awarded Not Subject to Forfeiture

'

'

'

'

'

'2 years

'

'

'

'

'

'

'

'

'

Compensation expense related to stock option grants

2,700,000

2,200,000

6,700,000

5,400,000

'

'

'

'

'

'

'

'

'

'

'

Weighted average fair value per option for all options

'

'

'

'

'

'

'

'

'

'

'

'

'

$9.66

$7.51

Total intrinsic value of options exercised

'

'

26,600,000

28,800,000

'

'

'

'

'

'

'

'

'

'

'

Total unrecognized compensation cost related to nonvested options

$31,600,000

'

$31,600,000

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average period, years

'

'

'4 years

'

'

'

'

'

'

'

'

'

'

'

'

Stock_Option_Plans_BlackSchole

Stock Option Plans - Black-Scholes Option Pricing Model with Weighted Average (Detail)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'	'
Expected dividend yield	3.00%	3.50%
Expected risk-free interest rate	1.80%	1.20%
Volatility	28.90%	29.60%
Expected life (in years)	'5 years 6 months	'6 years

Stock_Option_Plans_Stock_Optio

Stock Option Plans - Stock Option Activity and Related Information (Detail) (USD $)	9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Shares Under Option, Beginning balance	8.3
Shares Under Option, Granted	1.9
Shares Under Option, Exercised	-1.5
Shares Under Option, Forfeited or canceled	-0.1
Shares Under Option, Ending balance	8.6
Shares Under Option, Exercisable at end of period	2.8
Shares Under Option, Ending vested and expected to vest	8.4
Weighted Average Exercise Price, Beginning balance	$31.35
Weighted Average Exercise Price, Granted	$46.86
Weighted Average Exercise Price, Exercised	$28.94
Weighted Average Exercise Price, Forfeited or canceled	$28.56
Weighted Average Exercised Price, Ending balance	$35.31
Weighted Average Exercise Price, Exercisable at end of period	$26.96
Weighted Average Exercise price, Ending vested and expected to vest	$35.18
Weighted Average Remaining Contractual Term (in years), Ending balance	'4 years 1 month 24 days
Weighted Average Remaining Contractual Term (in years), Exercisable at end of period	'2 years 29 days
Weighted Average Remaining Contractual Term (in years), Ending vested and expected to vested	'4 years 1 month 13 days
Aggregate Intrinsic Value, Ending Balance	$89.30
Aggregate Intrinsic Value, Exercisable at end of period	51.8
Aggregate Intrinsic Value, Ending vested and expected to vest	$88.70

Stock_Option_Plans_Stock_Optio1

Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) (USD $)	9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Range of Exercise Prices, minimum	$21.28	'
Range of Exercise Prices, maximum	$46.87	'
Option Outstanding, Number Outstanding	8.6	'
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	'4 years 1 month 24 days	'
Option Outstanding, Weighted Average Exercise Price	$35.31	$31.35
Options Exercisable, Number Exercisable	2.8	'
Option Exercisable, Weighted Average Exercise Price	$26.96	'
Exercise Prices Range $ 21.28 - $ 27.25 [Member]	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Range of Exercise Prices, minimum	$21.28	'
Range of Exercise Prices, maximum	$27.25	'
Option Outstanding, Number Outstanding	2.4	'
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	'1 year 9 months 26 days	'
Option Outstanding, Weighted Average Exercise Price	$25.81	'
Options Exercisable, Number Exercisable	2	'
Option Exercisable, Weighted Average Exercise Price	$25.80	'
Exercise Prices Range $ 27.35 - $ 35.71 [Member]	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Range of Exercise Prices, minimum	$27.35	'
Range of Exercise Prices, maximum	$35.71	'
Option Outstanding, Number Outstanding	2.6	'
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	'3 years 9 months 4 days	'
Option Outstanding, Weighted Average Exercise Price	$33.04	'
Options Exercisable, Number Exercisable	0.8	'
Option Exercisable, Weighted Average Exercise Price	$29.86	'
Exercise Prices Range $ 35.95 - $ 39.17 [Member]	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Range of Exercise Prices, minimum	$35.95	'
Range of Exercise Prices, maximum	$39.17	'
Option Outstanding, Number Outstanding	1.7	'
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	'5 years 5 months 12 days	'
Option Outstanding, Weighted Average Exercise Price	$39.15	'
Options Exercisable, Number Exercisable	'	'
Option Exercisable, Weighted Average Exercise Price	'	'
Exercise Prices Range $ 46.87 - $ 46.87 [Member]	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Range of Exercise Prices, minimum	$46.16	'
Range of Exercise Prices, maximum	$46.87	'
Option Outstanding, Number Outstanding	1.9	'
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	'6 years 5 months 12 days	'
Option Outstanding, Weighted Average Exercise Price	$46.87	'
Options Exercisable, Number Exercisable	'	'
Option Exercisable, Weighted Average Exercise Price	'	'

Deferred_Compensation_Addition

Deferred Compensation - Additional information (Detail) (USD $)	3 Months Ended				9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Investments And Employee Deferred Compensation Plan [Line Items]	'	'	'	'	'	'	'
Deferred Equity Participation Plan, distributions to key executives, age	'	'	'	'	'Age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement	'	'
Age 62 Plan [Member]	'	'	'	'	'	'	'
Investments And Employee Deferred Compensation Plan [Line Items]	'	'	'	'	'	'	'
Compensation approved by committee, value	'	$9.20	'	$8	'	'	'
Charge to compensation expenses related to awards	2.4	'	2	'	5.6	5.3	'
Unearned deferred compensation, value	'	'	'	'	30.7	'	26.3
Unearned deferred compensation, shares	'	'	'	'	2.3	'	2.1
Total intrinsic value of unvested equity based awards	'	'	'	'	102.5	'	96.4
Cash and equity awards with aggregate fair value vested and distributed to participants	'	'	'	'	1.3	0.7	'
Deferred Cash Participation Plan (DCPP) [Member]	'	'	'	'	'	'	'
Investments And Employee Deferred Compensation Plan [Line Items]	'	'	'	'	'	'	'
Compensation approved by committee, value	'	2.9	'	2.7	'	'	'
Charge to compensation expenses related to awards	0.7	'	0.7	'	2.2	1.5	'
Cash and equity awards with aggregate fair value vested and distributed to participants	'	'	'	'	$0.10	'	'

Restricted_Stock_Performance_S1

Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail) (USD $)

9 Months Ended

9 Months Ended

0 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

0 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

9 Months Ended

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Mar. 12, 2014

Mar. 13, 2013

Sep. 30, 2014

Mar. 31, 2014

Sep. 30, 2013

Mar. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2013

Mar. 31, 2013

Mar. 12, 2014

Sep. 30, 2014

Sep. 30, 2014

Mar. 31, 2014

Mar. 12, 2014

Mar. 31, 2013

Mar. 13, 2013

Mar. 31, 2012

Mar. 16, 2012

Mar. 08, 2011

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

Times

Minimum [Member]

Executive Officer [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Unvested Restricted Stock [Member]

Unvested Restricted Stock [Member]

2011 Provisional Cash Awards [Member]

2011 Provisional Cash Awards [Member]

2011 Provisional Cash Awards [Member]

Restricted Stock Plan [Member]

Restricted Stock Plan [Member]

Restricted Stock Plan [Member]

Restricted Stock Plan [Member]

Restricted Stock Plan [Member]

Performance Shares [Member]

Performance Shares [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

Cash Awards [Member]

2013 Provisional Cash Awards [Member]

2013 Provisional Cash Awards [Member]

2013 Provisional Cash Awards [Member]

2012 Provisional Cash Awards [Member]

2012 Provisional Cash Awards [Member]

2012 Provisional Cash Awards [Member]

2012 Provisional Cash Awards [Member]

Minimum [Member]

Minimum [Member]

Executive Officer [Member]

Executive Officer [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Officer and Key Employees [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation, shares outstanding, Value

'

'

'

'

'

'

$2,000,000

'

'

'

$2,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation, shares outstanding

8,600,000

8,300,000

'

'

'

'

2,000,000

'

'

'

2,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares granted in the period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33,741

19,250

323,600

17,000

345,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value of grants in period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,500,000

900,000

15,200,000

800,000

13,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share based payment award vesting date

'

'

'

'

'

'

'

12-Mar-18

'

13-Mar-17

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Minimum age of employee with not subject to award forfeiture on condition compliance

'

'

'

'55 years

'

'

'

'

'

'

'

'

'

'

'55 years

'55 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Period of Service from Grant Date Stock Options Awarded Not Subject to Forfeiture

'

'

'2 years

'

'

'

'

'

'

'

'

'

'2 years

'2 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted, exercise percentage, year one

'

'

'

'

34.00%

34.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

34.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted, exercise percentage, year two

'

'

'

'

33.00%

33.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted, exercise percentage, year three

'

'

'

'

33.00%

33.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Restricted stock or unit expense

'

'

'

'

'

'

3,100,000

'

2,300,000

'

9,600,000

7,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total intrinsic value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

55,000,000

46,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity awards with an aggregate fair value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9,700,000

8,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Performance unit awards approved, Shares

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

48,800

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Performance unit awards approved, Fair value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Performance unit awards, Terms

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'Granted units for the 2014 provisional award will fully vest based on continuous employment through January 1, 2017, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable in 2017.

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Provisional compensation cash awards approved for future grant by compensation committee, value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,800,000

'

10,500,000

'

13,100,000

14,400,000

'

'

'

'

'

'

'

Provisional compensation cash award approved for future grant by compensation committee, units

'

'

'

'

229,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.4

'

'

'

'

'

'

'

'

'

263,000

'

365,000

269,000

432,000

368,000

464,000

'

'

'

'

'

'

'

Performance period, years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vesting period, years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ultimate award value, multiples of original value of the units, minimum

0.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ultimate award value, multiples of original value of the units, maximum

1.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash-based compensation awards, expenses

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,600,000

0

6,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,500,000

4,500,000

0

1,800,000

2,000,000

6,300,000

5,400,000

Grants vested in period fair value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$17,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Retirement_Plans_Components_of

Retirement Plans - Components of Net Periodic Pension Benefit Cost (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]	'	'	'	'
Service cost	$0.10	$0.20	$0.30	$0.40
Interest cost on benefit obligation	3.2	2.9	9.6	8.8
Expected return on plan assets	-4.7	-4.2	-14.1	-12.8
Amortization of net actuarial loss	0.6	2	1.8	5.9
Net periodic benefit (earnings) cost	($0.80)	$0.90	($2.40)	$2.30

Retirement_Plans_Additional_In

Retirement Plans - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended
	Sep. 12, 2014	Sep. 30, 2014	Sep. 30, 2013
	Employees
Compensation and Retirement Disclosure [Abstract]	'	'	'
Minimum contribution by employer	'	$0	$0
Discretionary contributions by employer	'	0	6,300,000
Aggregate lump sum payout	$73,000,000	'	'
Number of employees covered in the plan	2,200	'	'
Defined benefit plan, description	'Eligible participants have from September 12, 2014 to November 12, 2014 to accept the offer, and the lump-sum payments will be made in November and December of 2014, and the accelerated reduced annuity payments will begin as of December 1, 2014.	'	'

Investments_Investments_Report

Investments - Investments Reported in Other Current and Non-Current Assets (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Equity Method Investments [Line Items]	'	'
Assets	$90.60	$90.40
Funding Commitments	2.9	'
Chem-Mod LLC [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	4	4
Funding Commitments	'	'
Chem-Mod International LLC [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	2	2
Funding Commitments	'	'
C-Quest Technologies LLC and C-Quest Technologies International LLC [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	'	2
Funding Commitments	'	'
Clean-Coal Investments [Member] | Controlling Interest [Member] | Fourteen 2009 Era Clean Coal Plants [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	23.2	18.3
Funding Commitments	'	'
Clean-Coal Investments [Member] | Controlling Interest [Member] | Nineteen 2011 Era Clean Coal Plants [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	57.2	59.3
Funding Commitments	'	'
Clean-Coal Investments [Member] | Non-controlling Interest [Member] | One 2011 Era Clean Coal Plant [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	1	1.1
Funding Commitments	'	'
Other Investments [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Assets	3.2	3.7
Funding Commitments	$2.90	'

Investments_Investments_Report1

Investments - Investments Reported in Other Current and Non-Current Assets (Parenthetical) (Detail) (Clean-Coal Investments [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
	Plant	Plant
	Entity	Entity
Schedule of Equity Method Investments [Line Items]	'	'
Number of variable interest entities	1	'
Fourteen 2009 Era Clean Coal Plants [Member] | Controlling Interest [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Number of coal plants	14	14
Number of variable interest entities	5	5
One 2011 Era Clean Coal Plant [Member] | Non-controlling Interest [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Number of coal plants	1	1
Number of variable interest entities	1	1
Nineteen 2011 Era Clean Coal Plants [Member] | Controlling Interest [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Number of coal plants	19	19
Number of variable interest entities	13	13

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	Sep. 01, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Mar. 31, 2014	Aug. 01, 2013	Sep. 30, 2014
In Millions, unless otherwise specified		Chem-Mod Clean-Coal Venture - U.S. And Canadian Operations [Member]	Chem-Mod Clean-Coal Venture [Member]	Chem-Mod International LLC [Member]	C-Quest Technologies LLC and C-Quest Technologies International LLC [Member]	C-Quest Technologies LLC and C-Quest Technologies International LLC [Member]	C-Quest Technologies LLC and C-Quest Technologies International LLC [Member]	C-Quest Technologies LLC and C-Quest Technologies International LLC [Member]
								Change In Option On Delivery Of Additional Interest [Member]
Schedule of Equity Method Investments [Line Items]	'	'	'	'	'	'	'	'
Ownership interest held	99.00%	46.54%	'	31.52%	12.00%	'	'	'
Total assets of variable interest entities	'	'	$11	'	'	'	'	'
Total liabilities of variable interest entities	'	'	1	'	'	'	'	'
Total revenue of limited liability companies	'	'	52.5	'	'	'	'	'
Total expenses of limited liability companies	'	'	29.1	'	'	'	'	'
Non-controlling interest	'	'	26.9	'	'	'	'	'
Increase in ownership interest	'	'	'	'	4.00%	'	'	'
Option to acquire additional interest, percent	'	'	'	'	19.00%	'	'	15.00%
Option to acquire additional interest, total price	'	'	'	'	9.5	'	'	7.5
End date for acquiring additional interest	'	'	'	'	1-Aug-16	'	'	'
Loans to majority owners	'	'	'	'	'	'	$2	'
Interest rate of loan	'	'	'	'	'	'	2.00%	'
Maturity date of of loan	'	'	'	'	15-May-14	'	'	'
Loan description	'	'	'	'	'On August 1, 2013, we loaned the majority owner $2.0 million at a 2% interest rate, which was to mature on May 15, 2014. Also on August 1, 2013, the option to acquire the 19% interests was extended to August 15, 2016. The loan was to be repaid in cash or by delivery of an additional 4% ownership interest in C-Quest's global operations. On March 31, 2014, we accepted payment of the loan by delivery of the additional 4% ownership interest, therefore our option is reduced to 15% and the remaining purchase price is reduced to $7.5 million.	'	'	'
Delivery of additional ownership interest	'	'	'	'	'	4.00%	'	'

Investments_Clean_Coal_Investm

Investments - Clean Coal Investments - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

9 Months Ended

9 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 01, 2013

Sep. 30, 2014

Sep. 01, 2013

Sep. 30, 2014

Mar. 01, 2014

Mar. 01, 2013

Sep. 30, 2014

Mar. 01, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Plant

Limited Liability Company [Member]

Notes Payable, Other Payables [Member]

2009 Era Plants [Member]

2009 Era Plants [Member]

2009 Era Plants [Member]

2011 Era Plants [Member]

2011 Era Plants [Member]

2011 Era Plants [Member]

Long Term Production Contracts [Member]

Clean-Coal Investments [Member]

Clean-Coal Investments [Member]

Clean-Coal Investments [Member]

Clean-Coal Investments [Member]

Clean-Coal Investments [Member]

Clean-Coal Investments [Member]

Chem-Mod LLC [Member]

Chem-Mod LLC [Member]

Chem-Mod LLC [Member]

Plant

Plant

Notes Payable, Other Payables [Member]

Plant

Entity

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

VIE [Member]

Plant

2009 Era Plants [Member]

2011 Era Plants [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Plant

Plant

Schedule of Equity Method Investments [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of clean coal production plants owned

'

'

'

'

'

'

'

'

'

'

'

'

'

27

'

'

'

'

'

'

34

14

20

Number of additional plants acquired

'

'

'

'

'

'

'

'

'

12

'

5

'

'

'

'

'

'

'

'

'

'

'

Number of additional plants acquired with ownership interest range one

'

'

'

'

'

'

'

'

'

9

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of additional plants acquired with ownership interest range two

'

'

'

'

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional nine plants acquired

'

'

'

'

'

'

'

'

'

24.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional nine plants acquired

'

'

'

'

'

'

'

'

'

49.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional three plants acquired

'

'

'

'

'

'

'

'

'

25.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional three plants acquired

'

'

'

'

'

'

'

'

'

60.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

Total revenues

$1,286.80

$835.80

$3,381.10

$2,289.40

'

'

'

$191.20

'

'

$131.50

'

$60.50

'

'

'

'

'

'

'

'

'

'

Total expenses

1,199.10

750.3

3,140

2,064.20

'

'

'

197.7

'

'

138

'

67.2

'

'

'

'

'

'

'

'

'

'

Purchase of consideration received

'

'

'

'

'

'

'

8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payment of cash and other consideration

'

'

'

'

'

'

'

5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Gain on purchase of additional interest

25.6

'

25.6

'

'

'

'

11.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Prior percentage of equity interest in limited liability company

'

'

'

'

'

'

'

25.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional percentage of equity interest in limited liability company upon acquisition

'

'

'

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed assets and other amortizable intangible assets acquired upon acquisition

26.3

'

26.3

'

'

'

'

26.3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Carrying value of prior non-controlling interest in limited liability company on acquisition date

15.5

'

15.5

'

'

'

'

6.8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other assets acquired upon acquisition

3.3

'

3.3

'

'

'

'

4.8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest acquired in a limited liability company

'

'

'

'

99.00%

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount of promissory note

'

'

'

'

10

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchase price paid in cash

'

'

'

'

4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate on promissory note

'

'

'

'

'

'

3.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional seven plants acquired

'

'

'

'

'

'

'

'

49.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional seven plants acquired

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional one plant acquired

'

'

'

'

'

'

'

'

'

'

'

48.80%

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional one plant acquired

'

'

'

'

'

'

'

'

'

'

'

90.00%

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional three plants acquired

'

'

'

'

'

'

'

'

'

'

'

49.00%

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional three plants acquired

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

Ownership interest before additional one plant acquired

'

'

'

'

'

'

'

'

'

'

'

98.00%

'

'

'

'

'

'

'

'

'

'

'

Ownership interest after additional one plant acquired

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

Amount received from co investor as part of the acquisition

'

'

0.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other liabilities acquired upon acquisition

4.5

'

4.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of clean coal production plants seeking and negotiating for long term production contract

'

'

7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of variable interest entities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1

'

'

'

'

'

'

'

'

Total assets of limited liability companies

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.4

'

'

'

Total liability of limited liability companies

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.3

'

'

'

Total revenues of limited liability companies

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

28.9

'

'

'

Total expenses of limited liability companies

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

35.4

'

'

'

Additional investment per plant under new long-term production contract, net of co-investor funds

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5

'

30

'

40

'

'

'

'

Estimated tax effected average additional investment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$2.50

'

'

'

'

'

'

'

'

Idle period during move and redeployment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'12 months

'

'18 months

'

'

'

'

'

Investments_Other_Investments_

Investments - Other Investments - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 01, 2013
In Millions, unless otherwise specified	Venture
	Investment
Schedule of Equity Method Investments [Line Items]	'	'	'
Assets	$90.60	$90.40	'
Ownership interest held	'	'	99.00%
Non controlling interest in venture capital funds number	4	'	'
Non controlling interest certified low-income housing developments	12	'	'
Non controlling interest in real estate entities	2	'	'
Carrying value of investments in real estate entities	0	'	'
Other Investments [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Assets	3.2	3.7	'
Other Investments [Member] | Four Venture Capital Funds [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Assets	2.7	'	'
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Assets	60	'	'
Debt	20	'	'
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Twelve Certified Low-Income Housing Developments [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Carrying value of investments	0	'	'
Investment Management Company [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Ownership interest held	20.00%	'	'
Cost of acquiring equity interest	$0.50	'	'

Commitments_Contingencies_and_2

Commitments, Contingencies and Off-Balance Sheet Arrangements - Contractual Obligations (Detail) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Note Purchase Agreements [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	'
Contractual Obligations, Payments Due by Period, 2015	'
Contractual Obligations, Payments Due by Period, 2016	50
Contractual Obligations, Payments Due by Period, 2017	300
Contractual Obligations, Payments Due by Period, 2018	100
Contractual Obligations, Payments Due by Period, Thereafter	1,675
Contractual Obligations, Payments Due by Period, Total	2,125
Credit Agreement [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	147
Contractual Obligations, Payments Due by Period, 2015	'
Contractual Obligations, Payments Due by Period, 2016	'
Contractual Obligations, Payments Due by Period, 2017	'
Contractual Obligations, Payments Due by Period, 2018	'
Contractual Obligations, Payments Due by Period, Thereafter	'
Contractual Obligations, Payments Due by Period, Total	147
Premium Financing Debt Facility [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	149.2
Contractual Obligations, Payments Due by Period, 2015	'
Contractual Obligations, Payments Due by Period, 2016	'
Contractual Obligations, Payments Due by Period, 2017	'
Contractual Obligations, Payments Due by Period, 2018	'
Contractual Obligations, Payments Due by Period, Thereafter	'
Contractual Obligations, Payments Due by Period, Total	149.2
Total Debt Obligations [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	329.4
Contractual Obligations, Payments Due by Period, 2015	100.4
Contractual Obligations, Payments Due by Period, 2016	150.4
Contractual Obligations, Payments Due by Period, 2017	397.5
Contractual Obligations, Payments Due by Period, 2018	177.5
Contractual Obligations, Payments Due by Period, Thereafter	2,072.10
Contractual Obligations, Payments Due by Period, Total	3,227.30
Operating Lease Obligations [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	29.4
Contractual Obligations, Payments Due by Period, 2015	104.5
Contractual Obligations, Payments Due by Period, 2016	88.5
Contractual Obligations, Payments Due by Period, 2017	72.8
Contractual Obligations, Payments Due by Period, 2018	55.1
Contractual Obligations, Payments Due by Period, Thereafter	242.4
Contractual Obligations, Payments Due by Period, Total	592.7
Less Sublease Arrangements [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	-2.3
Contractual Obligations, Payments Due by Period, 2015	-1.4
Contractual Obligations, Payments Due by Period, 2016	-0.7
Contractual Obligations, Payments Due by Period, 2017	-0.4
Contractual Obligations, Payments Due by Period, 2018	-0.1
Contractual Obligations, Payments Due by Period, Thereafter	'
Contractual Obligations, Payments Due by Period, Total	-4.9
Outstanding Purchase Obligations [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	9.5
Contractual Obligations, Payments Due by Period, 2015	21.1
Contractual Obligations, Payments Due by Period, 2016	3.2
Contractual Obligations, Payments Due by Period, 2017	1
Contractual Obligations, Payments Due by Period, 2018	0.4
Contractual Obligations, Payments Due by Period, Thereafter	'
Contractual Obligations, Payments Due by Period, Total	35.2
Total Contractual Obligations [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	366
Contractual Obligations, Payments Due by Period, 2015	224.6
Contractual Obligations, Payments Due by Period, 2016	241.4
Contractual Obligations, Payments Due by Period, 2017	470.9
Contractual Obligations, Payments Due by Period, 2018	232.9
Contractual Obligations, Payments Due by Period, Thereafter	2,314.50
Contractual Obligations, Payments Due by Period, Total	3,850.30
Interest on Debt [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Contractual Obligations, Payments Due by Period, 2014	33.2
Contractual Obligations, Payments Due by Period, 2015	100.4
Contractual Obligations, Payments Due by Period, 2016	100.4
Contractual Obligations, Payments Due by Period, 2017	97.5
Contractual Obligations, Payments Due by Period, 2018	77.5
Contractual Obligations, Payments Due by Period, Thereafter	397.1
Contractual Obligations, Payments Due by Period, Total	$806.10

Commitments_Contingencies_and_3

Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		153 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014
	Entity	Entity	Entity	Entity	Entity
			sqft
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Acquired property through lease area, sqft	'	'	306,000	'	'
Acquired property through lease percentage of building	'	'	60.00%	'	'
Operating lease commitment, expiration date	'	'	28-Feb-18	'	'
Number of companies acquired	17	20	49	53	333
Aggregate amount of maximum earnout obligations related to acquisitions	'	'	$517.90	'	'
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet	'	'	185.4	'	'
Income tax credits and adjustments	'	'	117	'	'
Tax-Advantaged Investments No Longer Held [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Total indemnifications	32	'	32	'	32
Letter of Credit [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Debt	5	'	5	'	5
Number of letters of credit issued	'	'	1	'	'
Self-Insurance Deductibles [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Number of letters of credit issued	'	'	2	'	'
Self-Insurance Deductibles [Member] | Letter of Credit [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Liabilities recorded on self-insurance	9.3	'	9.3	'	9.3
Debt	9.3	'	9.3	'	9.3
Rent-A-Captive Facility [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Number of letters of credit issued	'	'	7	'	'
Rent-A-Captive Facility [Member] | Letter of Credit [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Debt	6.3	'	6.3	'	6.3
Errors and Omissions [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Insurance claims, amount retained	'	'	5	'	'
Amount of losses in excess of retained amounts	175	'	175	'	175
Minimum [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Ownership interest	1.00%	'	1.00%	'	1.00%
Number of micro-captive insurance companies organized or managed	'	'	100	'	'
Minimum [Member] | Errors and Omissions [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Actuarial range value	1.4	'	1.4	'	1.4
Maximum [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Ownership interest	50.00%	'	50.00%	'	50.00%
Maximum [Member] | Errors and Omissions [Member]	'	'	'	'	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'	'	'	'	'
Actuarial range value	5.4	'	$5.40	'	5.4

Commitments_Contingencies_and_4

Commitments, Contingencies and Off-Balance Sheet Arrangements - Off-Balance Sheet Commitments (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Amount of Commitment Expiration by Period - 2014	$35.30
Amount of Commitment Expiration by Period - 2015	0
Amount of Commitment Expiration by Period - 2016	0
Amount of Commitment Expiration by Period - 2017	0
Amount of Commitment Expiration by Period - 2018	0
Amount of Commitment Expiration by Period - Thereafter	44.6
Total Amounts Committed	79.9
Letters of Credit [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Amount of Commitment Expiration by Period - 2014	0
Amount of Commitment Expiration by Period - 2015	0
Amount of Commitment Expiration by Period - 2016	0
Amount of Commitment Expiration by Period - 2017	0
Amount of Commitment Expiration by Period - 2018	0
Amount of Commitment Expiration by Period - Thereafter	20.6
Total Amounts Committed	20.6
Crombie/OAMPS (CO) [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Amount of Commitment Expiration by Period - 2014	35.3
Amount of Commitment Expiration by Period - 2015	0
Amount of Commitment Expiration by Period - 2016	0
Amount of Commitment Expiration by Period - 2017	0
Amount of Commitment Expiration by Period - 2018	0
Amount of Commitment Expiration by Period - Thereafter	0
Total Amounts Committed	35.3
Financial Guarantees [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Amount of Commitment Expiration by Period - 2014	0
Amount of Commitment Expiration by Period - 2015	0
Amount of Commitment Expiration by Period - 2016	0
Amount of Commitment Expiration by Period - 2017	0
Amount of Commitment Expiration by Period - 2018	0
Amount of Commitment Expiration by Period - Thereafter	21.1
Total Amounts Committed	21.1
Funding Commitments [Member]	'
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]	'
Amount of Commitment Expiration by Period - 2014	0
Amount of Commitment Expiration by Period - 2015	0
Amount of Commitment Expiration by Period - 2016	0
Amount of Commitment Expiration by Period - 2017	0
Amount of Commitment Expiration by Period - 2018	0
Amount of Commitment Expiration by Period - Thereafter	2.9
Total Amounts Committed	$2.90

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Earnings (Loss) - Schedule of Accumulated Other Comprehensive Earnings (Loss) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014
In Millions, unless otherwise specified			Pension Liability [Member]	Foreign Currency Translation [Member]	Fair Value of Derivative Instruments [Member]	Accumulated Other Comprehensive Earnings (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'
Beginning Balance	($83.70)	($2.60)	($25.60)	$22.10	$0.90	($2.60)
Net change in period	'	'	1.4	-82	-0.5	-81.1
Ending Balance	($83.70)	($2.60)	($24.20)	($59.90)	$0.40	($83.70)

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Earnings (Loss) - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'
Expense related to pension liability reclassified from accumulated other comprehensive earnings (loss)	$1,800,000	$5,900,000
Income (expense) related to fair value of derivative investments reclassified from accumulated other comprehensive earnings (loss)	500,000	600,000
Foreign currency translation reclassified from accumulated other comprehensive earnings (loss)	$0	$0

Segment_Information_Additional

Segment Information - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2014
	Segment
Segment Reporting [Abstract]	'
Number of reportable operating segments	3

Segment_Information_Schedule_o

Segment Information - Schedule of Segment Reporting Information by Segment (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	$1,286.80	$835.80	$3,381.10	$2,289.40	'
Earnings (Loss) before income taxes	87.7	85.5	241.1	225.2	'
Identifiable assets at September 30, 2014 and 2013	9,988	'	9,988	'	6,860.50
Brokerage [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	799.8	546.3	2,111	1,551.60	'
Earnings (Loss) before income taxes	124.2	97.3	311.1	250.5	'
Identifiable assets at September 30, 2014 and 2013	8,404.20	4,661.90	8,404.20	4,661.90	'
Risk Management [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	168.3	149.7	496.4	459.5	'
Earnings (Loss) before income taxes	20.2	17.9	59.8	59.6	'
Identifiable assets at September 30, 2014 and 2013	593.9	546.2	593.9	546.2	'
Corporate [Member]	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'
Total revenues	318.7	139.8	773.7	278.3	'
Earnings (Loss) before income taxes	-56.7	-29.7	-129.8	-84.9	'
Identifiable assets at September 30, 2014 and 2013	$989.90	$762.10	$989.90	$762.10	'