Arthur J. Gallagher & Co. (AJG) 10-Q 29 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
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 Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	185,252,000

Consolidated Statement of Earni

Consolidated Statement of Earnings - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues before reimbursements	$ 1,957.5	$ 1,802.9
Total revenues	1,990.6	1,837.7
Compensation	837.1	775.8
Operating	262.5	216.1
Reimbursements	33.1	34.8
Cost of revenues from clean coal activities	382.5	431.2
Interest	40.2	31.3
Depreciation	34	30.6
Amortization	76.5	68.2
Change in estimated acquisition earnout payables	2.9	7.4
Total expenses	1,668.8	1,595.4
Earnings before income taxes	321.8	242.3
Benefit for income taxes	(29.9)	(43.7)
Net earnings	351.7	286
Net earnings attributable to noncontrolling interests	17.6	12.3
Net earnings attributable to controlling interests	$ 334.1	$ 273.7
Basic net earnings per share	$ 1.81	$ 1.51
Diluted net earnings per share	1.77	1.48
Dividends declared per common share	$ 0.43	$ 0.41
Commissions [Member]
Total revenues	$ 940.4	$ 839.4
Broker Fees [Member]
Total revenues	464.7	448.1
Supplemental Revenue Member [Member]
Total revenues	56.7	52
Contingent Revenue [Member]
Total revenues	48	34.9
Investment income [Member]
Total revenues	18.3	13.4
Gains On Divestitures [Member]
Total revenues	57.1	2.9
Clean Coal Activities [Member]
Total revenues	372.3	412.2
Reimbursements [Member]
Total revenues	$ 33.1	$ 34.8

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Earnings - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net earnings	$ 351.7	$ 286
Change in pension liability, net of taxes	1.6	7
Foreign currency translation, net of taxes in 2019	74.5	62.3
Change in fair value of derivative investments, net of taxes	(11.8)	(6.8)
Comprehensive earnings	416	348.5
Comprehensive earnings attributable to noncontrolling interests	18.2	14.5
Comprehensive earnings attributable to controlling interests	$ 397.8	$ 334

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Cash and cash equivalents	$ 871.5	$ 607.2
Restricted cash	1,669.3	1,629.6
Premiums and fees receivable	6,253.2	4,857.5
Other current assets	875.5	1,024.4
Total current assets	9,669.5	8,118.7
Fixed assets - net	450.2	436.9
Deferred income taxes	869.9	806.2
Other noncurrent assets	630.7	573.6
Right-of-use assets	368.8
Goodwill	4,800.9	4,625.6
Amortizable intangible assets - net	1,841.4	1,773
Total assets	18,631.4	16,334
Premiums payable to underwriting enterprises	6,741.4	5,740.2
Accrued compensation and other current liabilities	999.6	1,055.1
Deferred revenue - current	402.1	379.3
Premium financing debt	134.8	154
Corporate related borrowings - current	360	365
Total current liabilities	8,637.9	7,693.6
Corporate related borrowings - noncurrent	3,690.3	3,091.4
Deferred revenue - noncurrent	78	78.4
Lease liabilities - noncurrent	329.9
Other noncurrent liabilities	937.1	900.9
Total liabilities	13,673.2	11,764.3
Stockholders' equity:
Common stock - issued and outstanding 185.3 shares in 2019 and 184.0 shares in 2018	185.3	184
Capital in excess of par value	3,606.3	3,541.9
Retained earnings	1,810.2	1,558.6
Accumulated other comprehensive loss	(721.5)	(785.6)
Stockholders' equity attributable to controlling interests	4,880.3	4,498.9
Stockholders' equity attributable to noncontrolling interests	77.9	70.8
Total stockholders' equity	4,958.2	4,569.7
Total liabilities and stockholders' equity	$ 18,631.4	$ 16,334

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - shares shares in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Common stock - issued shares	185.3	184
Common stock - outstanding shares	185.3	184

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net earnings	$ 351.7	$ 286
Adjustments to reconcile net earnings to net cash used by operating activities:
Net gain on investments and other	(57.2)	(2)
Depreciation and amortization	110.5	98.8
Change in estimated acquisition earnout payables	2.9	7.4
Amortization of deferred compensation and restricted stock	10	9.9
Stock-based and other noncash compensation expense	3.6	4.8
Payments on acquisition earnouts in excess of original estimates	(7.1)	(9)
Effect of changes in foreign exchange rates	2.6	1.3
Net change in premiums and fees receivable	(1,285.6)	(1,505.4)
Net change in deferred revenue	18.6	29.3
Net change in premiums payable to underwriting enterprises	876.9	979.4
Net change in other current assets	133.4	119.1
Net change in accrued compensation and other current liabilities	(209)	(165.4)
Net change in income taxes payable	35.5	16.2
Net change in deferred income taxes	(67.8)	(75.6)
Net change in other noncurrent assets and liabilities	(15.2)	(12.4)
Net cash used by operating activities	(96.2)	(217.6)
Cash flows from investing activities:
Capital expenditures	(39.3)	(31.1)
Cash paid for acquisitions, net of cash and restricted cash acquired	(175.6)	(57.3)
Net proceeds from sales of operations/books of business	74	2.2
Net funding of investment transactions	(0.4)	(0.7)
Net cash used by investing activities	(141.3)	(86.9)
Cash flows from financing activities:
Payments on acquisition earnouts	(8.2)	(9.4)
Proceeds from issuance of common stock	32.8	32.3
Repurchases of common stock		(11.3)
Payments to noncontrolling interests	(10.7)	(8.6)
Dividends paid	(79.6)	(76.1)
Net borrowings on premium financing debt facility	(20.5)	(30.3)
Borrowings on line of credit facility	1,025	815
Repayments on line of credit facility	(1,030)	(645)
Net borrowings of corporate related long-term debt	600
Debt acquisition costs	(0.2)
Settlements on terminated interest rate swaps	(1.2)	2.9
Net cash provided by financing activities	507.4	69.5
Effect of changes in foreign exchange rates on cash and cash equivalents and restricted cash	34.1	38.7
Net increase (decrease) in cash, cash equivalents and restricted cash	304	(196.3)
Cash, cash equivalents and restricted cash at beginning of period	2,236.8	2,305
Cash, cash equivalents and restricted cash at end of period	$ 2,540.8	$ 2,108.7

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	As Previously Reported [Member]	Common Stock [Member]	Common Stock [Member]As Previously Reported [Member]	Capital in Excess of Par Value [Member]	Capital in Excess of Par Value [Member]As Previously Reported [Member]	Retained Earnings [Member]	Retained Earnings [Member]As Previously Reported [Member]	Accumulated Other Comprehensive Earnings (Loss) [Member]	Accumulated Other Comprehensive Earnings (Loss) [Member]As Previously Reported [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member]As Previously Reported [Member]
Beginning Balance at Dec. 31, 2017		$ 4,164.9		$ 181		$ 3,388.2		$ 1,095.9		$ (559.9)		$ 59.7
Beginning Balance (in shares) at Dec. 31, 2017			181	181
Adoption of Topic 606 (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2017	$ 134.8						$ 125.9		$ 4.5		$ 4.4
Beginning Balance, as restated at Dec. 31, 2017	4,299.7		$ 181		$ 3,388.2		1,221.8		(555.4)		64.1
Reclassification of the income tax effects within accumulated other comprehensive loss related to the Tax Act							6.6		(6.6)
Net earnings	286						273.7				12.3
Dividends paid to noncontrolling interests	(8.7)										(8.7)
Net change in pension asset/liability, net of taxes	7								7
Foreign currency translation	64.5								62.3		2.2
Change in fair value of derivative instruments, net of taxes	(6.8)								(6.8)
Compensation expense related to stock option plan grants	4.8				4.8
Common stock issued in: purchase transactions	6.5		$ 0.1		6.4
Common stock issued in: purchase transactions (in shares)			0.1
Stock option plans	28.2		$ 0.8		27.4
Stock option plans (in shares)			0.8
Employee stock purchase plan	4.1		$ 0.1		4
Employee stock purchase plan (in shares)			0.1
Deferred compensation and restricted stock	(14.1)		$ 0.2		(14.3)
Deferred compensation and restricted stock (in shares)			0.2
Common stock repurchases	(11.3)		$ (0.1)		(11.2)
Common stock repurchases (in shares)			(0.1)
Cash dividends declared on common stock	(75.4)						(75.4)
Ending Balance at Mar. 31, 2018	4,584.5		$ 182.1		3,405.3		1,426.7		(499.5)		69.9
Ending Balance (in shares) at Mar. 31, 2018			182.1
Beginning Balance at Dec. 31, 2018	4,569.7		$ 184		3,541.9		1,558.6		(785.6)		70.8
Beginning Balance (in shares) at Dec. 31, 2018			184
Adoption of Topic 606 (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2018	(2.4)						(2.2)		(0.2)
Net earnings	351.7						334.1				17.6
Net purchase of subsidiary shares from noncontrolling interests	(0.3)				(0.2)						(0.1)
Dividends paid to noncontrolling interests	(11)										(11)
Net change in pension asset/liability, net of taxes	1.6								1.6
Foreign currency translation	75.1								74.5		0.6
Change in fair value of derivative instruments, net of taxes	(11.8)								(11.8)
Compensation expense related to stock option plan grants	3.6				3.6
Common stock issued in: purchase transactions	37		$ 0.5		36.5
Common stock issued in: purchase transactions (in shares)			0.5
Stock option plans	$ 28.1		$ 0.7		27.4
Stock option plans (in shares)	0.7		0.7
Employee stock purchase plan	$ 4.7		$ 0.1		4.6
Employee stock purchase plan (in shares)			0.1
Deferred compensation and restricted stock	(7.5)				(7.5)
Cash dividends declared on common stock	(80.3)						(80.3)
Ending Balance at Mar. 31, 2019	$ 4,958.2		$ 185.3		$ 3,606.3		$ 1,810.2		$ (721.5)		$ 77.9
Ending Balance (in shares) at Mar. 31, 2019			185.3

Consolidated Statement of Sto_2

Consolidated Statement of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Tax effect on net change in pension asset/liability	$ 1	$ 4.6
Net change in fair value of derivative instruments, tax	4.4	$ 1.2
Foreign currency translation, net of taxes	$ 2.5

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies Terms Used in Notes to Consolidated Financial Statements ASU - Accounting Standards Update. FASB - The Financial Accounting Standards Board. GAAP - U.S. generally accepted accounting principles. IRC - Internal Revenue Code. IRS - Internal Revenue Service. Underwriting enterprises 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, consulting and third party claims settlement and administration services to both domestic and international entities through three reportable operating segments. Our brokers, agents and administrators act as intermediaries between underwriting enterprises and our clients. Our brokerage segment operations provide brokerage and consulting services to companies and entities of all types, including commercial, not-for-profit, public entities, and, to a lesser extent, individuals, in the areas of insurance placement, risk of loss management, and management of employer sponsored benefit programs. Our risk management segment operations provide contract claim settlement, claim administration, loss control services and risk management consulting for commercial, not-for-profit, captive and public entities, and various other organizations that choose to self-insure property/casualty coverages or choose to use a third-party claims management organization rather than the claim services provided by underwriting enterprises. The corporate segment reports the financial information related to our debt and other corporate costs, clean energy investments, external acquisition-related expenses and the impact of foreign currency translation. Clean energy investments consist of our investments in limited liability companies that own 34 commercial clean coal production facilities producing refined coal using Chem-Mod LLC’s proprietary technologies. We believe these operations produce refined coal that qualifies for tax credits under IRC Section 45. We do not assume underwriting risk on a net basis, other than with respect to de minimis amounts necessary to provide minimum or regulatory capital to organize captives, pools, specialized underwriters or risk-retention groups. Rather, capital necessary for events of loss coverages is provided by underwriting enterprises. Investment income and other revenues are primarily generated from our premium financing operations, our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. In addition, our share of the net earnings related to partially owned entities that are accounted for using the equity method is included in investment income. We are headquartered in Rolling Meadows, Illinois, have operations in 35 countries and offer client-service capabilities in more than 150 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, 2018, except as disclosed in Note 2, 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, 2018. In the preparation of our unaudited consolidated financial statements as of March 31, 2019, 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. Use of Estimates The preparation of our consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These accounting principles require us to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses, and the disclosure of contingent assets and liabilities at the date of our consolidated financial statements. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible assets, right-of-use assets, investments (including our IRC Section 45 investments), income taxes, revenue recognition, deferred costs, stock-based compensation, claims handling obligations, retirement plans, litigation and contingencies. We base our estimates on historical experience and various assumptions that we believe to be reasonable based on specific circumstances. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.

Effect of New Accounting Pronou

Effect of New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Effect of New Accounting Pronouncements	2. Effect of New Accounting Pronouncements Leases In February 2016, the FASB issued ASU No. 2016-02, Leases , ASC Topic 842, as subsequently amended by ASU No. 2018-11, Leases: Targeted Improvements, requiring us to recognize lease right-of-use assets and lease liabilities on our balance sheet. As a lessee, we are required to disclose qualitative and quantitative information about leasing arrangements to enable a user of our financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. We adopted ASC Topic 842 for all leases effective January 1, 2019, using the modified retrospective approach allowing us to initially apply the new lease standard at the adoption date and recognize a cumulative effect adjustment to the opening balance of retained earnings in the first quarter of 2019. Consequently, the reporting for the comparative prior year periods presented in 2019 will continue to be in accordance with the previous lease guidance under ASC Topic 840, including comparative disclosure requirements. We elected the package of practical expedients to carryforward historical identification and classification of leases that commenced before January 1, 2019 and to not re-assess initial direct costs for leases commencing before January 1, 2019. We also elected the lessee practical expedient, by class of underlying asset (e.g., office space), to not separate non-lease components such as lessor-provided maintenance and property management services from the associated lease component. The new lease accounting standard requires us to recognize lease right-of-use assets and lease liabilities on our balance sheet, which are established at the inception of a lease by computing a net present value of the future lease payments. Right-of-use assets are amortized to expense, and the discount amount related to lease liabilities is accreted to expense, over the lease term. The amortization of the right-of-use asset is calculated as the difference between the straight-line lease expense and the interest calculated on the lease liability. Rent payments are applied against the lease liabilities. Adoption of the new standard resulted in the recording of net right-of-use assets and lease liabilities of approximately $379.6 million and $420.3 million, respectively, and the reclassification of net rent related asset and liabilities of $38.3 million as of January 1, 2019. $2.4 Hedge Accounting In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The guidance was issued to improve and more closely align a company’s financial reporting of its hedging relationships with the objective of a company’s risk management activities. Among other provisions, the new standard (1) eliminates the separate measurement and reporting of hedge ineffectiveness and (2) permits an entity to recognize in earnings the initial value of an excluded component under a systematic and rational method over the life of the derivative instrument. In accordance with ASU 2017-12, certain provisions were required to be applied on a modified retrospective basis, which requires a cumulative effect adjustment to accumulated other comprehensive income with a corresponding adjustment to retained earnings as of the beginning of the fiscal year of adoption. In addition, certain provisions in the guidance require modifications to existing presentation and disclosure requirements on a prospective basis. We adopted ASU 2017-12 on January 1, 2019. In accordance with the transition provisions of ASU 2017-12, we modified the recognition model for the excluded component from a mark-to-market approach to an amortization approach for our cash flow hedges with forward points existing as of the adoption date. The cumulative-effect related to this change resulted in an adjustment of $0.2 . See Note 14 for disclosures relating to our derivative and hedging activities. Income Taxes In February 2018, the FASB issued ASU No. 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of tax effects stranded in Accumulated Other Comprehensive Income (AOCI). This new guidance gave entities the option to reclassify to retained earnings stranded tax effects related to the change in federal tax rate for all items accounted for in other comprehensive earnings (OCI). These entities could also elect to reclassify other stranded tax effects that relate to the Tax Cuts and Jobs Act (which we refer to as the Tax Act) but do not directly relate to the change in the federal rate (e.g., state taxes or changing from a worldwide tax system to a territorial system). Tax effects that are stranded in OCI for other reasons (e.g., prior changes in tax law or a change in valuation allowance) cannot be reclassified. All entities were required to make new disclosures, regardless of whether they elect to reclassify stranded amounts. Entities are required to disclose whether or not they elected to reclassify the tax effects related to the Tax Act as well as their policy for releasing income tax effects from accumulated OCI. Under Topic 740-10-45-15, the effects of changes in tax rates and laws on deferred tax balances are recorded as a component of tax expense related to continuing operations for the period in which the law was enacted, even if the assets and liabilities related to items of accumulated OCI. The enactment of the Tax Act on December 22, 2017 resulted in stakeholder concerns about this accounting treatment. The new guidance was effective for all entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption was permitted for reporting periods, including interim periods, for which financial statements have not yet been issued or made available for issuance. An entity was able to choose whether to apply the guidance retrospectively to each period in which the effect of the Tax Act is recognized or to apply the guidance in the period of adoption. We adopted this new guidance effective January 1, 2018, which resulted in a $6.6 million increase in retained earnings and a corresponding decrease in accumulated other comprehensive earnings (loss). This reclassification relates to the income tax effects of lowering the corporate income tax rate from 35.0% to 21.0% on deferred income taxes established on pension plan liabilities and the fair value of derivative instruments. Credit Impairment In June 2016, the FASB issued ASU No. 2016 -13, (Topic 326): Measurement of Credit Losses on Financial Instruments. Under the new guidance an entity is required to measure all credit losses on certain financial instruments, including trade receivables and various off-balance sheet credit exposures, using an expected credit loss model. This model incorporates past experience, current conditions and reasonable and supportable forecasts affecting collectability of these instruments. An entity will apply the new guidance through a cumulative-effect adjustment to retained earnings as of the beginning of the year of adoption. The guidance is effective January 1, 2020, with early adoption permitted. We are still assessing the timing and impact that adopting this new guidance will have on our consolidated financial statements. Disclosure Framework In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Requirements for Fair Value Measurement. This new guidance modifies various disclosure requirements for fair value measurements, including in certain part those related to Level 3 fair value measurements. The new guidance is effective January 1, 2020, with early adoption permitted. Certain portions of the guidance must be adopted prospectively while others must be adopted retrospectively to all periods presented. In August 2018, the FASB also issued ASU No. 2018-14, Compensation-Retirement Benefits-Defined Benefit Plans-General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. This new guidance modifies various disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The new guidance is effective January 1, 2020, with early adoption permitted. Retrospective adoption is required. We do not expect adoption of either standard will have a material impact on our consolidated financial statements. Intangibles - Goodwill and Other In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new guidance eliminates Step 2 of the goodwill impairment test. Instead, the updated guidance requires an entity to perform its annual or interim goodwill impairment test by comparing the fair value of the reporting unit to its carrying value, and recognizing a non-cash impairment charge for the amount by which the carrying value exceeds the reporting unit’s fair value with the loss not exceeding the total amount of goodwill allocated to that reporting unit. The new guidance is effective beginning January 1, 2020, with early adoption permitted, and will be applied on a prospective basis. The new guidance currently has no impact on our consolidated financial statements; however, we will evaluate the impact of this updated guidance on future annual or interim goodwill impairment tests performed. Internal-use Software In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This new accounting guidance requires deferral of certain implementation costs associated with a cloud computing arrangement, or hosting arrangement, thereby aligning deferral of such costs with implementation costs associated with developing internal-use software. Accounting for the service component of a hosting arrangement remains unchanged. An entity will defer these implementation costs over the term of the hosting arrangement, including optional renewal periods that are reasonably certain of exercise. Amounts expensed would be presented through operating expense, rather than depreciation or amortization. The new guidance is effective January 1, 2020, with early adoption permitted. An entity may adopt the guidance either prospectively for all cloud computing arrangement implementation costs incurred on or after the effective date or retrospectively, including comparative periods. We are currently assessing the impact that adopting this guidance will have on our consolidated financial statements.

Business Combinations

Business Combinations	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Business Combinations	3. Business Combinations During the three-month period ended March 31, 2019, 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 Date of Acquisition Common Shares Issued Common Share Value Cash Paid Accrued Liability Escrow Deposited Recorded Earnout Payable Total Recorded Purchase Price Maximum Potential Earnout Payable (000s) Inversion Holding Company Company, LLC (IHC) January 1, 2019 452 $ 35.9 $ 31.2 $ — $ 4.5 $ 20.9 $ 92.5 $ 35.0 Jones Brown Inc. (JBI) January 1, 2019 — — 65.9 — 8.7 — 74.6 — Nine other acquisitions completed in 2019 — — 79.7 0.1 6.0 14.9 100.7 46.1 452 $ 35.9 $ 176.8 $ 0.1 $ 19.2 $ 35.8 $ 267.8 $ 81.1 On December 22, 2018, we signed a definitive agreement to acquire 100% of the equity of Stackhouse Poland Group Limited (which we refer to as Stackhouse Poland) headquartered in Guildford, Surrey, U.K., for approximately $350.0 million of cash consideration. The transaction was subject to regulatory approval and it closed on April 5, 2019. On March 3, 2019, we signed a definitive agreement to acquire the global aerospace operations of Jardine Lloyd Thompson Group plc (JLT) for approximately £130.0 million of cash upfront consideration, plus £60.0 million of contingent consideration. The agreement provides for the acquisition of all assets within JLT’s global aerospace retail and wholesale insurance broking division, which includes operations in the U.K., U.S., Canada, Australia, New Zealand and 10 other countries spanning Europe, Latin America and Asia. The agreement also includes the assets of Hayward Aviation, a UK insurance broker that specializes in aviation for high-net worth individuals and smaller airlines. The transaction is subject to regulatory approval and is expected to close in the second quarter of 2019. Common shares issued in connection with acquisitions are valued at closing market prices as of the effective date of the applicable acquisition or on the days when the shares are issued if purchase consideration is deferred. 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 17.5% for our 2019 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. The discount rate was 8.0% for all of our 2019 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 March 31, 2019 and 2018, we recognized $5.6 million and $5.1 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 March 31, 2019 and 2018, we recognized $2.7 million of income and $2.3 million of expense, respectively, related to net adjustments in the estimated fair value of the liability for earnout obligations in connection with revised projections of future performance for 33 and 39 acquisitions, respectively. The aggregate amount of maximum earnout obligations related to acquisitions was $618.9 million as of March 31, 2019, of which $293.6 million was recorded in the consolidated balance sheet as of March 31, 2019, 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 three-month period ended March 31, 2019 (in millions): IHC JBI Nine Other Acquisitions Total Cash $ — $ 2.7 $ 1.0 $ 3.7 Other current assets 3.8 22.2 14.6 40.6 Fixed assets 0.3 1.1 0.5 1.9 Noncurrent assets 0.5 2.9 2.1 5.5 Goodwill 41.8 51.2 38.5 131.5 Expiration lists 50.6 22.7 57.3 130.6 Non-compete agreements 1.1 0.8 0.2 2.1 Total assets acquired 98.1 103.6 114.2 315.9 Current liabilities 5.1 26.1 12.3 43.5 Total liabilities assumed 5.6 29.0 13.5 48.1 Total net assets acquired $ 92.5 $ 74.6 $ 100.7 $ 267.8 Among other things, these acquisitions allow us to expand into desirable geographic locations, further extend our presence in the retail and wholesale insurance brokerage services 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 and non-compete agreements in the amounts of $131.5 million, $130.6 million and $2.1 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 3.0% to 4.4% and 3.5% to 11.0% for our 2018 acquisitions, respectively, for which valuations were performed in 2018. 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 11.5% to 14.0% for our 2018 acquisitions for which valuations were performed in 2018. 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 (two to fifteen years for expiration lists, three to five years for non-compete agreements and two 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 were 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 as a component of amortization expense. Of the $130.6 million of expiration lists and $2.1 million of non-compete agreements related to our acquisitions made during the three-month period ended March 31, 2019, $22.7 million and $0.8 million, respectively, is not expected to be deductible for income tax purposes. Accordingly, we recorded a deferred tax liability of $5.8 million, and a corresponding amount of goodwill, in the three-month period ended March 31, 2019, related to the nondeductible amortizable intangible assets. Our consolidated financial statements for the three-month period ended March 31, 2019 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, 2018 (in millions, except per share data): Three-month period ended March 31, 2019 2018 Total revenues $ 1,993.0 $ 1,855.9 Net earnings attributable to controlling interests 334.3 275.6 Basic net earnings per share 1.81 1.51 Diluted net earnings per share 1.77 1.49 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, 2018, nor are they necessarily indicative of future operating results. Annualized revenues of entities acquired during the three-month period ended March 31, 2019 totaled approximately $71.2 million. For the three-month period ended March 31, 2019, total revenues and net earnings recorded in our unaudited consolidated statement of earnings related to our acquisitions made during the three-month period ended March 31, 2019 in the aggregate, were $18.8 million and $2.1 million, respectively.

Contracts with Customers

Contracts with Customers	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Contracts with Customers	4. Contracts with Customers Contract Assets and Liabilities/Contract Balances Information about unbilled receivables, contract assets and contract liabilities from contracts with customers is as follows (in millions): March 31, 2019 December 31, 2018 Unbilled receivables $ 767.7 $ 496.2 Deferred contract costs 55.1 91.6 Deferred revenue 480.1 457.7 The unbilled receivables primarily relate to our rights to consideration for work completed but not billed at the reporting date. These are transferred to the receivables when the client is billed. The deferred contract costs represent the costs we incur to fulfill a new or renewal contract with our clients prior to the effective date of the contract. These costs are expensed on the contract effective date. The deferred revenue represents the remaining performance obligations under our contracts. Significant changes in the deferred revenue balances, which include foreign currency translation adjustments, during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2018 $ 284.7 $ 173.0 $ 457.7 Incremental deferred revenue 162.8 41.7 204.5 Revenue recognized during the three-month period ended March 31, 2019 included in deferred revenue at December 31, 2018 (137.6 ) (44.1 ) (181.7 ) Deferred revenue recognized from business acquisitions (0.4 ) — (0.4 ) Deferred revenue at March 31, 2019 $ 309.5 $ 170.6 $ 480.1 Remaining Performance Obligations Remaining performance obligations represent the portion of the contract price for which work has not been performed. As of March 31, 2019, the aggregate amount of the contract price allocated to remaining performance obligations was $480.1 million. The estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period is as follows (in millions): Brokerage Risk Management Total 2019 (remaining nine months) $ 252.0 $ 80.7 $ 332.7 2020 32.9 36.3 69.2 2021 19.7 18.0 37.7 2022 3.8 10.4 14.2 2023 0.6 6.1 6.7 Thereafter 0.5 19.1 19.6 Total $ 309.5 $ 170.6 $ 480.1 Deferred Contract Costs We capitalize costs incurred to fulfill contracts as “deferred contract costs” which are included in other current assets in our consolidated balance sheet. Deferred contract costs were $55.1 million and $91.6 million as of March 31, 2019 and December 31, 2018, respectively. Capitalized fulfillment costs are amortized on the contract effective date. The amount of amortization of the deferred contract costs was $113.4 million and $100.4 million for the three-month periods ended March 31, 2019 and 2018, respectively. We have applied the practical expedient to recognize the incremental costs of obtaining contracts as an expense when incurred if the amortization period of the assets that we otherwise would have recognized is one year or less for our brokerage segment. These costs are included in compensation and operating expenses in our consolidated statement of earnings.

Other Financial Data

Other Financial Data	3 Months Ended
	Mar. 31, 2019
Other Financial Data Disclosure [Abstract]
Other Financial Data	5. Other Financial Data Other Current Assets Major classes of other current assets consist of the following (in millions): March 31, December 31, 2019 2018 Premium finance advances and loans $ 305.1 $ 316.2 Accrued supplemental, direct bill and other receivables 306.3 348.2 Refined coal production related receivables 114.0 160.2 Deferred contract costs 55.1 91.6 Prepaid expenses 95.0 108.2 Total other current assets $ 875.5 $ 1,024.4 The premium finance loans represent short-term loans which we make to many of our brokerage related clients and other non-brokerage clients to finance their premiums paid to underwriting enterprises. These premium finance loans are primarily generated by three Australian and New Zealand premium finance subsidiaries. Financing receivables are carried at amortized cost. Given that these receivables carry a fairly rapid delinquency period of only seven

Intangible Assets

Intangible Assets	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	6. Intangible Assets The carrying amount of goodwill at March 31, 2019 and December 31, 2018 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Management Corporate Total At March 31, 2019 United States $ 2,794.5 $ 29.6 $ — $ 2,824.1 United Kingdom 784.2 9.6 — 793.8 Canada 437.4 — — 437.4 Australia 409.2 0.3 — 409.5 New Zealand 213.3 10.3 — 223.6 Other foreign 109.8 — 2.7 112.5 Total goodwill $ 4,748.4 $ 49.8 $ 2.7 $ 4,800.9 At December 31, 2018 United States $ 2,715.3 $ 29.6 $ — $ 2,744.9 United Kingdom 753.7 9.2 — 762.9 Canada 378.6 — — 378.6 Australia 406.3 0.3 — 406.6 New Zealand 209.6 10.2 — 219.8 Other foreign 110.1 — 2.7 112.8 Total goodwill $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 The changes in the carrying amount of goodwill for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Balance as of December 31, 2018 $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Goodwill acquired during the period 131.5 — — 131.5 Goodwill adjustments due to appraisals and other acquisition adjustments 8.4 — — 8.4 Goodwill written-off related to sales of business (6.6 ) — — (6.6 ) Foreign currency translation adjustments during the period 41.5 0.5 — 42.0 Balance as of March 31, 2019 $ 4,748.4 $ 49.8 $ 2.7 $ 4,800.9 Major classes of amortizable intangible assets at March 31, 2019 and December 31, 2018 consist of the following (in millions): March 31, December 31, 2019 2018 Expiration lists $ 3,529.6 $ 3,379.4 Accumulated amortization - expiration lists (1,758.8 ) (1,676.8 ) 1,770.8 1,702.6 Non-compete agreements 60.7 58.0 Accumulated amortization - non-compete agreements (49.8 ) (48.5 ) 10.9 9.5 Trade names 86.4 86.0 Accumulated amortization - trade names (26.7 ) (25.1 ) 59.7 60.9 Net amortizable assets $ 1,841.4 $ 1,773.0 Estimated aggregate amortization expense for each of the next five years and thereafter is as follows: 2019 (remaining nine months) $ 226.3 2020 286.7 2021 262.8 2022 237.5 2023 213.5 Thereafter 614.6 Total $ 1,841.4

Credit and Other Debt Agreement

Credit and Other Debt Agreements	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Credit and Other Debt Agreements	7. Credit and Other Debt Agreements The following is a summary of our corporate and other debt (in millions): March 31, 2019 December 31, 2018 Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 3.20%, balloon due June 24, 2019 $ 50.0 $ 50.0 Semi-annual payments of interest, fixed rate of 5.85%, balloon due November 30, 2019 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.48%, balloon due June 24, 2020 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due July 10, 2020 50.0 50.0 Semi-annual payments of interest, fixed rate of 5.18%, balloon due February 10, 2021 75.0 75.0 Semi-annual payments of interest, fixed rate of 3.69%, balloon due June 14, 2022 200.0 200.0 Semi-annual payments of interest, fixed rate of 5.49%, balloon due February 10, 2023 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.13%, balloon due June 24, 2023 200.0 200.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.65%, balloon due 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.72%, balloon due February 13, 2024 100.0 — Semi-annual payments of interest, fixed rate of 4.58%, balloon due February 27, 2024 325.0 325.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.40%, balloon due 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.31%, balloon due June 24, 2025 200.0 200.0 Semi-annual payments of interest, fixed rate of 4.85%, balloon due February 13, 2026 140.0 — Semi-annual payments of interest, fixed rate of 4.73%, balloon due February 27, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.40%, balloon due June 2, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.36%, balloon due June 24, 2026 150.0 150.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due June 27, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due August 2, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.14%, balloon due August 4, 2027 98.0 98.0 Semi-annual payments of interest, fixed rate of 3.46%, balloon due December 1, 2027 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.55%, balloon due June 2, 2028 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 13, 2028 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.04%, balloon due February 13, 2029 100.0 — Semi-annual payments of interest, fixed rate of 4.98%, balloon due February 27, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due June 27, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due August 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.44%, balloon due June 13, 2030 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.14%, balloon due March 13, 2031 180.0 — Semi-annual payments of interest, fixed rate of 4.70%, balloon due June 2, 2031 25.0 25.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 27, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due August 2, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.59%, balloon due June 13, 2033 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.29%, balloon due March 13, 2034 40.0 — Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 75.0 Semi-annual payments of interest, fixed rate of 5.45%, balloon due March 13, 2039 40.0 — Total Note Purchase Agreements 3,798.0 3,198.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires April 8, 2021 260.0 265.0 Premium Financing Debt Facility - expires May 18, 2020: Periodic payments of interest and principal, Interbank rates plus 1.05% for Facility B; plus 0.55% for Facilities C and D Facility B AUD denominated tranche 106.5 133.9 NZD denominated tranche 2.7 10.1 Facility C and D AUD denominated tranche 15.4 — NZD denominated tranche 10.2 10.0 Total Premium Financing Debt Facility 134.8 154.0 Total corporate and other debt 4,192.8 3,617.0 Less unamortized debt acquisition costs on Note Purchase Agreements (7.7 ) (6.6 ) Net corporate and other debt $ 4,185.1 $ 3,610.4

Earnings per Share

Earnings per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings per Share	8. 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 March 31, 2019 2018 Net earnings attributable to controlling interests $ 334.1 $ 273.7 Weighted average number of common shares outstanding 184.5 181.5 Dilutive effect of stock options using the treasury stock method 3.9 3.5 Weighted average number of common and common equivalent shares outstanding 188.4 185.0 Basic net earnings per share $ 1.81 $ 1.51 Diluted net earnings per share $ 1.77 $ 1.48 Anti-dilutive stock-based awards of 1.4 million and 0.2 million shares were outstanding at March 31, 2019 and 2018, respectively, but were excluded in the computation of the dilutive effect of stock-based awards for the three-month periods then ended. These stock-based awards were excluded from the computation because the stock-based awards ’ 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	3 Months Ended
	Mar. 31, 2019
Text Block [Abstract]
Stock Option Plans	9. Stock Option Plans On May 16, 2017, our stockholders approved the Arthur J. Gallagher & Co. 2017 Long-Term Incentive Plan (which we refer to as the LTIP), which replaced our previous stockholder-approved Arthur J. Gallagher & Co. 2014 Long-Term Incentive Plan (which we refer to as the 2014 LTIP). The LTIP term began May 16, 2017 and terminates on the date of the annual meeting of stockholders in 2027, 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 annual number of shares delivered under the LTIP. The LTIP provides for non-qualified and incentive stock options, stock appreciation rights, restricted stock and restricted stock units, any or all of which may be made contingent upon the achievement of performance criteria. 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 will be 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 prior equity plans 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. 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 2.8 million at March 31, 2019. 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 14, 2019, the compensation committee granted 1,283,300 options under the 2017 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 2022, 2023 and 2024, respectively. On March 15, 2018, the compensation committee granted 1,261,000 options under the 2017 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 2021, 2022 and 2023, respectively. The 2019 and 2018 options expire seven years from the date of grant, or earlier in the event of certain terminations of employment. For our executive officers age 55 or older, stock options awarded after 2012 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. During the three-month periods ended March 31, 2019 and 2018, we recognized $3.6 million and $4.8 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: 2019 2018 Expected dividend yield 1.7 % 2.3 % Expected risk-free interest rate 2.5 % 2.7 % Volatility 15.6 % 15.1 % Expected life (in years) 5.5 5.5 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. The weighted average fair value per option for all options granted during the three-month periods ended March 31, 2019 and 2018, as determined on the grant date using the Black-Scholes option pricing model, was $10.71 and $9.27, respectively. The following is a summary of our stock option activity and related information for 2019 (in millions, except exercise price and year data): Three-month period ended March 31, 2019 Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Beginning balance 8.8 $ 50.16 Granted 1.3 79.59 Exercised (0.7 ) 41.11 Forfeited or canceled (0.1 ) 51.52 Ending balance 9.3 $ 54.92 4.24 $ 217.2 Exercisable at end of period 3.2 $ 44.68 2.47 $ 106.2 Ending unvested and expected to vest 5.8 $ 59.61 5.10 $ 108.6 Options with respect to 13.0 million shares (less any shares of restricted stock issued under the LTIP - see Note 11 to these unaudited consolidated financial statements) were available for grant under the LTIP at March 31, 2019. The total intrinsic value of options exercised during the three-month periods ended March 31, 2019 and 2018 was $27.6 million and $29.3 million, respectively. As of March 31, 2019, we had approximately $40.5 million of total unrecognized compensation expense related to nonvested options. We expect to recognize that cost over a weighted average period of approximately four years. Other information regarding stock options outstanding and exercisable at March 31, 2019 is summarized as follows (in millions, except exercise price and year data): Options Outstanding Options Exercisable Weighted Average Remaining Weighted Weighted Contractual Average Average Number Term Exercise Number Exercise Range of Exercise Prices Outstanding (in years) Price Exercisable Price $ 39.17 — $ 39.17 0.6 0.95 $ 39.17 0.6 $ 39.17 43.71 — 43.71 2.2 3.96 43.71 0.7 43.71 46.17 — 46.87 2.5 2.51 46.47 1.9 46.56 47.92 63.60 1.5 4.96 56.81 — — 70.74 — 70.74 1.2 5.96 70.74 — — 79.59 — 79.59 1.3 6.96 79.59 — — $ 39.17 — $ 79.59 9.3 4.24 $ 54.92 3.2 $ 44.68

Deferred Compensation

Deferred Compensation	3 Months Ended
	Mar. 31, 2019
Compensation Related Costs [Abstract]
Deferred Compensation	10. Deferred Compensation We have a Deferred Equity Participation Plan (which we refer to as the DEPP), 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 DEPP, we typically contribute cash in an amount approved by the compensation committee to a rabbi trust on behalf of the executives participating in the DEPP, 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 DEPP 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. DEPP awards are generally made annually in the first quarter. In addition, we annually make awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after the earlier of fifteen years or the participant reaching age 65. All contributions to the plan (including sub-plans) 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 DEPP 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, 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 quarters of 2019 and 2018, the compensation committee approved $10.1 million and $11.5 million, respectively, of awards in the aggregate to certain key executives under the DEPP that were contributed to the rabbi trust in the first quarters of 2019 and 2018, 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 2019 and 2018 awards. During the three-month periods ended March 31, 2019 and 2018, we charged $2.0 million and $1.9 million, respectively, to compensation expense related to these awards. In the first quarters of 2019 and 2018, the compensation committee approved $2.6 million and $0.9 million, respectively, of awards under the sub-plans referred to above, which were contributed to the rabbi trust in the first quarters of 2019 and 2018, respectively. During the three-month periods ended March 31, 2019 and 2018, we charged $0.5 million and $0.5 million, respectively, to compensation expense related to these awards. There were no distributions from the sub-plans during the three-month period ended March 31, 2019. At March 31, 2019 and December 31, 2018, we recorded $69.0 million (related to 2.9 million shares) and $57.6 million (related to 2.7 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 March 31, 2019 and December 31, 2018 was $224.0 million and $199.8 million, respectively. During the three-month period ended March 31, 2019, cash and equity awards with an aggregate fair value of $0.8 million was vested and distributed to executives under the DEPP. During the three-month period ended March 31, 2018, there were no distributions under the DEPP. 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 vesting and/or distributions no sooner than five years from the date of awards. Under the provisions of the DCPP, we typically contribute cash in an amount approved by the 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 quarters of 2019 and 2018, the compensation committee approved $2.4 million and $5.6 million, respectively, of awards in the aggregate to certain key executives under the DCPP that were contributed to the rabbi trust in the second quarters of 2019 and 2018, respectively. During the three-month periods ended March 31, 2019 and 2018, we charged $1.1 million and $0.8 million, respectively, to compensation expense related to these awards. There were no distributions from the DCPP during the three-month periods ended March 31, 2019 and 2018.

Restricted Stock, Performance S

Restricted Stock, Performance Share and Cash Awards	3 Months Ended
	Mar. 31, 2019
Text Block [Abstract]
Restricted Stock, Performance Share and Cash Awards	11. Restricted Stock, Performance Share and Cash Awards Restricted Stock Awards As discussed in Note 9 to these unaudited consolidated financial statements, on May 16, 2017, our stockholders approved the LTIP, which replaced our previous stockholder-approved 2014 LTIP. The LTIP provides for the grant of a stock award either as restricted stock or as restricted stock units to officers, employees and non-employee directors. 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 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 4.0 million. At March 31, 2019, 2.8 million shares were available for grant under the LTIP for such awards. In the first quarters of 2019 and 2018, we granted 399,900 and 420,200 restricted stock units, respectively, to employees under the LTIP, with an aggregate fair value of $31.8 million and $28.7 million, respectively, at the date of grant. These 2019 and 2018 awards of restricted stock units vest as follows: 399,900 420,200 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 March 31, 2019 and 2018, we recognized $6.4 million and $6.5 million, respectively, to compensation expense related to restricted stock unit awards granted in 2012 through 2019. The total intrinsic value of unvested restricted stock units at March 31, 2019 and 2018 was $142.2 million and $121.9 million, respectively. During the three-month periods ended March 31, 2019, no equity awards were vested and distributed to employees under this plan. During the three-month period ended March 31, 2018, equity awards (including accrued dividends) with an aggregate fair value of $21.2 million, were vested and distributed to employees under this plan. Performance Share Awards On March 14, 2019 and March 15, 2018, pursuant to the LTIP, the compensation committee approved 73,600 and 78,200, respectively of provisional performance unit awards, with an aggregate fair value of $5.8 million and $5.3 million, respectively, for future grants to our officers and key employees. Each performance unit award was equivalent to the value of one share of our common stock on the date such provisional award was approved. The 2019 and 2018 awards are subject to a three-year performance period that begins on January 1, 2019 and 2018, respectively, and vest on the three-year anniversary of the date of grant ( March 14, 2022 Cash Awards On March 14, 2019, pursuant to our Performance Unit Program (which we refer to as the Program), the compensation committee approved provisional cash awards of $16.5 million in the aggregate for future grants to our officers and key employees that are denominated in units ( 206,800 On March 15, 2018, pursuant to our Performance Unit Program (which we refer to as the Program), the compensation committee approved provisional cash awards of $15.0 million in the aggregate for future grants to our officers and key employees that are denominated in units ( 219,000 On March 16, 2017, pursuant to the Program, the compensation committee approved provisional cash awards of $14.3 million in the aggregate for future grant to our officers and key employees that are denominated in units ( 255,000 January 1, 2020 On March 17, 2016, pursuant to the Program, the compensation committee approved provisional cash awards of $17.4 million in the aggregate for future grant to our officers and key employees that are denominated in units ( 397,000 January 1, 2019 During the three-month period ended March 31, 2019, cash awards related to the 2016 provisional award with an aggregate fair value of $22.4 million ( 341,000 269,000

Investments

Investments	3 Months Ended
	Mar. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Investments	12. Investments The following is a summary of our investments, included in other noncurrent assets in the consolidated balance sheet (in millions): March 31, 2019 December 31, 2018 Chem-Mod LLC $ 4.0 $ 4.0 Chem-Mod International LLC 2.0 2.0 Clean-coal investments: Controlling interest in six limited liability companies that own fourteen 2009 Era Clean Coal Plants 3.8 5.1 Non-controlling interest in one limited liability company that owns one 2011 Era Clean Coal Plant 0.4 0.4 Controlling interest in seventeen limited liability companies that own nineteen 2011 Era Clean Coal Plants 39.8 43.0 Other investments 4.9 5.0 Total investments $ 54.9 $ 59.5

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	13. Leases We have operating leases primarily related to branch facilities, data centers, sales offices, and agent locations, automobiles and office equipment. Many of our leases include both lease (fixed rent payments) and non-lease components (common-area or other maintenance costs) which are accounted for as a single lease component as we have elected the practical expedient to group lease and non-lease components for all leases. Variable lease payments, such as periodically indexed and/or market adjustments, are presented as lease expense in the period in which they are incurred. Since we did not elect the short-term policy election, we record leases of 12 months or less on the balance sheet. We exclude options to extend or terminate a lease from our recognition as part of our right-of-use assets and lease liabilities until those options are reasonably certain and/or executed. We do not have any material guarantees, options to purchase, or restrictive covenants related to our leases. As our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the lease commencement date in determining the present value of the lease payments. We consider qualitative factors including our derived credit rating, notched adjustments for collateralization, lease term, and, if significant, adjustments to our collateralized rate to borrow in the same currency in which the lease is denominated. The components of lease expense are as follows (in millions): Statement of Earnings Three-month period Lease Components Classification ended March 31, 2019 Operating lease expense Operating expense $ 29.5 Variable lease expense Operating expense 4.5 Sublease income Investment income (0.3 ) Net lease expense $ 33.7 Variable lease cost consist primarily of common area and other maintenance costs for our lease facilities, as well as variable lease payments related to indexed and/or market adjustments. Our sublease income derives primarily from a few office lease arrangements and we have no significant sublease losses. Supplemental Cash Flow Information Related to Leases (in millions) Three-month period ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 28.5 Right-of-use assets obtained in exchange for new operating lease liabilities 1.6 We present all noncash transactions related to adjustments to the lease liability or right-of- use asset as noncash transactions. This includes all noncash charges related to any modification or reassessment events triggering remeasurement. Supplemental balance sheet information related to leases is as follows (in millions, except lease term and discount rate): Lease Components Balance Sheet Classification March 31, 2019 Lease right-of-use assets Right-of-use assets $ 368.8 Other current lease liabilities Accrued compensation and other current liabilities $ 80.8 Lease liabilities Lease liabilities - noncurrent 329.9 Total lease liabilities $ 410.7 Weighted-average remaining lease term, years 5.7 years Weighted-average discount rate 3.7 % Maturities of operating lease liabilities for each of the next five years and thereafter are as follows: 2019 (remaining nine months) $ 79.7 2020 93.0 2021 79.4 2022 61.6 2023 48.3 Thereafter 94.2 Total lease payments 456.2 Less interest (45.5 ) Total $ 410.7 Our leases have remaining lease terms of 0.2 years to 13.7 years, some of which may include options to extend the leases for up to 5.0 years As of March 31, 2019, we had an additional lease that has not yet commenced of $0.8 million. This lease will commence in 2019 with a lease term of 6.4 years.

Derivatives and Hedging Activit

Derivatives and Hedging Activity	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activity	14. Derivatives and Hedging Activity We adopted ASC 2017-12 on January 1, 2019. Among other provisions, the new standard required modification to existing presentation and disclosure requirements on a prospective basis. As such, certain disclosures below conform to the disclosure requirements prior to the adoption of ASC 2017-12. We are exposed to market risks, including changes in foreign currency exchange rates and interest rates. To manage the risk related to these exposures, we enter into various derivative instruments that reduce these risks by creating offsetting exposures. We generally do not enter into derivative transactions for trading or speculative purposes. Foreign Exchange Risk Management We are exposed to foreign exchange risk when we earn revenues, pay expenses, or enter into monetary intercompany transfers denominated in a currency that differs from our functional currency, or other transactions that are denominated in a currency other than our functional currency. We use foreign exchange derivatives, typically forward contracts and options, to reduce our overall exposure to the effects of currency fluctuations on cash flows. These exposures are hedged, on average, for less than three years. Interest Rate Risk Management We enter into various long-term debt agreements. We use interest rate derivatives, typically swaps, to reduce our exposure to the effects of interest rate fluctuations on the forecasted interest rates for up to three years into the future. We have not received or pledged any collateral related to derivative arrangements at March 31, 2019. The notional and fair values of derivatives designated as hedging instruments are as follows at March 31, 2019 and December 31, 2018 (in millions): Derivative Assets Derivative Liabilities Instrument Notional Amount Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value At March 31, 2019 Interest rate contracts $ 750.0 Other current assets $ 0.6 Accrued compensation and other current liabilities $ 29.8 Foreign exchange contracts (1) 41.2 Other current assets 1.0 Accrued compensation and other current liabilities 2.7 Other noncurrent assets 4.2 Other noncurrent liabilities 4.0 Total $ 791.2 $ 5.8 $ 36.5 At December 31 , 2018 Interest rate contracts $ 850.0 Other current assets $ 3.0 Accrued compensation and other current liabilities $ 13.0 Foreign exchange contracts (1) 51.4 Other current assets 0.9 Accrued compensation and other current liabilities 4.9 Other noncurrent assets 5.7 Other noncurrent liabilities 7.9 Total $ 901.4 $ 9.6 $ 25.8 (1) Included within foreign exchange contracts at March 31, 2019 were $248.8 million of call options offset with $248.8 million of put options, and $26.9 million of buy forwards offset with $68.1 million of sell forwards. Included within foreign exchange contracts at December 31, 2018 were $276.4 million of call options offset with $276.4 million of put options, and $23.1 million of buy forwards offset with $72.9 million of sell forwards. The effect of cash flow hedge accounting on accumulated other comprehensive earnings (loss) for the three-month periods ended March 31, 2019 and 2018 were as follows (in millions): Instrument Amount of Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing Statement of Earnings Classification Three-month period ended March 31, 2019 Interest rate contracts $ (20.9 ) $ (0.3 ) $ — Interest expense Foreign exchange contracts 3.7 (0.1 ) (0.2 ) Commission revenue (0.2 ) 0.4 Compensation expense (0.1 ) 0.2 Operating expense Total $ (17.2 ) $ (0.7 ) $ 0.4 Three-month period ended March 31, 2018 Interest rate contracts $ 4.2 $ 0.2 Interest expense Foreign exchange contracts 4.3 0.7 Commission revenue 0.5 Compensation expense 0.4 Operating expense Total $ 8.5 $ 1.8 (1) For the three-month period ended March 31, 2019, of $0.1 million. We estimate that approximately $1.7 million of pretax loss currently included within accumulated other comprehensive loss will be reclassified into earnings in the next twelve months.

Commitments, Contingencies and

Commitments, Contingencies and Off-Balance Sheet Arrangements	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Off-Balance Sheet Arrangements	15. Commitments, Contingencies and Off-Balance Sheet Arrangements In connection with our investing and operating activities, we have entered into certain contractual 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 and purchase commitments at March 31, 2019 were as follows (in millions): Payments Due by Period Contractual Obligations 2019 2020 2021 2022 2023 Thereafter Total Note purchase agreements $ 100.0 $ 100.0 $ 75.0 $ 200.0 $ 300.0 $ 3,023.0 $ 3,798.0 Credit Agreement 260.0 — — — — — 260.0 Premium Financing Debt Facility 134.8 — — — — — 134.8 Interest on debt 126.1 163.1 157.9 152.6 142.9 616.6 1,359.2 Total debt obligations 620.9 263.1 232.9 352.6 442.9 3,639.6 5,552.0 Operating lease obligations 79.7 93.0 79.4 61.6 48.3 94.2 456.2 Less sublease arrangements (0.9 ) (0.7 ) (0.7 ) (0.3 ) (0.3 ) (0.9 ) (3.8 ) Outstanding purchase obligations 41.0 37.9 29.5 14.2 7.9 23.1 153.6 Total contractual obligations $ 740.7 $ 393.3 $ 341.1 $ 428.1 $ 498.8 $ 3,756.0 $ 6,158.0 The amounts presented in the table above may not necessarily reflect our actual future cash funding requirements, because the actual timing of the future payments made may vary from the stated contractual obligation. See Note 3 to these unaudited consolidated financial statements for a discussion of commitments as of March 31, 2019 to acquire 100% of the equity of Stackhouse Poland Group Limited and to acquire the global aerospace operations of Jardine Lloyd Thompson Group plc (JLT) in the second quarter of 2019. Note Purchase Agreements, Credit Agreement and Premium Financing Debt Facility - 7 to these unaudited consolidated financial statements for a summary of the amounts outstanding under 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 2850 Golf Road, Rolling Meadows, Illinois, where we have approximately 360,000 square feet of space and will accommodate approximately 2,000 employees at peak capacity. 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 - The amount disclosed in the contractual obligations table above represents the aggregate amount of unrecorded purchase obligations that we had outstanding at March 31, 2019. 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, and financial guarantees as of March 31, 2019 were as follows (in millions): Amount of Commitment Expiration by Period Total Amounts Off-Balance Sheet Commitments 2019 2020 2021 2022 2023 Thereafter Committed Letters of credit $ 1.3 $ — $ — $ — $ — $ 17.0 $ 18.3 Financial guarantees 0.2 0.2 0.2 0.2 0.2 0.6 1.6 Total commitments $ 1.5 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 17.6 $ 19.9 Since commitments may expire unused, the amounts presented in the table above do not necessarily reflect our actual future cash funding requirements. See 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 518 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 2013 to 2019 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 potential 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 $618.9 million, of which $293.6 million was recorded in our consolidated balance sheet as of March 31, 2019 based on the estimated fair value of the expected future payments to be made. 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 March 31, 2019 or December 31, 2018, that was recourse to us. At March 31, 2019, we had posted two letters of credit totaling $10.2 million, in the aggregate, related to our self-insurance deductibles, for which we had a recorded liability of $15.3 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 March 31, 2019, we had posted seven letters of credit totaling $6.3 million to allow certain of our captive operations to meet minimum statutory surplus requirements plus additional collateral related to premium and claim funds held in a fiduciary capacity, one letter of credit totaling $1.3 million for collateral related to claim funds held in a fiduciary capacity by a recent acquisition, and one letter of credit totaling $0.5 million as a security deposit for a 2015 acquisition’s lease. 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, investigations and reviews by regulatory and taxing authorities into various matters related to our business, including our operational, compliance and finance functions. Neither the outcomes of these matters nor their effect upon our business, financial condition or results of operations can be determined at this time. On April 18, 2018, Nalco Company (which we refer to as Nalco) filed patent infringement lawsuits in the Western District of Wisconsin against two unaffiliated power plants that burn refined coal using the Chem-Mod TM TM Our micro-captive advisory services are under investigation by the IRS. Additionally, the IRS has initiated audits for the 2012 tax year of over 100 of the micro-captive underwriting enterprises 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 specific allegations relating to our operations or the pre-acquisition activities of Tribeca, an adverse determination could subject us to penalties and negatively affect our defense of the class action lawsuit described below. We may also experience lost earnings due to the negative effect of an extended IRS investigation. In the period from 2016 to 2018, our micro-captive operations contributed less than $3.2 million of net earnings and less than $5.0 million in EBITDAC to our consolidated results in any one year. Due to the fact that the IRS has not made any allegation against us or completed all of its audits of our clients, we are not able to reasonably estimate the amount of any potential loss in connection with this investigation. On December 7, 2018, a class action lawsuit was filed against us, our subsidiary Artex Risk Solutions, Inc. (which we refer to as Artex) and other defendants including Tribeca, in the District of Arizona. An amended complaint was filed on March 29, 2019. The named plaintiffs are micro-captive clients of Artex or Tribeca and their related entities and owners who had IRS Section 831(b) tax benefits disallowed by the IRS. The complaint attempts to state various causes of action and alleges that the defendants defrauded the plaintiffs by marketing and managing micro-captives with the knowledge that the captives did not constitute bona fide 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 $350.0 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 March 31, 2019 consolidated balance sheet is above the lower end of the most recently determined actuarial range by $0.7 million and below the upper end of the actuarial range by $7.9 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. We recorded tax benefits in connection with our ownership in these investments. At March 31, 2019, we had exposure on $108.0 million of previously earned tax credits. Under the Tax Act, we expect that these previously earned tax credits will be refunded for tax years beginning 2018 and ending in 2021, according to a specific formula. 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. Due to the contingent nature of this exposure and our related assessment of its likelihood, no reserve has been recorded in our March 31, 2019 consolidated balance sheet related to this exposure.

Supplemental Disclosures of Cas

Supplemental Disclosures of Cash Flow Information	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
Supplemental Disclosures of Cash Flow Information	16. Supplemental Disclosures of Cash Flow Information Three-month period ended March 31, Supplemental disclosures of cash flow information (in millions): 2019 2018 Interest paid $ 29.5 $ 28.0 Income taxes (recovered) paid, net (1.8 ) 11.6 The following is a reconciliation of our March 31 cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the three-month periods ended March 31, 2019 and 2018 (in millions): March 31, 2019 2018 Cash and cash equivalents $ 871.5 $ 697.9 Restricted cash 1,669.3 1,410.8 Total cash, cash equivalents and restricted cash $ 2,540.8 $ 2,108.7

Accumulated Other Comprehensive

Accumulated Other Comprehensive Earnings (Loss)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Accumulated Other Comprehensive Earnings (Loss)	17. Accumulated Other Comprehensive Earnings (Loss) The after-tax components of our accumulated other comprehensive earnings (loss) attributable to controlling interests consist of the following: Foreign Fair Value of Accumulated Pension Currency Derivative Comprehensive Liability Translation Investments Earnings (Loss) Balance as of December 31, 2018 $ (61.2 ) $ (719.0 ) $ (5.4 ) $ (785.6 ) Cumulative effect of adoption of new accounting standards — — (0.2 ) (0.2 ) Net change in period 1.6 74.5 (11.8 ) 64.3 Balance as of March 31, 2019 $ (59.6 ) $ (644.5 ) $ (17.4 ) $ (721.5 ) The foreign currency translation during the three-month period ended March 31, 2019 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 and the U.K. During the three-month periods ended March 31, 2019 and 2018, $1.8 million and $1.2 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 three-month periods ended March 31, 2019 and 2018, $(0.7) million of income and $1.8 million of expense, respectively, related to the fair value of derivative investments, was reclassified from accumulated other comprehensive earnings (loss) to the statement of earnings. During the three-month periods ended March 31, 2019 and 2018, no amounts related to foreign currency translation were reclassified from accumulated other comprehensive earnings (loss) to the statement of earnings.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Segment Information	18. Segment Information We have three reportable operating 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 underwriting enterprises and through fees charged to our clients. Our brokers, agents and administrators act as intermediaries between underwriting enterprises and our clients and we do not assume net underwriting risks. The risk management segment provides contract claim settlement and administration services for enterprises and public entities that choose to self-insure some or all of their property/casualty coverages and for underwriting enterprises 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. Our risk management segment also provides risk management consulting services that are recognized as the services are delivered. The corporate segment manages our clean energy and other investments. In addition, the corporate segment reports the financial information related to our debt and other corporate costs, external acquisition-related expenses and the impact of foreign currency translation. 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 periods ended March 31, 2019 and 2018 is as follows (in millions): Three-month period ended March 31, 2019 2018 Brokerage Total revenues $ 1,381.9 $ 1,195.6 Earnings before income taxes $ 412.4 $ 318.9 Identifiable assets at March 31, 2019 and 2018 $ 15,981.8 $ 13,784.2 Risk Management Total revenues $ 236.4 $ 229.9 Earnings before income taxes $ 22.0 $ 21.6 Identifiable assets at March 31, 2019 and 2018 $ 806.6 $ 735.9 Corporate Total revenues $ 372.3 $ 412.2 Loss before income taxes $ (112.6 ) $ (98.2 ) Identifiable assets at March 31, 2019 and 2018 $ 1,843.0 $ 1,607.4 Disaggregation of Revenue We disaggregate our revenue from contracts with clients by type and geographic location for each of our segments, as we believe it best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. Revenues by type and segment for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: Commissions $ 940.4 $ — $ — $ 940.4 Fees 261.8 202.9 — 464.7 Supplemental revenues 56.7 — — 56.7 Contingent revenues 48.0 — — 48.0 Investment income 17.9 0.4 — 18.3 Net gains on divestitures 57.1 — — 57.1 Revenues from clean coal activities — — 372.3 372.3 Revenues before reimbursements 1,381.9 203.3 372.3 1,957.5 Reimbursements — 33.1 — 33.1 Total revenues $ 1,381.9 $ 236.4 $ 372.3 $ 1,990.6 Revenues by geographical location and segment for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: United States $ 1,006.5 $ 198.5 $ 372.3 $ 1,577.3 United Kingdom 203.6 10.2 — 213.8 Australia 46.0 22.5 — 68.5 Canada 57.3 1.2 — 58.5 New Zealand 30.3 4.0 — 34.3 Other foreign 38.2 — — 38.2 Total revenues $ 1,381.9 $ 236.4 $ 372.3 $ 1,990.6 Revenues by type and segment for the three-month period ended March 31, 2018 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: Commissions $ 839.4 $ — $ — $ 839.4 Fees 253.2 194.9 — 448.1 Supplemental revenues 52.0 — — 52.0 Contingent revenues 34.9 — — 34.9 Investment income 13.2 0.2 — 13.4 Net gains on divestitures 2.9 — — 2.9 Revenues from clean coal activities — — 412.2 412.2 Revenues before reimbursements 1,195.6 195.1 412.2 1,802.9 Reimbursements — 34.8 — 34.8 Total revenues $ 1,195.6 $ 229.9 $ 412.2 $ 1,837.7 Revenues by geographical location and segment for the three-month period ended March 31, 2018 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: United States $ 852.8 $ 192.7 $ 412.2 $ 1,457.7 United Kingdom 191.0 9.0 — 200.0 Australia 43.6 23.7 — 67.3 Canada 42.8 1.0 — 43.8 New Zealand 30.1 3.5 — 33.6 Other foreign 35.3 — — 35.3 Total revenues $ 1,195.6 $ 229.9 $ 412.2 $ 1,837.7

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Nature of Operations and Basis of Presentation	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, consulting and third party claims settlement and administration services to both domestic and international entities through three reportable operating segments. Our brokers, agents and administrators act as intermediaries between underwriting enterprises and our clients. Our brokerage segment operations provide brokerage and consulting services to companies and entities of all types, including commercial, not-for-profit, public entities, and, to a lesser extent, individuals, in the areas of insurance placement, risk of loss management, and management of employer sponsored benefit programs. Our risk management segment operations provide contract claim settlement, claim administration, loss control services and risk management consulting for commercial, not-for-profit, captive and public entities, and various other organizations that choose to self-insure property/casualty coverages or choose to use a third-party claims management organization rather than the claim services provided by underwriting enterprises. The corporate segment reports the financial information related to our debt and other corporate costs, clean energy investments, external acquisition-related expenses and the impact of foreign currency translation. Clean energy investments consist of our investments in limited liability companies that own 34 commercial clean coal production facilities producing refined coal using Chem-Mod LLC’s proprietary technologies. We believe these operations produce refined coal that qualifies for tax credits under IRC Section 45. We do not assume underwriting risk on a net basis, other than with respect to de minimis amounts necessary to provide minimum or regulatory capital to organize captives, pools, specialized underwriters or risk-retention groups. Rather, capital necessary for events of loss coverages is provided by underwriting enterprises. Investment income and other revenues are primarily generated from our premium financing operations, our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. In addition, our share of the net earnings related to partially owned entities that are accounted for using the equity method is included in investment income. We are headquartered in Rolling Meadows, Illinois, have operations in 35 countries and offer client-service capabilities in more than 150 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, 2018, except as disclosed in Note 2, 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, 2018. In the preparation of our unaudited consolidated financial statements as of March 31, 2019, 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.
Use of Estimates	Use of Estimates The preparation of our consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These accounting principles require us to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses, and the disclosure of contingent assets and liabilities at the date of our consolidated financial statements. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible assets, right-of-use assets, investments (including our IRC Section 45 investments), income taxes, revenue recognition, deferred costs, stock-based compensation, claims handling obligations, retirement plans, litigation and contingencies. We base our estimates on historical experience and various assumptions that we believe to be reasonable based on specific circumstances. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.

Business Combinations (Tables)

Business Combinations (Tables)	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Acquisition Method for Recording Business Combinations	During the three-month period ended March 31, 2019, 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 Date of Acquisition Common Shares Issued Common Share Value Cash Paid Accrued Liability Escrow Deposited Recorded Earnout Payable Total Recorded Purchase Price Maximum Potential Earnout Payable (000s) Inversion Holding Company Company, LLC (IHC) January 1, 2019 452 $ 35.9 $ 31.2 $ — $ 4.5 $ 20.9 $ 92.5 $ 35.0 Jones Brown Inc. (JBI) January 1, 2019 — — 65.9 — 8.7 — 74.6 — Nine other acquisitions completed in 2019 — — 79.7 0.1 6.0 14.9 100.7 46.1 452 $ 35.9 $ 176.8 $ 0.1 $ 19.2 $ 35.8 $ 267.8 $ 81.1
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 three-month period ended March 31, 2019 (in millions): IHC JBI Nine Other Acquisitions Total Cash $ — $ 2.7 $ 1.0 $ 3.7 Other current assets 3.8 22.2 14.6 40.6 Fixed assets 0.3 1.1 0.5 1.9 Noncurrent assets 0.5 2.9 2.1 5.5 Goodwill 41.8 51.2 38.5 131.5 Expiration lists 50.6 22.7 57.3 130.6 Non-compete agreements 1.1 0.8 0.2 2.1 Total assets acquired 98.1 103.6 114.2 315.9 Current liabilities 5.1 26.1 12.3 43.5 Total liabilities assumed 5.6 29.0 13.5 48.1 Total net assets acquired $ 92.5 $ 74.6 $ 100.7 $ 267.8
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, 2018 (in millions, except per share data): Three-month period ended March 31, 2019 2018 Total revenues $ 1,993.0 $ 1,855.9 Net earnings attributable to controlling interests 334.3 275.6 Basic net earnings per share 1.81 1.51 Diluted net earnings per share 1.77 1.49

Contracts with Customers (Table

Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2019
Summary of Unbilled Receivables, Contract Assets and Contract Liabilities from Contracts with Customers	Information about unbilled receivables, contract assets and contract liabilities from contracts with customers is as follows (in millions): March 31, 2019 December 31, 2018 Unbilled receivables $ 767.7 $ 496.2 Deferred contract costs 55.1 91.6 Deferred revenue 480.1 457.7
Summary of Changes in Deferred Revenue Balances	Significant changes in the deferred revenue balances, which include foreign currency translation adjustments, during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2018 $ 284.7 $ 173.0 $ 457.7 Incremental deferred revenue 162.8 41.7 204.5 Revenue recognized during the three-month period ended March 31, 2019 included in deferred revenue at December 31, 2018 (137.6 ) (44.1 ) (181.7 ) Deferred revenue recognized from business acquisitions (0.4 ) — (0.4 ) Deferred revenue at March 31, 2019 $ 309.5 $ 170.6 $ 480.1
Summary of Expected Revenue Related to Performance Obligations	The estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period is as follows (in millions): Brokerage Risk Management Total 2019 (remaining nine months) $ 252.0 $ 80.7 $ 332.7 2020 32.9 36.3 69.2 2021 19.7 18.0 37.7 2022 3.8 10.4 14.2 2023 0.6 6.1 6.7 Thereafter 0.5 19.1 19.6 Total $ 309.5 $ 170.6 $ 480.1

Other Financial Data (Tables)

Other Financial Data (Tables)	3 Months Ended
	Mar. 31, 2019
Other Financial Data Disclosure [Abstract]
Schedule of other current assets	Major classes of other current assets consist of the following (in millions): March 31, December 31, 2019 2018 Premium finance advances and loans $ 305.1 $ 316.2 Accrued supplemental, direct bill and other receivables 306.3 348.2 Refined coal production related receivables 114.0 160.2 Deferred contract costs 55.1 91.6 Prepaid expenses 95.0 108.2 Total other current assets $ 875.5 $ 1,024.4

Intangible Assets (Tables)

Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations	The carrying amount of goodwill at March 31, 2019 and December 31, 2018 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Management Corporate Total At March 31, 2019 United States $ 2,794.5 $ 29.6 $ — $ 2,824.1 United Kingdom 784.2 9.6 — 793.8 Canada 437.4 — — 437.4 Australia 409.2 0.3 — 409.5 New Zealand 213.3 10.3 — 223.6 Other foreign 109.8 — 2.7 112.5 Total goodwill $ 4,748.4 $ 49.8 $ 2.7 $ 4,800.9 At December 31, 2018 United States $ 2,715.3 $ 29.6 $ — $ 2,744.9 United Kingdom 753.7 9.2 — 762.9 Canada 378.6 — — 378.6 Australia 406.3 0.3 — 406.6 New Zealand 209.6 10.2 — 219.8 Other foreign 110.1 — 2.7 112.8 Total goodwill $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6
Changes in Carrying Amount of Goodwill	The changes in the carrying amount of goodwill for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Balance as of December 31, 2018 $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Goodwill acquired during the period 131.5 — — 131.5 Goodwill adjustments due to appraisals and other acquisition adjustments 8.4 — — 8.4 Goodwill written-off related to sales of business (6.6 ) — — (6.6 ) Foreign currency translation adjustments during the period 41.5 0.5 — 42.0 Balance as of March 31, 2019 $ 4,748.4 $ 49.8 $ 2.7 $ 4,800.9
Major Classes of Amortizable Intangible Assets	Major classes of amortizable intangible assets at March 31, 2019 and December 31, 2018 consist of the following (in millions): March 31, December 31, 2019 2018 Expiration lists $ 3,529.6 $ 3,379.4 Accumulated amortization - expiration lists (1,758.8 ) (1,676.8 ) 1,770.8 1,702.6 Non-compete agreements 60.7 58.0 Accumulated amortization - non-compete agreements (49.8 ) (48.5 ) 10.9 9.5 Trade names 86.4 86.0 Accumulated amortization - trade names (26.7 ) (25.1 ) 59.7 60.9 Net amortizable assets $ 1,841.4 $ 1,773.0
Estimated Aggregate Amortization Expense	Estimated aggregate amortization expense for each of the next five years and thereafter is as follows: 2019 (remaining nine months) $ 226.3 2020 286.7 2021 262.8 2022 237.5 2023 213.5 Thereafter 614.6 Total $ 1,841.4

Credit and Other Debt Agreeme_2

Credit and Other Debt Agreements (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Summary of Corporate and Other Debt	The following is a summary of our corporate and other debt (in millions): March 31, 2019 December 31, 2018 Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 3.20%, balloon due June 24, 2019 $ 50.0 $ 50.0 Semi-annual payments of interest, fixed rate of 5.85%, balloon due November 30, 2019 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.48%, balloon due June 24, 2020 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due July 10, 2020 50.0 50.0 Semi-annual payments of interest, fixed rate of 5.18%, balloon due February 10, 2021 75.0 75.0 Semi-annual payments of interest, fixed rate of 3.69%, balloon due June 14, 2022 200.0 200.0 Semi-annual payments of interest, fixed rate of 5.49%, balloon due February 10, 2023 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.13%, balloon due June 24, 2023 200.0 200.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.65%, balloon due 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.72%, balloon due February 13, 2024 100.0 — Semi-annual payments of interest, fixed rate of 4.58%, balloon due February 27, 2024 325.0 325.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.40%, balloon due 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.31%, balloon due June 24, 2025 200.0 200.0 Semi-annual payments of interest, fixed rate of 4.85%, balloon due February 13, 2026 140.0 — Semi-annual payments of interest, fixed rate of 4.73%, balloon due February 27, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.40%, balloon due June 2, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.36%, balloon due June 24, 2026 150.0 150.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due June 27, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due August 2, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.14%, balloon due August 4, 2027 98.0 98.0 Semi-annual payments of interest, fixed rate of 3.46%, balloon due December 1, 2027 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.55%, balloon due June 2, 2028 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 13, 2028 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.04%, balloon due February 13, 2029 100.0 — Semi-annual payments of interest, fixed rate of 4.98%, balloon due February 27, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due June 27, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due August 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.44%, balloon due June 13, 2030 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.14%, balloon due March 13, 2031 180.0 — Semi-annual payments of interest, fixed rate of 4.70%, balloon due June 2, 2031 25.0 25.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 27, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due August 2, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.59%, balloon due June 13, 2033 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.29%, balloon due March 13, 2034 40.0 — Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 75.0 Semi-annual payments of interest, fixed rate of 5.45%, balloon due March 13, 2039 40.0 — Total Note Purchase Agreements 3,798.0 3,198.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires April 8, 2021 260.0 265.0 Premium Financing Debt Facility - expires May 18, 2020: Periodic payments of interest and principal, Interbank rates plus 1.05% for Facility B; plus 0.55% for Facilities C and D Facility B AUD denominated tranche 106.5 133.9 NZD denominated tranche 2.7 10.1 Facility C and D AUD denominated tranche 15.4 — NZD denominated tranche 10.2 10.0 Total Premium Financing Debt Facility 134.8 154.0 Total corporate and other debt 4,192.8 3,617.0 Less unamortized debt acquisition costs on Note Purchase Agreements (7.7 ) (6.6 ) Net corporate and other debt $ 4,185.1 $ 3,610.4

Earnings per Share (Tables)

Earnings per Share (Tables)	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 2018 Net earnings attributable to controlling interests $ 334.1 $ 273.7 Weighted average number of common shares outstanding 184.5 181.5 Dilutive effect of stock options using the treasury stock method 3.9 3.5 Weighted average number of common and common equivalent shares outstanding 188.4 185.0 Basic net earnings per share $ 1.81 $ 1.51 Diluted net earnings per share $ 1.77 $ 1.48

Stock Option Plans (Tables)

Stock Option Plans (Tables)	3 Months Ended
	Mar. 31, 2019
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: 2019 2018 Expected dividend yield 1.7 % 2.3 % Expected risk-free interest rate 2.5 % 2.7 % Volatility 15.6 % 15.1 % Expected life (in years) 5.5 5.5
Stock Option Activity and Related Information	The following is a summary of our stock option activity and related information for 2019 (in millions, except exercise price and year data): Three-month period ended March 31, 2019 Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Beginning balance 8.8 $ 50.16 Granted 1.3 79.59 Exercised (0.7 ) 41.11 Forfeited or canceled (0.1 ) 51.52 Ending balance 9.3 $ 54.92 4.24 $ 217.2 Exercisable at end of period 3.2 $ 44.68 2.47 $ 106.2 Ending unvested and expected to vest 5.8 $ 59.61 5.10 $ 108.6
Other Information Regarding Stock Options Outstanding and Exercisable	Options Outstanding Options Exercisable Weighted Average Remaining Weighted Weighted Contractual Average Average Number Term Exercise Number Exercise Range of Exercise Prices Outstanding (in years) Price Exercisable Price $ 39.17 — $ 39.17 0.6 0.95 $ 39.17 0.6 $ 39.17 43.71 — 43.71 2.2 3.96 43.71 0.7 43.71 46.17 — 46.87 2.5 2.51 46.47 1.9 46.56 47.92 63.60 1.5 4.96 56.81 — — 70.74 — 70.74 1.2 5.96 70.74 — — 79.59 — 79.59 1.3 6.96 79.59 — — $ 39.17 — $ 79.59 9.3 4.24 $ 54.92 3.2 $ 44.68

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Investments Reported in Other Current and Non-Current Assets	The following is a summary of our investments, included in other noncurrent assets in the consolidated balance sheet (in millions): March 31, 2019 December 31, 2018 Chem-Mod LLC $ 4.0 $ 4.0 Chem-Mod International LLC 2.0 2.0 Clean-coal investments: Controlling interest in six limited liability companies that own fourteen 2009 Era Clean Coal Plants 3.8 5.1 Non-controlling interest in one limited liability company that owns one 2011 Era Clean Coal Plant 0.4 0.4 Controlling interest in seventeen limited liability companies that own nineteen 2011 Era Clean Coal Plants 39.8 43.0 Other investments 4.9 5.0 Total investments $ 54.9 $ 59.5

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Summary of Lease, Cost	The components of lease expense are as follows (in millions): Statement of Earnings Three-month period Lease Components Classification ended March 31, 2019 Operating lease expense Operating expense $ 29.5 Variable lease expense Operating expense 4.5 Sublease income Investment income (0.3 ) Net lease expense $ 33.7
Summary of Supplemental Cash Flow Information Related to Leases	Supplemental Cash Flow Information Related to Leases (in millions) Three-month period ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 28.5 Right-of-use assets obtained in exchange for new operating lease liabilities 1.6
Summary of Supplemental balance sheet information related to leases	Supplemental balance sheet information related to leases is as follows (in millions, except lease term and discount rate): Lease Components Balance Sheet Classification March 31, 2019 Lease right-of-use assets Right-of-use assets $ 368.8 Other current lease liabilities Accrued compensation and other current liabilities $ 80.8 Lease liabilities Lease liabilities - noncurrent 329.9 Total lease liabilities $ 410.7 Weighted-average remaining lease term, years 5.7 years Weighted-average discount rate 3.7 %
Maturities of operating lease liabilities	Maturities of operating lease liabilities for each of the next five years and thereafter are as follows: 2019 (remaining nine months) $ 79.7 2020 93.0 2021 79.4 2022 61.6 2023 48.3 Thereafter 94.2 Total lease payments 456.2 Less interest (45.5 ) Total $ 410.7

Derivatives and Hedging Activ_2

Derivatives and Hedging Activity (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Notional and Fair Values of Derivative Instruments	The notional and fair values of derivatives designated as hedging instruments are as follows at March 31, 2019 and December 31, 2018 (in millions): Derivative Assets Derivative Liabilities Instrument Notional Amount Balance Sheet Classification Fair Value Balance Sheet Classification Fair Value At March 31, 2019 Interest rate contracts $ 750.0 Other current assets $ 0.6 Accrued compensation and other current liabilities $ 29.8 Foreign exchange contracts (1) 41.2 Other current assets 1.0 Accrued compensation and other current liabilities 2.7 Other noncurrent assets 4.2 Other noncurrent liabilities 4.0 Total $ 791.2 $ 5.8 $ 36.5 At December 31 , 2018 Interest rate contracts $ 850.0 Other current assets $ 3.0 Accrued compensation and other current liabilities $ 13.0 Foreign exchange contracts (1) 51.4 Other current assets 0.9 Accrued compensation and other current liabilities 4.9 Other noncurrent assets 5.7 Other noncurrent liabilities 7.9 Total $ 901.4 $ 9.6 $ 25.8 (1) Included within foreign exchange contracts at March 31, 2019 were $248.8 million of call options offset with $248.8 million of put options, and $26.9 million of buy forwards offset with $68.1 million of sell forwards. Included within foreign exchange contracts at December 31, 2018 were $276.4 million of call options offset with $276.4 million of put options, and $23.1 million of buy forwards offset with $72.9 million of sell forwards.
Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	The effect of cash flow hedge accounting on accumulated other comprehensive earnings (loss) for the three-month periods ended March 31, 2019 and 2018 were as follows (in millions): Instrument Amount of Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing Statement of Earnings Classification Three-month period ended March 31, 2019 Interest rate contracts $ (20.9 ) $ (0.3 ) $ — Interest expense Foreign exchange contracts 3.7 (0.1 ) (0.2 ) Commission revenue (0.2 ) 0.4 Compensation expense (0.1 ) 0.2 Operating expense Total $ (17.2 ) $ (0.7 ) $ 0.4 Three-month period ended March 31, 2018 Interest rate contracts $ 4.2 $ 0.2 Interest expense Foreign exchange contracts 4.3 0.7 Commission revenue 0.5 Compensation expense 0.4 Operating expense Total $ 8.5 $ 1.8 (1) For the three-month period ended March 31, 2019, of $0.1 million.

Commitments, Contingencies an_2

Commitments, Contingencies and Off-Balance Sheet Arrangements (Tables)	3 Months Ended
	Mar. 31, 2019
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 and purchase commitments at March 31, 2019 were as follows (in millions): Payments Due by Period Contractual Obligations 2019 2020 2021 2022 2023 Thereafter Total Note purchase agreements $ 100.0 $ 100.0 $ 75.0 $ 200.0 $ 300.0 $ 3,023.0 $ 3,798.0 Credit Agreement 260.0 — — — — — 260.0 Premium Financing Debt Facility 134.8 — — — — — 134.8 Interest on debt 126.1 163.1 157.9 152.6 142.9 616.6 1,359.2 Total debt obligations 620.9 263.1 232.9 352.6 442.9 3,639.6 5,552.0 Operating lease obligations 79.7 93.0 79.4 61.6 48.3 94.2 456.2 Less sublease arrangements (0.9 ) (0.7 ) (0.7 ) (0.3 ) (0.3 ) (0.9 ) (3.8 ) Outstanding purchase obligations 41.0 37.9 29.5 14.2 7.9 23.1 153.6 Total contractual obligations $ 740.7 $ 393.3 $ 341.1 $ 428.1 $ 498.8 $ 3,756.0 $ 6,158.0
Off-Balance Sheet Commitments	Off-Balance Sheet Commitments - Our total unrecorded commitments associated with outstanding letters of credit, and financial guarantees as of March 31, 2019 were as follows (in millions): Amount of Commitment Expiration by Period Total Amounts Off-Balance Sheet Commitments 2019 2020 2021 2022 2023 Thereafter Committed Letters of credit $ 1.3 $ — $ — $ — $ — $ 17.0 $ 18.3 Financial guarantees 0.2 0.2 0.2 0.2 0.2 0.6 1.6 Total commitments $ 1.5 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 17.6 $ 19.9

Supplemental Disclosures of C_2

Supplemental Disclosures of Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
Supplemental disclosures of cash flow information	Three-month period ended March 31, Supplemental disclosures of cash flow information (in millions): 2019 2018 Interest paid $ 29.5 $ 28.0 Income taxes (recovered) paid, net (1.8 ) 11.6
Summary of Cash, Cash Equivalents and Restricted Cash	The following is a reconciliation of our March 31 cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the three-month periods ended March 31, 2019 and 2018 (in millions): March 31, 2019 2018 Cash and cash equivalents $ 871.5 $ 697.9 Restricted cash 1,669.3 1,410.8 Total cash, cash equivalents and restricted cash $ 2,540.8 $ 2,108.7

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Earnings (Loss) (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests	The after-tax components of our accumulated other comprehensive earnings (loss) attributable to controlling interests consist of the following: Foreign Fair Value of Accumulated Pension Currency Derivative Comprehensive Liability Translation Investments Earnings (Loss) Balance as of December 31, 2018 $ (61.2 ) $ (719.0 ) $ (5.4 ) $ (785.6 ) Cumulative effect of adoption of new accounting standards — — (0.2 ) (0.2 ) Net change in period 1.6 74.5 (11.8 ) 64.3 Balance as of March 31, 2019 $ (59.6 ) $ (644.5 ) $ (17.4 ) $ (721.5 )

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information by Segment	Three-month period ended March 31, 2019 2018 Brokerage Total revenues $ 1,381.9 $ 1,195.6 Earnings before income taxes $ 412.4 $ 318.9 Identifiable assets at March 31, 2019 and 2018 $ 15,981.8 $ 13,784.2 Risk Management Total revenues $ 236.4 $ 229.9 Earnings before income taxes $ 22.0 $ 21.6 Identifiable assets at March 31, 2019 and 2018 $ 806.6 $ 735.9 Corporate Total revenues $ 372.3 $ 412.2 Loss before income taxes $ (112.6 ) $ (98.2 ) Identifiable assets at March 31, 2019 and 2018 $ 1,843.0 $ 1,607.4
Summary of Revenues by Type and Segment	Revenues by type and segment for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: Commissions $ 940.4 $ — $ — $ 940.4 Fees 261.8 202.9 — 464.7 Supplemental revenues 56.7 — — 56.7 Contingent revenues 48.0 — — 48.0 Investment income 17.9 0.4 — 18.3 Net gains on divestitures 57.1 — — 57.1 Revenues from clean coal activities — — 372.3 372.3 Revenues before reimbursements 1,381.9 203.3 372.3 1,957.5 Reimbursements — 33.1 — 33.1 Total revenues $ 1,381.9 $ 236.4 $ 372.3 $ 1,990.6 Revenues by type and segment for the three-month period ended March 31, 2018 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: Commissions $ 839.4 $ — $ — $ 839.4 Fees 253.2 194.9 — 448.1 Supplemental revenues 52.0 — — 52.0 Contingent revenues 34.9 — — 34.9 Investment income 13.2 0.2 — 13.4 Net gains on divestitures 2.9 — — 2.9 Revenues from clean coal activities — — 412.2 412.2 Revenues before reimbursements 1,195.6 195.1 412.2 1,802.9 Reimbursements — 34.8 — 34.8 Total revenues $ 1,195.6 $ 229.9 $ 412.2 $ 1,837.7
Summary of Geographical Location and Segment	Revenues by geographical location and segment for the three-month period ended March 31, 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: United States $ 1,006.5 $ 198.5 $ 372.3 $ 1,577.3 United Kingdom 203.6 10.2 — 213.8 Australia 46.0 22.5 — 68.5 Canada 57.3 1.2 — 58.5 New Zealand 30.3 4.0 — 34.3 Other foreign 38.2 — — 38.2 Total revenues $ 1,381.9 $ 236.4 $ 372.3 $ 1,990.6 Revenues by geographical location and segment for the three-month period ended March 31, 2018 are as follows (in millions): Brokerage Risk Management Corporate Total Revenues: United States $ 852.8 $ 192.7 $ 412.2 $ 1,457.7 United Kingdom 191.0 9.0 — 200.0 Australia 43.6 23.7 — 67.3 Canada 42.8 1.0 — 43.8 New Zealand 30.1 3.5 — 33.6 Other foreign 35.3 — — 35.3 Total revenues $ 1,195.6 $ 229.9 $ 412.2 $ 1,837.7

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019CountrySegment
Significant Accounting Policies [Line Items]
Number of reportable operating segments | Segment	3
Number of commercial clean coal production facilities	34
Number of countries in which the company has operations	35
Number of countries in which the company does business through a network of correspondent brokers and consultants	150

Effect of New Accounting Pron_2

Effect of New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Corporate income tax rate	21.00%	21.00%	35.00%
Operating lease right of use assets	$ 368.8			$ 379.6
Operating lease liabilities	410.7			420.3
Net rent related asset and liabilities				38.3
Cumulative effect of adoption of new accounting standards				2.4
Reclassification from accumulated other comprehensive income, current period, before tax	0.2
Accumulated Other Comprehensive Earnings (Loss) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting standards	$ (0.2)			$ (0.2)
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings		$ 6.6

Business Combinations - Acquisi

Business Combinations - Acquisition Method for Recording Business Combinations (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)shares
Business Acquisition [Line Items]
Common Shares Issued | shares	452
Common Share Value	$ 35,900,000
Cash Paid	176,800,000
Accrued Liability	100,000
Escrow Deposited	19,200,000
Recorded Earnout Payable	35,800,000
Total Recorded Purchase Price	267,800,000
Maximum Potential Earnout Payable	$ 81,100,000
Inverson Holding Company - Company, LLC (IHC) [Member]
Business Acquisition [Line Items]
Common Shares Issued | shares	452
Common Share Value	$ 35,900,000
Cash Paid	31,200,000
Escrow Deposited	4,500,000
Recorded Earnout Payable	20,900,000
Total Recorded Purchase Price	92,500,000
Maximum Potential Earnout Payable	35,000,000
James Brown Inc. (JBI) [Member]
Business Acquisition [Line Items]
Cash Paid	65,900,000
Escrow Deposited	8,700,000
Total Recorded Purchase Price	74,600,000
Nine Other Acquisition [Member]
Business Acquisition [Line Items]
Cash Paid	79,700,000
Accrued Liability	100,000
Escrow Deposited	6,000,000
Recorded Earnout Payable	14,900,000
Total Recorded Purchase Price	100,700,000
Maximum Potential Earnout Payable	$ 46,100,000

Business Combinations - Acqui_2

Business Combinations - Acquisition Method for Recording Business Combinations (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2019
Inverson Holding Company - Company, LLC (IHC) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 1, 2019
James Brown Inc. (JBI) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 1, 2019
Nine Other Acquisition [Member]
Business Acquisition [Line Items]
Effective Year of Acquisition	2019

Business Combinations - Additio

Business Combinations - Additional Information (Detail) £ in Millions	Mar. 03, 2019GBP (£)	Dec. 22, 2018USD ($)	Mar. 31, 2019USD ($)Entity	Mar. 31, 2018USD ($)Entity	Mar. 31, 2019USD ($)Entity
Business Acquisition [Line Items]
Accretion of the discount on acquisition			$ 5,600,000	$ 5,100,000
Number of companies acquired | Entity			33	39	518
Aggregate amount of maximum earnout obligations related to acquisitions			$ 618,900,000
Expense related to net adjustments to estimated fair value of liability for earnout obligations			2,700,000	$ 2,300,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet			293,600,000
Goodwill			131,500,000		$ 131,500,000
Expiration lists			130,600,000		130,600,000
Non-compete agreements			2,100,000		2,100,000
Total revenues related to acquisitions in the aggregate			1,993,000,000	$ 1,855,900,000
Brokerage and Risk Management [Member]
Business Acquisition [Line Items]
Goodwill			131,500,000		131,500,000
Expiration lists			130,600,000		130,600,000
Non-compete agreements			$ 2,100,000		$ 2,100,000
Minimum [Member] | Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 years
Minimum [Member] | Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			3 years
Minimum [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			2 years
Maximum [Member] | Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			15 years
Maximum [Member] | Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			5 years
Maximum [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years			15 years
2018 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input			3		3
2018 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input			4.4		4.4
2018 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input			11.5		11.5
2018 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input			14		14
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Minimum [Member]
Business Acquisition [Line Items]
Attrition rate			3.50%
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Maximum [Member]
Business Acquisition [Line Items]
Attrition rate			11.00%
Business Acquisition [Member]
Business Acquisition [Line Items]
Annualized revenue of business acquisitions			$ 71,200,000
Total revenues related to acquisitions in the aggregate			18,800,000
Net earnings			2,100,000
Business Acquisition [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Expiration lists			130,600,000		$ 130,600,000
Non-compete agreements			2,100,000		2,100,000
Deferred tax liability			5,800,000		5,800,000
Business Acquisition [Member] | Expiration Lists [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes			22,700,000		22,700,000
Business Acquisition [Member] | Non-Compete Agreements [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes			$ 800,000		$ 800,000
Stackhouse Poland Group Limited [Member] | United Kingdom, Pounds | Definitive Agreement [Member]
Business Acquisition [Line Items]
Cash consideration		$ 350,000,000
Percentage of interest acquired in acquired entity		100.00%
Jardine Lloyd Thompson Group plc (JLT) [Member] | Definitive Agreement [Member]
Business Acquisition [Line Items]
Cash consideration | £	£ 130
Business Combination, Contingent Consideration, Liability | £	£ 60
2019 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input			5		5
2019 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input			17.5		17.5
2019 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Discount Rate [Member]
Business Acquisition [Line Items]
Measurement input			8		8

Business Combinations - Summary

Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) $ in Millions	Mar. 31, 2019USD ($)
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	$ 3.7
Other current assets	40.6
Fixed assets	1.9
Noncurrent assets	5.5
Goodwill	131.5
Expiration lists	130.6
Non-compete agreements	2.1
Total assets acquired	315.9
Current liabilities	43.5
Total liabilities assumed	48.1
Total net assets acquired	267.8
Inverson Holding Company - Company, LLC (IHC) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Other current assets	3.8
Fixed assets	0.3
Noncurrent assets	0.5
Goodwill	41.8
Expiration lists	50.6
Non-compete agreements	1.1
Total assets acquired	98.1
Current liabilities	5.1
Total liabilities assumed	5.6
Total net assets acquired	92.5
James Brown Inc. (JBI) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	2.7
Other current assets	22.2
Fixed assets	1.1
Noncurrent assets	2.9
Goodwill	51.2
Expiration lists	22.7
Non-compete agreements	0.8
Total assets acquired	103.6
Current liabilities	26.1
Total liabilities assumed	29
Total net assets acquired	74.6
Nine Other Acquisition [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	1
Other current assets	14.6
Fixed assets	0.5
Noncurrent assets	2.1
Goodwill	38.5
Expiration lists	57.3
Non-compete agreements	0.2
Total assets acquired	114.2
Current liabilities	12.3
Total liabilities assumed	13.5
Total net assets acquired	$ 100.7

Business Combinations - Summa_2

Business Combinations - Summary of Unaudited Pro Forma Historical Results (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Business Combinations [Abstract]
Total revenues	$ 1,993	$ 1,855.9
Net earnings attributable to controlling interests	$ 334.3	$ 275.6
Basic net earnings per share	$ 1.81	$ 1.51
Diluted net earnings per share	$ 1.77	$ 1.49

Contracts with Customers - Summ

Contracts with Customers - Summary of Unbilled Receivables, Contract Assets and Contract Liabilities from Contracts with Customers (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Contract with Customer, Asset and Liability [Abstract]
Unbilled receivables	$ 767.7	$ 496.2
Deferred contract costs	55.1	91.6
Deferred revenue	$ 480.1	$ 457.7

Contracts with Customers - Su_2

Contracts with Customers - Summary of Changes in Deferred Revenue Balances (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	$ 457.7
Incremental deferred revenue	204.5
Revenue recognized during the three-month period ended March 31, 2019 included in deferred revenue at December 31, 2018	(181.7)
Deferred revenue recognized from business acquisitions	(0.4)
Deferred revenue ending balance	480.1
Brokerage [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	284.7
Incremental deferred revenue	162.8
Revenue recognized during the three-month period ended March 31, 2019 included in deferred revenue at December 31, 2018	(137.6)
Deferred revenue recognized from business acquisitions	(0.4)
Deferred revenue ending balance	309.5
Risk Management [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	173
Incremental deferred revenue	41.7
Revenue recognized during the three-month period ended March 31, 2019 included in deferred revenue at December 31, 2018	(44.1)
Deferred revenue ending balance	$ 170.6

Contracts with Customers - Addi

Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 480.1
Deferred contract costs	55.1	$ 91.6
Amortization of deferred contract costs	$ 113.4		$ 100.4

Contracts with Customers - Su_3

Contracts with Customers - Summary of Expected Revenue Related to Performance Obligations (Detail) $ in Millions	Mar. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 480.1
2019 (remaining nine months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	332.7
2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	69.2
2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	37.7
2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	14.2
2023 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	6.7
Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	19.6
Brokerage [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	309.5
Brokerage [Member] | 2019 (remaining nine months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	252
Brokerage [Member] | 2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	32.9
Brokerage [Member] | 2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	19.7
Brokerage [Member] | 2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	3.8
Brokerage [Member] | 2023 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	0.6
Brokerage [Member] | Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	0.5
Risk Management [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	170.6
Risk Management [Member] | 2019 (remaining nine months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	80.7
Risk Management [Member] | 2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	36.3
Risk Management [Member] | 2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	18
Risk Management [Member] | 2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	10.4
Risk Management [Member] | 2023 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	6.1
Risk Management [Member] | Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 19.1

Other Financial Data - (Other C

Other Financial Data - (Other Current Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Premium finance advances and loans	$ 305.1	$ 316.2
Accrued supplemental, direct bill and other receivables	306.3	348.2
Refined coal production related receivables	114	160.2
Deferred contract costs	55.1	91.6
Prepaid expenses	95	108.2
Total other current assets	$ 875.5	$ 1,024.4

Other Financial Data - (Other_2

Other Financial Data - (Other Current Assets) (Additional Information) (Details)	3 Months Ended
	Mar. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Collateralized delinquency period of receivables	7 days

Intangible Assets - Carrying Am

Intangible Assets - Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Total goodwill	$ 4,800.9	$ 4,625.6
Unites States [Member]
Goodwill [Line Items]
Total goodwill	2,824.1	2,744.9
United Kingdom [Member]
Goodwill [Line Items]
Total goodwill	793.8	762.9
Canada [Member]
Goodwill [Line Items]
Total goodwill	437.4	378.6
Australia [Member]
Goodwill [Line Items]
Total goodwill	409.5	406.6
New Zealand [Member]
Goodwill [Line Items]
Total goodwill	223.6	219.8
Other Foreign [Member]
Goodwill [Line Items]
Total goodwill	112.5	112.8
Brokerage [Member]
Goodwill [Line Items]
Total goodwill	4,748.4	4,573.6
Brokerage [Member] | Unites States [Member]
Goodwill [Line Items]
Total goodwill	2,794.5	2,715.3
Brokerage [Member] | United Kingdom [Member]
Goodwill [Line Items]
Total goodwill	784.2	753.7
Brokerage [Member] | Canada [Member]
Goodwill [Line Items]
Total goodwill	437.4	378.6
Brokerage [Member] | Australia [Member]
Goodwill [Line Items]
Total goodwill	409.2	406.3
Brokerage [Member] | New Zealand [Member]
Goodwill [Line Items]
Total goodwill	213.3	209.6
Brokerage [Member] | Other Foreign [Member]
Goodwill [Line Items]
Total goodwill	109.8	110.1
Risk Management [Member]
Goodwill [Line Items]
Total goodwill	49.8	49.3
Risk Management [Member] | Unites States [Member]
Goodwill [Line Items]
Total goodwill	29.6	29.6
Risk Management [Member] | United Kingdom [Member]
Goodwill [Line Items]
Total goodwill	9.6	9.2
Risk Management [Member] | Australia [Member]
Goodwill [Line Items]
Total goodwill	0.3	0.3
Risk Management [Member] | New Zealand [Member]
Goodwill [Line Items]
Total goodwill	10.3	10.2
Corporate [Member]
Goodwill [Line Items]
Total goodwill	2.7	2.7
Corporate [Member] | Other Foreign [Member]
Goodwill [Line Items]
Total goodwill	$ 2.7	$ 2.7

Intangible Assets - Changes in

Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Goodwill [Line Items]
Beginning Balance	$ 4,625.6
Goodwill acquired during the period	131.5
Goodwill adjustments due to appraisals and other acquisition adjustments	8.4
Goodwill written-off related to sales of business	(6.6)
Foreign currency translation adjustments during the period	42
Ending Balance	4,800.9
Brokerage [Member]
Goodwill [Line Items]
Beginning Balance	4,573.6
Goodwill acquired during the period	131.5
Goodwill adjustments due to appraisals and other acquisition adjustments	8.4
Goodwill written-off related to sales of business	(6.6)
Foreign currency translation adjustments during the period	41.5
Ending Balance	4,748.4
Risk Management [Member]
Goodwill [Line Items]
Beginning Balance	49.3
Foreign currency translation adjustments during the period	0.5
Ending Balance	49.8
Corporate [Member]
Goodwill [Line Items]
Beginning Balance	2.7
Ending Balance	$ 2.7

Intangible Assets - Major Class

Intangible Assets - Major Classes of Amortizable Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net	$ 1,841.4	$ 1,773
Expiration Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	3,529.6	3,379.4
Accumulated amortization	(1,758.8)	(1,676.8)
Amortizable intangible assets, net	1,770.8	1,702.6
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	60.7	58
Accumulated amortization	(49.8)	(48.5)
Amortizable intangible assets, net	10.9	9.5
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	86.4	86
Accumulated amortization	(26.7)	(25.1)
Amortizable intangible assets, net	$ 59.7	$ 60.9

Intangible Assets - Estimated A

Intangible Assets - Estimated Aggregate Amortization Expense (Detail) $ in Millions	Mar. 31, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2019 (remaining nine months)	$ 226.3
2020	286.7
2021	262.8
2022	237.5
2023	213.5
Thereafter	614.6
Total	$ 1,841.4

Credit and Other Debt Agreeme_3

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 4,192.8	$ 3,617
Less unamortized debt acquisition costs on Note Purchase Agreements	(7.7)	(6.6)
Semi-annual payments of interest, Net	4,185.1	3,610.4
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	3,798	3,198
Fixed Rate of 3.20%, Balloon Due June 24, 2019 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 5.85%, balloon Due November 30, 2019 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Quarterly payments of interest	50	50
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	325	325
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Quarterly payments of interest	50	50
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	140
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175	175
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175	175
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	150	150
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	98	98
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.44% Balloon Due June 13, 2030 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	180
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	25	25
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.59%, Balloon due June 13, 2033 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	40
Fixed Rate of 4.69% Balloon Due June 13, 2038 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	40
Prime or LIBOR Plus up to 1.45%, Expires April 8, 2021 [Member] | Multi Currency Credit Agreement [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	260	265
Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | AUD Denominated Tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	106.5	133.9
Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | NZD Denominated Tranche [Member] | Facility B [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	2.7	10.1
Interbank Rates Plus 0.55%, Expires May 18 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	134.8	154
Interbank Rates Plus 0.55%, Expires May 18 2020 [Member] | AUD Denominated Tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	15.4
Interbank Rates Plus 0.55%, Expires May 18 2020 [Member] | NZD Denominated Tranche [Member] | Facility C and D [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 10.2	$ 10

Credit and Other Debt Agreeme_4

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 3.20%, Balloon Due June 24, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.20%	3.20%
Periodic payments of interest and principal, expiry date	2019	2019
Fixed Rate of 5.85%, balloon Due November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.85%	5.85%
Periodic payments of interest and principal, expiry date	2019	2019
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.48%	3.48%
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.99%	3.99%
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.18%	5.18%
Periodic payments of interest and principal, expiry date	2021	2021
Prime or LIBOR Plus up to 1.45%, Expires April 8, 2021 [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.45%	1.45%
Periodic payments of interest and principal, expiry date	2021	2021
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.69%	3.69%
Periodic payments of interest and principal, expiry date	2022	2022
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.49%	5.49%
Periodic payments of interest and principal, expiry date	2023	2023
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.13%	4.13%
Periodic payments of interest and principal, expiry date	2023	2023
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.65%	1.65%
Periodic payments of interest and principal, expiry date	2023	2023
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.72%	4.72%
Periodic payments of interest and principal, expiry date	2024	2024
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.58%	4.58%
Periodic payments of interest and principal, expiry date	2024	2024
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.40%	1.40%
Periodic payments of interest and principal, expiry date	2024	2024
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.31%	4.31%
Periodic payments of interest and principal, expiry date	2025	2025
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.85%	4.85%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.73%	4.73%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.40%	4.40%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.36%	4.36%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.14%	4.14%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.46%	3.46%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.55%	4.55%
Periodic payments of interest and principal, expiry date	2028	2028
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2028	2028
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.04%	5.04%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.98%	4.98%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.44% Balloon Due June 13, 2030 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.44%	4.44%
Periodic payments of interest and principal, expiry date	2030	2030
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.14%	5.14%
Periodic payments of interest and principal, expiry date	2031	2031
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.70%	4.70%
Periodic payments of interest and principal, expiry date	2031	2031
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2032	2032
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2032	2032
Fixed Rate of 4.59% Balloon Due June 13, 2033 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.59%	4.59%
Periodic payments of interest and principal, expiry date	2033	2033
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.29%	5.29%
Periodic payments of interest and principal, expiry date	2034	2034
Fixed Rate of 4.69% Balloon Due June 13, 2038 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.69%	4.69%
Periodic payments of interest and principal, expiry date	2038	2038
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.45%	5.45%
Periodic payments of interest and principal, expiry date	2039	2039
Facility B [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.05%	1.05%
Facility C and D [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	0.55%	0.55%

Earnings Per Share - Computatio

Earnings Per Share - Computation of Basic and Diluted Net EPS (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net earnings attributable to controlling interests	$ 334.1	$ 273.7
Weighted average number of common shares outstanding	184.5	181.5
Dilutive effect of stock options using the treasury stock method	3.9	3.5
Weighted average number of common and common equivalent shares outstanding	188.4	185
Basic net earnings per share	$ 1.81	$ 1.51
Diluted net earnings per share	$ 1.77	$ 1.48

Earnings Per Share - Additional

Earnings Per Share - Additional information (Detail) - shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Anti-dilutive stock-based awards shares outstanding	1.4	0.2

Stock Option Plans - Additional

Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 14, 2019	Mar. 15, 2018	Mar. 31, 2019	Mar. 31, 2018
Stock Option Plans [Line Items]
Maximum number of shares available			399,900	420,200
Compensation expense related to stock option grants			$ 3.6	$ 4.8
Total intrinsic value of options exercised			27.6	$ 29.3
Total unrecognized compensation cost related to nonvested options			$ 40.5
Weighted average period, years			4 years
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum number of shares available			2,800,000
Shares available for grant			13,000,000
2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Number of years options expire from date of grant			7 years
Officer and Key Employees [Member] | 2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Shares available for grant	1,283,300	1,261,000
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%	33.00%
Maximum [Member] | Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum period for the exercise of stock options, years			7 years	7 years
Minimum [Member] | Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant			100.00%
Minimum [Member] | 2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture			2 years	2 years
Minimum [Member] | Executive Officer [Member] | 2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance			55 years	55 years
Black-Scholes Option Pricing Model [Member]
Stock Option Plans [Line Items]
Weighted average fair value per option for all options			$ 10.71	$ 9.27

Stock Option Plans - Black-Scho

Stock Option Plans - Black-Scholes Option Pricing Model with Weighted Average (Detail)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	1.70%	2.30%
Expected risk-free interest rate	2.50%	2.70%
Volatility	15.60%	15.10%
Expected life (in years)	5 years 6 months	5 years 6 months

Stock Option Plans - Stock Opti

Stock Option Plans - Stock Option Activity and Related Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Under Option, Beginning balance | shares	8.8
Shares Under Option, Granted | shares	1.3
Shares Under Option, Exercised | shares	(0.7)
Shares Under Option, Forfeited or canceled | shares	(0.1)
Shares Under Option, Ending balance | shares	9.3
Shares Under Option, Exercisable at end of year | shares	3.2
Shares Under Option, Ending unvested and expected to vest | shares	5.8
Weighted Average Exercise Price, Beginning balance | $ / shares	$ 50.16
Weighted Average Exercise Price, Granted | $ / shares	79.59
Weighted Average Exercise Price, Exercised | $ / shares	41.11
Weighted Average Exercise Price, Forfeited or canceled | $ / shares	51.52
Weighted Average Exercise Price, Ending balance | $ / shares	54.92
Weighted Average Exercise Price, Exercisable at end of year | $ / shares	44.68
Weighted Average Exercise Price, Ending unvested and expected to vest | $ / shares	$ 59.61
Weighted Average Remaining Contractual Term (in years), Ending balance	4 years 2 months 26 days
Weighted Average Remaining Contractual Term (in years), Exercisable at end of year	2 years 5 months 19 days
Weighted Average Remaining Contractual Term (in years), Ending unvested and expected to vest	5 years 1 month 6 days
Aggregate Intrinsic Value, Ending Balance | $	$ 217.2
Aggregate Intrinsic Value, Exercisable at end of year | $	106.2
Aggregate Intrinsic Value, Ending unvested and expected to vest | $	$ 108.6

Stock Option Plans - Stock Op_2

Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	$ 39.17
Range of Exercise Prices, maximum	$ 79.59
Option Outstanding, Number Outstanding	9.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 2 months 26 days
Option Outstanding, Weighted Average Exercise Price	$ 54.92	$ 50.16
Options Exercisable, Number Exercisable	3.2
Option Exercisable, Weighted Average Exercise Price	$ 44.68
Exercise Prices Range $ 39.17 - $ 39.17 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	39.17
Range of Exercise Prices, maximum	$ 39.17
Option Outstanding, Number Outstanding	0.6
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	11 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 39.17
Options Exercisable, Number Exercisable	0.6
Option Exercisable, Weighted Average Exercise Price	$ 39.17
Exercise Prices Range $ 43.71 - $ 43.71 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	43.71
Range of Exercise Prices, maximum	$ 43.71
Option Outstanding, Number Outstanding	2.2
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	3 years 11 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 43.71
Options Exercisable, Number Exercisable	0.7
Option Exercisable, Weighted Average Exercise Price	$ 43.71
Exercise Prices Range $ 46.17 - $ 46.87 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	46.17
Range of Exercise Prices, maximum	$ 46.87
Option Outstanding, Number Outstanding	2.5
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	2 years 6 months 3 days
Option Outstanding, Weighted Average Exercise Price	$ 46.47
Options Exercisable, Number Exercisable	1.9
Option Exercisable, Weighted Average Exercise Price	$ 46.56
Exercise Prices Range $ 47.92 - $ 63.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	47.92
Range of Exercise Prices, maximum	$ 63.60
Option Outstanding, Number Outstanding	1.5
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 11 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 56.81
Exercise Prices Range $ 70.74 - $ 70.74 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	70.74
Range of Exercise Prices, maximum	$ 70.74
Option Outstanding, Number Outstanding	1.2
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	5 years 11 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 70.74
Exercise Prices Range $ 79.59 - $ 79.59 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	79.59
Range of Exercise Prices, maximum	$ 79.59
Option Outstanding, Number Outstanding	1.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 11 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 79.59

Deferred Compensation - Additio

Deferred Compensation - Additional information (Detail) - USD ($) shares in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
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.
Deferred Equity Participation Sub-plans, distributions to key executives, age	Age 65
Deferred Equity Participation Sub-plans, distributions requisite service description	we annually make awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after the earlier of fifteen years or the participant reaching age 65.
Deferred Equity Participation Plan (DEPP) [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	$ 10,100,000	$ 11,500,000
Charge to compensation expenses related to awards	2,000,000	1,900,000
Cash and equity awards with aggregate fair value vested and distributed to participants	0
Unearned deferred compensation, value	$ 69,000,000		$ 57,600,000
Unearned deferred compensation, shares	2.9		2.7
Total intrinsic value of unvested equity based awards	$ 224,000,000		$ 199,800,000
Deferred Cash Participation Plan (DCPP) [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	2,400,000	5,600,000
Charge to compensation expenses related to awards	1,100,000	800,000
Cash and equity awards with aggregate fair value vested and distributed to participants	800,000
Deferred Equity Participation Plan Sub Plans [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	2,600,000	900,000
Charge to compensation expenses related to awards	500,000	$ 500,000
Cash and equity awards with aggregate fair value vested and distributed to participants	$ 0

Restricted Stock, Performance_2

Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail)	Mar. 14, 2019USD ($)shares	Mar. 15, 2018USD ($)shares	Mar. 31, 2019USD ($)Timesshares	Mar. 31, 2018USD ($)shares	Mar. 31, 2017shares	Mar. 31, 2016	Dec. 31, 2018shares	Mar. 16, 2017USD ($)shares	Mar. 17, 2016USD ($)shares
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Share-based compensation, shares outstanding | shares			9,300,000				8,800,000
Shares granted in the period | shares			399,900	420,200
Long Term Incentive Plan [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Share-based compensation, shares outstanding, Value			$ 4,000,000
Share-based compensation, shares outstanding | shares			2,800,000
Shares granted in the period | shares			2,800,000
Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Shares granted in the period | shares			399,900	420,200
Fair value of grants in period			$ 31,800,000	$ 28,700,000
Share based payment award vesting date			Mar. 14, 2024	Mar. 15, 2023
Restricted stock or unit expense			$ 6,400,000	$ 6,500,000
Unvested Restricted Stock [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Total intrinsic value			142,200,000	121,900,000
Equity awards with an aggregate fair value				21,200,000
Performance Shares [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Equity awards with an aggregate fair value			$ 5,700,000	3,700,000
Shares authorized | shares	73,600	78,200
Performance unit awards approved, Fair value	$ 5,800,000	$ 5,300,000
Provisional awards, terms			Granted units for the 2019 and 2018 provisional awards will fully vest based on continuous employment through March 14, 2022 and March 15, 2021, respectively, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable thereafter.
Performance awards period, years			1 year
Vesting period, years			2 years
2019 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date			Jan. 1, 2022
Cash-based compensation awards, expenses			$ 1,900,000
2017 Performance Share Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional awards, terms			The 2019 and 2018 awards are subject to a three-year performance period that begins on January 1, 2019 and 2018, respectively, and vest on the three-year anniversary of the date of grant (March 14, 2022 and March 15, 2021).
Performance awards period, years			3 days
Vesting period, years			3 years
Performance awards expiration date			Mar. 14, 2022
2017 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date			Jan. 1, 2020
Cash-based compensation awards, expenses			$ 2,400,000	2,000,000
2016 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date					Jan. 1, 2019
Provisional compensation cash award approved for future grant by compensation committee, units | shares			341,000
Cash-based compensation awards, expenses			$ 22,400,000	$ 4,200,000
2015 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date						Jan. 1, 2019
Provisional compensation cash award approved for future grant by compensation committee, units | shares				269,000
Cash-based compensation awards, expenses				$ 15,800,000
Minimum [Member] | Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture			2 years
Officer and Key Employees [Member] | Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional awards, terms			The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2021, 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.
Performance awards period, years			1 year
Vesting period, years			3 years
Provisional compensation cash awards approved for future grant by compensation committee, value	$ 16,500,000	$ 15,000,000						$ 14,300,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares	206,800	219,000	190,000	242,000				255,000
Ultimate award value, multiples of original value of the units, minimum | Times			0.5
Ultimate award value, multiples of original value of the units, maximum | Times			1.5
Officer and Key Employees [Member] | 2016 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Provisional compensation cash awards approved for future grant by compensation committee, value									$ 17,400,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares					383,000				397,000
Executive Officer [Member] | Minimum [Member] | Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance			55 years	55 years

Investments - Investments Repor

Investments - Investments Reported in Other Current and Non-Current Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Assets	$ 54.9	$ 59.5
Chem-Mod LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	4	4
Chem-Mod International LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	2	2
Clean-Coal Investments [Member] | Controlling Interest [Member] | Fourteen 2009 Era Clean Coal Plants [Member]
Schedule of Equity Method Investments [Line Items]
Assets	3.8	5.1
Clean-Coal Investments [Member] | Controlling Interest [Member] | Nineteen 2011 Era Clean Coal Plants [Member]
Schedule of Equity Method Investments [Line Items]
Assets	39.8	43
Clean-Coal Investments [Member] | Noncontrolling Interests [Member] | One 2011 Era Clean Coal Plant [Member]
Schedule of Equity Method Investments [Line Items]
Assets	0.4	0.4
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 4.9	$ 5

Leases - Additional Information

Leases - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Operating Lease, Weighted Average Remaining Lease Term	5 years 8 months 12 days
Lessee, Operating Lease, Option to Extend	5.0 years
Operating Lease Liability Not Yet Commenced	$ 0.8
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	6 years 4 months 24 days
Maximum [Member]
Operating Lease, Weighted Average Remaining Lease Term	13 years 8 months 12 days
Minimum [Member]
Operating Lease, Weighted Average Remaining Lease Term	2 months 12 days

Leases - (Components of Lease E

Leases - (Components of Lease Expense) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Net lease expense	$ 33.7
Operating
Operating lease expense	29.5
Variable lease expense	4.5
Investment Income
Sublease income	$ (0.3)

Leases - (Supplemental Cash Flo

Leases - (Supplemental Cash Flow Information Related to Leases) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 28.5
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 1.6

Leases - (Supplemental balance

Leases - (Supplemental balance sheet information related to leases) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
Lease right-of-use assets	$ 368.8	$ 379.6
Other current lease liabilities	80.8
Lease liabilities	329.9
Total	$ 410.7	$ 420.3
Weighted-average remaining lease term, years	5 years 8 months 12 days
Weighted-average discount rate	3.70%

Leases - (Maturities of operati

Leases - (Maturities of operating lease liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
2019 (remaining nine months)	$ 79.7
2020	93
2021	79.4
2022	61.6
2023	48.3
Thereafter	94.2
Total lease payments	456.2
Less interest	(45.5)
Total	$ 410.7	$ 420.3

Derivatives and Hedging Activ_3

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Detail) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional Amount		$ 791,200,000	$ 901,400,000
Derivatives Assets		5,800,000	9,600,000
Derivative Liabilities		36,500,000	25,800,000
Other noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives Assets		4,200,000	5,700,000
Other noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities		4,000,000	7,900,000
Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		750,000,000	850,000,000
Interest Rate Contracts [Member] | Other current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives Assets		600,000	3,000,000
Interest Rate Contracts [Member] | Accrued compensation and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities		29,800,000	13,000,000
Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	41,200,000	51,400,000
Foreign Exchange Contracts [Member] | Other current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives Assets	[1]	1,000,000	900,000
Foreign Exchange Contracts [Member] | Accrued compensation and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	[1]	$ 2,700,000	$ 4,900,000
[1]	Included within foreign exchange contracts at March 31, 2019 were $248.8 million of call options offset with $248.8 million of put options, and $26.9 million of buy forwards offset with $68.1 million of sell forwards. Included within foreign exchange contracts at December 31, 2018 were $276.4 million of call options offset with $276.4 million of put options, and $23.1 million of buy forwards offset with $72.9 million of sell forwards.

Derivatives and Hedging Activ_4

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Parenthetical) (Detail) - Foreign Exchange Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	$ 248.8	$ 276.4
Put Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	248.8	276.4
Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	26.9	23.1
Forward Contracts [Member] | Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	$ 68.1	$ 72.9

Derivatives and Hedging Activ_5

Derivatives and Hedging Activity - Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Earnings	[1]	$ (17.2)	$ 8.5
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings		(0.7)	1.8
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		0.4
Commission revenue [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Earnings	[1]	3.7	4.3
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings		(0.1)	0.7
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		(0.2)
Compensation expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings		(0.2)	0.5
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		0.4
Operating expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings		(0.1)	0.4
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		0.2
Interest expense [Member] | Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Earnings	[1]	(20.9)	4.2
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Earnings into Earnings		(0.3)	$ 0.2
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		$ 0
[1]	For the three-month period ended March 31, 2019, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in Other comprehensive earnings was a loss of $0.1 million.

Derivatives and Hedging Activ_6

Derivatives and Hedging Activity - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	$ 75.1	$ 64.5
Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	$ 0.1
Scenario, Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Estimated pretax loss to be reclassified from accumulated other comprehensive loss into earnings			$ 1.7

Commitments, Contingencies an_3

Commitments, Contingencies and Off-Balance Sheet Arrangements - Contractual Obligations (Detail) $ in Millions	Mar. 31, 2019USD ($)
Note Purchase Agreements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	$ 100
Contractual Obligations, Payments Due by Period, 2020	100
Contractual Obligations, Payments Due by Period, 2021	75
Contractual Obligations, Payments Due by Period, 2022	200
Contractual Obligations, Payments Due by Period, 2023	300
Contractual Obligations, Payments Due by Period, Thereafter	3,023
Contractual Obligations, Payments Due by Period, Total	3,798
Multi Currency Credit Agreement [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	260
Contractual Obligations, Payments Due by Period, Total	260
Premium Financing Debt Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	134.8
Contractual Obligations, Payments Due by Period, Total	134.8
Interest On Debt [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	126.1
Contractual Obligations, Payments Due by Period, 2020	163.1
Contractual Obligations, Payments Due by Period, 2021	157.9
Contractual Obligations, Payments Due by Period, 2022	152.6
Contractual Obligations, Payments Due by Period, 2023	142.9
Contractual Obligations, Payments Due by Period, Thereafter	616.6
Contractual Obligations, Payments Due by Period, Total	1,359.2
Total Debt Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	620.9
Contractual Obligations, Payments Due by Period, 2020	263.1
Contractual Obligations, Payments Due by Period, 2021	232.9
Contractual Obligations, Payments Due by Period, 2022	352.6
Contractual Obligations, Payments Due by Period, 2023	442.9
Contractual Obligations, Payments Due by Period, Thereafter	3,639.6
Contractual Obligations, Payments Due by Period, Total	5,552
Operating Lease Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	79.7
Contractual Obligations, Payments Due by Period, 2020	93
Contractual Obligations, Payments Due by Period, 2021	79.4
Contractual Obligations, Payments Due by Period, 2022	61.6
Contractual Obligations, Payments Due by Period, 2023	48.3
Contractual Obligations, Payments Due by Period, Thereafter	94.2
Contractual Obligations, Payments Due by Period, Total	456.2
Less Sublease Arrangements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	(0.9)
Contractual Obligations, Payments Due by Period, 2020	(0.7)
Contractual Obligations, Payments Due by Period, 2021	(0.7)
Contractual Obligations, Payments Due by Period, 2022	(0.3)
Contractual Obligations, Payments Due by Period, 2023	(0.3)
Contractual Obligations, Payments Due by Period, Thereafter	(0.9)
Contractual Obligations, Payments Due by Period, Total	(3.8)
Outstanding Purchase Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	41
Contractual Obligations, Payments Due by Period, 2020	37.9
Contractual Obligations, Payments Due by Period, 2021	29.5
Contractual Obligations, Payments Due by Period, 2022	14.2
Contractual Obligations, Payments Due by Period, 2023	7.9
Contractual Obligations, Payments Due by Period, Thereafter	23.1
Contractual Obligations, Payments Due by Period, Total	153.6
Total Contractual Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2019	740.7
Contractual Obligations, Payments Due by Period, 2020	393.3
Contractual Obligations, Payments Due by Period, 2021	341.1
Contractual Obligations, Payments Due by Period, 2022	428.1
Contractual Obligations, Payments Due by Period, 2023	498.8
Contractual Obligations, Payments Due by Period, Thereafter	3,756
Contractual Obligations, Payments Due by Period, Total	$ 6,158

Commitments, Contingencies an_4

Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail)	Dec. 22, 2018USD ($)Employee	Mar. 31, 2019USD ($)ft²EmployeesEntityLetterOfCredit	Mar. 31, 2018Entity	Mar. 31, 2019USD ($)ft²EntityLetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of square feet | ft²		360,000		360,000
Number of employees will accommodate at new facility | Employees		2,000
Number of companies acquired | Entity		33	39	518
Aggregate amount of maximum earnout obligations related to acquisitions		$ 618,900,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet		$ 293,600,000
Definitive Agreement [Member] | Stackhouse Poland Group Limited [Member] | United Kingdom, Pounds
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Cash consideration	$ 350,000,000
Number of employees will accommodate at new facility | Employee	500
Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive period		15 years
Letter of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 1,300,000		$ 1,300,000
Number of letters of credit issued | LetterOfCredit		1		1
Letter of Credit [Member] | Security Deposit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 500,000		$ 500,000
Number of letters of credit issued | LetterOfCredit		1		1
Letter of Credit [Member] | Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 10,200,000		$ 10,200,000
Liabilities recorded on self-insurance		$ 15,300,000		$ 15,300,000
Number of letters of credit issued | LetterOfCredit		2		2
Letter of Credit [Member] | Rent-A-Captive Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 6,300,000		$ 6,300,000
Number of letters of credit issued | LetterOfCredit		7		7
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		1.00%		1.00%
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		50.00%		50.00%

Commitments, Contingencies an_5

Commitments, Contingencies and Off-Balance Sheet Arrangements - Off-Balance Sheet Commitments (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2019	$ 1.5
Amount of Commitment Expiration by Period - 2020	0.2
Amount of Commitment Expiration by Period - 2021	0.2
Amount of Commitment Expiration by Period - 2022	0.2
Amount of Commitment Expiration by Period - 2023	0.2
Amount of Commitment Expiration by Period - Thereafter	17.6
Total Amounts Committed	19.9
Letters of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2019	1.3
Amount of Commitment Expiration by Period - Thereafter	17
Total Amounts Committed	18.3
Financial Guarantees [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2019	0.2
Amount of Commitment Expiration by Period - 2020	0.2
Amount of Commitment Expiration by Period - 2021	0.2
Amount of Commitment Expiration by Period - 2022	0.2
Amount of Commitment Expiration by Period - 2023	0.2
Amount of Commitment Expiration by Period - Thereafter	0.6
Total Amounts Committed	$ 1.6

Supplemental Disclosures of C_3

Supplemental Disclosures of Cash Flow Information - Cash Flow (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash and Cash Equivalents [Abstract]
Interest paid	$ 29.5	$ 28
Income taxes recovered, net	$ (1.8)
Income taxes paid, net		$ 11.6

Supplemental Disclosures of C_4

Supplemental Disclosures of Cash Flow Information - Cash Equivalents And Restricted Cash (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 871.5	$ 607.2	$ 697.9
Restricted cash	1,669.3	1,629.6	1,410.8
Total cash, cash equivalents and restricted cash	$ 2,540.8	$ 2,236.8	$ 2,108.7	$ 2,305

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Earnings (Loss) - Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (785.6)
Cumulative effect of adoption of new accounting standards		$ 2.4
Ending Balance	(721.5)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(61.2)
Net change in period	1.6
Ending Balance	(59.6)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(719)
Net change in period	74.5
Ending Balance	(644.5)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5.4)
Cumulative effect of adoption of new accounting standards	(0.2)
Net change in period	(11.8)
Ending Balance	(17.4)
Accumulated Other Comprehensive Earnings (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(785.6)
Cumulative effect of adoption of new accounting standards	(0.2)	$ (0.2)
Net change in period	64.3
Ending Balance	$ (721.5)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Earnings - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Expense related to pension liability reclassified from accumulated other comprehensive earnings	$ 1.8	$ 1.2
(Income) expense related to fair value of derivative investments reclassified from accumulated other comprehensive earnings	(0.7)	1.8
Foreign currency translation reclassified from accumulated other comprehensive earnings	$ 0	$ 0

Segment Information - Additiona

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019Segment
Segment Reporting [Abstract]
Number of reportable operating segments	3

Segment Information - Schedule

Segment Information - Schedule of Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 1,990.6	$ 1,837.7
Earnings (loss) before income taxes	321.8	242.3
Identifiable assets at March 31, 2019 and 2018	18,631.4		$ 16,334
Operating Segments [Member] | Brokerage [Member]
Segment Reporting Information [Line Items]
Total revenues	1,381.9	1,195.6
Earnings (loss) before income taxes	412.4	318.9
Identifiable assets at March 31, 2019 and 2018	15,981.8	13,784.2
Operating Segments [Member] | Risk Management [Member]
Segment Reporting Information [Line Items]
Total revenues	236.4	229.9
Earnings (loss) before income taxes	22	21.6
Identifiable assets at March 31, 2019 and 2018	806.6	735.9
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Total revenues	372.3	412.2
Earnings (loss) before income taxes	(112.6)	(98.2)
Identifiable assets at March 31, 2019 and 2018	$ 1,843	$ 1,607.4

Segment Information - Summary o

Segment Information - Summary of Revenues by Type and Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues before reimbursements	$ 1,957.5	$ 1,802.9
Total revenues	1,990.6	1,837.7
Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	1,381.9	1,195.6
Total revenues	1,381.9	1,195.6
Risk Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	203.3	195.1
Total revenues	236.4	229.9
Corporate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	372.3	412.2
Total revenues	372.3	412.2
Commissions [Member]
Segment Reporting Information [Line Items]
Total revenues	940.4	839.4
Commissions [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	940.4	839.4
Broker Fees [Member]
Segment Reporting Information [Line Items]
Total revenues	464.7	448.1
Broker Fees [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	261.8	253.2
Broker Fees [Member] | Risk Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	202.9	194.9
Supplemental Revenue Member [Member]
Segment Reporting Information [Line Items]
Total revenues	56.7	52
Supplemental Revenue Member [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	56.7	52
Contingent Revenue [Member]
Segment Reporting Information [Line Items]
Total revenues	48	34.9
Contingent Revenue [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	48	34.9
Investment income [Member]
Segment Reporting Information [Line Items]
Total revenues	18.3	13.4
Investment income [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	17.9	13.2
Investment income [Member] | Risk Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0.4	0.2
Net gains on divestitures [Member]
Segment Reporting Information [Line Items]
Total revenues	57.1	2.9
Net gains on divestitures [Member] | Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	57.1	2.9
Clean Coal Activities [Member]
Segment Reporting Information [Line Items]
Total revenues	372.3	412.2
Clean Coal Activities [Member] | Corporate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	372.3	412.2
Reimbursements [Member]
Segment Reporting Information [Line Items]
Total revenues	33.1	34.8
Reimbursements [Member] | Risk Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 33.1	$ 34.8

Segment Information - Summary_2

Segment Information - Summary of Geographical Location and Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 1,990.6	$ 1,837.7
Unites States [Member]
Segment Reporting Information [Line Items]
Total revenues	1,577.3	1,457.7
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total revenues	213.8	200
Australia [Member]
Segment Reporting Information [Line Items]
Total revenues	68.5	67.3
Canada [Member]
Segment Reporting Information [Line Items]
Total revenues	58.5	43.8
New Zealand [Member]
Segment Reporting Information [Line Items]
Total revenues	34.3	33.6
Other Foreign [Member]
Segment Reporting Information [Line Items]
Total revenues	38.2	35.3
Brokerage [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,381.9	1,195.6
Brokerage [Member] | Unites States [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,006.5	852.8
Brokerage [Member] | United Kingdom [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	203.6	191
Brokerage [Member] | Australia [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	46	43.6
Brokerage [Member] | Canada [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	57.3	42.8
Brokerage [Member] | New Zealand [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	30.3	30.1
Brokerage [Member] | Other Foreign [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	38.2	35.3
Risk Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	236.4	229.9
Risk Management [Member] | Unites States [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	198.5	192.7
Risk Management [Member] | United Kingdom [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	10.2	9
Risk Management [Member] | Australia [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	22.5	23.7
Risk Management [Member] | Canada [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1.2	1
Risk Management [Member] | New Zealand [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	4	3.5
Corporate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	372.3	412.2
Corporate [Member] | Unites States [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 372.3	$ 412.2