Arthur J. Gallagher & Co. (AJG) 10-Q 27 Jul 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2018shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	AJG
Entity Registrant Name	GALLAGHER ARTHUR J & CO
Entity Central Index Key	354,190
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	182,612,000

Consolidated Statement of Earni

Consolidated Statement of Earnings (Unaudited) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	[1]	Jun. 30, 2018	Jun. 30, 2017	[1]
Revenues before reimbursements	$ 1,625	$ 1,454.3		$ 3,427.9	$ 3,067.6
Total revenues	1,660.4	1,489.5		3,498.1	3,135.9
Compensation	724.7	666.9		1,500.5	1,378.7
Operating	222.8	204.2		438.9	403.7
Reimbursements	35.4	35.2		70.2	68.3
Interest	33.9	31.6		65.2	61.5
Depreciation	30.8	30.2		61.4	59.7
Amortization	73.4	65.1		141.6	129.4
Change in estimated acquisition earnout payables	(6)	5.1		1.4	16.9
Total expenses	1,556.8	1,435.4		3,152.2	2,882.2
Earnings before income taxes	103.6	54.1		345.9	253.7
Benefit for income taxes	(20.1)	(24.2)		(63.8)	(66.6)
Net earnings	123.7	78.3		409.7	320.3
Net earnings attributable to noncontrolling interests	8.8	8.3		21.1	21.5
Net earnings attributable to controlling interests	$ 114.9	$ 70		$ 388.6	$ 298.8
Basic net earnings per share	$ 0.63	$ 0.39		$ 2.14	$ 1.67
Diluted net earnings per share	0.62	0.39		2.10	1.65
Dividends declared per common share	$ 0.41	$ 0.39		$ 0.82	$ 0.78
Commissions [Member]
Total revenues	$ 688	$ 618.2		$ 1,527.4	$ 1,378.9
Broker Fees [Member]
Total revenues	422.2	386.9		870.3	791.9
Supplemental Revenue Member [Member]
Total revenues	48.1	35.8		100.1	83.1
Contingent Revenue [Member]
Total revenues	21.8	21.3		56.7	56.3
Investment income [Member]
Total revenues	15.8	14.4		29.2	26.7
Gains on Books of Business Sales [Member]
Total revenues	6.1	1.1		9	2.5
Clean Coal Activities [Member]
Total revenues	422.4	376.4		834.6	728.2
Cost of revenues from clean coal activities	441.8	397.1		873	764
Product and Service, Other [Member]
Total revenues	0.6	0.2		0.6
Reimbursements [Member]
Total revenues	$ 35.4	$ 35.2		$ 70.2	$ 68.3
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Earnings (Unaudited) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	[1]	Jun. 30, 2018	Jun. 30, 2017	[1]
Statement of Comprehensive Income [Abstract]
Net earnings	$ 123.7	$ 78.3		$ 409.7	$ 320.3
Change in pension liability, net of taxes	(5.5)	1.4		1.5	2.6
Foreign currency translation	(150.7)	33.5		(88.4)	89.4
Change in fair value of derivative investments, net of taxes	4.3	2.3		(2.5)	8.8
Comprehensive earnings (loss)	(28.2)	115.5		320.3	421.1
Comprehensive earnings attributable to noncontrolling interests	3.3	8.7		17.8	23.5
Comprehensive earnings (loss) attributable to controlling interests	$ (31.5)	$ 106.8		$ 302.5	$ 397.6
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	[1]
Statement of Financial Position [Abstract]
Cash and cash equivalents	$ 652.2	$ 681.2
Restricted cash	1,692.5	1,623.8
Premiums and fees receivable	5,142.2	4,082.8
Other current assets	878.1	881.6
Total current assets	8,365	7,269.4
Fixed assets - net	427.6	412.2
Deferred income taxes	716.3	851.6
Other noncurrent assets	586.7	567.1
Goodwill	4,403.9	4,164.8
Amortizable intangible assets - net	1,731	1,644.6
Total assets	16,230.5	14,909.7
Premiums payable to underwriting enterprises	5,982.7	4,986
Accrued compensation and other current liabilities	844.6	947.8
Deferred revenue - current	395.2	355.3
Premium financing debt	111.1	151.1
Corporate related borrowings - current	235	290
Total current liabilities	7,568.6	6,730.2
Corporate related borrowings - noncurrent	3,141	2,691.9
Deferred revenue - noncurrent	76.6	75.3
Other noncurrent liabilities	931.2	1,112.6
Total liabilities	11,717.4	10,610
Stockholders' equity:
Common stock - issued and outstanding 182.6 shares in 2018 and 181.0 shares in 2017	182.6	181
Capital in excess of par value	3,446.4	3,388.2
Retained earnings	1,466	1,221.8
Accumulated other comprehensive loss	(651.4)	(555.4)
Stockholders' equity attributable to controlling interests	4,443.6	4,235.6
Stockholders' equity attributable to noncontrolling interests	69.5	64.1
Total stockholders' equity	4,513.1	4,299.7
Total liabilities and stockholders' equity	$ 16,230.5	$ 14,909.7
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - shares shares in Millions	Jun. 30, 2018	Dec. 31, 2017	[1]
Statement of Financial Position [Abstract]
Common stock - issued shares	182.6	181
Common stock - outstanding shares	182.6	181
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Statement of Cash

Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	[1]
Cash flows from operating activities:
Net earnings	$ 409.7	$ 320.3
Adjustments to reconcile net earnings to net cash provided by operating activities:
Net gain on investments and other	(7.6)	(2.7)
Depreciation and amortization	203	189.1
Change in estimated acquisition earnout payables	1.4	16.9
Amortization of deferred compensation and restricted stock	21.9	16.9
Stock-based and other noncash compensation expense	6.4	8.5
Payments on acquisition earnouts in excess of original estimates	(20)	(16.9)
Effect of changes in foreign exchange rates	(1.4)	0.9
Net change in premiums and fees receivable	(1,097.3)	(1,534.4)
Net change in deferred revenue	32.4	29.7
Net change in premiums payable to underwriting enterprises	1,106.9	1,379.4
Net change in other current assets	1	33.3
Net change in accrued compensation and other current liabilities	(135.7)	(57.8)
Net change in income taxes payable	4.7	(11.6)
Net change in deferred income taxes	(146.4)	(90.5)
Net change in other noncurrent assets and liabilities	(65.7)	(20.2)
Net cash provided by operating activities	313.3	260.9
Cash flows from investing activities:
Capital expenditures	(62.7)	(65.6)
Cash paid for acquisitions, net of cash and restricted cash acquired	(395.4)	(214.1)
Net proceeds from sales of operations/books of business	12.1	2.6
Net funding of investment transactions	0.3	(6.3)
Net cash used by investing activities	(445.7)	(283.4)
Cash flows from financing activities:
Payments on acquisition earnouts	(25.1)	(25.8)
Proceeds from issuance of common stock	47.7	34.9
Repurchases of common stock	(11.3)
Payments to noncontrolling interests	(22.2)	(15.5)
Dividends paid	(150.9)	(141.6)
Net borrowings on premium financing debt facility	(34.5)	(31.3)
Borrowings on line of credit facility	1,805	2,110
Repayments on line of credit facility	(1,860)	(2,070)
Net borrowings of corporate related long-term debt	450	250
Settlements on terminated interest rate swaps	2.9	8.3
Net cash provided by financing activities	201.6	119
Effect of changes in foreign exchange rates on cash and cash equivalents and restricted cash	(29.5)	34.8
Net increase in cash, cash equivalents and restricted cash	39.7	131.3
Cash, cash equivalents and restricted cash at beginning of period	2,305	1,937.6
Cash, cash equivalents and restricted cash at end of period	2,344.7	2,068.9
Supplemental disclosures of cash flow information:
Interest paid	65.9	61.9
Income taxes paid	$ 40.5	$ 38.8
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity (Unaudited) - 6 months ended Jun. 30, 2018 - 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, as previously reported at Dec. 31, 2017	$ 4,299.7	[1]	$ 4,164.9		$ 181		$ 3,388.2		$ 1,095.9		$ (559.9)		$ 59.7
Adoption of ASC Topic 606 (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2017	134.8							$ 125.9		$ 4.5		$ 4.4
Balance, as restated at Dec. 31, 2017 at Dec. 31, 2017	4,299.7			$ 181		$ 3,388.2		1,221.8		(555.4)		64.1
Beginning Balance (in shares) at Dec. 31, 2017				181
Reclassification of the income tax effects within accumulated other comprehensive loss related to the Tax Act								6.6		(6.6)
Net earnings	409.7							388.6				21.1
Net purchase of subsidiary shares from noncontrolling interests	2.9					(1.6)						4.5
Dividends paid to noncontrolling interests	(16.9)											(16.9)
Net change in pension asset/liability, net of taxes	1.5									1.5
Foreign currency translation	(91.7)									(88.4)		(3.3)
Change in fair value of derivative instruments, net of taxes	(2.5)									(2.5)
Compensation expense related to stock option plan grants	6.4					6.4
Common stock issued in: Six purchase transactions	20.7			$ 0.3		20.4
Common stock issued in: Six purchase transactions (In shares)				0.3
Stock option plans	$ 34.6			$ 1		33.6
Stock option plans (in shares)	1			1
Employee stock purchase plan	$ 13.1			$ 0.2		12.9
Employee stock purchase plan (in shares)				0.2
Deferred compensation and restricted stock	(2.1)			$ 0.2		(2.3)
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	(151)							(151)
Ending Balance at Jun. 30, 2018	$ 4,513.1			$ 182.6		$ 3,446.4		$ 1,466		$ (651.4)		$ 69.5
Ending Balance (in shares) at Jun. 30, 2018				182.6
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Consolidated Statement of Stoc8

Consolidated Statement of Stockholders' Equity (Unaudited) (Parenthetical) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Statement of Stockholders' Equity [Abstract]
Tax effect on net change in pension asset/liability	$ 0.9
Net change in fair value of derivative instruments, tax	$ 0.7

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies Terms Used in Notes to Consolidated Financial Statements ASC ASC Topic 606 No. 2014-09, ASU FASB GAAP IRC IRS Underwriting enterprises VIE 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, not-for-profit, Chem-Mod LLC’s 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 generated from our premium financing operations and our investment portfolio, which includes our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. We are headquartered in Rolling Meadows, Illinois, have operations in 34 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, 2017, 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 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 are also required to make certain judgments and estimates that affect the disclosed and recorded amounts of revenues and expenses related to the impact of the adoption of and accounting under ASC Topic 606. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible 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. Revenue Recognition Our revenues are derived from commissions and fees as primarily specified in a written contract, or unwritten business understanding, with our clients or underwriting enterprises. We also recognize investment income over time from our invested assets and invested assets we hold on behalf of our clients or underwriting enterprises. BROKERAGE SEGMENT Our brokerage segment generates revenues by: (i) Identifying, negotiating and placing all forms of insurance or reinsurance coverage, as well as providing risk-shifting, risk-sharing and risk-mitigation consulting services, principally related to property/casualty, life, health, welfare and disability insurance. We also provide these services through, or in conjunction with, other unrelated agents and brokers, consultants and management advisors. (ii) Acting as an agent or broker for multiple underwriting enterprises by providing services such as sales, marketing, selecting, negotiating, underwriting, servicing and placing insurance coverage on their behalf. (iii) Providing consulting services related to health and welfare benefits, voluntary benefits, executive benefits, compensation, retirement planning, institutional investment and fiduciary, actuarial, compliance, private insurance exchange, human resource technology, communications and benefits administration. (iv) Providing management and administrative services to captives, pools, risk-retention groups, healthcare exchanges, small underwriting enterprises, such as accounting, claims and loss processing assistance, feasibility studies, actuarial studies, data analytics and other administrative services. The majority of our brokerage contracts and service understandings are for a period of one year or less. Commissions and fees The primary source of revenues for our brokerage services are commissions from underwriting enterprises, based on a percentage of premiums paid by our clients, or fees received from clients based on an agreed level of service usually in lieu of commissions. Commissions are fixed at the contract effective date and generally are based on a percentage of premiums for insurance coverage or employee head count for employer sponsored benefit plans. Commissions depend upon a large number of factors, including the type of risk being placed, the particular underwriting enterprise’s demand, the expected loss experience of the particular risk of coverage, and historical benchmarks surrounding the level of effort necessary for us to place and service the insurance contract. Rather than being tied to the amount of premiums, fees are most often based on an expected level of effort to provide our services. Whether we are paid a commission or a fee, the vast majority of our services are associated with the placement of an insurance (or insurance-like) contract. Accordingly, we recognize approximately 70% of our commission and fee revenues on the effective date of the underlying insurance contract. The amount of revenue we recognize is based on our costs to provide our services up and through that effective date, including an appropriate estimate of our profit margin on a portfolio basis (a practical expedient as defined in ASC Topic 606). Based on the proportion of additional services we provide in each period after the effective date of the insurance contract, including an appropriate estimate of our profit margin, we recognize approximately 20% of our commission and fee revenues in the first three months, and the remaining 10% thereafter. These periods may be different than the underlying premium payment patterns of the insurance contracts, but the vast majority of our services are fully provided within one year of the insurance contract effective date. For consulting and advisory services, we recognize our revenue in the period in which we provide the service or advice. For management and administrative services, our revenue is recognized ratably over the contract period consistent with the performance of our obligations, mostly over an annual term. Supplemental revenues Certain underwriting enterprises may pay us additional revenues for the volume of premium placed with them and for insights into our sales pipeline, our sales capabilities or our risk selection knowledge. These amounts are in excess of the commission and fee revenues discussed above, and not all business we place with underwriting enterprises is eligible for supplemental revenues. Unlike contingent revenues, discussed below, these revenues are a fixed amount or fixed percentage of premium of the underlying eligible insurance contracts. For supplemental revenue contracts based on a fixed percentage of premium, our obligation to the underwriting enterprise is substantially completed upon the effective date of the underlying insurance contract and revenue is fully earned at that time. For supplemental revenue contracts based on a fixed amount, revenue is recognized ratably over the contract period consistent with the performance of our obligations, almost always over an annual term. We receive these revenues on a quarterly or annual basis. Contingent revenues Certain underwriting enterprises may pay us additional revenues for our sales capabilities, our risk selection knowledge, or our administrative efficiencies. These amounts are in excess of the commission or fee revenues discussed above, and not all business we place with participating underwriting enterprises is eligible for contingent revenues. Unlike supplemental revenues, also discussed above, these revenues are variable, generally based on growth, the loss experience of the underlying insurance contracts, and/or our efficiency in processing the business. We generally operate under calendar year contracts, but we do not receive these revenues from the underwriting enterprises until the following calendar year, generally in the first and second quarters, after verification of the performance indicators outlined in the contracts. Accordingly, during each reporting period, we must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. We base our estimates each period on a contract-by-contract Sub-brokerage Sub-brokerage revenues. Sub-brokerage sub-brokers RISK MANAGEMENT SEGMENT Revenues for our risk management segment are comprised of fees generally negotiated (i) on a per-claim Per-claim Where we operate under a contract with our fee established on a per claim basis, our obligation is to process claims for a term specified within the contract. Because it is impractical to recognize our revenues on an individual claim by claim basis, we recognize revenue plus an appropriate estimate of our profit margin on a portfolio basis by grouping claims with similar characteristics (a practical expedient as defined in ASC Topic 606). We apply actuarially-determined, historical-based patterns to determine our future service obligations, without applying a present value discount. Cost-plus fees Where we provide services and generate revenues on a cost-plus basis, we recognize revenue over the contract period consistent with the performance of our obligations. Performance-based fees Certain clients pay us additional fee revenues for our efficiency in managing claims or on the basis of claim outcome effectiveness. These amounts are in excess of the fee revenues discussed above. These revenues are variable, generally based on performance metrics set forth in the underlying contracts. We generally operate under multi-year contracts with fiscal year measurement periods. We do not receive these fees, if earned, until the following year after verification of the performance metrics outlined in the contracts. Each period we base our estimates on a contract-by-contract Reimbursements Reimbursements represent amounts received from clients reimbursing us for certain third-party costs associated with providing our claims management services. In certain service partner relationships, we are considered a principal because we direct the third party, control the specified service and combine the services provided into an integrated solution. Given this principal relationship, we are required to recognize revenue gross and service partner vendor fees in the operating expense in our consolidated statement of earnings. Deferred Costs We incur costs to provide brokerage and risk management services. Those costs are either (i) costs to obtain a contract or (ii) costs to fulfill such contract, or (iii) all other costs. (i) Costs to obtain - we incur costs to obtain a contract with a client. Those costs would not have been incurred if the contract had not been obtained. Almost all of our costs to obtain are incurred prior to, or on, the effective date of the contract and consist primarily of incentive compensation we pay to our production employees. Our costs to obtain are expensed as incurred as described in Note 3 to these unaudited consolidated financial statements. (ii) Costs to fulfill - we incur costs to fulfill a contract (or anticipated contract) with a client. Those costs are incurred prior to the effective date of the contract and relate to fulfilling our primary placement obligations to our clients. Our costs to fulfil prior to the effective date are capitalized and amortized on the effective date. These fulfilment activities include collecting underwriting information from our client, assessing their insurance needs and negotiating their placement with one or more underwriting enterprises. The majority of costs that we incur relate to compensation and benefits of our client service employees. Costs incurred during preplacement activities are expected to be recovered in the future. If the capitalized costs are no longer deemed to be recoverable, then they would be expensed. (iii) Other costs that are not costs to obtain or fulfill are expensed as incurred. Examples include other operating costs such as rent, utilities, management costs, overhead costs, legal and other professional fees, technology costs, insurance related costs, communication and advertising, and travel and entertainment. Depreciation, amortization and change in estimated acquisition earnout payable are expensed as incurred.

Effect of New Accounting Pronou

Effect of New Accounting Pronouncements	6 Months Ended
	Jun. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Effect of New Accounting Pronouncements	2. Effect of New Accounting Pronouncements Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, Hedge Accounting In August 2017, the FASB issued ASU No. 2017-12, last-of-layer Presentation of Net Periodic Pension and Postretirement Benefit Cost In March 2017, the FASB issued ASU No. 2017-07, Form 10-K Business Combinations In January 2017, the FASB issued ASU No. 2017-01, Intangibles - Goodwill and Other In January 2017, the FASB issued ASU No. 2017-04, non-cash Leases In February 2016, the FASB issued ASU No. 2016-02, right-of-use While we are continuing to assess all potential impacts of the new guidance, we anticipate this guidance will have an impact on our consolidated financial statements. We currently believe the most significant impact relates to our real estate operating leases and the related recognition of right-of-use Income Taxes In October 2016, the FASB issued ASU No. 2016-16, In February 2018, the FASB issued ASU No. 2018-02, ASC 740-10-45-15, In March 2018, the FASB issued ASU No. 2018-05 Restricted Cash In November 2016, the FASB issued ASU No. 2016-18, 2016-18 The following is a reconciliation of our June 30 cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the six-month June 30, 2018 2017 Cash and cash equivalents $ 652.2 $ 587.8 Restricted cash 1,692.5 1,481.1 Total cash, cash equivalents and restricted cash $ 2,344.7 $ 2,068.9

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	3. Revenue from Contracts with Customers New Accounting Statement Impact on Consolidated Financial Statements As a result of adopting a new revenue recognition accounting statement, we restated our consolidated financial statements from amounts previously reported. The primary impacts of the adoption of the new revenue recognition guidance to our segments are detailed as follows. Brokerage segment Revenue - The primary reason for the increase in the amount of revenue recognized relates to our employee benefit brokerage business. Historically we recognized this revenue throughout the contract period as underlying client exposure units became certain. Under the new guidance, the full year revenue under each of these contracts is now estimated at the effective date of the underlying policies resulting in acceleration of revenue recognized, with a reassessment at each reporting date. This also causes a shift in the timing of revenue recognized in the interim periods as a majority of these annual contracts incept in the first quarter. Partially offsetting this interim impact is the recognition of contingent revenues related to our brokerage business as these revenues are now estimated and accrued throughout the year as the underlying business is placed with the underwriting enterprises rather than our historical practice of recognizing the majority of these revenues in the first quarter, because this is typically when we receive cash or the related policy detail or other carrier specific information from the underwriting enterprise. Expense - Risk management segment Revenue Expense - Corporate segment The timing related to recognition of revenue in our corporate segment remains substantially unchanged. While there is no material impact on our annual after tax earnings, there is a material change to our after tax earnings in the interim quarterly periods, as income tax credits are recognized based on our quarterly consolidated pretax earnings patterns. Impact on 2017 Consolidated Financial Statements The consolidated statement of earnings line items, which reflect the adoption of the new revenue recognition guidance, are as follows (in millions, except per share data): Three-month period ended June 30, 2017 As Previously Impact of As Restated for Commissions $ 690.2 $ (72.0 ) $ 618.2 Fees 410.9 (24.0 ) 386.9 Supplemental revenues 41.5 (5.7 ) 35.8 Contingent revenues 29.5 (8.2 ) 21.3 Investment income 13.6 0.8 14.4 Gains on books of business sales 1.1 — 1.1 Revenues from clean coal activities 376.4 — 376.4 Other net revenues 0.2 — 0.2 Revenues before reimbursements 1,563.4 (109.1 ) 1,454.3 Reimbursements — 35.2 35.2 Total revenues 1,563.4 (73.9 ) 1,489.5 Compensation 675.7 (8.8 ) 666.9 Operating 211.6 (7.4 ) 204.2 Reimbursements — 35.2 35.2 Cost of revenues from clean coal activities 397.1 — 397.1 Interest 31.6 — 31.6 Depreciation 30.2 — 30.2 Amortization 65.1 — 65.1 Change in estimated acquisition earnout payables 5.1 — 5.1 Total expenses 1,416.4 19.0 1,435.4 Earnings before income taxes 147.0 (92.9 ) 54.1 Benefit for income taxes (33.4 ) 9.2 (24.2 ) Net earnings 180.4 (102.1 ) 78.3 Net earnings attributable to noncontrolling interests 8.5 (0.2 ) 8.3 Net earnings attributable to controlling interests $ 171.9 $ (101.9 ) $ 70.0 Basic net earnings per share $ 0.96 $ (0.57 ) $ 0.39 Diluted net earnings per share 0.95 (0.56 ) 0.39 Dividends declared per common share 0.39 — 0.39 Six-month period ended June 30, 2017 As Previously Impact of As Restated for Commissions $ 1,280.7 $ 98.2 $ 1,378.9 Fees 781.4 10.5 791.9 Supplemental revenues 76.0 7.1 83.1 Contingent revenues 82.9 (26.6 ) 56.3 Investment income 24.4 2.3 26.7 Gains on books of business sales 2.5 — 2.5 Revenues from clean coal activities 728.2 — 728.2 Revenues before reimbursements 2,976.1 91.5 3,067.6 Reimbursements — 68.3 68.3 Total revenues 2,976.1 159.8 3,135.9 Compensation 1,333.3 45.4 1,378.7 Operating 412.0 (8.3 ) 403.7 Reimbursements — 68.3 68.3 Cost of revenues from clean coal activities 764.0 — 764.0 Interest 61.5 — 61.5 Depreciation 59.7 — 59.7 Amortization 129.4 — 129.4 Change in estimated acquisition earnout payables 16.9 — 16.9 Total expenses 2,776.8 105.4 2,882.2 Earnings before income taxes 199.3 54.4 253.7 Benefit for income taxes (48.9 ) (17.7 ) (66.6 ) Net earnings 248.2 72.1 320.3 Net earnings attributable to noncontrolling interests 20.6 0.9 21.5 Net earnings attributable to controlling interests $ 227.6 $ 71.2 $ 298.8 Basic net earnings per share $ 1.27 $ 0.40 $ 1.67 Diluted net earnings per share 1.26 0.39 1.65 Dividends declared per common share 0.78 — 0.78 Select consolidated statement of comprehensive earnings line items, which reflect the adoption of the new revenue recognition guidance, are as follows (in millions): Three-month period ended June 30, 2017 As Previously Impact of Adoption of As Restated for Net earnings $ 180.4 $ (102.1 ) $ 78.3 Change in pension liability, net of taxes 1.4 — 1.4 Foreign currency translation 33.9 (0.4 ) 33.5 Change in fair value of derivative instruments, net of taxes 2.3 — 2.3 Comprehensive earnings 218.0 (102.5 ) 115.5 Comprehensive earnings attributable to noncontrolling interests 8.9 (0.2 ) 8.7 Comprehensive earnings attributable to controlling interests $ 209.1 $ (102.3 ) $ 106.8 Six-month period ended June 30, 2017 As Previously Impact of As Restated for Net earnings $ 248.2 $ 72.1 $ 320.3 Change in pension liability, net of taxes 2.6 — 2.6 Foreign currency translation 92.3 (2.9 ) 89.4 Change in fair value of derivative instruments, net of taxes 8.8 — 8.8 Comprehensive earnings 351.9 69.2 421.1 Comprehensive earnings attributable to noncontrolling interests 22.6 0.9 23.5 Comprehensive earnings attributable to controlling interests $ 329.3 $ 68.3 $ 397.6 Select balance sheet line items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): December 31, 2017 As Previously Impact of As Restated for Assets Premium and fees receivables $ 2,157.2 $ 1,925.6 $ 4,082.8 Other current assets 708.4 173.2 881.6 Deferred income taxes 905.1 (53.5 ) 851.6 Other noncurrent assets 567.0 0.1 567.1 Goodwill 4,197.9 (33.1 ) 4,164.8 Liabilities Premiums payable to underwriting enterprises 3,475.9 1,510.1 4,986.0 Accrued compensation and other current liabilities 864.1 83.7 947.8 Deferred revenue - current/unearned fees 74.8 280.5 355.3 Other current liabilities 56.4 (56.4 ) — Deferred revenue - noncurrent — 75.3 75.3 Other noncurrent liabilities 1,128.3 (15.7 ) 1,112.6 Stockholders’ equity Retained earnings 1,095.9 125.9 1,221.8 Accumulated other comprehensive loss (559.9 ) 4.5 (555.4 ) Stockholders’ equity attributable to controlling interests 4,105.2 130.4 4,235.6 Stockholders’ equity attributable to noncontrolling interests 59.7 4.4 64.1 Select consolidated statement of cash flows line items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): Six-month As Previously Impact of As Restated for Cash flows from operating activities Net earnings $ 248.2 $ 72.1 $ 320.3 Adjustments to reconcile net earnings to net cash provided by operating activities: Net change in premiums and fees receivable (478.7 ) (1,055.7 ) (1,534.4 ) Net change in deferred revenue — 29.7 29.7 Net change in premiums payable to underwriting enterprises 445.1 934.3 1,379.4 Net change in other current assets (17.4 ) 50.7 33.3 Net change in accrued compensation and other current liabilities (77.0 ) 19.2 (57.8 ) Net change in deferred income taxes (72.9 ) (17.6 ) (90.5 ) Net change in other noncurrent assets and liabilities (18.4 ) (1.8 ) (20.2 ) Select statement of stockholders’ equity items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): Retained Accumulated Stockholders’ Total Balance at December 31, 2017, as reported $ 1,095.9 $ (559.9 ) $ 59.7 $ 4,164.9 Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017 125.9 4.5 4.4 134.8 Balance at December 31, 2017, as restated $ 1,221.8 $ (555.4 ) $ 64.1 $ 4,299.7 Contract Assets and Liabilities/Contract Balances Information about unbilled receivables, contract assets and contract liabilities from contracts with customers is as follows (in millions): June 30, 2018 December 31, 2017, As Restated Unbilled receivables $ 608.7 $ 415.2 Deferred contract costs 55.0 83.3 Deferred revenue 471.8 430.6 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 during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2017 $ 258.7 $ 171.9 $ 430.6 Incremental deferred revenue 204.1 73.4 277.5 Revenue recognized during the six-month (181.0 ) (68.2 ) (249.2 ) Deferred revenue recognized from business acquisitions 12.9 — 12.9 Deferred revenue at June 30, 2018 $ 294.7 $ 177.1 $ 471.8 Remaining Performance Obligations Remaining performance obligations represent the portion of the contract price for which work has not been performed. As of June 30, 2018, the aggregate amount of the contract price allocated to remaining performance obligations was $471.8 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 2018 (remaining six months) $ 224.3 $ 69.9 $ 294.2 2019 59.6 47.5 107.1 2020 8.2 19.9 28.1 2021 1.7 11.0 12.7 2022 0.4 6.8 7.2 Thereafter 0.5 22.0 22.5 Total $ 294.7 $ 177.1 $ 471.8 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 $55.0 million and $83.3 million as of June 30, 2018 and December 31, 2017, respectively. Capitalized fulfillment costs are amortized on the contract effective date. The amount of amortization of the deferred contract costs was $168.5 million and $153.4 million for the six-month As part of our adoption of the new revenue recognition guidance, we have elected to apply 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.

Business Combinations

Business Combinations	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Business Combinations	4. Business Combinations During the six-month Name and Effective Date of Acquisition Common Common Cash Paid Accrued Escrow Recorded Total Maximum (000s) Market Financial Group, Ltd and Austin Consulting Group Inc. (MFG) January 1, 2018 53 $ 3.7 $ 33.9 $ — $ 4.2 $ 4.0 $ 45.8 $ 7.0 McGregor & Associates (M&A) March 1, 2018 — — 13.5 — 2.5 5.1 21.1 12.0 Pronto Insurance (PI) June 5, 2018 — — 294.8 — 18.7 — 313.5 — Sixteen other acquisitions completed in 2018 220 12.2 82.0 0.4 9.9 21.9 126.4 52.1 273 $ 15.9 $ 424.2 $ 0.4 $ 35.3 $ 31.0 $ 506.8 $ 71.1 On June 26, 2018, we signed a definitive agreement to acquire 100% of the equity interest of Chicago, Illinois-based Reassurance Holdings, Inc., including its wholly-owned subsidiaries Coverdell & Co., Inc. and Carefree Marketing, Inc. for approximately $97.7 million of cash consideration and $24.4 million of common stock consideration, plus a maximum potential earnout of approximately $21.5 million. The transaction was subject to customary closing conditions and closed on July 6, 2018. Common shares issued in connection with acquisitions are valued at closing market prices as of the effective date of the applicable acquisition. We record escrow deposits that are returned to us as a result of adjustments to net assets acquired as reductions of goodwill when the escrows are settled. The maximum potential earnout payables disclosed in the foregoing table represent the maximum amount of additional consideration that could be paid pursuant to the terms of the purchase agreement for the applicable acquisition. The amounts recorded as earnout payables, which are primarily based upon the estimated future operating results of the acquired entities over a two- 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 3.0% to 15.0% for our 2018 acquisitions. We estimated future payments using the earnout formula and performance targets specified in each purchase agreement and these financial projections. We then discounted these payments to present value using a risk-adjusted rate that takes into consideration market-based rates of return that reflect the ability of the acquired entity to achieve the targets. These discount rates generally ranged from 8.0% to 9.5% for all of our 2018 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 June 30, 2018 and 2017, we recognized $4.9 million and $5.2 million, respectively, of expense in our consolidated statement of earnings related to the accretion of the discount recorded for earnout obligations in connection with our acquisitions. During the six-month six-month The following is a summary of the estimated fair values of the net assets acquired at the date of each acquisition made in the six-month MFG M&A PI Sixteen Total Cash $ 0.1 $ — $ 7.2 $ 5.0 $ 12.3 Other current assets 3.0 0.5 35.3 20.6 59.4 Fixed assets 0.4 1.4 2.6 0.4 4.8 Noncurrent assets — — 8.3 — 8.3 Goodwill 24.7 5.2 194.1 70.5 294.5 Expiration lists 20.2 15.1 105.7 63.0 204.0 Non-compete 0.1 0.1 0.3 1.2 1.7 Trade names — — 35.4 — 35.4 Total assets acquired 48.5 22.3 388.9 160.7 620.4 Current liabilities 2.3 0.4 31.5 19.3 53.5 Noncurrent liabilities 0.4 0.8 43.9 15.0 60.1 Total liabilities assumed 2.7 1.2 75.4 34.3 113.6 Total net assets acquired $ 45.8 $ 21.1 $ 313.5 $ 126.4 $ 506.8 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 risk management industries and increase the volume of general services currently provided. The excess of the purchase price over the estimated fair value of the tangible net assets acquired at the acquisition date was allocated to goodwill, expiration lists, non-compete 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 3.5% and 5.0% to 10.0%, respectively, for our 2017 and 2018 acquisitions 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 12.0% to 14.0% for our 2017 and 2018 acquisitions for which valuations were performed in 2018. The fair value of non-compete non-compete Expiration lists, non-compete non-compete six-month six-month Of the $204.0 million of expiration lists, $1.7 million of non-compete six-month six-month Our consolidated financial statements for the six-month Three-month period ended Six-month period ended 2018 2017 2018 2017 Total revenues $ 1,683.4 $ 1,525.8 $ 3,560.7 $ 3,211.6 Net earnings attributable to controlling interests 116.8 71.9 395.8 306.0 Basic net earnings per share 0.64 0.40 2.17 1.70 Diluted net earnings per share 0.63 0.40 2.13 1.69 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, 2017, nor are they necessarily indicative of future operating results. Annualized revenues of entities acquired during the six-month six-month six-month

Other Current Assets

Other Current Assets	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Current Assets	5. Other Current Assets Major classes of other current assets consist of the following (in millions): June 30, December 31, Premium finance advances and loans $ 302.8 $ 305.5 Accrued supplemental, direct bill and other receivables 251.9 244.5 Refined coal production related receivables 173.0 156.8 Deferred contract costs 55.0 83.3 Prepaid expenses 95.4 91.5 Total other current assets $ 878.1 $ 881.6 The premium finance loans represent short-term loans which we make to many of our brokerage related clients and other non-brokerage

Intangible Assets

Intangible Assets	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	6. Intangible Assets The carrying amount of goodwill at June 30, 2018 and December 31, 2017 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Corporate Total At June 30, 2018 United States $ 2,545.3 $ 25.1 $ — $ 2,570.4 United Kingdom 732.1 7.1 — 739.2 Canada 360.0 — — 360.0 Australia 400.7 — — 400.7 New Zealand 204.5 10.4 — 214.9 Other foreign 115.9 — 2.8 118.7 Total goodwill - net $ 4,358.5 $ 42.6 $ 2.8 $ 4,403.9 Brokerage Risk Corporate Total At December 31, 2017 United States $ 2,280.9 $ 25.8 $ — $ 2,306.7 United Kingdom 738.5 7.2 — 745.7 Canada 374.0 — — 374.0 Australia 416.6 — — 416.6 New Zealand 209.3 9.6 — 218.9 Other foreign 99.9 — 3.0 102.9 Total goodwill - net $ 4,119.2 $ 42.6 $ 3.0 $ 4,164.8 The changes in the carrying amount of goodwill for the six-month Brokerage Risk Corporate Total Balance as of December 31, 2017, as previously reported $ 4,152.3 $ 42.6 $ 3.0 $ 4,197.9 Adoption of ASC Topic 606 (33.1 ) — — (33.1 ) Balance at December 31, 2017, as restated 4,119.2 42.6 3.0 4,164.8 Goodwill acquired during the period 291.8 2.7 — 294.5 Goodwill adjustments due to appraisals and other acquisition adjustments 2.5 (2.3 ) — 0.2 Foreign currency translation adjustments during the period (55.0 ) (0.4 ) (0.2 ) (55.6 ) Balance as of June 30, 2018 $ 4,358.5 $ 42.6 $ 2.8 $ 4,403.9 Major classes of amortizable intangible assets at June 30, 2018 and December 31, 2017 consist of the following (in millions): June 30, December 31, Expiration lists $ 3,233.4 $ 3,055.9 Accumulated amortization - expiration lists (1,547.5 ) (1,422.1 ) 1,685.9 1,633.8 Non-compete 54.9 53.5 Accumulated amortization - non-compete (47.4 ) (46.1 ) 7.5 7.4 Trade names 60.6 25.9 Accumulated amortization - trade names (23.0 ) (22.5 ) 37.6 3.4 Net amortizable assets $ 1,731.0 $ 1,644.6 Estimated aggregate amortization expense for each of the next five years and thereafter is as follows: 2018 (remaining six months) $ 137.7 2019 263.9 2020 247.3 2021 224.0 2022 200.7 Thereafter 657.4 Total $ 1,731.0

Credit and Other Debt Agreement

Credit and Other Debt Agreements	6 Months Ended
	Jun. 30, 2018
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): June 30, December 31, Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 2.80%, balloon due June 24, 2018 $ — $ 50.0 Semi-annual payments of interest, fixed rate of 5.85%, $50 million due November 30, 2018 and November 30, 2019 100.0 100.0 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 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 4.58%, 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 — 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 4.73%, 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 — 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 — 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 — Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 — Total Note Purchase Agreements 3,248.0 2,798.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires April 8, 2021 135.0 190.0 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 85.0 116.4 NZD denominated tranche — 5.7 Facility C and D AUD denominated tranche 15.8 18.5 NZD denominated tranche 10.3 10.5 Total Premium Financing Debt Facility 111.1 151.1 Total corporate and other debt 3,494.1 3,139.1 Less unamortized debt acquisition costs on Note Purchase Agreements (7.0 ) (6.1 ) Net corporate and other debt $ 3,487.1 $ 3,133.0

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2018
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 Six-month period ended 2018 2017 2018 2017 Net earnings attributable to controlling interests $ 114.9 $ 70.0 $ 388.6 $ 298.8 Weighted average number of common shares outstanding 182.4 179.9 181.9 179.4 Dilutive effect of stock options using the treasury stock method 3.1 1.7 3.3 1.7 Weighted average number of common and common equivalent shares outstanding 185.5 181.6 185.2 181.1 Basic net earnings per share $ 0.63 $ 0.39 $ 2.14 $ 1.67 Diluted net earnings per share $ 0.62 $ 0.39 $ 2.10 $ 1.65 Options to purchase 1.7 million and 1.7 million shares of common stock were outstanding at June 30, 2018 and 2017, respectively, but were not included in the computation of the dilutive effect of stock options for the three-month six-month

Stock Option Plans

Stock Option Plans	6 Months Ended
	Jun. 30, 2018
Text Block [Abstract]
Stock Option Plans	9. Stock Option Plans On May 16, 2017, our stockholders approved the Arthur J. Gallagher 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 non-qualified 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 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 3.5 million at June 30, 2018. The LTIP provides for the grant of stock options, which may be either tax-qualified non-qualified non-qualified tax-qualified non-qualified tax-qualified 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 non-transferable. 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. On March 16, 2017, the compensation committee granted 1,650,400 options under the 2014 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 2020, 2021 and 2022, respectively. The 2018 and 2017 options expire seven years from the date of grant, or earlier in the event of certain terminations of employment. For certain of our executive officers age 55 or older, stock options awarded in 2018 and 2017 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. No awards were made during the second quarter of 2018 or 2017. During the three-month periods ended June 30, 2018 and 2017, we recognized $1.6 million and $4.4 million, respectively, of compensation expense related to our stock option grants. During the six-month 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: 2018 2017 Expected dividend yield 2.3 % 2.8 % Expected risk-free interest rate 2.7 % 2.3 % Volatility 15.1 % 27.2 % Expected life (in years) 5.5 5.0 Option valuation models require the input of highly subjective assumptions including the expected stock price volatility. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options which have no vesting restrictions and are fully transferable. Because our employee and director stock options have characteristics significantly different from those of traded options, and because changes in the selective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models do not necessarily provide a reliable single measure of the fair value of our employee and non-employee six-month The following is a summary of our stock option activity and related information for 2018 (in millions, except exercise price and year data): Six-month Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Beginning balance 9.5 $ 45.27 Granted 1.3 70.74 Exercised (1.0 ) 36.37 Forfeited or canceled (0.2 ) 48.73 Ending balance 9.6 $ 49.49 4.20 $ 158.2 Exercisable at end of period 2.7 $ 42.22 2.21 $ 62.8 Ending vested and expected to vest 6.6 $ 52.05 4.95 $ 93.8 Options with respect to 14.7 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 June 30, 2018. The total intrinsic value of options exercised during the six-month Other information regarding stock options outstanding and exercisable at June 30, 2018 is summarized as follows (in millions, except exercise price and year data): Options Outstanding Options Exercisable Range of Exercise Prices Number Weighted Weighted Number Weighted $ 35.71 - $ 39.17 1.4 1.35 $ 37.92 1.4 $ 37.92 43.71 - 43.71 2.3 4.72 43.71 — — 46.17 - 46.87 3.0 3.24 46.49 1.3 46.61 47.92 - 63.60 1.6 5.70 56.80 — — 70.74 - 70.74 1.3 6.71 70.74 — — $ 35.71 - $ 70.74 9.6 4.20 $ 49.49 2.7 $ 42.22

Deferred Compensation

Deferred Compensation	6 Months Ended
	Jun. 30, 2018
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 one-year one-year sub-plans sub-plans) 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 quarter of 2018 and 2017, the compensation committee approved $11.5 million and $14.0 million, respectively, of awards in the aggregate to certain key executives under the DEPP that were contributed to the rabbi trust in first quarters of 2018 and 2017, respectively. No awards were made during the second quarter of 2018 or 2017. 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 2018 and 2017 awards. During the three-month periods ended June 30, 2018 and 2017, we charged $2.4 million and $3.0 million, respectively, to compensation expense related to these awards. During the six-month In the first quarter of 2018 and of 2017, the compensation committee approved $0.9 million and $4.0 million, respectively, of awards under the sub-plans six-month sub-plans six-month At June 30, 2018 and December 31, 2017, we recorded $62.9 million (related to 2.8 million shares) and $54.7 million (related to 2.6 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 June 30, 2018 and December 31, 2017 was $183.4 million and $166.0 million, respectively. During the six-month six-month We have a Deferred Cash Participation Plan (which we refer to as the DCPP), which is a non-qualified three-month six-month six-month

Restricted Stock, Performance S

Restricted Stock, Performance Share and Cash Awards	6 Months Ended
	Jun. 30, 2018
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. 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 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 June 30, 2018, 3.5 million shares were available for grant under the LTIP for such awards. In the first quarter of 2018 and 2017, we granted 420,200 and 477,500 restricted stock units, respectively, to employees under the LTIP, with an aggregate fair value of $28.7 million and $26.8 million, respectively, at the date of grant. These 2018 and 2017 awards of restricted stock units vest as follows: 420,200 units granted in first quarter 2018 and 477,500 units granted in first quarter 2017, vest in full based on continued employment through March 15, 2022 and March 16, 2021, respectively. For certain of our executive officers age 55 or older, restricted stock units awarded in 2018 and 2017 are not subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. In the second quarter of 2018 and 2017, we granted 18,900 and 21,600 restricted stock units, respectively, to our board members under the LTIP, with a one-year 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 June 30, 2018 and 2017, we recognized $8.2 million and $6.5 million, respectively, to compensation expense related to restricted stock unit awards granted in 2008 through 2018. During the six-month six-month Performance Share Awards On March 15, 2018 and March 16, 2017, pursuant to the LTIP, the compensation committee approved 78,200 and 86,250, respectively of provisional performance unit awards, with an aggregate fair value of $5.3 million and $4.9 million, respectively, for future grants to our officers. Each performance unit award was equivalent to the value of one share of our common stock on the date such provisional award was approved. The 2018 and 2017 awards are subject to a three-year performance period that begins on January 1, 2018 and 2017, respectively, and vest on the three-year anniversary of the date of grant (March 15, 2021 and March 16, 2020). For the 2018 and 2017 awards, at the discretion of the compensation committee and determined based on our performance, the eligible officer will be granted a percentage of the provisional performance unit award based on a new performance measure, growth in adjusted EBITDAC per share. Granted units for the 2018 and 2017 provisional awards will fully vest based on continuous employment through March 16, 2021 and 2020, respectively, and will be settled in shares of our common stock on a one-for-one six-month Cash Awards 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 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. The Program consists of a one-year two-year six-month 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 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2017 provisional awards were similar to the terms of the 2018 provisional awards. Based on our performance for 2017, we granted 242,000 units under the Program in first quarter 2018 that will fully vest on January 1, 2020. During the three-month period ended June 30, 2018, we recognized $1.9 million to compensation expense related to these awards. During the six-month six-month 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 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2016 provisional awards were similar to the terms of the 2017 provisional awards. Based on our performance for 2016, we granted 383,000 units under the Program in first quarter 2017 that will fully vest on January 1, 2019. During the three-month periods ended June 30, 2018 and 2017, we recognized $2.4 million and $2.7 million, respectively, to compensation expense related to these awards. During the six-month On March 11, 2015, pursuant to the Program, the compensation committee approved provisional cash awards of $14.6 million in the aggregate for future grant to our officers and key employees that are denominated in units (315,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2015 provisional awards were similar to the terms of the 2016 provisional awards. Based on our performance for 2015, we granted 294,000 units under the Program in first quarter 2016 that fully vested on January 1, 2018. During the three-month period ended June 30, 2017, we recognized $1.9 million to compensation expense related to these awards. During the six-month During the six-month six-month

Investments

Investments	6 Months Ended
	Jun. 30, 2018
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, and the related funding commitments (in millions): June 30, 2018 December 31, Funding 2017 Assets Commitments Assets Chem-Mod $ 4.0 $ — $ 4.0 Chem-Mod 2.0 — 2.0 Clean-coal investments: Controlling interest in six limited liability companies that own fourteen 2009 Era Clean Coal Plants 7.6 — 10.2 Non-controlling 0.5 — 0.6 Controlling interest in seventeen limited liability companies that own nineteen 2011 Era Clean Coal Plants 51.1 — 58.5 Other investments 4.7 — 3.8 Total investments $ 69.9 $ — $ 79.1

Derivatives and Hedging Activit

Derivatives and Hedging Activity	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activity	13. Derivatives and Hedging Activity 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 two 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 two years into the future. We have not received or pledged any collateral related to derivative arrangements at June 30, 2018. The notional and fair values of derivative instruments are as follows at June 30, 2018 and December 31, 2017 (in millions): Notional Amount Derivative Assets (1) Derivative Liabilities (2) June 30, 2018 Dec 31, 2017 June 30, 2018 Dec 31, 2017 June 30, 2018 Dec 31, 2017 Derivatives accounted for as hedges: Interest rate contracts $ 200.0 $ 200.0 $ 5.2 $ 2.2 $ — $ — Foreign exchange contracts (3) 24.0 18.7 2.7 8.1 6.2 2.9 Total $ 224.0 $ 218.7 $ 7.9 $ 10.3 $ 6.2 $ 2.9 (1) Included within other current assets, $7.1 million and $7.7 million at June 30, 2018 and December 31, 2017, respectively, and other noncurrent assets, $0.8 million and $2.7 million at June 30, 2018 and December 31, 2017, respectively. (2) Included within other current liabilities, $3.7 million and $1.6 million at June 30, 2018 and December 31, 2017, respectively, and other noncurrent liabilities, $2.5 million and $1.3 million at June 30, 2018 and December 31, 2017, respectively. (3) Included within foreign exchange contracts at June 30, 2018 were $96.3 million of call options offset with $92.0 million of put options, and $27.2 million of buy forwards. Included within foreign exchange contracts at December 31, 2017 were $141.0 million of call options offset with $141.0 million of put options, and $13.3 million of buy forwards offset with $31.0 million of sell forwards. The amounts of derivative gains (losses) recognized in accumulated other comprehensive loss for the six-month Commission Compensation Operating Interest Revenue Expense Expense Expense Total June 30, 2018 Cash flow hedges: Interest rate contracts $ — $ — $ — $ 5.9 $ 5.9 Foreign exchange contracts (2.5 ) (2.1 ) (1.5 ) — (6.1 ) Total $ (2.5 ) $ (2.1 ) $ (1.5 ) $ 5.9 $ (0.2 ) June 30, 2017 Cash flow hedges: Interest rate contracts $ — $ — $ — $ (3.0 ) $ (3.0 ) Foreign exchange contracts 6.0 2.0 1.4 — 9.4 Total $ 6.0 $ 2.0 $ 1.4 $ (3.0 ) $ 6.4 The amounts of derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) for the six-month Commission Compensation Operating Interest Revenue Expense Expense Expense Total June 30, 2018 Cash flow hedges: Interest rate contracts $ — $ — $ — $ 0.5 $ 0.5 Foreign exchange contracts 1.1 0.9 0.6 — 2.6 Total $ 1.1 $ 0.9 $ 0.6 $ 0.5 $ 3.1 June 30, 2017 Cash flow hedges: Interest rate contracts $ — $ — $ — $ — $ — Foreign exchange contracts (5.3 ) 0.7 0.5 — (4.1 ) Total $ (5.3 ) $ 0.7 $ 0.5 $ — $ (4.1 ) We estimate that approximately $2.2 million of pretax loss currently included within accumulated other comprehensive loss will be reclassified into earnings in the next twelve months. The amount of gain (loss) recognized in earnings on the ineffective portion of derivatives for the six-month

Commitments, Contingencies and

Commitments, Contingencies and Off-Balance Sheet Arrangements	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Off-Balance Sheet Arrangements	14. Commitments, Contingencies and Off-Balance 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, operating leases and purchase commitments at June 30, 2018 were as follows (in millions): Payments Due by Period Contractual Obligations 2018 2019 2020 2021 2022 Thereafter Total Note purchase agreements $ 50.0 $ 100.0 $ 100.0 $ 75.0 $ 200.0 $ 2,723.0 $ 3,248.0 Credit Agreement 135.0 — — — — — 135.0 Premium Financing Debt Facility 111.1 — — — — — 111.1 Interest on debt 70.4 137.4 132.7 127.9 122.4 557.6 1,148.4 Total debt obligations 366.5 237.4 232.7 202.9 322.4 3,280.6 4,642.5 Operating lease obligations 54.7 100.1 85.6 73.3 57.3 144.9 515.9 Less sublease arrangements (0.8 ) (0.8 ) (0.6 ) (0.6 ) (0.4 ) (1.2 ) (4.4 ) Outstanding purchase obligations 24.4 38.0 26.5 14.2 10.8 28.7 142.6 Funding related to the acquistion of Reassurance Holdings, Inc., (see Note 4) 122.1 — — — — — 122.1 Total contractual obligations $ 566.9 $ 374.7 $ 344.2 $ 289.8 $ 390.1 $ 3,453.0 $ 5,418.7 The amounts presented in the table above may not necessarily reflect our actual future cash funding requirements, because the actual timing of future payments may vary from the stated contractual obligation. Note Purchase Agreements, Credit Agreement and Premium Financing Debt Facility - Operating Lease Obligations - tax-increment 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 Outstanding Purchase Obligations - Off-Balance - Total Amount of Commitment Expiration by Period Amounts Off-Balance 2018 2019 2020 2021 2022 Thereafter Committed Letters of credit $ — $ — $ — $ — $ — $ 16.5 $ 16.5 Financial guarantees 0.1 0.2 0.2 0.2 0.2 0.8 1.7 Total commitments $ 0.1 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 17.3 $ 18.2 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 Since January 1, 2002, we have acquired 478 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 2018 that contain potential earnout obligations, such obligations are measured at fair value as of the acquisition date and are included on that basis in the recorded purchase price consideration for the respective acquisition. The amounts recorded as earnout payables are primarily based upon estimated future operating results of the acquired entities over a two- Off-Balance - At June 30, 2018, we had posted two letters of credit totaling $9.7 million, in the aggregate, related to our self-insurance rent-a-captive Litigation, Regulatory and Taxation Matters - non-compete On April 18, 2018, Nalco Company (Nalco) filed patent infringement lawsuits in the Western District of Wisconsin against two unaffiliated power plants that burn refined coal using the Chem-Mod LLC Chem-Mod LLC Chem-Mod LLC Chem-Mod Chem-Mod LLC Chem-Mod LLC. Chem-Mod LLC 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, if the IRS were to successfully assert that the micro-captives organized and/or managed by us do not meet the requirements of IRC Section 831(b), we could be held liable to pay monetary claims by the IRS and/or our micro-captive clients, and our future earnings from our micro-captive operations could be materially adversely affected, any of which events could negatively impact the overall captive business and adversely affect our consolidated results of operations and financial condition. In the period from 2015 to 2017, our micro-captive operations contributed less than $3.5 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 its audits of our clients, we are not able to reasonably estimate the amount of any potential loss in connection with this investigation. Contingent Liabilities - Tax-advantaged Due to the contingent nature of this exposure and our related assessment of its likelihood, no reserve has been recorded in our June 30, 2018 consolidated balance sheet related to this exposure.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Earnings (Loss)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Accumulated Other Comprehensive Earnings (Loss)	15. Accumulated Other Comprehensive Earnings (Loss) The after-tax Pension Foreign Fair Value of Accumulated Balance as of December 31, 2017, as previously reported $ (43.0 ) $ (525.8 ) $ 8.9 $ (559.9 ) Adoption of ASC Topic 606 — 4.5 — 4.5 Balance as of December 31, 2017, as restated (43.0 ) (521.3 ) 8.9 (555.4 ) Reclassifications to retained earnings of income tax effects related to the Tax Act (7.9 ) — 1.3 (6.6 ) Net change in period 1.5 (88.4 ) (2.5 ) (89.4 ) Balance as of June 30, 2018 $ (49.4 ) $ (609.7 ) $ 7.7 $ (651.4 ) The foreign currency translation during the six-month During the six-month six-month six-month

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Segment Information	16. Segment Information We have three reportable segments: brokerage, risk management and corporate. The brokerage segment is primarily comprised of our retail and wholesale insurance brokerage operations. The brokerage segment generates revenues through commissions paid by 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 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 per-service 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 and external acquisition-related expenses. Allocations of investment income and certain expenses are based on reasonable assumptions and estimates primarily using revenue, headcount and other information. We allocate the provision for income taxes to the brokerage and risk management segments using the local country statutory rates. Reported operating results by segment would change if different methods were applied. Financial information relating to our segments for the three-month and six-month Three-month period Six-month ended June 30, ended June 30, 2017 2017 2018 As Restated for 2018 As Restated for Brokerage Total revenues $ 1,000.1 $ 896.1 $ 2,195.7 $ 1,981.0 Earnings before income taxes $ 170.6 $ 125.1 $ 489.5 $ 401.6 Identifiable assets at June 30, 2018 and 2017 $ 13,779.0 $ 13,202.9 Risk Management Total revenues $ 237.3 $ 216.8 $ 467.2 $ 426.7 Earnings before income taxes $ 24.0 $ 20.6 $ 45.6 $ 42.7 Identifiable assets at June 30, 2018 and 2017 $ 739.5 $ 714.7 Corporate Total revenues $ 423.0 $ 376.6 $ 835.2 $ 728.2 Loss before income taxes $ (91.0 ) $ (91.6 ) $ (189.2 ) $ (190.6 ) Identifiable assets at June 30, 2018 and 2017 $ 1,712.0 $ 1,761.8 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 June 30, 2018 are as follows (in millions): Brokerage Risk Corporate Total Revenues: Commissions $ 688.0 $ — $ — $ 688.0 Fees 220.4 201.8 — 422.2 Supplemental revenues 48.1 — — 48.1 Contingent revenues 21.8 — — 21.8 Investment income 15.7 0.1 — 15.8 Gains on books of business sales 6.1 — — 6.1 Revenues from clean coal activities — — 422.4 422.4 Other net revenues — — 0.6 0.6 Revenues before reimbursements 1,000.1 201.9 423.0 1,625.0 Reimbursements — 35.4 — 35.4 Total revenues $ 1,000.1 $ 237.3 $ 423.0 $ 1,660.4 Revenues by type and segment for the six-month Brokerage Risk Corporate Total Revenues: Commissions $ 1,527.4 $ — $ — $ 1,527.4 Fees 473.6 396.7 — 870.3 Supplemental revenues 100.1 — — 100.1 Contingent revenues 56.7 — — 56.7 Investment income 28.9 0.3 — 29.2 Gains on books of business sales 9.0 — — 9.0 Revenues from clean coal activities — — 834.6 834.6 Other net revenues — — 0.6 0.6 Revenues before reimbursements 2,195.7 397.0 835.2 3,427.9 Reimbursements — 70.2 — 70.2 Total revenues $ 2,195.7 $ 467.2 $ 835.2 $ 3,498.1 Revenues by geographical location and segment for the three-month period ended June 30, 2018 are as follows (in millions): Brokerage Risk Corporate Total Revenues: United States $ 615.5 $ 197.3 $ 423.0 $ 1,235.8 United Kingdom 204.4 8.8 — 213.2 Australia 53.9 25.7 — 79.6 Canada 47.8 1.2 — 49.0 New Zealand 39.4 4.3 — 43.7 Other foreign 39.1 — — 39.1 Total revenues $ 1,000.1 $ 237.3 $ 423.0 $ 1,660.4 Revenues by geographical location and segment for the six-month Brokerage Risk Corporate Total Revenues: United States $ 1,468.3 $ 390.1 $ 835.2 $ 2,693.6 United Kingdom 395.4 17.7 — 413.1 Australia 97.5 49.4 — 146.9 Canada 90.6 2.2 — 92.8 New Zealand 69.5 7.8 — 77.3 Other foreign 74.4 — — 74.4 Total revenues $ 2,195.7 $ 467.2 $ 835.2 $ 3,498.1 Revenues by type and segment for the three-month period ended June 30, 2017, as restated for the adoption of ASC Topic 606, are as follows (in millions): Brokerage Risk Corporate Total Revenues: Commissions $ 618.2 $ — $ — $ 618.2 Fees 205.5 181.4 — 386.9 Supplemental revenues 35.8 — — 35.8 Contingent revenues 21.3 — — 21.3 Investment income 14.2 0.2 — 14.4 Gains on books of business sales 1.1 — — 1.1 Revenues from clean coal activities — — 376.4 376.4 Other net gains — — 0.2 0.2 Revenues before reimbursements 896.1 181.6 376.6 1,454.3 Reimbursements — 35.2 — 35.2 Total revenues $ 896.1 $ 216.8 $ 376.6 $ 1,489.5 Revenues by type and segment for the six-month Brokerage Risk Corporate Total Revenues: Commissions $ 1,378.9 $ — $ — $ 1,378.9 Fees 433.8 358.1 — 791.9 Supplemental revenues 83.1 — — 83.1 Contingent revenues 56.3 — — 56.3 Investment income 26.4 0.3 — 26.7 Gains on books of business sales 2.5 — — 2.5 Revenues from clean coal activities — — 728.2 728.2 Revenues before reimbursements 1,981.0 358.4 728.2 3,067.6 Reimbursements — 68.3 — 68.3 Total revenues $ 1,981.0 $ 426.7 $ 728.2 $ 3,135.9 Revenues by geographical location and segment for the three-month period ended June 30, 2017, as restated for the adoption of ASC Topic 606, are as follows (in millions): Brokerage Risk Corporate Total Revenues: United States $ 552.1 $ 185.3 $ 376.6 $ 1,114.0 United Kingdom 184.7 7.2 — 191.9 Australia 52.0 19.1 — 71.1 Canada 36.6 0.9 — 37.5 New Zealand 36.8 4.3 — 41.1 Other foreign 33.9 — — 33.9 Total revenues $ 896.1 $ 216.8 $ 376.6 $ 1,489.5 Revenues by geographical location and segment for the six-month Brokerage Risk Corporate Total Revenues: United States $ 1,345.1 $ 367.7 $ 728.2 $ 2,441.0 United Kingdom 346.0 13.6 — 359.6 Australia 92.3 37.8 — 130.1 Canada 68.7 1.7 — 70.4 New Zealand 63.9 5.9 — 69.8 Other foreign 65.0 — — 65.0 Total revenues $ 1,981.0 $ 426.7 $ 728.2 $ 3,135.9

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Changes and Error Corrections [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, not-for-profit, Chem-Mod LLC’s 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 generated from our premium financing operations and our investment portfolio, which includes our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. We are headquartered in Rolling Meadows, Illinois, have operations in 34 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, 2017, 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
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 are also required to make certain judgments and estimates that affect the disclosed and recorded amounts of revenues and expenses related to the impact of the adoption of and accounting under ASC Topic 606. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible 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.
Revenue Recognition	Revenue Recognition Our revenues are derived from commissions and fees as primarily specified in a written contract, or unwritten business understanding, with our clients or underwriting enterprises. We also recognize investment income over time from our invested assets and invested assets we hold on behalf of our clients or underwriting enterprises. BROKERAGE SEGMENT Our brokerage segment generates revenues by: (i) Identifying, negotiating and placing all forms of insurance or reinsurance coverage, as well as providing risk-shifting, risk-sharing and risk-mitigation consulting services, principally related to property/casualty, life, health, welfare and disability insurance. We also provide these services through, or in conjunction with, other unrelated agents and brokers, consultants and management advisors. (ii) Acting as an agent or broker for multiple underwriting enterprises by providing services such as sales, marketing, selecting, negotiating, underwriting, servicing and placing insurance coverage on their behalf. (iii) Providing consulting services related to health and welfare benefits, voluntary benefits, executive benefits, compensation, retirement planning, institutional investment and fiduciary, actuarial, compliance, private insurance exchange, human resource technology, communications and benefits administration. (iv) Providing management and administrative services to captives, pools, risk-retention groups, healthcare exchanges, small underwriting enterprises, such as accounting, claims and loss processing assistance, feasibility studies, actuarial studies, data analytics and other administrative services. The majority of our brokerage contracts and service understandings are for a period of one year or less. Commissions and fees The primary source of revenues for our brokerage services are commissions from underwriting enterprises, based on a percentage of premiums paid by our clients, or fees received from clients based on an agreed level of service usually in lieu of commissions. Commissions are fixed at the contract effective date and generally are based on a percentage of premiums for insurance coverage or employee head count for employer sponsored benefit plans. Commissions depend upon a large number of factors, including the type of risk being placed, the particular underwriting enterprise’s demand, the expected loss experience of the particular risk of coverage, and historical benchmarks surrounding the level of effort necessary for us to place and service the insurance contract. Rather than being tied to the amount of premiums, fees are most often based on an expected level of effort to provide our services. Whether we are paid a commission or a fee, the vast majority of our services are associated with the placement of an insurance (or insurance-like) contract. Accordingly, we recognize approximately 70% of our commission and fee revenues on the effective date of the underlying insurance contract. The amount of revenue we recognize is based on our costs to provide our services up and through that effective date, including an appropriate estimate of our profit margin on a portfolio basis (a practical expedient as defined in ASC Topic 606). Based on the proportion of additional services we provide in each period after the effective date of the insurance contract, including an appropriate estimate of our profit margin, we recognize approximately 20% of our commission and fee revenues in the first three months, and the remaining 10% thereafter. These periods may be different than the underlying premium payment patterns of the insurance contracts, but the vast majority of our services are fully provided within one year of the insurance contract effective date. For consulting and advisory services, we recognize our revenue in the period in which we provide the service or advice. For management and administrative services, our revenue is recognized ratably over the contract period consistent with the performance of our obligations, mostly over an annual term. Supplemental revenues Certain underwriting enterprises may pay us additional revenues for the volume of premium placed with them and for insights into our sales pipeline, our sales capabilities or our risk selection knowledge. These amounts are in excess of the commission and fee revenues discussed above, and not all business we place with underwriting enterprises is eligible for supplemental revenues. Unlike contingent revenues, discussed below, these revenues are a fixed amount or fixed percentage of premium of the underlying eligible insurance contracts. For supplemental revenue contracts based on a fixed percentage of premium, our obligation to the underwriting enterprise is substantially completed upon the effective date of the underlying insurance contract and revenue is fully earned at that time. For supplemental revenue contracts based on a fixed amount, revenue is recognized ratably over the contract period consistent with the performance of our obligations, almost always over an annual term. We receive these revenues on a quarterly or annual basis. Contingent revenues Certain underwriting enterprises may pay us additional revenues for our sales capabilities, our risk selection knowledge, or our administrative efficiencies. These amounts are in excess of the commission or fee revenues discussed above, and not all business we place with participating underwriting enterprises is eligible for contingent revenues. Unlike supplemental revenues, also discussed above, these revenues are variable, generally based on growth, the loss experience of the underlying insurance contracts, and/or our efficiency in processing the business. We generally operate under calendar year contracts, but we do not receive these revenues from the underwriting enterprises until the following calendar year, generally in the first and second quarters, after verification of the performance indicators outlined in the contracts. Accordingly, during each reporting period, we must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. We base our estimates each period on a contract-by-contract Sub-brokerage Sub-brokerage revenues. Sub-brokerage sub-brokers RISK MANAGEMENT SEGMENT Revenues for our risk management segment are comprised of fees generally negotiated (i) on a per-claim Per-claim Where we operate under a contract with our fee established on a per claim basis, our obligation is to process claims for a term specified within the contract. Because it is impractical to recognize our revenues on an individual claim by claim basis, we recognize revenue plus an appropriate estimate of our profit margin on a portfolio basis by grouping claims with similar characteristics (a practical expedient as defined in ASC Topic 606). We apply actuarially-determined, historical-based patterns to determine our future service obligations, without applying a present value discount. Cost-plus fees Where we provide services and generate revenues on a cost-plus basis, we recognize revenue over the contract period consistent with the performance of our obligations. Performance-based fees Certain clients pay us additional fee revenues for our efficiency in managing claims or on the basis of claim outcome effectiveness. These amounts are in excess of the fee revenues discussed above. These revenues are variable, generally based on performance metrics set forth in the underlying contracts. We generally operate under multi-year contracts with fiscal year measurement periods. We do not receive these fees, if earned, until the following year after verification of the performance metrics outlined in the contracts. Each period we base our estimates on a contract-by-contract Reimbursements Reimbursements represent amounts received from clients reimbursing us for certain third-party costs associated with providing our claims management services. In certain service partner relationships, we are considered a principal because we direct the third party, control the specified service and combine the services provided into an integrated solution. Given this principal relationship, we are required to recognize revenue gross and service partner vendor fees in the operating expense in our consolidated statement of earnings. Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09,
Deferred Costs	Deferred Costs We incur costs to provide brokerage and risk management services. Those costs are either (i) costs to obtain a contract or (ii) costs to fulfill such contract, or (iii) all other costs. (i) Costs to obtain - we incur costs to obtain a contract with a client. Those costs would not have been incurred if the contract had not been obtained. Almost all of our costs to obtain are incurred prior to, or on, the effective date of the contract and consist primarily of incentive compensation we pay to our production employees. Our costs to obtain are expensed as incurred as described in Note 3 to these unaudited consolidated financial statements. (ii) Costs to fulfill - we incur costs to fulfill a contract (or anticipated contract) with a client. Those costs are incurred prior to the effective date of the contract and relate to fulfilling our primary placement obligations to our clients. Our costs to fulfil prior to the effective date are capitalized and amortized on the effective date. These fulfilment activities include collecting underwriting information from our client, assessing their insurance needs and negotiating their placement with one or more underwriting enterprises. The majority of costs that we incur relate to compensation and benefits of our client service employees. Costs incurred during preplacement activities are expected to be recovered in the future. If the capitalized costs are no longer deemed to be recoverable, then they would be expensed. (iii) Other costs that are not costs to obtain or fulfill are expensed as incurred. Examples include other operating costs such as rent, utilities, management costs, overhead costs, legal and other professional fees, technology costs, insurance related costs, communication and advertising, and travel and entertainment. Depreciation, amortization and change in estimated acquisition earnout payable are expensed as incurred.
Hedge Accounting	Hedge Accounting In August 2017, the FASB issued ASU No. 2017-12, last-of-layer
Presentation of Net Periodic Pension and Postretirement Benefit Cost	Presentation of Net Periodic Pension and Postretirement Benefit Cost In March 2017, the FASB issued ASU No. 2017-07, Form 10-K
Business Combinations	Business Combinations In January 2017, the FASB issued ASU No. 2017-01,
Intangibles - Goodwill and Other	Intangibles - Goodwill and Other In January 2017, the FASB issued ASU No. 2017-04, non-cash
Leases	Leases In February 2016, the FASB issued ASU No. 2016-02, right-of-use While we are continuing to assess all potential impacts of the new guidance, we anticipate this guidance will have an impact on our consolidated financial statements. We currently believe the most significant impact relates to our real estate operating leases and the related recognition of right-of-use
Income Taxes	Income Taxes In October 2016, the FASB issued ASU No. 2016-16, In February 2018, the FASB issued ASU No. 2018-02, ASC 740-10-45-15, In March 2018, the FASB issued ASU No. 2018-05
Restricted Cash	Restricted Cash In November 2016, the FASB issued ASU No. 2016-18, 2016-18

Effect of New Accounting Pron26

Effect of New Accounting Pronouncements (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Changes and Error Corrections [Abstract]
Summary of Cash, Cash Equivalents and Restricted Cash	The following is a reconciliation of our June 30 cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the six-month June 30, 2018 2017 Cash and cash equivalents $ 652.2 $ 587.8 Restricted cash 1,692.5 1,481.1 Total cash, cash equivalents and restricted cash $ 2,344.7 $ 2,068.9

Revenue from Contracts with C27

Revenue from Contracts with Customers (Tables)	6 Months Ended
	Jun. 30, 2018
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): June 30, 2018 December 31, 2017, As Restated Unbilled receivables $ 608.7 $ 415.2 Deferred contract costs 55.0 83.3 Deferred revenue 471.8 430.6
Summary of Changes in Deferred Revenue Balances	Significant changes in the deferred revenue balances during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2017 $ 258.7 $ 171.9 $ 430.6 Incremental deferred revenue 204.1 73.4 277.5 Revenue recognized during the six-month (181.0 ) (68.2 ) (249.2 ) Deferred revenue recognized from business acquisitions 12.9 — 12.9 Deferred revenue at June 30, 2018 $ 294.7 $ 177.1 $ 471.8
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 2018 (remaining six months) $ 224.3 $ 69.9 $ 294.2 2019 59.6 47.5 107.1 2020 8.2 19.9 28.1 2021 1.7 11.0 12.7 2022 0.4 6.8 7.2 Thereafter 0.5 22.0 22.5 Total $ 294.7 $ 177.1 $ 471.8
Accounting Standards Update 2014-09 [Member]
Summary of Consolidated Statement Line Items, which Reflect Adoption of New Revenue Recognition Guidance	The consolidated statement of earnings line items, which reflect the adoption of the new revenue recognition guidance, are as follows (in millions, except per share data): Three-month period ended June 30, 2017 As Previously Impact of As Restated for Commissions $ 690.2 $ (72.0 ) $ 618.2 Fees 410.9 (24.0 ) 386.9 Supplemental revenues 41.5 (5.7 ) 35.8 Contingent revenues 29.5 (8.2 ) 21.3 Investment income 13.6 0.8 14.4 Gains on books of business sales 1.1 — 1.1 Revenues from clean coal activities 376.4 — 376.4 Other net revenues 0.2 — 0.2 Revenues before reimbursements 1,563.4 (109.1 ) 1,454.3 Reimbursements — 35.2 35.2 Total revenues 1,563.4 (73.9 ) 1,489.5 Compensation 675.7 (8.8 ) 666.9 Operating 211.6 (7.4 ) 204.2 Reimbursements — 35.2 35.2 Cost of revenues from clean coal activities 397.1 — 397.1 Interest 31.6 — 31.6 Depreciation 30.2 — 30.2 Amortization 65.1 — 65.1 Change in estimated acquisition earnout payables 5.1 — 5.1 Total expenses 1,416.4 19.0 1,435.4 Earnings before income taxes 147.0 (92.9 ) 54.1 Benefit for income taxes (33.4 ) 9.2 (24.2 ) Net earnings 180.4 (102.1 ) 78.3 Net earnings attributable to noncontrolling interests 8.5 (0.2 ) 8.3 Net earnings attributable to controlling interests $ 171.9 $ (101.9 ) $ 70.0 Basic net earnings per share $ 0.96 $ (0.57 ) $ 0.39 Diluted net earnings per share 0.95 (0.56 ) 0.39 Dividends declared per common share 0.39 — 0.39 Six-month period ended June 30, 2017 As Previously Impact of As Restated for Commissions $ 1,280.7 $ 98.2 $ 1,378.9 Fees 781.4 10.5 791.9 Supplemental revenues 76.0 7.1 83.1 Contingent revenues 82.9 (26.6 ) 56.3 Investment income 24.4 2.3 26.7 Gains on books of business sales 2.5 — 2.5 Revenues from clean coal activities 728.2 — 728.2 Revenues before reimbursements 2,976.1 91.5 3,067.6 Reimbursements — 68.3 68.3 Total revenues 2,976.1 159.8 3,135.9 Compensation 1,333.3 45.4 1,378.7 Operating 412.0 (8.3 ) 403.7 Reimbursements — 68.3 68.3 Cost of revenues from clean coal activities 764.0 — 764.0 Interest 61.5 — 61.5 Depreciation 59.7 — 59.7 Amortization 129.4 — 129.4 Change in estimated acquisition earnout payables 16.9 — 16.9 Total expenses 2,776.8 105.4 2,882.2 Earnings before income taxes 199.3 54.4 253.7 Benefit for income taxes (48.9 ) (17.7 ) (66.6 ) Net earnings 248.2 72.1 320.3 Net earnings attributable to noncontrolling interests 20.6 0.9 21.5 Net earnings attributable to controlling interests $ 227.6 $ 71.2 $ 298.8 Basic net earnings per share $ 1.27 $ 0.40 $ 1.67 Diluted net earnings per share 1.26 0.39 1.65 Dividends declared per common share 0.78 — 0.78 Select consolidated statement of comprehensive earnings line items, which reflect the adoption of the new revenue recognition guidance, are as follows (in millions): Three-month period ended June 30, 2017 As Previously Impact of Adoption of As Restated for Net earnings $ 180.4 $ (102.1 ) $ 78.3 Change in pension liability, net of taxes 1.4 — 1.4 Foreign currency translation 33.9 (0.4 ) 33.5 Change in fair value of derivative instruments, net of taxes 2.3 — 2.3 Comprehensive earnings 218.0 (102.5 ) 115.5 Comprehensive earnings attributable to noncontrolling interests 8.9 (0.2 ) 8.7 Comprehensive earnings attributable to controlling interests $ 209.1 $ (102.3 ) $ 106.8 Six-month period ended June 30, 2017 As Previously Impact of As Restated for Net earnings $ 248.2 $ 72.1 $ 320.3 Change in pension liability, net of taxes 2.6 — 2.6 Foreign currency translation 92.3 (2.9 ) 89.4 Change in fair value of derivative instruments, net of taxes 8.8 — 8.8 Comprehensive earnings 351.9 69.2 421.1 Comprehensive earnings attributable to noncontrolling interests 22.6 0.9 23.5 Comprehensive earnings attributable to controlling interests $ 329.3 $ 68.3 $ 397.6 Select balance sheet line items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): December 31, 2017 As Previously Impact of As Restated for Assets Premium and fees receivables $ 2,157.2 $ 1,925.6 $ 4,082.8 Other current assets 708.4 173.2 881.6 Deferred income taxes 905.1 (53.5 ) 851.6 Other noncurrent assets 567.0 0.1 567.1 Goodwill 4,197.9 (33.1 ) 4,164.8 Liabilities Premiums payable to underwriting enterprises 3,475.9 1,510.1 4,986.0 Accrued compensation and other current liabilities 864.1 83.7 947.8 Deferred revenue - current/unearned fees 74.8 280.5 355.3 Other current liabilities 56.4 (56.4 ) — Deferred revenue - noncurrent — 75.3 75.3 Other noncurrent liabilities 1,128.3 (15.7 ) 1,112.6 Stockholders’ equity Retained earnings 1,095.9 125.9 1,221.8 Accumulated other comprehensive loss (559.9 ) 4.5 (555.4 ) Stockholders’ equity attributable to controlling interests 4,105.2 130.4 4,235.6 Stockholders’ equity attributable to noncontrolling interests 59.7 4.4 64.1 Select consolidated statement of cash flows line items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): Six-month As Previously Impact of As Restated for Cash flows from operating activities Net earnings $ 248.2 $ 72.1 $ 320.3 Adjustments to reconcile net earnings to net cash provided by operating activities: Net change in premiums and fees receivable (478.7 ) (1,055.7 ) (1,534.4 ) Net change in deferred revenue — 29.7 29.7 Net change in premiums payable to underwriting enterprises 445.1 934.3 1,379.4 Net change in other current assets (17.4 ) 50.7 33.3 Net change in accrued compensation and other current liabilities (77.0 ) 19.2 (57.8 ) Net change in deferred income taxes (72.9 ) (17.6 ) (90.5 ) Net change in other noncurrent assets and liabilities (18.4 ) (1.8 ) (20.2 ) Select statement of stockholders’ equity items, which reflect the adoption of the new revenue recognition guidance are as follows (in millions): Retained Accumulated Stockholders’ Total Balance at December 31, 2017, as reported $ 1,095.9 $ (559.9 ) $ 59.7 $ 4,164.9 Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017 125.9 4.5 4.4 134.8 Balance at December 31, 2017, as restated $ 1,221.8 $ (555.4 ) $ 64.1 $ 4,299.7

Business Combinations (Tables)

Business Combinations (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Acquisition Method for Recording Business Combinations	During the six-month Name and Effective Date of Acquisition Common Common Cash Paid Accrued Escrow Recorded Total Maximum (000s) Market Financial Group, Ltd and Austin Consulting Group Inc. (MFG) January 1, 2018 53 $ 3.7 $ 33.9 $ — $ 4.2 $ 4.0 $ 45.8 $ 7.0 McGregor & Associates (M&A) March 1, 2018 — — 13.5 — 2.5 5.1 21.1 12.0 Pronto Insurance (PI) June 5, 2018 — — 294.8 — 18.7 — 313.5 — Sixteen other acquisitions completed in 2018 220 12.2 82.0 0.4 9.9 21.9 126.4 52.1 273 $ 15.9 $ 424.2 $ 0.4 $ 35.3 $ 31.0 $ 506.8 $ 71.1
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 six-month MFG M&A PI Sixteen Total Cash $ 0.1 $ — $ 7.2 $ 5.0 $ 12.3 Other current assets 3.0 0.5 35.3 20.6 59.4 Fixed assets 0.4 1.4 2.6 0.4 4.8 Noncurrent assets — — 8.3 — 8.3 Goodwill 24.7 5.2 194.1 70.5 294.5 Expiration lists 20.2 15.1 105.7 63.0 204.0 Non-compete 0.1 0.1 0.3 1.2 1.7 Trade names — — 35.4 — 35.4 Total assets acquired 48.5 22.3 388.9 160.7 620.4 Current liabilities 2.3 0.4 31.5 19.3 53.5 Noncurrent liabilities 0.4 0.8 43.9 15.0 60.1 Total liabilities assumed 2.7 1.2 75.4 34.3 113.6 Total net assets acquired $ 45.8 $ 21.1 $ 313.5 $ 126.4 $ 506.8
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, 2017 (in millions, except per share data): Three-month period ended Six-month period ended 2018 2017 2018 2017 Total revenues $ 1,683.4 $ 1,525.8 $ 3,560.7 $ 3,211.6 Net earnings attributable to controlling interests 116.8 71.9 395.8 306.0 Basic net earnings per share 0.64 0.40 2.17 1.70 Diluted net earnings per share 0.63 0.40 2.13 1.69

Other Current Assets (Tables)

Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Summary of Major Classes of Other Current Assets	Major classes of other current assets consist of the following (in millions): June 30, December 31, Premium finance advances and loans $ 302.8 $ 305.5 Accrued supplemental, direct bill and other receivables 251.9 244.5 Refined coal production related receivables 173.0 156.8 Deferred contract costs 55.0 83.3 Prepaid expenses 95.4 91.5 Total other current assets $ 878.1 $ 881.6

Intangible Assets (Tables)

Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations	The carrying amount of goodwill at June 30, 2018 and December 31, 2017 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Corporate Total At June 30, 2018 United States $ 2,545.3 $ 25.1 $ — $ 2,570.4 United Kingdom 732.1 7.1 — 739.2 Canada 360.0 — — 360.0 Australia 400.7 — — 400.7 New Zealand 204.5 10.4 — 214.9 Other foreign 115.9 — 2.8 118.7 Total goodwill - net $ 4,358.5 $ 42.6 $ 2.8 $ 4,403.9 Brokerage Risk Corporate Total At December 31, 2017 United States $ 2,280.9 $ 25.8 $ — $ 2,306.7 United Kingdom 738.5 7.2 — 745.7 Canada 374.0 — — 374.0 Australia 416.6 — — 416.6 New Zealand 209.3 9.6 — 218.9 Other foreign 99.9 — 3.0 102.9 Total goodwill - net $ 4,119.2 $ 42.6 $ 3.0 $ 4,164.8
Changes in Carrying Amount of Goodwill	The changes in the carrying amount of goodwill for the six-month Brokerage Risk Corporate Total Balance as of December 31, 2017, as previously reported $ 4,152.3 $ 42.6 $ 3.0 $ 4,197.9 Adoption of ASC Topic 606 (33.1 ) — — (33.1 ) Balance at December 31, 2017, as restated 4,119.2 42.6 3.0 4,164.8 Goodwill acquired during the period 291.8 2.7 — 294.5 Goodwill adjustments due to appraisals and other acquisition adjustments 2.5 (2.3 ) — 0.2 Foreign currency translation adjustments during the period (55.0 ) (0.4 ) (0.2 ) (55.6 ) Balance as of June 30, 2018 $ 4,358.5 $ 42.6 $ 2.8 $ 4,403.9
Major Classes of Amortizable Intangible Assets	Major classes of amortizable intangible assets at June 30, 2018 and December 31, 2017 consist of the following (in millions): June 30, December 31, Expiration lists $ 3,233.4 $ 3,055.9 Accumulated amortization - expiration lists (1,547.5 ) (1,422.1 ) 1,685.9 1,633.8 Non-compete 54.9 53.5 Accumulated amortization - non-compete (47.4 ) (46.1 ) 7.5 7.4 Trade names 60.6 25.9 Accumulated amortization - trade names (23.0 ) (22.5 ) 37.6 3.4 Net amortizable assets $ 1,731.0 $ 1,644.6
Estimated Aggregate Amortization Expense	Estimated aggregate amortization expense for each of the next five years and thereafter is as follows: 2018 (remaining six months) $ 137.7 2019 263.9 2020 247.3 2021 224.0 2022 200.7 Thereafter 657.4 Total $ 1,731.0

Credit and Other Debt Agreeme31

Credit and Other Debt Agreements (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Summary of Corporate and Other Debt	The following is a summary of our corporate and other debt (in millions): June 30, December 31, Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 2.80%, balloon due June 24, 2018 $ — $ 50.0 Semi-annual payments of interest, fixed rate of 5.85%, $50 million due November 30, 2018 and November 30, 2019 100.0 100.0 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 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 4.58%, 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 — 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 4.73%, 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 — 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 — 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 — Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 — Total Note Purchase Agreements 3,248.0 2,798.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires April 8, 2021 135.0 190.0 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 85.0 116.4 NZD denominated tranche — 5.7 Facility C and D AUD denominated tranche 15.8 18.5 NZD denominated tranche 10.3 10.5 Total Premium Financing Debt Facility 111.1 151.1 Total corporate and other debt 3,494.1 3,139.1 Less unamortized debt acquisition costs on Note Purchase Agreements (7.0 ) (6.1 ) Net corporate and other debt $ 3,487.1 $ 3,133.0

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2018
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 Six-month period ended 2018 2017 2018 2017 Net earnings attributable to controlling interests $ 114.9 $ 70.0 $ 388.6 $ 298.8 Weighted average number of common shares outstanding 182.4 179.9 181.9 179.4 Dilutive effect of stock options using the treasury stock method 3.1 1.7 3.3 1.7 Weighted average number of common and common equivalent shares outstanding 185.5 181.6 185.2 181.1 Basic net earnings per share $ 0.63 $ 0.39 $ 2.14 $ 1.67 Diluted net earnings per share $ 0.62 $ 0.39 $ 2.10 $ 1.65

Stock Option Plans (Tables)

Stock Option Plans (Tables)	6 Months Ended
	Jun. 30, 2018
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: 2018 2017 Expected dividend yield 2.3 % 2.8 % Expected risk-free interest rate 2.7 % 2.3 % Volatility 15.1 % 27.2 % Expected life (in years) 5.5 5.0
Stock Option Activity and Related Information	The following is a summary of our stock option activity and related information for 2018 (in millions, except exercise price and year data): Six-month Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Beginning balance 9.5 $ 45.27 Granted 1.3 70.74 Exercised (1.0 ) 36.37 Forfeited or canceled (0.2 ) 48.73 Ending balance 9.6 $ 49.49 4.20 $ 158.2 Exercisable at end of period 2.7 $ 42.22 2.21 $ 62.8 Ending vested and expected to vest 6.6 $ 52.05 4.95 $ 93.8
Other Information Regarding Stock Options Outstanding and Exercisable	Other information regarding stock options outstanding and exercisable at June 30, 2018 is summarized as follows (in millions, except exercise price and year data): Options Outstanding Options Exercisable Range of Exercise Prices Number Weighted Weighted Number Weighted $ 35.71 - $ 39.17 1.4 1.35 $ 37.92 1.4 $ 37.92 43.71 - 43.71 2.3 4.72 43.71 — — 46.17 - 46.87 3.0 3.24 46.49 1.3 46.61 47.92 - 63.60 1.6 5.70 56.80 — — 70.74 - 70.74 1.3 6.71 70.74 — — $ 35.71 - $ 70.74 9.6 4.20 $ 49.49 2.7 $ 42.22

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2018
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, and the related funding commitments (in millions): June 30, 2018 December 31, Funding 2017 Assets Commitments Assets Chem-Mod $ 4.0 $ — $ 4.0 Chem-Mod 2.0 — 2.0 Clean-coal investments: Controlling interest in six limited liability companies that own fourteen 2009 Era Clean Coal Plants 7.6 — 10.2 Non-controlling 0.5 — 0.6 Controlling interest in seventeen limited liability companies that own nineteen 2011 Era Clean Coal Plants 51.1 — 58.5 Other investments 4.7 — 3.8 Total investments $ 69.9 $ — $ 79.1

Derivatives and Hedging Activ35

Derivatives and Hedging Activity (Tables)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Notional and Fair Values of Derivative Instruments	The notional and fair values of derivative instruments are as follows at June 30, 2018 and December 31, 2017 (in millions): Notional Amount Derivative Assets (1) Derivative Liabilities (2) June 30, 2018 Dec 31, 2017 June 30, 2018 Dec 31, 2017 June 30, 2018 Dec 31, 2017 Derivatives accounted for as hedges: Interest rate contracts $ 200.0 $ 200.0 $ 5.2 $ 2.2 $ — $ — Foreign exchange contracts (3) 24.0 18.7 2.7 8.1 6.2 2.9 Total $ 224.0 $ 218.7 $ 7.9 $ 10.3 $ 6.2 $ 2.9 (1) Included within other current assets, $7.1 million and $7.7 million at June 30, 2018 and December 31, 2017, respectively, and other noncurrent assets, $0.8 million and $2.7 million at June 30, 2018 and December 31, 2017, respectively. (2) Included within other current liabilities, $3.7 million and $1.6 million at June 30, 2018 and December 31, 2017, respectively, and other noncurrent liabilities, $2.5 million and $1.3 million at June 30, 2018 and December 31, 2017, respectively. (3) Included within foreign exchange contracts at June 30, 2018 were $96.3 million of call options offset with $92.0 million of put options, and $27.2 million of buy forwards. Included within foreign exchange contracts at December 31, 2017 were $141.0 million of call options offset with $141.0 million of put options, and $13.3 million of buy forwards offset with $31.0 million of sell forwards.
Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	The amounts of derivative gains (losses) recognized in accumulated other comprehensive loss for the six-month Commission Compensation Operating Interest Revenue Expense Expense Expense Total June 30, 2018 Cash flow hedges: Interest rate contracts $ — $ — $ — $ 5.9 $ 5.9 Foreign exchange contracts (2.5 ) (2.1 ) (1.5 ) — (6.1 ) Total $ (2.5 ) $ (2.1 ) $ (1.5 ) $ 5.9 $ (0.2 ) June 30, 2017 Cash flow hedges: Interest rate contracts $ — $ — $ — $ (3.0 ) $ (3.0 ) Foreign exchange contracts 6.0 2.0 1.4 — 9.4 Total $ 6.0 $ 2.0 $ 1.4 $ (3.0 ) $ 6.4 The amounts of derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) for the six-month Commission Compensation Operating Interest Revenue Expense Expense Expense Total June 30, 2018 Cash flow hedges: Interest rate contracts $ — $ — $ — $ 0.5 $ 0.5 Foreign exchange contracts 1.1 0.9 0.6 — 2.6 Total $ 1.1 $ 0.9 $ 0.6 $ 0.5 $ 3.1 June 30, 2017 Cash flow hedges: Interest rate contracts $ — $ — $ — $ — $ — Foreign exchange contracts (5.3 ) 0.7 0.5 — (4.1 ) Total $ (5.3 ) $ 0.7 $ 0.5 $ — $ (4.1 )

Commitments, Contingencies an36

Commitments, Contingencies and Off-Balance Sheet Arrangements (Tables)	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligations	Our future minimum cash payments, including interest, associated with our contractual obligations pursuant to the note purchase agreements, Credit Agreement, Premium Financing Debt Facility, operating leases and purchase commitments at June 30, 2018 were as follows (in millions): Payments Due by Period Contractual Obligations 2018 2019 2020 2021 2022 Thereafter Total Note purchase agreements $ 50.0 $ 100.0 $ 100.0 $ 75.0 $ 200.0 $ 2,723.0 $ 3,248.0 Credit Agreement 135.0 — — — — — 135.0 Premium Financing Debt Facility 111.1 — — — — — 111.1 Interest on debt 70.4 137.4 132.7 127.9 122.4 557.6 1,148.4 Total debt obligations 366.5 237.4 232.7 202.9 322.4 3,280.6 4,642.5 Operating lease obligations 54.7 100.1 85.6 73.3 57.3 144.9 515.9 Less sublease arrangements (0.8 ) (0.8 ) (0.6 ) (0.6 ) (0.4 ) (1.2 ) (4.4 ) Outstanding purchase obligations 24.4 38.0 26.5 14.2 10.8 28.7 142.6 Funding related to the acquistion of Reassurance Holdings, Inc., (see Note 4) 122.1 — — — — — 122.1 Total contractual obligations $ 566.9 $ 374.7 $ 344.2 $ 289.8 $ 390.1 $ 3,453.0 $ 5,418.7
Off-Balance Sheet Commitments	Off-Balance - Total Amount of Commitment Expiration by Period Amounts Off-Balance 2018 2019 2020 2021 2022 Thereafter Committed Letters of credit $ — $ — $ — $ — $ — $ 16.5 $ 16.5 Financial guarantees 0.1 0.2 0.2 0.2 0.2 0.8 1.7 Total commitments $ 0.1 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 17.3 $ 18.2

Accumulated Other Comprehensi37

Accumulated Other Comprehensive Earnings (Loss) (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests	The after-tax Pension Foreign Fair Value of Accumulated Balance as of December 31, 2017, as previously reported $ (43.0 ) $ (525.8 ) $ 8.9 $ (559.9 ) Adoption of ASC Topic 606 — 4.5 — 4.5 Balance as of December 31, 2017, as restated (43.0 ) (521.3 ) 8.9 (555.4 ) Reclassifications to retained earnings of income tax effects related to the Tax Act (7.9 ) — 1.3 (6.6 ) Net change in period 1.5 (88.4 ) (2.5 ) (89.4 ) Balance as of June 30, 2018 $ (49.4 ) $ (609.7 ) $ 7.7 $ (651.4 )

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information by Segment	Financial information relating to our segments for the three-month and six-month Three-month period Six-month ended June 30, ended June 30, 2017 2017 2018 As Restated for 2018 As Restated for Brokerage Total revenues $ 1,000.1 $ 896.1 $ 2,195.7 $ 1,981.0 Earnings before income taxes $ 170.6 $ 125.1 $ 489.5 $ 401.6 Identifiable assets at June 30, 2018 and 2017 $ 13,779.0 $ 13,202.9 Risk Management Total revenues $ 237.3 $ 216.8 $ 467.2 $ 426.7 Earnings before income taxes $ 24.0 $ 20.6 $ 45.6 $ 42.7 Identifiable assets at June 30, 2018 and 2017 $ 739.5 $ 714.7 Corporate Total revenues $ 423.0 $ 376.6 $ 835.2 $ 728.2 Loss before income taxes $ (91.0 ) $ (91.6 ) $ (189.2 ) $ (190.6 ) Identifiable assets at June 30, 2018 and 2017 $ 1,712.0 $ 1,761.8
Summary of Revenues by Type and Segment	Revenues by type and segment for the three-month period ended June 30, 2018 are as follows (in millions): Brokerage Risk Corporate Total Revenues: Commissions $ 688.0 $ — $ — $ 688.0 Fees 220.4 201.8 — 422.2 Supplemental revenues 48.1 — — 48.1 Contingent revenues 21.8 — — 21.8 Investment income 15.7 0.1 — 15.8 Gains on books of business sales 6.1 — — 6.1 Revenues from clean coal activities — — 422.4 422.4 Other net revenues — — 0.6 0.6 Revenues before reimbursements 1,000.1 201.9 423.0 1,625.0 Reimbursements — 35.4 — 35.4 Total revenues $ 1,000.1 $ 237.3 $ 423.0 $ 1,660.4 Revenues by type and segment for the six-month Brokerage Risk Corporate Total Revenues: Commissions $ 1,527.4 $ — $ — $ 1,527.4 Fees 473.6 396.7 — 870.3 Supplemental revenues 100.1 — — 100.1 Contingent revenues 56.7 — — 56.7 Investment income 28.9 0.3 — 29.2 Gains on books of business sales 9.0 — — 9.0 Revenues from clean coal activities — — 834.6 834.6 Other net revenues — — 0.6 0.6 Revenues before reimbursements 2,195.7 397.0 835.2 3,427.9 Reimbursements — 70.2 — 70.2 Total revenues $ 2,195.7 $ 467.2 $ 835.2 $ 3,498.1 Revenues by type and segment for the three-month period ended June 30, 2017, as restated for the adoption of ASC Topic 606, are as follows (in millions): Brokerage Risk Corporate Total Revenues: Commissions $ 618.2 $ — $ — $ 618.2 Fees 205.5 181.4 — 386.9 Supplemental revenues 35.8 — — 35.8 Contingent revenues 21.3 — — 21.3 Investment income 14.2 0.2 — 14.4 Gains on books of business sales 1.1 — — 1.1 Revenues from clean coal activities — — 376.4 376.4 Other net gains — — 0.2 0.2 Revenues before reimbursements 896.1 181.6 376.6 1,454.3 Reimbursements — 35.2 — 35.2 Total revenues $ 896.1 $ 216.8 $ 376.6 $ 1,489.5 Revenues by type and segment for the six-month Brokerage Risk Corporate Total Revenues: Commissions $ 1,378.9 $ — $ — $ 1,378.9 Fees 433.8 358.1 — 791.9 Supplemental revenues 83.1 — — 83.1 Contingent revenues 56.3 — — 56.3 Investment income 26.4 0.3 — 26.7 Gains on books of business sales 2.5 — — 2.5 Revenues from clean coal activities — — 728.2 728.2 Revenues before reimbursements 1,981.0 358.4 728.2 3,067.6 Reimbursements — 68.3 — 68.3 Total revenues $ 1,981.0 $ 426.7 $ 728.2 $ 3,135.9
Summary of Geographical Location and Segment	Revenues by geographical location and segment for the three-month period ended June 30, 2018 are as follows (in millions): Brokerage Risk Corporate Total Revenues: United States $ 615.5 $ 197.3 $ 423.0 $ 1,235.8 United Kingdom 204.4 8.8 — 213.2 Australia 53.9 25.7 — 79.6 Canada 47.8 1.2 — 49.0 New Zealand 39.4 4.3 — 43.7 Other foreign 39.1 — — 39.1 Total revenues $ 1,000.1 $ 237.3 $ 423.0 $ 1,660.4 Revenues by geographical location and segment for the six-month Brokerage Risk Corporate Total Revenues: United States $ 1,468.3 $ 390.1 $ 835.2 $ 2,693.6 United Kingdom 395.4 17.7 — 413.1 Australia 97.5 49.4 — 146.9 Canada 90.6 2.2 — 92.8 New Zealand 69.5 7.8 — 77.3 Other foreign 74.4 — — 74.4 Total revenues $ 2,195.7 $ 467.2 $ 835.2 $ 3,498.1 Revenues by geographical location and segment for the three-month period ended June 30, 2017, as restated for the adoption of ASC Topic 606, are as follows (in millions): Brokerage Risk Corporate Total Revenues: United States $ 552.1 $ 185.3 $ 376.6 $ 1,114.0 United Kingdom 184.7 7.2 — 191.9 Australia 52.0 19.1 — 71.1 Canada 36.6 0.9 — 37.5 New Zealand 36.8 4.3 — 41.1 Other foreign 33.9 — — 33.9 Total revenues $ 896.1 $ 216.8 $ 376.6 $ 1,489.5 Revenues by geographical location and segment for the six-month Brokerage Risk Corporate Total Revenues: United States $ 1,345.1 $ 367.7 $ 728.2 $ 2,441.0 United Kingdom 346.0 13.6 — 359.6 Australia 92.3 37.8 — 130.1 Canada 68.7 1.7 — 70.4 New Zealand 63.9 5.9 — 69.8 Other foreign 65.0 — — 65.0 Total revenues $ 1,981.0 $ 426.7 $ 728.2 $ 3,135.9

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018CountrySegment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable operating segments | Segment	3
Number of commercial clean coal production facilities	34
Number of countries in which the company has operations	34
Number of countries in which the company does business through a network of correspondent brokers and consultants	150
Description of contracts renewal period	One year or less.
Percentage of commission and fee revenues on the effective date	70.00%
Percentage of commission and fee revenues in the first three months	20.00%
Percentage of commission and fee revenues after the first three months	10.00%

Effect of New Accounting Pron40

Effect of New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	Jan. 01, 2016	Jun. 30, 2018	Jun. 30, 2017	[1]	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Corporate income tax rate		21.00%			35.00%
Net cash provided by operating activities		$ 313.3	$ 260.9
Effect of changes in foreign exchange rates on cash, cash equivalents and restricted cash		(29.5)	$ 34.8
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities					$ 55.5
Cash paid for acquisitions, net of cash and restricted cash					11.1
Effect of changes in foreign exchange rates on cash, cash equivalents and restricted cash					$ 22.4
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption recognized as an increase to retained earnings	$ 125.3
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in retained earnings		$ 6.6
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Effect of New Accounting Pron41

Effect of New Accounting Pronouncements - Summary of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017		Jun. 30, 2017		Dec. 31, 2016	[1]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Cash and cash equivalents	$ 652.2	$ 681.2	[1]	$ 587.8
Restricted cash	1,692.5	1,623.8	[1]	1,481.1
Total cash, cash equivalents and restricted cash	$ 2,344.7	$ 2,305		$ 2,068.9	[1]	$ 1,937.6
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C42

Revenue from Contracts with Customers - Summary of Consolidated Statement of Earnings Line Items, which Reflect Adoption of New Revenue Recognition Guidance (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues before reimbursements	$ 1,625	$ 1,454.3	[1]	$ 3,427.9	$ 3,067.6	[1]
Total revenues	1,660.4	1,489.5	[1]	3,498.1	3,135.9	[1]
Compensation	724.7	666.9	[1]	1,500.5	1,378.7	[1]
Operating	222.8	204.2	[1]	438.9	403.7	[1]
Reimbursements	35.4	35.2	[1]	70.2	68.3	[1]
Interest	33.9	31.6	[1]	65.2	61.5	[1]
Depreciation	30.8	30.2	[1]	61.4	59.7	[1]
Amortization	73.4	65.1	[1]	141.6	129.4	[1]
Change in estimated acquisition earnout payables	(6)	5.1	[1]	1.4	16.9	[1]
Total expenses	1,556.8	1,435.4	[1]	3,152.2	2,882.2	[1]
Earnings before income taxes	103.6	54.1	[1]	345.9	253.7	[1]
Benefit for income taxes	(20.1)	(24.2)	[1]	(63.8)	(66.6)	[1]
Net earnings	123.7	78.3	[1]	409.7	320.3	[1]
Net earnings attributable to noncontrolling interests	8.8	8.3	[1]	21.1	21.5	[1]
Net earnings attributable to controlling interests	$ 114.9	$ 70	[1]	$ 388.6	$ 298.8	[1]
Basic net earnings per share	$ 0.63	$ 0.39	[1]	$ 2.14	$ 1.67	[1]
Diluted net earnings per share	0.62	0.39	[1]	2.10	1.65	[1]
Dividends declared per common share	$ 0.41	$ 0.39	[1]	$ 0.82	$ 0.78	[1]
Commissions [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 688	$ 618.2	[1]	$ 1,527.4	$ 1,378.9	[1]
Broker Fees [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	422.2	386.9	[1]	870.3	791.9	[1]
Supplemental Revenue Member [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	48.1	35.8	[1]	100.1	83.1	[1]
Contingent Revenue [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	21.8	21.3	[1]	56.7	56.3	[1]
Investment income [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	15.8	14.4	[1]	29.2	26.7	[1]
Gains on Books of Business Sales [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	6.1	1.1	[1]	9	2.5	[1]
Clean Coal Activities [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	422.4	376.4	[1]	834.6	728.2	[1]
Cost of revenues from clean coal activities	441.8	397.1	[1]	873	764	[1]
Product and Service, Other [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	0.6	0.2	[1]	0.6
Reimbursements [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 35.4	35.2	[1]	$ 70.2	68.3	[1]
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues before reimbursements		1,563.4			2,976.1
Total revenues		1,563.4			2,976.1
Compensation		675.7			1,333.3
Operating		211.6			412
Interest		31.6			61.5
Depreciation		30.2			59.7
Amortization		65.1			129.4
Change in estimated acquisition earnout payables		5.1			16.9
Total expenses		1,416.4			2,776.8
Earnings before income taxes		147			199.3
Benefit for income taxes		(33.4)			(48.9)
Net earnings		180.4			248.2
Net earnings attributable to noncontrolling interests		8.5			20.6
Net earnings attributable to controlling interests		$ 171.9			$ 227.6
Basic net earnings per share		$ 0.96			$ 1.27
Diluted net earnings per share		0.95			1.26
Dividends declared per common share		$ 0.39			$ 0.78
As Previously Reported [Member] | Commissions [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		$ 690.2			$ 1,280.7
As Previously Reported [Member] | Broker Fees [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		410.9			781.4
As Previously Reported [Member] | Supplemental Revenue Member [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		41.5			76
As Previously Reported [Member] | Contingent Revenue [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		29.5			82.9
As Previously Reported [Member] | Investment income [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		13.6			24.4
As Previously Reported [Member] | Gains on Books of Business Sales [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		1.1			2.5
As Previously Reported [Member] | Clean Coal Activities [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		376.4			728.2
Cost of revenues from clean coal activities		397.1			764
As Previously Reported [Member] | Product and Service, Other [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		0.2
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues before reimbursements		(109.1)			91.5
Total revenues		(73.9)			159.8
Compensation		(8.8)			45.4
Operating		(7.4)			(8.3)
Reimbursements		35.2			68.3
Total expenses		19			105.4
Earnings before income taxes		(92.9)			54.4
Benefit for income taxes		9.2			(17.7)
Net earnings		(102.1)			72.1
Net earnings attributable to noncontrolling interests		(0.2)			0.9
Net earnings attributable to controlling interests		$ (101.9)			$ 71.2
Basic net earnings per share		$ (0.57)			$ 0.40
Diluted net earnings per share		$ (0.56)			$ 0.39
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Commissions [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		$ (72)			$ 98.2
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Broker Fees [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		(24)			10.5
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Supplemental Revenue Member [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		(5.7)			7.1
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Contingent Revenue [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		(8.2)			(26.6)
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Investment income [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		0.8			2.3
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member] | Reimbursements [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		$ 35.2			$ 68.3
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C43

Revenue from Contracts with Customers - Summary of Consolidated Statement of Comprehensive Earnings Line Items, which Reflect Adoption of New Revenue Recognition Guidance (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net earnings	$ 123.7	$ 78.3	[1]	$ 409.7	$ 320.3	[1]
Change in pension liability, net of taxes	(5.5)	1.4	[1]	1.5	2.6	[1]
Foreign currency translation	(150.7)	33.5	[1]	(88.4)	89.4	[1]
Change in fair value of derivative instruments, net of taxes	4.3	2.3	[1]	(2.5)	8.8	[1]
Comprehensive earnings	(28.2)	115.5	[1]	320.3	421.1	[1]
Comprehensive earnings attributable to noncontrolling interests	3.3	8.7	[1]	17.8	23.5	[1]
Comprehensive earnings attributable to controlling interests	$ (31.5)	106.8	[1]	$ 302.5	397.6	[1]
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net earnings		180.4			248.2
Change in pension liability, net of taxes		1.4			2.6
Foreign currency translation		33.9			92.3
Change in fair value of derivative instruments, net of taxes		2.3			8.8
Comprehensive earnings		218			351.9
Comprehensive earnings attributable to noncontrolling interests		8.9			22.6
Comprehensive earnings attributable to controlling interests		209.1			329.3
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net earnings		(102.1)			72.1
Foreign currency translation		(0.4)			(2.9)
Comprehensive earnings		(102.5)			69.2
Comprehensive earnings attributable to noncontrolling interests		(0.2)			0.9
Comprehensive earnings attributable to controlling interests		$ (102.3)			$ 68.3
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C44

Revenue from Contracts with Customers - Summary of Balance Sheet Line Items, which Reflect Adoption of New Revenue Recognition Guidance (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premium and fees receivables	$ 5,142.2	$ 4,082.8	[1]
Other current assets	878.1	881.6	[1]
Deferred income taxes	716.3	851.6	[1]
Other noncurrent assets	586.7	567.1	[1]
Goodwill	4,403.9	4,164.8	[1]
Liabilities
Premiums payable to underwriting enterprises	5,982.7	4,986	[1]
Accrued compensation and other current liabilities	844.6	947.8	[1]
Deferred revenue - current/unearned fees	395.2	355.3	[1]
Deferred revenue - noncurrent	76.6	75.3	[1]
Other noncurrent liabilities	931.2	1,112.6	[1]
Stockholders' equity
Retained earnings	1,466	1,221.8	[1]
Accumulated other comprehensive loss	(651.4)	(555.4)	[1]
Stockholders' equity attributable to controlling interests	4,443.6	4,235.6	[1]
Stockholders' equity attributable to noncontrolling interests	$ 69.5	64.1	[1]
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Goodwill		(33.1)
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premium and fees receivables		2,157.2
Other current assets		708.4
Deferred income taxes		905.1
Other noncurrent assets		567
Goodwill		4,197.9
Liabilities
Premiums payable to underwriting enterprises		3,475.9
Accrued compensation and other current liabilities		864.1
Deferred revenue - current/unearned fees		74.8
Other current liabilities		56.4
Other noncurrent liabilities		1,128.3
Stockholders' equity
Retained earnings		1,095.9
Accumulated other comprehensive loss		(559.9)
Stockholders' equity attributable to controlling interests		4,105.2
Stockholders' equity attributable to noncontrolling interests		59.7
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Premium and fees receivables		1,925.6
Other current assets		173.2
Deferred income taxes		(53.5)
Other noncurrent assets		0.1
Goodwill		(33.1)
Liabilities
Premiums payable to underwriting enterprises		1,510.1
Accrued compensation and other current liabilities		83.7
Deferred revenue - current/unearned fees		280.5
Other current liabilities		(56.4)
Deferred revenue - noncurrent		75.3
Other noncurrent liabilities		(15.7)
Stockholders' equity
Retained earnings		125.9
Accumulated other comprehensive loss		4.5
Stockholders' equity attributable to controlling interests		130.4
Stockholders' equity attributable to noncontrolling interests		$ 4.4
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C45

Revenue from Contracts with Customers - Summary of Consolidated Statement of Cash Flows Line Items, which Reflect Adoption of New Revenue Recognition Guidance (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net earnings	$ 123.7	$ 78.3	[1]	$ 409.7	$ 320.3	[1]
Adjustments to reconcile net earnings to net cash provided by operating activities:
Net change in premiums and fees receivable					(1,534.4)
Net change in deferred revenue				32.4	29.7	[1]
Net change in premiums payable to underwriting enterprises				1,106.9	1,379.4	[1]
Net change in other current assets				1	33.3	[1]
Net change in accrued compensation and other current liabilities				(135.7)	(57.8)	[1]
Net change in deferred income taxes				(146.4)	(90.5)	[1]
Net change in other noncurrent assets and liabilities				$ (65.7)	(20.2)	[1]
As Previously Reported [Member]
Cash flows from operating activities
Net earnings		180.4			248.2
Adjustments to reconcile net earnings to net cash provided by operating activities:
Net change in premiums and fees receivable					(478.7)
Net change in premiums payable to underwriting enterprises					445.1
Net change in other current assets					(17.4)
Net change in accrued compensation and other current liabilities					(77)
Net change in deferred income taxes					(72.9)
Net change in other noncurrent assets and liabilities					(18.4)
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Cash flows from operating activities
Net earnings		$ (102.1)			72.1
Adjustments to reconcile net earnings to net cash provided by operating activities:
Net change in premiums and fees receivable					(1,055.7)
Net change in deferred revenue					29.7
Net change in premiums payable to underwriting enterprises					934.3
Net change in other current assets					50.7
Net change in accrued compensation and other current liabilities					19.2
Net change in deferred income taxes					(17.6)
Net change in other noncurrent assets and liabilities					$ (1.8)
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C46

Revenue from Contracts with Customers - Summary of Statement of Stockholders' Equity Items, which Reflect Adoption of New Revenue Recognition Guidance (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported	$ 4,513.1	$ 4,299.7	[1]
Balance at December 31, 2017, as restated		4,299.7
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		134.8
As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported		4,164.9
Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		134.8
Retained Earnings [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported	1,466
Balance at December 31, 2017, as restated		1,221.8
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		125.9
Retained Earnings [Member] | As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported		1,095.9
Retained Earnings [Member] | Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		125.9
Accumulated Other Comprehensive Earnings (Loss) [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported	(651.4)
Balance at December 31, 2017, as restated		(555.4)
Accumulated Other Comprehensive Earnings (Loss) [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		4.5
Accumulated Other Comprehensive Earnings (Loss) [Member] | As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported		(559.9)
Accumulated Other Comprehensive Earnings (Loss) [Member] | Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		4.5
Noncontrolling Interests [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported	$ 69.5
Balance at December 31, 2017, as restated		64.1
Noncontrolling Interests [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		4.4
Noncontrolling Interests [Member] | As Previously Reported [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Balance at December 31, 2017, as reported		59.7
Noncontrolling Interests [Member] | Impact of Adoption of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative-effect adjustment due to ASC Topic 606 as of December 31, 2017		$ 4.4
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Revenue from Contracts with C47

Revenue from Contracts with Customers - Summary of Unbilled Receivables, Contract Assets and Contract Liabilities from Contracts with Customers (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Contract with Customer, Asset and Liability [Abstract]
Unbilled receivables	$ 608.7	$ 415.2
Deferred contract costs	55	83.3
Deferred revenue	$ 471.8	$ 430.6

Revenue from Contracts with C48

Revenue from Contracts with Customers - Summary of Changes in Deferred Revenue Balances (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	$ 430.6
Incremental deferred revenue	277.5
Revenue recognized during the six-month period ended June 30, 2018 included in deferred revenue at December 31, 2017	(249.2)
Deferred revenue recognized from business acquisitions	12.9
Deferred revenue ending balance	471.8
Brokerage [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	258.7
Incremental deferred revenue	204.1
Revenue recognized during the six-month period ended June 30, 2018 included in deferred revenue at December 31, 2017	(181)
Deferred revenue recognized from business acquisitions	12.9
Deferred revenue ending balance	294.7
Risk Management [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	171.9
Incremental deferred revenue	73.4
Revenue recognized during the six-month period ended June 30, 2018 included in deferred revenue at December 31, 2017	(68.2)
Deferred revenue ending balance	$ 177.1

Revenue from Contracts with C49

Revenue from Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 471.8
Deferred contract costs	55	$ 83.3
Amortization of deferred contract costs	$ 168.5		$ 153.4

Revenue from Contracts with C50

Revenue from Contracts with Customers - Summary of Expected Revenue Related to Performance Obligations (Detail) $ in Millions	Jun. 30, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 471.8
2018 (Remaining Six Months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	294.2
2019 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	107.1
2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	28.1
2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	12.7
2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	7.2
Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	22.5
Brokerage [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	294.7
Brokerage [Member] | 2018 (Remaining Six Months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	224.3
Brokerage [Member] | 2019 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	59.6
Brokerage [Member] | 2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	8.2
Brokerage [Member] | 2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	1.7
Brokerage [Member] | 2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	0.4
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	177.1
Risk Management [Member] | 2018 (Remaining Six Months) [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	69.9
Risk Management [Member] | 2019 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	47.5
Risk Management [Member] | 2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	19.9
Risk Management [Member] | 2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	11
Risk Management [Member] | 2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	6.8
Risk Management [Member] | Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 22

Business Combinations - Acquisi

Business Combinations - Acquisition Method for Recording Business Combinations (Detail) - USD ($) shares in Thousands	Jun. 26, 2018	Jun. 30, 2018
Business Acquisition [Line Items]
Common Shares Issued		273
Common Share Value	$ 24,400,000	$ 15,900,000
Cash Paid		424,200,000
Accrued Liability		400,000
Escrow Deposited		35,300,000
Recorded Earnout Payable		31,000,000
Total Recorded Purchase Price		506,800,000
Maximum Potential Earnout Payable		$ 71,100,000
Market Financial Group, Ltd and Austin Consulting Group Inc. (MFG) [Member]
Business Acquisition [Line Items]
Common Shares Issued		53
Common Share Value		$ 3,700,000
Cash Paid		33,900,000
Escrow Deposited		4,200,000
Recorded Earnout Payable		4,000,000
Total Recorded Purchase Price		45,800,000
Maximum Potential Earnout Payable		7,000,000
McGregor & Associates (M&A) [Member]
Business Acquisition [Line Items]
Cash Paid		13,500,000
Escrow Deposited		2,500,000
Recorded Earnout Payable		5,100,000
Total Recorded Purchase Price		21,100,000
Maximum Potential Earnout Payable		12,000,000
Pronto Insurance (PI) [Member]
Business Acquisition [Line Items]
Cash Paid		294,800,000
Escrow Deposited		18,700,000
Total Recorded Purchase Price		$ 313,500,000
Sixteen Other Acquisitions [Member]
Business Acquisition [Line Items]
Common Shares Issued		220
Common Share Value		$ 12,200,000
Cash Paid		82,000,000
Accrued Liability		400,000
Escrow Deposited		9,900,000
Recorded Earnout Payable		21,900,000
Total Recorded Purchase Price		126,400,000
Maximum Potential Earnout Payable		$ 52,100,000

Business Combinations - Acqui52

Business Combinations - Acquisition Method for Recording Business Combinations (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2018
Market Financial Group, Ltd and Austin Consulting Group Inc. (MFG) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jan. 1, 2018
McGregor & Associates (M&A) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Mar. 1, 2018
Pronto Insurance (PI) [Member]
Business Acquisition [Line Items]
Effective Date of Acquisition	Jun. 5, 2018
Sixteen Other Acquisitions [Member]
Business Acquisition [Line Items]
Effective Year of Acquisition	2,018

Business Combinations - Additio

Business Combinations - Additional Information (Detail)	Jun. 26, 2018USD ($)	Jun. 30, 2018USD ($)Entity	Jun. 30, 2017USD ($)Entity	Jun. 30, 2018USD ($)Entity	Jun. 30, 2017USD ($)Entity	Jun. 30, 2018USD ($)Entity
Business Acquisition [Line Items]
Maximum Potential Earnout Payable		$ 71,100,000		$ 71,100,000		$ 71,100,000
Percentage of interest acquired in acquired entity	100.00%
Business acquisition, consideration paid in shares	$ 24,400,000			15,900,000
Accretion of the discount on acquisition		4,900,000	$ 5,200,000	10,000,000	$ 10,300,000
Expense related to net adjustments to estimated fair value of liability for earnout obligations		$ 10,900,000	$ 100,000	$ 8,600,000	$ 6,600,000
Number of companies acquired | Entity		49	46	76	65	478
Aggregate amount of maximum earnout obligations related to acquisitions		$ 552,300,000		$ 552,300,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet		266,900,000		266,900,000
Goodwill		294,500,000		294,500,000		$ 294,500,000
Expiration lists		204,000,000		204,000,000		204,000,000
Non-compete agreements		1,700,000		1,700,000		1,700,000
Trade names		35,400,000		35,400,000		35,400,000
Write-off of amortizable intangible assets		5,600,000	$ 1,700,000	5,600,000	$ 1,700,000
Total revenues related to acquisitions in the aggregate		1,683,400,000	$ 1,525,800,000	3,560,700,000	$ 3,211,600,000
Brokerage and Risk Management [Member]
Business Acquisition [Line Items]
Goodwill		294,500,000		294,500,000		294,500,000
Expiration lists		204,000,000		204,000,000		204,000,000
Non-compete agreements		1,700,000		1,700,000		1,700,000
Trade names		$ 35,400,000		$ 35,400,000		$ 35,400,000
Expiration Lists [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years				2 years
Expiration Lists [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years				15 years
Non-Compete Agreements [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years				3 years
Non-Compete Agreements [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years				5 years
Trade Names [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years				2 years
Trade Names [Member] | Maximum [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		3
2018 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input		15		15		15
2018 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input		8		8		8
2018 Acquisitions [Member] | Valuation, Market Approach [Member] | Measurement Input, Discount Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input		9.5		9.5		9.5
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Minimum [Member]
Business Acquisition [Line Items]
Attrition rate				5.00%	5.00%
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Maximum [Member]
Business Acquisition [Line Items]
Attrition rate				10.00%	10.00%
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input		3,000,000	3,000,000	3,000,000	3,000,000	3,000,000
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Long-term Revenue Growth Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input		3,500,000	3,500,000	3,500,000	3,500,000	3,500,000
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Discount Rate [Member] | Minimum [Member]
Business Acquisition [Line Items]
Measurement input		12,000,000	12,000,000	12,000,000	12,000,000	12,000,000
2017 Acquisitions [Member] | Valuation, Income Approach [Member] | Measurement Input, Discount Rate [Member] | Maximum [Member]
Business Acquisition [Line Items]
Measurement input		14,000,000	14,000,000	14,000,000	14,000,000	14,000,000
Business Acquisition [Member]
Business Acquisition [Line Items]
Annualized revenue of business acquisitions				$ 175,100,000
Total revenues related to acquisitions in the aggregate				26,700,000
Net earnings				3,200,000
Business Acquisition [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Expiration lists		$ 204,000,000		204,000,000		$ 204,000,000
Non-compete agreements		1,700,000		1,700,000		1,700,000
Trade names		35,400,000		35,400,000		35,400,000
Deferred tax liability		35,800,000		35,800,000		35,800,000
Goodwill related to nondeductible amortizable intangible assets				35,800,000
Business Acquisition [Member] | Expiration Lists [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		132,700,000		132,700,000		132,700,000
Business Acquisition [Member] | Non-Compete Agreements [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		1,100,000		1,100,000		1,100,000
Business Acquisition [Member] | Trade Names [Member] | Brokerage [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		$ 35,400,000		$ 35,400,000		$ 35,400,000
DiBrina Group (DBG) [Member] | Canada [Member] | Definitive Agreement [Member]
Business Acquisition [Line Items]
Cash consideration	97,700,000
Maximum Potential Earnout Payable	$ 21,500,000

Business Combinations - Summary

Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) $ in Millions	Jun. 30, 2018USD ($)
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	$ 12.3
Other current assets	59.4
Fixed assets	4.8
Noncurrent assets	8.3
Goodwill	294.5
Expiration lists	204
Non-compete agreements	1.7
Trade names	35.4
Total assets acquired	620.4
Current liabilities	53.5
Noncurrent liabilities	60.1
Total liabilities assumed	113.6
Total net assets acquired	506.8
Market Financial Group, Ltd and Austin Consulting Group Inc. (MFG) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	0.1
Other current assets	3
Fixed assets	0.4
Goodwill	24.7
Expiration lists	20.2
Non-compete agreements	0.1
Total assets acquired	48.5
Current liabilities	2.3
Noncurrent liabilities	0.4
Total liabilities assumed	2.7
Total net assets acquired	45.8
McGregor & Associates (M&A) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Other current assets	0.5
Fixed assets	1.4
Goodwill	5.2
Expiration lists	15.1
Non-compete agreements	0.1
Total assets acquired	22.3
Current liabilities	0.4
Noncurrent liabilities	0.8
Total liabilities assumed	1.2
Total net assets acquired	21.1
Pronto Insurance (PI) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	7.2
Other current assets	35.3
Fixed assets	2.6
Noncurrent assets	8.3
Goodwill	194.1
Expiration lists	105.7
Non-compete agreements	0.3
Trade names	35.4
Total assets acquired	388.9
Current liabilities	31.5
Noncurrent liabilities	43.9
Total liabilities assumed	75.4
Total net assets acquired	313.5
Sixteen Other Acquisitions [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash	5
Other current assets	20.6
Fixed assets	0.4
Goodwill	70.5
Expiration lists	63
Non-compete agreements	1.2
Total assets acquired	160.7
Current liabilities	19.3
Noncurrent liabilities	15
Total liabilities assumed	34.3
Total net assets acquired	$ 126.4

Business Combinations - Summa55

Business Combinations - Summary of Unaudited Pro Forma Historical Results (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Combinations [Abstract]
Total revenues	$ 1,683.4	$ 1,525.8	$ 3,560.7	$ 3,211.6
Net earnings attributable to controlling interests	$ 116.8	$ 71.9	$ 395.8	$ 306
Basic net earnings per share	$ 0.64	$ 0.40	$ 2.17	$ 1.70
Diluted net earnings per share	$ 0.63	$ 0.40	$ 2.13	$ 1.69

Other Current Assets - Summary

Other Current Assets - Summary of Major Classes of Other Current Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Premium finance advances and loans	$ 302.8	$ 305.5
Accrued supplemental, direct bill and other receivables	251.9	244.5
Refined coal production related receivables	173	156.8
Deferred contract costs	55	83.3
Prepaid expenses	95.4	91.5
Total other current assets	$ 878.1	$ 881.6	[1]
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Other Current Assets - Addition

Other Current Assets - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
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	Jun. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Total goodwill - net	$ 4,403.9	$ 4,164.8	[1]
Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	2,570.4	2,306.7
United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	739.2	745.7
Canada [Member]
Goodwill [Line Items]
Total goodwill - net	360	374
Australia [Member]
Goodwill [Line Items]
Total goodwill - net	400.7	416.6
New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	214.9	218.9
Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	118.7	102.9
Brokerage [Member]
Goodwill [Line Items]
Total goodwill - net	4,358.5	4,119.2
Brokerage [Member] | Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	2,545.3	2,280.9
Brokerage [Member] | United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	732.1	738.5
Brokerage [Member] | Canada [Member]
Goodwill [Line Items]
Total goodwill - net	360	374
Brokerage [Member] | Australia [Member]
Goodwill [Line Items]
Total goodwill - net	400.7	416.6
Brokerage [Member] | New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	204.5	209.3
Brokerage [Member] | Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	115.9	99.9
Risk Management [Member]
Goodwill [Line Items]
Total goodwill - net	42.6	42.6
Risk Management [Member] | Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	25.1	25.8
Risk Management [Member] | United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	7.1	7.2
Risk Management [Member] | New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	10.4	9.6
Corporate [Member]
Goodwill [Line Items]
Total goodwill - net	2.8	3
Corporate [Member] | Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	$ 2.8	$ 3
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Intangible Assets - Changes in

Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Goodwill [Line Items]
Beginning Balance	$ 4,164.8	[1]
Goodwill acquired during the period	294.5
Goodwill adjustments due to appraisals and other acquisition adjustments	0.2
Foreign currency translation adjustments during the period	(55.6)
Ending Balance	4,403.9
As Previously Reported [Member]
Goodwill [Line Items]
Beginning Balance	4,197.9
Accounting Standards Update 2014-09 [Member]
Goodwill [Line Items]
Beginning Balance	(33.1)
Brokerage [Member]
Goodwill [Line Items]
Beginning Balance	4,119.2
Goodwill acquired during the period	291.8
Goodwill adjustments due to appraisals and other acquisition adjustments	2.5
Foreign currency translation adjustments during the period	(55)
Ending Balance	4,358.5
Brokerage [Member] | As Previously Reported [Member]
Goodwill [Line Items]
Beginning Balance	4,152.3
Brokerage [Member] | Accounting Standards Update 2014-09 [Member]
Goodwill [Line Items]
Beginning Balance	(33.1)
Risk Management [Member]
Goodwill [Line Items]
Beginning Balance	42.6
Goodwill acquired during the period	2.7
Goodwill adjustments due to appraisals and other acquisition adjustments	(2.3)
Foreign currency translation adjustments during the period	(0.4)
Ending Balance	42.6
Risk Management [Member] | As Previously Reported [Member]
Goodwill [Line Items]
Beginning Balance	42.6
Corporate [Member]
Goodwill [Line Items]
Beginning Balance	3
Foreign currency translation adjustments during the period	(0.2)
Ending Balance	2.8
Corporate [Member] | As Previously Reported [Member]
Goodwill [Line Items]
Beginning Balance	$ 3
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Intangible Assets - Major Class

Intangible Assets - Major Classes of Amortizable Intangible Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net	$ 1,731	$ 1,644.6	[1]
Expiration Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	3,233.4	3,055.9
Accumulated amortization	(1,547.5)	(1,422.1)
Amortizable intangible assets, net	1,685.9	1,633.8
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	54.9	53.5
Accumulated amortization	(47.4)	(46.1)
Amortizable intangible assets, net	7.5	7.4
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	60.6	25.9
Accumulated amortization	(23)	(22.5)
Amortizable intangible assets, net	$ 37.6	$ 3.4
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Intangible Assets - Estimated A

Intangible Assets - Estimated Aggregate Amortization Expense (Detail) $ in Millions	Jun. 30, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2018 (remaining six months)	$ 137.7
2,019	263.9
2,020	247.3
2,021	224
2,022	200.7
Thereafter	657.4
Total	$ 1,731

Credit and Other Debt Agreeme62

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 3,494.1	$ 3,139.1
Less unamortized debt acquisition costs on Note Purchase Agreements	(7)	(6.1)
Semi-annual payments of interest, Net	3,487.1	3,133
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	3,248	2,798
Fixed Rate of 2.80%, Balloon Due June 24, 2018 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		50
Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member] | Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
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 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]
Debt Instrument [Line Items]
Quarterly payments of interest	50	50
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]
Debt Instrument [Line Items]
Quarterly payments of interest	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 4.73%, 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
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
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]
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]
Debt Instrument [Line Items]
Semi-annual payments of interest	125
Fixed Rate of 4.69% Balloon Due June 13, 2038 [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75
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	135	190
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	85	116.4
Interbank Rates Plus 1.05% 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	15.8	18.5
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		5.7
Interbank Rates Plus 0.55%, Expires May 18 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	111.1	151.1
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	$ 10.3	$ 10.5

Credit and Other Debt Agreeme63

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	May 18, 2019	May 18, 2019
Fixed Rate of 2.80%, Balloon Due June 24, 2018 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	2.80%	2.80%
Periodic payments of interest and principal, expiry date	Jun. 24, 2018	Jun. 24, 2018
Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.85%	5.85%
Long-Term debt maturities repayments in 2018	$ 50	$ 50
Long-Term debt maturities repayments in 2019	$ 50	$ 50
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	Jun. 24, 2019	Jun. 24, 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	Jun. 24, 2020	Jun. 24, 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	Jul. 10, 2020	Jul. 10, 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	Feb. 10, 2021	Feb. 10, 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	Jun. 14, 2022	Jun. 14, 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	Feb. 10, 2023	Feb. 10, 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	Jun. 24, 2023	Jun. 24, 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	Aug. 2, 2023	Aug. 2, 2023
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
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	Feb. 27, 2024	Feb. 27, 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	Jun. 13, 2024	Jun. 13, 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	Jun. 24, 2025	Jun. 24, 2025
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	Feb. 27, 2026	Feb. 27, 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	Jun. 2, 2026	Jun. 2, 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	Jun. 24, 2026	Jun. 24, 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	Jun. 27, 2027	Jun. 27, 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	Aug. 2, 2027	Aug. 2, 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	Aug. 4, 2027	Aug. 4, 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	Dec. 1, 2027	Dec. 1, 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	Jun. 2, 2028	Jun. 2, 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	Jun. 13, 2028	Jun. 13, 2028
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	Feb. 27, 2029	Feb. 27, 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	Jun. 27, 2029	Jun. 27, 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	Aug. 2, 2029	Aug. 2, 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	Jun. 13, 2030	Jun. 13, 2030
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	Jun. 2, 2031	Jun. 2, 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	Jun. 27, 2032	Jun. 27, 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	Aug. 2, 2032	Aug. 2, 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	Jun. 13, 2033	Jun. 13, 2033
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	Jun. 13, 2038	Jun. 13, 2038
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	Apr. 8, 2021	Apr. 8, 2021
First Installment [Member] | Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Nov. 30, 2018	Nov. 30, 2018
Second Installment [Member] | Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Nov. 30, 2019	Nov. 30, 2019
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 0.55%, 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			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net earnings attributable to controlling interests	$ 114.9	$ 70	[1]	$ 388.6	$ 298.8	[1]
Weighted average number of common shares outstanding	182.4	179.9		181.9	179.4
Dilutive effect of stock options using the treasury stock method	3.1	1.7		3.3	1.7
Weighted average number of common and common equivalent shares outstanding	185.5	181.6		185.2	181.1
Basic net earnings per share	$ 0.63	$ 0.39	[1]	$ 2.14	$ 1.67	[1]
Diluted net earnings per share	$ 0.62	$ 0.39	[1]	$ 2.10	$ 1.65	[1]
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Earnings Per Share - Additional

Earnings Per Share - Additional information (Detail) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Options to purchase common stock shares outstanding	1.7	1.7	1	1

Stock Option Plans - Additional

Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 15, 2018	Mar. 16, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Stock Option Plans [Line Items]
Compensation expense related to stock option grants			$ 1.6	$ 4.4	$ 6.4	$ 8.5
Total intrinsic value of options exercised					33.4	$ 22.8
Total unrecognized compensation cost related to nonvested options			$ 39.7		$ 39.7
Weighted average period, years					4 years
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum number of shares available					3,500,000
Shares available for grant			14,700,000		14,700,000
2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Number of years options expire from date of grant					7 years	7 years
Officer and Key Employees [Member] | 2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Shares available for grant	1,261,000		0	0	0	0
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%
Officer and Key Employees [Member] | 2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Shares available for grant		1,650,400
Stock options granted, exercise percentage, on the third anniversary date of the grant		34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant		33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant		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
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] | 2014 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] | 2014 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					$ 9.27	$ 11.42

Stock Option Plans - Black-Scho

Stock Option Plans - Black-Scholes Option Pricing Model with Weighted Average (Detail)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	2.30%	2.80%
Expected risk-free interest rate	2.70%	2.30%
Volatility	15.10%	27.20%
Expected life (in years)	5 years 6 months	5 years

Stock Option Plans - Stock Opti

Stock Option Plans - Stock Option Activity and Related Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)$ / sharesshares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Under Option, Beginning balance | shares	9.5
Shares Under Option, Granted | shares	1.3
Shares Under Option, Exercised | shares	(1)
Shares Under Option, Forfeited or canceled | shares	(0.2)
Shares Under Option, Ending balance | shares	9.6
Shares Under Option, Exercisable at end of year | shares	2.7
Shares Under Option, Ending vested and expected to vest | shares	6.6
Weighted Average Exercise Price, Beginning balance | $ / shares	$ 45.27
Weighted Average Exercise Price, Granted | $ / shares	70.74
Weighted Average Exercise Price, Exercised | $ / shares	36.37
Weighted Average Exercise Price, Forfeited or canceled | $ / shares	48.73
Weighted Average Exercised Price, Ending balance | $ / shares	49.49
Weighted Average Exercise Price, Exercisable at end of year | $ / shares	42.22
Weighted Average Exercise price, Ending vested and expected to vest | $ / shares	$ 52.05
Weighted Average Remaining Contractual Term (in years), Ending balance	4 years 2 months 12 days
Weighted Average Remaining Contractual Term (in years), Exercisable at end of year	2 years 2 months 16 days
Weighted Average Remaining Contractual Term (in years), Ending vested and expected to vest	4 years 11 months 12 days
Aggregate Intrinsic Value, Ending Balance | $	$ 158.2
Aggregate Intrinsic Value, Exercisable at end of year | $	62.8
Aggregate Intrinsic Value, Ending vested and expected to vest | $	$ 93.8

Stock Option Plans - Stock Op69

Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	$ 35.71
Range of Exercise Prices, maximum	$ 70.74
Option Outstanding, Number Outstanding	9.6
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 2 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 49.49	$ 45.27
Options Exercisable, Number Exercisable	2.7
Option Exercisable, Weighted Average Exercise Price	$ 42.22
Exercise Prices Range $ 35.71 - $ 39.17 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	35.71
Range of Exercise Prices, maximum	$ 39.17
Option Outstanding, Number Outstanding	1.4
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	1 year 4 months 6 days
Option Outstanding, Weighted Average Exercise Price	$ 37.92
Options Exercisable, Number Exercisable	1.4
Option Exercisable, Weighted Average Exercise Price	$ 37.92
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	2.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 8 months 19 days
Option Outstanding, 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	3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	3 years 2 months 27 days
Option Outstanding, Weighted Average Exercise Price	$ 46.49
Options Exercisable, Number Exercisable	1.3
Option Exercisable, Weighted Average Exercise Price	$ 46.61
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	1.6
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	5 years 8 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 56.80
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	1.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 8 months 16 days
Option Outstanding, Weighted Average Exercise Price	$ 70.74

Deferred Compensation - Additio

Deferred Compensation - Additional information (Detail) - USD ($) shares in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
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 made 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	$ 0	$ 11,500,000	$ 0	$ 14,000,000
Charge to compensation expenses related to awards	2,400,000		3,000,000		$ 4,300,000	$ 4,400,000
Cash and equity awards with aggregate fair value vested and distributed to participants	0		0
Unearned deferred compensation, value	$ 62,900,000		$ 2,800,000
Unearned deferred compensation, shares	54.7		2.6
Total intrinsic value of unvested equity based awards	$ 183,400,000		$ 166,000,000
Deferred Cash Participation Plan (DCPP) [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value					5,600,000	5,100,000
Charge to compensation expenses related to awards	1,000,000		700,000		1,800,000	1,100,000
Cash and equity awards with aggregate fair value vested and distributed to participants					0	0
Deferred Equity Participation Plan Sub Plans [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	0	$ 900,000	0	$ 4,000,000
Charge to compensation expenses related to awards	$ 600,000		$ 500,000		1,100,000	$ 900,000
Cash and equity awards with aggregate fair value vested and distributed to participants					$ 0

Restricted Stock, Performance71

Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail)	3 Months Ended					6 Months Ended
	Jun. 30, 2018USD ($)shares	Mar. 31, 2018USD ($)shares	Jun. 30, 2017USD ($)shares	Mar. 31, 2017USD ($)shares	Mar. 31, 2016shares	Jun. 30, 2018USD ($)shares	Jun. 30, 2017USD ($)shares	Dec. 31, 2017shares	Mar. 16, 2017USD ($)shares	Mar. 17, 2016USD ($)shares	Mar. 11, 2015USD ($)shares
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Share-based compensation, shares outstanding | shares	9,600,000					9,600,000		9,500,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares	269,000		199,000			269,000	199,000
Grants vested in period fair value	$ 15,800,000		$ 9,300,000			$ 15,800,000	$ 9,300,000
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					$ 4,000,000
Share-based compensation, shares outstanding | shares	3,500,000					3,500,000
Shares granted in the period | shares						3,500,000
Restricted Stock Units (RSUs) [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Shares granted in the period | shares	18,900	420,200	21,600	477,500
Fair value of grants in period	$ 1,300,000	$ 28,700,000	$ 1,200,000	$ 26,800,000
Share based payment award vesting date						Mar. 15, 2022	Mar. 16, 2021
Restricted stock or unit expense	$ 8,200,000		$ 6,500,000			$ 14,600,000	$ 10,500,000
Restricted Stock Units (RSUs) [Member] | Minimum [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	2 years
Restricted Stock Units (RSUs) [Member] | Executive Officer [Member] | Minimum [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
Performance Shares [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Shares granted in the period | shares	0		0
Equity awards with an aggregate fair value						$ 3,700,000	$ 2,800,000
Shares authorized | shares	78,200		86,250			78,200	86,250
Performance unit awards approved, Fair value						$ 5,300,000	$ 4,900,000
Provisional awards, terms						Granted units for the 2018 and 2017 provisional awards will fully vest based on continuous employment through March 16, 2021 and 2020, respectively, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable thereafter.
Performance awards expiration date						Mar. 15, 2021	Mar. 16, 2020
Performance awards period, years						3 years	3 years
Vesting period, years						3 years	3 years
Performance Shares [Member] | Minimum [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	2 years
Performance Shares [Member] | Executive Officer [Member] | Minimum [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
Unvested Restricted Stock [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Total intrinsic value	$ 125,700,000		$ 102,700,000			$ 125,700,000	$ 102,700,000
Equity awards with an aggregate fair value						$ 22,400,000	$ 19,600,000
Cash Awards [Member] | Officer and Key Employees [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Shares granted in the period | shares	0		0			0	0
Provisional awards, terms						The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2020, 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						2 years
Provisional compensation cash awards approved for future grant by compensation committee, value	$ 15,000,000	$ 15,000,000				$ 15,000,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares	219,000	219,000				219,000
Ultimate award value, multiples of original value of the units, minimum						0.5
Ultimate award value, multiples of original value of the units, maximum						1.5
2018 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date						Jan. 1, 2021
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	$ 1,900,000					$ 3,900,000	$ 0
2017 Provisional Cash Awards [Member] | Officer and Key Employees [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									$ 14,300,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares	242,000					242,000			255,000
2016 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date				Jan. 1, 2019
Cash-based compensation awards, expenses	$ 2,400,000		$ 2,700,000			$ 6,600,000	5,300,000
2016 Provisional Cash Awards [Member] | Officer and Key Employees [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
2015 Provisional Cash Awards [Member]
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]
Performance awards expiration date					Jan. 1, 2018
Cash-based compensation awards, expenses			$ 1,900,000				$ 5,000,000
2015 Provisional Cash Awards [Member] | Officer and Key Employees [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											$ 14,600,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares					294,000						315,000

Investments - Investments Repor

Investments - Investments Reported in Other Current and Non-Current Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Assets	$ 69.9	$ 79.1
Funding Commitments	0
Chem-Mod LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	4	4
Funding Commitments	0
Chem-Mod International LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	2	2
Funding Commitments	0
Clean-Coal Investments [Member] | Controlling Interest [Member] | 14 2009 Era Clean Coal Plants [Member]
Schedule of Equity Method Investments [Line Items]
Assets	7.6	10.2
Funding Commitments	0
Clean-Coal Investments [Member] | Controlling Interest [Member] | 19 2011 Era Clean Coal Plants [Member]
Schedule of Equity Method Investments [Line Items]
Assets	51.1	58.5
Funding Commitments	0
Clean-Coal Investments [Member] | Noncontrolling Interests [Member] | One 2011 Era Clean Coal Plant [Member]
Schedule of Equity Method Investments [Line Items]
Assets	0.5	0.6
Funding Commitments	0
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	4.7	$ 3.8
Funding Commitments	$ 0

Investments - Investments Rep73

Investments - Investments Reported in Other Current and Non-Current Assets (Parenthetical) (Detail) - Clean-Coal Investments [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2018EntityPlant	Dec. 31, 2017EntityPlant
14 2009 Era Clean Coal Plants [Member] | Controlling Interest [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants | Plant	14	14
Number of variable interest entities | Entity	6	6
One 2011 Era Clean Coal Plant [Member] | Noncontrolling Interests [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants | Plant	1	1
Number of variable interest entities | Entity	1	1
19 2011 Era Clean Coal Plants [Member] | Controlling Interest [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants | Plant	19	19
Number of variable interest entities | Entity	17	17

Derivatives and Hedging Activ74

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Detail) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional Amount	$ 224,000,000	$ 218,700,000
Derivatives Assets	7,900,000	10,300,000
Derivative Liabilities	6,200,000	2,900,000
Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	200,000,000	200,000,000
Derivatives Assets	5,200,000	2,200,000
Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	24,000,000	18,700,000
Derivatives Assets	2,700,000	8,100,000
Derivative Liabilities	$ 6,200,000	$ 2,900,000

Derivatives and Hedging Activ75

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Parenthetical) (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets - current	$ 7.1	$ 7.7
Derivative assets - non current	0.8	2.7
Derivative liabilities - current	3.7	1.6
Derivative liabilities - non current	2.5	1.3
Foreign Exchange Contracts [Member] | Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	96.3	141
Foreign Exchange Contracts [Member] | Put Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	92	141
Foreign Exchange Contracts [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	$ 27.2	13.3
Foreign Exchange Contracts [Member] | Forward Contracts [Member] | Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts		$ 31

Derivatives and Hedging Activ76

Derivatives and Hedging Activity - Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	$ (0.2)	$ 6.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	3.1	(4.1)
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	5.9	(3)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.5
Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(6.1)	9.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	2.6	(4.1)
Commission Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(2.5)	6
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	1.1	(5.3)
Commission Revenue [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(2.5)	6
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	1.1	(5.3)
Compensation Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(2.1)	2
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.9	0.7
Compensation Expense [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(2.1)	2
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.9	0.7
Operating Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(1.5)	1.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.6	0.5
Operating Expense [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	(1.5)	1.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.6	0.5
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	5.9	(3)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	0.5
Interest Expense [Member] | Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gains (losses) recognized in accumulated other comprehensive loss	5.9	$ (3)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion)	$ 0.5

Derivatives and Hedging Activ77

Derivatives and Hedging Activity - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
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 two years.
Interest exchange 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 two years into the future.
Gain (loss) related to hedge ineffectiveness	$ (0.1)	$ 0.4
Scenario, Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Estimated pretax loss to be reclassified from accumulated other comprehensive loss into earnings			$ 2.2

Commitments, Contingencies an78

Commitments, Contingencies and Off-Balance Sheet Arrangements - Contractual Obligations (Detail) $ in Millions	Jun. 30, 2018USD ($)
Note Purchase Agreements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	$ 50
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, Thereafter	2,723
Contractual Obligations, Payments Due by Period, Total	3,248
Multi Currency Credit Agreement [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	135
Contractual Obligations, Payments Due by Period, Total	135
Premium Financing Debt Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	111.1
Contractual Obligations, Payments Due by Period, Total	111.1
Interest On Debt [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	70.4
Contractual Obligations, Payments Due by Period, 2019	137.4
Contractual Obligations, Payments Due by Period, 2020	132.7
Contractual Obligations, Payments Due by Period, 2021	127.9
Contractual Obligations, Payments Due by Period, 2022	122.4
Contractual Obligations, Payments Due by Period, Thereafter	557.6
Contractual Obligations, Payments Due by Period, Total	1,148.4
Total Debt Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	366.5
Contractual Obligations, Payments Due by Period, 2019	237.4
Contractual Obligations, Payments Due by Period, 2020	232.7
Contractual Obligations, Payments Due by Period, 2021	202.9
Contractual Obligations, Payments Due by Period, 2022	322.4
Contractual Obligations, Payments Due by Period, Thereafter	3,280.6
Contractual Obligations, Payments Due by Period, Total	4,642.5
Operating Lease Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	54.7
Contractual Obligations, Payments Due by Period, 2019	100.1
Contractual Obligations, Payments Due by Period, 2020	85.6
Contractual Obligations, Payments Due by Period, 2021	73.3
Contractual Obligations, Payments Due by Period, 2022	57.3
Contractual Obligations, Payments Due by Period, Thereafter	144.9
Contractual Obligations, Payments Due by Period, Total	515.9
Less Sublease Arrangements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	(0.8)
Contractual Obligations, Payments Due by Period, 2019	(0.8)
Contractual Obligations, Payments Due by Period, 2020	(0.6)
Contractual Obligations, Payments Due by Period, 2021	(0.6)
Contractual Obligations, Payments Due by Period, 2022	(0.4)
Contractual Obligations, Payments Due by Period, Thereafter	(1.2)
Contractual Obligations, Payments Due by Period, Total	(4.4)
Outstanding Purchase Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	24.4
Contractual Obligations, Payments Due by Period, 2019	38
Contractual Obligations, Payments Due by Period, 2020	26.5
Contractual Obligations, Payments Due by Period, 2021	14.2
Contractual Obligations, Payments Due by Period, 2022	10.8
Contractual Obligations, Payments Due by Period, Thereafter	28.7
Contractual Obligations, Payments Due by Period, Total	142.6
Funding Related to Acquisition of Reassurance Holdings, Inc [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	122.1
Contractual Obligations, Payments Due by Period, Total	122.1
Total Contractual Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2018	566.9
Contractual Obligations, Payments Due by Period, 2019	374.7
Contractual Obligations, Payments Due by Period, 2020	344.2
Contractual Obligations, Payments Due by Period, 2021	289.8
Contractual Obligations, Payments Due by Period, 2022	390.1
Contractual Obligations, Payments Due by Period, Thereafter	3,453
Contractual Obligations, Payments Due by Period, Total	$ 5,418.7

Commitments, Contingencies an79

Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail)	3 Months Ended		6 Months Ended		198 Months Ended
	Jun. 30, 2018USD ($)ft²EntityLetterOfCredit	Jun. 30, 2017Entity	Jun. 30, 2018USD ($)ft²EntityLetterOfCreditEmployees	Jun. 30, 2017Entity	Jun. 30, 2018USD ($)ft²EntityLetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of square feet | ft²	360,000		360,000		360,000
Number of employees will accommodate at new facility | Employees			2,000
Acquired property through lease area, sqft | ft²			306,000
Acquired property through lease percentage of building			60.00%
Operating lease commitment, expiration date			Feb. 28, 2018
Number of companies acquired | Entity	49	46	76	65	478
Aggregate amount of maximum earnout obligations related to acquisitions	$ 552,300,000		$ 552,300,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet	266,900,000		$ 266,900,000
Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive period			15 years
Economic development for growing economy tax credit	10,000,000		$ 10,000,000		$ 10,000,000
Letter of Credit [Member] | Security Deposit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	$ 500,000		$ 500,000		$ 500,000
Number of letters of credit issued | LetterOfCredit	1		1		1
Letter of Credit [Member] | Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt	$ 9,700,000		$ 9,700,000		$ 9,700,000
Liabilities recorded on self-insurance	$ 14,900,000		$ 14,900,000		$ 14,900,000
Number of letters of credit issued | LetterOfCredit	2		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		$ 6,300,000
Number of letters of credit issued | LetterOfCredit	7		7		7
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	1.00%		1.00%		1.00%
Minimum [Member] | Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive	$ 60,000,000		$ 60,000,000		$ 60,000,000
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest	50.00%		50.00%		50.00%
Maximum [Member] | Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive	$ 80,000,000		$ 80,000,000		$ 80,000,000

Commitments, Contingencies an80

Commitments, Contingencies and Off-Balance Sheet Arrangements - Off-Balance Sheet Commitments (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2018	$ 0.1
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 - Thereafter	17.3
Total Amounts Committed	18.2
Letters of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - Thereafter	16.5
Total Amounts Committed	16.5
Financial Guarantees [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2018	0.1
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 - Thereafter	0.8
Total Amounts Committed	$ 1.7

Commitments, Contingencies an81

Commitments, Contingencies and Off-Balance Sheet Arrangements - Litigation, Regulatory and Taxation Matters- Additional Information (Detail) $ in Millions	6 Months Ended	24 Months Ended
	Jun. 30, 2018Companies	Dec. 31, 2017USD ($)
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of micro-captive insurance companies organized or managed | Companies	100
Micro-captive operations, net earnings and EBITDAC, description	In the period from 2015 to 2017, our micro-captive operations contributed less than $3.5 million of net earnings and less than $5.0 million in EBITDAC to our consolidated results in any one year.
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Micro-captive operations, net earnings		$ 3.5
Micro-captive operations, EBITDAC		$ 5

Commitments, Contingencies an82

Commitments, Contingencies and Off-Balance Sheet Arrangements - Contingent Liabilities - Additional Information (Detail) - Errors and Omissions [Member]	6 Months Ended
	Jun. 30, 2018USD ($)
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained	$ 5,000,000
Amount of losses in excess of retained amounts	175,000,000
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value	7,100,000
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value	$ 1,600,000

Commitments, Contingencies an83

Commitments, Contingencies and Off-Balance Sheet Arrangements - Tax - advantaged Investments No Longer Held - Additional Information (Detail) $ in Millions	12 Months Ended
	Jun. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Income tax credits and adjustments	$ 108.2

Accumulated Other Comprehensi84

Accumulated Other Comprehensive Earnings (Loss) - Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (555.4)	[1]
Ending Balance	(651.4)
As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(559.9)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(43)
Reclassifications to retained earnings of income tax effects related to the Tax Act	(7.9)
Net change in period	1.5
Ending Balance	(49.4)
Pension Liability [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(43)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(521.3)
Net change in period	(88.4)
Ending Balance	(609.7)
Foreign Currency Translation [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(525.8)
Foreign Currency Translation [Member] | Accounting Standards Update 2014-09 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	4.5
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	8.9
Reclassifications to retained earnings of income tax effects related to the Tax Act	1.3
Net change in period	(2.5)
Ending Balance	7.7
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	8.9
Accumulated Other Comprehensive Earnings (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(555.4)
Reclassifications to retained earnings of income tax effects related to the Tax Act	(6.6)
Net change in period	(89.4)
Ending Balance	(651.4)
Accumulated Other Comprehensive Earnings (Loss) [Member] | As Previously Reported [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(559.9)
Accumulated Other Comprehensive Earnings (Loss) [Member] | Accounting Standards Update 2014-09 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 4.5
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Accumulated Other Comprehensi85

Accumulated Other Comprehensive Earnings - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Expense related to pension liability reclassified from accumulated other comprehensive earnings	$ 2,400,000	$ 2,700,000
Income (expense) related to fair value of derivative investments reclassified from accumulated other comprehensive earnings	3,100,000	4,100,000
Foreign currency translation reclassified from accumulated other comprehensive earnings	$ 0	$ 0

Segment Information - Additiona

Segment Information - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018Segment
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			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017		Dec. 31, 2017	[1]
Segment Reporting Information [Line Items]
Total revenues	$ 1,660.4	$ 1,489.5	[1]	$ 3,498.1	$ 3,135.9	[1]
Earnings before income taxes	103.6	54.1	[1]	345.9	253.7	[1]
Identifiable assets at June 30, 2018 and 2017	16,230.5			16,230.5			$ 14,909.7
Operating Segments [Member] | Brokerage [Member]
Segment Reporting Information [Line Items]
Total revenues	1,000.1	896.1		2,195.7	1,981
Earnings before income taxes	170.6	125.1		489.5	401.6
Identifiable assets at June 30, 2018 and 2017	13,779	13,202.9		13,779	13,202.9
Operating Segments [Member] | Risk Management [Member]
Segment Reporting Information [Line Items]
Total revenues	237.3	216.8		467.2	426.7
Earnings before income taxes	24	20.6		45.6	42.7
Identifiable assets at June 30, 2018 and 2017	739.5	714.7		739.5	714.7
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Total revenues	423	376.6		835.2	728.2
Earnings before income taxes	(91)	(91.6)		(189.2)	(190.6)
Identifiable assets at June 30, 2018 and 2017	$ 1,712	$ 1,761.8		$ 1,712	$ 1,761.8
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Segment Information - Summary o

Segment Information - Summary of Revenues by Type and Segment (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues before reimbursements	$ 1,625	$ 1,454.3	[1]	$ 3,427.9	$ 3,067.6	[1]
Total revenues	1,660.4	1,489.5	[1]	3,498.1	3,135.9	[1]
Commissions [Member]
Segment Reporting Information [Line Items]
Total revenues	688	618.2	[1]	1,527.4	1,378.9	[1]
Broker Fees [Member]
Segment Reporting Information [Line Items]
Total revenues	422.2	386.9	[1]	870.3	791.9	[1]
Supplemental Revenue Member [Member]
Segment Reporting Information [Line Items]
Total revenues	48.1	35.8	[1]	100.1	83.1	[1]
Contingent Revenue [Member]
Segment Reporting Information [Line Items]
Total revenues	21.8	21.3	[1]	56.7	56.3	[1]
Investment income [Member]
Segment Reporting Information [Line Items]
Total revenues	15.8	14.4	[1]	29.2	26.7	[1]
Gains on Books of Business Sales [Member]
Segment Reporting Information [Line Items]
Total revenues	6.1	1.1	[1]	9	2.5	[1]
Clean Coal Activities [Member]
Segment Reporting Information [Line Items]
Total revenues	422.4	376.4	[1]	834.6	728.2	[1]
Product and Service, Other [Member]
Segment Reporting Information [Line Items]
Total revenues	0.6	0.2	[1]	0.6
Reimbursements [Member]
Segment Reporting Information [Line Items]
Total revenues	35.4	35.2	[1]	70.2	68.3	[1]
Operating Segments [Member] | Brokerage [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	1,000.1	896.1		2,195.7	1,981
Total revenues	1,000.1	896.1		2,195.7	1,981
Operating Segments [Member] | Brokerage [Member] | Commissions [Member]
Segment Reporting Information [Line Items]
Total revenues	688	618.2		1,527.4	1,378.9
Operating Segments [Member] | Brokerage [Member] | Broker Fees [Member]
Segment Reporting Information [Line Items]
Total revenues	220.4	205.5		473.6	433.8
Operating Segments [Member] | Brokerage [Member] | Supplemental Revenue Member [Member]
Segment Reporting Information [Line Items]
Total revenues	48.1	35.8		100.1	83.1
Operating Segments [Member] | Brokerage [Member] | Contingent Revenue [Member]
Segment Reporting Information [Line Items]
Total revenues	21.8	21.3		56.7	56.3
Operating Segments [Member] | Brokerage [Member] | Investment income [Member]
Segment Reporting Information [Line Items]
Total revenues	15.7	14.2		28.9	26.4
Operating Segments [Member] | Brokerage [Member] | Gains on Books of Business Sales [Member]
Segment Reporting Information [Line Items]
Total revenues	6.1	1.1		9	2.5
Operating Segments [Member] | Risk Management [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	201.9	181.6		397	358.4
Total revenues	237.3	216.8		467.2	426.7
Operating Segments [Member] | Risk Management [Member] | Broker Fees [Member]
Segment Reporting Information [Line Items]
Total revenues	201.8	181.4		396.7	358.1
Operating Segments [Member] | Risk Management [Member] | Investment income [Member]
Segment Reporting Information [Line Items]
Total revenues	0.1	0.2		0.3	0.3
Operating Segments [Member] | Risk Management [Member] | Reimbursements [Member]
Segment Reporting Information [Line Items]
Total revenues	35.4	35.2		70.2	68.3
Operating Segments [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements	423	376.6		835.2	728.2
Total revenues	423	376.6		835.2	728.2
Operating Segments [Member] | Corporate [Member] | Clean Coal Activities [Member]
Segment Reporting Information [Line Items]
Total revenues	422.4	376.4		834.6	$ 728.2
Operating Segments [Member] | Corporate [Member] | Product and Service, Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 0.6	$ 0.2		$ 0.6
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

Segment Information - Summary89

Segment Information - Summary of Geographical Location and Segment (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 1,660.4	$ 1,489.5	[1]	$ 3,498.1	$ 3,135.9	[1]
Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	1,000.1	896.1		2,195.7	1,981
Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	237.3	216.8		467.2	426.7
Operating Segments [Member] | Corporate [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	423	376.6		835.2	728.2
Unites States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	1,235.8	1,114		2,693.6	2,441
Unites States [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	615.5	552.1		1,468.3	1,345.1
Unites States [Member] | Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	197.3	185.3		390.1	367.7
Unites States [Member] | Operating Segments [Member] | Corporate [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	423	376.6		835.2	728.2
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	213.2	191.9		413.1	359.6
United Kingdom [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	204.4	184.7		395.4	346
United Kingdom [Member] | Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	8.8	7.2		17.7	13.6
Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	79.6	71.1		146.9	130.1
Australia [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	53.9	52		97.5	92.3
Australia [Member] | Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	25.7	19.1		49.4	37.8
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	49	37.5		92.8	70.4
Canada [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	47.8	36.6		90.6	68.7
Canada [Member] | Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	1.2	0.9		2.2	1.7
New Zealand [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	43.7	41.1		77.3	69.8
New Zealand [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	39.4	36.8		69.5	63.9
New Zealand [Member] | Operating Segments [Member] | Risk Management [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	4.3	4.3		7.8	5.9
Other Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	39.1	33.9		74.4	65
Other Foreign [Member] | Operating Segments [Member] | Brokerage [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 39.1	$ 33.9		$ 74.4	$ 65
[1]	See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.