Paychex (PAYX) 10-Q 28 Mar 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Feb. 28, 2018shares
Document and Entity Information [Abstract]
Entity Registrant Name	PAYCHEX INC
Entity Filer Category	Large Accelerated Filer
Entity Central Index Key	723,531
Amendment Flag	false
Document Type	10-Q
Trading Symbol	PAYX
Document Fiscal Period Focus	Q3
Document Period End Date	Feb. 28, 2018
Document Fiscal Year Focus	2,018
Current Fiscal Year End Date	--05-31
Entity Common Stock, Shares Outstanding	359,275,368

Consolidated Statements of Inco

Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Revenue:
Service revenue	$ 848.4	$ 782.6	$ 2,464	$ 2,316.1
Interest on funds held for clients	18.1	13.2	45.8	36.6
Total revenue	866.5	795.8	2,509.8	2,352.7
Expenses:
Operating expenses	270.7	236.8	751.5	688.2
Selling, general and administrative expenses	303.3	252.4	788.6	723.8
Total expenses	574	489.2	1,540.1	1,412
Operating income	292.5	306.6	969.7	940.7
Investment income, net	2.3	1.2	6.1	3.6
Income before income taxes	294.8	307.8	975.8	944.3
Income taxes	34.4	105.3	270.6	322.3
Net income	260.4	202.5	705.2	622
Other comprehensive (loss)/income, net of tax:
Unrealized (losses)/gains on securities, net of tax	(17.5)	21.4	(46.7)	(24.6)
Total other comprehensive (loss)/income, net of tax	(17.5)	21.4	(46.7)	(24.6)
Comprehensive income	$ 242.9	$ 223.9	$ 658.5	$ 597.4
Basic earnings per share	$ 0.72	$ 0.56	$ 1.96	$ 1.73
Diluted earnings per share	$ 0.72	$ 0.56	$ 1.95	$ 1.71
Weighted-average common shares outstanding	359.2	359	359.1	360
Weighted-average common shares outstanding, assuming dilution	362	361.8	361.6	362.8
Cash dividends per common share	$ 0.50	$ 0.46	$ 1.50	$ 1.38

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Assets
Cash and cash equivalents	$ 323.9	$ 184.6
Corporate investments	97.3	138.8
Interest receivable	31.5	35.9
Accounts receivable, net of allowance for doubtful accounts	550.5	507.5
Prepaid income taxes	22.9	45
Prepaid expenses and other current assets	77.9	58.3
Current assets before funds held for clients	1,104	970.1
Funds held for clients	3,944.7	4,301.9
Total current assets	5,048.7	5,272
Long-term corporate investments	405.4	454
Property and equipment, net of accumulated depreciation	397.2	337.2
Intangible assets, net of accumulated amortization	105.1	57.6
Goodwill	827.4	657.1
Prepaid income taxes	24.9	24.9
Other long-term assets	34.1	30.9
Total assets	6,842.8	6,833.7
Liabilities
Accounts payable	71.9	57.2
Accrued compensation and related items	356.3	280.5
Short-term borrowings	57.7
Deferred revenue	23.7	22.9
Other current liabilities	142.2	91.9
Current liabilities before client fund obligations	651.8	452.5
Client fund obligations	3,971.9	4,272.6
Total current liabilities	4,623.7	4,725.1
Accrued income taxes	51.8	45.6
Deferred income taxes	41.9	33.9
Other long-term liabilities	79.9	73.8
Total liabilities	4,797.3	4,878.4
Commitments and contingencies - Note L
Stockholders' equity
Common stock, $0.01 par value; Authorized: 600.0 shares; Issued and outstanding: 359.3 shares as of February 28, 2018 and 359.4 shares as of May 31, 2017	3.6	3.6
Additional paid-in capital	1,107.2	1,030
Retained earnings	961.4	901.7
Accumulated other comprehensive (loss)/income	(26.7)	20
Total stockholders' equity	2,045.5	1,955.3
Total liabilities and stockholders' equity	$ 6,842.8	$ 6,833.7

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Feb. 28, 2018	May 31, 2017
Stockholders' equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	359,300,000	359,400,000
Common stock, shares outstanding	359,300,000	359,400,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017
Operating activities
Net income	$ 705.2	$ 622
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization on property and equipment and intangible assets	102.3	90.7
Amortization of premiums and discounts on available-for-sale securities, net	50.1	55
Stock-based compensation costs	29.4	26.5
Provision for deferred income taxes	6.5
Provision for allowance for doubtful accounts	3.3	3.4
Net realized gains on sales of available-for-sale securities	(0.1)	(0.1)
Changes in operating assets and liabilities:
Interest receivable	4.4	4.1
Accounts receivable	(6.2)	(24.6)
Prepaid expenses and other current assets	9.7	(32.1)
Accounts payable and other current liabilities	80.9	37.5
Net change in other long-term assets and liabilities	3.4	(13.1)
Net cash provided by operating activities	988.9	769.3
Investing activities
Purchases of available-for-sale securities	(36,422.2)	(36,029.5)
Proceeds from sales and maturities of available-for-sale securities	37,162.9	35,617.4
Net change in funds held for clients’ money market securities and other cash equivalents	(409.1)	(459.8)
Purchases of property and equipment	(122)	(66.8)
Acquisition of businesses, net of cash acquired	(178.5)
Purchases of other assets	(6.7)	(8.4)
Net cash provided by/(used in) investing activities	24.4	(947.1)
Financing activities
Net change in client fund obligations	(300.7)	819.8
Net proceeds from short-term borrowings	57.7	55.4
Dividends paid	(538.7)	(496.9)
Repurchases of common shares	(94.1)	(166.2)
Activity related to equity-based plans	1.8	24.1
Net cash (used in)/provided by financing activities	(874)	236.2
Increase in cash and cash equivalents	139.3	58.4
Cash and cash equivalents, beginning of fiscal year	184.6	131.5
Cash and cash equivalents, end of period	$ 323.9	$ 189.9

Description of Business, Basis

Description of Business, Basis of Presentation, and Significant Accounting Policies	9 Months Ended
	Feb. 28, 2018
Description of Business, Basis of Presentation, and Significant Accounting Policies [Abstract]
Description of Business, Basis of Presentation, and Significant Accounting Policies	Note A: Description of Business, Basis of Presentation, and Significant Accounting Policies  Description of business: Paychex, Inc. and its wholly owned subsidiaries (collectively, the “Company” or “Paychex”) is a leading provider of integrated human capital management (“HCM”) solutions for payroll, human resource (“HR”), retirement, and insurance services for small- to medium-sized businesses in the United States (“U.S.”). The Company also has operations in Europe. Effective February 28, 2018, the Company acquired Lessor Group (“Lessor”), headquartered in Denmark and serving clients in Northern Europe. Refer to Note C for further details. Paychex, a Delaware corporation formed in 1979, reports as one segment. Substantially all of the Company’s revenue is generated within the U.S. The Company also generates revenue within Europe, which represented less than one percent of the Company's total revenue for each of the three and nine months ended February 28, 2018 and February 28, 2017 . Long-lived assets in Europe were approximately 13% of total long-lived assets of the Company as of February 28, 2018 and were insignificant as of May 31, 2017 .  Basis of presentation: The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to the Quarterly Report on Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statement presentation. The consolidated financial statements include the consolidated accounts of the Company with all intercompany transactions eliminated. In the opinion of management, the information furnished herein reflects all adjustments (consisting of items of a normal recurring nature), which are necessary for a fair statement of the results for the interim period. These financial statements should be read in conjunction with the Company’s consolidated financial statements and related Notes to Consolidated Financial Statements presented in the Company’s Annual Report on Form 10-K (“Form 10-K”) for the fiscal year ended May 31, 2017 (“fiscal 2017 ”). Operating result s and cash flows for the period ended February 28, 2018 are not necessarily indicative of the results that may be expected for other interim periods or for the fiscal year ending May 31, 2018 (“fiscal 2018 ”).  Subsequent event: During the three months ended February 28, 2018, the Company began negotiations to terminate certain license agreements and acquire rights to certain client lists in order to resolve a contractual dispute with certain licensees. The negotiations were completed in March 2018. The Company recorded $32.6 million on its Consolidated Balance Sheets within other current liabilities as of February 28, 2018, and $24.7 million, net of tax, in its Consolidated Statements of Income and Comprehensive Income for the three months ended February 28, 2018 related to the termination of these license agreements. In addition, the Company acquired rights to certain client lists as it relates to this agreement in March 2018 for a cost of approximately $30.0 million.  PEO insurance reserves: As part of the professional employer organization (“PEO”), the Company offers workers' compensation insurance and health insurance to client companies for the benefit of client employees. For workers' compensation insurance, reserves are established to provide for the estimated costs of paying claims up to per occurrence liability limits. The Company’s maximum individual claims liability is $1.3 million under both its fiscal 2018 and fiscal 2017 workers’ compensation insurance policies.  Under the minimum premium insurance plan offering within the PEO, the Company's health benefits insurance reserves are established to provide for the payment of claims liability charges in accordance with its service contract with the insurance carrier. The Company's maximum individual claims liability is $0.3 million under both its calendar 2018 and calendar 2017 minimum premium insurance plan policies.  Estimating the ultimate cost of future claims is an uncertain and complex process based upon historical loss experience and actuarial loss projections, and is subject to change due to multiple factors, including economic trends, changes in legal liability law, and damage awards, all of which could materially impact the reserves as reported in the consolidated financial statements. Accordingly, final claim settlements may vary from the present estimates, particularly with workers' compensation insurance where those payments may not occur until well into the future. The Company regularly reviews the adequacy of its estimated insurance reserves. Adjustments to previously established insurance reserves are reflected in the results of operations for the period in which such adjustments are identified. Such insurance reserve adjustments could be significant, reflecting any combination of new and adverse or favorable trends.  Stock-based compensation costs: The Company has issued stock-based awards to employees and directors consisting of stock options, restricted stock awards, restricted stock units, performance shares, performance-based restricted stock, and performance stock options. The Company accounts for all stock-based awards to employees and directors as compensation costs in the consolidated financial statements based on their fair values measured as of the date of grant. These costs are recognized over the requisite service period. Stock-based compensation costs recognized were $10.3 million and $29.4 million for the three and nine months ended February 28, 2018 , respectively, as compared with $8.9 million and $ 26.5 million for the three and nine months ended February 28, 2017 , respectively. The methods and assumptions used in the determination of the fair value of stock-based awards are consistent with those described in the Company’s fiscal 2017 Form 10-K .  Recently adopted accounting pronouncements: In January 2018, the Company early adopted Accounting Standards Update (“ASU”) No. 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business.” ASU No. 2017-01 clarifies the definition of a business in order to allow for the evaluation of whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The adoption of ASU 2017-01 did not have a material impact on the Company’s consolidated financial statements. Recently issued accounting pronouncements: In February 2018, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” ASU No. 2018-02 allows entities to reclassify certain stranded income tax effects from accumulated other comprehensive income to retained earnings resulting from the Tax Cuts and Jobs Act (the “Tax Act”), enacted on December 22, 2017. The guidance also requires additional financial statement disclosures to clarify the effects of adoption. ASU No. 2018-02 should be applied either in the period of adoption or retrospectively to each period or periods in which the eff ect of the change in the U.S. F ederal corporate income tax rate in the Tax Act is recognized. This guidance is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years, with early adoption permitted. This guidance is applicable to the Company’s fiscal year beginning June 1, 2019. The Company is currently evaluating the potential effects of this guidance on its consolidated financial statements.  In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” ASU No. 2016-02 improves transparency and comparability among companies by recognizing lease assets and lease liabilities on the balance sheet and by disclosing key information about leasing arrangements. ASU No. 2016-02 is effective for public business entities for annual periods, including interim periods within those annual periods, beginning after December 15, 2018, with early adoption permitted. This guidance is applicable to the Company's fiscal year beginning June 1, 2019. The Company is in the preliminary stages of gathering data and assessing the impact of the new lease accounting standard and the Company anticipates that the adoption of the new lease accounting standard will result in additional assets and liabilities being recorded on its Consolidated Balance Sheets. In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” This guidance, as amended by subsequent ASUs on the topic, outlines a single comprehensive model for determining revenue recognition for contracts with customers, and supersedes current guidance on revenue recognition in Accounting Standards Codification (“ASC”) Topic 605, “Revenue Recognition.” Entities have the option to apply the new guidance under a full retrospective approach to each prior reporting period presented or a modified retrospective approach with a cumulative effect of initially applying the new guidance recognized at the date of initial application within the consolidated financial statements. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods. The Company did not elect to early-adopt the new standard, and will adopt the new standard in its fiscal year beginning June 1, 2018. The analysis of the new standard and its impact to the Company is nearly complete as the Company is in the process of finalizing its conclusions. Further, the Company currently anticipates applying the guidance under the full retrospective approach. The Company’s ability to adopt using the full retrospective method is dependent on system readiness and the completion of the analysis of information necessary to restate prior period consolidated financial statements. While the evaluation of the impact of the new revenue recognition standard on its consolidated financial statements has not yet been finalized, the Company anticipates the provisions to primarily impact the manner in which it treats certain costs to obtain contracts and costs to fulfill contracts. Generally, in relation to these items, the new standard will result in the Company deferring additional costs on the Consolidated Balance Sheets and subsequently amortizing them to the Consolidated Statements of Income and Comprehensive Income over the estimated average life of the client. The Company does not expect the provisions of the new standard will have a material impact on the timing or the amount of revenue it recognizes. The Company has also not yet fully determined the impacts of the disclosure requirements under the new standard, and is evaluating the way it will disaggregate revenue into categories that show how economic factors affect the nature, timing, and uncertainty of revenue and cash flows generated from contracts with customers. Additionally, while the Company is in the process of assessing its accounting considerations to ensure its ability to record, report, and analyze results under the new standard, it is not expecting significant changes in its business processes or systems.  Other recent authoritative guidance issued by the FASB (including technical corrections to the ASC), the American Institute of Certified Public Accountants, and the Securities Exchange Commission (“SEC”) during the nine months ended February 28, 2018 did not, or are not expected to, have a material effect on the Company’s consolidated financial statements.

Basic and Diluted Earnings Per

Basic and Diluted Earnings Per Share	9 Months Ended
	Feb. 28, 2018
Basic and Diluted Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Share	 Note B: Basic and Diluted Earnings Per Share  Basic and diluted earnings per share were calculated as follows:      For the three months ended For the nine months ended  February 28, February 28,  In millions, except per share amounts 2018 2017 2018 2017  Basic earnings per share:  Net income $ 260.4 $ 202.5 $ 705.2 $ 622.0  Weighted-average common shares outstanding 359.2 359.0 359.1 360.0  Basic earnings per share $ 0.72 $ 0.56 $ 1.96 $ 1.73  Diluted earnings per share:  Net income $ 260.4 $ 202.5 $ 705.2 $ 622.0  Weighted-average common shares outstanding 359.2 359.0 359.1 360.0  Dilutive effect of common share equivalents 2.8 2.8 2.5 2.8  Weighted-average common shares outstanding, assuming dilution 362.0 361.8 361.6 362.8  Diluted earnings per share $ 0.72 $ 0.56 $ 1.95 $ 1.71  Weighted-average anti-dilutive common share equivalents — 0.7 0.8 0.7  Weighted-average common share equivalents that have an anti-dilutive impact are excluded from the computation of diluted earnings per share.  For the three months ended February 28, 2018 and February 28, 2017 , 0.1 million and 0.4 million shares, respectively, of the Company’s common stock were issued in connection with the exercise or vesting of stock-based awards. For the nine months ended February 28, 2018 and February 28, 2017 , 0.9 million and 1.8 million shares, respectively, of the Company’s common stock were issued in connection with the exercise or vesting of stock-based awards. In addition, for the nine months ended February 28, 2018 , 0.6 million shares of the Company’s common stock were issued in relation to a business acquisition completed in August 2017. Refer to Note C for further details.  In July 2016, the Company announced that its Board of Directors approved a program to repurchase up to $350.0 million of the Company’s common stock, with authorization expiring in May 2019 . The purpose of the program is to manage common stock dilution. No shares were repurchased during the three months ended February 28, 2018 and February 28, 2017 . During the nine months ended February 28, 2018 and February 28, 2017 , the Company repurchased 1.6 million shares for $94.1 million and 2.9 million shares for $ 166.2 million, respectively. Of the shares repurchased during the nine months ended February 28, 2017 , $59.7 million were repurchased under a previously authorized common stock repurchase program. All shares repurchased were retired. 

Business Combinations

Business Combinations	9 Months Ended
	Feb. 28, 2018
Business Combinations [Abstract]
Business Combinations	Note C: Business Combinations  Effective February 28, 2018 , the Company completed its acquisition of Lessor. Upon closing, Lessor became a wholly owned subsidiary of the Company. Lessor is a market-leading provider of payroll and HCM software solutions headquartered in Denmark and serving clients in Northern Europe. The Company believes that the acquisition will provide additional opportunities for growth in Europe. The purchase price was $160.6 million, net of cash acquired. Goodwill in the amount of $119.2 million was recorded as a result of the acquisition, which is not tax-deductible. The goodwill recorded is provisional and subject to change, pending completion of a final valuation of Lessor. However, further changes to goodwill resulting from the acquisition are not anticipated to be material to the Company’s Consolidated Balance Sheets.  Effective August 18, 2017 , the Company acquired HR Outsourcing Holdings, Inc. (“HROI”) and all of its operating subsidiaries. HROI is a national PEO that provides HR solutions to small- and medium-sized businesses in more than 35 states. The acquisition expands the Company’s presence in the PEO industry. The purchase price was $75.4 million and was comprised of $42.2 million of cash plus $33.2 million issued in the form of Paychex common stock. Goodwill in the amount of $51.1 million was recorded as a result of the acquisition, which is not tax-deductible.  The financial results of both Lessor and HROI are included in the Company’s consolidated financial statements from the respective date s of acquisition. The Company concluded that these acquisitions were not material to its results of operations and financial position. Therefore, pro-forma financial information has been excluded.

Investment Income, Net

Investment Income, Net	9 Months Ended
	Feb. 28, 2018
Investment Income, Net [Abstract]
Investment Income, Net	Note D: Investment Income, Net  Investment income, net, consisted of the following items:      For the three months ended For the nine months ended  February 28, February 28,  In millions 2018 2017 2018 2017  Interest income on corporate funds $ 3.1 $ 2.4 $ 8.7 $ 7.2  Interest expense (1.1) (0.6) (3.2) (1.9)  Net gain/(loss) from equity-method investments 0.3 (0.6) 0.6 (1.7)  Investment income, net $ 2.3 $ 1.2 $ 6.1 $ 3.6

Funds Held for Clients and Corp

Funds Held for Clients and Corporate Investments	9 Months Ended
	Feb. 28, 2018
Funds Held for Clients and Corporate Investments [Abstract]
Funds Held for Clients and Corporate Investments	Note E: Funds Held for Clients and Corporate Investments  Funds held for clients and corporate investments are as follows:      February 28, 2018  Gross Gross  Amortized unrealized unrealized Fair  In millions cost gains losses value  Type of issue:  Funds held for clients' money market securities and other cash equivalents $ 673.9 $ — $ — $ 673.9  Available-for-sale securities:  Corporate bonds 305.8 0.1 (6.5) 299.4  General obligation municipal bonds 1,303.8 2.6 (10.6) 1,295.8  Pre-refunded municipal bonds (1) 64.7 0.6 (0.1) 65.2  Revenue municipal bonds 851.3 1.7 (7.9) 845.1  U.S. government agency securities 410.2 — (14.8) 395.4  Variable rate demand notes 854.7 — — 854.7  Total available-for-sale securities 3,790.5 5.0 (39.9) 3,755.6  Other 15.8 2.1 — 17.9  Total funds held for clients and corporate investments $ 4,480.2 $ 7.1 $ (39.9) $ 4,447.4     May 31, 2017  Gross Gross  Amortized unrealized unrealized Fair  In millions cost gains losses value  Type of issue:  Funds held for clients' money market securities and other cash equivalents $ 264.8 $ — $ — $ 264.8  Available-for-sale securities:  Corporate bonds 208.6 2.7 (0.5) 210.8  General obligation municipal bonds 1,422.0 21.2 (0.9) 1,442.3  Pre-refunded municipal bonds (1) 54.6 0.9 — 55.5  Revenue municipal bonds 929.2 12.5 (0.8) 940.9  U.S. government agency securities 328.9 0.5 (3.6) 325.8  Variable rate demand notes 1,637.9 — — 1,637.9  Total available-for-sale securities 4,581.2 37.8 (5.8) 4,613.2  Other 14.8 1.9 — 16.7  Total funds held for clients and corporate investments $ 4,860.8 $ 39.7 $ (5.8) $ 4,894.7  (1) Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.  Included in money market securities and other cash equivalents as of February 28, 2018 were bank demand deposit accounts, time deposits, commercial paper, and money market funds. Included in money market securities and other cash equivalents as of May 31, 2017 were bank demand deposit accounts and money market funds.  Classification of investments on the Consolidated Balance Sheets is as follows:      February 28, May 31,  In millions 2018 2017  Funds held for clients $ 3,944.7 $ 4,301.9  Corporate investments 97.3 138.8  Long-term corporate investments 405.4 454.0  Total funds held for clients and corporate investments $ 4,447.4 $ 4,894.7  The Company’s available-for-sale securities reflected a net unrealized loss of $34.9 million as of February 28, 2018 compared with a net unrealized gain of $ 32.0 million as of May 31, 2017 . Included in the net unrealized loss as of February 28, 2018 were 859 available-for-sale securities in an unrealized loss position. Included in the net unrealized gain as of May 31, 2017 were 216 available-for-sale securities in an unrealized loss position. The available-for-sale securities in an unrealized loss position were as follows:      February 28, 2018  Securities in an unrealized loss position for less than twelve months Securities in an unrealized loss position for more than twelve months Total  Gross Gross Gross  unrealized Fair unrealized Fair unrealized Fair  In millions losses value losses value losses value  Type of issue:  Corporate bonds $ (5.2) $ 252.1 $ (1.3) $ 34.7 $ (6.5) $ 286.8  General obligation municipal bonds (8.0) 735.5 (2.6) 71.4 (10.6) 806.9  Pre-refunded municipal bonds (0.1) 7.2 — 0.5 (0.1) 7.7  Revenue municipal bonds (6.1) 435.7 (1.8) 51.6 (7.9) 487.3  U.S. government agency securities (6.8) 219.3 (8.0) 176.1 (14.8) 395.4  Total $ (26.2) $ 1,649.8 $ (13.7) $ 334.3 $ (39.9) $ 1,984.1     May 31, 2017  Securities in an unrealized loss position for less than twelve months Securities in an unrealized loss position for more than twelve months Total  Gross Gross Gross  unrealized Fair unrealized Fair unrealized Fair  In millions losses value losses value losses value  Type of issue:  Corporate bonds $ (0.5) $ 43.6 $ — $ — $ (0.5) $ 43.6  General obligation municipal bonds (0.9) 188.8 — — (0.9) 188.8  Pre-refunded municipal bonds — 9.2 — — — 9.2  Revenue municipal bonds (0.8) 154.8 — 1.0 (0.8) 155.8  U.S. government agency securities (3.6) 210.0 — — (3.6) 210.0  Total $ (5.8) $ 606.4 $ — $ 1.0 $ (5.8) $ 607.4  The Company regularly reviews its investment portfolios to determine if any investment is other-than-temporarily impaired due to changes in credit risk or other potential valuation concerns. The Company believes that the investments held as of February 28, 2018 that had gross unrealized losses of $39.9 million were not other-than-temporarily impaired. The Company believes that it is probable that the principal and interest will be collected in accordance with contractual terms, and that the unrealized losses on these securities were due to changes in interest rates and were not due to increased credit risk or other valuation concerns. A majority of the securities in an unrealized loss position as of February 28, 2018 and May 31, 2017 held an AA rating or better. The Company does not intend to sell these investments until the recovery of their amortized cost basis or maturity, and further believes that it is not more-likely-than-not that it will be required to sell these investments prior to that time. The Company’s assessment that an investment is not other-than-temporarily impaired could change in the future due to new developments or changes in the Company’s strategies or assumptions related to any particular investment.  Realized gains and losses on the sales of securities are determined by specific identification of the amortized cost basis of each security. On the Consolidated Statements of Income and Comprehensive Income, realized gains and losses from funds held for clients are included in interest on funds held for clients and realized gains and losses from corporate investments are included in investment income, net. Realized gains and losses were insignificant for the three and nine months ended February 28, 2018 and February 28, 2017 .  The amortized cost and fair value of available-for-sale securities that had stated maturities as of February 28, 2018 are shown below by contractual maturity. Expected maturities can differ from contractual maturities because borrowers may have the right to prepay obligations without prepayment penalties.      February 28, 2018   Amortized Fair  In millions cost value  Maturity date:  Due in one year or less $ 317.9 $ 317.9  Due after one year through three years 820.5 819.9  Due after three years through five years 998.1 990.7  Due after five years 1,654.0 1,627.1  Total $ 3,790.5 $ 3,755.6  Variable rate demand notes are primarily categorized as due after five years in the table above as the contractual maturities on these securities are typically 20 to 3 0 years. Although these securities are issued as long-term securities, they are priced and traded as short-term instruments because of the liquidity provided through the tender feature.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Feb. 28, 2018
Fair Value Measurements [Abstract]
Fair Value Measurements	Note F: Fair Value Measurements  Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price), in an orderly transaction between market participants at the measurement date. The accounting standards related to fair value measurements include a hierarchy for information and valuations used in measuring fair value that is broken down into three levels based on reliability, as follows:  · Level 1 valuations are based on quoted prices in active markets for identical instruments that the Company can access at the measurement date.  · Level 2 valuations are based on inputs other than quoted prices included in Level 1 that are observable for the instrument, either directly or indirectly, for substantially the full term of the asset or liability including the following:  o quoted prices for similar, but not identical, instruments in active markets;  o quoted prices for identical or similar instruments in markets that are not active;  o inputs other than quoted prices that are observable for the instrument; or  o inputs that are derived principally from or corroborated by observable market data by correlation or other means.  · Level 3 valuations are based on information that is unobservable and significant to the overall fair value measurement.  The carrying values of cash and cash equivalents, accounts receivable, net of allowance for doubtful accounts, accounts payable and short-term borrowings, when used by the Company, approximate fair value due to the short maturities of these instruments. Marketable securities included in funds held for clients and corporate investments consist primarily of securities classified as available-for-sale and are recorded at fair value on a recurring basis.  The Company’s financial assets and liabilities measured at fair value on a recurring basis were as follows:      February 28, 2018  Quoted Significant  prices in other Significant  Carrying active observable unobservable  value markets inputs inputs  In millions (Fair value) (Level 1) (Level 2) (Level 3)  Assets:  Cash equivalents:  Commercial paper $ 225.0 $ — $ 225.0 $ —  Time deposits 150.0 150.0 — —  Money market securities 30.0 30.0 — —  Total cash equivalents $ 405.0 $ 180.0 $ 225.0 $ —  Available-for-sale securities:  Corporate bonds $ 299.4 $ — $ 299.4 $ —  General obligation municipal bonds 1,295.8 — 1,295.8 —  Pre-refunded municipal bonds 65.2 — 65.2 —  Revenue municipal bonds 845.1 — 845.1 —  U.S. government agency securities 395.4 — 395.4 —  Variable rate demand notes 854.7 — 854.7 —  Total available-for-sale securities $ 3,755.6 $ — $ 3,755.6 $ —  Other $ 17.9 $ 17.9 $ — $ —  Liabilities:  Other long-term liabilities $ 17.9 $ 17.9 $ — $ —     May 31, 2017  Quoted Significant  prices in other Significant  Carrying active observable unobservable  value markets inputs inputs  In millions (Fair value) (Level 1) (Level 2) (Level 3)  Assets:  Available-for-sale securities:  Corporate bonds $ 210.8 $ — $ 210.8 $ —  General obligation municipal bonds 1,442.3 — 1,442.3 —  Pre-refunded municipal bonds 55.5 — 55.5 —  Revenue municipal bonds 940.9 — 940.9 —  U.S. government agency securities 325.8 — 325.8 —  Variable rate demand notes 1,637.9 — 1,637.9 —  Total available-for-sale securities $ 4,613.2 $ — $ 4,613.2 $ —  Other $ 16.7 $ 16.7 $ — $ —  Liabilities:  Other long-term liabilities $ 16.7 $ 16.7 $ — $ —  In determining the fair value of its assets and liabilities, the Company predominately uses the market approach. Money market securities, which are cash equivalents, are valued based on quoted market prices in active markets. Time deposits are considered Level 1 investments as they are highly liquid and have a short-term maturity period, usually no longer than overnight. Commercial paper is included in Level 2 because it may not trade on a daily basis. Available-for-sale securities, including municipal bonds, variable rate demand notes, corporate bonds, and U.S. government agency securities, are included in Level 2 and are valued utilizing inputs obtained from an independent pricing service. To determine the fair value of the Company’s Level 2 available-for-sale securities, the independent pricing service uses a variety of inputs, including benchmark yields, reported trades, non-binding broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data, new issue data, and monthly payment information. The Company has not adjusted the prices obtained from the independent pricing service because it believes that they are appropriately valued.  Assets included as other are mutual fund investments, consisting of participants’ eligible deferral contributions under the Company’s non-qualified and unfunded deferred compensation plans. The related liability is reported as other long-term liabilities. The mutual funds are valued based on quoted market prices in active markets.  The preceding methods described may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, although the Company believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

Accounts Receivable, Net of All

Accounts Receivable, Net of Allowance for Doubtful Accounts	9 Months Ended
	Feb. 28, 2018
Accounts Receivable, Net of Allowance for Doubtful Accounts [Abstract]
Accounts Receivable, Net of Allowance for Doubtful Accounts	Note G: Accounts Receivable, Net of Allowance for Doubtful Accounts  The components of accounts receivable, net of allowance for doubtful accounts, consisted of the following:      February 28, May 31,  In millions 2018 2017  PEO receivables (1) $ 172.8 $ 137.8  Purchased receivables (2) 281.4 257.3  Other trade receivables (3) 103.6 118.4  Total accounts receivable, gross 557.8 513.5  Less: Allowance for doubtful accounts 7.3 6.0  Accounts receivable, net of allowance for doubtful accounts $ 550.5 $ 507.5 (1) PEO receivables are primarily client wages and related tax withholdings since the last payroll processed. Balances will vary based on timing of the last payroll processed and the end of the reporting period. In addition, balances as of February 28, 2018 include receivable balances for HROI, acquired in August 2017. Refer to Note C for further details. (2) Purchased receivables relate to payroll funding arrangements with clients in the temporary staffing industry. (3) Other trade receivables primarily relate to other ongoing services provided to our clients and can vary based on the timing of these services and the end of the reporting period.  No single client had a material impact on total accounts receivable, service revenue, or results of operations.

Property and Equipment, Net of

Property and Equipment, Net of Accumulated Depreciation	9 Months Ended
	Feb. 28, 2018
Property and Equipment, Net of Accumulated Depreciation [Abstract]
Property and Equipment, Net of Accumulated Depreciation	 Note H: Property and Equipment, Net of Accumulated Depreciation  The components of property and equipment, at cost, consisted of the following:      February 28, May 31,  In millions 2018 2017  Land and improvements $ 10.7 $ 8.3  Buildings and improvements 126.4 103.5  Data processing equipment 208.9 199.7  Software (1) 545.0 496.1  Furniture, fixtures, and equipment 114.0 115.2  Leasehold improvements 109.3 109.5  Construction in progress (1) 56.4 18.7  Total property and equipment, gross 1,170.7 1,051.0  Less: Accumulated depreciation 773.5 713.8  Property and equipment, net of accumulated depreciation $ 397.2 $ 337.2 (1) Software includes both purchased software and costs capitalized related to internally developed software placed in service. Capitalized costs related to internally developed software that has not yet been placed in service is included in construction in progress.  Depreciation expense was $31.5 million and $88.0 million for the three and nine months ended February 28, 2018 , respectively, compared to $26.4 million and $77.2 million for the three and nine months ended February 28, 2017 , respectively.  In August 2017, the Company announced its plan for a new multi-building Paychex campus based in Rochester, NY. This involves the purchase of five buildings and the renovation of over 300,000 square feet of existing space for a total estimated cost of approximately $60 million. The new campus will result in the consolidation of currently leased space in the Rochester area. During the three months ended November 30, 2017, the Company completed the purchase of these buildings for a combined cost of approximately $34.7 million and placed approximately $16.0 million in escrow for building renovations, which are in-process. In connection with this project, approximately $31.5 million is included in the Company’s construction in progress balance as of February 28, 2018. In addition, in September 2017, the Company entered into a transaction with the County of Monroe Industrial Development Agency for purposes of obtaining public benefits and inducements, expiring on December 31, 2039 . The public inducements include exemption from sales and use taxes for goods and services directly related to the renovations of the new multi-building campus. 

Goodwill and Intangible Assets,

Goodwill and Intangible Assets, Net of Accumulated Amortization	9 Months Ended
	Feb. 28, 2018
Goodwill and Intangible Assets, Net of Accumulated Amortization [Abstract]
Goodwill and Intangible Assets, Net of Accumulated Amortization	Note I: Goodwill and Intangible Assets, Net of Accumulated Amortization  The Company had goodwill balances on its Consolidated Balance Sheets of $827.4 million as of February 28, 2018 and $657.1 million as of May 31, 2017. The increase of $170.3 million in goodwill since May 31, 2017 was the result of the acquisitions of HROI in August 2017 and Lessor in February 2018. Refer to Note C for further details.  The Company has certain intangible assets with finite lives. The components of intangible assets, at cost, consisted of the following:      February 28, May 31,  In millions 2018 2017  Client lists (1) $ 308.4 $ 293.5  Other intangible assets 5.7 5.4  Total intangible assets, gross 314.1 298.9  Less: Accumulated amortization 209.0 241.3  Intangible assets, net of accumulated amortization $ 105.1 $ 57.6  (1) Client lists include current estimates of amounts acquired from Lessor as of February 28, 2018. Refer to Note C for further details.  Amortization expense relating to intangible assets was $5.1 million and $14.3 million for the three and nine months ended February 28, 2018 , respectively, compared to $4.6 million and $ 13.5 million for the three and nine months ended February 28, 2017 , respectively.  As of February 28, 2018 , the estimated amortization expense relating to intangible asset balances for the full year fiscal 2018 and the following four fiscal years is as follows:    In millions Estimated amortization Year ending May 31, expense  2018 $ 21.6  2019 25.3  2020 20.8  2021 16.8  2022 13.0 

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss)/Income	9 Months Ended
	Feb. 28, 2018
Accumulated Other Comprehensive (Loss)/Income [Abstract]
Accumulated Other Comprehensive (Loss)/ Income	Note J: Accumulated Other Comprehensive (Loss)/Income  The change in unrealized gains and losses, net of applicable taxes, related to investments in available-for-sale securities is the primary component reported in accumulated other comprehensive (loss)/income on the Company’s Consolidated Balance Sheets. The changes in accumulated other comprehensive (loss)/income are as follows:     For the three months ended For the nine months ended  February 28, February 28,  In millions 2018 2017 2018 2017  Beginning balance $ (9.2) $ (16.8) $ 20.0 $ 29.2  Other comprehensive (loss)/income:  Unrealized (losses)/gains on available-for-sale securities, net of tax (17.5) 21.4 (46.7) (24.6)  Total other comprehensive (loss)/income, net of tax (17.5) 21.4 (46.7) (24.6)  Ending balance $ (26.7) $ 4.6 $ (26.7) $ 4.6   Total tax (benefit)/expense included in other comprehensive income $ (3.2) $ 12.3 $ (20.1) $ (14.0)  Reclassification adjustments out of accumulated other comprehensive (loss)/income for realized gains and losses on the sale of available-for-sale securities were insignificant for the three and nine months ended February 28, 2018 and February 28, 2017 . Those reclassification adjustments are reflected in interest on funds held for clients on the Consolidated Statements of Income and Comprehensive Income.

Short-term Financing

Short-term Financing	9 Months Ended
	Feb. 28, 2018
Short-term Financing [Abstract]
Short-term Financing	 Note K: Short-term Financing  The Company maintains credit facilities, letters of credit, and lines of credit as part of its normal and recurring business operations.  Credit Facilities: The Company maintains three committed, unsecured credit facilities, as follows:     Bank Borrower (1) Date Entered Expiration Date Maximum Amount Available Purpose  JP Morgan Chase Bank, N.A. (2) Paychex of New York, LLC August 5, 2015 August 5, 2020 $1 Billion To meet short-term funding requirements.  JP Morgan Chase Bank, N.A. (2) Paychex of New York, LLC August 17, 2017 August 17, 2022 $500 Million To meet short-term funding requirements.  PNC Bank, National Association (“PNC”) Paychex Advance, LLC March 17, 2016 March 17, 2020 $150 Million To finance working capital needs and general corporate purposes. (1) Borrower is a wholly owned subsidiary of the Company. (2) JP Morgan Chase Bank, N.A. (“JPM”) acts as the administrative agent for this syndicated credit facility.  For all credit facilities, obligations under any facility are guaranteed by the Company and certain of its subsidiaries and will bear interest at competitive rates based on options provided to the borrower. Upon the expiration date, any borrowings outstanding will mature and be payable on such date .  JPM $1 Billion Credit Facility: There were no borrowings outstanding under this credit facility as of February 28, 2018 or May 31, 2017 . Details of borrowings under this credit facility d uring the three and nine months ended February 28, 2018 and February 28, 2017 are as follows:     For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2017 2018 2017  Number of days borrowed 2 8 21 27  Maximum amount borrowed $ 200.0 $ 250.0 $ 700.0 $ 350.0  Weighted-average amount borrowed $ 125.0 $ 81.3 $ 311.9 $ 183.3  Weighted-average interest rate 4.25 % 2.24 % 4.24 % 2.68 %  The Company typically borrows on an overnight basis. In addition to overnight borrowings, during the nine months ended February 28, 2018 , the Company borrowed $100.0 million for a three -day period at a weighted-average interest rate of 4.25% . During the three months ended February 28, 2017, the Company borrowed $50.0 million for eight days at a weighted average LIBOR-based interest rate of 1.44% . During the nine months ended February 28, 2017, the Company borrowed $150.0 million for seven days and $50.0 million for 18 days at a weighted-average LIBOR-based interest rate of 1.40% .  JPM $500 Million Credit Facility: There were no borrowings outstanding under this credit facility as of February 28, 2018. During the nine months ended February 28, 2018, the Company borrowed against this credit facility for the first time. Details of borrowings under this credit facility during the three and nine months ended February 28, 2018 are as follows:      For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2018  Number of days borrowed 19 39  Maximum amount borrowed $ 75.0 $ 400.0  Weighted-average amount borrowed $ 75.0 $ 147.2  Weighted-average interest rate 2.19 % 2.69 %  In addition to overnight borrowings, during the three months ended February 28, 2018 , the Company borrowed $75.0 million for 19 days at a weighted-average LIBOR-based interest rate of 2.19% . During the nine months ended February 28, 2018, the Company borrowed $300.0 million for seven days and $75.0 million for 30 days at weighted averag e LIBOR-based interest rates of 2.13% and 2.19% , respectively.  PNC $150 Million Credit Facility: As of February 28, 2018 , the Company had $57.7 million outstanding under this credit facility, which remains outstanding as of the date of this report. There were no borrowings outstanding under this credit facility as of May 31, 2017 . Details of borrowings under this credit facility during the three and nine months ended February 28, 2018 and February 28, 2017 , are as follows:     For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2017 2018 2017  Number of days borrowed 90 90 269 267  Maximum amount borrowed $ 59.9 $ 55.6 $ 59.9 $ 55.6  Weighted-average amount borrowed $ 59.1 $ 55.3 $ 57.6 $ 52.6  Weighted-average interest rate 2.01 % 1.27 % 1.83 % 1.13 % All of the Company’s credit facilities contain various financial and operational covenants that are usual and customary for such arrangements. The Company was in compliance with all of these covenants as of February 28, 2018 . Certain lenders under these credit facilities, and their respective affiliates, have performed, and may in the future perform for the Company, various commercial banking, investment banking, underwriting, and other financial advisory services, for which they have received, and will continue to receive in the future, customary fees and expenses.  Letters of credit: The Company had irrevocable standby letters of credit outstanding totaling $56.8 million and $47.3 million as of February 28, 2018 and May 31, 2017 , respectively, required to secure commitments for certain insurance policies. The letters of credit expire at various dates between April 2018 and December 2018 . No amounts were outstanding on these letters of credit as of or during the nine months ended February 28, 2018 and February 28, 2017 , or as of May 31, 2017 . Lines of credit: Effective August 17, 2017, the Company terminated four uncommitted, secured, short-term lines of credit totaling $900.0 million. The lines of credit were available to the Company at market rates of interest and were primarily used to meet short-term funding requirements related to deposit account overdrafts and client fund obligations arising from electronic payment transactions on behalf of clients in the ordinary course of business. There were no amounts outstanding under these lines of credit during the nine months ended February 28, 2018 and February 28, 2017, or as of May 31, 2017. The Company does not have any other open lines of credit as of the date of this report.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Feb. 28, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies	Note L: Commitments and Contingencies  Other commitments: The Company enters into various purchase commitments with vendors in the ordinary course of business. The Company had outstanding commitments to purchase approximately $5.8 million and $7.4 million of capital assets as of February 28, 2018 and May 31, 2017 , respectively.  In the normal course of business, the Company makes representations and warranties that guarantee the performance of services under service arrangements with clients. Historically, there have been no material losses related to such guarantees. In addition, the Company has entered into indemnification agreements with its officers and directors, which require the Company to defend and, if necessary, indemnify these individuals for certain pending or future claims as they relate to their services provided to the Company.  The Company currently self-insures the deductible portion of various insured exposures under certain employee benefit plans. The estimated loss exposure under these insurance arrangements is recorded in other current liabilities on the Consolidated Balance Sheets. Historically, the amounts accrued have not been material and are not material as of February 28, 2018 . The Company also maintains insurance coverage in addition to its purchased primary insurance policies for gap coverage for employment practices liability, errors and omissions, warranty liability, theft and embezzlement, cyber threats, and acts of terrorism; and capacity for deductibles and self-insured retentions through its captive insurance company.  Contingencies: The Company is subject to various claims and legal matters that arise in the normal course of its business. These include disputes or potential disputes related to breach of contract, tort, breach of fiduciary duty, employment-related claims, tax claims, and other matters.  The Company’s management currently believes that resolution of any outstanding legal matters will not have a material adverse effect on the Company’s financial position or results of operations. However, legal matters are subject to inherent uncertainties and there exists the possibility that the ultimate resolution of these matters could have a material adverse impact on the Company’s financial position and results of operations in the period in which any such effect is recorded.

Income Taxes

Income Taxes	9 Months Ended
	Feb. 28, 2018
Income Taxes [Abstract]
Income Taxes	Note M: Income Taxes  The Company’s effective income tax rate was 11.7% and 34.2% for the three months ended February 28, 2018 and February 28, 2017 , respectively, and 27.7% and 34.1% for the nine months ended February 28, 2018 and February 28, 2017 , respectively. The effective income tax rates for the three and nine months ended February 28, 2018 were significantly impacted by the enactment of the Tax Act. In addition, t he effective income tax rates in these periods were impacted by the recognition of a net discrete tax benefit related to employee stoc k-based compensation payments.  The Tax Act makes bro ad and complex changes to U.S. F ederal corporate income taxation including, but not limited to : (i) reducing the corporate tax rate from 35% to 21% (a blended statutory tax rate of 29.2% for fiscal 2018); (ii) creating new or furthering limitations to the deductibility of officer compensation, interest, meals, entertainment and other expenses; and (iii) changing from a worldwide to a territorial taxation system. In December 2017, the staff of the SEC issued guidance under Staff Accounting Bulletin (“SAB”) No. 118, “Income Tax Accounting Implications of the Tax Cuts and Jobs Act,” allowing taxpayers to record provisional amounts for reasonable estimates when they do not have the necessary information available, prepared or analyzed in reasonable detail to complete their accounting for certain income tax effects of the Tax Act. The SEC also issued rules that would allow for a measurement period of up to one year after the enactment date of the Tax Act to finalize the related tax impacts.  As a result of the Tax Act, the Company recorded estimated tax benefits of $56.9 million, including a one-time net tax benefit of $20.8 million related to the revaluation of the Company’s net deferred tax liabilities and a net tax benefit of $36.1 million recognized in the third quarter related to the change in the Company’s annual effective income tax rate for fiscal 2018 applied to income before taxes for the first six months of fiscal 2018 . These amounts totaled $0.06 per diluted share and $0.10 per diluted share, respectively. This analysis is complete except for provisional amounts that were determined in accordance with SAB No. 118 related to certain equity compensation arrangements. Further Internal Revenue Service guidance related to whether these compensation arrangements meet the transition rule under the Tax Act is expected to be released within the next nine months and any change to the provisional amounts as a result of this further guidance is not anticipated to be material. 

Description of Business, Basi19

Description of Business, Basis of Presentation, and Significant Accounting Policies (Policy)	9 Months Ended
	Feb. 28, 2018
Description of Business, Basis of Presentation, and Significant Accounting Policies [Abstract]
Description of Business	Description of business: Paychex, Inc. and its wholly owned subsidiaries (collectively, the “Company” or “Paychex”) is a leading provider of integrated human capital management (“HCM”) solutions for payroll, human resource (“HR”), retirement, and insurance services for small- to medium-sized businesses in the United States (“U.S.”). The Company also has operations in Europe. Effective February 28, 2018, the Company acquired Lessor Group (“Lessor”), headquartered in Denmark and serving clients in Northern Europe. Refer to Note C for further details. Paychex, a Delaware corporation formed in 1979, reports as one segment. Substantially all of the Company’s revenue is generated within the U.S. The Company also generates revenue within Europe, which represented less than one percent of the Company's total revenue for each of the three and nine months ended February 28, 2018 and February 28, 2017 . Long-lived assets in Europe were approximately 13% of total long-lived assets of the Company as of February 28, 2018 and were insignificant as of May 31, 2017 .
Basis of Presentation	Basis of presentation: The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions to the Quarterly Report on Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statement presentation. The consolidated financial statements include the consolidated accounts of the Company with all intercompany transactions eliminated. In the opinion of management, the information furnished herein reflects all adjustments (consisting of items of a normal recurring nature), which are necessary for a fair statement of the results for the interim period. These financial statements should be read in conjunction with the Company’s consolidated financial statements and related Notes to Consolidated Financial Statements presented in the Company’s Annual Report on Form 10-K (“Form 10-K”) for the fiscal year ended May 31, 2017 (“fiscal 2017 ”). Operating result s and cash flows for the period ended February 28, 2018 are not necessarily indicative of the results that may be expected for other interim periods or for the fiscal year ending May 31, 2018 (“fiscal 2018 ”).
Subsequent Event	Subsequent event: During the three months ended February 28, 2018, the Company began negotiations to terminate certain license agreements and acquire rights to certain client lists in order to resolve a contractual dispute with certain licensees. The negotiations were completed in March 2018. The Company recorded $32.6 million on its Consolidated Balance Sheets within other current liabilities as of February 28, 2018, and $24.7 million, net of tax, in its Consolidated Statements of Income and Comprehensive Income for the three months ended February 28, 2018 related to the termination of these license agreements. In addition, the Company acquired rights to certain client lists as it relates to this agreement in March 2018 for a cost of approximately $30.0 million.
PEO Insurance Reserves	PEO insurance reserves: As part of the professional employer organization (“PEO”), the Company offers workers' compensation insurance and health insurance to client companies for the benefit of client employees. For workers' compensation insurance, reserves are established to provide for the estimated costs of paying claims up to per occurrence liability limits. The Company’s maximum individual claims liability is $1.3 million under both its fiscal 2018 and fiscal 2017 workers’ compensation insurance policies.  Under the minimum premium insurance plan offering within the PEO, the Company's health benefits insurance reserves are established to provide for the payment of claims liability charges in accordance with its service contract with the insurance carrier. The Company's maximum individual claims liability is $0.3 million under both its calendar 2018 and calendar 2017 minimum premium insurance plan policies.  Estimating the ultimate cost of future claims is an uncertain and complex process based upon historical loss experience and actuarial loss projections, and is subject to change due to multiple factors, including economic trends, changes in legal liability law, and damage awards, all of which could materially impact the reserves as reported in the consolidated financial statements. Accordingly, final claim settlements may vary from the present estimates, particularly with workers' compensation insurance where those payments may not occur until well into the future. The Company regularly reviews the adequacy of its estimated insurance reserves. Adjustments to previously established insurance reserves are reflected in the results of operations for the period in which such adjustments are identified. Such insurance reserve adjustments could be significant, reflecting any combination of new and adverse or favorable trends.
Stock-Based Compensation Costs	Stock-based compensation costs: The Company has issued stock-based awards to employees and directors consisting of stock options, restricted stock awards, restricted stock units, performance shares, performance-based restricted stock, and performance stock options. The Company accounts for all stock-based awards to employees and directors as compensation costs in the consolidated financial statements based on their fair values measured as of the date of grant. These costs are recognized over the requisite service period. Stock-based compensation costs recognized were $10.3 million and $29.4 million for the three and nine months ended February 28, 2018 , respectively, as compared with $8.9 million and $ 26.5 million for the three and nine months ended February 28, 2017 , respectively. The methods and assumptions used in the determination of the fair value of stock-based awards are consistent with those described in the Company’s fiscal 2017 Form 10-K .
Recently Adopted and Issued Accounting Pronouncements	Recently adopted accounting pronouncements: In January 2018, the Company early adopted Accounting Standards Update (“ASU”) No. 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business.” ASU No. 2017-01 clarifies the definition of a business in order to allow for the evaluation of whether transactions should be accounted for as acquisitions or disposals of assets or businesses. The adoption of ASU 2017-01 did not have a material impact on the Company’s consolidated financial statements. Recently issued accounting pronouncements: In February 2018, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” ASU No. 2018-02 allows entities to reclassify certain stranded income tax effects from accumulated other comprehensive income to retained earnings resulting from the Tax Cuts and Jobs Act (the “Tax Act”), enacted on December 22, 2017. The guidance also requires additional financial statement disclosures to clarify the effects of adoption. ASU No. 2018-02 should be applied either in the period of adoption or retrospectively to each period or periods in which the eff ect of the change in the U.S. F ederal corporate income tax rate in the Tax Act is recognized. This guidance is effective for fiscal years beginning after December 15, 2018, and for interim periods within those fiscal years, with early adoption permitted. This guidance is applicable to the Company’s fiscal year beginning June 1, 2019. The Company is currently evaluating the potential effects of this guidance on its consolidated financial statements.  In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” ASU No. 2016-02 improves transparency and comparability among companies by recognizing lease assets and lease liabilities on the balance sheet and by disclosing key information about leasing arrangements. ASU No. 2016-02 is effective for public business entities for annual periods, including interim periods within those annual periods, beginning after December 15, 2018, with early adoption permitted. This guidance is applicable to the Company's fiscal year beginning June 1, 2019. The Company is in the preliminary stages of gathering data and assessing the impact of the new lease accounting standard and the Company anticipates that the adoption of the new lease accounting standard will result in additional assets and liabilities being recorded on its Consolidated Balance Sheets. In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” This guidance, as amended by subsequent ASUs on the topic, outlines a single comprehensive model for determining revenue recognition for contracts with customers, and supersedes current guidance on revenue recognition in Accounting Standards Codification (“ASC”) Topic 605, “Revenue Recognition.” Entities have the option to apply the new guidance under a full retrospective approach to each prior reporting period presented or a modified retrospective approach with a cumulative effect of initially applying the new guidance recognized at the date of initial application within the consolidated financial statements. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods. The Company did not elect to early-adopt the new standard, and will adopt the new standard in its fiscal year beginning June 1, 2018. The analysis of the new standard and its impact to the Company is nearly complete as the Company is in the process of finalizing its conclusions. Further, the Company currently anticipates applying the guidance under the full retrospective approach. The Company’s ability to adopt using the full retrospective method is dependent on system readiness and the completion of the analysis of information necessary to restate prior period consolidated financial statements. While the evaluation of the impact of the new revenue recognition standard on its consolidated financial statements has not yet been finalized, the Company anticipates the provisions to primarily impact the manner in which it treats certain costs to obtain contracts and costs to fulfill contracts. Generally, in relation to these items, the new standard will result in the Company deferring additional costs on the Consolidated Balance Sheets and subsequently amortizing them to the Consolidated Statements of Income and Comprehensive Income over the estimated average life of the client. The Company does not expect the provisions of the new standard will have a material impact on the timing or the amount of revenue it recognizes. The Company has also not yet fully determined the impacts of the disclosure requirements under the new standard, and is evaluating the way it will disaggregate revenue into categories that show how economic factors affect the nature, timing, and uncertainty of revenue and cash flows generated from contracts with customers. Additionally, while the Company is in the process of assessing its accounting considerations to ensure its ability to record, report, and analyze results under the new standard, it is not expecting significant changes in its business processes or systems.  Other recent authoritative guidance issued by the FASB (including technical corrections to the ASC), the American Institute of Certified Public Accountants, and the Securities Exchange Commission (“SEC”) during the nine months ended February 28, 2018 did not, or are not expected to, have a material effect on the Company’s consolidated financial statements.

Basic and Diluted Earnings Pe20

Basic and Diluted Earnings Per Share (Tables)	9 Months Ended
	Feb. 28, 2018
Basic and Diluted Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Share	   For the three months ended For the nine months ended  February 28, February 28,  In millions, except per share amounts 2018 2017 2018 2017  Basic earnings per share:  Net income $ 260.4 $ 202.5 $ 705.2 $ 622.0  Weighted-average common shares outstanding 359.2 359.0 359.1 360.0  Basic earnings per share $ 0.72 $ 0.56 $ 1.96 $ 1.73  Diluted earnings per share:  Net income $ 260.4 $ 202.5 $ 705.2 $ 622.0  Weighted-average common shares outstanding 359.2 359.0 359.1 360.0  Dilutive effect of common share equivalents 2.8 2.8 2.5 2.8  Weighted-average common shares outstanding, assuming dilution 362.0 361.8 361.6 362.8  Diluted earnings per share $ 0.72 $ 0.56 $ 1.95 $ 1.71  Weighted-average anti-dilutive common share equivalents — 0.7 0.8 0.7 

Investment Income, Net (Tables)

Investment Income, Net (Tables)	9 Months Ended
	Feb. 28, 2018
Investment Income, Net [Abstract]
Schedule of Investment Income, Net	   For the three months ended For the nine months ended  February 28, February 28,  In millions 2018 2017 2018 2017  Interest income on corporate funds $ 3.1 $ 2.4 $ 8.7 $ 7.2  Interest expense (1.1) (0.6) (3.2) (1.9)  Net gain/(loss) from equity-method investments 0.3 (0.6) 0.6 (1.7)  Investment income, net $ 2.3 $ 1.2 $ 6.1 $ 3.6 

Funds Held for Clients and Co22

Funds Held for Clients and Corporate Investments (Tables)	9 Months Ended
	Feb. 28, 2018
Funds Held for Clients and Corporate Investments [Abstract]
Funds Held for Clients and Corporate Investments	   February 28, 2018  Gross Gross  Amortized unrealized unrealized Fair  In millions cost gains losses value  Type of issue:  Funds held for clients' money market securities and other cash equivalents $ 673.9 $ — $ — $ 673.9  Available-for-sale securities:  Corporate bonds 305.8 0.1 (6.5) 299.4  General obligation municipal bonds 1,303.8 2.6 (10.6) 1,295.8  Pre-refunded municipal bonds (1) 64.7 0.6 (0.1) 65.2  Revenue municipal bonds 851.3 1.7 (7.9) 845.1  U.S. government agency securities 410.2 — (14.8) 395.4  Variable rate demand notes 854.7 — — 854.7  Total available-for-sale securities 3,790.5 5.0 (39.9) 3,755.6  Other 15.8 2.1 — 17.9  Total funds held for clients and corporate investments $ 4,480.2 $ 7.1 $ (39.9) $ 4,447.4     May 31, 2017  Gross Gross  Amortized unrealized unrealized Fair  In millions cost gains losses value  Type of issue:  Funds held for clients' money market securities and other cash equivalents $ 264.8 $ — $ — $ 264.8  Available-for-sale securities:  Corporate bonds 208.6 2.7 (0.5) 210.8  General obligation municipal bonds 1,422.0 21.2 (0.9) 1,442.3  Pre-refunded municipal bonds (1) 54.6 0.9 — 55.5  Revenue municipal bonds 929.2 12.5 (0.8) 940.9  U.S. government agency securities 328.9 0.5 (3.6) 325.8  Variable rate demand notes 1,637.9 — — 1,637.9  Total available-for-sale securities 4,581.2 37.8 (5.8) 4,613.2  Other 14.8 1.9 — 16.7  Total funds held for clients and corporate investments $ 4,860.8 $ 39.7 $ (5.8) $ 4,894.7  (1) Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations. 
Classification of Investments on Consolidated Balance Sheets	   February 28, May 31,  In millions 2018 2017  Funds held for clients $ 3,944.7 $ 4,301.9  Corporate investments 97.3 138.8  Long-term corporate investments 405.4 454.0  Total funds held for clients and corporate investments $ 4,447.4 $ 4,894.7 
Securities in Unrealized Loss Position	   February 28, 2018  Securities in an unrealized loss position for less than twelve months Securities in an unrealized loss position for more than twelve months Total  Gross Gross Gross  unrealized Fair unrealized Fair unrealized Fair  In millions losses value losses value losses value  Type of issue:  Corporate bonds $ (5.2) $ 252.1 $ (1.3) $ 34.7 $ (6.5) $ 286.8  General obligation municipal bonds (8.0) 735.5 (2.6) 71.4 (10.6) 806.9  Pre-refunded municipal bonds (0.1) 7.2 — 0.5 (0.1) 7.7  Revenue municipal bonds (6.1) 435.7 (1.8) 51.6 (7.9) 487.3  U.S. government agency securities (6.8) 219.3 (8.0) 176.1 (14.8) 395.4  Total $ (26.2) $ 1,649.8 $ (13.7) $ 334.3 $ (39.9) $ 1,984.1     May 31, 2017  Securities in an unrealized loss position for less than twelve months Securities in an unrealized loss position for more than twelve months Total  Gross Gross Gross  unrealized Fair unrealized Fair unrealized Fair  In millions losses value losses value losses value  Type of issue:  Corporate bonds $ (0.5) $ 43.6 $ — $ — $ (0.5) $ 43.6  General obligation municipal bonds (0.9) 188.8 — — (0.9) 188.8  Pre-refunded municipal bonds — 9.2 — — — 9.2  Revenue municipal bonds (0.8) 154.8 — 1.0 (0.8) 155.8  U.S. government agency securities (3.6) 210.0 — — (3.6) 210.0  Total $ (5.8) $ 606.4 $ — $ 1.0 $ (5.8) $ 607.4 
Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity	   February 28, 2018   Amortized Fair  In millions cost value  Maturity date:  Due in one year or less $ 317.9 $ 317.9  Due after one year through three years 820.5 819.9  Due after three years through five years 998.1 990.7  Due after five years 1,654.0 1,627.1  Total $ 3,790.5 $ 3,755.6 

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Feb. 28, 2018
Fair Value Measurements [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	   February 28, 2018  Quoted Significant  prices in other Significant  Carrying active observable unobservable  value markets inputs inputs  In millions (Fair value) (Level 1) (Level 2) (Level 3)  Assets:  Cash equivalents:  Commercial paper $ 225.0 $ — $ 225.0 $ —  Time deposits 150.0 150.0 — —  Money market securities 30.0 30.0 — —  Total cash equivalents $ 405.0 $ 180.0 $ 225.0 $ —  Available-for-sale securities:  Corporate bonds $ 299.4 $ — $ 299.4 $ —  General obligation municipal bonds 1,295.8 — 1,295.8 —  Pre-refunded municipal bonds 65.2 — 65.2 —  Revenue municipal bonds 845.1 — 845.1 —  U.S. government agency securities 395.4 — 395.4 —  Variable rate demand notes 854.7 — 854.7 —  Total available-for-sale securities $ 3,755.6 $ — $ 3,755.6 $ —  Other $ 17.9 $ 17.9 $ — $ —  Liabilities:  Other long-term liabilities $ 17.9 $ 17.9 $ — $ —     May 31, 2017  Quoted Significant  prices in other Significant  Carrying active observable unobservable  value markets inputs inputs  In millions (Fair value) (Level 1) (Level 2) (Level 3)  Assets:  Available-for-sale securities:  Corporate bonds $ 210.8 $ — $ 210.8 $ —  General obligation municipal bonds 1,442.3 — 1,442.3 —  Pre-refunded municipal bonds 55.5 — 55.5 —  Revenue municipal bonds 940.9 — 940.9 —  U.S. government agency securities 325.8 — 325.8 —  Variable rate demand notes 1,637.9 — 1,637.9 —  Total available-for-sale securities $ 4,613.2 $ — $ 4,613.2 $ —  Other $ 16.7 $ 16.7 $ — $ —  Liabilities:  Other long-term liabilities $ 16.7 $ 16.7 $ — $ — 

Accounts Receivable, Net of A24

Accounts Receivable, Net of Allowance for Doubtful Accounts (Tables)	9 Months Ended
	Feb. 28, 2018
Accounts Receivable, Net of Allowance for Doubtful Accounts [Abstract]
Components of Accounts Receivable, Net of Allowance for Doubtful Accounts	    February 28, May 31,  In millions 2018 2017  PEO receivables (1) $ 172.8 $ 137.8  Purchased receivables (2) 281.4 257.3  Other trade receivables (3) 103.6 118.4  Total accounts receivable, gross 557.8 513.5  Less: Allowance for doubtful accounts 7.3 6.0  Accounts receivable, net of allowance for doubtful accounts $ 550.5 $ 507.5 (1) PEO receivables are primarily client wages and related tax withholdings since the last payroll processed. Balances will vary based on timing of the last payroll processed and the end of the reporting period. In addition, balances as of February 28, 2018 include receivable balances for HROI, acquired in August 2017. Refer to Note C for further details. (2) Purchased receivables relate to payroll funding arrangements with clients in the temporary staffing industry. (3) Other trade receivables primarily relate to other ongoing services provided to our clients and can vary based on the timing of these services and the end of the reporting period.

Property and Equipment, Net o25

Property and Equipment, Net of Accumulated Depreciation (Tables)	9 Months Ended
	Feb. 28, 2018
Property and Equipment, Net of Accumulated Depreciation [Abstract]
Components of Property and Equipment, at Cost	   February 28, May 31,  In millions 2018 2017  Land and improvements $ 10.7 $ 8.3  Buildings and improvements 126.4 103.5  Data processing equipment 208.9 199.7  Software (1) 545.0 496.1  Furniture, fixtures, and equipment 114.0 115.2  Leasehold improvements 109.3 109.5  Construction in progress (1) 56.4 18.7  Total property and equipment, gross 1,170.7 1,051.0  Less: Accumulated depreciation 773.5 713.8  Property and equipment, net of accumulated depreciation $ 397.2 $ 337.2 (1) Software includes both purchased software and costs capitalized related to internally developed software placed in service. Capitalized costs related to internally developed software that has not yet been placed in service is included in construction in progress. 

Goodwill and Intangible Asset26

Goodwill and Intangible Assets, Net of Accumulated Amortization (Tables)	9 Months Ended
	Feb. 28, 2018
Goodwill and Intangible Assets, Net of Accumulated Amortization [Abstract]
Components of Intangible Assets, at Cost	    February 28, May 31,  In millions 2018 2017  Client lists (1) $ 308.4 $ 293.5  Other intangible assets 5.7 5.4  Total intangible assets, gross 314.1 298.9  Less: Accumulated amortization 209.0 241.3  Intangible assets, net of accumulated amortization $ 105.1 $ 57.6  (1) Client lists include current estimates of amounts acquired from Lessor as of February 28, 2018. Refer to Note C for further details.
Estimated Amortization Expense	 In millions Estimated amortization Year ending May 31, expense  2018 $ 21.6  2019 25.3  2020 20.8  2021 16.8  2022 13.0 

Accumulated Other Comprehensi27

Accumulated Other Comprehensive (Loss)/Income (Tables)	9 Months Ended
	Feb. 28, 2018
Accumulated Other Comprehensive (Loss)/Income [Abstract]
Changes in Accumulated Other Comprehensive (Loss)/ Income	   For the three months ended For the nine months ended  February 28, February 28,  In millions 2018 2017 2018 2017  Beginning balance $ (9.2) $ (16.8) $ 20.0 $ 29.2  Other comprehensive (loss)/income:  Unrealized (losses)/gains on available-for-sale securities, net of tax (17.5) 21.4 (46.7) (24.6)  Total other comprehensive (loss)/income, net of tax (17.5) 21.4 (46.7) (24.6)  Ending balance $ (26.7) $ 4.6 $ (26.7) $ 4.6   Total tax (benefit)/expense included in other comprehensive income $ (3.2) $ 12.3 $ (20.1) $ (14.0) 

Short-term Financing (Tables)

Short-term Financing (Tables) - Revolving Credit Facility [Member]	9 Months Ended
	Feb. 28, 2018
Line of Credit Facility [Line Items]
Description of Credit Facilities	   Bank Borrower (1) Date Entered Expiration Date Maximum Amount Available Purpose  JP Morgan Chase Bank, N.A. (2) Paychex of New York, LLC August 5, 2015 August 5, 2020 $1 Billion To meet short-term funding requirements.  JP Morgan Chase Bank, N.A. (2) Paychex of New York, LLC August 17, 2017 August 17, 2022 $500 Million To meet short-term funding requirements.  PNC Bank, National Association (“PNC”) Paychex Advance, LLC March 17, 2016 March 17, 2020 $150 Million To finance working capital needs and general corporate purposes. (1) Borrower is a wholly owned subsidiary of the Company. (2) JP Morgan Chase Bank, N.A. (“JPM”) acts as the administrative agent for this syndicated credit facility.
JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Credit Facility Amount Borrowed	  For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2017 2018 2017  Number of days borrowed 2 8 21 27  Maximum amount borrowed $ 200.0 $ 250.0 $ 700.0 $ 350.0  Weighted-average amount borrowed $ 125.0 $ 81.3 $ 311.9 $ 183.3  Weighted-average interest rate 4.25 % 2.24 % 4.24 % 2.68 % 
JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Credit Facility Amount Borrowed	   For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2018  Number of days borrowed 19 39  Maximum amount borrowed $ 75.0 $ 400.0  Weighted-average amount borrowed $ 75.0 $ 147.2  Weighted-average interest rate 2.19 % 2.69 % 
PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]
Line of Credit Facility [Line Items]
Credit Facility Amount Borrowed	  For the three months ended For the nine months ended  February 28, February 28,  $ in millions 2018 2017 2018 2017  Number of days borrowed 90 90 269 267  Maximum amount borrowed $ 59.9 $ 55.6 $ 59.9 $ 55.6  Weighted-average amount borrowed $ 59.1 $ 55.3 $ 57.6 $ 52.6  Weighted-average interest rate 2.01 % 1.27 % 1.83 % 1.13 % 

Description of Business, Basi29

Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions	Feb. 28, 2018USD ($)	Mar. 31, 2018USD ($)	Feb. 28, 2018USD ($)	Feb. 28, 2017USD ($)	Feb. 28, 2018USD ($)segment	Feb. 28, 2017USD ($)	May 31, 2017USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment					1
Other current liabilities related to termination of license agreements	$ 32.6		$ 32.6		$ 32.6
Cost related to termination of license agreement			24.7
Maximum individual workers' compensation claims liability					1.3		$ 1.3
Maximum individual health insurance claims liability					0.3		$ 0.3
Stock-based compensation costs recognized			$ 10.3	$ 8.9	$ 29.4	$ 26.5
Subsequent Event [Member]
Accounting Policies [Line Items]
Cost expected to acquire rights to client lists		$ 30
Europe [Member] | Revenue [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage			1.00%	1.00%	1.00%	1.00%
Europe [Member] | Long Lived Assets [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage	13.00%

Basic and Diluted Earnings Pe30

Basic and Diluted Earnings Per Share (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Authorized in May 2014 [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired, values				$ 59.7
Authorized in July 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Expiration date			May 31, 2019
Approved repurchase amount	$ 350		$ 350
Common stock repurchased and retired, shares	0	0	1.6	2.9
Common stock repurchased and retired, values			$ 94.1	$ 166.2
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock issued in connection with exercise or vesting of stock-based awards	0.1	0.4	0.9	1.8
Common stock issued related to acquisition			0.6

Basic and Diluted Earnings Pe31

Basic and Diluted Earnings Per Share (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Basic earnings per share:
Net income	$ 260.4	$ 202.5	$ 705.2	$ 622
Weighted-average common shares outstanding	359.2	359	359.1	360
Basic earnings per share	$ 0.72	$ 0.56	$ 1.96	$ 1.73
Diluted earnings per share:
Dilutive effect of common share equivalents	2.8	2.8	2.5	2.8
Weighted-average common shares outstanding, assuming dilution	362	361.8	361.6	362.8
Diluted earnings per share	$ 0.72	$ 0.56	$ 1.95	$ 1.71
Weighted-average anti-dilutive common share equivalents		0.7	0.8	0.7

Business Combinations (Narrativ

Business Combinations (Narrative) (Details) $ in Millions	Feb. 28, 2018USD ($)	Aug. 18, 2017USD ($)state	Feb. 28, 2018USD ($)
Business Acquisition [Line Items]
Goodwill acquired			$ 170.3
Lessor Group [Member]
Business Acquisition [Line Items]
Effective acquisition date			Feb. 28, 2018
Purchase price	$ 160.6
Goodwill acquired	$ 119.2
HR Outsourcing, Inc. [Member]
Business Acquisition [Line Items]
Effective acquisition date			Aug. 18, 2017
Purchase price		$ 75.4
Cash portion of purchase price		42.2
Common stock issued portion of purchase price		33.2
Goodwill acquired		$ 51.1
HR Outsourcing, Inc. [Member] | Minimum [Member]
Business Acquisition [Line Items]
Number of states in which HR Solutions services are provided | state		35

Investment Income, Net (Schedul

Investment Income, Net (Schedule of Investment Income, Net) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Investment Income, Net [Abstract]
Interest income on corporate funds	$ 3.1	$ 2.4	$ 8.7	$ 7.2
Interest expense	(1.1)	(0.6)	(3.2)	(1.9)
Net gain/(loss) from equity-method investments	0.3	(0.6)	0.6	(1.7)
Investment income, net	$ 2.3	$ 1.2	$ 6.1	$ 3.6

Funds Held for Clients and Co34

Funds Held for Clients and Corporate Investments (Narrative) (Details) $ in Millions	9 Months Ended
	Feb. 28, 2018USD ($)security	May 31, 2017USD ($)security
Schedule of Available-for-sale Securities [Line Items]
Net unrealized loss on available-for-sale securities	$ 34.9
Net unrealized gain on available-for-sale securities		$ 32
Number of available-for-sale securities in an unrealized loss position | security	859	216
Gross unrealized losses on available-for-sale securities	$ 39.9	$ 5.8
Variable Rate Demand Notes [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities contractual maturities	20 years
Variable Rate Demand Notes [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities contractual maturities	30 years

Funds Held for Clients and Co35

Funds Held for Clients and Corporate Investments (Funds Held for Clients and Corporate Investments) (Details) - USD ($) $ in Millions		Feb. 28, 2018	May 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Funds held for clients' money market securities and other cash equivalents, Amortized cost		$ 673.9	$ 264.8
Funds held for clients' money market securities and other cash equivalents, Gross unrealized gains
Funds held for clients' money market securities and other cash equivalents, Gross unrealized losses
Funds held for clients' money market securities and other cash equivalents, Fair value		673.9	264.8
Available-for-sale securities, Amortized cost		3,790.5	4,581.2
Available-for-sale securities, Gross unrealized gains		5	37.8
Available-for-sale securities, Gross unrealized losses		(39.9)	(5.8)
Available-for-sale securities, Fair value		3,755.6	4,613.2
Other, Amortized cost		15.8	14.8
Other, Gross unrealized gains		2.1	1.9
Other, Gross unrealized losses
Other, Fair value		17.9	16.7
Total funds held for clients and corporate investments, Amortized cost		4,480.2	4,860.8
Total funds held for clients and corporate investments, Gross unrealized gains		7.1	39.7
Total funds held for clients and corporate investments, Gross unrealized losses		(39.9)	(5.8)
Total funds held for clients and corporate investments, Fair value		4,447.4	4,894.7
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		305.8	208.6
Available-for-sale securities, Gross unrealized gains		0.1	2.7
Available-for-sale securities, Gross unrealized losses		(6.5)	(0.5)
Available-for-sale securities, Fair value		299.4	210.8
General Obligation Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		1,303.8	1,422
Available-for-sale securities, Gross unrealized gains		2.6	21.2
Available-for-sale securities, Gross unrealized losses		(10.6)	(0.9)
Available-for-sale securities, Fair value		1,295.8	1,442.3
Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	[1]	64.7	54.6
Available-for-sale securities, Gross unrealized gains	[1]	0.6	0.9
Available-for-sale securities, Gross unrealized losses	[1]	(0.1)
Available-for-sale securities, Fair value	[1]	65.2	55.5
Revenue Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		851.3	929.2
Available-for-sale securities, Gross unrealized gains		1.7	12.5
Available-for-sale securities, Gross unrealized losses		(7.9)	(0.8)
Available-for-sale securities, Fair value		845.1	940.9
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		410.2	328.9
Available-for-sale securities, Gross unrealized gains			0.5
Available-for-sale securities, Gross unrealized losses		(14.8)	(3.6)
Available-for-sale securities, Fair value		395.4	325.8
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		854.7	1,637.9
Available-for-sale securities, Gross unrealized gains
Available-for-sale securities, Gross unrealized losses
Available-for-sale securities, Fair value		$ 854.7	$ 1,637.9
[1]	Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.

Funds Held for Clients and Co36

Funds Held for Clients and Corporate Investments (Classification of Investments on Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Funds held for clients	$ 3,944.7	$ 4,301.9
Corporate investments	97.3	138.8
Long-term corporate investments	405.4	454
Total funds held for clients and corporate investments, Fair value	$ 4,447.4	$ 4,894.7

Funds Held for Clients and Co37

Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	$ (26.2)	$ (5.8)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(13.7)
Total, Gross unrealized losses	(39.9)	(5.8)
Securities in an unrealized loss position for less than twelve months, Fair value	1,649.8	606.4
Securities in an unrealized loss position for more than twelve months, Fair value	334.3	1
Total, Fair value	1,984.1	607.4
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	(5.2)	(0.5)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(1.3)
Total, Gross unrealized losses	(6.5)	(0.5)
Securities in an unrealized loss position for less than twelve months, Fair value	252.1	43.6
Securities in an unrealized loss position for more than twelve months, Fair value	34.7
Total, Fair value	286.8	43.6
General Obligation Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	(8)	(0.9)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(2.6)
Total, Gross unrealized losses	(10.6)	(0.9)
Securities in an unrealized loss position for less than twelve months, Fair value	735.5	188.8
Securities in an unrealized loss position for more than twelve months, Fair value	71.4
Total, Fair value	806.9	188.8
Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	(0.1)
Total, Gross unrealized losses	(0.1)
Securities in an unrealized loss position for less than twelve months, Fair value	7.2	9.2
Securities in an unrealized loss position for more than twelve months, Fair value	0.5
Total, Fair value	7.7	9.2
Revenue Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	(6.1)	(0.8)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(1.8)
Total, Gross unrealized losses	(7.9)	(0.8)
Securities in an unrealized loss position for less than twelve months, Fair value	435.7	154.8
Securities in an unrealized loss position for more than twelve months, Fair value	51.6	1
Total, Fair value	487.3	155.8
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses	(6.8)	(3.6)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(8)
Total, Gross unrealized losses	(14.8)	(3.6)
Securities in an unrealized loss position for less than twelve months, Fair value	219.3	210
Securities in an unrealized loss position for more than twelve months, Fair value	176.1
Total, Fair value	$ 395.4	$ 210

Funds Held for Clients and Co38

Funds Held for Clients and Corporate Investments (Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity) (Details) - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Due in one year or less, Amortized cost	$ 317.9
Due after one year through three years, Amortized cost	820.5
Due after three years through five years, Amortized cost	998.1
Due after five years, Amortized cost	1,654
Available-for-sale securities, Amortized cost	3,790.5	$ 4,581.2
Due in one year or less, Fair value	317.9
Due after one year through three years, Fair value	819.9
Due after three years through five years, Fair value	990.7
Due after five years, Fair value	1,627.1
Available-for-sale securities, Fair value	$ 3,755.6	$ 4,613.2

Fair Value Measurements (Financ

Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 405
Available-for-sale securities	3,755.6	$ 4,613.2
Other	17.9	16.7
Other long-term liabilities	17.9	16.7
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	225
Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	150
Money Market Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	30
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	299.4	210.8
General Obligation Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,295.8	1,442.3
Pre-Refunded Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	65.2	55.5
Revenue Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	845.1	940.9
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	395.4	325.8
Variable Rate Demand Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	854.7	1,637.9
Quoted Prices in Active Markets (Level 1) [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	180
Available-for-sale securities
Other	17.9	16.7
Other long-term liabilities	17.9	16.7
Quoted Prices in Active Markets (Level 1) [Member] | Commercial Paper [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Quoted Prices in Active Markets (Level 1) [Member] | Time Deposits [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	150
Quoted Prices in Active Markets (Level 1) [Member] | Money Market Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	30
Quoted Prices in Active Markets (Level 1) [Member] | Corporate Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Quoted Prices in Active Markets (Level 1) [Member] | General Obligation Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Quoted Prices in Active Markets (Level 1) [Member] | Pre-Refunded Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Quoted Prices in Active Markets (Level 1) [Member] | Revenue Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Quoted Prices in Active Markets (Level 1) [Member] | U.S. Government Agency Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Quoted Prices in Active Markets (Level 1) [Member] | Variable Rate Demand Notes [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	225
Available-for-sale securities	3,755.6	4,613.2
Other
Other long-term liabilities
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	225
Significant Other Observable Inputs (Level 2) [Member] | Time Deposits [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Significant Other Observable Inputs (Level 2) [Member] | Money Market Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	299.4	210.8
Significant Other Observable Inputs (Level 2) [Member] | General Obligation Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,295.8	1,442.3
Significant Other Observable Inputs (Level 2) [Member] | Pre-Refunded Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	65.2	55.5
Significant Other Observable Inputs (Level 2) [Member] | Revenue Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	845.1	940.9
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Agency Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	395.4	325.8
Significant Other Observable Inputs (Level 2) [Member] | Variable Rate Demand Notes [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	854.7	1,637.9
Significant Unobservable Inputs (Level 3) [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Available-for-sale securities
Other
Other long-term liabilities
Significant Unobservable Inputs (Level 3) [Member] | Commercial Paper [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Significant Unobservable Inputs (Level 3) [Member] | Time Deposits [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Significant Unobservable Inputs (Level 3) [Member] | Money Market Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents
Significant Unobservable Inputs (Level 3) [Member] | Corporate Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Unobservable Inputs (Level 3) [Member] | General Obligation Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Unobservable Inputs (Level 3) [Member] | Pre-Refunded Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Unobservable Inputs (Level 3) [Member] | Revenue Municipal Bonds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government Agency Securities [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Significant Unobservable Inputs (Level 3) [Member] | Variable Rate Demand Notes [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities

Accounts Receivable, Net of A40

Accounts Receivable, Net of Allowance for Doubtful Accounts (Components of Accounts Receivable, Net of Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions		Feb. 28, 2018	May 31, 2017
Total accounts receivable, gross		$ 557.8	$ 513.5
Less: Allowance for doubtful accounts		7.3	6
Accounts receivable, net of allowance for doubtful accounts		550.5	507.5
PEO Receivables [Member]
Total accounts receivable, gross	[1]	172.8	137.8
Purchased Receivables [Member]
Total accounts receivable, gross	[2]	281.4	257.3
Other Trade Receivables [Member]
Total accounts receivable, gross	[3]	$ 103.6	$ 118.4
[1]	PEO receivables are primarily client wages and related tax withholdings since the last payroll processed. Balances will vary based on timing of the last payroll processed and the end of the reporting period. In addition, balances as of February 28, 2018 include receivable balances for HROI, acquired in August 2017. Refer to Note C for further details.
[2]	Purchased receivables relate to payroll funding arrangements with clients in the temporary staffing industry.
[3]	Other trade receivables primarily relate to other ongoing services provided to our clients and can vary based on the timing of these services and the end of the reporting period.

Property and Equipment, Net o41

Property and Equipment, Net of Accumulated Depreciation (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended			9 Months Ended
	Sep. 30, 2017	Aug. 31, 2017USD ($)ft²item	Feb. 28, 2018USD ($)	Nov. 30, 2017USD ($)	Feb. 28, 2017USD ($)	Feb. 28, 2018USD ($)	Feb. 28, 2017USD ($)
Property, Plant and Equipment [Line Items]
Depreciation expense			$ 31.5		$ 26.4	$ 88	$ 77.2
Cost of building purchased						122	$ 66.8
Multi-Building Campus [Member] | County Of Monroe Industrial Development Agency [Member]
Property, Plant and Equipment [Line Items]
Public benefits and inducements expiration date	Dec. 31, 2039
Multi-Building Campus [Member] | Rochester, NY [Member]
Property, Plant and Equipment [Line Items]
Number of buildings planned to be purchased | item		5
Renovation square feet | ft²		300,000
Estimated cost of buildings to be purchased and building renovations		$ 60
Cost of building purchased				$ 34.7
Escrow for building renovations				$ 16
Construction in progress			$ 31.5			$ 31.5

Property and Equipment, Net o42

Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($) $ in Millions		Feb. 28, 2018	May 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		$ 1,170.7	$ 1,051
Less: Accumulated depreciation		773.5	713.8
Property and equipment, net of accumulated depreciation		397.2	337.2
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		10.7	8.3
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		126.4	103.5
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		208.9	199.7
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	[1]	545	496.1
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		114	115.2
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross		109.3	109.5
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	[1]	$ 56.4	$ 18.7
[1]	Software includes both purchased software and costs capitalized related to internally developed software placed in service. Capitalized costs related to internally developed software that has not yet been placed in service is included in construction in progress.

Goodwill and Intangible Asset43

Goodwill and Intangible Assets, Net of Accumulated Amortization (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017	May 31, 2017
Goodwill and Intangible Assets, Net of Accumulated Amortization [Abstract]
Goodwill	$ 827.4		$ 827.4		$ 657.1
Increased in goodwill result of HROI acquisition			170.3
Amortization expense	$ 5.1	$ 4.6	$ 14.3	$ 13.5

Goodwill and Intangible Asset44

Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions		Feb. 28, 2018	May 31, 2017
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross		$ 314.1	$ 298.9
Less: Accumulated amortization		209	241.3
Intangible assets, net of accumulated amortization		105.1	57.6
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	[1]	308.4	293.5
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross		$ 5.7	$ 5.4
[1]	Client lists include current estimates of amounts acquired from Lessor as of February 28, 2018. Refer to Note C for further details.

Goodwill and Intangible Asset45

Goodwill and Intangible Assets, Net of Accumulated Amortization (Estimated Amortization Expense) (Details) $ in Millions	Feb. 28, 2018USD ($)
Year ending May 31
2,018	$ 21.6
2,019	25.3
2,020	20.8
2,021	16.8
2,022	$ 13

Accumulated Other Comprehensi46

Accumulated Other Comprehensive (Loss)/ Income (Changes in Accumulated Other Comprehensive (Loss)/Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Accumulated Other Comprehensive (Loss)/Income [Abstract]
Beginning balance	$ (9.2)	$ (16.8)	$ 20	$ 29.2
Unrealized (losses)/gains on available-for-sale securities, net of tax	(17.5)	21.4	(46.7)	(24.6)
Total other comprehensive (loss)/income, net of tax	(17.5)	21.4	(46.7)	(24.6)
Ending balance	(26.7)	4.6	(26.7)	4.6
Total tax (benefit)/expense included in other comprehensive income	$ (3.2)	$ 12.3	$ (20.1)	$ (14)

Short-term Financing (Narrative

Short-term Financing (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018USD ($)	Feb. 28, 2017USD ($)	Feb. 28, 2018USD ($)	Feb. 28, 2017USD ($)	Aug. 17, 2017USD ($)loan	May 31, 2017USD ($)
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Amounts outstanding	$ 0		$ 0			$ 0
Maximum amount borrowed	$ 200	$ 250	$ 700	$ 350
Number of days borrowed	2 days	8 days	21 days	27 days
Weighted-average interest rate	4.25%	2.24%	4.24%	2.68%
Weighted-average amount borrowed	$ 125	$ 81.3	$ 311.9	$ 183.3
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Three Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed			$ 100
Number of days borrowed			3 days
Weighted-average interest rate			4.25%
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Eight Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed		$ 50
Number of days borrowed		8 days
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Eight Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate		1.44%
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed				$ 150
Number of days borrowed				7 days
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Eighteen Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed				$ 50
Number of days borrowed				18 days
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven And Eighteen Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate				1.40%
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Amounts outstanding	0		$ 0
Maximum amount borrowed	$ 75		$ 400
Number of days borrowed	19 days		39 days
Weighted-average interest rate	2.19%		2.69%
Weighted-average amount borrowed	$ 75		$ 147.2
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed			$ 300
Number of days borrowed			7 days
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Seven Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate			2.13%
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Nineteen Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed	$ 75
Number of days borrowed	19 days
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Nineteen Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate	2.19%
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Thirty Days [Member]
Line of Credit Facility [Line Items]
Maximum amount borrowed			$ 75
Number of days borrowed			30 days
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Thirty Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate			2.19%
Revolving Credit Facility [Member] | PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]
Line of Credit Facility [Line Items]
Amounts outstanding	$ 57.7		$ 57.7			0
Maximum amount borrowed	$ 59.9	$ 55.6	$ 59.9	$ 55.6
Number of days borrowed	90 days	90 days	269 days	267 days
Weighted-average interest rate	2.01%	1.27%	1.83%	1.13%
Weighted-average amount borrowed	$ 59.1	$ 55.3	$ 57.6	$ 52.6
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	56.8		56.8			47.3
Amounts outstanding	0	0	0	0		0
Line of Credit [Member]
Line of Credit Facility [Line Items]
Number of terminated lines of credit | loan					4
Amounts outstanding	$ 0	$ 0	$ 0	$ 0		$ 0
Maximum borrowing capacity					$ 900
Minimum [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Expiration Date			Apr. 1, 2018
Maximum [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Expiration Date			Dec. 1, 2018

Short-term Financing (Descripti

Short-term Financing (Description of Credit Facilities) (Details) $ in Millions	9 Months Ended
	Feb. 28, 2018USD ($)	[1]
Paychex of New York, LLC [Member] | JP Morgan Chase Bank, N.A. [Member] | JPM $1 Billion Credit Facility [Member]
Line of Credit Facility [Line Items]
Date Entered	Aug. 5, 2015	[2]
Expiration Date	Aug. 5, 2020	[2]
Maximum Amount Available	$ 1,000	[2]
Paychex of New York, LLC [Member] | JP Morgan Chase Bank, N.A. [Member] | JPM $500 Million Credit Facility [Member]
Line of Credit Facility [Line Items]
Date Entered	Aug. 17, 2017	[2]
Expiration Date	Aug. 17, 2022	[2]
Maximum Amount Available	$ 500	[2]
Paychex Advance, LLC [Member] | PNC Bank, National Association [Member] | PNC $150 Million Credit Facility [Member]
Line of Credit Facility [Line Items]
Date Entered	Mar. 17, 2016
Expiration Date	Mar. 17, 2020
Maximum Amount Available	$ 150
[1]	Borrower is a wholly owned subsidiary of the Company.
[2]	JP Morgan Chase Bank, N.A. ("JPM") acts as the administrative agent for this syndicated credit facility.

Short-term Financing (Credit Fa

Short-term Financing (Credit Facility Amount Borrowed) (Details) - Revolving Credit Facility [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Number of days borrowed	2 days	8 days	21 days	27 days
Maximum amount borrowed	$ 200	$ 250	$ 700	$ 350
Weighted-average amount borrowed	$ 125	$ 81.3	$ 311.9	$ 183.3
Weighted-average interest rate	4.25%	2.24%	4.24%	2.68%
JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Number of days borrowed	19 days		39 days
Maximum amount borrowed	$ 75		$ 400
Weighted-average amount borrowed	$ 75		$ 147.2
Weighted-average interest rate	2.19%		2.69%
PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]
Line of Credit Facility [Line Items]
Number of days borrowed	90 days	90 days	269 days	267 days
Maximum amount borrowed	$ 59.9	$ 55.6	$ 59.9	$ 55.6
Weighted-average amount borrowed	$ 59.1	$ 55.3	$ 57.6	$ 52.6
Weighted-average interest rate	2.01%	1.27%	1.83%	1.13%

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Feb. 28, 2018	May 31, 2017
Commitments and Contingencies [Abstract]
Commitments to purchase capital assets	$ 5.8	$ 7.4

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Nov. 30, 2017	Feb. 28, 2018	Feb. 28, 2017	Dec. 31, 2018	May 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Effective income tax rate	11.70%	34.20%		27.70%	34.10%
Corporate income tax rate								35.00%
Subsequent Event [Member]
Income Tax Contingency [Line Items]
Blended statutory tax rate							29.20%
Diluted earnings per share related to change in net deferred tax liabilities	$ 0.06			$ 0.06
Diluted earnings per share related to change in annual effective tax rate			$ 0.10
Scenario, Plan [Member]
Income Tax Contingency [Line Items]
Corporate income tax rate						21.00%
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Estimated tax benefits	$ 56.9			$ 56.9
Net tax benefit related to change in net deferred tax liabilities	$ 20.8			$ 20.8
Net tax benefit related to change in annual effective tax rate			$ 36.1