Paychex (PAYX) 10-Q 6 Oct 17 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Aug. 31, 2017	Sep. 30, 2017
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	Q1
Document Period End Date	Aug. 31, 2017
Document Fiscal Year Focus	2,018
Current Fiscal Year End Date	--05-31
Entity Common Stock, Shares Outstanding		358,994,637

Consolidated Statements of Inco

Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Revenue:
Service revenue	$ 803.1	$ 773.5
Interest on funds held for clients	13.7	12
Total revenue	816.8	785.5
Expenses:
Operating expenses	232.1	225.1
Selling, general and administrative expenses	239.7	237.4
Total expenses	471.8	462.5
Operating income	345	323
Investment income, net	2.1	1.5
Income before income taxes	347.1	324.5
Income taxes	119.3	107.1
Net income	227.8	217.4
Other comprehensive income, net of tax:
Unrealized gains on securities, net of tax	4.4	10
Total other comprehensive income, net of tax	4.4	10
Comprehensive income	$ 232.2	$ 227.4
Basic earnings per share	$ 0.63	$ 0.60
Diluted earnings per share	$ 0.63	$ 0.60
Weighted-average common shares outstanding	358.9	361
Weighted-average common shares outstanding, assuming dilution	361.3	364.1
Cash dividends per common share	$ 0.50	$ 0.46

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Aug. 31, 2017	May 31, 2017
Assets
Cash and cash equivalents	$ 234.4	$ 184.6
Corporate investments	133.8	138.8
Interest receivable	32	35.9
Accounts receivable, net of allowance for doubtful accounts	538.6	507.5
Prepaid income taxes		45
Prepaid expenses and other current assets	81.6	58.3
Current assets before funds held for clients	1,020.4	970.1
Funds held for clients	4,953.1	4,301.9
Total current assets	5,973.5	5,272
Long-term corporate investments	483.2	454
Property and equipment, net of accumulated depreciation	328.6	337.2
Intangible assets, net of accumulated amortization	79.2	57.6
Goodwill	698	657.1
Prepaid income taxes	24.9	24.9
Other long-term assets	32.1	30.9
Total assets	7,619.5	6,833.7
Liabilities
Accounts payable	74.6	57.2
Accrued compensation and related items	277	280.5
Accrued income taxes	4.1
Short-term borrowings	57.2
Deferred revenue	24.7	22.9
Other current liabilities	100	91.9
Current liabilities before client fund obligations	537.6	452.5
Client fund obligations	4,918.1	4,272.6
Total current liabilities	5,455.7	4,725.1
Accrued income taxes	47.9	45.6
Deferred income taxes	95.4	33.9
Other long-term liabilities	76.7	73.8
Total liabilities	5,675.7	4,878.4
Commitments and contingencies - Note L
Stockholders' equity
Common stock, $0.01 par value; Authorized: 600.0 shares; Issued and outstanding: 358.9 shares as of August 31, 2017 and 359.4 shares as of May 31, 2017, respectively.	3.6	3.6
Additional paid-in capital	1,072.1	1,030
Retained earnings	843.7	901.7
Accumulated other comprehensive income	24.4	20
Total stockholders' equity	1,943.8	1,955.3
Total liabilities and stockholders' equity	$ 7,619.5	$ 6,833.7

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Aug. 31, 2017	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	358,900,000	359,400,000
Common stock, shares outstanding	358,900,000	359,400,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Operating activities
Net income	$ 227.8	$ 217.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization on property and equipment and intangible assets	32	29.7
Amortization of premiums and discounts on available-for-sale securities	17.1	18.6
Stock-based compensation costs	8.7	9.1
Provision for deferred income taxes	59.2	14.1
Provision for allowance for doubtful accounts	0.7	1.2
Net realized gains on sales of available-for-sale securities		(0.1)
Changes in operating assets and liabilities:
Interest receivable	3.9	4.4
Accounts receivable	(15.4)	(78.1)
Prepaid expenses and other current assets	28.2	6.6
Accounts payable and other current liabilities	(19.2)	60.9
Net change in other long-term assets and liabilities	0.6	10.9
Net cash provided by operating activities	343.6	294.7
Investing activities
Purchases of available-for-sale securities	(8,646.7)	(14,777)
Proceeds from sales and maturities of available-for-sale securities	8,892	14,920.3
Net change in funds held for clients’ money market securities and other cash equivalents	(929.7)	257.3
Purchases of property and equipment	(18)	(20.3)
Acquisition of businesses, net of cash acquired	(8.2)
Purchases of other assets	(0.4)
Net cash (used in)/provided by investing activities	(711)	380.3
Financing activities
Net change in client fund obligations	645.5	(567.8)
Net proceeds from short-term borrowings	57.2	51.3
Dividends paid	(179.1)	(166.3)
Repurchases of common shares	(94.1)
Activity related to equity-based plans	(12.3)	6.3
Net cash provided by/(used in) financing activities	417.2	(676.5)
Increase/(decrease) in cash and cash equivalents	49.8	(1.5)
Cash and cash equivalents, beginning of fiscal year	184.6	131.5
Cash and cash equivalents, end of period	$ 234.4	$ 130

Description of Business, Basis

Description of Business, Basis of Presentation, and Significant Accounting Policies	3 Months Ended
	Aug. 31, 2017
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 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 Germany. 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 Germany, which represented less than one percent of the Company's total revenue for each of the three months ended August 31, 2017 and August 31, 2016 . Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company as of August 31, 2017 and May 31, 2017 . T he Company disposed of equity-method investments for a joint-venture in Brazil and a minority investment in a Canadian entity during the fiscal year ended May 31, 2017 (“fiscal 2017”), neither of which was significant.  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 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 fiscal 2017 . Operating results and cash flows for the three months ended August 31, 2017 are not necessarily indicative of the results that may be expected for other interim periods or for the full fiscal year ending May 31, 2018 (“fiscal 2018 ”).  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 2017 and calendar 2016 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 $8.7 million for the three months ended August 31, 2017, as compared with $9.1 million for the three months ended August 31, 2016. 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: There were no recently adopted accounting pronouncements during the three months ended August 31, 2017. Recently issued accounting pronouncements: In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 application permitted. This guidance is applicable to the Company's fiscal year beginning June 1, 2019. The Company is currently evaluating this guidance to determine the potential impact on its consolidated financial statements. 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, with early adopt ion permitted for the annual reporting periods beginning after December 15, 2016. 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 and forecasting considerations to ensure its ability to record, report, forecast, 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 and Exchange Commission during the three months ended August 31, 2017 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	3 Months Ended
	Aug. 31, 2017
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  August 31,  In millions, except per share amounts 2017 2016  Basic earnings per share:  Net income $ 227.8 $ 217.4  Weighted-average common shares outstanding 358.9 361.0  Basic earnings per share $ 0.63 $ 0.60  Diluted earnings per share:  Net income $ 227.8 $ 217.4  Weighted-average common shares outstanding 358.9 361.0  Dilutive effect of common share equivalents 2.4 3.1  Weighted-average common shares outstanding, assuming dilution 361.3 364.1  Diluted earnings per share $ 0.63 $ 0.60  Weighted-average anti-dilutive common share equivalents 1.1 0.5  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 August 31, 2017 and August 31, 2016 , 0.5 million and 1.3 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 three months ended August 31, 2017, 0.6 million shares of the Company’s c ommon stock were issued in relation to an immaterial business acquisition completed in August 2017. Refer to Note C below 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. During the three months ended August 31, 2017, the Company repurchased 1.6 million shares for $94.1 million under this program. The Company did no t repurchase any of its common stock during the three months ended August 31, 2016 . All shares repurchased were retired.

Business Combination

Business Combination	3 Months Ended
	Aug. 31, 2017
Business Combination [Abstract]
Business Combination	 Note C: Business Combination  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 $40.9 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 the valuation of the assets acquired and liabilities assumed. However, further changes to goodwill as a result of the acquisition are not anticipated to be material to the Company’s Consolidated Balance Sheets.  The financial results of HROI are included in the Company’s consolidated financial statements from the date of acquisition. The Company concluded that the acquisition was not material to its results of operations and financial position. Therefore, pro-forma financial information has been excluded.

Investment Income, Net

Investment Income, Net	3 Months Ended
	Aug. 31, 2017
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  August 31,  In millions 2017 2016  Interest income on corporate funds $ 2.9 $ 2.4  Interest expense (0.8) (0.7)  Net loss from equity-method investments — (0.2)  Investment income, net $ 2.1 $ 1.5

Funds Held for Clients and Corp

Funds Held for Clients and Corporate Investments	3 Months Ended
	Aug. 31, 2017
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:      August 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 $ 1,194.6 $ — $ — $ 1,194.6  Available-for-sale securities:  Corporate bonds 263.9 3.6 (0.3) 267.2  General obligation municipal bonds 1,407.4 23.2 (0.4) 1,430.2  Pre-refunded municipal bonds (1) 60.9 1.1 — 62.0  Revenue municipal bonds 921.3 13.5 (0.2) 934.6  U.S. government agency securities 368.6 0.8 (2.7) 366.7  Variable rate demand notes 1,296.8 — — 1,296.8  Total available-for-sale securities 4,318.9 42.2 (3.6) 4,357.5  Other 15.8 2.2 — 18.0  Total funds held for clients and corporate investments $ 5,529.3 $ 44.4 $ (3.6) $ 5,570.1     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 August 31, 2017 were bank demand deposit accounts, time deposits, 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:      August 31, May 31,  In millions 2017 2017  Funds held for clients $ 4,953.1 $ 4,301.9  Corporate investments 133.8 138.8  Long-term corporate investments 483.2 454.0  Total funds held for clients and corporate investments $ 5,570.1 $ 4,894.7  The Company’s available-for-sale securities reflected net unrealized gains of $38.6 million and $ 32.0 million as of August 31, 2017 and May 31, 2017 , respectively. Included in the net unrealized gain totals as of August 31, 2017 and May 31, 2017 , there were 149 and 216 available-for-sale securities in an unrealized loss position, respectively. The available-for-sale securities in an unrealized loss position were as follows:      August 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 $ (0.2) $ 34.1 $ (0.1) $ 6.6 $ (0.3) $ 40.7  General obligation municipal bonds (0.3) 78.2 (0.1) 12.1 (0.4) 90.3  Pre-refunded municipal bonds — 9.1 — — — 9.1  Revenue municipal bonds (0.1) 70.6 (0.1) 12.3 (0.2) 82.9  U.S. government agency securities (1.8) 144.3 (0.9) 39.1 (2.7) 183.4  Total $ (2.4) $ 336.3 $ (1.2) $ 70.1 $ (3.6) $ 406.4     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 August 31, 2017 that had unrealized losses of $3.6 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 August 31, 2017 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 were insignificant for the three months ended August 31, 2017 and August 31, 201 6. There were no realized losses for the three months ended August 31, 2017 and August 31, 2016.  The amortized cost and fair value of available-for-sale securities that had stated maturities as of August 31, 2017 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.      August 31, 2017  Amortized Fair  In millions cost value  Maturity date:  Due in one year or less $ 286.3 $ 287.0  Due after one year through three years 803.0 812.0  Due after three years through five years 1,026.3 1,048.5  Due after five years 2,203.3 2,210.0  Total $ 4,318.9 $ 4,357.5  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	3 Months Ended
	Aug. 31, 2017
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:      August 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:  Cash equivalents:  Time deposits $ 50.0 $ 50.0 $ — $ —  Money market securities 30.4 30.4 — —  Total cash equivalents $ 80.4 $ 80.4 $ — $ —  Available-for-sale securities:  Corporate bonds $ 267.2 $ — $ 267.2 $ —  General obligation municipal bonds 1,430.2 — 1,430.2 —  Pre-refunded municipal bonds 62.0 — 62.0 —  Revenue municipal bonds 934.6 — 934.6 —  U.S. government agency securities 366.7 — 366.7 —  Variable rate demand notes 1,296.8 — 1,296.8 —  Total available-for-sale securities $ 4,357.5 $ — $ 4,357.5 $ —  Other $ 18.0 $ 18.0 $ — $ —  Liabilities:  Other long-term liabilities $ 18.0 $ 18.0 $ — $ —     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. Time deposits and money market securities, which are cash equivalents, are valued based on quoted market prices in active markets. Available-for-sale securities, including municipal bonds, 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	3 Months Ended
	Aug. 31, 2017
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:      August 31, May 31,  In millions 2017 2017  PEO receivables (1) $ 115.4 $ 137.8  Purchased receivables (2) 284.4 257.3  Other trade receivables (3) 144.5 118.4  Total accounts receivable, gross 544.3 513.5  Less: Allowance for doubtful accounts 5.7 6.0  Accounts receivable, net of allowance for doubtful accounts $ 538.6 $ 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 August 31, 2017 include receivables balances acquired from HROI. Refer to Note C for further details of this immaterial business acquisition. (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	3 Months Ended
	Aug. 31, 2017
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:      August 31, May 31,  In millions 2017 2017  Land and improvements $ 8.3 $ 8.3  Buildings and improvements 103.6 103.5  Data processing equipment 207.8 199.7  Software (1) 503.9 496.1  Furniture, fixtures, and equipment 115.3 115.2  Leasehold improvements 111.5 109.5  Construction in progress (1) 17.7 18.7  Total property and equipment, gross 1,068.1 1,051.0  Less: Accumulated depreciation 739.5 713.8  Property and equipment, net of accumulated depreciation $ 328.6 $ 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 $28.1 million for the three months ended August 31, 2017 compared to $25.3 million for the three months ended August 31, 2016 .  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 in Rochester for an estimated cost of $60 million. Subsequent to August 31, 2017, and as of the date of this report, the Company has completed the purchase of two of these buildings for a combined cost of $19.5 million. Renovations on the buildings purchased have not yet commenced. In addition, in September 2017, the Company entered into a transaction with the County of Monroe Industrial Development Agency (“COMIDA”) 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	3 Months Ended
	Aug. 31, 2017
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 $698.0 million as of August 31, 2017 and $657.1 million as of May 31, 2017. The increase of $40.9 million in goodwill since May 31, 2017 was the result of the acquisition of HROI in August 2017. Refer to Note C for further information.  The Company has certain intangible assets with finite lives. The components of intangible assets, at cost, consisted of the following:      August 31, May 31,  In millions 2017 2017  Client lists $ 318.7 $ 293.5  Other intangible assets 5.4 5.4  Total intangible assets, gross 324.1 298.9  Less: Accumulated amortization 244.9 241.3  Intangible assets, net of accumulated amortization $ 79.2 $ 57.6  Amortization expense relating to intangible assets was $3.9 million for the three months ended August 31, 2017 compared to $4.4 million for the three months ended August 31, 2016 .  As of August 31, 2017 , 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 $ 20.1  2019 17.3  2020 13.9  2021 10.9  2022 8.2 

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	3 Months Ended
	Aug. 31, 2017
Accumulated Other Comprehensive Income [Abstract]
Accumulated Other Comprehensive Income	Note J: Accumulated Other Comprehensive 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 income on the Company’s Consolidated Balance Sheets. The changes in accumulated other comprehensive income are as follows:      For the three months ended  August 31,  In millions 2017 2016  Beginning balance $ 20.0 $ 29.2  Other comprehensive income:  Unrealized gains on available-for-sale securities, net of tax 4.4 10.0  Total other comprehensive income, net of tax 4.4 10.0  Ending balance $ 24.4 $ 39.2   Total tax expense included in other comprehensive income $ 2.4 $ 5.7  Reclassification adjustments out of accumulated other comprehensive income for realized gains and losses on the sale of available-for-sale securities were insignificant for the three months ended August 31, 2017 and August 31, 2016. 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	3 Months Ended
	Aug. 31, 2017
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 August 31, 2017 or May 31, 2017. Details of borrowings under this credit facility d uring the three months ended August 31, 2017 and August 31, 2016 are as follows:     For the three months ended  August 31,  $ in millions 2017 2016  Number of days borrowed 13 4  Maximum amount borrowed $ 660.0 $ 350.0  Weighted-average amount borrowed $ 278.8 $ 237.5  Weighted-average interest rate 4.23 % 3.50 %  The Company typically borrows on an overnight basis. In addition to overnight borrowings, during the three months ended August 31, 2017, the Company borrowed $100.0 million for a three -day period at a weighted-average LIBOR-based interest rate of 4.25% . Subsequent to August 31, 2017, the Company borrowed two times, on an overnight basis, $650.0 million on a weight ed-average basis under this credit facility .  JPM $500 Million Credit Facility: There were no borrowings outstanding under this credit facility during the three months ended August 31, 2017. Subsequent to August 31, 2017, the Company borrowed two times, on an overnight basis, $212.5 million on a weight ed-average basis under this credit facility .  PNC $150 Million Credit Facility: As of August 31 , 2017, the Company has $57.2 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 months ended August 31, 2017 and August 31, 2016, are as follows:      For the three months ended  August 31,  $ in millions 2017 2016  Number of days borrowed 88 84  Maximum amount borrowed $ 57.2 $ 51.3  Weighted-average amount borrowed $ 55.8 $ 51.3  Weighted-average interest rate 1.67 % 1.01 % 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 August 31, 2017 . 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 $52.8 million and $47.3 million as of August 31, 2017 and May 31, 2017, respectively, required to secure commitments for certain insurance policies. The letters of credit expire at various dates between December 2017 and July 2018 and are collateralized by securities held in the Company’s investment portfolios. No amounts were outstanding on these letters of credit during the three months ended August 31, 2017 and August 31, 2016, 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 three months ended August 31, 2017 and August 31, 2016, or as of May 31, 2017.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Aug. 31, 2017
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 $5.0 million and $7.4 million of capital assets as of August 31, 2017 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.  Paychex currently self-insures the deductible portion of various insured exposures under certain employee benefit plans. The Company’s 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 August 31, 2017 . 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, patent, 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	3 Months Ended
	Aug. 31, 2017
Income Taxes [Abstract]
Income Taxes	Note M: Income Taxes  The Company’s effective income tax rate was 34.4% and 33.0% for the three months ended August 31, 2017 and August 31, 2016 , respectively. The effective income tax rates in both periods were impacted by the recognition of a net discrete tax benefit related to employee stock-based compensation payments. The net discrete tax benefit impacted the three months ended August 31, 2017 and August 31, 2016 by approximately $0.01 per diluted share and $0.04 per diluted share, respectively. 

Description of Business, Basi19

Description of Business, Basis of Presentation, and Significant Accounting Policies (Policy)	3 Months Ended
	Aug. 31, 2017
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 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 Germany. 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 Germany, which represented less than one percent of the Company's total revenue for each of the three months ended August 31, 2017 and August 31, 2016 . Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company as of August 31, 2017 and May 31, 2017 . T he Company disposed of equity-method investments for a joint-venture in Brazil and a minority investment in a Canadian entity during the fiscal year ended May 31, 2017 (“fiscal 2017”), neither of which was significant.
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 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 fiscal 2017 . Operating results and cash flows for the three months ended August 31, 2017 are not necessarily indicative of the results that may be expected for other interim periods or for the full fiscal year ending May 31, 2018 (“fiscal 2018 ”).
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 2017 and calendar 2016 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 $8.7 million for the three months ended August 31, 2017, as compared with $9.1 million for the three months ended August 31, 2016. 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 Recently Issued Accounting Pronouncements	Recently adopted accounting pronouncements: There were no recently adopted accounting pronouncements during the three months ended August 31, 2017. Recently issued accounting pronouncements: In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 application permitted. This guidance is applicable to the Company's fiscal year beginning June 1, 2019. The Company is currently evaluating this guidance to determine the potential impact on its consolidated financial statements. 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, with early adopt ion permitted for the annual reporting periods beginning after December 15, 2016. 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 and forecasting considerations to ensure its ability to record, report, forecast, 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 and Exchange Commission during the three months ended August 31, 2017 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)	3 Months Ended
	Aug. 31, 2017
Basic and Diluted Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Share	   For the three months ended  August 31,  In millions, except per share amounts 2017 2016  Basic earnings per share:  Net income $ 227.8 $ 217.4  Weighted-average common shares outstanding 358.9 361.0  Basic earnings per share $ 0.63 $ 0.60  Diluted earnings per share:  Net income $ 227.8 $ 217.4  Weighted-average common shares outstanding 358.9 361.0  Dilutive effect of common share equivalents 2.4 3.1  Weighted-average common shares outstanding, assuming dilution 361.3 364.1  Diluted earnings per share $ 0.63 $ 0.60  Weighted-average anti-dilutive common share equivalents 1.1 0.5 

Investment Income, Net (Tables)

Investment Income, Net (Tables)	3 Months Ended
	Aug. 31, 2017
Investment Income, Net [Abstract]
Schedule of Investment Income, Net	   For the three months ended  August 31,  In millions 2017 2016  Interest income on corporate funds $ 2.9 $ 2.4  Interest expense (0.8) (0.7)  Net loss from equity-method investments — (0.2)  Investment income, net $ 2.1 $ 1.5 

Funds Held for Clients and Co22

Funds Held for Clients and Corporate Investments (Tables)	3 Months Ended
	Aug. 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Funds Held for Clients and Corporate Investments	   August 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 $ 1,194.6 $ — $ — $ 1,194.6  Available-for-sale securities:  Corporate bonds 263.9 3.6 (0.3) 267.2  General obligation municipal bonds 1,407.4 23.2 (0.4) 1,430.2  Pre-refunded municipal bonds (1) 60.9 1.1 — 62.0  Revenue municipal bonds 921.3 13.5 (0.2) 934.6  U.S. government agency securities 368.6 0.8 (2.7) 366.7  Variable rate demand notes 1,296.8 — — 1,296.8  Total available-for-sale securities 4,318.9 42.2 (3.6) 4,357.5  Other 15.8 2.2 — 18.0  Total funds held for clients and corporate investments $ 5,529.3 $ 44.4 $ (3.6) $ 5,570.1     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	   August 31, May 31,  In millions 2017 2017  Funds held for clients $ 4,953.1 $ 4,301.9  Corporate investments 133.8 138.8  Long-term corporate investments 483.2 454.0  Total funds held for clients and corporate investments $ 5,570.1 $ 4,894.7 
Securities in Unrealized Loss Position	   August 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 $ (0.2) $ 34.1 $ (0.1) $ 6.6 $ (0.3) $ 40.7  General obligation municipal bonds (0.3) 78.2 (0.1) 12.1 (0.4) 90.3  Pre-refunded municipal bonds — 9.1 — — — 9.1  Revenue municipal bonds (0.1) 70.6 (0.1) 12.3 (0.2) 82.9  U.S. government agency securities (1.8) 144.3 (0.9) 39.1 (2.7) 183.4  Total $ (2.4) $ 336.3 $ (1.2) $ 70.1 $ (3.6) $ 406.4     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	   August 31, 2017  Amortized Fair  In millions cost value  Maturity date:  Due in one year or less $ 286.3 $ 287.0  Due after one year through three years 803.0 812.0  Due after three years through five years 1,026.3 1,048.5  Due after five years 2,203.3 2,210.0  Total $ 4,318.9 $ 4,357.5 

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Aug. 31, 2017
Fair Value Measurements [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	   August 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:  Cash equivalents:  Time deposits $ 50.0 $ 50.0 $ — $ —  Money market securities 30.4 30.4 — —  Total cash equivalents $ 80.4 $ 80.4 $ — $ —  Available-for-sale securities:  Corporate bonds $ 267.2 $ — $ 267.2 $ —  General obligation municipal bonds 1,430.2 — 1,430.2 —  Pre-refunded municipal bonds 62.0 — 62.0 —  Revenue municipal bonds 934.6 — 934.6 —  U.S. government agency securities 366.7 — 366.7 —  Variable rate demand notes 1,296.8 — 1,296.8 —  Total available-for-sale securities $ 4,357.5 $ — $ 4,357.5 $ —  Other $ 18.0 $ 18.0 $ — $ —  Liabilities:  Other long-term liabilities $ 18.0 $ 18.0 $ — $ —     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)	3 Months Ended
	Aug. 31, 2017
Accounts Receivable, Net of Allowance for Doubtful Accounts [Abstract]
Components of Accounts Receivable, Net of Allowance for Doubtful Accounts	    August 31, May 31,  In millions 2017 2017  PEO receivables (1) $ 115.4 $ 137.8  Purchased receivables (2) 284.4 257.3  Other trade receivables (3) 144.5 118.4  Total accounts receivable, gross 544.3 513.5  Less: Allowance for doubtful accounts 5.7 6.0  Accounts receivable, net of allowance for doubtful accounts $ 538.6 $ 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 August 31, 2017 include receivables balances acquired from HROI. Refer to Note C for further details of this immaterial business acquisition. (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)	3 Months Ended
	Aug. 31, 2017
Property and Equipment, Net of Accumulated Depreciation [Abstract]
Components of Property and Equipment, at Cost	   August 31, May 31,  In millions 2017 2017  Land and improvements $ 8.3 $ 8.3  Buildings and improvements 103.6 103.5  Data processing equipment 207.8 199.7  Software (1) 503.9 496.1  Furniture, fixtures, and equipment 115.3 115.2  Leasehold improvements 111.5 109.5  Construction in progress (1) 17.7 18.7  Total property and equipment, gross 1,068.1 1,051.0  Less: Accumulated depreciation 739.5 713.8  Property and equipment, net of accumulated depreciation $ 328.6 $ 337.2 

Goodwill and Intangible Asset26

Goodwill and Intangible Assets, Net of Accumulated Amortization (Tables)	3 Months Ended
	Aug. 31, 2017
Goodwill and Intangible Assets, Net of Accumulated Amortization [Abstract]
Components of Intangible Assets, at Cost	   August 31, May 31,  In millions 2017 2017  Client lists $ 318.7 $ 293.5  Other intangible assets 5.4 5.4  Total intangible assets, gross 324.1 298.9  Less: Accumulated amortization 244.9 241.3  Intangible assets, net of accumulated amortization $ 79.2 $ 57.6 
Estimated Amortization Expense	  In millions Estimated amortization  Year ending May 31, Expense  2018 $ 20.1  2019 17.3  2020 13.9  2021 10.9  2022 8.2 

Accumulated Other Comprehensi27

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Aug. 31, 2017
Accumulated Other Comprehensive Income [Abstract]
Changes in Accumulated Other Comprehensive Income	   For the three months ended  August 31,  In millions 2017 2016  Beginning balance $ 20.0 $ 29.2  Other comprehensive income:  Unrealized gains on available-for-sale securities, net of tax 4.4 10.0  Total other comprehensive income, net of tax 4.4 10.0  Ending balance $ 24.4 $ 39.2   Total tax expense included in other comprehensive income $ 2.4 $ 5.7 

Short-term Financing (Tables)

Short-term Financing (Tables) - Revolving Credit Facility [Member]	3 Months Ended
	Aug. 31, 2017
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  August 31,  $ in millions 2017 2016  Number of days borrowed 13 4  Maximum amount borrowed $ 660.0 $ 350.0  Weighted-average amount borrowed $ 278.8 $ 237.5  Weighted-average interest rate 4.23 % 3.50 % 
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  August 31,  $ in millions 2017 2016  Number of days borrowed 88 84  Maximum amount borrowed $ 57.2 $ 51.3  Weighted-average amount borrowed $ 55.8 $ 51.3  Weighted-average interest rate 1.67 % 1.01 % 

Description of Business, Basi29

Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2017USD ($)segment	Aug. 31, 2016USD ($)	May 31, 2017USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment	1
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	$ 8.7	$ 9.1
Germany [Member] | Total Revenue [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Percentage of total revenue less than one percent	1.00%	1.00%

Basic and Diluted Earnings Pe30

Basic and Diluted Earnings Per Share (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Authorized in July 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Expiration date	May 31, 2019
Approved repurchase amount	$ 350
Common stock repurchased and retired, shares	1.6	0
Common stock repurchased and retired, values	$ 94.1
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Common stock issued in connection with exercise or vesting of stock-based awards	0.5	1.3
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
	Aug. 31, 2017	Aug. 31, 2016
Basic and Diluted Earnings Per Share [Abstract]
Net income	$ 227.8	$ 217.4
Basic earnings per share:
Weighted-average common shares outstanding	358.9	361
Basic earnings per share	$ 0.63	$ 0.60
Diluted earnings per share:
Dilutive effect of common share equivalents	2.4	3.1
Weighted-average common shares outstanding, assuming dilution	361.3	364.1
Diluted earnings per share	$ 0.63	$ 0.60
Weighted-average anti-dilutive common share equivalents	1.1	0.5

Business Combination (Narrative

Business Combination (Narrative) (Details) $ in Millions	3 Months Ended
	Aug. 31, 2017USD ($)state
Business Acquisition [Line Items]
Goodwill acquired	$ 40.9
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	$ 40.9
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
	Aug. 31, 2017	Aug. 31, 2016
Investment Income, Net [Abstract]
Interest income on corporate funds	$ 2.9	$ 2.4
Interest expense	(0.8)	(0.7)
Net loss from equity-method investments		(0.2)
Investment income, net	$ 2.1	$ 1.5

Funds Held for Clients and Co34

Funds Held for Clients and Corporate Investments (Narrative) (Details) $ in Millions	3 Months Ended
	Aug. 31, 2017USD ($)security	Aug. 31, 2016USD ($)	May 31, 2017USD ($)security
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gain on available-for-sale securities	$ 38.6		$ 32
Number of available-for-sale securities in an unrealized loss position | security	149		216
Gross unrealized losses on available-for-sale securities	$ 3.6		$ 5.8
Realized losses on available-for-sale securities	$ 0	$ 0
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		Aug. 31, 2017	May 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Funds held for clients money market securities and other cash equivalents, Amortized cost		$ 1,194.6	$ 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		1,194.6	264.8
Available-for-sale securities, Amortized cost		4,318.9	4,581.2
Available-for-sale securities, Gross unrealized gains		42.2	37.8
Available-for-sale securities, Gross unrealized losses		(3.6)	(5.8)
Available-for-sale securities, Fair value		4,357.5	4,613.2
Other, Amortized cost		15.8	14.8
Other, Gross unrealized gains		2.2	1.9
Other, Gross unrealized losses
Other, Fair value		18	16.7
Total funds held for clients and corporate investments, Amortized cost		5,529.3	4,860.8
Total funds held for clients and corporate investments, Gross unrealized gains		44.4	39.7
Total funds held for clients and corporate investments, Gross unrealized losses		(3.6)	(5.8)
Total funds held for clients and corporate investments, Fair value		5,570.1	4,894.7
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		263.9	208.6
Available-for-sale securities, Gross unrealized gains		3.6	2.7
Available-for-sale securities, Gross unrealized losses		(0.3)	(0.5)
Available-for-sale securities, Fair value		267.2	210.8
General Obligation Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		1,407.4	1,422
Available-for-sale securities, Gross unrealized gains		23.2	21.2
Available-for-sale securities, Gross unrealized losses		(0.4)	(0.9)
Available-for-sale securities, Fair value		1,430.2	1,442.3
Pre-Refunded Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	[1]	60.9	54.6
Available-for-sale securities, Gross unrealized gains	[1]	1.1	0.9
Available-for-sale securities, Gross unrealized losses	[1]
Available-for-sale securities, Fair value	[1]	62	55.5
Revenue Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		921.3	929.2
Available-for-sale securities, Gross unrealized gains		13.5	12.5
Available-for-sale securities, Gross unrealized losses		(0.2)	(0.8)
Available-for-sale securities, Fair value		934.6	940.9
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		368.6	328.9
Available-for-sale securities, Gross unrealized gains		0.8	0.5
Available-for-sale securities, Gross unrealized losses		(2.7)	(3.6)
Available-for-sale securities, Fair value		366.7	325.8
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost		1,296.8	1,637.9
Available-for-sale securities, Gross unrealized gains
Available-for-sale securities, Gross unrealized losses
Available-for-sale securities, Fair value		$ 1,296.8	$ 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	Aug. 31, 2017	May 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Funds held for clients	$ 4,953.1	$ 4,301.9
Corporate investments	133.8	138.8
Long-term corporate investments	483.2	454
Total funds held for clients and corporate investments, Fair value	$ 5,570.1	$ 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	Aug. 31, 2017	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	$ (2.4)	$ (5.8)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(1.2)
Total, Gross unrealized losses	(3.6)	(5.8)
Securities in an unrealized loss position for less than twelve months, Fair value	336.3	606.4
Securities in an unrealized loss position for more than twelve months, Fair value	70.1	1
Total, Fair value	406.4	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	(0.2)	(0.5)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(0.1)
Total, Gross unrealized losses	(0.3)	(0.5)
Securities in an unrealized loss position for less than twelve months, Fair value	34.1	43.6
Securities in an unrealized loss position for more than twelve months, Fair value	6.6
Total, Fair value	40.7	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	(0.3)	(0.9)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(0.1)
Total, Gross unrealized losses	(0.4)	(0.9)
Securities in an unrealized loss position for less than twelve months, Fair value	78.2	188.8
Securities in an unrealized loss position for more than twelve months, Fair value	12.1
Total, Fair value	90.3	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, Fair value	9.1	9.2
Total, Fair value	9.1	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	(0.1)	(0.8)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(0.1)
Total, Gross unrealized losses	(0.2)	(0.8)
Securities in an unrealized loss position for less than twelve months, Fair value	70.6	154.8
Securities in an unrealized loss position for more than twelve months, Fair value	12.3	1
Total, Fair value	82.9	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	(1.8)	(3.6)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses	(0.9)
Total, Gross unrealized losses	(2.7)	(3.6)
Securities in an unrealized loss position for less than twelve months, Fair value	144.3	210
Securities in an unrealized loss position for more than twelve months, Fair value	39.1
Total, Fair value	$ 183.4	$ 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	Aug. 31, 2017	May 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Due in one year or less, Amortized cost	$ 286.3
Due after one year through three years, Amortized cost	803
Due after three years through five years, Amortized cost	1,026.3
Due after five years, Amortized cost	2,203.3
Available-for-sale securities, Amortized cost	4,318.9	$ 4,581.2
Due in one year or less, Fair value	287
Due after one year through three years, Fair value	812
Due after three years through five years, Fair value	1,048.5
Due after five years, Fair value	2,210
Available-for-sale securities, Fair value	$ 4,357.5	$ 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	Aug. 31, 2017	May 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 80.4
Available-for-sale securities	4,357.5	$ 4,613.2
Other	18	16.7
Other long-term liabilities	18	16.7
Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	50
Money Market Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	30.4
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	267.2	210.8
General Obligation Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,430.2	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	62	55.5
Revenue Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	934.6	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	366.7	325.8
Variable Rate Demand Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,296.8	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	80.4
Other	18	16.7
Other long-term liabilities	18	16.7
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	50
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	30.4
Significant Other Observable Inputs (Level 2) [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,357.5	4,613.2
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	267.2	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	1,430.2	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	62	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	934.6	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	366.7	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	1,296.8	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] | 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		Aug. 31, 2017	May 31, 2017
Total accounts receivable, gross		$ 544.3	$ 513.5
Less: Allowance for doubtful accounts		5.7	6
Accounts receivable, net of allowance for doubtful accounts		538.6	507.5
PEO Receivables [Member]
Total accounts receivable, gross	[1]	115.4	137.8
Purchased Receivables [Member]
Total accounts receivable, gross	[2]	284.4	257.3
Other Trade Receivables [Member]
Total accounts receivable, gross	[3]	$ 144.5	$ 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 August 31, 2017 include receivables balances acquired from HROI. Refer to Note C for further details of this immaterial business acquisition.
[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
	Oct. 05, 2017USD ($)item	Sep. 30, 2017	Aug. 31, 2017USD ($)ft²item	Aug. 31, 2017USD ($)ft²item	Aug. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
Depreciation expense				$ 28.1	$ 25.3
Cost of building purchased				$ 18	$ 20.3
Multi-Building Campus [Member] | Subsequent Event [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	5
Renovation square feet | ft²			300,000	300,000
Estimated cost of building to be purchased			$ 60
Multi-Building Campus [Member] | Rochester, NY [Member] | Subsequent Event [Member]
Property, Plant and Equipment [Line Items]
Number of buildings purchased | item	2
Cost of building purchased	$ 19.5

Property and Equipment, Net o42

Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($) $ in Millions	Aug. 31, 2017	May 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,068.1	$ 1,051
Less: Accumulated depreciation	739.5	713.8
Property and equipment, net of accumulated depreciation	328.6	337.2
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	8.3	8.3
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	103.6	103.5
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	207.8	199.7
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	503.9	496.1
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	115.3	115.2
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	111.5	109.5
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 17.7	$ 18.7

Goodwill and Intangible Asset43

Goodwill and Intangible Assets, Net of Accumulated Amortization (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	May 31, 2017
Goodwill and Intangible Assets, Net of Accumulated Amortization [Abstract]
Goodwill	$ 698		$ 657.1
Increased in goodwill result of HROI acquisition	40.9
Amortization expense	$ 3.9	$ 4.4

Goodwill and Intangible Asset44

Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	Aug. 31, 2017	May 31, 2017
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	$ 324.1	$ 298.9
Less: Accumulated amortization	244.9	241.3
Intangible assets, net of accumulated amortization	79.2	57.6
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	318.7	293.5
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	$ 5.4	$ 5.4

Goodwill and Intangible Asset45

Goodwill and Intangible Assets, Net of Accumulated Amortization (Estimated Amortization Expense) (Details) $ in Millions	Aug. 31, 2017USD ($)
Year ending May 31
2,018	$ 20.1
2,019	17.3
2,020	13.9
2,021	10.9
2,022	$ 8.2

Accumulated Other Comprehensi46

Accumulated Other Comprehensive Income (Changes in Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Accumulated Other Comprehensive Income [Abstract]
Beginning balance	$ 20	$ 29.2
Unrealized gains on available-for-sale securities, net of tax	4.4	10
Total other comprehensive income, net of tax	4.4	10
Ending balance	24.4	39.2
Total tax expense included in other comprehensive income	$ 2.4	$ 5.7

Short-term Financing (Narrative

Short-term Financing (Narrative) (Details) $ in Millions	Sep. 01, 2017USD ($)	Aug. 31, 2017USD ($)	Aug. 31, 2016USD ($)	Aug. 17, 2017USD ($)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
Maximum amount borrowed		$ 660	$ 350
Number of days borrowed		13 days	4 days
Weighted-average interest rate		4.23%	3.50%
Weighted-average amount borrowed		$ 278.8	$ 237.5
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
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Three Days [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Weighted-average interest rate		4.25%
Revolving Credit Facility [Member] | JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Two Overnight Basis [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Weighted-average amount borrowed	$ 650
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
Revolving Credit Facility [Member] | JPM $500 Million Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member] | Two Overnight Basis [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Weighted-average amount borrowed	$ 212.5
Revolving Credit Facility [Member] | PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]
Line of Credit Facility [Line Items]
Amounts outstanding		57.2			0
Maximum amount borrowed		$ 57.2	$ 51.3
Number of days borrowed		88 days	84 days
Weighted-average interest rate		1.67%	1.01%
Weighted-average amount borrowed		$ 55.8	$ 51.3
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		52.8			47.3
Amounts outstanding		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
Maximum borrowing capacity				$ 900
Minimum [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Expiration Date		Dec. 1, 2017
Maximum [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Expiration Date		Jul. 1, 2018

Short-term Financing (Descripti

Short-term Financing (Description of Credit Facilities) (Details) $ in Millions	3 Months Ended
	Aug. 31, 2017USD ($)	[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
	Aug. 31, 2017	Aug. 31, 2016
JPM $1 Billion Credit Facility [Member] | JP Morgan Chase Bank, N.A. [Member]
Line of Credit Facility [Line Items]
Number of days borrowed	13 days	4 days
Maximum amount borrowed	$ 660	$ 350
Weighted-average amount borrowed	$ 278.8	$ 237.5
Weighted-average interest rate	4.23%	3.50%
PNC $150 Million Credit Facility [Member] | PNC Bank, National Association [Member]
Line of Credit Facility [Line Items]
Number of days borrowed	88 days	84 days
Maximum amount borrowed	$ 57.2	$ 51.3
Weighted-average amount borrowed	$ 55.8	$ 51.3
Weighted-average interest rate	1.67%	1.01%

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Aug. 31, 2017	May 31, 2017
Commitments and Contingencies [Abstract]
Commitments to purchase capital assets	$ 5	$ 7.4

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - $ / shares	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Income Taxes [Abstract]
Effective income tax rate	34.40%	33.00%
Diluted earnings per share impact of discrete tax benefit	$ 0.01	$ 0.04