Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017	Jul. 01, 2019	Jun. 30, 2016
Summary of Significant Accounting Policies [Line Items]
Net Income (Loss) Attributable to Parent	$ 475,500,000	$ 753,700,000	$ 558,200,000	$ 505,400,000	$ 140,900,000	$ 661,000,000	$ 670,400,000	$ 412,600,000	$ 2,292,800,000	$ 1,884,900,000	$ 1,787,800,000
Provision for income taxes									712,800,000	397,700,000	829,100,000
Operating Leases, Rent Expense									$ 270,100,000	$ 234,900,000	$ 234,500,000
Percent of Level Two Investment Pricing Inputs Provided by Independent Pricing Service	99.00%								99.00%
Basic weighted average shares outstanding (in shares)									435.0	440.6	447.8
Effect of Employee Stock Option Shares									1.0	1.1	0.9
Effect of Employee Restricted Stock Shares									1.6	1.6	1.6
Diluted weighted average shares outstanding (in shares)									437.6	443.3	450.3
EPS from continuing operations, Basic (in dollars per share)	$ 1.10	$ 1.74	$ 1.28	$ 1.16	$ 0.32	$ 1.50	$ 1.52	$ 0.93	$ 5.27	$ 4.28	$ 3.99
EPS from continuing operations, Diluted (in dollars per share)	$ 1.09	$ 1.73	$ 1.27	$ 1.15	$ 0.32	$ 1.49	$ 1.51	$ 0.93	$ 5.24	$ 4.25	$ 3.97
Options excluded from the calculation of diluted earnings per share because their exercise prices exceeded the average market price (in shares)									0.7	0.9	1.0
Unrecognized Tax Benefits	$ 54,200,000				$ 45,200,000				$ 54,200,000	$ 45,200,000	$ 74,600,000		$ 27,400,000
Threshold of coverage for all losses per occurrence covered by reinsurance arrangement, next fiscal year									1,000,000
Concentration Risk, Credit Risk, Financial Instruments, Off-balance Sheet Risk									242,000,000
Payments for Reinsurance									215,000,000
Tax Settlements Future Impact Potential On Earnings Maximum									3,000,000
Debt Instrument, Face Amount	2,000,000,000								2,000,000,000
Net Cash Provided by (Used in) Operating Activities									2,688,300,000	2,515,200,000	2,125,900,000
Max Expected Cash Payment On Tax Settlements									10,000,000
Total assets	41,887,700,000				$ 38,849,100,000				41,887,700,000	38,849,100,000	$ 38,886,900,000
Letters of Credit Outstanding, Amount	$ 0.0								$ 0.0
Revenue, Capitalized Costs Fulfillment Period, Description of Timing									The expected client relationship period ranges from three to eight years.
Minimum [Member]
Summary of Significant Accounting Policies [Line Items]
Revenue, Service Agreements, Term									30 days
Internal Use Software Life of Asset									3 years
Minimum [Member] | Data Processing Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									3 years
Minimum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									20 years
Minimum [Member] | Furniture and Fixtures [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									4 years
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Revenue, Service Agreements, Term									5 years
Internal Use Software Life of Asset									5 years
Maximum [Member] | Data Processing Equipment [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									10 years
Maximum [Member] | Building [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									40 years
Maximum [Member] | Furniture and Fixtures [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant, and Equipment Useful Life									7 years
Notes due on 2020 [Member]
Summary of Significant Accounting Policies [Line Items]
Debt Instrument, Term									5 years
Notes due on 2025 [Member]
Summary of Significant Accounting Policies [Line Items]
Debt Instrument, Term									10 years
Accounting Standards Update 2016-02 [Member] | Minimum [Member] | Forecast [Member]
Summary of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset												$ 600,000,000
Operating Lease, Liability												500,000,000
Accounting Standards Update 2016-02 [Member] | Maximum [Member] | Forecast [Member]
Summary of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset												700,000,000
Operating Lease, Liability												$ 600,000,000
Retained Earnings [Member]
Summary of Significant Accounting Policies [Line Items]
Stockholders' Equity Note, Spinoff Transaction										$ 42,300,000