Corporate Investments and Funds Held For Clients (Narrative) (Details) - USD ($)	3 Months Ended
	Sep. 30, 2020		Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Earliest Corporate bond debt maturity date	October 2020
Latest corporate debt maturity date	September 2030
Fair market value	$ 21,205,100,000	[1]	$ 21,576,600,000	[2]
Earliest U.S. treasury maturity date	October 2020
Latest U.S treasury maturity date	December 2029
Client fund obligation repayment period	1 year
Client funds obligations	$ 29,098,400,000		25,831,600,000
Client funds held in grantor trust	$ 26,805,600,000		$ 23,740,000,000.0
Client funds investments with original maturities	ninety days or less
Percentage of the available-for-sale securities were rated AAA Or AA	79.00%
Fair Value, Inputs, Level 1
Debt Securities, Available-for-sale [Line Items]
Fair market value	$ 0
Fair Value, Inputs, Level 3
Debt Securities, Available-for-sale [Line Items]
Fair market value	0
Asset-Backed Auto Loan Receivables
Debt Securities, Available-for-sale [Line Items]
Fair market value	1,520,800,000
Fixed Rate Credit Card
Debt Securities, Available-for-sale [Line Items]
Fair market value	1,100,400,000
Asset-Backed Equipment Lease Receivable
Debt Securities, Available-for-sale [Line Items]
Fair market value	321,900,000
Rate Reduction
Debt Securities, Available-for-sale [Line Items]
Fair market value	97,100,000
Federal Farm Credit Banks
Debt Securities, Available-for-sale [Line Items]
Fair market value	614,700,000
Federal Home Loan Banks
Debt Securities, Available-for-sale [Line Items]
Fair market value	590,800,000
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair market value	576,700,000
Debt Security, Corporate, Non-US
Debt Securities, Available-for-sale [Line Items]
Fair market value	197,300,000
Sovereign bonds
Debt Securities, Available-for-sale [Line Items]
Fair market value	$ 77,200,000

[1] Included within available-for-sale securities are corporate investments with fair values of $3.4 million and funds held for clients with fair values of $21,201.7 million. All available-for-sale securities were included in Level 2 of the fair value hierarchy.

[2] Included within available-for-sale securities are corporate investments with fair values of $13.6 million and funds held for clients with fair values of $21,563.0 million. All available-for-sale securities were included in Level 2 of the fair value hierarchy.