Corporate Investments and Funds Held for Clients - Schedule of Corporate Investments and Funds Held for Clients (Details) - USD ($)	Sep. 30, 2026	Jun. 30, 2026
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents, and restricted cash	$ 10,705,400,000
Money market securities, cash and other cash equivalents - Amortized Cost	3,277,000,000	$ 4,230,100,000
Available-for-sale, Amortized Cost	38,885,100,000	38,160,500,000
Available-for-sale, Gross Unrealized Gains	9,500,000	115,200,000
Available-for-sale, Gross Unrealized Losses	(1,322,300,000)	(574,400,000)
Available-for-sale, Fair Value	37,572,300,000	37,701,300,000
Total corporate investments and funds held for clients - Amortized Cost	49,590,500,000	48,785,700,000
Total corporate investments and funds held for clients - Gross Unrealized Gains	9,500,000	115,200,000
Total corporate investments and funds held for clients - Gross Unrealized Losses	(1,322,300,000)	(574,400,000)
Total corporate investments and funds held for clients -  Fair Value	48,277,700,000	48,326,500,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	18,790,100,000	18,643,300,000
Available-for-sale, Gross Unrealized Gains	1,100,000	48,100,000
Available-for-sale, Gross Unrealized Losses	(757,100,000)	(342,000,000.0)
Available-for-sale, Fair Value	18,034,100,000	18,349,400,000
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	10,990,500,000	10,873,100,000
Available-for-sale, Gross Unrealized Gains	1,600,000	17,800,000
Available-for-sale, Gross Unrealized Losses	(226,100,000)	(57,400,000)
Available-for-sale, Fair Value	10,766,000,000	10,833,500,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	2,756,700,000	2,437,300,000
Available-for-sale, Gross Unrealized Gains	1,400,000	10,400,000
Available-for-sale, Gross Unrealized Losses	(51,200,000)	(15,000,000.0)
Available-for-sale, Fair Value	2,706,900,000	2,432,700,000
Canadian government obligations and Canadian government agency obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	1,953,400,000	2,055,000,000
Available-for-sale, Gross Unrealized Gains	2,500,000	13,900,000
Available-for-sale, Gross Unrealized Losses	(52,200,000)	(22,000,000.0)
Available-for-sale, Fair Value	1,903,700,000	2,046,900,000
Canadian provincial bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	1,183,200,000	1,186,200,000
Available-for-sale, Gross Unrealized Gains	2,600,000	15,300,000
Available-for-sale, Gross Unrealized Losses	(39,900,000)	(19,600,000)
Available-for-sale, Fair Value	1,145,900,000	1,181,900,000
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	925,200,000	930,300,000
Available-for-sale, Gross Unrealized Gains	0	1,900,000
Available-for-sale, Gross Unrealized Losses	(96,100,000)	(70,500,000)
Available-for-sale, Fair Value	829,100,000	861,700,000
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	815,200,000
Available-for-sale, Gross Unrealized Gains	300,000
Available-for-sale, Gross Unrealized Losses	(23,200,000)
Available-for-sale, Fair Value	792,300,000
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Amortized Cost	1,470,800,000	2,035,300,000
Available-for-sale, Gross Unrealized Gains	0	7,800,000
Available-for-sale, Gross Unrealized Losses	(76,500,000)	(47,900,000)
Available-for-sale, Fair Value	1,394,300,000	1,995,200,000
Corporate Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Fair Value	245,200,000	138,600,000
Funds Held For Clients
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Fair Value	$ 37,327,100,000	37,562,700,000
Money market securities, cash and other cash equivalents
Debt Securities, Available-for-sale [Line Items]
Money market securities, cash and other cash equivalents - Amortized Cost		10,625,200,000
Money market securities and other cash equivalents -  Fair Value		$ 10,625,200,000