New Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net decrease / (increase) in restricted cash and cash equivalents held to satisfy client funds obligations		$ 0.0
Net cash flows provided by / (used in) investing activities	$ (292.6)	(396.9)
Effect of exchange rate changes on cash, cash equivalents, restricted cash, and restricted cash equivalents	14.2	(16.3)
Net change in cash, cash equivalents, restricted cash, and restricted cash equivalents	(2,098.4)	(9,597.0)
Cash, cash equivalents, restricted cash, and restricted cash equivalents, end of period	$ 6,083.2	5,861.6	$ 8,181.6	$ 15,458.6
Accounting Standards Update 2016-18 | As previously reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net decrease / (increase) in restricted cash and cash equivalents held to satisfy client funds obligations		9,160.8
Net cash flows provided by / (used in) investing activities		8,763.9
Effect of exchange rate changes on cash, cash equivalents, restricted cash, and restricted cash equivalents		5.4
Net change in cash, cash equivalents, restricted cash, and restricted cash equivalents		(414.5)
Cash, cash equivalents, restricted cash, and restricted cash equivalents, end of period		2,776.6
Accounting Standards Update 2016-18 | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net decrease / (increase) in restricted cash and cash equivalents held to satisfy client funds obligations		(9,160.8)
Net cash flows provided by / (used in) investing activities		(9,160.8)
Effect of exchange rate changes on cash, cash equivalents, restricted cash, and restricted cash equivalents		(21.7)
Net change in cash, cash equivalents, restricted cash, and restricted cash equivalents		(9,182.5)
Cash, cash equivalents, restricted cash, and restricted cash equivalents, end of period		$ 3,085.0