Goodwill and Intangibles Assets, net (Changes In Goodwill) (Details) $ in Millions	3 Months Ended
	Sep. 30, 2018 USD ($)
Goodwill [Roll Forward]
Balance at June 30, 2018	$ 2,243.5
Additions and other adjustments	88.4
Currency translation adjustments	(6.9)
Balance at September 30, 2018	2,325.0
Employer Services
Goodwill [Roll Forward]
Balance at June 30, 2018	2,238.7
Additions and other adjustments	88.4
Currency translation adjustments	(6.9)
Balance at September 30, 2018	2,320.2
PEO Services
Goodwill [Roll Forward]
Balance at June 30, 2018	4.8
Additions and other adjustments	0.0
Currency translation adjustments	0.0
Balance at September 30, 2018	$ 4.8