Goodwill and Intangibles Assets, net (Changes In Goodwill) (Details) $ in Millions	6 Months Ended
	Dec. 31, 2017 USD ($)
Goodwill [Roll Forward]
Balance at June 30, 2017	$ 1,741.0
Additions and other adjustments, net	403.8
Currency translation adjustments	19.5
Balance at December 31, 2017	2,164.3
Employer Services
Goodwill [Roll Forward]
Balance at June 30, 2017	1,736.2
Additions and other adjustments, net	403.8
Currency translation adjustments	19.5
Balance at December 31, 2017	2,159.5
PEO Services
Goodwill [Roll Forward]
Balance at June 30, 2017	4.8
Additions and other adjustments, net	0.0
Currency translation adjustments	0.0
Balance at December 31, 2017	$ 4.8