Interim Financial Data By Segment (Financial Data By Strategic Business Unit Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 2,583.0	$ 2,405.7	$ 5,105.5	$ 4,635.2
Earnings before income taxes	579.7	484.6	1,039.0	921.0
Employer Services [Member]
Segment Reporting Information [Line Items]
Revenues	1,827.1	1,707.2	3,577.5	3,306.5
Earnings before income taxes	447.0	438.0	857.0	820.4
PEO Services [Member]
Segment Reporting Information [Line Items]
Revenues	413.8	358.2	814.4	699.5
Earnings before income taxes	42.4	35.9	78.9	64.0
Dealer Services [Member]
Segment Reporting Information [Line Items]
Revenues	412.6	386.0	820.4	732.2
Earnings before income taxes	70.5	57.5	133.6	107.2
Other [Member]
Segment Reporting Information [Line Items]
Revenues	1.4	3.1	4.1	6.5
Earnings before income taxes	47.0	(35.2)	13.9	(53.7)
Foreign exchange [Member]
Segment Reporting Information [Line Items]
Revenues	(14.9)	(12.6)	(5.2)	(45.2)
Earnings before income taxes		(4.5)	0.7	(7.7)
Client fund interest [Member]
Segment Reporting Information [Line Items]
Revenues	(57.0)	(36.2)	(105.7)	(64.3)
Earnings before income taxes	(57.0)	(36.2)	(105.7)	(64.3)
Cost of capital charge [Member]
Segment Reporting Information [Line Items]
Earnings before income taxes	$ 29.8	$ 29.1	$ 60.6	$ 55.1