Revenues and Operating Earnings Based on Originating Location (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Segment Reporting Information [Line Items]
Revenues	$ 654.7	$ 636.0	$ 608.9	$ 600.2	$ 541.8	$ 495.0	$ 483.9	$ 463.5	$ 2,499.8		$ 1,984.2		$ 1,937.7
Operating earnings (loss)									428.0	[1]	316.0	[1]	296.1	[1]
Domestic
Segment Reporting Information [Line Items]
Revenues									1,750.2		1,422.6		1,399.5
Operating earnings (loss)									246.9		181.3		178.2
Foreign
Segment Reporting Information [Line Items]
Revenues									749.6		561.6		538.2
Operating earnings (loss)									$ 181.1		$ 134.7		$ 117.9

[1] Operating earnings includes an allocation of corporate IT costs, employee benefits and general and administrative costs based on the proportion of each segments' systems users, number of employees and sales, respectively.