Financial Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenue	$ 688.5	$ 531.3	$ 1,976.1	$ 1,713.6
Operating, SG&A	394.7	316.0	1,089.2	938.7
Adjusted Operating Income	293.8	215.3	886.9	774.9
Depreciation and amortization	24.1	19.0	69.7	58.5
Restructuring		0.2		0.1
Operating income	269.7	196.1	817.2	716.3
MIS
Segment Reporting Information [Line Items]
Revenue	491.3	368.2	1,419.8	1,251.0
Operating, SG&A	252.4	200.5	684.0	606.1
Adjusted Operating Income	238.9	167.7	735.8	644.9
Depreciation and amortization	11.0	9.9	32.9	31.0
Restructuring		0.2		0.1
Operating income	227.9	157.6	702.9	613.8
MA
Segment Reporting Information [Line Items]
Revenue	218.1	182.5	617.7	519.4
Operating, SG&A	163.2	134.9	466.6	389.4
Adjusted Operating Income	54.9	47.6	151.1	130.0
Depreciation and amortization	13.1	9.1	36.8	27.5
Operating income	41.8	38.5	114.3	102.5
Eliminations
Segment Reporting Information [Line Items]
Revenue	(20.9)	(19.4)	(61.4)	(56.8)
Operating, SG&A	$ (20.9)	$ (19.4)	$ (61.4)	$ (56.8)