Segment Information (Financial Information By Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Revenue	$ 646.8	$ 577.1
Expenses:
Operating, SG&A	354.3	309.3
Restructuring
Depreciation and amortization	23.5	17.7
Total	377.8	327.0
Operating income	269.0	250.1
MIS [Member]
Segment Reporting Information [Line Items]
Revenue	469.8	428.6
Expenses:
Operating, SG&A	220.9	200.6
Restructuring
Depreciation and amortization	11.2	8.7
Total	232.1	209.3
Operating income	237.7	219.3
MA [Member]
Segment Reporting Information [Line Items]
Revenue	197.1	167.1
Expenses:
Operating, SG&A	153.5	127.3
Restructuring
Depreciation and amortization	12.3	9.0
Total	165.8	136.3
Operating income	31.3	30.8
Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(20.1)	(18.6)
Expenses:
Operating, SG&A	(20.1)	(18.6)
Restructuring
Total	$ (20.1)	$ (18.6)