Total Assets by Segment (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Total Assets	$ 3,662.3		$ 2,876.1
MIS
Segment Reporting Information [Line Items]
Total Assets	912.6		725.9
MA
Segment Reporting Information [Line Items]
Total Assets	1,262.2		1,289.7
Corporate
Segment Reporting Information [Line Items]
Total Assets	$ 1,487.5	[1]	$ 860.5	[1]

[1] Represents common assets that are shared between each segment or utilized by the corporate entity. Such assets primarily include cash and cash equivalents, short-term investments, unallocated property and equipment and deferred taxes.