Segment Information (Total Assets By Segment) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	$ 2,521.3		$ 2,540.3
MIS [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	591.3		639.0
MA [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	821.2		910.0
Corporate [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total Assets	$ 1,108.8	[1]	$ 991.3	[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.