Segment Information (Total Assets By Segment) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Total Assets	$ 2,994.4		$ 2,876.1
MIS [Member]
Segment Reporting Information [Line Items]
Total Assets	878.3		725.9
MA [Member]
Segment Reporting Information [Line Items]
Total Assets	1,318.1		1,289.7
Corporate Assets [Member]
Segment Reporting Information [Line Items]
Total Assets	$ 798.0	[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.