Segment Information (Financial Information By Segment) (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Revenue	$ 531.3	$ 513.3	$ 1,713.6	$ 1,467.7
Operating, SG&A	316.0	305.9	938.7	842.4
Restructuring	0.2	0.4	0.1
Depreciation and amortization	19.0	18.1	58.5	49.1
Total expenses	335.2	324.4	997.3	891.5
Operating income	196.1	188.9	716.3	576.2
MIS [Member]
Segment Reporting Information [Line Items]
Revenue	368.2	373.7	1,251.0	1,068.6
Operating, SG&A	200.0	204.3	604.2	562.0
Restructuring	0.1	0.3
Depreciation and amortization	9.8	10.3	30.8	26.3
Total expenses	209.9	214.9	635.0	588.3
Operating income	158.3	158.8	616.0	480.3
MA [Member]
Segment Reporting Information [Line Items]
Revenue	182.5	157.4	519.4	452.4
Operating, SG&A	135.4	119.4	391.3	333.7
Restructuring	0.1	0.1	0.1
Depreciation and amortization	9.2	7.8	27.7	22.8
Total expenses	144.7	127.3	419.1	356.5
Operating income	37.8	30.1	100.3	95.9
Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(19.4)	(17.8)	(56.8)	(53.3)
Operating, SG&A	(19.4)	(17.8)	(56.8)	(53.3)
Total expenses	$ (19.4)	$ (17.8)	$ (56.8)	$ (53.3)

The total of direct operating costs and costs related to selling the Company's products and services, as well as all other general and administrative expenses. Operating expenses include costs associated with the development and production of the Company's products and services and their delivery to customers. These expenses principally include employee compensation and benefits and travel costs that are incurred in connection with these activities. Selling, general and administrative costs include such items as compensation and benefits for corporate officers and staff and compensation and other expenses related to sales of products. They also include items such as office rent, business insurance, professional fees and gains and losses from sales and disposals of assets.

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The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

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