Consolidated Statements Of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements Of Operations [Abstract]
Revenue	$ 646.8	$ 577.1
Expenses
Operating	185.5	160.8
Selling, general and administrative	168.8	148.5
Depreciation and amortization	23.5	17.7
Total expenses	377.8	327.0
Operating Income	269.0	250.1
Non-operating (expense) income, net
Interest expense, net	(10.3)	(18.2)
Other non-operating (expense) income, net	(0.1)	3.3
Total non-operating (expense) income, net	(10.4)	(14.9)
Income before provisions for income taxes	258.6	235.2
Provision for income taxes	83.1	78.1
Net income	175.5	157.1
Less: Net income attributable to noncontrolling interests	2.0	1.6
Net income attributable to Moody's	$ 173.5	$ 155.5
Earnings per share attributable to Moody's common shareholders
Basic	$ 0.78	$ 0.68
Diluted	$ 0.76	$ 0.67
Weighted average number of shares outstanding
Basic	223.4	228.9
Diluted	227.4	231.4