Consolidated Statements Of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 175.5	$ 157.1
Foreign currency translation adjustments	28.6	22.9
Cash flow hedges:
Net unrealized losses on cash flow hedges (net of tax of $0.1 million in 2012)	(0.1)
Reclassification adjustment for losses included in net income (net of tax of $0.4 million in both 2012 and 2011)	0.6	0.7
Cash flow hedges, Total	0.5	0.7
Pension and Other Post-Retirement Benefits:
Amortization of actuarial losses and prior service costs included in net income(net of tax of $1.1 million and $0.6 million in 2012 and 2011, respectively)	1.7	0.8
Comprehensive income	206.3	181.5
Less: comprehensive income attributable to noncontrolling interests	4.0	2.0
Comprehensive income attributable to Moody's	$ 202.3	$ 179.5