Consolidated Statements Of Shareholders' Equity (Deficit) (USD $) In Millions	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Moody's Shareholders' Equity (Deficit) [Member]	Non-Controlling Interests [Member]	Comprehensive Income (Loss) Shareholders' Of Moody's Corporation [Member]	Comprehensive Income (Loss) Non-Controlling Interests [Member]	Total Comprehensive Income (Loss) [Member]	Total
Beginning balance at Dec. 31, 2008	$ 3.4	$ 392.7	$ 3,023.2	$ (4,361.6)	$ (52.1)	$ (994.4)	$ 8.3				$ (986.1)
Beginning balance, shares at Dec. 31, 2008	342.9			(107.8)
Net income			402.0			402.0	5.1	402.0	5.1	407.1	407.1
Dividends			(96.2)			(96.2)	(3.7)				(99.9)
Stock-based compensation		57.9				57.9					57.9
Shares issued for stock-based compensation plans, net		(53.4)		73.1		19.7					19.7
Shares issued for stock-based compensation plans, net, shares				1.8
Net excess tax benefit (shortfalls) upon settlement of stock-based compensation awards		(6.1)				(6.1)					(6.1)
Currency translation adjustment, (net of tax)					22.2	22.2	0.4	22.2	0.4	22.6	22.6
Net actuarial losses and prior service cost (net of tax)					(10.4)	(10.4)		(10.4)		(10.4)	(10.4)
Amortization and recognition of prior service costs and actuarial losses, (net of tax)					0.6	0.6		0.6		0.6	0.6
Net unrealized gain (loss) on cash flow hedges (net of tax)					(1.5)	(1.5)		(1.5)		(1.5)	(1.5)
Comprehensive income								412.9	5.5	418.4
Ending balance at Dec. 31, 2009	3.4	391.1	3,329.0	(4,288.5)	(41.2)	(606.2)	10.1				(596.1)
Ending balance, shares at Dec. 31, 2009	342.9			(106.0)
Net income			507.8			507.8	5.6	507.8	5.6	513.4	513.4
Dividends			(100.6)			(100.6)	(4.8)				(105.4)
Stock-based compensation		56.9				56.9					56.9
Shares issued for stock-based compensation plans, net		(70.2)		104.8		34.6					34.6
Shares issued for stock-based compensation plans, net, shares				2.5
Net excess tax benefit (shortfalls) upon settlement of stock-based compensation awards		13.7				13.7					13.7
Treasury shares repurchased				(223.6)		(223.6)					(223.6)
Treasury shares repurchased, shares				(8.6)
Currency translation adjustment, (net of tax)					11.5	11.5	0.3	11.5	0.3	11.8	11.8
Net actuarial losses and prior service cost (net of tax)					(7.3)	(7.3)		(7.3)		(7.3)	(7.3)
Amortization and recognition of prior service costs and actuarial losses, (net of tax)					2.9	2.9		2.9		2.9	2.9
Net unrealized gain (loss) on cash flow hedges (net of tax)					0.7	0.7		0.7		0.7	0.7
Comprehensive income								515.6	5.9	521.5
Ending balance at Dec. 31, 2010	3.4	391.5	3,736.2	(4,407.3)	(33.4)	(309.6)	11.2				(298.4)
Ending balance, shares at Dec. 31, 2010	342.9			(112.1)
Net income			571.4			571.4	5.6	571.4	5.6	577.0	577.0
Dividends			(131.5)			(131.5)	(5.1)				(136.6)
Stock-based compensation		56.9				56.9					56.9
Shares issued for stock-based compensation plans, net		(59.2)		105.6		46.4					46.4
Shares issued for stock-based compensation plans, net, shares				2.6
Net excess tax benefit (shortfalls) upon settlement of stock-based compensation awards		7.2				7.2					7.2
Excess of consideration paid over carrying value of additional investment in KIS Pricing		(1.9)				(1.9)					(1.9)
Purchase of KIS Pricing shares from noncontrolling interest							(1.0)				(1.0)
Treasury shares repurchased				(333.8)		(333.8)					(333.8)
Treasury shares repurchased, shares				(11.0)
Currency translation adjustment, (net of tax)					(46.9)	(46.9)	(0.1)	(46.9)	(0.1)	(47.0)	(47.0)
Net actuarial losses and prior service cost (net of tax)					(34.2)	(34.2)		(34.2)		(34.2)	(34.2)
Amortization and recognition of prior service costs and actuarial losses, (net of tax)					4.4	4.4		4.4		4.4	4.4
Net unrealized gain (loss) on cash flow hedges (net of tax)					2.6	2.6		2.6		2.6	2.6
Comprehensive income								497.3	5.5	502.8
Ending balance at Dec. 31, 2011	$ 3.4	$ 394.5	$ 4,176.1	$ (4,635.5)	$ (107.5)	$ (169.0)	$ 10.6				$ (158.4)
Ending balance, shares at Dec. 31, 2011	342.9			(120.5)