CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net income	$ 218,500,000	$ 186,800,000	$ 764,600,000	$ 606,300,000
Foreign currency translation adjustment-Pre Tax Amount	(99,500,000)	48,100,000	(90,200,000)	(24,700,000)
Foreign currency translation adjustment-Tax Amount	0	0	0	0
Foreign currency translation adjustments-Net of Tax	(99,500,000)	48,100,000	(90,200,000)	(24,700,000)
Cash Flow And Net Investment Hedges [Abstract]
Net unrealized gain (losses) on cash flow and net investment hedges- Pre Tax	20,300,000	(2,700,000)	14,000,000	(1,700,000)
Net unrealized gain (losses) on cash flow and net investment hedges-Tax Amount	(8,200,000)	1,200,000	(5,600,000)	700,000
Net unrealized losses on cash flow and net investment hedges	12,100,000	(1,500,000)	8,400,000	(1,000,000)
Reclassification of losses included in net income-Pre Tax			0	(700,000)
Reclassification of losses included in net income-Tax Amount			0	200,000
Reclassification of losses included in net income- Net of Tax			0	(500,000)
Pension and Other Retirement Benefits Net of Tax [Abstract]
Amortization of actuarial losses and prior service costs included in net income (pre-tax)	(1,800,000)	(3,100,000)	(5,500,000)	(9,000,000)
Amortization of actuarial losses and prior service costs included in net income (tax)	(700,000)	(1,300,000)	(3,000,000)	(3,700,000)
Amortization of actuarial losses and prior service costs included in net income	(1,100,000)	(1,800,000)	(2,500,000)	(5,300,000)
Net actuarial losses and prior service costs	0	0	(4,100,000)	500,000
Total other comprehensive income (loss)-Pre Tax	(77,400,000)	49,800,000	(73,200,000)	(14,500,000)
Net current period other comprehensive income/(loss)	(8,900,000)	(100,000)	(5,800,000)	(3,600,000)
Total other comprehensive income (loss)-Net of Tax	(86,300,000)	49,700,000	(79,000,000)	(18,100,000)
Comprehensive income (loss)	132,200,000	236,500,000	685,600,000	588,200,000
Comprehensive income attributable to noncontrolling interests and redeemable noncontrolling interest	3,300,000	2,900,000	12,200,000	8,500,000
Comprehensive income attributable to Moody's	128,900,000	233,600,000	673,400,000	579,700,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	0	1,300,000	4,400,000	1.3
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax	0	0	0	0
Total Reclassifications	$ 0	$ 1,300,000	$ 4,400,000	$ 1.3