CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total Moody's Shareholders' Equity (Deficit)	Non-Controlling Interests
Beginning Balance (in shares) at Dec. 31, 2014		342.9			(138.5)
Beginning Balance at Dec. 31, 2014	$ 42.9	$ 3.4	$ 383.9	$ 6,044.3	$ (6,384.2)	$ (235.2)	$ (187.8)	$ 230.7
Net income	949.6			941.3			941.3	8.3
Dividends	(283.6)			(276.6)			(276.6)	(7.0)
Stock-based compensation	87.5		87.5				87.5
Shares issued for stock-based compensation plans, net	29.6		(63.5)		$ 93.1		29.6
Shares issued for stock-based compensation plans, net (in shares)					2.6
Net excess tax benefit upon settlement of stock-based compensation awards	43.4		43.4				43.4
Treasury shares repurchased, shares					(10.9)
Treasury shares repurchased	(1,098.1)				$ (1,098.1)		(1,098.1)
Currency translation adjustment	(125.3)					(125.3)	(125.3)
Net actuarial losses and prior service costs - Net of Tax	11.4					11.4	11.4
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	8.3					8.3	8.3
Unrealized Gains On Available For Sale Securities	2.4					2.4	2.4
Net unrealized gain on cash flow hedges	(1.1)					(1.1)	(1.1)
Ending Balance (in shares) at Dec. 31, 2015		342.9			(146.8)
Ending Balance at Dec. 31, 2015	(333.0)	$ 3.4	451.3	6,709.0	$ (7,389.2)	(339.5)	(565.0)	232.0
Net income	275.8			266.6			266.6	9.2
Dividends	(293.4)			(286.7)			(286.7)	(6.7)
Stock-based compensation	98.4		98.4				98.4
Shares issued for stock-based compensation plans, net	33.4		(65.0)		$ 98.4		33.4
Shares issued for stock-based compensation plans, net (in shares)					2.3
Net excess tax benefit upon settlement of stock-based compensation awards	32.0		32.0				32.0
Purchase of noncontrolling interest	(49.1)		(39.5)				(39.5)	(9.6)
Treasury shares repurchased, shares					(7.7)
Treasury shares repurchased	(738.8)				$ (738.8)		(738.8)
Currency translation adjustment	(64.2)					(34.2)	(34.2)	(30.0)
Net actuarial losses and prior service costs - Net of Tax	0.2					0.2	0.2
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	6.0					6.0	6.0
Unrealized Gains On Available For Sale Securities	2.6					(0.2)	(0.2)	2.8
Net unrealized gain on cash flow hedges	2.8					2.8	2.8
Ending Balance (in shares) at Dec. 31, 2016		342.9			(152.2)
Ending Balance at Dec. 31, 2016	(1,027.3)	$ 3.4	477.2	6,688.9	$ (8,029.6)	(364.9)	(1,225.0)	197.7
Net income	1,007.7			1,000.6			1,000.6	7.1
Dividends	(222.8)			(219.5)			(219.5)	(3.3)
Adoption of ASU 2016-16	(4.6)			(4.6)			(4.6)
Stock-based compensation	123.2		123.2				123.2
Shares issued for stock-based compensation plans, net	9.3		(67.1)		$ 76.4		9.3
Shares issued for stock-based compensation plans, net (in shares)					1.9
Purchase of noncontrolling interest	(5.7)		(4.7)				(4.7)	(1.0)
Treasury shares repurchased, shares					(1.6)
Treasury shares repurchased	(199.7)				$ (199.7)		(199.7)
Currency translation adjustment	189.3					176.3	176.3	13.0
Net actuarial losses and prior service costs - Net of Tax	12.6					12.6	12.6
Amortization of actuarial losses and prior service costs included in net income - Net of Tax	5.4					5.4	5.4
Unrealized Gains On Available For Sale Securities	(1.5)					(0.8)	(0.8)	(0.7)
Net unrealized gain on cash flow hedges	(0.8)					(0.8)	(0.8)
Ending Balance (in shares) at Dec. 31, 2017		3.4			(151.9)
Ending Balance at Dec. 31, 2017	$ (114.9)	$ 342.9	$ 528.6	$ 7,465.4	$ (8,152.9)	$ (172.2)	$ (327.7)	$ 212.8