Revenue by Line of Business within Each Reportable Segment (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 873,500,000	$ 756,000,000	$ 1,640,700,000	$ 1,487,800,000
Moodys Investors Service [Member]
Segment Reporting Information [Line Items]
Revenues	643,600,000	556,300,000	1,190,900,000	1,096,400,000
Intersegment revenue	21,900,000	19,000,000	43,400,000	37,900,000
Moodys Investors Service [Member] | Corporate Finance [Member]
Segment Reporting Information [Line Items]
Revenues	320,900,000	262,900,000	585,300,000	521,200,000
Moodys Investors Service [Member] | Structured Finance [Member]
Segment Reporting Information [Line Items]
Revenues	110,600,000	97,200,000	205,900,000	190,200,000
Moodys Investors Service [Member] | Financial Institutions [Member]
Segment Reporting Information [Line Items]
Revenues	92,200,000	84,500,000	177,600,000	171,000,000
Moodys Investors Service [Member] | Public Project And Infrastructure Finance [Member]
Segment Reporting Information [Line Items]
Revenues	98,000,000	92,700,000	178,700,000	176,100,000
Moodys Investors Service [Member] | External Revenues
Segment Reporting Information [Line Items]
Revenues	621,700,000	537,300,000	1,147,500,000	1,058,500,000
Moodys Analytics [Member]
Segment Reporting Information [Line Items]
Revenues	255,100,000	221,400,000	499,800,000	434,800,000
Intersegment revenue	3,300,000	2,700,000	6,600,000	5,500,000
Moodys Analytics [Member] | Research Data And Analytics [Member]
Segment Reporting Information [Line Items]
Revenues	144,700,000	130,300,000	285,600,000	259,900,000
Moodys Analytics [Member] | Enterprise Risk Solutions [Member]
Segment Reporting Information [Line Items]
Revenues	67,200,000	60,200,000	127,000,000	113,200,000
Moodys Analytics [Member] | Professional Services [Member]
Segment Reporting Information [Line Items]
Revenues	39,900,000	28,200,000	80,600,000	56,200,000
Moodys Analytics [Member] | External Revenues
Segment Reporting Information [Line Items]
Revenues	251,800,000	218,700,000	493,200,000	429,300,000
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (25,200,000)	$ (21,700,000)	$ (50,000,000)	$ (43,400,000)