Revenue by Line of Business within Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 816.1	$ 865.6
Moodys Investors Service [Member]
Segment Reporting Information [Line Items]
Revenues	549.1	624.6
Moodys Investors Service [Member] | Corporate Finance [Member]
Segment Reporting Information [Line Items]
Revenues	240.3	298.7
Moodys Investors Service [Member] | Structured Finance [Member]
Segment Reporting Information [Line Items]
Revenues	90.6	101.3
Moodys Investors Service [Member] | Financial Institutions [Member]
Segment Reporting Information [Line Items]
Revenues	94.9	93.8
Moodys Investors Service [Member] | Public Project And Infrastructure Finance [Member]
Segment Reporting Information [Line Items]
Revenues	91.5	100.7
Moodys Investors Service [Member] | Rating Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	517.3	594.5
Moodys Investors Service [Member] | MIS Other [Member]
Segment Reporting Information [Line Items]
Revenues	7.8	7.8
Moodys Investors Service [Member] | External Revenues [Member]
Segment Reporting Information [Line Items]
Revenues	525.1	602.3
Moodys Investors Service [Member] | Intersegment Royality [Member]
Segment Reporting Information [Line Items]
Revenues	24.0	22.3
Moodys Analytics [Member]
Segment Reporting Information [Line Items]
Revenues	293.8	266.6
Moodys Analytics [Member] | Research Data And Analytics [Member]
Segment Reporting Information [Line Items]
Revenues	164.9	149.6
Moodys Analytics [Member] | Enterprise Risk Solutions [Member]
Segment Reporting Information [Line Items]
Revenues	89.5	77.1
Moodys Analytics [Member] | Professional Services [Member]
Segment Reporting Information [Line Items]
Revenues	36.6	36.6
Moodys Analytics [Member] | External Revenues [Member]
Segment Reporting Information [Line Items]
Revenues	291.0	263.3
Moodys Analytics [Member] | Intersegment Royality [Member]
Segment Reporting Information [Line Items]
Revenues	2.8	3.3
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	$ (26.8)	$ (25.6)