Financial Information by Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Revenue	$ 767.2	$ 731.8
Operating, SG&A	411.1	427.8
Adjusted Operating Income	356.1	304.0
Expenses:
Depreciation and amortization	23.1	23.6
Operating Income	333.0	280.4
Moodys Investors Service [Member]
Segment Reporting Information [Line Items]
Revenue	547.3	540.1
Operating, SG&A	245.7	284.3
Adjusted Operating Income	301.6	255.8
Expenses:
Depreciation and amortization	11.4	11.3
Operating Income	290.2	244.5
Moodys Analytics [Member]
Segment Reporting Information [Line Items]
Revenue	244.7	213.4
Operating, SG&A	190.2	165.2
Adjusted Operating Income	54.5	48.2
Expenses:
Depreciation and amortization	11.7	12.3
Operating Income	42.8	35.9
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenue	(24.8)	(21.7)
Operating, SG&A	(24.8)	(21.7)
Adjusted Operating Income	0	0
Expenses:
Depreciation and amortization	0	0
Operating Income	$ 0	$ 0