Financial Information by 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]
Instersegment Revenue	$ 873,500,000	$ 756,000,000	$ 1,640,700,000	$ 1,487,800,000
Operating, SG&A	439,500,000	382,100,000	850,600,000	809,900,000
Adjusted Operating Income	434,000,000	373,900,000	790,100,000	677,900,000
Expenses:
Depreciation and amortization	22,300,000	23,100,000	45,400,000	46,700,000
Operating Income	411,700,000	350,800,000	744,700,000	631,200,000
Moodys Investors Service [Member]
Segment Reporting Information [Line Items]
Instersegment Revenue	643,600,000	556,300,000	1,190,900,000	1,096,400,000
Operating, SG&A	268,900,000	236,200,000	514,600,000	520,500,000
Adjusted Operating Income	374,700,000	320,100,000	676,300,000	575,900,000
Expenses:
Depreciation and amortization	11,400,000	11,500,000	22,800,000	22,800,000
Operating Income	363,300,000	308,600,000	653,500,000	553,100,000
Moodys Analytics [Member]
Segment Reporting Information [Line Items]
Instersegment Revenue	255,100,000	221,400,000	499,800,000	434,800,000
Operating, SG&A	195,800,000	167,600,000	386,000,000	332,800,000
Adjusted Operating Income	59,300,000	53,800,000	113,800,000	102,000,000
Expenses:
Depreciation and amortization	10,900,000	11,600,000	22,600,000	23,900,000
Operating Income	48,400,000	42,200,000	91,200,000	78,100,000
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Instersegment Revenue	(25,200,000)	(21,700,000)	(50,000,000)	(43,400,000)
Operating, SG&A	(25,200,000)	(21,700,000)	(50,000,000)	(43,400,000)
Adjusted Operating Income			0	0
Expenses:
Depreciation and amortization			0	0
Operating Income			$ 0	$ 0