Activity in Goodwill (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Ending balance	$ 988.0us-gaap_Goodwill	$ 1,021.1us-gaap_Goodwill
Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	1,033.3	677.4
Additions/adjustments	0	397.8
FX translation	(33.1)	(41.9)
Ending balance	1,000.2	1,033.3
Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance	(12.2)	(12.2)
Additions/adjustments	0	0
FX translation
Ending balance	(12.2)	(12.2)
Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	1,021.1	665.2
Additions/adjustments	0	397.8
FX translation	(33.1)	(41.9)
Ending balance	988.0	1,021.1
Moodys Investors Service [Member] \| Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	298.7	11.4
Additions/adjustments	0	296.7
FX translation	(7.0)	(9.4)
Ending balance	291.7	298.7
Moodys Investors Service [Member] \| Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance
Additions/adjustments	0	0
FX translation
Ending balance	0
Moodys Investors Service [Member] \| Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	298.7	11.4
Additions/adjustments	0	296.7
FX translation	(7.0)	(9.4)
Ending balance	291.7	298.7
Moodys Analytics [Member] \| Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	734.6	666.0
Additions/adjustments	0	101.1
FX translation	(26.1)	(32.5)
Ending balance	708.5	734.6
Moodys Analytics [Member] \| Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance	(12.2)	(12.2)
Additions/adjustments	0	0
FX translation
Ending balance	(12.2)	(12.2)
Moodys Analytics [Member] \| Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	722.4	653.8
Additions/adjustments	0	101.1
FX translation	(26.1)	(32.5)
Ending balance	$ 696.3	$ 722.4

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e961-128460

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Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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