Activity in Goodwill (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Goodwill [Line Items]
Ending balance	$ 619.8	$ 637.1
Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	649.3	642.9
Additions/adjustments	0	(4.4)
Impairment charge		0
FX translation	(17.3)	10.8
Ending balance	632.0	649.3
Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance	(12.2)	0
Additions/adjustments	0	0
Impairment charge		12.2
FX translation	0	0
Ending balance	(12.2)	(12.2)
Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	637.1	642.9
Additions/adjustments	0	(4.4)
Impairment charge		12.2
FX translation	(17.3)	10.8
Ending balance	619.8	637.1
Moodys Investors Service [Member] \| Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	11.5	11.0
Additions/adjustments	0	0
Impairment charge		0
FX translation	(0.6)	0.5
Ending balance	10.9	11.5
Moodys Investors Service [Member] \| Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance	0	0
Additions/adjustments	0	0
Impairment charge		0
FX translation	0	0
Ending balance	0	0
Moodys Investors Service [Member] \| Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	11.5	11.0
Additions/adjustments	0	0
Impairment charge		0
FX translation	(0.6)	0.5
Ending balance	10.9	11.5
Moodys Analytics [Member] \| Gross Goodwill [Member]
Goodwill [Line Items]
Beginning balance	637.8	631.9
Additions/adjustments	0	(4.4)
Impairment charge		0
FX translation	(16.7)	10.3
Ending balance	621.1	637.8
Moodys Analytics [Member] \| Accumulated Impairment Charge [Member]
Goodwill [Line Items]
Beginning balance	(12.2)	0
Additions/adjustments	0	0
Impairment charge		12.2
FX translation	0	0
Ending balance	(12.2)	(12.2)
Moodys Analytics [Member] \| Net Goodwill [Member]
Goodwill [Line Items]
Beginning balance	625.6	631.9
Additions/adjustments	0	(4.4)
Impairment charge		12.2
FX translation	(16.7)	10.3
Ending balance	$ 608.9	$ 625.6

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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+ Details

- Definition

Loss recognized during the period that results from the write-down of goodwill after comparing the implied fair value of reporting unit goodwill with the carrying amount of that goodwill. Goodwill is assessed at least annually for impairment.

+ References

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+ Details

- Definition

The increase (decrease) in the recorded value of goodwill for foreign currency translation adjustments and purchase accounting adjustments needed to revise the carrying amount of goodwill to fair value.

+ References

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+ Details