Income Taxes Paid (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014
Income Taxes [Line Items]
Taxes Paid Deferred	$ 50.0

Estimated federal tax payments made in the first quarter of 2013. These estimated payments were paid later than in prior years due to IRS relief provisions regarding Hurricane Sandy.

No definition available.

Name:	mco_TaxesPaidDeferred
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration