Revenues - Additional Information (Detail) $ in Millions	Sep. 30, 2018 USD ($)
MIS [Member]
Disaggregation of Revenue [Line Items]
Unbilled Receivables	$ 349.4
MA [Member]
Disaggregation of Revenue [Line Items]
Unbilled Receivables	$ 57.0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration