Adjustment to Retained Earnings (Detail) - Retained Earnings [Member] - New Revenue Accounting Standard [Member] $ in Millions	Jun. 30, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	$ 156.0
Capitalization of Work-In-Process for In-Progress Ratings [Member] | Other Current Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	9.0
Other Adjustments [Member] | Various Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	4.0
Increase in Tax Liability [Member] | Deferred Tax Liabilities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	(43.0)
MA [Member] | Recognition of Deferred Revenue / Increase in Unbilled Receivables [Member] | Deferred Revenue Accounts Receivable and Other Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	108.0
MA [Member] | Increase to Capitalized Sales Commissions [Member] | Other current assets, Other assets, Accounts Payable and Accrued Liabilities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Item]
Effect of adoption adjustment Reduction to retained earnings	$ 78.0