Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) reportingUnit	Dec. 31, 2018 USD ($)
Capitalized Contract Cost [Line Items]
Number of reporting units | reportingUnit	7
MIS
Capitalized Contract Cost [Line Items]
Number of reporting units | reportingUnit	2
MA
Capitalized Contract Cost [Line Items]
Number of reporting units | reportingUnit	5
Deferred cost balance	$ 159	$ 110
MA | Selling, General and Administrative Expenses
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization	53	38
Capitalization of Work-In-Process for In-Progress Ratings | MIS
Capitalized Contract Cost [Line Items]
Deferred cost balance	11	11
Capitalization of Work-In-Process for In-Progress Ratings | MIS | Operating Expense
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization	42	40
Royalty Cost | MA
Capitalized Contract Cost [Line Items]
Deferred cost balance	40	35
Royalty Cost | MA | Selling, General and Administrative Expenses
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization	$ 56	$ 54
Subscription and Maintenance Contracts | MA | Minimum
Capitalized Contract Cost [Line Items]
Revenue, contractual coverage period (years)	3 years
General customer contract payment condition (days)	30 days
Subscription and Maintenance Contracts | MA | Maximum
Capitalized Contract Cost [Line Items]
Revenue, contractual coverage period (years)	5 years
General customer contract payment condition (days)	60 days