Schedule of Changes in the Deferred Revenue Balances (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Deferred revenue - current	$ 998.7	$ 883.6
Deferred revenue - noncurrent	127.8	$ 140.0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Balance at January 1, 2018	946.3
Revenue recognized that was included in the contract liability balance at the beginning of the period	(267.3)
Increases due to billings excluding amounts recognized as revenue during the period	434.7
Effect of exchange rate changes	12.8
Total Changes in deferred revenue	180.2
Balance at March 31, 2018	1,126.5
MIS [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue - current	273.4
Deferred revenue - noncurrent	124.1
MIS [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Balance at January 1, 2018	334.7
Revenue recognized that was included in the contract liability balance at the beginning of the period	(93.4)
Increases due to billings excluding amounts recognized as revenue during the period	154.9
Effect of exchange rate changes	1.3
Total Changes in deferred revenue	62.8
Balance at March 31, 2018	397.5
MA [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue - current	725.3
Deferred revenue - noncurrent	3.7
MA [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Balance at January 1, 2018	611.6
Revenue recognized that was included in the contract liability balance at the beginning of the period	(173.9)
Increases due to billings excluding amounts recognized as revenue during the period	279.8
Effect of exchange rate changes	11.5
Total Changes in deferred revenue	117.4
Balance at March 31, 2018	$ 729.0