Revenues - Schedule of Changes in the Deferred Revenue Balances (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Change In Contract with Customer Liability [Abstract]
Total Changes in deferred revenue	$ 103.9	$ 167.7
Deferred revenue - current	1,062.3	998.7	$ 953.4
Deferred revenue - noncurrent	120.9	127.8	$ 122.3
Foreign Exchange [Member]
Change In Contract with Customer Liability [Abstract]
Beginning Balance	1,075.7	946.3
Revenue recognized that was included in the contract liability balance at the beginning of the period	(399.5)	(345.4)
Increases due to billings excluding amounts recognized as revenue during the period	501.9	512.8
Effect of exchange rate changes	5.1	12.8
Total Changes in deferred revenue	107.5	180.2
Ending Balance	1,183.2	1,126.5
MIS [Member]
Change In Contract with Customer Liability [Abstract]
Deferred revenue - current	271.6	273.4
Deferred revenue - noncurrent	116.7	124.1
MIS [Member] | Foreign Exchange [Member]
Change In Contract with Customer Liability [Abstract]
Beginning Balance	325.4	334.7
Revenue recognized that was included in the contract liability balance at the beginning of the period	(92.8)	(93.4)
Increases due to billings excluding amounts recognized as revenue during the period	155.2	154.9
Effect of exchange rate changes	0.5	1.3
Total Changes in deferred revenue	62.9	62.8
Ending Balance	388.3	397.5
MA [Member]
Change In Contract with Customer Liability [Abstract]
Deferred revenue - current	790.7	725.3
Deferred revenue - noncurrent	4.2	3.7
MA [Member] | Foreign Exchange [Member]
Change In Contract with Customer Liability [Abstract]
Beginning Balance	750.3	611.6
Revenue recognized that was included in the contract liability balance at the beginning of the period	(306.7)	(252.0)
Increases due to billings excluding amounts recognized as revenue during the period	346.7	357.9
Effect of exchange rate changes	4.6	11.5
Total Changes in deferred revenue	44.6	117.4
Ending Balance	$ 794.9	$ 729.0