Contingencies (Detail) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Provision for income taxes	$ (32,100,000)		$ (24,200,000)	$ (77,300,000)	$ (64,200,000)
Ramirez v. Trans Union LLC [Member] | Judicial Ruling [Member] | Punitive Damages [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Awarded, Value		$ 32,000,000.0				$ 52,000,000.0
Loss Contingency, Loss in Period		30,500,000
Provision for income taxes		7,600,000
Per person [Member] | Ramirez v. Trans Union LLC [Member] | Judicial Ruling [Member] | Punitive Damages [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Awarded, Value		$ 3,936.88				$ 6,353.08