INFORMATION ABOUT RECEIVABLES, REVENUES, AND SERVICES. (Services Concentration and Receivables) (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Concentration Risk [Line Items]
Net revenues			$ 1,595.8	$ 1,426.7	$ 4,473.8	$ 4,149.2
Accounts receivable	$ 714.8	$ 646.6	714.8		714.8
T. Rowe Price investment products
Concentration Risk [Line Items]
Net revenues			1,302.3	$ 1,180.9	3,652.8	$ 3,421.9
Accounts receivable	$ 442.0	$ 424.8	$ 442.0		$ 442.0
Outside U.S. | Assets under management | Investment advisory clients | Geographic concentration
Concentration Risk [Line Items]
Concentration risk, percentage	8.70%	6.90%