INFORMATION ABOUT RECEIVABLES, REVENUES, AND SERVICES. (Services Concentration and Receivables) (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Concentration Risk [Line Items]
Net revenues			$ 1,415.4	$ 1,395.2	$ 2,878.0	$ 2,722.5
Accounts receivable	$ 655.7	$ 646.6	655.7		655.7
T. Rowe Price investment products
Concentration Risk [Line Items]
Net revenues			1,142.8	$ 1,147.6	2,350.5	$ 2,241.0
Accounts receivable	$ 410.6	$ 424.8	$ 410.6		$ 410.6
Outside U.S. | Assets under management | Investment advisory clients | Geographic concentration
Concentration Risk [Line Items]
Concentration risk, percentage	8.20%	6.90%