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INFORMATION ABOUT RECEIVABLES, REVENUES, AND SERVICES. (Services Concentration and Receivables) (Details) - USD ($) $ in Millions			3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Concentration Risk [Line Items]
Net revenues			$ 1,462.6	$ 1,327.3
Accounts receivable	$ 585.3	$ 646.6	585.3
T. Rowe Price investment products
Concentration Risk [Line Items]
Net revenues			1,207.7	$ 1,093.4
Accounts receivable	$ 374.3	$ 424.8	$ 374.3
Outside U.S. \| Assets under management \| Investment advisory clients \| Geographic concentration
Concentration Risk [Line Items]
Concentration risk, percentage	7.40%	6.90%