FAIR VALUE MEASUREMENTS - Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Discretionary investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	$ 572.4	$ 258.8
Seed capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	345.7	262.8
Level 1 | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in money market funds	3,223.3	2,309.8
Other investments	1.0	0.1
Investments in affiliated collateralized loan obligations	0.0	0.0
Total	5,145.1	3,770.9
Level 1 | Fair value, measurements, recurring | Discretionary investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	572.4	258.8
Level 1 | Fair value, measurements, recurring | Seed capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	288.2	209.4
Level 1 | Fair value, measurements, recurring | Deferred compensation liabilities economic hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	1,060.2	992.8
Level 2 | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in money market funds	0.0	0.0
Other investments	0.0	0.0
Investments in affiliated collateralized loan obligations	3.8	6.3
Total	61.3	59.7
Level 2 | Fair value, measurements, recurring | Discretionary investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	0.0	0.0
Level 2 | Fair value, measurements, recurring | Seed capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	57.5	53.4
Level 2 | Fair value, measurements, recurring | Deferred compensation liabilities economic hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	0.0	0.0
Level 3 | Fair value, measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in money market funds	0.0	0.0
Other investments	71.5	0.0
Investments in affiliated collateralized loan obligations	0.0	0.0
Total	$ 71.5	0.0
Measurement input	8.99%
Level 3 | Fair value, measurements, recurring | Discretionary investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	$ 0.0	0.0
Level 3 | Fair value, measurements, recurring | Seed capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	0.0	0.0
Level 3 | Fair value, measurements, recurring | Deferred compensation liabilities economic hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
T. Rowe Price investment products	$ 0.0	$ 0.0