CONSOLIDATED T. ROWE PRICE INVESTMENT PRODUCTS. (Fair Value Measurements) (Details) - Fair value, measurements, recurring - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 1,870.9	$ 1,355.6
Other investments	2.0	0.0
Total	3,593.5	3,309.7
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Other investments	0.6	0.0
Total	10.9	9.9
Consolidated T. Rowe Price investment products | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	5.1	9.1
Equity securities	277.0	162.8
Fixed income securities	0.0	0.0
Other investments	2.7	2.7
Total	284.8	174.6
Liabilities	(0.2)	(0.4)
Consolidated T. Rowe Price investment products | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	1.1
Equity securities	761.6	724.5
Fixed income securities	1,262.4	1,248.6
Other investments	25.4	33.8
Total	2,049.4	2,008.0
Liabilities	$ (12.8)	$ (11.2)