CONSOLIDATED T. ROWE PRICE INVESTMENT PRODUCTS. (Net Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 2,228.2		$ 1,781.8
Investments	3,030.8		2,939.8
Other assets	231.7		234.4
Total assets	10,134.6		9,330.4
Liabilities	1,665.9		1,107.3
Attributable to redeemable non-controlling interests	1,340.2	$ 1,090.1	1,121.0	$ 1,102.9	$ 1,012.3	$ 740.3
Consolidated T. Rowe Price investment products
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	2,395.8		2,237.7
Attributable to T. Rowe Price Group	1,055.6		1,116.7
Attributable to redeemable non-controlling interests	1,340.2		1,121.0
Consolidated T. Rowe Price investment products | Reportable entities
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	78.0		76.5
Investments	2,329.1		2,172.4
Other assets	35.2		28.0
Total assets	2,442.3		2,276.9
Liabilities	46.5		39.2
Net assets	2,395.8		2,237.7
Consolidated T. Rowe Price investment products | Reportable entities | T. Rowe Price investment products
Condensed Balance Sheet Statements, Captions [Line Items]
Investments	18.9		40.2
Consolidated T. Rowe Price investment products | Money Market Funds | Reportable entities | T. Rowe Price investment products
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	5.1		9.1
Voting interest entities
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	177.3		289.4
Attributable to T. Rowe Price Group	126.2		199.6
Attributable to redeemable non-controlling interests	51.1		89.8
Voting interest entities | Reportable entities
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	5.2		9.9
Investments	178.8		281.1
Other assets	3.0		10.6
Total assets	187.0		301.6
Liabilities	9.7		12.2
Net assets	177.3		289.4
Variable interest entities
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	2,218.5		1,948.3
Attributable to T. Rowe Price Group	929.4		917.1
Attributable to redeemable non-controlling interests	1,289.1		1,031.2
Variable interest entities | Reportable entities
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	72.8		66.6
Investments	2,150.3		1,891.3
Other assets	32.2		17.4
Total assets	2,255.3		1,975.3
Liabilities	36.8		27.0
Net assets	$ 2,218.5		$ 1,948.3