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CONSOLIDATED T. ROWE PRICE INVESTMENT PRODUCTS. (Net Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,802.4		$ 1,425.2
Investments	2,575.2		2,453.4
Other assets	253.7		253.7
Total assets	8,912.3		7,689.3
Liabilities	1,320.9		824.7
Attributable to redeemable non-controlling interests	1,012.3	$ 886.7	740.3	$ 739.2	$ 546.5	$ 992.8
Consolidated T. Rowe Price investment products [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	2,100.9		1,641.7
Attributable to T. Rowe Price Group	1,088.6		901.4
Attributable to redeemable non-controlling interests	1,012.3		740.3
Consolidated T. Rowe Price investment products [Member] \| Reportable entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	110.7		70.1
Investments	2,023.0		1,584.0
Other assets	69.7		26.3
Total assets	2,203.4		1,680.4
Liabilities	102.5		38.7
Net assets	2,100.9		1,641.7
Consolidated T. Rowe Price investment products [Member] \| Reportable entities [Member] \| T. Rowe Price investment products [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Investments	41.1		43.8
Voting interest entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	301.6		271.8
Attributable to T. Rowe Price Group	203.8		175.3
Attributable to redeemable non-controlling interests	97.8		96.5
Voting interest entities [Member] \| Reportable entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	15.2		18.5
Investments	301.9		261.3
Other assets	11.2		8.0
Total assets	328.3		287.8
Liabilities	26.7		16.0
Net assets	301.6		271.8
Variable interest entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Net assets	1,799.3		1,369.9
Attributable to T. Rowe Price Group	884.8		726.1
Attributable to redeemable non-controlling interests	914.5		643.8
Variable interest entities [Member] \| Reportable entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	95.5		51.6
Investments	1,721.1		1,322.7
Other assets	58.5		18.3
Total assets	1,875.1		1,392.6
Liabilities	75.8		22.7
Net assets	1,799.3		1,369.9
Money Market Funds [Member] \| Consolidated T. Rowe Price investment products [Member] \| Reportable entities [Member] \| T. Rowe Price investment products [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 14.2		$ 18.5