Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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INVESTMENTS. (Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investment [Line Items]
U.S. Treasury note	$ 1.0		$ 1.0		$ 1.0
Total	2,575.2		2,575.2		2,453.4
Net unrealized gains (losses) on T. Rowe Price investments product recognized in nonoperating income	28.7	$ 8.0	79.3	$ 6.1
Gains (losses) recognized upon deconsolidation	124.5	34.1	327.3	50.2
Reclassification out of accumulated other comprehensive income [Member] \| Currency translation adjustments [Member]
Investment [Line Items]
Gains (losses) recognized upon deconsolidation	0.1	0.5	0.2	3.6
Assets [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	(68.4)	97.1	(56.1)	(660.4)
Liability [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	(0.3)	23.7	(1.2)	18.5
Redeemable noncontrolling interest [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	(29.5)	$ 57.7	(9.1)	$ (575.2)
T. Rowe Price investment products [Member]
Investment [Line Items]
Investments held at fair value	1,546.2		1,546.2		1,538.4
Equity method investments	317.3		317.3		276.2
T. Rowe Price investment products designated as economic hedge of supplemental savings plan liability [Member]
Investment [Line Items]
Investments held at fair value	441.3		441.3		381.3
Investment partnerships and other investments [Member]
Investment [Line Items]
Investments held at fair value	100.4		100.4		99.6
Interest in UTI Asset Management Company Limited (India) [Member]
Investment [Line Items]
Equity method investments	$ 164.1		$ 164.1		$ 152.4
Equity method investment (ownership percentage)	26.00%		26.00%		26.00%
Investment partnerships and other investments [Member]
Investment [Line Items]
Equity method investments	$ 4.9		$ 4.9		$ 4.5