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
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Investment [Line Items]
U.S. Treasury note	$ 1.0		$ 1.0
Total	2,546.7		2,453.4
Net unrealized gains (losses) on T. Rowe Price investments product recognized in nonoperating income	50.6	$ (1.9)
Gains recognized upon deconsolidation	202.8	16.1
Reclassification out of accumulated other comprehensive income [Member] \| Currency translation adjustments [Member]
Investment [Line Items]
Gains recognized upon deconsolidation	0.1	3.1
Assets [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	(12.3)	757.5
Liability [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	(0.9)	(5.2)
Redeemable noncontrolling interest [Member]
Investment [Line Items]
Net increase (decrease) in assets, liabilities, and redeemable noncontrolling interest	20.4	$ (632.9)
T. Rowe Price investment products [Member]
Investment [Line Items]
Investments held at fair value	1,542.4		1,538.4
Equity method investments	308.7		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	429.2		381.3
Investment partnerships and other investments [Member]
Investment [Line Items]
Investments held at fair value	99.1		99.6
Interest in UTI Asset Management Company Limited (India) [Member]
Investment [Line Items]
Equity method investments	$ 161.3		$ 152.4
Equity method investment (ownership percentage)	26.00%		26.00%
Investment partnerships and other investments [Member]
Investment [Line Items]
Equity method investments	$ 5.0		$ 4.5