OTHER COMPREHENSIVE INCOME AND ACCUMULATED OTHER COMPREHENSIVE LOSS. (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at beginning of period	$ 6,750.7	$ 6,579.1	$ 7,102.1	$ 6,124.3
Other comprehensive income (loss)	9.5	(10.2)	0.3	(6.7)
Balances at end of period	7,128.5	6,839.8	7,128.5	6,839.8
Other comprehensive loss, net of tax, attributable to redeemable non-controlling interests	20.8	(17.4)	13.9	(17.7)
Currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at beginning of period	(52.2)	(38.5)	(43.0)	(42.0)
Other comprehensive income (loss) before reclassifications and income taxes	10.5	(13.6)	0.9	(9.0)
Reclassification adjustments recognized in non-operating income	0.0	0.1	(0.1)	(0.1)
Other comprehensive income (loss), before taxes	10.5	(13.5)	0.8	(9.1)
Net deferred tax benefits (income taxes)	(1.0)	3.4	(0.5)	2.5
Other comprehensive income (loss)	9.5	(10.1)	0.3	(6.6)
Balances at end of period	(42.7)	(48.6)	(42.7)	(48.6)
Currency translation adjustments \| Equity method investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at beginning of period	(54.4)	(43.8)	(46.9)	(48.8)
Other comprehensive income (loss) before reclassifications and income taxes	(2.0)	(1.0)	(9.4)	5.4
Reclassification adjustments recognized in non-operating income	0.0	0.0	0.0	0.0
Other comprehensive income (loss), before taxes	(2.0)	(1.0)	(9.4)	5.4
Net deferred tax benefits (income taxes)	2.1	0.3	2.0	(1.1)
Other comprehensive income (loss)	0.1	(0.7)	(7.4)	4.3
Balances at end of period	(54.3)	(44.5)	(54.3)	(44.5)
Consolidated T. Rowe Price investment products - variable interest entities \| Currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at beginning of period	2.2	5.3	3.9	6.8
Other comprehensive income (loss) before reclassifications and income taxes	12.5	(12.6)	10.3	(14.4)
Reclassification adjustments recognized in non-operating income	0.0	0.1	(0.1)	(0.1)
Other comprehensive income (loss), before taxes	12.5	(12.5)	10.2	(14.5)
Net deferred tax benefits (income taxes)	(3.1)	3.1	(2.5)	3.6
Other comprehensive income (loss)	9.4	(9.4)	7.7	(10.9)
Balances at end of period	$ 11.6	$ (4.1)	$ 11.6	$ (4.1)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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