INFORMATION ABOUT RECEIVABLES, REVENUES, AND SERVICES. (Investment Advisory Services) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue and Services [Line Items]
Net revenues	$ 1,462.6	$ 1,327.3
Average assets under management	1,162,700.0	1,043,500.0
Period end assets under management	1,008,800.0		$ 1,206,800.0
T. Rowe Price investment products
Revenue and Services [Line Items]
Net revenues	1,207.7	1,093.4
U.S. mutual funds
Revenue and Services [Line Items]
Net revenues	981.3	922.7
Average assets under management	654,300.0	610,100.0
Period end assets under management	562,300.0		682,700.0
U.S. mutual funds | Equity and blended assets
Revenue and Services [Line Items]
Average assets under management	525,000.0	487,600.0
Period end assets under management	443,600.0		552,400.0
U.S. mutual funds | Fixed income, including money market
Revenue and Services [Line Items]
Average assets under management	129,300.0	122,500.0
Period end assets under management	118,700.0		130,300.0
Subadvised and separate accounts and other investment products
Revenue and Services [Line Items]
Net revenues	451.6	378.3
Average assets under management	508,400.0	433,400.0
Period end assets under management	446,500.0		524,100.0
Subadvised and separate accounts and other investment products | Equity and blended assets
Revenue and Services [Line Items]
Average assets under management	396,300.0	332,900.0
Period end assets under management	340,900.0		412,100.0
Subadvised and separate accounts and other investment products | Fixed income, including money market
Revenue and Services [Line Items]
Average assets under management	112,100.0	100,500.0
Period end assets under management	105,600.0		$ 112,000.0
Other clients
Revenue and Services [Line Items]
Net revenues	29.7	26.3
Investment advisory fees
Revenue and Services [Line Items]
Net revenues	1,327.8	1,194.2
Investment advisory fees | U.S. mutual funds
Revenue and Services [Line Items]
Net revenues	876.2	815.9
Investment advisory fees | U.S. mutual funds | Equity and blended assets
Revenue and Services [Line Items]
Net revenues	749.8	694.5
Investment advisory fees | U.S. mutual funds | Fixed income, including money market
Revenue and Services [Line Items]
Net revenues	126.4	121.4
Investment advisory fees | Subadvised and separate accounts and other investment products
Revenue and Services [Line Items]
Net revenues	451.6	378.3
Investment advisory fees | Subadvised and separate accounts and other investment products | Equity and blended assets
Revenue and Services [Line Items]
Net revenues	385.2	318.8
Investment advisory fees | Subadvised and separate accounts and other investment products | Fixed income, including money market
Revenue and Services [Line Items]
Net revenues	66.4	59.5
Investment advisory fees | Other clients
Revenue and Services [Line Items]
Net revenues	0.0	0.0
Administrative fees
Revenue and Services [Line Items]
Net revenues	106.9	102.9
Administrative fees | U.S. mutual funds
Revenue and Services [Line Items]
Net revenues	77.2	76.6
Administrative fees | Subadvised and separate accounts and other investment products
Revenue and Services [Line Items]
Net revenues	0.0	0.0
Administrative fees | Other clients
Revenue and Services [Line Items]
Net revenues	29.7	26.3
Distribution and servicing fees
Revenue and Services [Line Items]
Net revenues	27.9	30.2
Distribution and servicing fees | U.S. mutual funds
Revenue and Services [Line Items]
Net revenues	27.9	30.2
Distribution and servicing fees | Subadvised and separate accounts and other investment products
Revenue and Services [Line Items]
Net revenues	0.0	0.0
Distribution and servicing fees | Other clients
Revenue and Services [Line Items]
Net revenues	$ 0.0	$ 0.0