CONSOLIDATED T. ROWE PRICE INVESTMENT PRODUCTS. (Fair Value Measurements) (Details) - Fair value, measurements, recurring [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in T. Rowe Price money market funds	$ 1,747.9	$ 1,726.4
Investments held at fair value	1,618.9	942.9
Total	3,366.8	2,669.3
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in T. Rowe Price money market funds	0.0	0.0
Investments held at fair value	19.9	17.4
Total	19.9	17.4
Consolidated T. Rowe Price investment products [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in T. Rowe Price money market funds	17.6	6.2
Total	243.5	543.5
Liabilities	(0.3)	(0.1)
Consolidated T. Rowe Price investment products [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents held in T. Rowe Price money market funds	0.1	0.7
Total	1,555.7	1,377.9
Liabilities	(7.9)	(13.7)
Consolidated T. Rowe Price investment products [Member] \| Equity securities [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	224.3	536.0
Consolidated T. Rowe Price investment products [Member] \| Equity securities [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	601.9	667.5
Consolidated T. Rowe Price investment products [Member] \| Fixed income securities [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	0.0	0.0
Consolidated T. Rowe Price investment products [Member] \| Fixed income securities [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	933.2	687.4
Consolidated T. Rowe Price investment products [Member] \| Other investments [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	1.6	1.3
Consolidated T. Rowe Price investment products [Member] \| Other investments [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments held at fair value	$ 20.5	$ 22.3

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Paragraph 1A
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Fair value of financial and nonfinancial obligations.

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