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BASIS OF PREPARATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES. (Property and equipment) (Details)	12 Months Ended
	Dec. 31, 2018
Computer and communications software and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	32 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	8 years
Furniture and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	6 years
Leased land [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	99 years

X

- Definition

Line items represent financial 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.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	duration

X

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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X

- Details

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Namespace Prefix:
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Balance Type:
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X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LeaseholdImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=trow_LeasedLandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: