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Debt - Narrative (Details) - USD ($)	Sep. 30, 2025	Sep. 05, 2025	Apr. 30, 2025	Mar. 31, 2025
Franklin Resources, Inc. [Member]
Debt Instrument [Line Items]
Unsecure debt	$ 1,200,000,000
Legg Mason [Member]
Debt Instrument [Line Items]
Unsecure debt	1,000,000,000
Notes Due August 2051 [Member] \| Franklin Resources, Inc. [Member]
Debt Instrument [Line Items]
Debt Face Amount	$ 350,000,000
Stated Interest Rate	2.95%
Notes Due October 2030 [Member] \| Franklin Resources, Inc. [Member]
Debt Instrument [Line Items]
Debt Face Amount	$ 850,000,000
Stated Interest Rate	1.60%
Commercial Paper [Member]
Debt Instrument [Line Items]
Line of credit Facility, maximum Borrowing capacity	$ 500,000,000
Notes Due July 2024 [Member] \| Legg Mason [Member]
Debt Instrument [Line Items]
Debt Face Amount				$ 400,000,000
Stated Interest Rate				2.85%
Interest Payable				$ 5,700,000
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit Facility, maximum Borrowing capacity			$ 1,100,000,000
Interest Payable		$ 5,500,000
Long-Term Line of Credit			$ 300,000,000