Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Stockholders' Equity [Member]	Nonredeemable Noncontrolling Interests [Member]
Beginning balance - Shares at Sep. 30, 2021		501.8
Beginning balance at Sep. 30, 2021		$ 50.2	$ 0.0	$ 11,550.8	$ (377.6)	$ 11,223.4
Beginning balance at Sep. 30, 2021							$ 587.2
Beginning balance at Sep. 30, 2021	$ 11,810.6
Stockholders' Equity [Roll Forward]
Net income attributable to Franklin Resources, Inc.	453.2			453.2		453.2
Nonredeemable noncontrolling interests	84.1						84.1
Net income	537.3
Other comprehensive income (loss)	(12.0)				(12.0)	(12.0)
Dividends declared on common stock	(148.9)			(148.9)		(148.9)
Repurchase of common stock - Shares		(0.7)
Repurchase of common stock - Amount	(21.7)	$ 0.0	(58.8)	37.1		(21.7)
Issuance of common stock - Shares		1.4
Issuance of common stock - Amount	47.7	$ 0.1	47.6			47.7
Stock-based compensation	11.2		11.2			11.2
Net subscriptions (distributions) and other	(27.8)						(27.8)
Ending balance - Shares at Dec. 31, 2021		502.5
Ending balance at Dec. 31, 2021		$ 50.3	0.0	11,892.2	(389.6)	11,552.9
Ending balance at Dec. 31, 2021							643.5
Ending balance at Dec. 31, 2021	12,196.4
Beginning balance - Shares at Sep. 30, 2022		499.6
Beginning balance at Sep. 30, 2022	11,474.6	$ 50.0	0.0	12,045.6	(621.0)	11,474.6
Beginning balance at Sep. 30, 2022	824.3						824.3
Beginning balance at Sep. 30, 2022	12,298.9
Stockholders' Equity [Roll Forward]
Net income attributable to Franklin Resources, Inc.	165.6			165.6		165.6
Nonredeemable noncontrolling interests	4.7						4.7
Net income	170.3
Other comprehensive income (loss)	124.7				124.7	124.7
Dividends declared on common stock	(153.6)			(153.6)		(153.6)
Repurchase of common stock - Shares		(0.5)
Repurchase of common stock - Amount	(14.2)	$ (0.1)	(69.1)	55.0		(14.2)
Issuance of common stock - Shares		1.2
Issuance of common stock - Amount	33.6	$ 0.1	33.5			33.6
Stock-based compensation	35.6		35.6			35.6
Net subscriptions (distributions) and other	95.9						95.9
Net deconsolidation of investment products	(35.7)						(35.7)
Ending balance - Shares at Dec. 31, 2022		500.3
Ending balance at Dec. 31, 2022	11,666.3	$ 50.0	$ 0.0	$ 12,112.6	$ (496.3)	$ 11,666.3
Ending balance at Dec. 31, 2022	889.2						$ 889.2
Ending balance at Dec. 31, 2022	$ 12,555.5