Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net Income	$ 607.9	$ 1,025.7	$ 1,333.2
Other Comprehensive Income (Loss)
Currency translation adjustments, net of tax	89.8	112.8	(244.6)
Net unrealized gains (losses) on defined benefit plans, net of tax	0.1	(1.3)	0.8
Net unrealized gains (losses) on investments, net of tax	(0.1)	0.2	0.4
Total other comprehensive income (loss)	89.8	111.7	(243.4)
Total comprehensive income	697.7	1,137.4	1,089.8
Less: comprehensive income (loss) attributable to
Redeemable noncontrolling interests	127.9	135.5	(46.9)
Nonredeemable noncontrolling interests	15.2	7.4	88.2
Comprehensive Income Attributable to Franklin Resources, Inc.	$ 554.6	$ 994.5	$ 1,048.5