Stockholders' Equity - Changes in Stockholders' Equity and Redeemable Noncontrolling Interests (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Oct. 01, 2014
Stockholders' Equity Rollforward
Beginning balance	$ 11,584.1
Beginning balance	628.3
Beginning balance	12,212.4
Net Income Attributable to Franklin Resources, Inc.	566.4		603.8
Nonredeemable noncontrolling interests	6.7		(17.2)
Net Income	566.3		596.0
Other comprehensive income (loss)	(60.7)		(3.2)
Ending balance	11,555.8
Ending balance	598.7
Ending balance	12,154.5
Franklin Resources, Inc. Stockholders' Equity [Member]
Stockholders' Equity Rollforward
Beginning balance	11,584.1		10,073.1
Net Income Attributable to Franklin Resources, Inc.	566.4		603.8
Net income (loss) reclassified to appropriated retained earnings			4.8
Other comprehensive income (loss)	(60.7)		(3.2)
Cash dividends on common stock	(405.6)		(75.9)
Repurchase of common stock	(151.2)		(137.1)
Other	37.0	[1]	41.6	[1]
Ending balance	11,555.8		10,507.1
Nonredeemable Noncontrolling Interests [Member]
Stockholders' Equity Rollforward
Beginning balance	628.3		612.4
Net income (loss) reclassified to appropriated retained earnings			(4.8)
New subscriptions (redemptions)	(36.3)		(13.1)
Ending balance	598.7		577.3
Total Stockholders' Equity [Member]
Stockholders' Equity Rollforward
Beginning balance	12,212.4		10,685.5
Net Income	573.1		586.6
Net income (loss) reclassified to appropriated retained earnings			0
Other comprehensive income (loss)	(60.7)		(3.2)
Cash dividends on common stock	(405.6)		(75.9)
Repurchase of common stock	(151.2)		(137.1)
New subscriptions (redemptions)	(36.3)		(13.1)
Other	37.0	[1]	41.6	[1]
Ending balance	12,154.5		11,084.4
New Accounting Pronouncement, Early Adoption, Effect [Member]
Stockholders' Equity Rollforward
Adjustment for adoption of new accounting guidance					$ (14.2)

[1] Primarily relates to stock-based compensation plans.