Consolidated Sponsored Investment Products - Schedule of Changes in Level 3 Assets and Liabilities of CSIPs (Details) - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Oct. 01, 2016
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Balance at beginning of period - assets	$ 292.6	$ 321.8
Realized and unrealized gains (losses) included in investment and other income, net - assets	(3.6)	0.0
Purchases - assets	23.2	2.5
Sales - assets	(6.5)	(9.6)
Foreign exchange revaluation	(3.8)	(2.7)
Balance at End of Period - assets	256.0	312.0
Change in unrealized gains (losses) included in net income relating to assets and liabilities held at period end	(3.6)	(0.8)
Equity Securities [Member]
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Balance at beginning of period - assets	160.3	191.6
Realized and unrealized gains (losses) included in investment and other income, net - assets	(3.3)	(1.1)
Purchases - assets	21.0	0.0
Sales - assets	(0.1)	0.0
Foreign exchange revaluation	(0.9)	(2.4)
Balance at End of Period - assets	131.6	188.1
Change in unrealized gains (losses) included in net income relating to assets and liabilities held at period end	(3.4)	(1.1)
Debt Securities [Member]
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Balance at beginning of period - assets	132.3	130.2
Realized and unrealized gains (losses) included in investment and other income, net - assets	(0.3)	1.1
Purchases - assets	2.2	2.5
Sales - assets	(6.4)	(9.6)
Foreign exchange revaluation	(2.9)	(0.3)
Balance at End of Period - assets	124.4	123.9
Change in unrealized gains (losses) included in net income relating to assets and liabilities held at period end	$ (0.2)	$ 0.3
ASU 2015-02 [Member]
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Adoption of new accounting guidance			$ (45.9)
ASU 2015-02 [Member] \| Equity Securities [Member]
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Adoption of new accounting guidance			(45.4)
ASU 2015-02 [Member] \| Debt Securities [Member]
Schedule Of Consolidated Sponsored Investment Products [Line Items]
Adoption of new accounting guidance			$ (0.5)

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[Line Items] for Tabular disclosure of qualitative and quantitative information related to sponsored investment products holds, whether or not such sponsored investment products (SIP) is included in the reporting entity's consolidated financial statements. Includes, but is not limited to, description of the significant judgments and assumptions made in determining whether a SIP (as defined) held by the entity requires the SIP (as defined) to be consolidated and (or) disclose information about its involvement with the SIP, individually or in aggregate (as applicable); the nature of restrictions, if any, on the consolidated SIP's assets and on the settlement of its liabilities reported by an entity in its statement of financial position, including the carrying amounts of such assets and liabilities; the nature of, and changes in, the risks associated with involvement in the SIP; how involvement with the SIP affects the entity's financial position, financial performance, and cash flows; the lack of recourse if creditors (or beneficial interest holders) of the consolidated SIP have no recourse to the general credit of the primary beneficiary (if applicable); the terms of arrangements, giving consideration to both explicit arrangements and implicit variable interests, if any, that could require the entity to provide financial support to the SIP, including events or circumstances that could expose the entity to a loss; the methodology used by the entity for determining whether or not it is the primary beneficiary of the sponsored investment products; the significant factors considered and judgments made in determining that the power to direct the activities of a SIP that most significantly impact the SIP's economic performance are shared (as defined); the carrying amounts and classification of assets and liabilities of the SIP included in the statement of financial position.

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This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets); the fair value of which assets and liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3).

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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