Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3044-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Consolidated Investment Products - Schedule of Financial Instruments of CIPs not Measured at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financial Assets [Abstract]
Cash and cash equivalents	$ 8,970.4	$ 8,749.7	$ 8,454.8	$ 8,483.3
Financial Liabilities [Abstract]
Debt	1,044.5	1,044.2
CIPs [Member]
Financial Assets [Abstract]
Cash and cash equivalents	262.9	226.4
Financial Liabilities [Abstract]
Debt	51.0	53.4
Carrying Value [Member]
Financial Assets [Abstract]
Cash and cash equivalents	8,707.5	8,523.3
Carrying Value [Member] \| CIPs [Member]
Financial Assets [Abstract]
Cash and cash equivalents	262.9	226.4
Financial Liabilities [Abstract]
Debt	51.0	53.4
Estimated Fair Value [Member] \| Level 1 [Member]
Financial Assets [Abstract]
Cash and cash equivalents	8,707.5	8,523.3
Estimated Fair Value [Member] \| CIPs [Member] \| Level 1 [Member]
Financial Assets [Abstract]
Cash and cash equivalents	262.9	226.4
Estimated Fair Value [Member] \| CIPs [Member] \| Level 3 [Member]
Financial Liabilities [Abstract]
Debt	$ 50.7	$ 53.1