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Assets and Liabilities, at Fair Value - Rollforward of Level 3 (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Rollforward of Level 3 Liabilities [Roll Forward] |  |  |
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability | $ 0.0 | $ (0.2) | $ (0.4)
Contingent Consideration [Member] |  |  |
Rollforward of Level 3 Liabilities [Roll Forward] |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | 1.0 | 0.8 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease) | 0.0 | 0.2 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements | (1.0) | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | 0.0 | 1.0 | 0.8
Equity Securities [Member] |  |  |
Rollforward of Level 3 Assets [Roll Forward] |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 0.1 | 0.2 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease) | (0.1) | (0.1) |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net | 0.0 | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 0.0 | 0.1 | 0.2
Corporate Debt Securities [Member] |  |  |
Rollforward of Level 3 Assets [Roll Forward] |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | $ 0.0 | 3.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings |  | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease) |  | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases |  | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements |  | (3.0) |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net |  | 0.0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value |  | $ 0.0 | $ 3.0

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- Definition Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e7008-128479 + Details
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- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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