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Assets and Liabilities, at Fair Value - Details of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Sep. 30, 2017
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Assets and Liabilities, at Fair Value [Abstract] |  |
Total Level 3 Assets | $ 0.1 | $ 0.1
Level 3 assets for which the company bears economic exposure | 0.1 | 0.1
Assets | 6,808.9 | 6,243.4
Assets, Fair Value Disclosure | $ 2,273.5 | $ 2,068.0
Total level 3 assets as a percentage of total assets | 0.00% | 0.00%
Level 3 assets for which the company bears economic exposure as a percertange of total assets | 0.00% | 0.00%
Total level 3 assets as a percentage of total financial assets at fair value | 0.00% | 0.00%

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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(12)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(11)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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