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Income Taxes - Gross Unrecognized (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits |  |
Balance at the beginning of the year | $ 102.1 | $ 87.9
Gross increase in current period's tax positions | 4.0 | 10.8
Gross increase in prior years' tax positions | 2.2 | 5.3
Gross decrease in prior years' tax positions | (14.4) |
Decrease due to settlement with tax authorities | (31.9) | (1.0)
Decrease due to lapse of statute of limitations | (1.7) | (1.1)
Gross change due to foreign exchange fluctuations | (0.3) | 0.2
Balance at the end of the year | 60.0 | 102.1
Income Taxes, additional disclosures |  |
Accrued interest, excluding any related income tax benefits | 15.5 | 15.1
Accrued penalties, excluding any related income tax benefits | $ 4.1 | $ 4.1

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- Definition Amount of increase (decrease) in unrecognized tax benefits resulting from foreign currency translation. + References No definition available. + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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