Summary of Significant Accounting Policies Effects of Early Adoption of New Accounting Pronouncement (Details) - USD ($) $ in Millions	Sep. 30, 2018	Oct. 01, 2017
New Accounting Pronouncement, Early Adoption [Line Items]
Long-term deferred income tax assets	$ 134.7	$ 795.4
Long-term deferred income tax liabilities (included in Other long-term liabilities)	$ 270.2	6.3
Net deferred tax asset		$ 789.1

Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

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Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, with jurisdictional netting and classified as noncurrent.

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences, with jurisdictional netting and classified as noncurrent.

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