Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all domestic and foreign income tax obligations due beyond one year or the operating cycle, whichever is longer. Alternate captions include income taxes payable, noncurrent.

Reference 1: 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(15)(1))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: 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)(15)(b)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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(24))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_AccruedIncomeTaxesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	(176.60%)	30.50%	106.30%	27.90%
FederalCorporateTaxRate	35.00%		35.00%			21.00%	35.00%
BlendedCorporateTaxRate	24.50%		24.50%		24.50%
ProvisionalDiscreteNetTaxExpense			$ 14.3
DTLProvisionalCorporateRateReductionNetBenefit			14.9
ProvisionalTransitionTaxObligation			28.9
ProvisionalTransitionTaxObligationCurrent			2.3
Accrued Income Taxes, Noncurrent	$ 26.6		$ 26.6