Accounting Pronouncements (Details) - USD ($) $ in Millions	1 Months Ended
Dec. 31, 2015	Dec. 31, 2017
Accounting Pronouncements
Proceeds from senior notes restricted in escrow account	$ 2,000.0
New Accounting Pronouncements, Retrospective adjustments
Prior period adjustments due to new accounting principle		$ 0.0
Cumulative effect adjustment to opening retained earnings, after tax		$ 0.0

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

Name:	us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration