Significant Accounting Policies Significant Accounting Policies Additional Information (Details) $ in Billions	Sep. 30, 2017 USD ($)
Minimum [Member]
Significant Accounting Policies [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	$ 1.0

Amount of lessee's right to use underlying asset under finance lease.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

Name:	us-gaap_FinanceLeaseRightOfUseAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant