Long-Term Financing Receivables (Reserve and Additional Information) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Receivables [Abstract]
Long Term Receivables High Credit Risk	$ 140	$ 170
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 18	$ 17

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant