Revenue Recognition Contract Cost Assets (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)
Contract cost assets
Total contract cost assets	$ 159
Practical expedient
Contract cost, practical expedient	true
Sales commissions
Contract cost assets
Total contract cost assets	$ 149
Installation costs
Contract cost assets
Total contract cost assets	$ 10

Indicates (true/false) whether practical expedient is elected to recognize incremental cost of obtaining contract as expense when incurred if amortization period would have been one year or less.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL51790836-203054

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130569-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68074990&loc=SL49131230-203052

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration