Deferred Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of deferred contract costs
Installations and conversions in progress	$ 66	$ 57
Installations and conversions completed, net	120	108
Sales commissions and other, net	176	145
Deferred contract costs, net	362	310
Amortization of deferred contract costs	$ 118	$ 87	$ 71

Deferred incremental direct costs incurred typically at a contract's inception so that the company may be in a position to fulfill all contractual obligations of an arrangement. The costs are directly related to specified activities under the arrangement and are deferred in order to match revenue that will be recognized after one year from the balance sheet date (or one operating cycle if longer). Excludes start-up costs (such as one-time activities related to opening a new facility, introducing a new product or service, establishing business with a new class of customers, preopening costs, and organization costs), which are expensed as incurred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.3(f).Q3)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 13.A.3(f).Q4)
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

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