Revenues Revenues Recognized from Performance Obligations Satisfied in Prior Periods (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Contract with Customer, Performance Obligation Satisfied in Previous Period [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 155	$ 97
Change in estimate variable consideration [Member]
Contract with Customer, Performance Obligation Satisfied in Previous Period [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 107	$ 87

Amount of revenue recognized from performance obligation satisfied or partially satisfied in previous reporting periods. Includes, but is not limited to, change in transaction price.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12A
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL108322424-203045

Name:	us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration