Revenues - Capitalized Costs to Fulfill Contract with Customer (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Balance - December 31, 2018	$ 400
Amortization expense	20
Costs capitalized	43
Balance - March 31, 2019	$ 423

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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