Operating Revenues - Remaining Performance Obligations Periods (Details)	9 Months Ended
Sep. 30, 2018
Minimum
Disaggregation of Revenue [Line Items]
Expected service period revenue is recognized	1 year
Maximum
Disaggregation of Revenue [Line Items]
Expected service period revenue is recognized	3 years

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration