Regulatory Matters (Details) - Union Gas Limited - Current assets—other - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
2014 Demand Side Management Deferrals
Regulatory Matters [Line Items]
Regulatory Assets	$ 9	$ 8
2015-2020 DSM Plan: 2016 Draft Rate Order
Regulatory Matters [Line Items]
Regulatory Assets	19
2015 Annual Deferrals
Regulatory Matters [Line Items]
Regulatory Assets	$ 18	$ 18

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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