Asset Retirement Obligations Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 910us-gaap_RegulatoryLiabilityNoncurrent	$ 879us-gaap_RegulatoryLiabilityNoncurrent
Cost of removal [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 873	$ 843

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_RegulatoryLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant