Balance Sheet Components (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts Receivable, Current		$ 6	$ 6	$ 6	$ 5
Loss Contingency, Damages Awarded, Value	$ 70	$ 9
Jointly Owned Electricity Generation Plant [Member]
Loss Contingency, Damages Awarded, Value	$ 6		$ 6	$ 44

Amount of damages awarded to the plaintiff in the legal matter.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration