Business Acquisitions and Dispositions Business Acquisitions and Dispositions - Potrero & EVgo (Details)			3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 26, 2016 USD ($)	Jun. 18, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 17, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Litigation Settlement, Amount								$ 12,000,000
Gain (Loss) on Disposition of Other Assets						$ 224,000,000	$ (14,000,000)	$ 4,000,000
Equity Method Investments						1,120,000,000	$ 1,045,000,000
Potrero LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	$ 86,000,000
Gain (Loss) on Disposition of Property Plant Equipment			$ 74,000,000
EVgo [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses		$ 39,000,000
Capital Contributions From Partners in Equity Method Investment									$ 15,000,000
Future Capital Contributions From Partners in Equity Method Investment									$ 7,000,000
Future Revenue Rights		70,000,000
Gain (Loss) on Disposition of Other Assets				$ 78,000,000
Gain (Loss) on Disposition of Business				27,000,000
Cash [Member] | Potrero LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	74,000,000
Cash [Member] | EVgo [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses		17,000,000
Closing costs [Member] | Potrero LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	8,000,000
Post-closing obligations [Member] | Potrero LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	$ 4,000,000
Working Capital Adjustment [Member] | EVgo [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses		$ 2,500,000
CPUC [Member] | EVgo [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Litigation Settlement, Amount					$ 102,500,000
Loss Contingency, Number of Fast Charge Stations to Be Installed in California					200
Loss Contingency, Number of Parking Spaces Required					10,000
Loss Contingency Accrual				$ 56,000,000		$ 47,000,000
EVgo [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity Method Investment, Ownership Percentage						35.00%
Equity Method Investments						$ 5,000,000