Assets Held For Sale (Details) - USD ($) $ in Millions		1 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2015	Oct. 31, 2015	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets			$ 183		$ 157
Non-utility property, less accumulated depreciation of $13			859		832
Total current liabilities			60		$ 89
Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and temporary cash investments			4
Accounts receivable less allowance for uncollectible accounts of $2			70
Accrued unbilled revenue			80
Other assets			5
Total current assets			159
Utility plant, less accumulated depreciation of $6			14
Non-utility property, less accumulated depreciation of $13			3
Non-utility property construction work in progress			1
Regulatory assets			3
Other assets			3
Total assets held for sale			183
Fair value of derivative liabilities			34
Accounts payable			5
Other			4
Total current liabilities			43
Fair value of derivative liabilities			14
Long-term debt			3
Total liabilities held for sale			60
Allowance for uncollectible accounts			2
Depreciation, utility plant			6
Depreciation, non-utility property			13
Retail Electric Supply Business | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and temporary cash investments			0
Accounts receivable less allowance for uncollectible accounts of $2			70
Accrued unbilled revenue			79
Other assets			4
Total current assets			153
Utility plant, less accumulated depreciation of $6			0
Non-utility property, less accumulated depreciation of $13			3
Non-utility property construction work in progress			1
Regulatory assets			0
Other assets			3
Total assets held for sale			160
Fair value of derivative liabilities			34
Accounts payable			5
Other			3
Total current liabilities			42
Fair value of derivative liabilities			14
Long-term debt			0
Total liabilities held for sale			56
Pike | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business		$ 16
Impairment of long-lived assets to be disposed of	$ 5
Impairment of long-lived assets to be disposed of, net of taxes	$ 3
Cash and temporary cash investments			4
Accounts receivable less allowance for uncollectible accounts of $2			0
Accrued unbilled revenue			1
Other assets			1
Total current assets			6
Utility plant, less accumulated depreciation of $6			14
Non-utility property, less accumulated depreciation of $13			0
Non-utility property construction work in progress			0
Regulatory assets			3
Other assets			0
Total assets held for sale			23
Fair value of derivative liabilities			0
Accounts payable			0
Other			1
Total current liabilities			1
Fair value of derivative liabilities			0
Long-term debt			3
Total liabilities held for sale			$ 4
Scenario, Forecast | Retail Electric Supply Business | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business				$ 200