Assets Held for Sale (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Dec. 31, 2015	Oct. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and temporary cash investments	$ 4		$ 4	$ 0	$ 0
Total current assets	157		157	0
Total current liabilities	89		89	$ 0
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		4
Accounts receivable, less allowance for uncollectible accounts of $8	64		64
Accrued unbilled revenue	65		65
Other assets	3		3
Total current assets	136		136
Utility plant, less accumulated depreciation of $6	14		14
Non-utility property, less accumulated depreciation of $13	4		4
Regulatory assets	3		3
Total assets held for sale	157		157
Fair value of derivative liabilities	65		65
Accounts payable	5		5
Other	3		3
Total current liabilities	73		73
Fair value of derivative liabilities	13		13
Long-term debt	3		3
Total liabilities held for sale	89		89
Allowance for uncollectible accounts	8
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		0
Accounts receivable, less allowance for uncollectible accounts of $8	64		64
Accrued unbilled revenue	64		64
Other assets	2		2
Total current assets	130		130
Utility plant, less accumulated depreciation of $6	0		0
Non-utility property, less accumulated depreciation of $13	4		4
Regulatory assets	0		0
Total assets held for sale	134		134
Fair value of derivative liabilities	65		65
Accounts payable	5		5
Other	1		1
Total current liabilities	71		71
Fair value of derivative liabilities	13		13
Long-term debt	0		0
Total liabilities held for sale	84		84
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 businesses		$ 16
Impairment charge on assets held for sale	5		5
Impairment of long-lived assets to be disposed of, net of tax	3
Cash and temporary cash investments	4		4
Accounts receivable, less allowance for uncollectible accounts of $8	0		0
Accrued unbilled revenue	1		1
Other assets	1		1
Total current assets	6		6
Utility plant, less accumulated depreciation of $6	14		14
Non-utility property, less accumulated depreciation of $13	0		0
Regulatory assets	3		3
Total assets held for sale	23		23
Fair value of derivative liabilities	0		0
Accounts payable	0		0
Other	2		2
Total current liabilities	2		2
Fair value of derivative liabilities	0		0
Long-term debt	3		3
Total liabilities held for sale	$ 5		$ 5