Significant Accounting Policies (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Other income	$ 196,000,000	$ 201,000,000	$ 173,000,000
Receivables due date	21 days
Threshold period past due for write-off of trade accounts receivable	150 days
Specific review of probable future collections based on receivable balances in excess of 90 days	30 days
Unbilled revenues	1,504,000,000	1,542,000,000
Regulatory liabilities	820,000,000	1,164,000,000
Property maintenance accrual period	18 months
Amortization of Intangible Assets	12,000,000	14,000,000	6,000,000
Excise and sales taxes net impact on statement of operations	0
Charitable Contributions to a Foundation	25,000,000	18,000,000	21,000,000
Refueling Outage [Member]
Significant Accounting Policies [Line Items]
Regulatory liabilities	16,000,000	26,000,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Notes receivable considered delinquent period	60 days
Finite-lived intangible asset, useful life	1 year
Maximum
Significant Accounting Policies [Line Items]
Notes receivable considered delinquent period	120 days
Finite-lived intangible asset, useful life	27 years
Unbilled Revenues [Member]
Significant Accounting Policies [Line Items]
Unbilled revenues	773,000,000	815,000,000
Public Utilities, Inventory, Natural Gas [Member]
Significant Accounting Policies [Line Items]
LIFO inventory amount	43,000,000	4,000,000
Excess of replacement costs over stated LIFO value	110,000,000	170,000,000
Power and Industrial Projects [Member]
Significant Accounting Policies [Line Items]
Other income	$ 78,000,000	$ 81,000,000	$ 63,000,000