Organization and Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and cash equivalents	$ 71	$ 65	$ 59	$ 68
Restricted cash	64	122
Accounts receivable	1,239	1,336
Other current assets	248	194
Property, plant and equipment	15,511	14,684
Securitized regulatory assets	280	413
Other assets	198	197
Total Assets	26,231	26,339
Liabilities [Abstract]
Current portion long-term debt, including, capital leases	896	817
Current regulatory liabilities	230	89
Other current liabilities	457	449
Mortgage bonds, notes and other	6,253	6,220
Securitization bonds	105	302
Capital lease obligations	8	12
Other long term liabilities	290	306
Variable Interest Entity Securitization [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Restricted cash	44	102
Accounts receivable	39	34
Inventories	0	0
Other current assets	0	0
Property, plant and equipment	0	0
Securitized regulatory assets	280	413
Other assets	5	7
Total Assets	368	556
Liabilities [Abstract]
Accounts payable and accrued current liabilities	2	11
Current portion long-term debt, including, capital leases	196	177
Current regulatory liabilities	48	50
Other current liabilities	0	0
Mortgage bonds, notes and other	0	0
Securitization bonds	105	302
Capital lease obligations	0	0
Other long term liabilities	8	7
Total Liabilities	359	547
Variable Interest Entity, Primary Beneficiary [Member]
Assets [Abstract]
Cash and cash equivalents	10	10
Restricted cash	7	7
Accounts receivable	17	7
Inventories	112	141
Other current assets	1	1
Property, plant and equipment	100	93
Securitized regulatory assets	0	0
Other assets	9	11
Total Assets	256	270
Liabilities [Abstract]
Accounts payable and accrued current liabilities	35	14
Current portion long-term debt, including, capital leases	9	8
Current regulatory liabilities	0	0
Other current liabilities	3	4
Mortgage bonds, notes and other	22	25
Securitization bonds	0	0
Capital lease obligations	7	11
Other long term liabilities	3	2
Total Liabilities	79	64
Consolidated Variable Interest Entity [Member]
Assets [Abstract]
Cash and cash equivalents	10	10
Restricted cash	51	109
Accounts receivable	56	41
Inventories	112	141
Other current assets	1	1
Property, plant and equipment	100	93
Securitized regulatory assets	280	413
Other assets	14	18
Total Assets	624	826
Liabilities [Abstract]
Accounts payable and accrued current liabilities	37	25
Current portion long-term debt, including, capital leases	205	185
Current regulatory liabilities	48	50
Other current liabilities	3	4
Mortgage bonds, notes and other	22	25
Securitization bonds	105	302
Capital lease obligations	7	11
Other long term liabilities	11	9
Total Liabilities	$ 438	$ 611