Organization and Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and cash equivalents	$ 46	$ 65	$ 185	$ 68
Restricted cash	112	122
Accounts receivable	1,314	1,336
Other current assets	115	194
Property, plant and equipment	15,190	14,684
Securitized regulatory assets	326	413
Other assets	199	197
Total Assets	25,944	26,339
Liabilities [Abstract]
Current portion long-term debt, including, capital leases	879	817
Other current liabilities	570	538
Mortgage bonds, notes and other	6,116	6,220
Securitization bonds	201	302
Capital lease obligations	9	12
Other long term liabilities	283	306
Variable Interest Entity Securitization [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Restricted cash	90	102
Accounts receivable	39	34
Inventories	0	0
Other current assets	0	0
Property, plant and equipment	0	0
Securitized regulatory assets	326	413
Other assets	6	7
Total Assets	461	556
Liabilities [Abstract]
Accounts payable and accrued current liabilities	9	11
Current portion long-term debt, including, capital leases	189	177
Current regulatory liabilities	45	50
Other current liabilities	0	0
Mortgage bonds, notes and other	0	0
Securitization bonds	201	302
Capital lease obligations	0	0
Other long term liabilities	8	7
Total Liabilities	452	547
Variable Interest Entity, Primary Beneficiary [Member]
Assets [Abstract]
Cash and cash equivalents	8	10
Restricted cash	6	7
Accounts receivable	16	7
Inventories	91	141
Other current assets	1	1
Property, plant and equipment	103	93
Securitized regulatory assets	0	0
Other assets	9	11
Total Assets	234	270
Liabilities [Abstract]
Accounts payable and accrued current liabilities	33	14
Current portion long-term debt, including, capital leases	8	8
Current regulatory liabilities	0	0
Other current liabilities	3	4
Mortgage bonds, notes and other	23	25
Securitization bonds	0	0
Capital lease obligations	8	11
Other long term liabilities	2	2
Total Liabilities	77	64
Consolidated Variable Interest Entity [Member]
Assets [Abstract]
Cash and cash equivalents	8	10
Restricted cash	96	109
Accounts receivable	55	41
Inventories	91	141
Other current assets	1	1
Property, plant and equipment	103	93
Securitized regulatory assets	326	413
Other assets	15	18
Total Assets	695	826
Liabilities [Abstract]
Accounts payable and accrued current liabilities	42	25
Current portion long-term debt, including, capital leases	197	185
Current regulatory liabilities	45	50
Other current liabilities	3	4
Mortgage bonds, notes and other	23	25
Securitization bonds	201	302
Capital lease obligations	8	11
Other long term liabilities	10	9
Total Liabilities	$ 529	$ 611