Organization and Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2010
Assets [Abstract]
Cash and cash equivalents	$ 218	$ 65	$ 57	$ 68
Restricted cash	65	122
Accounts receivable	1,460	1,336
Other current assets	158	194
Property, plant and equipment	14,866	14,684
Securitized regulatory assets	369	413
Other assets	196	197
Total Assets	25,949	26,339
Liabilities [Abstract]
Current portion long-term debt, including, capital leases	840	817
Other current liabilities	473	538
Mortgage bonds, notes and other	6,528	6,220
Securitization bonds	201	302
Capital lease obligations	9	12
Other long term liabilities	281	306
Variable Interest Entity Securitization [Member]
Assets [Abstract]
Cash and cash equivalents	0	0
Restricted cash	45	102
Accounts receivable	35	34
Inventories	0	0
Other current assets	0	0
Property, plant and equipment	0	0
Securitized regulatory assets	369	413
Other assets	7	7
Total Assets	456	556
Liabilities [Abstract]
Accounts payable and accrued current liabilities	2	11
Current portion long-term debt, including, capital leases	189	177
Current regulatory liabilities	46	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	446	547
Variable Interest Entity, Primary Beneficiary [Member]
Assets [Abstract]
Cash and cash equivalents	8	10
Restricted cash	6	7
Accounts receivable	6	7
Inventories	63	141
Other current assets	1	1
Property, plant and equipment	90	93
Securitized regulatory assets	0	0
Other assets	10	11
Total Assets	184	270
Liabilities [Abstract]
Accounts payable and accrued current liabilities	14	14
Current portion long-term debt, including, capital leases	8	8
Current regulatory liabilities	0	0
Other current liabilities	4	4
Mortgage bonds, notes and other	24	25
Securitization bonds	0	0
Capital lease obligations	8	11
Other long term liabilities	2	2
Total Liabilities	60	64
Consolidated Variable Interest Entity [Member]
Assets [Abstract]
Cash and cash equivalents	8	10
Restricted cash	51	109
Accounts receivable	41	41
Inventories	63	141
Other current assets	1	1
Property, plant and equipment	90	93
Securitized regulatory assets	369	413
Other assets	17	18
Total Assets	640	826
Liabilities [Abstract]
Accounts payable and accrued current liabilities	16	25
Current portion long-term debt, including, capital leases	197	185
Current regulatory liabilities	46	50
Other current liabilities	4	4
Mortgage bonds, notes and other	24	25
Securitization bonds	201	302
Capital lease obligations	8	11
Other long term liabilities	10	9
Total Liabilities	506	611
Variable Interest Entity Restricted [Member]
Assets [Abstract]
Cash and cash equivalents	6	8
Restricted cash	51	109
Accounts receivable	38	38
Inventories	3	3
Other current assets	0	1
Property, plant and equipment	47	49
Securitized regulatory assets	369	413
Other assets	17	18
Total Assets	531	639
Liabilities [Abstract]
Accounts payable and accrued current liabilities	3	12
Current portion long-term debt, including, capital leases	197	185
Current regulatory liabilities	46	50
Other current liabilities	4	3
Mortgage bonds, notes and other	24	25
Securitization bonds	201	302
Capital lease obligations	8	11
Other long term liabilities	8	8
Total Liabilities	$ 491	$ 596