Organization and Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets [Abstract]
Cash and cash equivalents	$ 65	$ 68	$ 65	$ 52
Restricted cash	122	147
Accounts receivable	1,336	1,317
Other current assets	194	196
Property, plant and equipment	14,684	13,746
Securitized regulatory assets	413	577
Other assets	197	199
Total Assets	26,339	26,009
Liabilities [Abstract]
Current portion long-term debt, including, capital leases	817	526
Other current liabilities	538	549
Mortgage bonds, notes and other	6,220	6,405
Securitization bonds	302	479
Capital lease obligations	12	23
Other long term liabilities	306	331
Variable Interest Entity Securitization [Member]
Assets [Abstract]
Cash and cash equivalents	0		0
Restricted cash	102		107
Accounts receivable	34		34
Inventories	0		0
Other current assets	0		0
Property, plant and equipment	0		0
Securitized regulatory assets	413		577
Other assets	7		10
Total Assets	556		728
Liabilities [Abstract]
Accounts payable and accrued current liabilities	11		14
Current portion long-term debt, including, capital leases	177		164
Other current liabilities	50		55
Mortgage bonds, notes and other	0		0
Securitization bonds	302		479
Capital lease obligations	0		0
Other long term liabilities	7		7
Total Liabilities	547		719
Variable Interest Entity, Primary Beneficiary [Member]
Assets [Abstract]
Cash and cash equivalents	10		25
Restricted cash	7		7
Accounts receivable	7		17
Inventories	141		183
Other current assets	1		1
Property, plant and equipment	93		73
Securitized regulatory assets	0		0
Other assets	11		6
Total Assets	270		312
Liabilities [Abstract]
Accounts payable and accrued current liabilities	14		24
Current portion long-term debt, including, capital leases	8		7
Other current liabilities	4		0
Mortgage bonds, notes and other	25		30
Securitization bonds	0		0
Capital lease obligations	11		14
Other long term liabilities	2		2
Total Liabilities	64		77
Consolidated Variable Interest Entity [Member]
Assets [Abstract]
Cash and cash equivalents	10		25
Restricted cash	109		114
Accounts receivable	41		51
Inventories	141		183
Other current assets	1		1
Property, plant and equipment	93		73
Securitized regulatory assets	413		577
Other assets	18		16
Total Assets	826		1,040
Liabilities [Abstract]
Accounts payable and accrued current liabilities	25		38
Current portion long-term debt, including, capital leases	185		171
Other current liabilities	54		55
Mortgage bonds, notes and other	25		30
Securitization bonds	302		479
Capital lease obligations	11		14
Other long term liabilities	9		9
Total Liabilities	611		796
Variable Interest Entity Restricted [Member]
Assets [Abstract]
Cash and cash equivalents	8		0
Restricted cash	109		114
Accounts receivable	38		36
Inventories	3		0
Other current assets	1		0
Property, plant and equipment	49		23
Securitized regulatory assets	413		577
Other assets	18		16
Total Assets	639		766
Liabilities [Abstract]
Accounts payable and accrued current liabilities	12		14
Current portion long-term debt, including, capital leases	185		171
Other current liabilities	53		55
Mortgage bonds, notes and other	25		30
Securitization bonds	302		479
Capital lease obligations	11		14
Other long term liabilities	8		8
Total Liabilities	$ 596		$ 771