Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
Securitized regulatory assets	$ 0	$ 34
ASSETS
Cash and cash equivalents	67	48	$ 60	$ 52
Restricted cash	21	120
Accounts receivable	1,242	1,504
Property, plant, and equipment, net	17,867	16,820
Total Assets	28,654	27,974
LIABILITIES
Current portion long-term debt, including capital leases	468	274
Current regulatory liabilities	67	153
Mortgage bonds, notes, and other	8,368	7,860
Capital lease obligations	8	3
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Securitized regulatory assets	0	34
ASSETS
Cash and cash equivalents	12	7
Restricted cash	6	104
Accounts receivable	14	41
Inventories	43	67
Property, plant, and equipment, net	70	81
Other current and long-term assets	4	7
Total Assets	149	341
LIABILITIES
Accounts payable and accrued current liabilities	11	11
Current portion long-term debt, including capital leases	9	115
Current regulatory liabilities	0	32
Mortgage bonds, notes, and other	11	15
Capital lease obligations	0	3
Other current and long-term liabilities	6	15
Total Liabilities	$ 37	191
Variable Interest Entity, Primary Beneficiary Securitization
Variable Interest Entity [Line Items]
Securitized regulatory assets		34
ASSETS
Cash and cash equivalents		0
Restricted cash		96
Accounts receivable		26
Inventories		0
Property, plant, and equipment, net		0
Other current and long-term assets		1
Total Assets		157
LIABILITIES
Accounts payable and accrued current liabilities		3
Current portion long-term debt, including capital leases		105
Current regulatory liabilities		32
Mortgage bonds, notes, and other		0
Capital lease obligations		0
Other current and long-term liabilities		9
Total Liabilities		149
Variable Interest Entity, Primary Beneficiary Other
Variable Interest Entity [Line Items]
Securitized regulatory assets		0
ASSETS
Cash and cash equivalents		7
Restricted cash		8
Accounts receivable		15
Inventories		67
Property, plant, and equipment, net		81
Other current and long-term assets		6
Total Assets		184
LIABILITIES
Accounts payable and accrued current liabilities		8
Current portion long-term debt, including capital leases		10
Current regulatory liabilities		0
Mortgage bonds, notes, and other		15
Capital lease obligations		3
Other current and long-term liabilities		6
Total Liabilities		$ 42