Organization and Basis of Presentation (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets [Abstract]
Cash and cash equivalents	$ 37	$ 48	$ 52	$ 65
Restricted cash	23	120
Accounts receivable	1,276	1,504
Property, plant, and equipment, net	18,034	16,820
Securitized regulatory assets	0	34
Total Assets	28,737	27,899	$ 25,935
Liabilities [Abstract]
Current portion long-term debt, including capital leases	473	274
Current regulatory liabilities	41	153
Mortgage bonds, notes, and other	8,340	7,860
Capital lease obligations	15	3
Variable Interest Entity, Primary Beneficiary, Restricted
Assets [Abstract]
Cash and cash equivalents	14	7
Restricted cash	8	104
Accounts receivable	18	41
Inventories	82	67
Property, plant, and equipment, net	66	81
Securitized regulatory assets	0	34
Other current and long-term assets	4	7
Total Assets	192	341
Liabilities [Abstract]
Accounts payable and accrued current liabilities	13	11
Current portion long-term debt, including capital leases	8	115
Current regulatory liabilities	0	32
Mortgage bonds, notes, and other	10	15
Capital lease obligations	0	3
Other current and long-term liabilities	6	15
Total Liabilities	$ 37	191
Variable Interest Entity, Primary Beneficiary Securitization
Assets [Abstract]
Cash and cash equivalents		0
Restricted cash		96
Accounts receivable		26
Inventories		0
Property, plant, and equipment, net		0
Securitized regulatory assets		34
Other current and long-term assets		1
Total Assets		157
Liabilities [Abstract]
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, Restricted
Assets [Abstract]
Cash and cash equivalents		7
Restricted cash		8
Accounts receivable		15
Inventories		67
Property, plant, and equipment, net		81
Securitized regulatory assets		0
Other current and long-term assets		6
Total Assets		184
Liabilities [Abstract]
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