Other Income and Expenses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Other income:
Equity allowance for funds used during construction	$ 23	$ 18	$ 71	$ 74
Increase in cash surrender value of life insurance policies	6	6	20	19
Other	7	2	12	10
Total utility other income	36	26	103	103
Competitive power generation and other income	1	1	2	7
Total other income	37	27	105	110
Other expenses:
Civic, political and related activities and donations	5	6	22	21
Other	4	4	14	14
Total utility other expenses	9	10	36	35
Competitive power generation and other expenses	1	1	0	2
Total other expenses	$ 10	$ 11	$ 36	$ 37