Condensed Consolidated Statements of Income (Unaudited) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Condensed Consolidated Statements of Income [Abstract]
Operating revenues	$ 216	$ 200	$ 450	$ 424
Operating expenses
Operation and maintenance	83	81	158	154
Depreciation and amortization	49	47	97	95
Taxes, other than income taxes	19	13	35	27
Total operating expenses	151	141	290	276
Operating income	65	59	160	148
Earnings from unconsolidated affiliate	3	3	7	7
Other income, net	9	4	17	9
Interest and debt expense	(35)	(37)	(72)	(75)
Affiliated interest income, net	4	4	7	7
Income before income taxes	46	33	119	96
Income tax expense	16	13	44	37
Net income	$ 30	$ 20	$ 75	$ 59