Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Condensed Consolidated Statements of Income and Comprehensive Income [Abstract]
Operating revenues	$ 134	$ 122	$ 381	$ 393
Operating expenses
Operation and maintenance	51	49	147	140
Depreciation and amortization	28	22	69	65
Taxes, other than income taxes	8	8	23	24
Total operating expenses	87	79	239	229
Operating income	47	43	142	164
Other income, net	0	1	1	2
Interest and debt expense	(22)	(23)	(66)	(70)
Affiliated interest income, net	6	4	12	12
Income before income taxes	31	25	89	108
Income tax expense	11	10	33	42
Net income	20	15	56	66
Other comprehensive income
Unrealized actuarial gains on postretirement benefit obligations (net of income taxes of $4 and $4 in 2011)	6	0	6	0
Total comprehensive income	$ 26	$ 15	$ 62	$ 66