Consolidated Statements of Income and Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements of Income and Comprehensive Income [Abstract]
Operating revenues	$ 509	$ 517	$ 593
Operating expenses
Operation and maintenance	206	193	202
Depreciation and amortization	92	88	83
Taxes, other than income taxes	31	32	29
Total operating expenses	329	313	314
Operating income	180	204	279
Other income, net	2	3	2
Interest and debt expense	(88)	(92)	(93)
Affiliated interest income, net	17	15	19
Income before income taxes	111	130	207
Income tax expense	42	47	79
Net income	69	83	128
Other comprehensive income
Unrealized actuarial gains on postretirement benefit obligations (net of income taxes of $3 in 2011)	3
Comprehensive income	$ 72	$ 83	$ 128