Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Condensed Consolidated Statements of Income and Comprehensive Income [Abstract]
Operating revenues	$ 268	$ 234
Operating expenses
Operation and maintenance	76	75
Depreciation and amortization	52	48
Taxes, other than income taxes	16	16
Total operating expenses	144	139
Operating income	124	95
Earnings from unconsolidated affiliate	3	4
Other income, net	2	8
Interest and debt expense	(35)	(37)
Affiliated interest income, net	3	3
Income before income taxes	97	73
Income tax expense	37	28
Net income	60	45
Other comprehensive income
Unrealized actuarial gains on postretirement benefit obligations	0	0
Comprehensive income	$ 60	$ 45