Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 TheNumberOfReportableSegments		Mar. 31, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Number of reportable segments	2
Electric	$ 177		$ 172
Natural gas	44		34
Revenues	221		206
Cost of fuel, energy and capacity	80		62
Natural gas purchased for resale	29		18
Gross margin	112		126
Operating and maintenance expense	34		48
Depreciation and amortization	26		25
Property and other taxes	6		6
Interest expense, net of allowance for debt funds	15		16
Allowance for equity funds	(1)		(1)
Other, net	(2)		(2)
Income before income tax expense	34		34
Assets	3,388			3,369
Electric Operations [Member]
Segment Reporting Information [Line Items]
Gross margin	97		110
Assets	2,952			2,957
Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Gross margin	15		16
Assets	347			335
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	$ 89	[1]		$ 77	[1]

[1] Consists principally of cash and cash equivalents.