Consolidated Statements of Operations (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Operating revenue	$ 2,337	$ 2,092	$ 2,145
Operating costs and expenses:
Cost of fuel, energy and capacity	1,076	835	813
Operating and maintenance	405	455	423
Depreciation and amortization	274	277	270
Property and other taxes	41	38	37
Merger-related	0	52	0
Total operating costs and expenses	1,796	1,657	1,543
Operating income	541	435	602
Other income (expense):
Interest expense	(208)	(215)	(215)
Allowance for borrowed funds	1	6	5
Allowance for equity funds	1	8	7
Other, net	22	5	(3)
Total other income (expense)	(184)	(196)	(206)
Income before income tax expense	357	239	396
Income tax expense	130	94	138
Net income	$ 227	$ 145	$ 258