Segment Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 TheNumberOfReportableSegments		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of Reportable Segments	2
Regulated electric	$ 779		$ 747		$ 726
Regulated natural gas	125		106		108
Revenues	904		853		834
Cost of fuel, energy and capacity	361		292		263
Natural gas purchased for resale	76		56		62
Cost of Sales	437		348		325
Gross Margin	467		505		509
Operating and maintenance expense	158		197		190
Depreciation and amortization	105		123		108
Operating Income (Loss)	178		140		188
Interest expense, net of borrowed funds	59		60		63
Income Tax Expense (Benefit)	47		33		40
Capital expenditures	196		157		211
Total assets	3,388		3,369		3,316
Electric Operations [Member]
Segment Reporting Information [Line Items]
Regulated electric	779		747		726
Cost of fuel, energy and capacity	361		292		263
Electric Domestic Regulated Gross Margin	418		455		463
Electricity, Utilities Operating Expense, Maintenance and Operations	140		176		169
Depreciation and amortization	90		106		95
Operating Income (Loss)	165		134		179
Electric, Interest Expense, net of allowance for borrowed funds	55		55		57
Income Tax Expense (Benefit)	43		32		40
Capital expenditures	177		141		191
Total assets	3,031		2,957		2,919
Regulated Gas [Member]
Segment Reporting Information [Line Items]
Regulated natural gas	125		106		108
Natural gas purchased for resale	76		56		62
Gas Domestic Regulated Gross Margin	49		50		46
Gas, Utilities Operating Expense, Maintenance and Operations	18		21		21
Depreciation and amortization	15		17		13
Operating Income (Loss)	13		6		9
Gas, Interest Expense, net of allowance for borrowed funds	4		5		6
Income Tax Expense (Benefit)	4		1		0
Capital expenditures	19		16		20
Total assets	327		335		319
Regulated common assets [Member]
Segment Reporting Information [Line Items]
Total assets	$ 30	[1]	$ 77	[1]	$ 78	[1]

[1] Consists principally of cash and cash equivalents not included in either the regulated electric or regulated natural gas segments.