Regulatory Matters (Details 3) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Detail of regulatory liabilities
Regulatory liabilities, current	$ 94,000,000	$ 139,000,000
Regulatory liabilities, non-current	689,120,000	614,063,000
Removal costs
Detail of regulatory liabilities
Regulatory liabilities, current	21,000,000	22,000,000
Regulatory liabilities, non-current	355,000,000	357,000,000
Asset retirement obligations.
Detail of regulatory liabilities
Regulatory liabilities, non-current	202,000,000	184,000,000
Renewable energy standard
Detail of regulatory liabilities
Regulatory liabilities, current	58,000,000	50,000,000
Deferred income taxes
Detail of regulatory liabilities
Regulatory liabilities, non-current	50,000,000
Spent nuclear fuel
Detail of regulatory liabilities
Regulatory liabilities, current	5,000,000	4,000,000
Regulatory liabilities, non-current	43,000,000	41,000,000
Deferred gains on utility property
Detail of regulatory liabilities
Regulatory liabilities, current	2,000,000	2,000,000
Regulatory liabilities, non-current	15,000,000	16,000,000
Income taxes-deferred investment tax credit
Detail of regulatory liabilities
Regulatory liabilities, non-current	9,000,000	1,000,000
Deferred Fuel and Purchased Power Costs
Detail of regulatory liabilities
Regulatory liabilities, current		58,000,000
Other,
Detail of regulatory liabilities
Regulatory liabilities, current	8,000,000	3,000,000
Regulatory liabilities, non-current	$ 15,000,000	$ 15,000,000