Regulatory Matters (Details 3) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Detail of regulatory liabilities
Regulatory liabilities, current	$ 143,000,000	$ 139,000,000
Regulatory liabilities, non-current	695,036,000	614,063,000
Removal costs
Detail of regulatory liabilities
Regulatory liabilities, current	19,000,000	22,000,000
Regulatory liabilities, non-current	358,000,000	357,000,000
Asset retirement obligations.
Detail of regulatory liabilities
Regulatory liabilities, non-current	213,000,000	184,000,000
Deferred Fuel and Purchased Power Costs
Detail of regulatory liabilities
Regulatory liabilities, current	54,000,000	58,000,000
Renewable energy standard
Detail of regulatory liabilities
Regulatory liabilities, current	57,000,000	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	4,000,000	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
Other,
Detail of regulatory liabilities
Regulatory liabilities, current	7,000,000	3,000,000
Regulatory liabilities, non-current	$ 16,000,000	$ 16,000,000