Regulatory Matters (Details 3) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Detail of regulatory liabilities
Regulatory liabilities, current	$ 88,000,000	$ 139,000,000
Regulatory liabilities, non-current	737,332,000	614,063,000
Removal costs
Detail of regulatory liabilities
Regulatory liabilities, current	22,000,000	22,000,000
Regulatory liabilities, non-current	349,000,000	357,000,000
Asset retirement obligations
Detail of regulatory liabilities
Regulatory liabilities, non-current	225,000,000	184,000,000
Renewable energy standard
Detail of regulatory liabilities
Regulatory liabilities, current	54,000,000	50,000,000
Income taxes - change in rates
Detail of regulatory liabilities
Regulatory liabilities, non-current	59,000,000
Spent nuclear fuel
Detail of regulatory liabilities
Regulatory liabilities, current	5,000,000	4,000,000
Regulatory liabilities, non-current	44,000,000	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	14,000,000	16,000,000
Income taxes - unamortized investment tax credit
Detail of regulatory liabilities
Regulatory liabilities, current	1,000,000
Regulatory liabilities, non-current	30,000,000	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	4,000,000	3,000,000
Regulatory liabilities, non-current	$ 16,000,000	$ 15,000,000