Regulatory Matters (Details 3) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Detail of regulatory liabilities
Regulatory liabilities, current	$ 90,000,000	$ 88,000,000
Regulatory liabilities, non-current	754,210,000	737,332,000
Removal costs
Detail of regulatory liabilities
Regulatory liabilities, current	24,000,000	22,000,000
Regulatory liabilities, non-current	344,000,000	349,000,000
Asset retirement obligations
Detail of regulatory liabilities
Regulatory liabilities, non-current	249,000,000	225,000,000
Renewable energy standard
Detail of regulatory liabilities
Regulatory liabilities, current	50,000,000	54,000,000
Income taxes - change in rates
Detail of regulatory liabilities
Regulatory liabilities, non-current	59,000,000	59,000,000
Spent nuclear fuel
Detail of regulatory liabilities
Regulatory liabilities, current	7,000,000	5,000,000
Regulatory liabilities, non-current	41,000,000	44,000,000
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	14,000,000
Income taxes-deferred investment tax credit
Detail of regulatory liabilities
Regulatory liabilities, current	1,000,000	1,000,000
Regulatory liabilities, non-current	32,000,000	30,000,000
Other
Detail of regulatory liabilities
Regulatory liabilities, current	6,000,000	4,000,000
Regulatory liabilities, non-current	$ 15,000,000	$ 16,000,000