Regulatory Matters (Details 2) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Detail of regulatory assets
Regulatory assets, current	$ 87,000,000	$ 62,000,000
Regulatory assets, non-current	977,975,000	986,370,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	663,000,000	669,000,000
Deferred income taxes
Detail of regulatory assets
Regulatory assets, current	3,000,000	3,000,000
Regulatory assets, non-current	82,000,000	69,000,000
Deferred Fuel and Purchased Power MTM Costs
Detail of regulatory assets
Regulatory assets, current	35,000,000	42,000,000
Regulatory assets, non-current	27,000,000	35,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000
Regulatory assets, non-current	34,000,000	46,000,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	35,000,000	36,000,000
Consolidation of VIEs
Detail of regulatory assets
Regulatory assets, non-current	34,000,000	33,000,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	34,000,000	32,000,000
Deferred Fuel and Purchased Power Costs
Detail of regulatory assets
Regulatory assets, current	32,000,000
Tax expense of Medicare subsidy
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	18,000,000	21,000,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	19,000,000	21,000,000
Pension and other post-retirement benefits deferral
Detail of regulatory assets
Regulatory assets, non-current	9,000,000
Demand side management
Detail of regulatory assets
Regulatory assets, current	3,000,000	12,000,000
Regulatory assets, non-current	2,000,000	6,000,000
Other:
Detail of regulatory assets
Regulatory assets, non-current	$ 21,000,000	$ 18,000,000