Regulatory Matters (Details 2) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Detail of regulatory assets
Regulatory assets, current	$ 97,000,000	$ 62,000,000
Regulatory assets, non-current	1,352,079,000	986,370,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	1,023,000,000	669,000,000
Income taxes - AFUDC equity
Detail of regulatory assets
Regulatory assets, current	3,000,000	3,000,000
Regulatory assets, non-current	81,000,000	69,000,000
Deferred Fuel and Purchased Power MTM Costs
Detail of regulatory assets
Regulatory assets, current	43,000,000	42,000,000
Regulatory assets, non-current	34,000,000	35,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000
Regulatory assets, non-current	32,000,000	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	35,000,000	33,000,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	33,000,000	32,000,000
Deferred Fuel and Purchased Power Costs
Detail of regulatory assets
Regulatory assets, current	28,000,000
Income taxes - 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
Income taxes - investment tax credit basis adjustment
Detail of regulatory assets
Regulatory assets, non-current	15,000,000
Pension and other postretirement benefits deferral
Detail of regulatory assets
Regulatory assets, non-current	12,000,000
Demand side management
Detail of regulatory assets
Regulatory assets, current	7,000,000	12,000,000
Regulatory assets, non-current	1,000,000	6,000,000
Other.
Detail of regulatory assets
Regulatory assets, current	2,000,000
Regulatory assets, non-current	$ 14,000,000	$ 18,000,000