Income Taxes (Details 2)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	2.40%	1.80%	2.10%
Employee stock plans dividend deduction	(1.10%)	(1.20%)	(1.40%)
Non-deductible book depreciation	0.70%	0.80%	0.90%
Difference in prior years' deferred and current tax rate	(0.10%)	(0.10%)	(0.10%)
AFUDC-Equity	(1.50%)	(2.20%)	(2.70%)
Production activities deduction			(0.70%)
ITC basis difference	(0.20%)	(0.40%)
Leveraged lease termination			(0.90%)
MC Asset Recovery			2.70%
Donations			(0.40%)
Other	(0.20%)	(0.20%)	(0.10%)
Effective income tax rate	35.00%	33.50%	34.40%