Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Rate as Compared to the Income Tax Expense Recorded in Our Consolidated Statements of Income) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Tax Expense (Benefit) [Abstract]
U.S. statutory rate	35.00%	35.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	1.60%	5.00%	2.40%
Valuation allowances	0.20%	0.10%	(0.40%)
Investment and production tax credits	(0.60%)	(0.30%)	(1.50%)
Amortization of investment tax credits	(0.10%)	0.00%	(0.10%)
AFUDC - equity	(0.60%)	(0.40%)	(1.00%)
Employee stock ownership plan deduction	(0.70%)	(0.30%)	(0.80%)
Pension and other benefits	(0.10%)	0.00%	(0.60%)
Domestic production activities deduction	0.00%	(0.40%)	(2.90%)
Goodwill-sale of U.S. non-Appalachian E&P business	0.00%	0.90%	0.00%
Legislative change	0.00%	1.10%	0.40%
Other, net	(0.40%)	0.10%	1.30%
Effective tax rate	34.30%	40.80%	31.80%