Income Taxes Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	35.00%		35.00%		35.00%
State income taxes, net of federal income tax benefit	3.00%		3.00%		2.00%
Federal income tax credits	(7.00%)	[1]	(9.00%)	[1]	(10.00%)	[1]
Other	(1.00%)		(2.00%)		1.00%
Effective income tax rate	30.00%		27.00%		28.00%
Years eligible for federal renewable electricity production tax credits	10 years

[1] Primarily attributable to the impact of federal renewable electricity production tax credits for qualifying wind-powered generating facilities that extend 10 years from the date the facilities were placed in service.