Accounting and Reporting for Power the Future Generating Units (Details)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Accounting and Reporting for Power the Future Generating Units (Textuals)
New generating units built	4
Pre-tax cost of capital used for current rates	14.00%
Weighted-average pre-tax cost of interest for capitalized interest		5.00%
Lease return on equity component, after tax	12.70%
OC 1 and OC 2 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
One time escalation of lease payments expected to be levelized	10.60%
Duration of one time escalation of lease payments	first five years