Accounting and Reporting for Power the Future Generating Units (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 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 [Member]
Public Utility Property Plant And Equipment [Line Items]
One time escalation of lease payments expected to be levelized	10.60%
Years before one time escalation of lease payments	first five years
OC 2 [Member]
Public Utility Property Plant And Equipment [Line Items]
One time escalation of lease payments expected to be levelized	10.60%
Years before one time escalation of lease payments	first five years