Leases (Narrative) (Details) - Sheboygan Falls Energy Facility [Member] - WPL [Member] $ in Millions	12 Months Ended
	Dec. 31, 2005 USD ($) lease_renewal_period_option
Leases [Line Items]
Capital lease, agreement term	20 years
Capital leases, renewal options (in number of renewal periods) | lease_renewal_period_option	2
Affiliated lease agreement monthly payments | $	$ 1.3
Basis for lease payments, debt to capital ratio	50.00%
Basis for lease payments, return on equity ratio	10.90%
Approved agreement terms, review period from date of the order	5 years
Capital lease asset amortization term	20 years