Leases Narrative (Details) (Sheboygan Falls Energy Facility [Member], WPL [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2005 lease_renewal_period_option
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Capital lease, agreement term	20 years
Capital leases, renewal options (in number of renewal periods)	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