|
Leases Narrative (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2012
Alliant Energy and WPL [Member]
|
Dec. 31, 2005
Sheboygan Falls Energy Facility [Member]
WPL [Member]
lease_renewal_period_option
|
Dec. 31, 2012
Synthetic Leases [Member]
Alliant Energy and WPL [Member]
|
|
| Leases [Line Items] | |||
| Residual value of assets | $ 4 | ||
| Operating synthetic leases, remaining term | 3 years | ||
| Capital lease, agreement term | 20 years | ||
| Capital leases, number of lease renewal period options | 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 | ||