|
Debt (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
9 Months Ended | ||
|---|---|---|---|
|
Sep. 30, 2012
|
Sep. 30, 2011
|
Dec. 31, 2011
|
|
| Debt Instrument [Line Items] | |||
| Amount outstanding | $ 70.4 | $ 102.8 | |
| Proceeds from issuance of long-term debt | 75.0 | 0.4 | |
|
Alliant Energy and IPL [Member]
|
|||
| Debt Instrument [Line Items] | |||
| Remaining maturity (in days) | 2 days | ||
| Weighted average interest rate | 0.40% | ||
|
Alliant Energy and IPL [Member] | Long-Term Debt [Member]
|
|||
| Debt Instrument [Line Items] | |||
| Amount outstanding | 50.0 | ||
|
Corporate Services [Domain] | 3.45% Senior Notes Due 2022 [Member]
|
|||
| Debt Instrument [Line Items] | |||
| Proceeds from issuance of long-term debt | $ 75.0 | ||
| Debt instrument, interest rate, stated percentage | 3.45% | ||