|
Debt (Other Short-Term Borrowings) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
|
Sep. 30, 2012
|
Sep. 30, 2011
|
Sep. 30, 2012
|
Sep. 30, 2011
|
|
| Debt Instrument [Line Items] | ||||
| Maximum amount outstanding (based on daily outstanding balances) | $ 185.3 | $ 22.1 | $ 185.3 | $ 96.5 |
| Average amount outstanding (based on daily outstanding balances) | 133.0 | 2.6 | 100.2 | 28.7 |
| Weighted average interest rates | 0.40% | 0.40% | 0.40% | 0.30% |
|
IPL [Member]
|
||||
| Debt Instrument [Line Items] | ||||
| Maximum amount outstanding (based on daily outstanding balances) | 19.5 | 18.0 | 35.4 | 54.4 |
| Average amount outstanding (based on daily outstanding balances) | 1.3 | 1.7 | 7.2 | 7.1 |
| Weighted average interest rates | 0.40% | 0.30% | 0.40% | 0.30% |
|
WPL [Member]
|
||||
| Debt Instrument [Line Items] | ||||
| Maximum amount outstanding (based on daily outstanding balances) | 35.6 | 0 | 35.6 | 96.5 |
| Average amount outstanding (based on daily outstanding balances) | $ 11.9 | $ 0 | $ 13.3 | $ 23.0 |
| Weighted average interest rates | 0.30% | 0.30% | 0.30% | |