v2.4.0.6

Redeemable Preferred Stock (Tables) | 12 Months Ended
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Dec. 31, 2012
Class of Stock [Line Items] |
Schedule of Carrying Value Of Cumulative Preferred Stock | Information related to the carrying value of cumulative preferred stock of subsidiaries, net at December 31 was as follows (dollars in millions):
Liquidation Preference/ Stated Value |  | Authorized Shares |  | Shares Outstanding |  | Series |  | Redemption (none are mandatorily redeemable) |  | 2012 |  | 2011
IPL: |  |  |  |  |  |  |  |  |  |  |  |
$25 |  | 16,000,000 |  | 6,000,000 |  | 8.375% |  | On or after March 15, 2013 |  |  | $150.0 |  |  |  | $150.0 |
Less: discount |  |  |  |  |  |  |  |  |  | (4.9 | ) |  | (4.9 | )
|  |  |  |  |  |  |  |  |  | 145.1 |  |  | 145.1 |
WPL: |  |  |  |  |  |  |  |  |  |  |  |
$100 |  | (a) |  | 99,970 |  | 4.50% |  | Any time |  | 10.0 |  |  | 10.0 |
$100 |  | (a) |  | 74,912 |  | 4.80% |  | Any time |  | 7.5 |  |  | 7.5 |
$100 |  | (a) |  | 64,979 |  | 4.96% |  | Any time |  | 6.5 |  |  | 6.5 |
$100 |  | (a) |  | 29,957 |  | 4.40% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 29,947 |  | 4.76% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 150,000 |  | 6.20% |  | Any time |  | 15.0 |  |  | 15.0 |
$25 |  | (a) |  | 599,460 |  | 6.50% |  | Any time |  | 15.0 |  |  | 15.0 |
|  |  |  |  |  |  |  |  |  | 60.0 |  |  | 60.0 |
Alliant Energy |  |  |  |  |  |  |  |  |  |  | $205.1 |  |  |  | $205.1 |
(a) | WPL has 3,750,000 authorized shares in total.
IPL [Member] |
Class of Stock [Line Items] |
Schedule of Carrying Value Of Cumulative Preferred Stock | Information related to the carrying value of cumulative preferred stock of subsidiaries, net at December 31 was as follows (dollars in millions):
Liquidation Preference/ Stated Value |  | Authorized Shares |  | Shares Outstanding |  | Series |  | Redemption (none are mandatorily redeemable) |  | 2012 |  | 2011
IPL: |  |  |  |  |  |  |  |  |  |  |  |
$25 |  | 16,000,000 |  | 6,000,000 |  | 8.375% |  | On or after March 15, 2013 |  |  | $150.0 |  |  |  | $150.0 |
Less: discount |  |  |  |  |  |  |  |  |  | (4.9 | ) |  | (4.9 | )
|  |  |  |  |  |  |  |  |  | 145.1 |  |  | 145.1 |
WPL: |  |  |  |  |  |  |  |  |  |  |  |
$100 |  | (a) |  | 99,970 |  | 4.50% |  | Any time |  | 10.0 |  |  | 10.0 |
$100 |  | (a) |  | 74,912 |  | 4.80% |  | Any time |  | 7.5 |  |  | 7.5 |
$100 |  | (a) |  | 64,979 |  | 4.96% |  | Any time |  | 6.5 |  |  | 6.5 |
$100 |  | (a) |  | 29,957 |  | 4.40% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 29,947 |  | 4.76% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 150,000 |  | 6.20% |  | Any time |  | 15.0 |  |  | 15.0 |
$25 |  | (a) |  | 599,460 |  | 6.50% |  | Any time |  | 15.0 |  |  | 15.0 |
|  |  |  |  |  |  |  |  |  | 60.0 |  |  | 60.0 |
Alliant Energy |  |  |  |  |  |  |  |  |  |  | $205.1 |  |  |  | $205.1 |
(a) | WPL has 3,750,000 authorized shares in total.
WPL [Member] |
Class of Stock [Line Items] |
Schedule of Carrying Value Of Cumulative Preferred Stock | Information related to the carrying value of cumulative preferred stock of subsidiaries, net at December 31 was as follows (dollars in millions):
Liquidation Preference/ Stated Value |  | Authorized Shares |  | Shares Outstanding |  | Series |  | Redemption (none are mandatorily redeemable) |  | 2012 |  | 2011
IPL: |  |  |  |  |  |  |  |  |  |  |  |
$25 |  | 16,000,000 |  | 6,000,000 |  | 8.375% |  | On or after March 15, 2013 |  |  | $150.0 |  |  |  | $150.0 |
Less: discount |  |  |  |  |  |  |  |  |  | (4.9 | ) |  | (4.9 | )
|  |  |  |  |  |  |  |  |  | 145.1 |  |  | 145.1 |
WPL: |  |  |  |  |  |  |  |  |  |  |  |
$100 |  | (a) |  | 99,970 |  | 4.50% |  | Any time |  | 10.0 |  |  | 10.0 |
$100 |  | (a) |  | 74,912 |  | 4.80% |  | Any time |  | 7.5 |  |  | 7.5 |
$100 |  | (a) |  | 64,979 |  | 4.96% |  | Any time |  | 6.5 |  |  | 6.5 |
$100 |  | (a) |  | 29,957 |  | 4.40% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 29,947 |  | 4.76% |  | Any time |  | 3.0 |  |  | 3.0 |
$100 |  | (a) |  | 150,000 |  | 6.20% |  | Any time |  | 15.0 |  |  | 15.0 |
$25 |  | (a) |  | 599,460 |  | 6.50% |  | Any time |  | 15.0 |  |  | 15.0 |
|  |  |  |  |  |  |  |  |  | 60.0 |  |  | 60.0 |
Alliant Energy |  |  |  |  |  |  |  |  |  |  | $205.1 |  |  |  | $205.1 |
(a) | WPL has 3,750,000 authorized shares in total.

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