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Condensed Consolidated Balance Sheets (Parenthetical) (USD $) | Sep. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Common stock, par value | $ 0.01 | $ 0.01
Common stock, shares authorized (in shares) | 240,000,000 | 240,000,000
Common stock, shares outstanding (in shares) | 110,943,669 | 110,987,400
Shares in deferred compensation trust (in shares) | 222,415 | 216,030
Shares in deferred compensation trust, weighted average cost per share (in dollars per share) | $ 34.87 | $ 33.61
IPL [Member] |  |
Common stock, par value | $ 2.50 | $ 2.50
Common stock, shares authorized (in shares) | 24,000,000 | 24,000,000
Common stock, shares outstanding (in shares) | 13,370,788 | 13,370,788
WPL [Member] |  |
Common stock, par value | $ 5.00 | $ 5.00
Common stock, shares authorized (in shares) | 18,000,000 | 18,000,000
Common stock, shares outstanding (in shares) | 13,236,601 | 13,236,601

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