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Consolidated Balance Sheets (Parenthetical) - $ / shares | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Common stock, par value (in dollars per share) | $ 0.01 | $ 0.01
Common stock, shares authorized (in shares) | 480,000,000 | 480,000,000
Common stock, shares outstanding (in shares) | 231,348,646 | 227,673,654
Shares in deferred compensation trust (in shares) | 463,365 | 441,695
Shares in deferred compensation trust, weighted average cost per share (in dollars per share) | $ 23.91 | $ 22.71
IPL [Member] |  |
Common stock, par value (in dollars per share) | $ 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 (in dollars per share) | $ 5 | $ 5
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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