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Consolidated Balance Sheets (Parenthetical) - $ / shares | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Common stock, par value (in dollars per share) |  | $ 0.01 | $ 0.01
Common stock, shares authorized (in shares) | [1] | 480,000,000 | 480,000,000
Common stock, shares outstanding (in shares) | [1] | 227,673,654 | 226,918,432
Shares in deferred compensation trust (in shares) | [1] | 441,695 | 430,186
Shares in deferred compensation trust, weighted average cost per share (in dollars per share) | [1] | $ 22.71 | $ 19.84
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
[1] | Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

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