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Asset Retirement Obligations (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Balance as of January 1 $ 16.6 $ 15.6
Accretion Expense 1.0 1.0
Balance as of December 31 17.6 16.6
Indianapolis Power And Light Company [Member]
   
Balance as of January 1 16.6 15.6
Accretion Expense 1.0 1.0
Balance as of December 31 $ 17.6 $ 16.6