Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011
IPL [Member] | Electricity [Member]
Notional Unit Amount Of Derivatives		254,000	1,120,000	299,000	1,673,000
WPL [Member] | Electricity [Member]
Notional Unit Amount Of Derivatives		404,000	1,340,000	521,000	2,265,000
Electricity [Member]
Notional Unit Amount Of Derivatives		658,000	2,460,000	820,000	3,938,000
IPL [Member] | FTRs [Member]
Notional Unit Amount Of Derivatives			14,000	9,000	23,000
WPL [Member] | FTRs [Member]
Notional Unit Amount Of Derivatives			9,000	6,000	15,000
FTRs [Member]
Notional Unit Amount Of Derivatives			23,000	15,000	38,000
IPL [Member] | Natural Gas [Member]
Notional Unit Amount Of Derivatives	225,000	3,415,000	16,479,000	17,288,000	37,407,000
WPL [Member] | Natural Gas [Member]
Notional Unit Amount Of Derivatives	225,000	3,482,000	15,435,000	7,606,000	26,748,000
Natural Gas [Member]
Notional Unit Amount Of Derivatives	450,000	6,897,000	31,914,000	25,049,000	64,310,000