Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] T in Thousands, MWh in Thousands, Dekatherms in Thousands	Dec. 31, 2015 Dekatherms T MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,868
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	809
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,059
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	9,880
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,622
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	4,258
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	104,096
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	55,985
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	48,111
Coal (tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	4,945
Coal (tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	1,966
Coal (tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	2,979