Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,303
Present value abandonment obligation	33
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,707
Indemnification obligations, maximum	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	588
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	105
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	8
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	97
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,278	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,194	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	84	[1]
Environmental Issue [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	6
Environmental Issue [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	7
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Indemnification obligations, maximum	98
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Indemnification obligations, maximum	$ 17

[1] Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased.