Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,278
Present value abandonment obligation	34
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,603
Indemnification obligations, maximum	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	661
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	95
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	12
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	83
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,175	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,127	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	48	[1]
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.