Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 site
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	$ 347
Present value abandonment obligation	32
IPL [Member]
Long-term Purchase Commitment [Line Items]
Number of sites monitoring and remediating (in sites)	27
WPL [Member]
Long-term Purchase Commitment [Line Items]
Number of sites monitoring and remediating (in sites)	5
Indemnifications [Member] | RMT [Member]
Long-term Purchase Commitment [Line Items]
Loss contingency, estimate of possible loss	3
Performance guarantees outstanding, 2014 [Member]
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	246
Performance guarantees outstanding, 2015 [Member]
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	53
Performance guarantees outstanding, 2016 [Member]
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	48
Scenario, Forecast [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2,518
Scenario, Forecast [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,955
Scenario, Forecast [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	560
Scenario, Forecast [Member] | Capital Purchase Obligation [Member] | Alliant Energy and IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	35
Environmental Issue [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Loss contingency, damages awarded, value	$ 7
Minimum [Member]
Long-term Purchase Commitment [Line Items]
Warranty period	12 months
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Warranty period	60 months
Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Concentration risk	57.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Concentration risk	66.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Concentration risk	80.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Long-term Purchase Commitment [Line Items]
Concentration risk	26.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Concentration risk	80.00%