Benefit Plans (Estimated Future And Actual Contributions) (Details) (USD $) In Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2011
Defined Benefit Pension Plans [Member]
Estimated Future and Actual Employer Contributions		$ 9
IPL [Member] | Other Postretirement Benefit Plans [Member]
Estimated Future and Actual Employer Contributions	2	3
WPL [Member] | Other Postretirement Benefit Plans [Member]
Estimated Future and Actual Employer Contributions	3	5
Other Postretirement Benefit Plans [Member]
Estimated Future and Actual Employer Contributions	6	9
Non-Qualified Defined Benefit Pension Plans [Member]
Estimated Future and Actual Employer Contributions	$ 5	$ 7