Leases (Schedule Of Operating Leases) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	$ 72	$ 73	$ 79
Operating leases rent expense, net	77	78	87
IPL [Member]
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	4	4	4
Operating leases rent expense, net	5	5	5
WPL [Member]
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	63	63	68
Operating leases rent expense, net	67	67	75
Purchased Power Agreements [Member]
Leases [Line Items]
Contingent rentals related to certain PPAs	4	4	7
Other contingent rentals	4	4	7
Purchased Power Agreements [Member] | WPL [Member]
Leases [Line Items]
Contingent rentals related to certain PPAs	4	4	7
Other contingent rentals	4	4	7
Other [Member]
Leases [Line Items]
Contingent rentals related to certain PPAs	1	1	1
Other contingent rentals	1	1	1
Other [Member] | IPL [Member]
Leases [Line Items]
Contingent rentals related to certain PPAs	1	1	1
Other contingent rentals	$ 1	$ 1	$ 1