Leases (Schedule Of Operating Leases) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	$ 69	$ 70	$ 70
Contingent rentals (primarily related to certain PPAs)	6	5	5
Total operating lease rental expenses	75	75	75
IPL [Member]
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	4	4	4
Contingent rentals (primarily related to certain PPAs)	0	1	1
Total operating lease rental expenses	4	5	5
WPL [Member]
Leases [Line Items]
Operating lease rental expenses (excluding contingent rentals)	64	63	63
Contingent rentals (primarily related to certain PPAs)	5	4	4
Total operating lease rental expenses	$ 69	$ 67	$ 67