Asset Retirement Obligations (AROs) (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 91.1		$ 75.9
Revisions in estimated cash flows	(9.9)	[1]	7.8	[1]
Liabilities settled	(2.6)		(0.5)
Liabilities incurred	16.0	[2]	4.0	[2]
Accretion expense	2.6		3.4
Balance, September 30	97.2		90.6
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	56.2		43.6
Revisions in estimated cash flows	(9.2)	[1]	7.7	[1]
Liabilities settled	(2.5)		(0.4)
Liabilities incurred	0	[2]	3.1	[2]
Accretion expense	1.4		2.1
Balance, September 30	45.9		56.1
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	34.9		32.3
Revisions in estimated cash flows	(0.7)	[1]	0.1	[1]
Liabilities settled	(0.1)		(0.1)
Liabilities incurred	7.6	[2]	0.9	[2]
Accretion expense	1.2		1.3
Balance, September 30	42.9		34.5
Sixth Street [Member] | IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revisions in estimated cash flows	(8.2)	[1]	7.0	[1]
Franklin County Wind Project [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred	8.4	[2]
Nelson Dewey [Member] | WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred	$ 7.6	[2]

[1] For the nine months ended September 30, 2012 and 2011, IPL recorded revisions in estimated cash flows of ($8.2) million and $7.0 million, respectively, based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.

[2] For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to its Nelson Dewey generating station.