Asset Retirement Obligations (AROs) (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, Jan.1	$ 91.1		$ 75.9
Revisions in estimated cash flows	(9.9)	[1]	(0.5)	[1]
Liabilities settled	(1.8)		(0.3)
Liabilities incurred	0.7		3.7
Accretion expense	1.8		2.2
Balance, June 30	81.9		81.0
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, Jan.1	56.2		43.6
Revisions in estimated cash flows	(9.2)	[1]	(0.2)	[1]
Liabilities settled	(1.7)		(0.2)
Liabilities incurred	0		2.9
Accretion expense	1.0		1.4
Balance, June 30	46.3		47.5
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, Jan.1	34.9		32.3
Revisions in estimated cash flows	(0.7)	[1]	(0.3)	[1]
Liabilities settled	(0.1)		(0.1)
Liabilities incurred	0		0.8
Accretion expense	0.8		0.8
Balance, June 30	34.9		33.5
Sixth Street [Member] | IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revisions in estimated cash flows	$ 8.2	[1]

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