Asset Retirement Obligations (AROs) (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 101.5		$ 91.1
Revisions in estimated cash flows	3.4	[1]	(9.9)	[1]
Liabilities settled	(0.1)		(1.8)
Liabilities incurred	0		0.7
Accretion expense	1.8		1.8
Balance, June 30	106.6		81.9
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	45.5		56.2
Revisions in estimated cash flows	0.8	[1]	(9.2)	[1]
Liabilities settled	0		(1.7)
Liabilities incurred	0		0
Accretion expense	0.8		1.0
Balance, June 30	47.1		46.3
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	46.9		34.9
Revisions in estimated cash flows	2.6	[1]	(0.7)	[1]
Liabilities settled	(0.1)		(0.1)
Liabilities incurred	0		0
Accretion expense	0.8		0.8
Balance, June 30	50.2		34.9
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.