Asset Retirement Obligations (AROs) (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 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	(0.9)		(2.6)
Liabilities incurred	0	[2]	16.0	[2]
Accretion expense	2.8		2.6
Balance, September 30	106.8		97.2
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)		(2.5)
Liabilities incurred	0	[2]	0	[2]
Accretion expense	1.3		1.4
Balance, September 30	47.5		45.9
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	(0.8)		(0.1)
Liabilities incurred	0	[2]	7.6	[2]
Accretion expense	1.2		1.2
Balance, September 30	49.9		42.9
Sixth Street [Member] | IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Revisions in estimated cash flows			(8.2)
Franklin County Wind Project [Member] | Resources [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred			8.4
Nelson Dewey [Member] | WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred			$ 7.6

[1] For the nine months ended September 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.

[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 Nelson Dewey.