Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 109.7		$ 101.5
Revisions in estimated cash flows	0		3.4
Liabilities settled	(1.0)		(0.9)
Liabilities incurred	16.5	[1]	0	[1]
Accretion expense	3.3		2.8
Balance, September 30	128.5		106.8
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	47.9		45.5
Revisions in estimated cash flows	0		0.8
Liabilities settled	(0.5)		(0.1)
Liabilities incurred	16.3	[1]	0	[1]
Accretion expense	1.6		1.3
Balance, September 30	65.3		47.5
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	52.4		46.9
Revisions in estimated cash flows	0		2.6
Liabilities settled	(0.5)		(0.8)
Liabilities incurred	0.2	[1]	0	[1]
Accretion expense	1.3		1.2
Balance, September 30	53.4		49.9
Sutherland [Member] | IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred	$ 12.0	[1]

[1] In 2014, IPL recorded AROs of $12.0 million related to its Sutherland Generating Station.