Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 109.7		$ 101.5
Liabilities settled	(0.5)		(0.1)
Liabilities incurred	16.5	[1]	0	[1]
Accretion expense	1.0		1.0
Balance, March 31	126.7		102.4
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	47.9		45.5
Liabilities settled	(0.3)		0
Liabilities incurred	16.3	[1]	0	[1]
Accretion expense	0.5		0.5
Balance, March 31	64.4		46.0
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	52.4		46.9
Liabilities settled	(0.2)		(0.1)
Liabilities incurred	0.2	[1]	0	[1]
Accretion expense	0.4		0.4
Balance, March 31	52.8		47.2
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.