Valuation And Qualifying Accounts and Reserves (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Provision for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 4.8	[1]	$ 4.0	[1]	$ 4.2	[1]
Charged to Expense	11.7	[1]	13.6	[1]	6.6	[1]
Charged to Other Accounts	4.1	[1],[2]	0.6	[1],[2]	1.2	[1],[2]
Deductions	15.5	[1],[3]	13.4	[1],[3]	8.0	[1],[3]
Ending Balance	5.1	[1]	4.8	[1]	4.0	[1]
Accumulated Provision for Uncollectible Accounts [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	0.7	[1]	0.7	[1]	0.9	[1]
Charged to Expense	11.5	[1]	12.7	[1]	6.4	[1]
Charged to Other Accounts	0	[1],[2]	0	[1],[2]	0	[1],[2]
Deductions	11.8	[1],[3]	12.7	[1],[3]	6.6	[1],[3]
Ending Balance	0.4	[1]	0.7	[1]	0.7	[1]
Accumulated Provision for Uncollectible Accounts [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	1.7		1.8		1.9
Charged to Expense	0		0		0.1
Charged to Other Accounts	4.1	[2]	0.6	[2]	1.2	[2]
Deductions	1.6	[3]	0.7	[3]	1.4	[3]
Ending Balance	4.2		1.7		1.8
Accumulated Provision for Other Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	38.2	[4]	33.4	[4]	25.9	[4]
Charged to Expense	12.5	[4]	23.2	[4]	9.6	[4]
Charged to Other Accounts	0	[2],[4]	0	[2],[4]	0	[2],[4]
Deductions	18.1	[3],[4]	18.4	[3],[4]	2.1	[3],[4]
Ending Balance	32.6	[4]	38.2	[4]	33.4	[4]
Accumulated Provision for Other Reserves [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	18.1	[4]	11.6	[4]	10.2	[4]
Charged to Expense	3.9	[4]	9.3	[4]	2.1	[4]
Charged to Other Accounts	0	[2],[4]	0	[2],[4]	0	[2],[4]
Deductions	11.4	[3],[4]	2.8	[3],[4]	0.7	[3],[4]
Ending Balance	10.6	[4]	18.1	[4]	11.6	[4]
Accumulated Provision for Other Reserves [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	16.2	[4]	13.5	[4]	11.7	[4]
Charged to Expense	2.5	[4]	8.8	[4]	3.1	[4]
Charged to Other Accounts	0	[2],[4]	0	[2],[4]	0	[2],[4]
Deductions	2.4	[3],[4]	6.1	[3],[4]	1.3	[3],[4]
Ending Balance	$ 16.3	[4]	$ 16.2	[4]	$ 13.5	[4]

[1] Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.

[2] Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets.

[3] Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.

[4] Other reserves are largely related to injury and damage claims arising in the ordinary course of business.