Valuation And Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Provision for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	$ 5.1	$ 4.8	$ 4.0
Charged to Expense	[1]	8.1	11.7	13.6
Charged to Other Accounts	[1],[2]	3.0	4.1	0.6
Deductions	[1],[3]	11.4	15.5	13.4
Ending Balance	[1]	4.8	5.1	4.8
Accumulated Provision for Uncollectible Accounts [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	0.4	0.7	0.7
Charged to Expense	[1]	8.1	11.5	12.7
Charged to Other Accounts	[1],[2]	0.0	0.0	0.0
Deductions	[1],[3]	7.9	11.8	12.7
Ending Balance	[1]	0.6	0.4	0.7
Accumulated Provision for Uncollectible Accounts [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		4.2	1.7	1.8
Charged to Expense		0.0	0.0	0.0
Charged to Other Accounts	[2]	3.0	4.1	0.6
Deductions	[3]	3.5	1.6	0.7
Ending Balance		3.7	4.2	1.7
Accumulated Provision for Other Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	32.6	38.2	33.4
Charged to Expense	[4]	6.5	12.5	23.2
Charged to Other Accounts	[2],[4]	0.0	0.0	0.0
Deductions	[3],[4]	12.0	18.1	18.4
Ending Balance	[4]	27.1	32.6	38.2
Accumulated Provision for Other Reserves [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	10.6	18.1	11.6
Charged to Expense	[4]	2.1	3.9	9.3
Charged to Other Accounts	[2],[4]	0.0	0.0	0.0
Deductions	[3],[4]	3.3	11.4	2.8
Ending Balance	[4]	9.4	10.6	18.1
Accumulated Provision for Other Reserves [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	16.3	16.2	13.5
Charged to Expense	[4]	0.7	2.5	8.8
Charged to Other Accounts	[2],[4]	0.0	0.0	0.0
Deductions	[3],[4]	5.6	2.4	6.1
Ending Balance	[4]	$ 11.4	$ 16.3	$ 16.2

[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.