Summary Of Significant Accounting Policies (Schedule Of Allowance For Doubtful Accounts) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	$ 4.8		$ 4.0
IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	0.7		0.7
WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	1.7		1.8
Customer [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	1.4	[1]	1.3	[1]
Customer [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	0	[1]	0	[1]
Customer [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	1.4	[1]	1.3	[1]
Other [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	3.4		2.7
Other [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	0.7		0.7
Other [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for doubtful accounts	$ 0.3		$ 0.5

[1] Refer to Note 5(a) for discussion of IPL’s allowance for doubtful accounts, which is included in its sales of accounts receivable program.