Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt issued	$ 3,348.4		$ 3,149.9
Decrease in accounts receivable - other	(49.2)		61.3		(54.3)
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold	238.0		198.4
Long-term debt issued	1,563.4		1,363.4
Decrease in accounts receivable - other	(55.9)		(0.7)		22.4
IPL [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party	170.0		160.0		160.0
IPL [Member] | March 2012 Through March 2014 [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party	180.0
IPL [Member] | March 2012 Through March 2014 [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party	150.0
IPL and WPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer accounts receivable, financing payment term	5 years
Franklin County Wind Project [Member] | American Recovery and Reinvestment Act of 2009 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reduction to carrying value			62
Decrease in accounts receivable - other	62.4
Senior Debentures [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt issued	1,525.0		1,275.0
Senior Debentures [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt issued	1,525.0		1,275.0
4.7% senior debenture, due 2043 [Member] | Senior Debentures [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt issued	250.0	[1]	0	[1]
4.7% senior debenture, due 2043 [Member] | Senior Debentures [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt issued	$ 250.0	[1]	$ 0	[1]
Whiting Petroleum Corporation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Obligations to pay on tax benefits, percentage	90.00%

[1] In 2013, IPL issued $250.0 million of 4.7% senior debentures due 2043. The proceeds from the issuance were used by IPL to reduce cash proceeds received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $65 million and for general working capital purposes.