Debt (Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Commercial paper:
Amount outstanding	$ 279.4		$ 217.5
Weighted average interest rates	0.20%		0.40%
Weighted average remaining maturity	4 days		11 days
Available credit facility capacity	720.6	[1]	732.5	[1]
IPL [Member]
Commercial paper:
Amount outstanding	0		26.3
Weighted average interest rates			0.40%
Weighted average remaining maturity			2 days
Available credit facility capacity	300.0	[1]	223.7	[1]
WPL [Member]
Commercial paper:
Amount outstanding	183.7		86.6
Weighted average interest rates	0.10%		0.30%
Weighted average remaining maturity	6 days		19 days
Available credit facility capacity	216.3	[1]	313.4	[1]
Long-term debt [Member]
Commercial paper:
Amount outstanding	0	[2]	50.0	[2]
Long-term debt [Member] | IPL [Member]
Commercial paper:
Amount outstanding	0	[2]	50.0	[2]
Long-term debt [Member] | Alliant Energy and IPL [Member]
Commercial paper:
Amount outstanding			$ 50.0

[1] At December 31, 2012, Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt. Refer to Note 9(b) for further discussion of $50.0 million of commercial paper outstanding at December 31, 2012 classified as long-term debt on Alliant Energy’s and IPL’s Consolidated Balance Sheets. Alliant Energy and its subsidiaries did not have any commercial paper classified as long-term debt as of December 31, 2013.

[2] At December 31, 2012, $50.0 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s Consolidated Balance Sheets due to the existence of long-term credit facilities that back-stop this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis.