Income Taxes (Schedule Of Open Tax Years By Major Tax Jurisdiction) (Details)	12 Months Ended
	Dec. 31, 2011
Consolidated Federal Income Tax Returns [Member] | Maximum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[1]
Consolidated Federal Income Tax Returns [Member] | Maximum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[1]
Consolidated Federal Income Tax Returns [Member] | Maximum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[1]
Consolidated Federal Income Tax Returns [Member] | Minimum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[1]
Consolidated Federal Income Tax Returns [Member] | Minimum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[1]
Consolidated Federal Income Tax Returns [Member] | Minimum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[1]
Consolidated Iowa Income Tax Returns [Member] | Maximum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[2]
Consolidated Iowa Income Tax Returns [Member] | Maximum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[2]
Consolidated Iowa Income Tax Returns [Member] | Maximum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010	[2]
Consolidated Iowa Income Tax Returns [Member] | Minimum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[2]
Consolidated Iowa Income Tax Returns [Member] | Minimum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[2]
Consolidated Iowa Income Tax Returns [Member] | Minimum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005	[2]
Wisconsin Income Tax Returns [Member] | Maximum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2008
Wisconsin Income Tax Returns [Member] | Maximum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2008
Wisconsin Income Tax Returns [Member] | Minimum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005
Wisconsin Income Tax Returns [Member] | Minimum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2005
Wisconsin Combined Tax Returns [Member] | Maximum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010
Wisconsin Combined Tax Returns [Member] | Maximum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010
Wisconsin Combined Tax Returns [Member] | Maximum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2010
Wisconsin Combined Tax Returns [Member] | Minimum [Member] | Alliant Energy Corporation [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2009
Wisconsin Combined Tax Returns [Member] | Minimum [Member] | IPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2009
Wisconsin Combined Tax Returns [Member] | Minimum [Member] | WPL [Member]
Income Tax Contingency [Line Items]
Open tax years by major tax jurisdiction	2009

[1] 2005 through 2009 are effectively settled excluding deductions included in Alliant Energy's 2008 and 2009 federal income tax returns for repair expenditures. The statute of limitations for 2005 through 2008 has been extended to Dec. 31, 2012.

[2] 2005 through 2007 are open for federal audit adjustments only.