Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended													12 Months Ended															1 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended										12 Months Ended					8 Months Ended		12 Months Ended			1 Months Ended		12 Months Ended	1 Months Ended					12 Months Ended		1 Months Ended	12 Months Ended										1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Commodity cost recovery [Member]	Dec. 31, 2012 Commodity cost recovery [Member]	Dec. 31, 2013 IPL's electric transmission assets sale [Member]	Dec. 31, 2012 IPL's electric transmission assets sale [Member]	Dec. 31, 2013 Cost of removal obligations [Member]	Dec. 31, 2012 Cost of removal obligations [Member]	Dec. 31, 2013 IPL's tax benefit riders [Member]	Dec. 31, 2012 IPL's tax benefit riders [Member]	Dec. 31, 2013 Other [Member]	Dec. 31, 2012 Other [Member]	Dec. 31, 2012 2012 Test Year Retail Electric Fuel Related Request Final Order [Member]	Dec. 31, 2013 WPL [Member]	Dec. 31, 2012 WPL [Member]	Dec. 31, 2011 WPL [Member]	Dec. 31, 2013 WPL [Member] Commodity cost recovery [Member]	Dec. 31, 2012 WPL [Member] Commodity cost recovery [Member]	Dec. 31, 2013 WPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2012 WPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2013 WPL [Member] Cost of removal obligations [Member]	Dec. 31, 2012 WPL [Member] Cost of removal obligations [Member]	Dec. 31, 2013 WPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2012 WPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 WPL [Member] Other [Member]	Dec. 31, 2012 WPL [Member] Other [Member]	Dec. 31, 2013 WPL [Member] WPL's Edgewater Unit 5 Purchase [Member]	Jan. 31, 2013 WPL [Member] 2013/2014 Test Period Retail Electric And Gas Final Order [Member]	Dec. 31, 2013 WPL [Member] 2013/2014 Test Period Retail Electric And Gas Final Order [Member] WPL's Edgewater Unit 5 Purchase [Member]	Dec. 31, 2013 WPL [Member] 2014 Test Year Retail Electric Fuel Related Request [Member]	Jan. 31, 2013 WPL [Member] 2013 Test Year Retail Electric Fuel Related Request [Member]	Dec. 31, 2013 WPL [Member] 2013 Test Year Retail Electric Fuel Related Request [Member]	Sep. 30, 2013 WPL [Member] 2012 Test Year Retail Electric Fuel Related Request Final Order [Member]	Jan. 31, 2012 WPL [Member] 2012 Test Year Retail Electric Fuel Related Request Final Order [Member]	Dec. 31, 2012 WPL [Member] 2012 Test Year Retail Electric Fuel Related Request Final Order [Member]	Dec. 31, 2013 IPL [Member]	Dec. 31, 2012 IPL [Member]	Dec. 31, 2011 IPL [Member]	Dec. 31, 2013 IPL [Member] Commodity cost recovery [Member]	Dec. 31, 2012 IPL [Member] Commodity cost recovery [Member]	Dec. 31, 2013 IPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2012 IPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2013 IPL [Member] Cost of removal obligations [Member]	Dec. 31, 2012 IPL [Member] Cost of removal obligations [Member]	Dec. 31, 2013 IPL [Member] Revenue Requirement Adjustment [Member]	Dec. 31, 2013 IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2012 IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 IPL [Member] Other [Member]	Dec. 31, 2012 IPL [Member] Other [Member]	Feb. 28, 2010 IPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2007 IPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2013 IPL [Member] IPL's electric transmission cost recovery [Member]	Dec. 31, 2010 IPL [Member] IPL's electric transmission cost recovery [Member]	Dec. 31, 2011 IPL [Member] Whispering Willow - East Wind Project [Member] Retail Electric Rate [Member] IPL's electric transmission assets sale [Member]	Jan. 31, 2013 IPL [Member] 2011 Test Year Retail Gas IA, Request [Member]	Jun. 30, 2012 IPL [Member] 2011 Test Year Retail Gas IA, Request [Member]	Dec. 31, 2013 IPL [Member] 2011 Test Year Retail Gas IA, Request [Member]	Nov. 30, 2011 IPL [Member] 2009 Test Year Retail Electric MN, Request [Member]	Jul. 31, 2010 IPL [Member] 2009 Test Year Retail Electric MN, Request [Member]	Nov. 30, 2011 IPL [Member] 2009 Test Year Retail Electric MN, Request [Member] Higher Base Rates [Member]	Nov. 30, 2011 IPL [Member] 2009 Test Year Retail Electric MN, Request [Member] Renewable Energy Rider [Member]	Nov. 30, 2011 IPL [Member] 2009 Test Year Retail Electric MN, Request [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2013 Alliant Energy and IPL [Member] Revenue Requirement Adjustment [Member]	Dec. 31, 2013 Alliant Energy and IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member]	Nov. 30, 2011 Alliant Energy and IPL [Member] Sutherland 4 [Member]	Dec. 31, 2011 Alliant Energy and IPL [Member] Sutherland 4 [Member]	Dec. 31, 2011 Alliant Energy and IPL [Member] 2009 Test Year Retail Electric IA, Final Order [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2012 Alliant Energy and IPL [Member] 2011 Test Year Retail Gas IA, Request [Member]	Dec. 31, 2011 Alliant Energy and IPL [Member] 2009 Test Year Retail Electric MN, Request [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2012 Alliant Energy and WPL [Member] 2013/2014 Test Period Retail Electric And Gas Final Order [Member]	Dec. 31, 2007 SO2 emission allowances [Member] IPL [Member]	Dec. 31, 2012 SO2 emission allowances [Member] Alliant Energy and IPL [Member]	Dec. 31, 2011 SO2 emission allowances [Member] Alliant Energy and IPL [Member]	Dec. 31, 2013 Iowa [Member] IPL [Member] IPL's electric transmission assets sale [Member]	Dec. 31, 2013 Iowa [Member] IPL [Member] IPL's electric transmission assets sale [Member]	Jan. 31, 2014 Subsequent Event [Member] WPL [Member] 2014 Test Year Retail Electric Fuel Related Request [Member]	Dec. 31, 2013 Scenario, Forecast [Member]	Dec. 31, 2013 Scenario, Forecast [Member] WPL [Member]	Dec. 31, 2013 Scenario, Forecast [Member] IPL [Member]	Dec. 31, 2013 Scenario, Forecast [Member] SO2 emission allowances [Member]		Dec. 31, 2013 Scenario, Forecast [Member] SO2 emission allowances [Member] IPL [Member]		Dec. 31, 2013 Electric [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2012 Electric [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2011 Electric [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 Electric [Member] Alliant Energy and IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member]	Dec. 31, 2012 Electric [Member] Alliant Energy and IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member]	Dec. 31, 2011 Electric [Member] Alliant Energy and IPL [Member] IPL's Tax Benefit Rider Decrease In Taxable Income [Member]	Dec. 31, 2014 Electric [Member] Scenario, Forecast [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 Gas [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 Gas [Member] IPL [Member] 2011 Test Year Retail Gas IA, Request [Member] Tax Benefit Rider [Member]	Dec. 31, 2013 Gas [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 Gas [Member] Scenario, Forecast [Member] IPL's tax benefit riders [Member]	Dec. 31, 2013 Electric And Gas [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]	Dec. 31, 2014 Revenue Requirement Adjustment [Member] Scenario, Forecast [Member] Alliant Energy and IPL [Member] IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return															$ 13																						$ 39
Period for simple average of actual costs incurred during test year																																					2 years
Minimum future commitments																																																																								34	34	34				2,583	552	2,028	34	[1]	34	[1]
Increase in regulatory assets	(140.5)	178.1	413.1												(69.1)	49.1	84.3																				(71.4)	129.0	328.8																												2.0				5.0			30.0
Amounts not probable of recovery																																																																										4
Electric production fuel and energy purchases	725.0	712.3	764.5												342.9	367.8	381.4																				382.1	344.5	383.1																																			2.0
Other operation and maintenance	620.7	590.0	630.2												258.4	240.0	255.2																				362.3	350.0	375.0																															5.0				2.0
Expenditure collection period after new rate implementation															5 years
Recovery of direct costs, recovery period																																																					5 years	5 years
Amortization of regulatory asset																																																					8
Ownership interest %																												25.00%		25.00%
Credit to utility other operation and maintenance																																																																			2				5
Regulatory asset impairment charge			9														7																						2
Recovery of direct costs																																																																		2
Recovery of direct costs, recovery period																																																																		25 years
Regulatory liabilities	821.5	916.1		7.5	17.7	21.6	32.5	418.9	408.7	265.4	355.8	40.8	46.3		206.6	214.7		2.0	12.5	0	0	141.2	140.7	0	0	20.0	16.4										614.9	701.4		5.5	5.2	21.6	32.5	277.7	268.0		265.4	355.8	20.8	29.9		89.0	41.0		3.0																														228.9									36.5
Increase (decrease) in regulatory liabilities	(90.8)	16.4	168.3												(8.5)	28.5	12.0																				(82.3)	(12.1)	156.3							(24.0)																						(19.0)		5.0					(8.0)										(79.0)	(83.0)	(61.0)				(85.0)	(11.0)			(12.0)	(90.0)	(15.0)
Income tax expense (benefit)	53.9	89.4	69.2												87.2	94.6	81.9																				(37.9)	(19.8)	(3.6)																										(4.0)																				(46.0)	(48.0)	(36.0)	(33.0)	(35.0)	(25.0)				(7.0)
Gas revenues from rate increase	464.8	396.3	476.7												190.9	169.6	200.4																				273.9	226.7	276.3																														5.0																							(11.0)
Reduction of Iowa retail electric customers' rates																																																			12
Regulatory liability amortization period																																																																												5 years
Authorized increase (decrease) in final rates, amount																													13			29			4																					11			11		8	2	1														19																36
Period after commencement of rate case proceeding																																																										12 months
Gas tax benefit rider term																																																																																													3 years
Authorized increase (decrease) in interim rates, amount																																																									9			14
Authorized increase (decrease) in interim rates, percent																																																									3.00%
Authorized increase (decrease) in final rates, percent																																3.00%																								4.00%																					2.00%
Increase to electric revenues	2,689.0	2,589.3	2,635.8												1,197.2	1,218.2	1,227.5																				1,491.8	1,371.1	1,408.3																									24.0
Annual bandwidth for fuel-related costs																															2.00%		2.00%			2.00%
Over-collection of fuel-related costs														17
Over-collection of fuel-related costs outside of approved range																																				11
Authorized refund to customers, including interest																																		$ 12

[1] Refer to Note 2 for discussion of $34 million of charges recognized by Alliant Energy and IPL in 2011 for forward contracts to purchase SO2 emission allowances.