Wisconsin Power & Light 10-Q 7 Nov 13 2013 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2013
Document Type	'10-Q
Amendment Flag	'false
Document Period End Date	30-Sep-13
Document Fiscal Year Focus	'2013
Document Fiscal Period Focus	'Q3
Entity Registrant Name	'ALLIANT ENERGY CORP
Entity Central Index Key	'0000352541
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Large Accelerated Filer
Entity Common Stock, Shares Outstanding	110,943,669
IPL [Member]	'
Entity Registrant Name	'INTERSTATE POWER & LIGHT CO
Entity Central Index Key	'0000052485
Entity Filer Category	'Non-accelerated Filer
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]	'
Entity Registrant Name	'WISCONSIN POWER & LIGHT CO
Entity Central Index Key	'0000107832
Entity Filer Category	'Non-accelerated Filer
Entity Common Stock, Shares Outstanding	13,236,601

Condensed_Consolidated_Stateme

Condensed Consolidated Statements Of Income (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Utility:	'	'	'	'
Electric	$798.10	$815.30	$2,043.40	$2,000.30
Gas	39.8	46.8	310.5	263.9
Other	17.4	12.2	52.4	39.7
Non-regulated	11.3	13.3	37.9	39.7
Total operating revenues	866.6	887.6	2,444.20	2,343.60
Utility:	'	'	'	'
Electric production fuel and energy purchases	205.4	221.6	542.5	550.4
Purchased electric capacity	58.6	84	167.6	216.2
Electric transmission service	110.5	94.9	313.8	255.7
Cost of gas sold	14.3	17.7	181.2	141.1
Other operation and maintenance	156.3	144.7	453.7	432.6
Non-regulated operation and maintenance	3.1	3.7	8.4	8.6
Depreciation and amortization	92.1	83.6	277.4	247.4
Taxes other than income taxes	24.9	23.7	74.3	73.5
Total operating expenses	665.2	673.9	2,018.90	1,925.50
Operating income	201.4	213.7	425.3	418.1
Interest expense and other:	'	'	'	'
Interest expense	42.5	38.3	127.6	115.8
Equity income from unconsolidated investments, net	-11.1	-10.4	-32.7	-30.4
Allowance for funds used during construction	-8.5	-5.8	-21.1	-14.4
Interest income and other	-0.6	-0.7	-1.7	-2.4
Total interest expense and other	22.3	21.4	72.1	68.6
Income from continuing operations before income taxes	179.1	192.3	353.2	349.5
Income tax expense (benefit)	17.6	39.3	40.2	83.8
Income from continuing operations, net of tax	161.5	153	313	265.7
Income (loss) from discontinued operations, net of tax	-1.3	1.7	-4.9	-2.3
Net income (loss)	160.2	154.7	308.1	263.4
Preferred dividend requirements of subsidiaries	2.6	4	15.3	11.9
Net income (loss) attributable to common shareowners	157.6	150.7	292.8	251.5
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,783	110,768	110,775	110,747
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,785	110,779	110,780	110,763
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):	'	'	'	'
Income from continuing operations, net of tax (in dollars per share)	$1.43	$1.34	$2.69	$2.29
Income (loss) from discontinued operations, net of tax (in dollars per share)	($0.01)	$0.02	($0.05)	($0.02)
Net income (in dollars per share)	$1.42	$1.36	$2.64	$2.27
Amounts attributable to common shareowners:	'	'	'	'
Income from continuing operations, net of tax	158.9	149	297.7	253.8
Income (loss) from discontinued operations, net of tax	-1.3	1.7	-4.9	-2.3
Net income (loss) attributable to common shareowners	157.6	150.7	292.8	251.5
Dividends declared per common share (in dollars per share)	$0.47	$0.45	$1.41	$1.35
IPL [Member]	'	'	'	'
Utility:	'	'	'	'
Electric	457.6	456.6	1,137.40	1,070.70
Gas	24.6	29.6	180.9	149.2
Other	12.2	11.5	37.4	37.2
Total operating revenues	494.4	497.7	1,355.70	1,257.10
Utility:	'	'	'	'
Electric production fuel and energy purchases	110.9	116.7	282.5	272.8
Purchased electric capacity	42.7	42.1	120.3	119.1
Electric transmission service	80	67.3	226	175.7
Cost of gas sold	9.3	12.9	103.2	80.5
Other operation and maintenance	90.5	86.4	264.2	257.1
Depreciation and amortization	47.6	47.3	142.8	141.1
Taxes other than income taxes	13.4	13	40.9	39.5
Total operating expenses	394.4	385.7	1,179.90	1,085.80
Operating income	100	112	175.8	171.3
Interest expense and other:	'	'	'	'
Interest expense	19.6	19.5	58.9	58.8
Allowance for funds used during construction	-5.8	-2.1	-14.3	-5.3
Interest income and other	0	0	-0.2	-0.2
Total interest expense and other	13.8	17.4	44.4	53.3
Income from continuing operations before income taxes	86.2	94.6	131.4	118
Income tax expense (benefit)	-26.4	-11.9	-37.4	-6.6
Net income (loss)	112.6	106.5	168.8	124.6
Preferred dividend requirements of subsidiaries	2.6	3.2	13.7	9.4
Net income (loss) attributable to common shareowners	110	103.3	155.1	115.2
Amounts attributable to common shareowners:	'	'	'	'
Net income (loss) attributable to common shareowners	110	103.3	155.1	115.2
WPL [Member]	'	'	'	'
Utility:	'	'	'	'
Electric	340.5	358.7	906	929.6
Gas	15.2	17.2	129.6	114.7
Other	5.2	0.7	15	2.5
Total operating revenues	360.9	376.6	1,050.60	1,046.80
Utility:	'	'	'	'
Electric production fuel and energy purchases	94.5	104.9	260	277.6
Purchased electric capacity	15.9	41.9	47.3	97.1
Electric transmission service	30.5	27.6	87.8	80
Cost of gas sold	5	4.8	78	60.6
Other operation and maintenance	65.8	58.3	189.5	175.5
Depreciation and amortization	42.7	35.8	129	104.8
Taxes other than income taxes	10.6	9.9	30.7	31.7
Total operating expenses	265	283.2	822.3	827.3
Operating income	95.9	93.4	228.3	219.5
Interest expense and other:	'	'	'	'
Interest expense	21.2	19.7	63.8	59.6
Equity income from unconsolidated investments, net	-11.1	-10.5	-32.7	-31.2
Allowance for funds used during construction	-2.7	-3.7	-6.8	-9.1
Total interest expense and other	7.4	5.5	24.3	19.3
Income from continuing operations before income taxes	88.5	87.9	204	200.2
Income tax expense (benefit)	27.2	31.2	64.7	75.5
Net income (loss)	61.3	56.7	139.3	124.7
Preferred dividend requirements of subsidiaries	0	0.8	1.6	2.5
Net income (loss) attributable to common shareowners	61.3	55.9	137.7	122.2
Amounts attributable to common shareowners:	'	'	'	'
Net income (loss) attributable to common shareowners	$61.30	$55.90	$137.70	$122.20

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Utility:	'	'
Electric plant in service	$9,228.40	$9,070.70
Gas plant in service	901.4	878.4
Other plant in service	521.6	506.2
Accumulated depreciation	-3,689.30	-3,513
Net plant	6,962.10	6,942.30
Construction work in progress:	'	'
Columbia Energy Center Units 1 and 2 emission controls (WPL)	247.9	130.4
Ottumwa Generating Station Unit 1 emission controls (IPL)	124.8	73.7
George Neal Generating Station Units 3 and 4 emission controls (IPL)	106.6	66.9
Other	222.9	147.8
Other, less accumulated depreciation	21	21.2
Total utility	7,685.30	7,382.30
Non-regulated and other:	'	'
Non-regulated Generation, less accumulated depreciation	251.4	258.6
Alliant Energy Corporate Services, Inc. and other, less accumulated depreciation	204.7	197.1
Total non-regulated and other	456.1	455.7
Total property, plant and equipment	8,141.40	7,838
Current assets:	'	'
Cash and cash equivalents	17.7	21.2
Accounts receivable, less allowance for doubtful accounts:	'	'
Customer	78.1	94.9
Unbilled utility revenues	64.7	81.4
Other	188.6	209.4
Production fuel, at weighted average cost	105.2	103.1
Materials and supplies, at weighted average cost	71.1	63.1
Gas stored underground, at weighted average cost	44.2	37.7
Regulatory assets	60.3	83.5
Deferred income tax assets	131.2	170.2
Other	119	129.8
Total current assets	880.1	994.3
Investments:	'	'
Investment in American Transmission Company LLC	268.3	257
Other	56.4	62
Total investments	324.7	319
Other assets:	'	'
Regulatory assets	1,535.90	1,528.90
Deferred charges and other	99.1	105.3
Total other assets	1,635	1,634.20
Total assets	10,981.20	10,785.50
Common equity:	'	'
Common stock	1.1	1.1
Additional paid-in capital	1,506.90	1,511.20
Retained earnings	1,767.30	1,630.70
Accumulated other comprehensive loss	-0.8	-0.8
Shares in deferred compensation trust - 222,415 and 216,030 shares at a weighted average cost of $34.87 and $33.61 per share	-7.8	-7.3
Total common equity	3,266.70	3,134.90
Cumulative preferred stock (Interstate Power and Light Company)	200	145.1
Noncontrolling interest	1.8	1.8
Total equity	3,468.50	3,281.80
Cumulative preferred stock (Wisconsin Power and Light Company)	0	60
Long-term debt, net (excluding current portion)	3,104.80	3,136.60
Total capitalization	6,573.30	6,478.40
Current liabilities:	'	'
Current maturities of long-term debt	48.4	1.5
Commercial paper	237.3	217.5
Accounts payable	368.7	339.3
Regulatory liabilities	174.9	189.7
Other	223.5	272
Total current liabilities	1,052.80	1,020
Other long-term liabilities and deferred credits:	'	'
Deferred income tax liabilities	2,063.90	1,934.20
Regulatory liabilities	662.7	726.4
Pension and other benefit obligations	356.6	364
Other	271.9	262.5
Total long-term liabilities and deferred credits	3,355.10	3,287.10
Commitments and contingencies (Note 12)	'	'
Total capitalization and liabilities	10,981.20	10,785.50
IPL [Member]	'	'
Utility:	'	'
Electric plant in service	4,902.30	4,815.20
Gas plant in service	451.8	441.4
Other plant in service	299	289.1
Accumulated depreciation	-2,014.30	-1,930.70
Net plant	3,638.80	3,615
Construction work in progress:	'	'
Ottumwa Generating Station Unit 1 emission controls (IPL)	124.8	73.7
George Neal Generating Station Units 3 and 4 emission controls (IPL)	106.6	66.9
Other	131.5	82.8
Other, less accumulated depreciation	19.8	19.8
Non-regulated and other:	'	'
Total property, plant and equipment	4,021.50	3,858.20
Current assets:	'	'
Cash and cash equivalents	6.3	4.5
Accounts receivable, less allowance for doubtful accounts:	'	'
Customer	130.1	95
Income tax refunds receivable	30	14.9
Production fuel, at weighted average cost	70.6	75.2
Materials and supplies, at weighted average cost	39.6	33.3
Gas stored underground, at weighted average cost	25.3	17.2
Regulatory assets	33.4	47.6
Deferred income tax assets	75.7	79.3
Other	38.9	24.6
Total current assets	449.9	391.6
Investments:	'	'
Total investments	17.9	17.6
Other assets:	'	'
Regulatory assets	1,182.60	1,170.30
Deferred charges and other	21.9	19.3
Total other assets	1,204.50	1,189.60
Total assets	5,693.80	5,457
Common equity:	'	'
Common stock	33.4	33.4
Additional paid-in capital	1,122.90	1,037.80
Retained earnings	507.4	448
Total common equity	1,663.70	1,519.20
Cumulative preferred stock (Interstate Power and Light Company)	200	145.1
Total equity	1,863.70	1,664.30
Long-term debt, net (excluding current portion)	1,336.40	1,359.50
Total capitalization	3,200.10	3,023.80
Current liabilities:	'	'
Current maturities of long-term debt	38.4	0
Commercial paper	0	26.3
Accounts payable	195.1	163.2
Accounts payable to associated companies	53.3	29.3
Regulatory liabilities	116.6	130.1
Other	113.9	119.9
Total current liabilities	517.3	468.8
Other long-term liabilities and deferred credits:	'	'
Deferred income tax liabilities	1,161	1,087.30
Regulatory liabilities	513.8	571.3
Pension and other benefit obligations	120.2	122.9
Other	181.4	182.9
Total long-term liabilities and deferred credits	1,976.40	1,964.40
Commitments and contingencies (Note 12)	'	'
Total capitalization and liabilities	5,693.80	5,457
WPL [Member]	'	'
Utility:	'	'
Electric plant in service	4,326.10	4,255.50
Gas plant in service	449.6	437
Other plant in service	222.6	217.1
Accumulated depreciation	-1,675	-1,582.30
Net plant	3,323.30	3,327.30
Leased Sheboygan Falls Energy Facility, less accumulated amortization	72.4	77
Construction work in progress:	'	'
Columbia Energy Center Units 1 and 2 emission controls (WPL)	247.9	130.4
Other	91.4	65
Other, less accumulated depreciation	1.2	1.4
Non-regulated and other:	'	'
Total property, plant and equipment	3,736.20	3,601.10
Current assets:	'	'
Cash and cash equivalents	6.6	0.7
Accounts receivable, less allowance for doubtful accounts:	'	'
Customer	70.6	83.3
Unbilled utility revenues	64.7	81.4
Other	41.9	48.5
Production fuel, at weighted average cost	34.6	27.9
Materials and supplies, at weighted average cost	29.7	28.5
Gas stored underground, at weighted average cost	18.9	20.5
Regulatory assets	26.9	35.9
Deferred income tax assets	44.9	85.6
Other	49.5	56.4
Total current assets	388.3	468.7
Investments:	'	'
Investment in American Transmission Company LLC	268.3	257
Other	19.2	19.6
Total investments	287.5	276.6
Other assets:	'	'
Regulatory assets	353.3	358.6
Deferred charges and other	51.3	57.6
Total other assets	404.6	416.2
Total assets	4,816.60	4,762.60
Common equity:	'	'
Common stock	66.2	66.2
Additional paid-in capital	959	959.2
Retained earnings	608.1	557.6
Total common equity	1,633.30	1,583
Cumulative preferred stock (Wisconsin Power and Light Company)	0	60
Long-term debt, net (excluding current portion)	1,323.50	1,331.50
Total capitalization	2,956.80	2,974.50
Current liabilities:	'	'
Current maturities of long-term debt	8.5	0
Commercial paper	143.4	86.6
Accounts payable	117.9	126.4
Accounts payable to associated companies	20.8	13.2
Regulatory liabilities	58.3	59.6
Accrued taxes	11.2	28.3
Other	59.2	71.4
Total current liabilities	419.3	385.5
Other long-term liabilities and deferred credits:	'	'
Deferred income tax liabilities	885.4	844.1
Regulatory liabilities	148.9	155.1
Capital lease obligations - Sheboygan Falls Energy Facility	95.7	99.1
Pension and other benefit obligations	156.8	159.7
Other	153.7	144.6
Total long-term liabilities and deferred credits	1,440.50	1,402.60
Commitments and contingencies (Note 12)	'	'
Total capitalization and liabilities	$4,816.60	$4,762.60

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Common stock, par value	$0.01	$0.01
Common stock, shares authorized (in shares)	240,000,000	240,000,000
Common stock, shares outstanding (in shares)	110,943,669	110,987,400
Shares in deferred compensation trust (in shares)	222,415	216,030
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$34.87	$33.61
IPL [Member]	'	'
Common stock, par value	$2.50	$2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]	'	'
Common stock, par value	$5	$5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:	'	'
Net income	$308.10	$263.40
Adjustments to reconcile net income to net cash flows from operating activities:	'	'
Depreciation and amortization	277.4	247.9
Other amortizations	29.1	41.3
Deferred taxes and investment tax credits	92.2	85.6
Equity income from unconsolidated investments, net	-32.7	-30.4
Distributions from equity method investments	26.6	25.7
Other	-14.1	-8.4
Other changes in assets and liabilities:	'	'
Accounts receivable	-12.8	50.9
Sales of accounts receivable	10	-85
Regulatory assets	-14.4	-73.5
Regulatory liabilities	-74.9	5
Deferred income taxes	75.4	90.5
Other	-26.8	-12.7
Net cash flows from operating activities	643.1	600.3
Cash flows used for investing activities:	'	'
Utility construction and acquisition expenditures	-524.4	-412.7
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	-35.9	-106.3
Proceeds from Franklin County wind project cash grant	62.4	0
Other	-15.3	1.3
Net cash flows used for investing activities	-513.2	-517.7
Cash flows from (used for) financing activities:	'	'
Common stock dividends	-156.2	-149.6
Preferred dividends paid by subsidiaries	-8.9	-11.9
Payments to redeem cumulative preferred stock	-211	0
Proceeds from issuance of cumulative preferred stock	200	0
Proceeds from issuance of long-term debt	0	75
Net change in commercial paper	34.8	17.6
Other	7.9	16
Net cash flows from (used for) financing activities	-133.4	-52.9
Net increase (decrease) in cash and cash equivalents	-3.5	29.7
Cash and cash equivalents at beginning of period	21.2	11.4
Cash and cash equivalents at end of period	17.7	41.1
Supplemental cash flows information:	'	'
Interest, net of capitalized interest	128.5	115.6
Income taxes, net of refunds	-9.7	-0.8
Significant non-cash investing and financing activities:	'	'
Accrued capital expenditures	100.5	123.8
IPL [Member]	'	'
Cash flows from operating activities:	'	'
Net income	168.8	124.6
Adjustments to reconcile net income to net cash flows from operating activities:	'	'
Depreciation and amortization	142.8	141.1
Other	1.2	-3.8
Other changes in assets and liabilities:	'	'
Accounts receivable	-53	-2.6
Sales of accounts receivable	10	-85
Regulatory assets	-9.8	-57.7
Regulatory liabilities	-68.3	-27.5
Deferred income taxes	71	88.9
Other	-3	-5.6
Net cash flows from operating activities	259.7	172.4
Cash flows used for investing activities:	'	'
Utility construction and acquisition expenditures	-274.3	-194.6
Other	-15.5	-16.5
Net cash flows used for investing activities	-289.8	-211.1
Cash flows from (used for) financing activities:	'	'
Common stock dividends	-95.7	-91.6
Preferred dividends paid by subsidiaries	-8.3	-9.4
Capital contributions from parent	90	80
Payments to redeem cumulative preferred stock	-150	0
Proceeds from issuance of cumulative preferred stock	200	0
Net change in commercial paper	-11.3	42.9
Other	7.2	20
Net cash flows from (used for) financing activities	31.9	41.9
Net increase (decrease) in cash and cash equivalents	1.8	3.2
Cash and cash equivalents at beginning of period	4.5	2.1
Cash and cash equivalents at end of period	6.3	5.3
Supplemental cash flows information:	'	'
Interest, net of capitalized interest	60.9	58.5
Income taxes, net of refunds	10.7	-11.3
Significant non-cash investing and financing activities:	'	'
Accrued capital expenditures	57.4	69.2
WPL [Member]	'	'
Cash flows from operating activities:	'	'
Net income	139.3	124.7
Adjustments to reconcile net income to net cash flows from operating activities:	'	'
Depreciation and amortization	129	104.8
Other amortizations	21.9	32.7
Deferred taxes and investment tax credits	71.6	89.3
Equity income from unconsolidated investments, net	-32.7	-31.2
Distributions from equity method investments	26.6	25.7
Other	-5.4	-8.9
Other changes in assets and liabilities:	'	'
Accounts receivable	28	9.9
Income tax refunds receivable	3.5	-22.3
Regulatory assets	-4.6	-15.8
Regulatory liabilities	-6.6	32.5
Accrued taxes	-17.1	0.3
Other	2.7	-2.1
Net cash flows from operating activities	356.2	339.6
Cash flows used for investing activities:	'	'
Utility construction and acquisition expenditures	-250.1	-218.1
Other	-2.3	5.6
Net cash flows used for investing activities	-252.4	-212.5
Cash flows from (used for) financing activities:	'	'
Common stock dividends	-87.2	-84.1
Preferred dividends paid by subsidiaries	-0.6	-2.5
Payments to redeem cumulative preferred stock	-61	0
Net change in commercial paper	56.8	-25.7
Other	-5.9	-1.3
Net cash flows from (used for) financing activities	-97.9	-113.6
Net increase (decrease) in cash and cash equivalents	5.9	13.5
Cash and cash equivalents at beginning of period	0.7	2.7
Cash and cash equivalents at end of period	6.6	16.2
Supplemental cash flows information:	'	'
Interest, net of capitalized interest	65.9	63.1
Income taxes, net of refunds	-0.6	7.9
Significant non-cash investing and financing activities:	'	'
Accrued capital expenditures	$39.20	$45

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Summary Of Significant Accounting Policies	'
	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
	(b) Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
	(c) Utility Property, Plant and Equipment -
	Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014.
	The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013.
	The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
	(d) Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member]	'
Summary Of Significant Accounting Policies	'
	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
	(b) Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
	(c) Utility Property, Plant and Equipment -
	Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014.
	The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013.
	The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
	(d) Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member]	'
Summary Of Significant Accounting Policies	'
	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
	(b) Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
	(c) Utility Property, Plant and Equipment -
	Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014.
	The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013.
	The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
	(d) Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

Utility_Rate_Cases

Utility Rate Cases	9 Months Ended
	Sep. 30, 2013
Utility Rate Cases [Line Items]	'
Utility Rate Cases	'
	UTILITY RATE CASES
	WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual base rates for WPL’s retail gas customers of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain customer base rates for its retail electric customers at their current levels through the end of 2014. The order included provisions that require WPL to defer a portion of its earnings if its annual return on common equity exceeds certain levels during 2013 or 2014 and allows WPL to request a change in retail base rates during this period if its annual return on common equity falls below a certain level. As of September 30, 2013, Alliant Energy and WPL did not record any material deferred amounts for these provisions.
	IPL’s Iowa Retail Gas Rate Case (2011 Test Year) - In May 2012, IPL filed a request with the IUB to increase annual rates for its Iowa retail gas customers. IPL’s request included a proposal to reduce customer bills utilizing a gas tax benefit rider over a three-year period by approximately $36 million in aggregate. In conjunction with the filing, IPL implemented an interim retail gas rate increase of $9 million, or approximately 3%, on an annual basis, effective June 4, 2012. In November 2012, the IUB approved a settlement agreement between IPL, the OCA and the Iowa Consumers Coalition related to IPL’s request, resulting in a final increase in annual rates for IPL’s Iowa retail gas customers of $11 million, or approximately 4%, effective January 10, 2013. The parties and the IUB also agreed to IPL’s proposed gas tax benefit rider. Refer to Note 1(b) for additional details on IPL’s gas tax benefit rider.
	IPL’s Iowa Retail Electric Rate Case (2009 Test Year) - In February 2013, the IUB issued an order allowing IPL to recognize a revenue requirement adjustment of $24 million for the year ended December 31, 2013 related to certain tax benefits from tax accounting method changes. The revenue requirement adjustment is recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider. For the three and nine months ended September 30, 2013, Alliant Energy and IPL recognized $7 million and $18 million, respectively, of the revenue requirement adjustment resulting in increases to electric revenues on their Condensed Consolidated Statements of Income.
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - In July 2013, WPL filed a request with the PSCW to increase annual rates for WPL’s retail electric customers by $31 million, or approximately 3%, to reflect anticipated increases in retail fuel-related costs in 2014. WPL currently expects a decision from the PSCW regarding this rate filing by the end of 2013.
	WPL’s Retail Fuel-related Rate Filing (2013 Test Year) - In December 2012, WPL received an order from the PSCW authorizing an annual retail electric rate decrease of $29 million, or approximately 3%, effective January 1, 2013 to reflect anticipated decreases in retail fuel-related costs in 2013 compared to the fuel-related cost estimates used to determine rates for 2012. WPL’s 2013 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. As of September 30, 2013, Alliant Energy and WPL did not record any material amounts for refunds anticipated to be paid to WPL’s retail electric customers.
	WPL’s Retail Fuel-related Rate Filing (2012 Test Year) - Retail fuel-related costs incurred by WPL in 2012 were lower than retail fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs for 2012 of approximately $17 million (including $11 million outside the approved range for 2012 recorded in “Regulatory liabilities” on Alliant Energy’s and WPL’s Condensed Consolidated Balance Sheets as of December 31, 2012). In August 2013, WPL received an order from the PSCW to refund $12 million, including interest, to its retail electric customers for these over-collections, which WPL completed in September 2013.
IPL [Member]	'
Utility Rate Cases [Line Items]	'
Utility Rate Cases	'
	UTILITY RATE CASES
	WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual base rates for WPL’s retail gas customers of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain customer base rates for its retail electric customers at their current levels through the end of 2014. The order included provisions that require WPL to defer a portion of its earnings if its annual return on common equity exceeds certain levels during 2013 or 2014 and allows WPL to request a change in retail base rates during this period if its annual return on common equity falls below a certain level. As of September 30, 2013, Alliant Energy and WPL did not record any material deferred amounts for these provisions.
	IPL’s Iowa Retail Gas Rate Case (2011 Test Year) - In May 2012, IPL filed a request with the IUB to increase annual rates for its Iowa retail gas customers. IPL’s request included a proposal to reduce customer bills utilizing a gas tax benefit rider over a three-year period by approximately $36 million in aggregate. In conjunction with the filing, IPL implemented an interim retail gas rate increase of $9 million, or approximately 3%, on an annual basis, effective June 4, 2012. In November 2012, the IUB approved a settlement agreement between IPL, the OCA and the Iowa Consumers Coalition related to IPL’s request, resulting in a final increase in annual rates for IPL’s Iowa retail gas customers of $11 million, or approximately 4%, effective January 10, 2013. The parties and the IUB also agreed to IPL’s proposed gas tax benefit rider. Refer to Note 1(b) for additional details on IPL’s gas tax benefit rider.
	IPL’s Iowa Retail Electric Rate Case (2009 Test Year) - In February 2013, the IUB issued an order allowing IPL to recognize a revenue requirement adjustment of $24 million for the year ended December 31, 2013 related to certain tax benefits from tax accounting method changes. The revenue requirement adjustment is recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider. For the three and nine months ended September 30, 2013, Alliant Energy and IPL recognized $7 million and $18 million, respectively, of the revenue requirement adjustment resulting in increases to electric revenues on their Condensed Consolidated Statements of Income.
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - In July 2013, WPL filed a request with the PSCW to increase annual rates for WPL’s retail electric customers by $31 million, or approximately 3%, to reflect anticipated increases in retail fuel-related costs in 2014. WPL currently expects a decision from the PSCW regarding this rate filing by the end of 2013.
	WPL’s Retail Fuel-related Rate Filing (2013 Test Year) - In December 2012, WPL received an order from the PSCW authorizing an annual retail electric rate decrease of $29 million, or approximately 3%, effective January 1, 2013 to reflect anticipated decreases in retail fuel-related costs in 2013 compared to the fuel-related cost estimates used to determine rates for 2012. WPL’s 2013 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. As of September 30, 2013, Alliant Energy and WPL did not record any material amounts for refunds anticipated to be paid to WPL’s retail electric customers.
	WPL’s Retail Fuel-related Rate Filing (2012 Test Year) - Retail fuel-related costs incurred by WPL in 2012 were lower than retail fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs for 2012 of approximately $17 million (including $11 million outside the approved range for 2012 recorded in “Regulatory liabilities” on Alliant Energy’s and WPL’s Condensed Consolidated Balance Sheets as of December 31, 2012). In August 2013, WPL received an order from the PSCW to refund $12 million, including interest, to its retail electric customers for these over-collections, which WPL completed in September 2013.
WPL [Member]	'
Utility Rate Cases [Line Items]	'
Utility Rate Cases	'
	UTILITY RATE CASES
	WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual base rates for WPL’s retail gas customers of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain customer base rates for its retail electric customers at their current levels through the end of 2014. The order included provisions that require WPL to defer a portion of its earnings if its annual return on common equity exceeds certain levels during 2013 or 2014 and allows WPL to request a change in retail base rates during this period if its annual return on common equity falls below a certain level. As of September 30, 2013, Alliant Energy and WPL did not record any material deferred amounts for these provisions.
	IPL’s Iowa Retail Gas Rate Case (2011 Test Year) - In May 2012, IPL filed a request with the IUB to increase annual rates for its Iowa retail gas customers. IPL’s request included a proposal to reduce customer bills utilizing a gas tax benefit rider over a three-year period by approximately $36 million in aggregate. In conjunction with the filing, IPL implemented an interim retail gas rate increase of $9 million, or approximately 3%, on an annual basis, effective June 4, 2012. In November 2012, the IUB approved a settlement agreement between IPL, the OCA and the Iowa Consumers Coalition related to IPL’s request, resulting in a final increase in annual rates for IPL’s Iowa retail gas customers of $11 million, or approximately 4%, effective January 10, 2013. The parties and the IUB also agreed to IPL’s proposed gas tax benefit rider. Refer to Note 1(b) for additional details on IPL’s gas tax benefit rider.
	IPL’s Iowa Retail Electric Rate Case (2009 Test Year) - In February 2013, the IUB issued an order allowing IPL to recognize a revenue requirement adjustment of $24 million for the year ended December 31, 2013 related to certain tax benefits from tax accounting method changes. The revenue requirement adjustment is recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider. For the three and nine months ended September 30, 2013, Alliant Energy and IPL recognized $7 million and $18 million, respectively, of the revenue requirement adjustment resulting in increases to electric revenues on their Condensed Consolidated Statements of Income.
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - In July 2013, WPL filed a request with the PSCW to increase annual rates for WPL’s retail electric customers by $31 million, or approximately 3%, to reflect anticipated increases in retail fuel-related costs in 2014. WPL currently expects a decision from the PSCW regarding this rate filing by the end of 2013.
	WPL’s Retail Fuel-related Rate Filing (2013 Test Year) - In December 2012, WPL received an order from the PSCW authorizing an annual retail electric rate decrease of $29 million, or approximately 3%, effective January 1, 2013 to reflect anticipated decreases in retail fuel-related costs in 2013 compared to the fuel-related cost estimates used to determine rates for 2012. WPL’s 2013 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. As of September 30, 2013, Alliant Energy and WPL did not record any material amounts for refunds anticipated to be paid to WPL’s retail electric customers.
	WPL’s Retail Fuel-related Rate Filing (2012 Test Year) - Retail fuel-related costs incurred by WPL in 2012 were lower than retail fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs for 2012 of approximately $17 million (including $11 million outside the approved range for 2012 recorded in “Regulatory liabilities” on Alliant Energy’s and WPL’s Condensed Consolidated Balance Sheets as of December 31, 2012). In August 2013, WPL received an order from the PSCW to refund $12 million, including interest, to its retail electric customers for these over-collections, which WPL completed in September 2013.

Receivables

Receivables	9 Months Ended
	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]	'
Receivables	'
	RECEIVABLES
	(a) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third-party financial institution through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. In exchange for the receivables sold, IPL receives cash proceeds from the third-party financial institution and deferred proceeds recorded in “Accounts receivable” on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
	As of September 30, 2013 and December 31, 2012, IPL sold $229.8 million and $198.4 million aggregate amounts of receivables, respectively. IPL’s maximum and average outstanding cash proceeds, and costs incurred related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$155.00	$150.00	$170.00	$160.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	132.7	95	132.5	124.2
	Costs incurred	0.3	0.4	1	1.1
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		September 30, 2013	December 31, 2012
	Customer accounts receivable	$158.80	$118.20
	Unbilled utility revenues	70.9	77.4
	Other receivables	0.1	2.8
	Receivables sold	229.8	198.4
	Less: cash proceeds (a)	140	130
	Deferred proceeds	89.8	68.4
	Less: allowance for doubtful accounts	2.9	1.6
	Fair value of deferred proceeds	$86.90	$66.80
	Outstanding receivables past due	$22.00	$16.10
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s Condensed Consolidated Statements of Cash Flows.
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Collections reinvested in receivables	$481.10	$522.90	$1,407.40	$1,334.70
	Credit losses, net of recoveries	3.9	3	7.8	7.3
	Refer to Note 8(b) for discussion of IPL’s issuance of $250 million of senior debentures in October 2013. A portion of the proceeds from the issuance was used by IPL to reduce cash proceeds received from the third-party financial institution under its sales of accounts receivable program.
	(b) Franklin County Wind Project Cash Grant - In accordance with the American Recovery and Reinvestment Act of 2009, Alliant Energy filed an application with the U.S. Department of the Treasury in February 2013 requesting a cash grant for a portion of the qualifying project expenditures of the Franklin County wind project that was placed into service in December 2012. In March 2013, Alliant Energy received the proceeds from the cash grant, resulting in a $62.4 million decrease in “Accounts receivable - other” on its Condensed Consolidated Balance Sheets during the nine months ended September 30, 2013. The grant proceeds were used by Alliant Energy to reduce short-term borrowings incurred during the construction of the wind project.
IPL [Member]	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'
Receivables	'
	RECEIVABLES
	(a) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third-party financial institution through wholly-owned and consolidated special purpose entities. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. In exchange for the receivables sold, IPL receives cash proceeds from the third-party financial institution and deferred proceeds recorded in “Accounts receivable” on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
	As of September 30, 2013 and December 31, 2012, IPL sold $229.8 million and $198.4 million aggregate amounts of receivables, respectively. IPL’s maximum and average outstanding cash proceeds, and costs incurred related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$155.00	$150.00	$170.00	$160.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	132.7	95	132.5	124.2
	Costs incurred	0.3	0.4	1	1.1
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		September 30, 2013	December 31, 2012
	Customer accounts receivable	$158.80	$118.20
	Unbilled utility revenues	70.9	77.4
	Other receivables	0.1	2.8
	Receivables sold	229.8	198.4
	Less: cash proceeds (a)	140	130
	Deferred proceeds	89.8	68.4
	Less: allowance for doubtful accounts	2.9	1.6
	Fair value of deferred proceeds	$86.90	$66.80
	Outstanding receivables past due	$22.00	$16.10
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s Condensed Consolidated Statements of Cash Flows.
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Collections reinvested in receivables	$481.10	$522.90	$1,407.40	$1,334.70
	Credit losses, net of recoveries	3.9	3	7.8	7.3
	Refer to Note 8(b) for discussion of IPL’s issuance of $250 million of senior debentures in October 2013. A portion of the proceeds from the issuance was used by IPL to reduce cash proceeds received from the third-party financial institution under its sales of accounts receivable program.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax [Line Items]	'
Income Taxes	'
	INCOME TAXES
	Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 1(b) for additional details of IPL’s tax benefit riders.
	Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences for which deferred tax is not recognized in the income statement pursuant to rate-making principles, substantially all of which relates to IPL. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three and nine months ended September 30, 2013 was repair expenditures at IPL.
	State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business.
	Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2013, Alliant Energy’s and WPL’s current deferred tax assets decreased $39.0 million and $40.7 million, respectively. The decrease in current deferred tax assets reflects a decrease in the estimated amount of net operating losses expected to be utilized in the next 12 months primarily due to the extension of bonus depreciation deductions in the first quarter of 2013 with the enactment of the ATR Act in January 2013.
	For the nine months ended September 30, 2013, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $129.7 million, $73.7 million and $41.3 million, respectively. These increases were primarily due to property-related differences resulting from bonus depreciation deductions and the effect of rate-making on property-related differences recorded during the nine months ended September 30, 2013. Alliant Energy’s and WPL’s increases were partially offset by the decrease of certain deferred tax assets discussed above, which decreased Alliant Energy’s and WPL’s non-current deferred tax liabilities.
	Carryforwards - At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172
	Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of September 30, 2013, Alliant Energy, IPL and WPL do not expect to have material changes to their unrecognized tax benefits during the next 12 months.
IPL [Member]	'
Income Tax [Line Items]	'
Income Taxes	'
	INCOME TAXES
	Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 1(b) for additional details of IPL’s tax benefit riders.
	Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences for which deferred tax is not recognized in the income statement pursuant to rate-making principles, substantially all of which relates to IPL. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three and nine months ended September 30, 2013 was repair expenditures at IPL.
	State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business.
	Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2013, Alliant Energy’s and WPL’s current deferred tax assets decreased $39.0 million and $40.7 million, respectively. The decrease in current deferred tax assets reflects a decrease in the estimated amount of net operating losses expected to be utilized in the next 12 months primarily due to the extension of bonus depreciation deductions in the first quarter of 2013 with the enactment of the ATR Act in January 2013.
	For the nine months ended September 30, 2013, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $129.7 million, $73.7 million and $41.3 million, respectively. These increases were primarily due to property-related differences resulting from bonus depreciation deductions and the effect of rate-making on property-related differences recorded during the nine months ended September 30, 2013. Alliant Energy’s and WPL’s increases were partially offset by the decrease of certain deferred tax assets discussed above, which decreased Alliant Energy’s and WPL’s non-current deferred tax liabilities.
	Carryforwards - At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172
	Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of September 30, 2013, Alliant Energy, IPL and WPL do not expect to have material changes to their unrecognized tax benefits during the next 12 months.
WPL [Member]	'
Income Tax [Line Items]	'
Income Taxes	'
	INCOME TAXES
	Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 1(b) for additional details of IPL’s tax benefit riders.
	Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences for which deferred tax is not recognized in the income statement pursuant to rate-making principles, substantially all of which relates to IPL. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three and nine months ended September 30, 2013 was repair expenditures at IPL.
	State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business.
	Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2013, Alliant Energy’s and WPL’s current deferred tax assets decreased $39.0 million and $40.7 million, respectively. The decrease in current deferred tax assets reflects a decrease in the estimated amount of net operating losses expected to be utilized in the next 12 months primarily due to the extension of bonus depreciation deductions in the first quarter of 2013 with the enactment of the ATR Act in January 2013.
	For the nine months ended September 30, 2013, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $129.7 million, $73.7 million and $41.3 million, respectively. These increases were primarily due to property-related differences resulting from bonus depreciation deductions and the effect of rate-making on property-related differences recorded during the nine months ended September 30, 2013. Alliant Energy’s and WPL’s increases were partially offset by the decrease of certain deferred tax assets discussed above, which decreased Alliant Energy’s and WPL’s non-current deferred tax liabilities.
	Carryforwards - At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172
	Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of September 30, 2013, Alliant Energy, IPL and WPL do not expect to have material changes to their unrecognized tax benefits during the next 12 months.

Benefit_Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2013
Benefit Plans	'
	BENEFIT PLANS
	(a) Pension and Other Postretirement Benefits Plans -
	Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
	Corporate Services provides services to IPL and WPL and, as a result, IPL and WPL are allocated pension and other postretirement benefits costs (credits) associated with Corporate Services employees. The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
	Estimated Future and Actual Employer Contributions - Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
	Cash Balance Plan - Refer to Note 12(c) for discussion of a class-action lawsuit filed against the Cash Balance Plan in 2008.
	401(k) Savings Plans - A significant number of Alliant Energy, IPL and WPL employees participate in defined contribution retirement plans (401(k) savings plans). For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
	(b) Equity-based Compensation Plans - A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7
	As of September 30, 2013, total unrecognized compensation cost related to share-based compensation awards was $7.2 million, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Utility - Other operation and maintenance” in the Condensed Consolidated Statements of Income.
	Performance Shares and Units - Alliant Energy assumes it will make future payouts of its performance shares and units in cash; therefore, performance shares and units are accounted for as liability awards.
	Performance Shares - A summary of the performance shares activity was as follows:
		2013			2012
		Shares (a)			Shares (a)
	Nonvested shares, January 1	145,277			236,979
	Granted	49,093			45,612
	Vested (b)	(54,430	)		(111,980	)
Forfeited	—			(25,334	)
Nonvested shares, September 30	139,940			145,277
(a)	Share amounts represent the target number of performance shares. Each performance share’s value is based on the price of one share of Alliant Energy’s common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
(b)	In 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). In 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares).
Performance Units - A summary of the performance unit activity was as follows:
	2013			2012
	Units (a)			Units (a)
Nonvested units, January 1	64,969			42,996
Granted	22,201			24,686
Vested (b)	(19,760	)		—
Forfeited	(1,498	)		(878	)
Nonvested units, September 30	65,912			66,804
(a)	Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.
(b)	In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at September 30, 2013 by year of grant were as follows:
	Performance Shares												Performance Units
	2013 Grant				2012 Grant				2011 Grant				2013 Grant			2012 Grant			2011 Grant
Nonvested awards	49,093				45,612				45,235				21,935			23,226			20,751
Alliant Energy common stock closing price on September 30, 2013		$49.55				$49.55				$49.55
Alliant Energy common stock closing price on grant date														$47.58			$43.05			$38.75
Estimated payout percentage based on performance criteria	103		%		100		%		130		%		103		%	100		%	130		%
Fair values of each nonvested award		$51.04				$49.55				$64.42				$49.01			$43.05			$50.38
At September 30, 2013, fair values of nonvested performance shares and units were calculated using a Monte Carlo simulation to determine the anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer groups. Expected volatility was based on historical volatilities using daily stock prices over the past three years. Expected dividend yields were calculated based on the most recent quarterly dividend rates announced prior to the measurement date and stock prices at the measurement date. The risk-free interest rate was based on the three-year U.S. Treasury rate in effect as of the measurement date.
Performance-contingent Restricted Stock - A summary of the performance-contingent restricted stock activity was as follows:
	2013							2012
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	211,651				$32.42			301,738				$32.60
Granted	49,093			47.58				45,612			43.05
Vested (a)	—			—				(65,172	)		32.56
Forfeited (b)	(101,822	)		23.67				(70,527	)		39.93
Nonvested shares, September 30	158,922			42.71				211,651			32.42
(a)	In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.
(b)	In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2013			2012
	Awards			Awards
Nonvested awards, January 1	59,639			46,676
Granted	39,530			36,936
Vested (a)	—			(21,605	)
Forfeited	(1,413	)		(1,533	)
Nonvested awards, September 30	97,756			60,474
(a)	In 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.
IPL [Member]	'
Benefit Plans	'
	BENEFIT PLANS
	(a) Pension and Other Postretirement Benefits Plans -
	Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
	Corporate Services provides services to IPL and WPL and, as a result, IPL and WPL are allocated pension and other postretirement benefits costs (credits) associated with Corporate Services employees. The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
	Estimated Future and Actual Employer Contributions - Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
	Cash Balance Plan - Refer to Note 12(c) for discussion of a class-action lawsuit filed against the Cash Balance Plan in 2008.
	401(k) Savings Plans - A significant number of Alliant Energy, IPL and WPL employees participate in defined contribution retirement plans (401(k) savings plans). For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
	(b) Equity-based Compensation Plans - A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7
	As of September 30, 2013, total unrecognized compensation cost related to share-based compensation awards was $7.2 million, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Utility - Other operation and maintenance” in the Condensed Consolidated Statements of Income.
	Performance Shares and Units - Alliant Energy assumes it will make future payouts of its performance shares and units in cash; therefore, performance shares and units are accounted for as liability awards.
	Performance Shares - A summary of the performance shares activity was as follows:
		2013			2012
		Shares (a)			Shares (a)
	Nonvested shares, January 1	145,277			236,979
	Granted	49,093			45,612
	Vested (b)	(54,430	)		(111,980	)
Forfeited	—			(25,334	)
Nonvested shares, September 30	139,940			145,277
(a)	Share amounts represent the target number of performance shares. Each performance share’s value is based on the price of one share of Alliant Energy’s common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
(b)	In 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). In 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares).
Performance Units - A summary of the performance unit activity was as follows:
	2013			2012
	Units (a)			Units (a)
Nonvested units, January 1	64,969			42,996
Granted	22,201			24,686
Vested (b)	(19,760	)		—
Forfeited	(1,498	)		(878	)
Nonvested units, September 30	65,912			66,804
(a)	Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.
(b)	In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at September 30, 2013 by year of grant were as follows:
	Performance Shares												Performance Units
	2013 Grant				2012 Grant				2011 Grant				2013 Grant			2012 Grant			2011 Grant
Nonvested awards	49,093				45,612				45,235				21,935			23,226			20,751
Alliant Energy common stock closing price on September 30, 2013		$49.55				$49.55				$49.55
Alliant Energy common stock closing price on grant date														$47.58			$43.05			$38.75
Estimated payout percentage based on performance criteria	103		%		100		%		130		%		103		%	100		%	130		%
Fair values of each nonvested award		$51.04				$49.55				$64.42				$49.01			$43.05			$50.38
At September 30, 2013, fair values of nonvested performance shares and units were calculated using a Monte Carlo simulation to determine the anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer groups. Expected volatility was based on historical volatilities using daily stock prices over the past three years. Expected dividend yields were calculated based on the most recent quarterly dividend rates announced prior to the measurement date and stock prices at the measurement date. The risk-free interest rate was based on the three-year U.S. Treasury rate in effect as of the measurement date.
Performance-contingent Restricted Stock - A summary of the performance-contingent restricted stock activity was as follows:
	2013							2012
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	211,651				$32.42			301,738				$32.60
Granted	49,093			47.58				45,612			43.05
Vested (a)	—			—				(65,172	)		32.56
Forfeited (b)	(101,822	)		23.67				(70,527	)		39.93
Nonvested shares, September 30	158,922			42.71				211,651			32.42
(a)	In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.
(b)	In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2013			2012
	Awards			Awards
Nonvested awards, January 1	59,639			46,676
Granted	39,530			36,936
Vested (a)	—			(21,605	)
Forfeited	(1,413	)		(1,533	)
Nonvested awards, September 30	97,756			60,474
(a)	In 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.
WPL [Member]	'
Benefit Plans	'
	BENEFIT PLANS
	(a) Pension and Other Postretirement Benefits Plans -
	Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
	Corporate Services provides services to IPL and WPL and, as a result, IPL and WPL are allocated pension and other postretirement benefits costs (credits) associated with Corporate Services employees. The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
	Estimated Future and Actual Employer Contributions - Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
	Cash Balance Plan - Refer to Note 12(c) for discussion of a class-action lawsuit filed against the Cash Balance Plan in 2008.
	401(k) Savings Plans - A significant number of Alliant Energy, IPL and WPL employees participate in defined contribution retirement plans (401(k) savings plans). For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
	(b) Equity-based Compensation Plans - A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7
	As of September 30, 2013, total unrecognized compensation cost related to share-based compensation awards was $7.2 million, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Utility - Other operation and maintenance” in the Condensed Consolidated Statements of Income.
	Performance Shares and Units - Alliant Energy assumes it will make future payouts of its performance shares and units in cash; therefore, performance shares and units are accounted for as liability awards.
	Performance Shares - A summary of the performance shares activity was as follows:
		2013			2012
		Shares (a)			Shares (a)
	Nonvested shares, January 1	145,277			236,979
	Granted	49,093			45,612
	Vested (b)	(54,430	)		(111,980	)
Forfeited	—			(25,334	)
Nonvested shares, September 30	139,940			145,277
(a)	Share amounts represent the target number of performance shares. Each performance share’s value is based on the price of one share of Alliant Energy’s common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
(b)	In 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). In 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares).
Performance Units - A summary of the performance unit activity was as follows:
	2013			2012
	Units (a)			Units (a)
Nonvested units, January 1	64,969			42,996
Granted	22,201			24,686
Vested (b)	(19,760	)		—
Forfeited	(1,498	)		(878	)
Nonvested units, September 30	65,912			66,804
(a)	Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.
(b)	In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at September 30, 2013 by year of grant were as follows:
	Performance Shares												Performance Units
	2013 Grant				2012 Grant				2011 Grant				2013 Grant			2012 Grant			2011 Grant
Nonvested awards	49,093				45,612				45,235				21,935			23,226			20,751
Alliant Energy common stock closing price on September 30, 2013		$49.55				$49.55				$49.55
Alliant Energy common stock closing price on grant date														$47.58			$43.05			$38.75
Estimated payout percentage based on performance criteria	103		%		100		%		130		%		103		%	100		%	130		%
Fair values of each nonvested award		$51.04				$49.55				$64.42				$49.01			$43.05			$50.38
At September 30, 2013, fair values of nonvested performance shares and units were calculated using a Monte Carlo simulation to determine the anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer groups. Expected volatility was based on historical volatilities using daily stock prices over the past three years. Expected dividend yields were calculated based on the most recent quarterly dividend rates announced prior to the measurement date and stock prices at the measurement date. The risk-free interest rate was based on the three-year U.S. Treasury rate in effect as of the measurement date.
Performance-contingent Restricted Stock - A summary of the performance-contingent restricted stock activity was as follows:
	2013							2012
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	211,651				$32.42			301,738				$32.60
Granted	49,093			47.58				45,612			43.05
Vested (a)	—			—				(65,172	)		32.56
Forfeited (b)	(101,822	)		23.67				(70,527	)		39.93
Nonvested shares, September 30	158,922			42.71				211,651			32.42
(a)	In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.
(b)	In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2013			2012
	Awards			Awards
Nonvested awards, January 1	59,639			46,676
Granted	39,530			36,936
Vested (a)	—			(21,605	)
Forfeited	(1,413	)		(1,533	)
Nonvested awards, September 30	97,756			60,474
(a)	In 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.

Common_Equity

Common Equity	9 Months Ended
	Sep. 30, 2013
Common Equity [Line Items]	'
Common Equity	'
	COMMON EQUITY
	Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
	Shares outstanding, January 1, 2013	110,987,400
	Equity-based compensation plans (Note 5(b))	(23,374	)
	Other	(20,357	)
	Shares outstanding, September 30, 2013	110,943,669
	Dividend Restrictions - As of September 30, 2013, IPL’s amount of retained earnings that were free of dividend restrictions was $507 million. As of September 30, 2013, WPL’s amount of retained earnings that were free of dividend restrictions was $32 million for the remainder of 2013.
	Restricted Net Assets of Subsidiaries - As of September 30, 2013, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.2 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the nine months ended September 30, 2013, IPL received capital contributions of $90.0 million from its parent company. For the nine months ended September 30, 2013, IPL and WPL each paid common stock dividends of $95.7 million and $87.2 million, respectively, to its parent company.
IPL [Member]	'
Common Equity [Line Items]	'
Common Equity	'
	COMMON EQUITY
	Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
	Shares outstanding, January 1, 2013	110,987,400
	Equity-based compensation plans (Note 5(b))	(23,374	)
	Other	(20,357	)
	Shares outstanding, September 30, 2013	110,943,669
	Dividend Restrictions - As of September 30, 2013, IPL’s amount of retained earnings that were free of dividend restrictions was $507 million. As of September 30, 2013, WPL’s amount of retained earnings that were free of dividend restrictions was $32 million for the remainder of 2013.
	Restricted Net Assets of Subsidiaries - As of September 30, 2013, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.2 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the nine months ended September 30, 2013, IPL received capital contributions of $90.0 million from its parent company. For the nine months ended September 30, 2013, IPL and WPL each paid common stock dividends of $95.7 million and $87.2 million, respectively, to its parent company.
WPL [Member]	'
Common Equity [Line Items]	'
Common Equity	'
	COMMON EQUITY
	Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
	Shares outstanding, January 1, 2013	110,987,400
	Equity-based compensation plans (Note 5(b))	(23,374	)
	Other	(20,357	)
	Shares outstanding, September 30, 2013	110,943,669
	Dividend Restrictions - As of September 30, 2013, IPL’s amount of retained earnings that were free of dividend restrictions was $507 million. As of September 30, 2013, WPL’s amount of retained earnings that were free of dividend restrictions was $32 million for the remainder of 2013.
	Restricted Net Assets of Subsidiaries - As of September 30, 2013, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.2 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the nine months ended September 30, 2013, IPL received capital contributions of $90.0 million from its parent company. For the nine months ended September 30, 2013, IPL and WPL each paid common stock dividends of $95.7 million and $87.2 million, respectively, to its parent company.

Redeemable_Preferred_Stock

Redeemable Preferred Stock	9 Months Ended
	Sep. 30, 2013
Redeemable Preferred Stock	'
	REDEEMABLE PREFERRED STOCK
	IPL - In March 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million. The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of “Additional paid-in capital” on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets during the nine months ended September 30, 2013. On or after March 15, 2018, IPL may, at its option, redeem the 5.1% cumulative preferred stock for cash at a redemption price of $25 per share plus accrued and unpaid dividends up to the redemption date.
	The articles of incorporation of IPL contain a provision that grants the holders of its 5.1% cumulative preferred stock voting rights to elect two members of IPL’s Board of Directors if preferred dividends equal to six or more quarterly dividend requirements (whether or not consecutive) are in arrears. Such voting rights would not provide the holders of IPL’s preferred stock control of the decision on redemption of IPL’s preferred stock and could not force IPL to exercise its call option. Therefore, IPL’s 5.1% cumulative preferred stock is presented in total equity on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets in a manner consistent with noncontrolling interests.
	In March 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	WPL - In March 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and WPL recorded a $1 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	Refer to Note 10 for information on the fair value of cumulative preferred stock.
IPL [Member]	'
Redeemable Preferred Stock	'
	REDEEMABLE PREFERRED STOCK
	IPL - In March 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million. The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of “Additional paid-in capital” on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets during the nine months ended September 30, 2013. On or after March 15, 2018, IPL may, at its option, redeem the 5.1% cumulative preferred stock for cash at a redemption price of $25 per share plus accrued and unpaid dividends up to the redemption date.
	The articles of incorporation of IPL contain a provision that grants the holders of its 5.1% cumulative preferred stock voting rights to elect two members of IPL’s Board of Directors if preferred dividends equal to six or more quarterly dividend requirements (whether or not consecutive) are in arrears. Such voting rights would not provide the holders of IPL’s preferred stock control of the decision on redemption of IPL’s preferred stock and could not force IPL to exercise its call option. Therefore, IPL’s 5.1% cumulative preferred stock is presented in total equity on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets in a manner consistent with noncontrolling interests.
	In March 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	WPL - In March 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and WPL recorded a $1 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	Refer to Note 10 for information on the fair value of cumulative preferred stock.
WPL [Member]	'
Redeemable Preferred Stock	'
	REDEEMABLE PREFERRED STOCK
	IPL - In March 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million. The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of “Additional paid-in capital” on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets during the nine months ended September 30, 2013. On or after March 15, 2018, IPL may, at its option, redeem the 5.1% cumulative preferred stock for cash at a redemption price of $25 per share plus accrued and unpaid dividends up to the redemption date.
	The articles of incorporation of IPL contain a provision that grants the holders of its 5.1% cumulative preferred stock voting rights to elect two members of IPL’s Board of Directors if preferred dividends equal to six or more quarterly dividend requirements (whether or not consecutive) are in arrears. Such voting rights would not provide the holders of IPL’s preferred stock control of the decision on redemption of IPL’s preferred stock and could not force IPL to exercise its call option. Therefore, IPL’s 5.1% cumulative preferred stock is presented in total equity on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets in a manner consistent with noncontrolling interests.
	In March 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	WPL - In March 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and WPL recorded a $1 million charge during the nine months ended September 30, 2013 related to this transaction in “Preferred dividend requirements” in their Condensed Consolidated Statements of Income.
	Refer to Note 10 for information on the fair value of cumulative preferred stock.

Debt

Debt	9 Months Ended
	Sep. 30, 2013
Debt Instrument [Line Items]	'
Debt	'
	DEBT
	(a) Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
	(b) Long-term Debt - As of September 30, 2013, $65 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s Condensed 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. As of September 30, 2013, this commercial paper balance had a remaining maturity of 2 days and a 0.25% interest rate.
	In October 2013, IPL issued $250 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 receivables program, reduce commercial paper classified as long-term debt and for general working capital purposes.
IPL [Member]	'
Debt Instrument [Line Items]	'
Debt	'
	DEBT
	(a) Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
	(b) Long-term Debt - As of September 30, 2013, $65 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s Condensed 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. As of September 30, 2013, this commercial paper balance had a remaining maturity of 2 days and a 0.25% interest rate.
	In October 2013, IPL issued $250 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 receivables program, reduce commercial paper classified as long-term debt and for general working capital purposes.
WPL [Member]	'
Debt Instrument [Line Items]	'
Debt	'
	DEBT
	(a) Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.

Investments

Investments	9 Months Ended
	Sep. 30, 2013
Schedule of Equity Method Investments [Line Items]	'
Investments	'
	INVESTMENTS
	Unconsolidated Equity Investments - Equity (income) loss from Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy												WPL
		Three Months						Nine Months						Three Months						Nine Months
		2013			2012			2013			2012			2013			2012			2013			2012
	ATC		($10.8	)		($10.4	)		($31.7	)		($30.6	)		($10.8	)		($10.4	)		($31.7	)		($30.6	)
	Other	(0.3		)	—			(1.0		)	0.2			(0.3		)	(0.1		)	(1.0		)	(0.6		)
			($11.1	)		($10.4	)		($32.7	)		($30.4	)		($11.1	)		($10.5	)		($32.7	)		($31.2	)
	Summary financial information from the unaudited financial statements of ATC for the three and nine months ended September 30 was as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013			2012
	Operating revenues		$160.40			$150.30			$464.30			$450.10
	Operating income	82.9			81.5			247.1			240
	Net income	62.7			60.5			184.5			177.9
WPL [Member]	'
Schedule of Equity Method Investments [Line Items]	'
Investments	'
	INVESTMENTS
	Unconsolidated Equity Investments - Equity (income) loss from Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy												WPL
		Three Months						Nine Months						Three Months						Nine Months
		2013			2012			2013			2012			2013			2012			2013			2012
	ATC		($10.8	)		($10.4	)		($31.7	)		($30.6	)		($10.8	)		($10.4	)		($31.7	)		($30.6	)
	Other	(0.3		)	—			(1.0		)	0.2			(0.3		)	(0.1		)	(1.0		)	(0.6		)
			($11.1	)		($10.4	)		($32.7	)		($30.4	)		($11.1	)		($10.5	)		($32.7	)		($31.2	)
	Summary financial information from the unaudited financial statements of ATC for the three and nine months ended September 30 was as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013			2012
	Operating revenues		$160.40			$150.30			$464.30			$450.10
	Operating income	82.9			81.5			247.1			240
	Net income	62.7			60.5			184.5			177.9

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2013
Fair Value Measurements	'
	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of Alliant Energy’s, IPL’s and WPL’s current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
	Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows:
	Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. As of September 30, 2013, Level 1 items included IPL’s 5.1% cumulative preferred stock. As of December 31, 2012, Level 1 items included IPL’s 8.375% cumulative preferred stock and WPL’s 4.50% cumulative preferred stock.
	Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. As of September 30, 2013 and December 31, 2012, Level 2 items included certain of IPL’s and WPL’s non-exchange traded commodity contracts and substantially all of the long-term debt instruments. Level 2 items as of December 31, 2012 also included the remainder of WPL’s cumulative preferred stock.
	Level 3 - Pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. As of September 30, 2013 and December 31, 2012, Level 3 items included IPL’s deferred proceeds, and IPL’s and WPL’s FTRs and certain non-exchange traded commodity contracts.
	The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and maintain risk policies that govern the use of such derivative instruments. As of September 30, 2013 and December 31, 2012, Alliant Energy’s, IPL’s and WPL’s derivative instruments were not designated as hedging instruments and included the following:
	Risk management purpose	Type of instrument
	Mitigate pricing volatility for:
	Electricity purchased to supply customers	Electric swap and physical purchase contracts (IPL and WPL)
	Fuel used to supply natural gas-fired electric generating facilities	Natural gas swap and physical purchase contracts (IPL and WPL)
		Natural gas options (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical purchase contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired generating facilities	Coal physical purchase contract with volumetric optionality (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical purchase and sale contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	IPL’s and WPL’s swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. IPL and WPL corroborated a portion of these indicative price quotations using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. IPL’s and WPL’s commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. IPL’s and WPL’s swap, option and physical forward commodity contracts were predominately at liquid trading points. IPL’s and WPL’s FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	Level 3 inputs include observable and unobservable inputs used in the fair value measurements of IPL’s and WPL’s commodity contracts. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of IPL’s and WPL’s commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement.
	Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of receivables program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 3(a) for additional information regarding deferred proceeds.
	Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 8(b) for additional information regarding long-term debt.
	Cumulative preferred stock - As of September 30, 2013, the fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the NYSE. As of December 31, 2012, the fair value of IPL’s 8.375% cumulative preferred stock was based on its closing market price quoted by the NYSE, the fair value of WPL’s 4.50% cumulative preferred stock was based on the closing market price quoted by the NYSE Amex LLC, and the fair value of WPL’s remaining preferred stock was calculated based on the market yield of similar securities. Refer to Note 7 for additional information regarding cumulative preferred stock.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
WPL	September 30, 2013										December 31, 2012
	Fair			Level			Level		Level		Fair		Level		Level		Level
	Value			1			2		3		Value		1		2		3
Assets:
Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
Capitalization and liabilities:
Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Alliant Energy, IPL and WPL generally record gains and losses from IPL’s and WPL’s derivative instruments with offsets to regulatory assets or regulatory liabilities, based on their fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities on the Condensed Consolidated Balance Sheets.
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
Transfers out of Level 3 (c)	—			9.3			—		—
Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
Purchases	50.9			35.8			—		—
Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
Transfers into Level 3 (b)	(0.1		)	—			—		—
Transfers out of Level 3 (c)	—			7.4			—		—
Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
Transfers into Level 3 (b)	—			(1.1		)	—		—
Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
Purchases	46.1			26.8			—		—
Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended September 30	2013			2012
Beginning balance, July 1		$1.90			$4.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
Transfers into Level 3 (b)	(9.8		)	(0.4		)
Transfers out of Level 3 (c)	—			1.9
Settlements	(1.6		)	(2.0		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Nine Months Ended September 30	2013			2012
Beginning balance, January 1		($0.6	)		($5.2	)
Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
Transfers into Level 3 (b)	(0.4		)	(0.6		)
Transfers out of Level 3 (c)	1			5.9
Purchases	4.8			9
Settlements	(6.4		)	(3.5		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Commodity Contracts - As of September 30, 2013, the fair value of Alliant Energy’s, IPL’s and WPL’s electric, natural gas and coal commodity contracts categorized as Level 3, excluding FTRs, were recognized as net derivative liabilities of $12.5 million, net derivative assets of $1.5 million and net derivative liabilities of $14.0 million, respectively. As of September 30, 2013, Alliant Energy’s, IPL’s and WPL’s FTRs classified as Level 3 were recognized as net derivative assets of $29.7 million, $27.1 million and $2.6 million, respectively.
IPL [Member]	'
Fair Value Measurements	'
	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of Alliant Energy’s, IPL’s and WPL’s current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
	Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows:
	Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. As of September 30, 2013, Level 1 items included IPL’s 5.1% cumulative preferred stock. As of December 31, 2012, Level 1 items included IPL’s 8.375% cumulative preferred stock and WPL’s 4.50% cumulative preferred stock.
	Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. As of September 30, 2013 and December 31, 2012, Level 2 items included certain of IPL’s and WPL’s non-exchange traded commodity contracts and substantially all of the long-term debt instruments. Level 2 items as of December 31, 2012 also included the remainder of WPL’s cumulative preferred stock.
	Level 3 - Pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. As of September 30, 2013 and December 31, 2012, Level 3 items included IPL’s deferred proceeds, and IPL’s and WPL’s FTRs and certain non-exchange traded commodity contracts.
	The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and maintain risk policies that govern the use of such derivative instruments. As of September 30, 2013 and December 31, 2012, Alliant Energy’s, IPL’s and WPL’s derivative instruments were not designated as hedging instruments and included the following:
	Risk management purpose	Type of instrument
	Mitigate pricing volatility for:
	Electricity purchased to supply customers	Electric swap and physical purchase contracts (IPL and WPL)
	Fuel used to supply natural gas-fired electric generating facilities	Natural gas swap and physical purchase contracts (IPL and WPL)
		Natural gas options (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical purchase contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired generating facilities	Coal physical purchase contract with volumetric optionality (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical purchase and sale contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	IPL’s and WPL’s swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. IPL and WPL corroborated a portion of these indicative price quotations using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. IPL’s and WPL’s commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. IPL’s and WPL’s swap, option and physical forward commodity contracts were predominately at liquid trading points. IPL’s and WPL’s FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	Level 3 inputs include observable and unobservable inputs used in the fair value measurements of IPL’s and WPL’s commodity contracts. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of IPL’s and WPL’s commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement.
	Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of receivables program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 3(a) for additional information regarding deferred proceeds.
	Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 8(b) for additional information regarding long-term debt.
	Cumulative preferred stock - As of September 30, 2013, the fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the NYSE. As of December 31, 2012, the fair value of IPL’s 8.375% cumulative preferred stock was based on its closing market price quoted by the NYSE, the fair value of WPL’s 4.50% cumulative preferred stock was based on the closing market price quoted by the NYSE Amex LLC, and the fair value of WPL’s remaining preferred stock was calculated based on the market yield of similar securities. Refer to Note 7 for additional information regarding cumulative preferred stock.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
WPL	September 30, 2013										December 31, 2012
	Fair			Level			Level		Level		Fair		Level		Level		Level
	Value			1			2		3		Value		1		2		3
Assets:
Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
Capitalization and liabilities:
Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Alliant Energy, IPL and WPL generally record gains and losses from IPL’s and WPL’s derivative instruments with offsets to regulatory assets or regulatory liabilities, based on their fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities on the Condensed Consolidated Balance Sheets.
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
Transfers out of Level 3 (c)	—			9.3			—		—
Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
Purchases	50.9			35.8			—		—
Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
Transfers into Level 3 (b)	(0.1		)	—			—		—
Transfers out of Level 3 (c)	—			7.4			—		—
Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
Transfers into Level 3 (b)	—			(1.1		)	—		—
Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
Purchases	46.1			26.8			—		—
Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended September 30	2013			2012
Beginning balance, July 1		$1.90			$4.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
Transfers into Level 3 (b)	(9.8		)	(0.4		)
Transfers out of Level 3 (c)	—			1.9
Settlements	(1.6		)	(2.0		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Nine Months Ended September 30	2013			2012
Beginning balance, January 1		($0.6	)		($5.2	)
Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
Transfers into Level 3 (b)	(0.4		)	(0.6		)
Transfers out of Level 3 (c)	1			5.9
Purchases	4.8			9
Settlements	(6.4		)	(3.5		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Commodity Contracts - As of September 30, 2013, the fair value of Alliant Energy’s, IPL’s and WPL’s electric, natural gas and coal commodity contracts categorized as Level 3, excluding FTRs, were recognized as net derivative liabilities of $12.5 million, net derivative assets of $1.5 million and net derivative liabilities of $14.0 million, respectively. As of September 30, 2013, Alliant Energy’s, IPL’s and WPL’s FTRs classified as Level 3 were recognized as net derivative assets of $29.7 million, $27.1 million and $2.6 million, respectively.
WPL [Member]	'
Fair Value Measurements	'
	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of Alliant Energy’s, IPL’s and WPL’s current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
	Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows:
	Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. As of September 30, 2013, Level 1 items included IPL’s 5.1% cumulative preferred stock. As of December 31, 2012, Level 1 items included IPL’s 8.375% cumulative preferred stock and WPL’s 4.50% cumulative preferred stock.
	Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. As of September 30, 2013 and December 31, 2012, Level 2 items included certain of IPL’s and WPL’s non-exchange traded commodity contracts and substantially all of the long-term debt instruments. Level 2 items as of December 31, 2012 also included the remainder of WPL’s cumulative preferred stock.
	Level 3 - Pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. As of September 30, 2013 and December 31, 2012, Level 3 items included IPL’s deferred proceeds, and IPL’s and WPL’s FTRs and certain non-exchange traded commodity contracts.
	The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and maintain risk policies that govern the use of such derivative instruments. As of September 30, 2013 and December 31, 2012, Alliant Energy’s, IPL’s and WPL’s derivative instruments were not designated as hedging instruments and included the following:
	Risk management purpose	Type of instrument
	Mitigate pricing volatility for:
	Electricity purchased to supply customers	Electric swap and physical purchase contracts (IPL and WPL)
	Fuel used to supply natural gas-fired electric generating facilities	Natural gas swap and physical purchase contracts (IPL and WPL)
		Natural gas options (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical purchase contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired generating facilities	Coal physical purchase contract with volumetric optionality (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical purchase and sale contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	IPL’s and WPL’s swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. IPL and WPL corroborated a portion of these indicative price quotations using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. IPL’s and WPL’s commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. IPL’s and WPL’s swap, option and physical forward commodity contracts were predominately at liquid trading points. IPL’s and WPL’s FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	Level 3 inputs include observable and unobservable inputs used in the fair value measurements of IPL’s and WPL’s commodity contracts. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of IPL’s and WPL’s commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement.
	Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of receivables program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 3(a) for additional information regarding deferred proceeds.
	Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 8(b) for additional information regarding long-term debt.
	Cumulative preferred stock - As of September 30, 2013, the fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the NYSE. As of December 31, 2012, the fair value of IPL’s 8.375% cumulative preferred stock was based on its closing market price quoted by the NYSE, the fair value of WPL’s 4.50% cumulative preferred stock was based on the closing market price quoted by the NYSE Amex LLC, and the fair value of WPL’s remaining preferred stock was calculated based on the market yield of similar securities. Refer to Note 7 for additional information regarding cumulative preferred stock.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
WPL	September 30, 2013										December 31, 2012
	Fair			Level			Level		Level		Fair		Level		Level		Level
	Value			1			2		3		Value		1		2		3
Assets:
Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
Capitalization and liabilities:
Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Alliant Energy, IPL and WPL generally record gains and losses from IPL’s and WPL’s derivative instruments with offsets to regulatory assets or regulatory liabilities, based on their fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities on the Condensed Consolidated Balance Sheets.
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
Transfers out of Level 3 (c)	—			9.3			—		—
Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
Purchases	50.9			35.8			—		—
Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended September 30	2013			2012			2013		2012
Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
Transfers into Level 3 (b)	(0.1		)	—			—		—
Transfers out of Level 3 (c)	—			7.4			—		—
Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Nine Months Ended September 30	2013			2012			2013		2012
Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
Transfers into Level 3 (b)	—			(1.1		)	—		—
Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
Purchases	46.1			26.8			—		—
Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended September 30	2013			2012
Beginning balance, July 1		$1.90			$4.70
Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
Transfers into Level 3 (b)	(9.8		)	(0.4		)
Transfers out of Level 3 (c)	—			1.9
Settlements	(1.6		)	(2.0		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Nine Months Ended September 30	2013			2012
Beginning balance, January 1		($0.6	)		($5.2	)
Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
Transfers into Level 3 (b)	(0.4		)	(0.6		)
Transfers out of Level 3 (c)	1			5.9
Purchases	4.8			9
Settlements	(6.4		)	(3.5		)
Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Commodity Contracts - As of September 30, 2013, the fair value of Alliant Energy’s, IPL’s and WPL’s electric, natural gas and coal commodity contracts categorized as Level 3, excluding FTRs, were recognized as net derivative liabilities of $12.5 million, net derivative assets of $1.5 million and net derivative liabilities of $14.0 million, respectively. As of September 30, 2013, Alliant Energy’s, IPL’s and WPL’s FTRs classified as Level 3 were recognized as net derivative assets of $29.7 million, $27.1 million and $2.6 million, respectively.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2013
Derivative [Line Items]	'
Derivative Instruments	'
	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 10 for detailed discussion of Alliant Energy’s, IPL’s and WPL’s derivative instruments as of September 30, 2013 and December 31, 2012.
	Notional Amounts - As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
	The notional amounts in the above table were computed by aggregating the absolute value of purchase and sale positions within commodities for each delivery year.
	Financial Statement Presentation - Alliant Energy, IPL and WPL record derivative instruments at fair value each reporting date on the balance sheet as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
	Credit Risk-related Contingent Features - Alliant Energy, IPL and WPL have entered into various agreements that contain credit risk-related contingent features including requirements for them to maintain certain credit ratings from each of the major credit rating agencies and/or limitations on their liability positions under the various agreements based upon their credit ratings. In the event of a downgrade in their credit ratings or if their liability positions exceed certain contractual limits, Alliant Energy, IPL or WPL may need to provide credit support in the form of letters of credit or cash collateral up to the amount of their exposure under the contracts, or may need to unwind the contracts and pay the underlying liability positions.
	Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. The aggregate fair value of all derivatives with credit risk-related contingent features that were in a net liability position on September 30, 2013 was $27.1 million, $6.7 million and $20.4 million for Alliant Energy, IPL and WPL, respectively. At September 30, 2013, Alliant Energy, IPL and WPL all had investment-grade credit ratings. If the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered on September 30, 2013, Alliant Energy, IPL and WPL would be required to post $27.1 million, $6.7 million and $20.4 million, respectively, of credit support to their counterparties.
	Balance Sheet Offsetting - Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4
	As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative assets in the above table include $0.9 million and $0, respectively, of cash collateral posted by one counterparty. As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative liabilities in the above table include $0 and $0.5 million, respectively, of cash collateral posted by IPL. Trade receivables and payables associated with derivative assets and derivative liabilities are also subject to a master netting arrangement. As of September 30, 2013 and December 31, 2012, these trade receivables and payables were insignificant and were not included in the above table.
IPL [Member]	'
Derivative [Line Items]	'
Derivative Instruments	'
	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 10 for detailed discussion of Alliant Energy’s, IPL’s and WPL’s derivative instruments as of September 30, 2013 and December 31, 2012.
	Notional Amounts - As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
	The notional amounts in the above table were computed by aggregating the absolute value of purchase and sale positions within commodities for each delivery year.
	Financial Statement Presentation - Alliant Energy, IPL and WPL record derivative instruments at fair value each reporting date on the balance sheet as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
	Credit Risk-related Contingent Features - Alliant Energy, IPL and WPL have entered into various agreements that contain credit risk-related contingent features including requirements for them to maintain certain credit ratings from each of the major credit rating agencies and/or limitations on their liability positions under the various agreements based upon their credit ratings. In the event of a downgrade in their credit ratings or if their liability positions exceed certain contractual limits, Alliant Energy, IPL or WPL may need to provide credit support in the form of letters of credit or cash collateral up to the amount of their exposure under the contracts, or may need to unwind the contracts and pay the underlying liability positions.
	Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. The aggregate fair value of all derivatives with credit risk-related contingent features that were in a net liability position on September 30, 2013 was $27.1 million, $6.7 million and $20.4 million for Alliant Energy, IPL and WPL, respectively. At September 30, 2013, Alliant Energy, IPL and WPL all had investment-grade credit ratings. If the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered on September 30, 2013, Alliant Energy, IPL and WPL would be required to post $27.1 million, $6.7 million and $20.4 million, respectively, of credit support to their counterparties.
	Balance Sheet Offsetting - Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4
	As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative assets in the above table include $0.9 million and $0, respectively, of cash collateral posted by one counterparty. As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative liabilities in the above table include $0 and $0.5 million, respectively, of cash collateral posted by IPL. Trade receivables and payables associated with derivative assets and derivative liabilities are also subject to a master netting arrangement. As of September 30, 2013 and December 31, 2012, these trade receivables and payables were insignificant and were not included in the above table.
WPL [Member]	'
Derivative [Line Items]	'
Derivative Instruments	'
	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Alliant Energy, IPL and WPL periodically use derivative instruments for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 10 for detailed discussion of Alliant Energy’s, IPL’s and WPL’s derivative instruments as of September 30, 2013 and December 31, 2012.
	Notional Amounts - As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
	The notional amounts in the above table were computed by aggregating the absolute value of purchase and sale positions within commodities for each delivery year.
	Financial Statement Presentation - Alliant Energy, IPL and WPL record derivative instruments at fair value each reporting date on the balance sheet as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
	Credit Risk-related Contingent Features - Alliant Energy, IPL and WPL have entered into various agreements that contain credit risk-related contingent features including requirements for them to maintain certain credit ratings from each of the major credit rating agencies and/or limitations on their liability positions under the various agreements based upon their credit ratings. In the event of a downgrade in their credit ratings or if their liability positions exceed certain contractual limits, Alliant Energy, IPL or WPL may need to provide credit support in the form of letters of credit or cash collateral up to the amount of their exposure under the contracts, or may need to unwind the contracts and pay the underlying liability positions.
	Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. The aggregate fair value of all derivatives with credit risk-related contingent features that were in a net liability position on September 30, 2013 was $27.1 million, $6.7 million and $20.4 million for Alliant Energy, IPL and WPL, respectively. At September 30, 2013, Alliant Energy, IPL and WPL all had investment-grade credit ratings. If the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered on September 30, 2013, Alliant Energy, IPL and WPL would be required to post $27.1 million, $6.7 million and $20.4 million, respectively, of credit support to their counterparties.
	Balance Sheet Offsetting - Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4
	As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative assets in the above table include $0.9 million and $0, respectively, of cash collateral posted by one counterparty. As of September 30, 2013 and December 31, 2012, both Alliant Energy’s and IPL’s net derivative liabilities in the above table include $0 and $0.5 million, respectively, of cash collateral posted by IPL. Trade receivables and payables associated with derivative assets and derivative liabilities are also subject to a master netting arrangement. As of September 30, 2013 and December 31, 2012, these trade receivables and payables were insignificant and were not included in the above table.

Commitments_And_Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure	'
	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Alliant Energy, IPL and WPL have entered into capital purchase obligations that contain minimum future commitments related to capital expenditures for certain of their emission controls and generation performance improvement projects. These projects include generation performance improvements at IPL’s Ottumwa Unit 1 and the installation of scrubbers and baghouses at WPL’s Columbia Units 1 and 2 to reduce SO2 and mercury emissions at the generating facility. At September 30, 2013, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to these projects were $64 million, $21 million and $43 million, respectively.
	(b) Operating Expense Purchase Obligations - Alliant Energy, IPL and WPL have entered into various commodity supply, transportation and storage contracts to meet their obligations to provide electricity and natural gas to IPL’s and WPL’s utility customers. Alliant Energy, IPL and WPL also enter into other operating expense purchase obligations with various vendors for other goods and services. At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.
	(c) Legal Proceedings -
	Cash Balance Plan - In 2008, a class-action lawsuit was filed against the Cash Balance Plan in the Court. The complaint alleged that certain Cash Balance Plan participants who received distributions prior to their normal retirement age did not receive the full benefit to which they were entitled in violation of ERISA because the Cash Balance Plan applied an improper interest crediting rate to project the cash balance account to their normal retirement age. These Cash Balance Plan participants were limited to individuals who, prior to normal retirement age, received a lump-sum distribution or an annuity payment. The Court originally certified two subclasses of plaintiffs that in aggregate include all persons vested or partially vested in the Cash Balance Plan who received these distributions from January 1, 1998 to August 17, 2006, including: (1) persons who received distributions from January 1, 1998 through February 28, 2002; and (2) persons who received distributions from March 1, 2002 to August 17, 2006.
	In June 2010, the Court issued an opinion and order that granted the plaintiffs’ motion for summary judgment on liability. In December 2010, the Court issued an opinion and order that decided the interest crediting rate that the Cash Balance Plan used to project the cash balance accounts of the plaintiffs during the class period should have been 8.2% and that a pre-retirement mortality discount would not be applied to the damages calculation. In May 2011, the Cash Balance Plan was amended and the Cash Balance Plan subsequently made approximately $10 million in additional payments in 2011 to certain former participants in the Cash Balance Plan. This amendment was required based on an agreement Alliant Energy reached with the IRS, which resulted in a favorable determination letter for the Cash Balance Plan in 2011. In November 2011, plaintiffs filed a motion for leave to file a supplemental complaint to assert that the 2011 amendment to the Cash Balance Plan was itself an ERISA violation. In March 2012, the Cash Balance Plan and the plaintiffs each filed motions for summary judgment related to the supplemental complaint, and the plaintiffs filed a motion for class certification, seeking to amend the class definition and for appointment of class representatives and class counsel.
	In July 2012, the Court issued an opinion and order granting plaintiffs’ motion for class certification, but only as to the interest crediting rate and the pre-retirement mortality discount claims of lump-sum recipients. As a result of the opinion and order, two new subclasses were certified in lieu of the prior subclass certification. Subclass A involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who received an interest crediting rate of less than 8.2% under the Cash Balance Plan as amended in May 2011. Subclass B involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who would have received a larger benefit under the Cash Balance Plan as amended in May 2011 if a pre-retirement mortality discount had not been applied. In the opinion and order, the Court then granted plaintiffs’ motion for summary judgment as to the two subclasses, and denied as moot the parties’ motions for summary judgment with respect to issues beyond the two subclasses.
	In August 2012, as amended in September 2012, the Court entered a final judgment for the two subclasses in the total amount of $18.7 million. The judgment amount includes pre-judgment interest through July 2012 and takes into account the approximate $10 million of additional benefits paid by the Cash Balance Plan following the Cash Balance Plan amendment in 2011. In September 2012, the Cash Balance Plan appealed the judgment, and the interlocutory orders that led to the judgment, to the Seventh Circuit Court of Appeals.
	The September 2012 judgment did not address any award for plaintiffs’ attorney’s fees or costs. In September 2012, the plaintiffs filed a motion with the Court for payment of plaintiffs’ attorney’s fees and costs in the amount of $9.6 million, of which $4.3 million was requested to be paid out of the common fund awarded to the two subclasses in the September 2012 judgment. In February 2013, the Court awarded plaintiffs’ attorney’s fees and costs in the amount of $6.4 million. The Court ordered that all of the fees and costs be paid from the $18.7 million judgment previously awarded and not be in addition to that judgment.
	In August 2013, the Seventh Circuit Court of Appeals ruled in favor of the Cash Balance Plan that the statute of limitations barred the claims of participants who received lump sum distributions more than six years before the case was filed and affirmed the remainder of the Court’s rulings. The case was remanded to the Court to determine damages. The Plaintiffs filed a petition with the Seventh Circuit Court of Appeals asking for rehearing of the statute of limitations decision, which was denied.
	Alliant Energy, IPL and WPL have not recognized any material loss contingency amounts for the final judgment of damages as of September 30, 2013. A material loss contingency for the judgment will not be recognized unless a final unappealable ruling is received, or a settlement is reached, which results in an amendment to the Cash Balance Plan and payment of additional benefits to Cash Balance Plan participants. Alliant Energy, IPL and WPL are currently unable to predict the final outcome of the class-action lawsuit or the ultimate impact on their financial condition or results of operations but believe an adverse outcome could have a material effect on their retirement plan funding and expense.
	Flood Damage Claims - In June 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In July 2013, the case was removed from state court to federal court based on federal jurisdiction. In September 2013, the U.S. District Court for the Northern District of Iowa dismissed the Plaintiffs’ claims and transferred the case for resolution to the Surface Transportation Board, the administrative agency that oversees the Interstate Commerce Commission Termination Act. In October 2013, the Plaintiffs appealed the federal court’s dismissal of the case to the Eighth Circuit Court of Appeals. Alliant Energy and CRANDIC believe the case is without merit and will continue to vigorously contest the case. As a result, Alliant Energy does not currently believe any material losses from these claims are both probable and reasonably estimated and therefore has not recognized any material loss contingency amounts for this complaint as of September 30, 2013. Due to the early stages of the claim and the lack of specific damages identified, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	(d) Guarantees and Indemnifications -
	RMT - In January 2013, Alliant Energy sold RMT. RMT provided renewable energy services including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy provided indemnifications to the buyer of RMT for losses resulting from potential breach of the representations and warranties made by Alliant Energy as of the sale date and for the potential breach of its obligations under the sale agreement. These indemnifications are limited to $3 million and expire in July 2014.
	In addition, Alliant Energy, as part of the sale, indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016.
	Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2013, Alliant Energy had $493 million of performance guarantees outstanding, with $146 million, $294 million and $53 million expiring in 2013, 2014 and 2015, respectively.
	Although Alliant Energy has received warranty claims related to certain of these projects, it currently believes that no material cash payments will be made and has not recognized any material liabilities related to these matters as of September 30, 2013. Refer to Note 14 for further discussion of RMT.
	Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Alliant Energy continues to guarantee the obligations related to the abandonment of certain platforms off the coast of California and related onshore plant and equipment that were owned by Whiting Petroleum prior to Alliant Energy’s sale of Whiting Petroleum. The guarantee does not include a maximum limit. As of September 30, 2013, the present value of the abandonment obligations is estimated at $31 million. Alliant Energy believes that no payments will be made under this guarantee. Alliant Energy has not recognized any material liabilities related to this guarantee as of September 30, 2013.
	(e) Environmental Matters -
	MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL may have future liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around the sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 27 and 5 sites, respectively.
	Alliant Energy, IPL and WPL record environmental liabilities related to these MGP sites based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. Management currently estimates the range of remaining costs to be incurred for the investigation, remediation and monitoring of these sites to be $15 million ($13 million for IPL and $2 million for WPL) to $32 million ($28 million for IPL and $4 million for WPL). At September 30, 2013, Alliant Energy, IPL and WPL recorded $20 million, $17 million and $3 million, respectively, in other current and non-current environmental liabilities for their remaining costs to be incurred for these MGP sites.
	WPL Consent Decree - In 2009, the EPA sent an NOV to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of Edgewater, Nelson Dewey and Columbia failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA.
	In April 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In June 2013, the Consent Decree was approved by the Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	SCR system at Edgewater Unit 5 by May 1, 2013 (placed in-service in December 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014;
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	SCR system at Columbia Unit 2 by December 31, 2018.
	WPL is also required to fuel switch or retire Nelson Dewey Units 1 and 2 and Edgewater Unit 3 by December 31, 2015, and Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2 and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. WPL paid a civil penalty of approximately $2 million and will complete approximately $7 million in environmental mitigation projects.
	Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers, except for costs related to certain of the environmental mitigation projects and the civil penalty.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, Alliant Energy, IPL and WPL are also monitoring various environmental regulations that may have a significant impact on their future operations. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, Alliant Energy, IPL and WPL are currently not able to determine the complete financial impact of these regulations but do believe that future capital investments and/or modifications to their electric generating facilities to comply with these regulations could be significant. Specific current, proposed or potential environmental matters that may require significant future expenditures include, among others: CAIR, Clean Air Visibility Rule, Utility MACT Rule, Wisconsin State Mercury Rule, Wisconsin RACT Rule, Industrial Boiler and Process Heater MACT Rule, Ozone NAAQS Rule, Fine Particle NAAQS Rule, Nitrogen Dioxide NAAQS Rule, SO2 NAAQS Rule, Federal Clean Water Act including Section 316(b), Wisconsin and Iowa State Thermal Rules, Hydroelectric Fish Passage Device, Effluent Limitation Guidelines, Coal Combustion Residuals, Polychlorinated Biphenyls, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including NSPS for GHG Emissions from Electric Utilities. Some recent developments concerning these environmental matters are included below:
	Water Quality -
	Effluent Limitation Guidelines are expected to require changes to discharge limits for wastewater from steam EGUs. In June 2013, the EPA published proposed effluent limitation guidelines for public comment. Compliance with these proposed guidelines would be required after July 1, 2017 but before July 1, 2022, depending on each facility’s wastewater permit cycle for existing steam EGUs and immediately upon operation for new steam EGUs constructed after the issuance of the final guidelines.
	GHG Emissions -
	EPA NSPS for GHG Emissions from Electric Utilities - In September 2013, the EPA issued revised proposed NSPS for GHG emissions for new fossil-fueled EGUs that would establish CO2 emissions limits for certain new EGUs. Marshalltown, if constructed, is expected to be impacted by these proposed standards and would be constructed to achieve compliance with these standards. Also, WPL’s potential generation investment could be impacted by these standards. A date for finalizing these standards has not yet been established. The EPA is expected to issue proposed and final NSPS for GHG for existing EGUs by June 1, 2014 and June 1, 2015, respectively, which would provide guidelines that states must follow to achieve required GHG reductions. SIPs that provide details of how these guidelines are to be met would be required from state agencies by June 30, 2016.
IPL [Member]	'
Commitments and Contingencies Disclosure	'
	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Alliant Energy, IPL and WPL have entered into capital purchase obligations that contain minimum future commitments related to capital expenditures for certain of their emission controls and generation performance improvement projects. These projects include generation performance improvements at IPL’s Ottumwa Unit 1 and the installation of scrubbers and baghouses at WPL’s Columbia Units 1 and 2 to reduce SO2 and mercury emissions at the generating facility. At September 30, 2013, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to these projects were $64 million, $21 million and $43 million, respectively.
	(b) Operating Expense Purchase Obligations - Alliant Energy, IPL and WPL have entered into various commodity supply, transportation and storage contracts to meet their obligations to provide electricity and natural gas to IPL’s and WPL’s utility customers. Alliant Energy, IPL and WPL also enter into other operating expense purchase obligations with various vendors for other goods and services. At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.
	(c) Legal Proceedings -
	Cash Balance Plan - In 2008, a class-action lawsuit was filed against the Cash Balance Plan in the Court. The complaint alleged that certain Cash Balance Plan participants who received distributions prior to their normal retirement age did not receive the full benefit to which they were entitled in violation of ERISA because the Cash Balance Plan applied an improper interest crediting rate to project the cash balance account to their normal retirement age. These Cash Balance Plan participants were limited to individuals who, prior to normal retirement age, received a lump-sum distribution or an annuity payment. The Court originally certified two subclasses of plaintiffs that in aggregate include all persons vested or partially vested in the Cash Balance Plan who received these distributions from January 1, 1998 to August 17, 2006, including: (1) persons who received distributions from January 1, 1998 through February 28, 2002; and (2) persons who received distributions from March 1, 2002 to August 17, 2006.
	In June 2010, the Court issued an opinion and order that granted the plaintiffs’ motion for summary judgment on liability. In December 2010, the Court issued an opinion and order that decided the interest crediting rate that the Cash Balance Plan used to project the cash balance accounts of the plaintiffs during the class period should have been 8.2% and that a pre-retirement mortality discount would not be applied to the damages calculation. In May 2011, the Cash Balance Plan was amended and the Cash Balance Plan subsequently made approximately $10 million in additional payments in 2011 to certain former participants in the Cash Balance Plan. This amendment was required based on an agreement Alliant Energy reached with the IRS, which resulted in a favorable determination letter for the Cash Balance Plan in 2011. In November 2011, plaintiffs filed a motion for leave to file a supplemental complaint to assert that the 2011 amendment to the Cash Balance Plan was itself an ERISA violation. In March 2012, the Cash Balance Plan and the plaintiffs each filed motions for summary judgment related to the supplemental complaint, and the plaintiffs filed a motion for class certification, seeking to amend the class definition and for appointment of class representatives and class counsel.
	In July 2012, the Court issued an opinion and order granting plaintiffs’ motion for class certification, but only as to the interest crediting rate and the pre-retirement mortality discount claims of lump-sum recipients. As a result of the opinion and order, two new subclasses were certified in lieu of the prior subclass certification. Subclass A involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who received an interest crediting rate of less than 8.2% under the Cash Balance Plan as amended in May 2011. Subclass B involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who would have received a larger benefit under the Cash Balance Plan as amended in May 2011 if a pre-retirement mortality discount had not been applied. In the opinion and order, the Court then granted plaintiffs’ motion for summary judgment as to the two subclasses, and denied as moot the parties’ motions for summary judgment with respect to issues beyond the two subclasses.
	In August 2012, as amended in September 2012, the Court entered a final judgment for the two subclasses in the total amount of $18.7 million. The judgment amount includes pre-judgment interest through July 2012 and takes into account the approximate $10 million of additional benefits paid by the Cash Balance Plan following the Cash Balance Plan amendment in 2011. In September 2012, the Cash Balance Plan appealed the judgment, and the interlocutory orders that led to the judgment, to the Seventh Circuit Court of Appeals.
	The September 2012 judgment did not address any award for plaintiffs’ attorney’s fees or costs. In September 2012, the plaintiffs filed a motion with the Court for payment of plaintiffs’ attorney’s fees and costs in the amount of $9.6 million, of which $4.3 million was requested to be paid out of the common fund awarded to the two subclasses in the September 2012 judgment. In February 2013, the Court awarded plaintiffs’ attorney’s fees and costs in the amount of $6.4 million. The Court ordered that all of the fees and costs be paid from the $18.7 million judgment previously awarded and not be in addition to that judgment.
	In August 2013, the Seventh Circuit Court of Appeals ruled in favor of the Cash Balance Plan that the statute of limitations barred the claims of participants who received lump sum distributions more than six years before the case was filed and affirmed the remainder of the Court’s rulings. The case was remanded to the Court to determine damages. The Plaintiffs filed a petition with the Seventh Circuit Court of Appeals asking for rehearing of the statute of limitations decision, which was denied.
	Alliant Energy, IPL and WPL have not recognized any material loss contingency amounts for the final judgment of damages as of September 30, 2013. A material loss contingency for the judgment will not be recognized unless a final unappealable ruling is received, or a settlement is reached, which results in an amendment to the Cash Balance Plan and payment of additional benefits to Cash Balance Plan participants. Alliant Energy, IPL and WPL are currently unable to predict the final outcome of the class-action lawsuit or the ultimate impact on their financial condition or results of operations but believe an adverse outcome could have a material effect on their retirement plan funding and expense.
	Flood Damage Claims - In June 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In July 2013, the case was removed from state court to federal court based on federal jurisdiction. In September 2013, the U.S. District Court for the Northern District of Iowa dismissed the Plaintiffs’ claims and transferred the case for resolution to the Surface Transportation Board, the administrative agency that oversees the Interstate Commerce Commission Termination Act. In October 2013, the Plaintiffs appealed the federal court’s dismissal of the case to the Eighth Circuit Court of Appeals. Alliant Energy and CRANDIC believe the case is without merit and will continue to vigorously contest the case. As a result, Alliant Energy does not currently believe any material losses from these claims are both probable and reasonably estimated and therefore has not recognized any material loss contingency amounts for this complaint as of September 30, 2013. Due to the early stages of the claim and the lack of specific damages identified, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	(d) Guarantees and Indemnifications -
	RMT - In January 2013, Alliant Energy sold RMT. RMT provided renewable energy services including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy provided indemnifications to the buyer of RMT for losses resulting from potential breach of the representations and warranties made by Alliant Energy as of the sale date and for the potential breach of its obligations under the sale agreement. These indemnifications are limited to $3 million and expire in July 2014.
	In addition, Alliant Energy, as part of the sale, indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016.
	Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2013, Alliant Energy had $493 million of performance guarantees outstanding, with $146 million, $294 million and $53 million expiring in 2013, 2014 and 2015, respectively.
	Although Alliant Energy has received warranty claims related to certain of these projects, it currently believes that no material cash payments will be made and has not recognized any material liabilities related to these matters as of September 30, 2013. Refer to Note 14 for further discussion of RMT.
	Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Alliant Energy continues to guarantee the obligations related to the abandonment of certain platforms off the coast of California and related onshore plant and equipment that were owned by Whiting Petroleum prior to Alliant Energy’s sale of Whiting Petroleum. The guarantee does not include a maximum limit. As of September 30, 2013, the present value of the abandonment obligations is estimated at $31 million. Alliant Energy believes that no payments will be made under this guarantee. Alliant Energy has not recognized any material liabilities related to this guarantee as of September 30, 2013.
	(e) Environmental Matters -
	MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL may have future liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around the sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 27 and 5 sites, respectively.
	Alliant Energy, IPL and WPL record environmental liabilities related to these MGP sites based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. Management currently estimates the range of remaining costs to be incurred for the investigation, remediation and monitoring of these sites to be $15 million ($13 million for IPL and $2 million for WPL) to $32 million ($28 million for IPL and $4 million for WPL). At September 30, 2013, Alliant Energy, IPL and WPL recorded $20 million, $17 million and $3 million, respectively, in other current and non-current environmental liabilities for their remaining costs to be incurred for these MGP sites.
	WPL Consent Decree - In 2009, the EPA sent an NOV to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of Edgewater, Nelson Dewey and Columbia failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA.
	In April 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In June 2013, the Consent Decree was approved by the Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	SCR system at Edgewater Unit 5 by May 1, 2013 (placed in-service in December 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014;
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	SCR system at Columbia Unit 2 by December 31, 2018.
	WPL is also required to fuel switch or retire Nelson Dewey Units 1 and 2 and Edgewater Unit 3 by December 31, 2015, and Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2 and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. WPL paid a civil penalty of approximately $2 million and will complete approximately $7 million in environmental mitigation projects.
	Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers, except for costs related to certain of the environmental mitigation projects and the civil penalty.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, Alliant Energy, IPL and WPL are also monitoring various environmental regulations that may have a significant impact on their future operations. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, Alliant Energy, IPL and WPL are currently not able to determine the complete financial impact of these regulations but do believe that future capital investments and/or modifications to their electric generating facilities to comply with these regulations could be significant. Specific current, proposed or potential environmental matters that may require significant future expenditures include, among others: CAIR, Clean Air Visibility Rule, Utility MACT Rule, Wisconsin State Mercury Rule, Wisconsin RACT Rule, Industrial Boiler and Process Heater MACT Rule, Ozone NAAQS Rule, Fine Particle NAAQS Rule, Nitrogen Dioxide NAAQS Rule, SO2 NAAQS Rule, Federal Clean Water Act including Section 316(b), Wisconsin and Iowa State Thermal Rules, Hydroelectric Fish Passage Device, Effluent Limitation Guidelines, Coal Combustion Residuals, Polychlorinated Biphenyls, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including NSPS for GHG Emissions from Electric Utilities. Some recent developments concerning these environmental matters are included below:
	Water Quality -
	Effluent Limitation Guidelines are expected to require changes to discharge limits for wastewater from steam EGUs. In June 2013, the EPA published proposed effluent limitation guidelines for public comment. Compliance with these proposed guidelines would be required after July 1, 2017 but before July 1, 2022, depending on each facility’s wastewater permit cycle for existing steam EGUs and immediately upon operation for new steam EGUs constructed after the issuance of the final guidelines.
	GHG Emissions -
	EPA NSPS for GHG Emissions from Electric Utilities - In September 2013, the EPA issued revised proposed NSPS for GHG emissions for new fossil-fueled EGUs that would establish CO2 emissions limits for certain new EGUs. Marshalltown, if constructed, is expected to be impacted by these proposed standards and would be constructed to achieve compliance with these standards. Also, WPL’s potential generation investment could be impacted by these standards. A date for finalizing these standards has not yet been established. The EPA is expected to issue proposed and final NSPS for GHG for existing EGUs by June 1, 2014 and June 1, 2015, respectively, which would provide guidelines that states must follow to achieve required GHG reductions. SIPs that provide details of how these guidelines are to be met would be required from state agencies by June 30, 2016.
WPL [Member]	'
Commitments and Contingencies Disclosure	'
	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Alliant Energy, IPL and WPL have entered into capital purchase obligations that contain minimum future commitments related to capital expenditures for certain of their emission controls and generation performance improvement projects. These projects include generation performance improvements at IPL’s Ottumwa Unit 1 and the installation of scrubbers and baghouses at WPL’s Columbia Units 1 and 2 to reduce SO2 and mercury emissions at the generating facility. At September 30, 2013, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to these projects were $64 million, $21 million and $43 million, respectively.
	(b) Operating Expense Purchase Obligations - Alliant Energy, IPL and WPL have entered into various commodity supply, transportation and storage contracts to meet their obligations to provide electricity and natural gas to IPL’s and WPL’s utility customers. Alliant Energy, IPL and WPL also enter into other operating expense purchase obligations with various vendors for other goods and services. At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.
	(c) Legal Proceedings -
	Cash Balance Plan - In 2008, a class-action lawsuit was filed against the Cash Balance Plan in the Court. The complaint alleged that certain Cash Balance Plan participants who received distributions prior to their normal retirement age did not receive the full benefit to which they were entitled in violation of ERISA because the Cash Balance Plan applied an improper interest crediting rate to project the cash balance account to their normal retirement age. These Cash Balance Plan participants were limited to individuals who, prior to normal retirement age, received a lump-sum distribution or an annuity payment. The Court originally certified two subclasses of plaintiffs that in aggregate include all persons vested or partially vested in the Cash Balance Plan who received these distributions from January 1, 1998 to August 17, 2006, including: (1) persons who received distributions from January 1, 1998 through February 28, 2002; and (2) persons who received distributions from March 1, 2002 to August 17, 2006.
	In June 2010, the Court issued an opinion and order that granted the plaintiffs’ motion for summary judgment on liability. In December 2010, the Court issued an opinion and order that decided the interest crediting rate that the Cash Balance Plan used to project the cash balance accounts of the plaintiffs during the class period should have been 8.2% and that a pre-retirement mortality discount would not be applied to the damages calculation. In May 2011, the Cash Balance Plan was amended and the Cash Balance Plan subsequently made approximately $10 million in additional payments in 2011 to certain former participants in the Cash Balance Plan. This amendment was required based on an agreement Alliant Energy reached with the IRS, which resulted in a favorable determination letter for the Cash Balance Plan in 2011. In November 2011, plaintiffs filed a motion for leave to file a supplemental complaint to assert that the 2011 amendment to the Cash Balance Plan was itself an ERISA violation. In March 2012, the Cash Balance Plan and the plaintiffs each filed motions for summary judgment related to the supplemental complaint, and the plaintiffs filed a motion for class certification, seeking to amend the class definition and for appointment of class representatives and class counsel.
	In July 2012, the Court issued an opinion and order granting plaintiffs’ motion for class certification, but only as to the interest crediting rate and the pre-retirement mortality discount claims of lump-sum recipients. As a result of the opinion and order, two new subclasses were certified in lieu of the prior subclass certification. Subclass A involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who received an interest crediting rate of less than 8.2% under the Cash Balance Plan as amended in May 2011. Subclass B involves persons who received a lump-sum distribution between January 1, 1998 and August 17, 2006, and who would have received a larger benefit under the Cash Balance Plan as amended in May 2011 if a pre-retirement mortality discount had not been applied. In the opinion and order, the Court then granted plaintiffs’ motion for summary judgment as to the two subclasses, and denied as moot the parties’ motions for summary judgment with respect to issues beyond the two subclasses.
	In August 2012, as amended in September 2012, the Court entered a final judgment for the two subclasses in the total amount of $18.7 million. The judgment amount includes pre-judgment interest through July 2012 and takes into account the approximate $10 million of additional benefits paid by the Cash Balance Plan following the Cash Balance Plan amendment in 2011. In September 2012, the Cash Balance Plan appealed the judgment, and the interlocutory orders that led to the judgment, to the Seventh Circuit Court of Appeals.
	The September 2012 judgment did not address any award for plaintiffs’ attorney’s fees or costs. In September 2012, the plaintiffs filed a motion with the Court for payment of plaintiffs’ attorney’s fees and costs in the amount of $9.6 million, of which $4.3 million was requested to be paid out of the common fund awarded to the two subclasses in the September 2012 judgment. In February 2013, the Court awarded plaintiffs’ attorney’s fees and costs in the amount of $6.4 million. The Court ordered that all of the fees and costs be paid from the $18.7 million judgment previously awarded and not be in addition to that judgment.
	In August 2013, the Seventh Circuit Court of Appeals ruled in favor of the Cash Balance Plan that the statute of limitations barred the claims of participants who received lump sum distributions more than six years before the case was filed and affirmed the remainder of the Court’s rulings. The case was remanded to the Court to determine damages. The Plaintiffs filed a petition with the Seventh Circuit Court of Appeals asking for rehearing of the statute of limitations decision, which was denied.
	Alliant Energy, IPL and WPL have not recognized any material loss contingency amounts for the final judgment of damages as of September 30, 2013. A material loss contingency for the judgment will not be recognized unless a final unappealable ruling is received, or a settlement is reached, which results in an amendment to the Cash Balance Plan and payment of additional benefits to Cash Balance Plan participants. Alliant Energy, IPL and WPL are currently unable to predict the final outcome of the class-action lawsuit or the ultimate impact on their financial condition or results of operations but believe an adverse outcome could have a material effect on their retirement plan funding and expense.
	Flood Damage Claims - In June 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In July 2013, the case was removed from state court to federal court based on federal jurisdiction. In September 2013, the U.S. District Court for the Northern District of Iowa dismissed the Plaintiffs’ claims and transferred the case for resolution to the Surface Transportation Board, the administrative agency that oversees the Interstate Commerce Commission Termination Act. In October 2013, the Plaintiffs appealed the federal court’s dismissal of the case to the Eighth Circuit Court of Appeals. Alliant Energy and CRANDIC believe the case is without merit and will continue to vigorously contest the case. As a result, Alliant Energy does not currently believe any material losses from these claims are both probable and reasonably estimated and therefore has not recognized any material loss contingency amounts for this complaint as of September 30, 2013. Due to the early stages of the claim and the lack of specific damages identified, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	(d) Guarantees and Indemnifications -
	RMT - In January 2013, Alliant Energy sold RMT. RMT provided renewable energy services including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy provided indemnifications to the buyer of RMT for losses resulting from potential breach of the representations and warranties made by Alliant Energy as of the sale date and for the potential breach of its obligations under the sale agreement. These indemnifications are limited to $3 million and expire in July 2014.
	In addition, Alliant Energy, as part of the sale, indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016.
	Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2013, Alliant Energy had $493 million of performance guarantees outstanding, with $146 million, $294 million and $53 million expiring in 2013, 2014 and 2015, respectively.
	Although Alliant Energy has received warranty claims related to certain of these projects, it currently believes that no material cash payments will be made and has not recognized any material liabilities related to these matters as of September 30, 2013. Refer to Note 14 for further discussion of RMT.
	Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Alliant Energy continues to guarantee the obligations related to the abandonment of certain platforms off the coast of California and related onshore plant and equipment that were owned by Whiting Petroleum prior to Alliant Energy’s sale of Whiting Petroleum. The guarantee does not include a maximum limit. As of September 30, 2013, the present value of the abandonment obligations is estimated at $31 million. Alliant Energy believes that no payments will be made under this guarantee. Alliant Energy has not recognized any material liabilities related to this guarantee as of September 30, 2013.
	(e) Environmental Matters -
	MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL may have future liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around the sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 27 and 5 sites, respectively.
	Alliant Energy, IPL and WPL record environmental liabilities related to these MGP sites based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. Management currently estimates the range of remaining costs to be incurred for the investigation, remediation and monitoring of these sites to be $15 million ($13 million for IPL and $2 million for WPL) to $32 million ($28 million for IPL and $4 million for WPL). At September 30, 2013, Alliant Energy, IPL and WPL recorded $20 million, $17 million and $3 million, respectively, in other current and non-current environmental liabilities for their remaining costs to be incurred for these MGP sites.
	WPL Consent Decree - In 2009, the EPA sent an NOV to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of Edgewater, Nelson Dewey and Columbia failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA.
	In April 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In June 2013, the Consent Decree was approved by the Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	SCR system at Edgewater Unit 5 by May 1, 2013 (placed in-service in December 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014;
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	SCR system at Columbia Unit 2 by December 31, 2018.
	WPL is also required to fuel switch or retire Nelson Dewey Units 1 and 2 and Edgewater Unit 3 by December 31, 2015, and Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2 and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. WPL paid a civil penalty of approximately $2 million and will complete approximately $7 million in environmental mitigation projects.
	Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers, except for costs related to certain of the environmental mitigation projects and the civil penalty.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, Alliant Energy, IPL and WPL are also monitoring various environmental regulations that may have a significant impact on their future operations. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, Alliant Energy, IPL and WPL are currently not able to determine the complete financial impact of these regulations but do believe that future capital investments and/or modifications to their electric generating facilities to comply with these regulations could be significant. Specific current, proposed or potential environmental matters that may require significant future expenditures include, among others: CAIR, Clean Air Visibility Rule, Utility MACT Rule, Wisconsin State Mercury Rule, Wisconsin RACT Rule, Industrial Boiler and Process Heater MACT Rule, Ozone NAAQS Rule, Fine Particle NAAQS Rule, Nitrogen Dioxide NAAQS Rule, SO2 NAAQS Rule, Federal Clean Water Act including Section 316(b), Wisconsin and Iowa State Thermal Rules, Hydroelectric Fish Passage Device, Effluent Limitation Guidelines, Coal Combustion Residuals, Polychlorinated Biphenyls, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including NSPS for GHG Emissions from Electric Utilities. Some recent developments concerning these environmental matters are included below:
	Water Quality -
	Effluent Limitation Guidelines are expected to require changes to discharge limits for wastewater from steam EGUs. In June 2013, the EPA published proposed effluent limitation guidelines for public comment. Compliance with these proposed guidelines would be required after July 1, 2017 but before July 1, 2022, depending on each facility’s wastewater permit cycle for existing steam EGUs and immediately upon operation for new steam EGUs constructed after the issuance of the final guidelines.
	GHG Emissions -
	EPA NSPS for GHG Emissions from Electric Utilities - In September 2013, the EPA issued revised proposed NSPS for GHG emissions for new fossil-fueled EGUs that would establish CO2 emissions limits for certain new EGUs. Marshalltown, if constructed, is expected to be impacted by these proposed standards and would be constructed to achieve compliance with these standards. Also, WPL’s potential generation investment could be impacted by these standards. A date for finalizing these standards has not yet been established. The EPA is expected to issue proposed and final NSPS for GHG for existing EGUs by June 1, 2014 and June 1, 2015, respectively, which would provide guidelines that states must follow to achieve required GHG reductions. SIPs that provide details of how these guidelines are to be met would be required from state agencies by June 30, 2016.

Segments_Of_Business

Segments Of Business	9 Months Ended
	Sep. 30, 2013
Segment Reporting Information [Line Items]	'
Segments Of Business	'
	SEGMENTS OF BUSINESS
	Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations.
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$798.10		$39.80			$17.40			$855.30		$11.30			$866.60
	Operating income (loss)	199.6		(3.4		)	(0.3		)	195.9		5.5			201.4
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									171.3		(12.4		)	158.9
	Loss from discontinued operations, net of tax									—		(1.3		)	(1.3		)
	Net income (loss) attributable to Alliant Energy common shareowners									171.3		(13.7		)	157.6
	Three Months Ended September 30, 2012
	Operating revenues		$815.30		$46.80			$12.20			$874.30		$13.30			$887.60
	Operating income	203.1		0.8			1.5			205.4		8.3			213.7
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									159.2		(10.2		)	149
	Income from discontinued operations, net of tax									—		1.7			1.7
	Net income (loss) attributable to Alliant Energy common shareowners									159.2		(8.5		)	150.7
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Nine Months Ended September 30, 2013
	Operating revenues		$2,043.40		$310.50			$52.40			$2,406.30		$37.90			$2,444.20
	Operating income	359.1		39.5			5.5			404.1		21.2			425.3
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									292.8		4.9			297.7
	Loss from discontinued operations, net of tax									—		(4.9		)	(4.9		)
	Net income attributable to Alliant Energy common shareowners									292.8		—			292.8
	Nine Months Ended September 30, 2012
	Operating revenues		$2,000.30		$263.90			$39.70			$2,303.90		$39.70			$2,343.60
	Operating income	354		32.1			4.7			390.8		27.3			418.1
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									237.4		16.4			253.8
	Loss from discontinued operations, net of tax									—		(2.3		)	(2.3		)
	Net income attributable to Alliant Energy common shareowners									237.4		14.1			251.5
	IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$457.60		$24.60			$12.20			$494.40
	Operating income (loss)	99.6		(0.7		)	1.1			100
	Earnings available for common stock									110
	Three Months Ended September 30, 2012
	Operating revenues		$456.60		$29.60			$11.50			$497.70
	Operating income	109.5		0.6			1.9			112
	Earnings available for common stock									103.3
	Nine Months Ended September 30, 2013
	Operating revenues		$1,137.40		$180.90			$37.40			$1,355.70
	Operating income	146.2		22.6			7			175.8
	Earnings available for common stock									155.1
	Nine Months Ended September 30, 2012
	Operating revenues		$1,070.70		$149.20			$37.20			$1,257.10
	Operating income	149.3		15.6			6.4			171.3
	Earnings available for common stock									115.2
	WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$340.50		$15.20			$5.20			$360.90
	Operating income (loss)	100		(2.7		)	(1.4		)	95.9
	Earnings available for common stock									61.3
	Three Months Ended September 30, 2012
Operating revenues		$358.70		$17.20			$0.70			$376.60
Operating income (loss)	93.6		0.2			(0.4		)	93.4
Earnings available for common stock									55.9
Nine Months Ended September 30, 2013
Operating revenues		$906.00		$129.60			$15.00			$1,050.60
Operating income (loss)	212.9		16.9			(1.5		)	228.3
Earnings available for common stock									137.7
Nine Months Ended September 30, 2012
Operating revenues		$929.60		$114.70			$2.50			$1,046.80
Operating income (loss)	204.7		16.5			(1.7		)	219.5
Earnings available for common stock									122.2
IPL [Member]	'
Segment Reporting Information [Line Items]	'
Segments Of Business	'
	SEGMENTS OF BUSINESS
	Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations.
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$798.10		$39.80			$17.40			$855.30		$11.30			$866.60
	Operating income (loss)	199.6		(3.4		)	(0.3		)	195.9		5.5			201.4
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									171.3		(12.4		)	158.9
	Loss from discontinued operations, net of tax									—		(1.3		)	(1.3		)
	Net income (loss) attributable to Alliant Energy common shareowners									171.3		(13.7		)	157.6
	Three Months Ended September 30, 2012
	Operating revenues		$815.30		$46.80			$12.20			$874.30		$13.30			$887.60
	Operating income	203.1		0.8			1.5			205.4		8.3			213.7
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									159.2		(10.2		)	149
	Income from discontinued operations, net of tax									—		1.7			1.7
	Net income (loss) attributable to Alliant Energy common shareowners									159.2		(8.5		)	150.7
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Nine Months Ended September 30, 2013
	Operating revenues		$2,043.40		$310.50			$52.40			$2,406.30		$37.90			$2,444.20
	Operating income	359.1		39.5			5.5			404.1		21.2			425.3
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									292.8		4.9			297.7
	Loss from discontinued operations, net of tax									—		(4.9		)	(4.9		)
	Net income attributable to Alliant Energy common shareowners									292.8		—			292.8
	Nine Months Ended September 30, 2012
	Operating revenues		$2,000.30		$263.90			$39.70			$2,303.90		$39.70			$2,343.60
	Operating income	354		32.1			4.7			390.8		27.3			418.1
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									237.4		16.4			253.8
	Loss from discontinued operations, net of tax									—		(2.3		)	(2.3		)
	Net income attributable to Alliant Energy common shareowners									237.4		14.1			251.5
	IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$457.60		$24.60			$12.20			$494.40
	Operating income (loss)	99.6		(0.7		)	1.1			100
	Earnings available for common stock									110
	Three Months Ended September 30, 2012
	Operating revenues		$456.60		$29.60			$11.50			$497.70
	Operating income	109.5		0.6			1.9			112
	Earnings available for common stock									103.3
	Nine Months Ended September 30, 2013
	Operating revenues		$1,137.40		$180.90			$37.40			$1,355.70
	Operating income	146.2		22.6			7			175.8
	Earnings available for common stock									155.1
	Nine Months Ended September 30, 2012
	Operating revenues		$1,070.70		$149.20			$37.20			$1,257.10
	Operating income	149.3		15.6			6.4			171.3
	Earnings available for common stock									115.2
	WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$340.50		$15.20			$5.20			$360.90
	Operating income (loss)	100		(2.7		)	(1.4		)	95.9
	Earnings available for common stock									61.3
	Three Months Ended September 30, 2012
Operating revenues		$358.70		$17.20			$0.70			$376.60
Operating income (loss)	93.6		0.2			(0.4		)	93.4
Earnings available for common stock									55.9
Nine Months Ended September 30, 2013
Operating revenues		$906.00		$129.60			$15.00			$1,050.60
Operating income (loss)	212.9		16.9			(1.5		)	228.3
Earnings available for common stock									137.7
Nine Months Ended September 30, 2012
Operating revenues		$929.60		$114.70			$2.50			$1,046.80
Operating income (loss)	204.7		16.5			(1.7		)	219.5
Earnings available for common stock									122.2
WPL [Member]	'
Segment Reporting Information [Line Items]	'
Segments Of Business	'
	SEGMENTS OF BUSINESS
	Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations.
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$798.10		$39.80			$17.40			$855.30		$11.30			$866.60
	Operating income (loss)	199.6		(3.4		)	(0.3		)	195.9		5.5			201.4
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									171.3		(12.4		)	158.9
	Loss from discontinued operations, net of tax									—		(1.3		)	(1.3		)
	Net income (loss) attributable to Alliant Energy common shareowners									171.3		(13.7		)	157.6
	Three Months Ended September 30, 2012
	Operating revenues		$815.30		$46.80			$12.20			$874.30		$13.30			$887.60
	Operating income	203.1		0.8			1.5			205.4		8.3			213.7
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									159.2		(10.2		)	149
	Income from discontinued operations, net of tax									—		1.7			1.7
	Net income (loss) attributable to Alliant Energy common shareowners									159.2		(8.5		)	150.7
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Nine Months Ended September 30, 2013
	Operating revenues		$2,043.40		$310.50			$52.40			$2,406.30		$37.90			$2,444.20
	Operating income	359.1		39.5			5.5			404.1		21.2			425.3
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									292.8		4.9			297.7
	Loss from discontinued operations, net of tax									—		(4.9		)	(4.9		)
	Net income attributable to Alliant Energy common shareowners									292.8		—			292.8
	Nine Months Ended September 30, 2012
	Operating revenues		$2,000.30		$263.90			$39.70			$2,303.90		$39.70			$2,343.60
	Operating income	354		32.1			4.7			390.8		27.3			418.1
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									237.4		16.4			253.8
	Loss from discontinued operations, net of tax									—		(2.3		)	(2.3		)
	Net income attributable to Alliant Energy common shareowners									237.4		14.1			251.5
	IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$457.60		$24.60			$12.20			$494.40
	Operating income (loss)	99.6		(0.7		)	1.1			100
	Earnings available for common stock									110
	Three Months Ended September 30, 2012
	Operating revenues		$456.60		$29.60			$11.50			$497.70
	Operating income	109.5		0.6			1.9			112
	Earnings available for common stock									103.3
	Nine Months Ended September 30, 2013
	Operating revenues		$1,137.40		$180.90			$37.40			$1,355.70
	Operating income	146.2		22.6			7			175.8
	Earnings available for common stock									155.1
	Nine Months Ended September 30, 2012
	Operating revenues		$1,070.70		$149.20			$37.20			$1,257.10
	Operating income	149.3		15.6			6.4			171.3
	Earnings available for common stock									115.2
	WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$340.50		$15.20			$5.20			$360.90
	Operating income (loss)	100		(2.7		)	(1.4		)	95.9
	Earnings available for common stock									61.3
	Three Months Ended September 30, 2012
Operating revenues		$358.70		$17.20			$0.70			$376.60
Operating income (loss)	93.6		0.2			(0.4		)	93.4
Earnings available for common stock									55.9
Nine Months Ended September 30, 2013
Operating revenues		$906.00		$129.60			$15.00			$1,050.60
Operating income (loss)	212.9		16.9			(1.5		)	228.3
Earnings available for common stock									137.7
Nine Months Ended September 30, 2012
Operating revenues		$929.60		$114.70			$2.50			$1,046.80
Operating income (loss)	204.7		16.5			(1.7		)	219.5
Earnings available for common stock									122.2

Discontinued_Operations_And_As

Discontinued Operations And Assets And Liabilities Held For Sale	9 Months Ended
	Sep. 30, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Discontinued Operations And Assets And Liabilities Held For Sale	'
	DISCONTINUED OPERATIONS AND ASSETS AND LIABILITIES HELD FOR SALE
	In January 2013, Alliant Energy sold RMT in order to narrow its strategic focus and risk profile. Alliant Energy does not currently believe that adjustments to the gain or loss related to the sale of RMT in periods after September 30, 2013 will be material. The operating results of RMT have been separately classified and reported as discontinued operations in Alliant Energy’s Condensed Consolidated Statements of Income. A summary of the components of discontinued operations in Alliant Energy’s Condensed Consolidated Statements of Income for the three and nine months ended September 30 was as follows (in millions):
		Three Months					Nine Months
		2013			2012		2013			2012
	Operating revenues		$—			$94.50		$0.90			$243.00
	Operating expenses	2.1			91.7		8.6			246.6
	Interest expense and other	—			0.2		—			0.4
	Income (loss) before income taxes	(2.1		)	2.6		(7.7		)	(4.0		)
	Income tax expense (benefit)	(0.8		)	0.9		(2.8		)	(1.7		)
	Income (loss) from discontinued operations, net of tax		($1.3	)		$1.70		($4.9	)		($2.3	)
	As of December 31, 2012, Alliant Energy’s Condensed Consolidated Balance Sheet included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
	Current assets		$27.90
	Current liabilities	31.4
	Net liabilities held for sale		($3.5	)

Asset_Retirement_Obligations_A

Asset Retirement Obligations (AROs)	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligations [Line Items]	'
Asset Retirement Obligations (AROs)	'
	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.
IPL [Member]	'
Asset Retirement Obligations [Line Items]	'
Asset Retirement Obligations (AROs)	'
	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.
WPL [Member]	'
Asset Retirement Obligations [Line Items]	'
Asset Retirement Obligations (AROs)	'
	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

Related_Parties

Related Parties	9 Months Ended
	Sep. 30, 2013
Related Party Transaction [Line Items]	'
Related Parties	'
	RELATED PARTIES
	System Coordination and Operating Agreement - IPL and WPL are parties to a system coordination and operating agreement whereby Corporate Services serves as agent on behalf of IPL and WPL. The agreement, which has been approved or reviewed by FERC and all state regulatory bodies having jurisdiction, provides a contractual basis for coordinated planning, construction, operation and maintenance of the electric generation systems of IPL and WPL. As agent of the agreement, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions. Corporate Services allocates a substantial portion of such sales and purchases among IPL and WPL based on invoices received from MISO, and the remaining sales and purchases based on procedures included in the agreement. The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
	Service Agreement - Pursuant to a service agreement, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services and a return on net assets. The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
	ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013		2012
	ATC billings to WPL		$24			$22			$72		$67
	WPL billings to ATC	2			3			9		7
	WPL owed ATC net amounts of $7 million as of September 30, 2013 and $6 million as of December 31, 2012.
IPL [Member]	'
Related Party Transaction [Line Items]	'
Related Parties	'
	RELATED PARTIES
	System Coordination and Operating Agreement - IPL and WPL are parties to a system coordination and operating agreement whereby Corporate Services serves as agent on behalf of IPL and WPL. The agreement, which has been approved or reviewed by FERC and all state regulatory bodies having jurisdiction, provides a contractual basis for coordinated planning, construction, operation and maintenance of the electric generation systems of IPL and WPL. As agent of the agreement, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions. Corporate Services allocates a substantial portion of such sales and purchases among IPL and WPL based on invoices received from MISO, and the remaining sales and purchases based on procedures included in the agreement. The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
	Service Agreement - Pursuant to a service agreement, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services and a return on net assets. The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
WPL [Member]	'
Related Party Transaction [Line Items]	'
Related Parties	'
	RELATED PARTIES
	System Coordination and Operating Agreement - IPL and WPL are parties to a system coordination and operating agreement whereby Corporate Services serves as agent on behalf of IPL and WPL. The agreement, which has been approved or reviewed by FERC and all state regulatory bodies having jurisdiction, provides a contractual basis for coordinated planning, construction, operation and maintenance of the electric generation systems of IPL and WPL. As agent of the agreement, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions. Corporate Services allocates a substantial portion of such sales and purchases among IPL and WPL based on invoices received from MISO, and the remaining sales and purchases based on procedures included in the agreement. The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
	Service Agreement - Pursuant to a service agreement, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services and a return on net assets. The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
	ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013		2012
	ATC billings to WPL		$24			$22			$72		$67
	WPL billings to ATC	2			3			9		7
	WPL owed ATC net amounts of $7 million as of September 30, 2013 and $6 million as of December 31, 2012.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	EARNINGS PER SHARE
	A reconciliation of the weighted average common shares outstanding used in the basic and diluted EPS calculation for the three and nine months ended September 30 was as follows (in thousands):
		Three Months		Nine Months
		2013	2012	2013	2012
	Weighted average common shares outstanding:
	Basic EPS calculation	110,783	110,768	110,775	110,747
	Effect of dilutive share-based awards	2	11	5	16
	Diluted EPS calculation	110,785	110,779	110,780	110,763
	For the three and nine months ended September 30, 2013 and 2012, there were no potentially dilutive securities excluded from the calculation of diluted EPS.

Summary_Of_Significant_Account1

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2013
Property, Plant and Equipment [Line Items]	'
General, Basis of Accounting	'
	The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates	'
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification	'
	Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities	'
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Utility Property, Plant and Equipment	'
	Utility Property, Plant and Equipment -
	Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014.
	The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013.
	The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
Comprehensive Income	'
	Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member]	'
Property, Plant and Equipment [Line Items]	'
General, Basis of Accounting	'
	The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates	'
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification	'
	Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities	'
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Utility Property, Plant and Equipment	'
	Utility Property, Plant and Equipment -
	Proposed Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In September 2013, IPL signed a definitive agreement to sell its Minnesota electric distribution assets to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives. Also in September 2013, IPL signed a definitive agreement to sell its Minnesota natural gas distribution assets to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. Proceeds from the sales are expected to be approximately $128 million in aggregate, subject to customary closing adjustments. The proceeds are expected to reduce Alliant Energy’s and IPL’s financing requirements. Pending all necessary federal and state regulatory approvals, including the MPUC, FERC and the IUB, the transactions are expected to be concluded in the second half of 2014.
	The sales price of the assets expected to be sold, which primarily consist of property, plant and equipment, and working capital items, is expected to result in a modest gain. Any after-tax gain realized from the transaction may be subject to refund to IPL’s customers. As of September 30, 2013, IPL’s assets and liabilities included in the sale agreements did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process. The operating results of IPL’s Minnesota electric and natural gas distribution businesses did not qualify as discontinued operations as of September 30, 2013.
	The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which is subject to FERC approval. The agreement contains a five-year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years. The agreement remains in effect unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. The tariffs include an annual true-up process for actual costs incurred. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97%. As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets is not expected to have a significant impact on IPL’s current generation plans.
Comprehensive Income	'
	Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member]	'
Property, Plant and Equipment [Line Items]	'
General, Basis of Accounting	'
	The interim unaudited condensed consolidated financial statements included herein have been prepared by Alliant Energy, IPL and WPL pursuant to the rules and regulations of the SEC. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the financial statements and the notes thereto included in Alliant Energy’s, IPL’s and WPL’s latest combined Annual Report on Form 10-K.
General, Use of Estimates	'
	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2013 are not necessarily indicative of results that may be expected for the year ending December 31, 2013. A change in management’s estimates or assumptions could have a material impact on Alliant Energy’s, IPL’s and WPL’s respective financial condition and results of operations during the period in which such change occurred.
General, Reclassification	'
	Certain prior period amounts in the Condensed Consolidated Financial Statements and Combined Notes to Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the notes herein have been revised to exclude discontinued operations and assets and liabilities held for sale for all periods presented.
Regulatory Assets and Regulatory Liabilities	'
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
	Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30, 2013, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to qualifying repair expenditures at IPL.
	Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recovered from customers in the future after any losses are realized and gains from derivative instruments are refunded to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the Condensed Consolidated Balance Sheets for the nine months ended September 30, 2013. Refer to Note 11 for additional details of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities in the above table decreased $67 million during the nine months ended September 30, 2013 due to the following items:
	Electric tax benefit rider - In January 2011, the IUB approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in February 2011 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $59 million of regulatory liabilities to credit Iowa retail electric customers’ bills during the nine months ended September 30, 2013.
	Gas tax benefit rider - In November 2012, the IUB approved a gas tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs and allocation of insurance proceeds from floods in 2008. IPL utilized $8 million of regulatory liabilities to credit Iowa retail gas customers’ bills during the nine months ended September 30, 2013.
	Refer to Note 4 for additional details regarding IPL’s tax benefit riders.
	Other - Based on the PSCW’s July 2012 order related to WPL’s 2013/2014 test period Wisconsin retail electric and gas rate case, WPL was authorized to recover previously incurred costs associated with the acquisition of a 25% ownership interest in Edgewater Unit 5 and proposed clean air compliance plan projects. As a result, Alliant Energy and WPL recorded a $5 million increase to regulatory assets, and a $5 million credit to “Utility - Other operation and maintenance” in their Condensed Consolidated Statements of Income during the nine months ended September 30, 2012.
Comprehensive Income	'
	Comprehensive Income - For the three and nine months ended September 30, 2013 and 2012, Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2013 and 2012, IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

Summary_Of_Significant_Account2

Summary Of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2013
Regulatory Assets	'
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
Regulatory Liabilities	'
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
IPL [Member]	'
Regulatory Assets	'
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
Regulatory Liabilities	'
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70
WPL [Member]	'
Regulatory Assets	'
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Tax-related		$813.60		$770.70		$783.60		$746.20		$30.00		$24.50
	Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
	AROs	66.9		62.4		38.8		38.6		28.1		23.8
	Emission allowances	30		30		30		30		—		—
	Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
	Environmental-related costs	26		34.9		21.8		30.3		4.2		4.6
	Other	107.7		125		67		77.2		40.7		47.8
			$1,596.20		$1,612.40		$1,216.00		$1,217.90		$380.20		$394.50
Regulatory Liabilities	'
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		September 30,		December 31,		September 30,		December 31,		September 30,		December 31,
		2013		2012		2013		2012		2013		2012
	Cost of removal obligations		$415.70		$408.70		$275.80		$268.00		$139.90		$140.70
	IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
	Energy conservation cost recovery	58.1		55.1		12.6		10		45.5		45.1
	IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
	Commodity cost recovery	7		17.7		1.1		5.2		5.9		12.5
	Other	43.7		46.3		27.8		29.9		15.9		16.4
			$837.60		$916.10		$630.40		$701.40		$207.20		$214.70

Receivables_Tables

Receivables (Tables)	9 Months Ended
	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]	'
Maximum And Average Outstanding Cash Proceeds	'
	IPL’s maximum and average outstanding cash proceeds, and costs incurred related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$155.00	$150.00	$170.00	$160.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	132.7	95	132.5	124.2
	Costs incurred	0.3	0.4	1	1.1
Receivables Sold Under The Agreement	'
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		September 30, 2013	December 31, 2012
	Customer accounts receivable	$158.80	$118.20
	Unbilled utility revenues	70.9	77.4
	Other receivables	0.1	2.8
	Receivables sold	229.8	198.4
	Less: cash proceeds (a)	140	130
	Deferred proceeds	89.8	68.4
	Less: allowance for doubtful accounts	2.9	1.6
	Fair value of deferred proceeds	$86.90	$66.80
	Outstanding receivables past due	$22.00	$16.10
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s Condensed Consolidated Statements of Cash Flows.
Additional Attributes Of Receivables Sold Under The Agreement	'
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Collections reinvested in receivables	$481.10	$522.90	$1,407.40	$1,334.70
	Credit losses, net of recoveries	3.9	3	7.8	7.3
IPL [Member]	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'
Maximum And Average Outstanding Cash Proceeds	'
	IPL’s maximum and average outstanding cash proceeds, and costs incurred related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)	$155.00	$150.00	$170.00	$160.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	132.7	95	132.5	124.2
	Costs incurred	0.3	0.4	1	1.1
Receivables Sold Under The Agreement	'
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		September 30, 2013	December 31, 2012
	Customer accounts receivable	$158.80	$118.20
	Unbilled utility revenues	70.9	77.4
	Other receivables	0.1	2.8
	Receivables sold	229.8	198.4
	Less: cash proceeds (a)	140	130
	Deferred proceeds	89.8	68.4
	Less: allowance for doubtful accounts	2.9	1.6
	Fair value of deferred proceeds	$86.90	$66.80
	Outstanding receivables past due	$22.00	$16.10
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s Condensed Consolidated Statements of Cash Flows.
Additional Attributes Of Receivables Sold Under The Agreement	'
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions):
		Three Months		Nine Months
		2013	2012	2013	2012
	Collections reinvested in receivables	$481.10	$522.90	$1,407.40	$1,334.70
	Credit losses, net of recoveries	3.9	3	7.8	7.3

Income_Taxes_Tables

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2013
Income Tax [Line Items]	'
Schedule Of Effective Income Tax Rates	'
	The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
Production Tax Credits (Net Of State Tax Impacts)	'
	For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
Summary Of Tax Credit Carryforwards	'
	At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172
IPL [Member]	'
Income Tax [Line Items]	'
Schedule Of Effective Income Tax Rates	'
	The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
Production Tax Credits (Net Of State Tax Impacts)	'
	For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
Summary Of Tax Credit Carryforwards	'
	At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172
WPL [Member]	'
Income Tax [Line Items]	'
Schedule Of Effective Income Tax Rates	'
	The overall income tax rates shown in the following table for the three and nine months ended September 30 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
		Alliant Energy					IPL					WPL
	Three Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.9	)	(10.3	)		(38.9	)		(34.2	)	—		—
	Production tax credits	(7.7	)	(5.5	)		(10.6	)		(8.6	)	(6.6	)	(4.3	)
	Effect of rate-making on property-related differences	(6.2	)	(4.7	)		(16.5	)		(11.2	)	(1.4	)	(1.1	)
	Other items, net	1.6		5.9			0.4			6.4		3.7		5.9
	Overall income tax rate	9.8	%	20.4	%		(30.6	%)		(12.6	%)	30.7	%	35.5	%
		Alliant Energy					IPL					WPL
	Nine Months Ended September 30	2013		2012			2013			2012		2013		2012
	Statutory federal income tax rate	35	%	35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(12.6	)	(11.0	)		(37.8	)		(34.5	)	—		—
	Production tax credits	(7.7	)	(6.0	)		(10.4	)		(8.6	)	(6.9	)	(5.5	)
	Effect of rate-making on property-related differences	(5.9	)	(4.3	)		(16.1	)		(10.6	)	(0.8	)	(1.5	)
	State apportionment change due to planned sale of RMT	—		4.3			—			6.9		—		3.5
	Other items, net	2.6		6			0.8			6.2		4.4		6.2
	Overall income tax rate	11.4	%	24	%		(28.5	%)		(5.6	%)	31.7	%	37.7	%
Production Tax Credits (Net Of State Tax Impacts)	'
	For the three and nine months ended September 30, production tax credits (net of state tax impacts) resulting from these wind projects are included in the table below (in millions). Production tax credits for Bent Tree - Phase I and Whispering Willow - East increased for the three- and nine-month periods primarily due to higher levels of electricity output generated by the wind projects.
		Three Months							Nine Months
		2013			2012				2013			2012
	Cedar Ridge (WPL)		$0.60			$0.70				$2.90			$3.00
	Bent Tree - Phase I (WPL)	2.2			1.8				9.2			6
	Subtotal (WPL)	2.8			2.5				12.1			9
	Whispering Willow - East (IPL)	2.3			2				10.3			8.7
			$5.10			$4.50				$22.40			$17.70
Summary Of Tax Credit Carryforwards	'
	At September 30, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$775			$266			2029
	State net operating losses	753			39				2018
	Federal tax credits	161			159				2022
						$464
	IPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$344			$118			2029
	State net operating losses	189			10				2018
	Federal tax credits	49			48				2022
						$176
	WPL	Carryforward			Deferred				Earliest
		Amount			Tax Assets				Expiration Date
	Federal net operating losses		$321			$110			2029
	State net operating losses	177			9				2018
	Federal tax credits	54			53				2022
						$172

Benefit_Plans_Tables

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
Schedule Of Qualified And Non-Qualified Pension And Other Post Retirement Benefits Costs	'
	The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
Estimated Future And Actual Employer Contributions	'
	Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Employees Participate In Defined Contribution Retirement Plans	'
	For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
Recognized Compensation Expense And Income Tax Benefits	'
	A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7
Schedule Of Equity Incentive Plans Activity	'
	Information related to fair values of nonvested performance shares and units at September 30, 2013 by year of grant were as follows:
		Performance Shares												Performance Units
		2013 Grant				2012 Grant				2011 Grant				2013 Grant			2012 Grant			2011 Grant
	Nonvested awards	49,093				45,612				45,235				21,935			23,226			20,751
	Alliant Energy common stock closing price on September 30, 2013		$49.55				$49.55				$49.55
	Alliant Energy common stock closing price on grant date														$47.58			$43.05			$38.75
	Estimated payout percentage based on performance criteria	103		%		100		%		130		%		103		%	100		%	130		%
	Fair values of each nonvested award		$51.04				$49.55				$64.42				$49.01			$43.05			$50.38
Performance Contingent Restricted Stock [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	A summary of the performance-contingent restricted stock activity was as follows:
		2013							2012
		Shares			Weighted				Shares			Weighted
					Average							Average
					Fair Value							Fair Value
	Nonvested shares, January 1	211,651				$32.42			301,738				$32.60
	Granted	49,093			47.58				45,612			43.05
	Vested (a)	—			—				(65,172	)		32.56
	Forfeited (b)	(101,822	)		23.67				(70,527	)		39.93
	Nonvested shares, September 30	158,922			42.71				211,651			32.42
	(a)	In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.
	(b)	In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.
Performance Contingent Cash Awards [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	A summary of the performance contingent cash awards activity was as follows:
		2013			2012
		Awards			Awards
	Nonvested awards, January 1	59,639			46,676
	Granted	39,530			36,936
	Vested (a)	—			(21,605	)
	Forfeited	(1,413	)		(1,533	)
	Nonvested awards, September 30	97,756			60,474
	(a)	In 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.
Performance Shares [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Schedule Of Equity Incentive Plans Activity	'
	A summary of the performance shares activity was as follows:
		2013			2012
		Shares (a)			Shares (a)
	Nonvested shares, January 1	145,277			236,979
	Granted	49,093			45,612
	Vested (b)	(54,430	)		(111,980	)
	Forfeited	—			(25,334	)
	Nonvested shares, September 30	139,940			145,277
	(a)	Share amounts represent the target number of performance shares. Each performance share’s value is based on the price of one share of Alliant Energy’s common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
	(b)	In 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). In 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares).
Performance Units [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	A summary of the performance unit activity was as follows:
		2013			2012
		Units (a)			Units (a)
	Nonvested units, January 1	64,969			42,996
	Granted	22,201			24,686
	Vested (b)	(19,760	)		—
	Forfeited	(1,498	)		(878	)
	Nonvested units, September 30	65,912			66,804
	(a)	Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.
	(b)	In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.
IPL [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
Schedule Of Qualified And Non-Qualified Pension And Other Post Retirement Benefits Costs	'
	The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
Estimated Future And Actual Employer Contributions	'
	Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Employees Participate In Defined Contribution Retirement Plans	'
	For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
Recognized Compensation Expense And Income Tax Benefits	'
	A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7
WPL [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Defined Benefit Pension And Other Postretirement Benefits Plans	'
	The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three and nine months ended September 30 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively.
	Alliant Energy	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$3.90				$3.30				$11.80				$10.00			$1.50			$1.70			$4.70			$5.20
	Interest cost	12.3				13				36.8				38.9			2.1			2.6			6.3			7.7
	Expected return on plan assets	(18.5		)		(17.2		)		(55.5		)		(51.6		)	(2.0		)	(1.9		)	(6.0		)	(5.7		)
	Amortization of prior service cost (credit)	0.1				0.1				0.2				0.2			(3.0		)	(3.0		)	(8.9		)	(9.0		)
	Amortization of actuarial loss	9				8.3				27.1				24.9			1.3			1.6			3.7			4.7
			$6.80				$7.50				$20.40				$22.40			($0.1	)		$1.00			($0.2	)		$2.90
	IPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$2.20				$1.80				$6.50				$5.60			$0.80			$0.70			$2.20			$2.20
	Interest cost	5.7				6.1				17.1				18.1			0.9			1.1			2.7			3.3
	Expected return on plan assets	(8.8		)		(8.2		)		(26.4		)		(24.5		)	(1.4		)	(1.3		)	(4.2		)	(3.9		)
	Amortization of prior service cost (credit)	—				—				0.1				0.1			(1.6		)	(1.5		)	(4.7		)	(4.7		)
	Amortization of actuarial loss	3.8				3.6				11.4				10.6			0.6			0.9			2			2.7
			$2.90				$3.30				$8.70				$9.90			($0.7	)		($0.1	)		($2.0	)		($0.4	)
	WPL	Defined Benefit Pension Plans															Other Postretirement Benefits Plans
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	Service cost		$1.50				$1.30				$4.40				$3.90			$0.60			$0.70			$1.80			$2.10
	Interest cost	5.2				5.4				15.5				16.2			0.8			1			2.5			3.1
	Expected return on plan assets	(8.0		)		(7.5		)		(23.9		)		(22.3		)	(0.4		)	(0.3		)	(1.0		)	(1.0		)
	Amortization of prior service cost (credit)	0.1				0.2				0.3				0.3			(0.9		)	(1.0		)	(2.9		)	(2.9		)
	Amortization of actuarial loss	4.2				3.9				12.8				11.8			0.5			0.6			1.5			1.7
			$3.00				$3.30				$9.10				$9.90			$0.60			$1.00			$1.90			$3.00
Schedule Of Qualified And Non-Qualified Pension And Other Post Retirement Benefits Costs	'
	The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs (credits) associated with Corporate Services employees providing services to IPL and WPL for the three and nine months ended September 30 (in millions):
		Pension Benefits Costs															Other Postretirement Benefits Costs (Credits)
		Three Months								Nine Months							Three Months						Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012
	IPL		$0.40				$0.40				$1.40				$1.40			($0.1	)		$—			($0.2	)		$0.10
	WPL	0.4				0.4				1.1				1			(0.1		)	0.1			(0.2		)	0.1
Estimated Future And Actual Employer Contributions	'
	Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):
		Estimated for Calendar Year 2013												Actual Through September 30, 2013
		Alliant Energy				IPL				WPL				Alliant Energy			IPL			WPL
	Defined benefit pension plans (a)		$2.30				$0.80				$0.20				$2.00			$0.70			$0.20
	Other postretirement benefits plans	3				—				3				2			—			2
	(a)	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Employees Participate In Defined Contribution Retirement Plans	'
	For the three and nine months ended September 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):
		Alliant Energy															IPL (a)												WPL (a)
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	401(k) costs		$4.70				$4.40				$14.70				$14.10			$2.40			$2.40			$7.60			$7.40			$2.10		$2.00		$6.50		$6.20
	(a)	IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.
Recognized Compensation Expense And Income Tax Benefits	'
	A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy															IPL												WPL
		Three Months								Nine Months							Three Months						Nine Months						Three Months				Nine Months
		2013				2012				2013				2012			2013			2012			2013			2012			2013		2012		2013		2012
	Compensation expense		$4.00				$0.10				$8.60				$3.80			$2.00			$0.10			$4.40			$2.00			$1.70		$0.10		$3.70		$1.70
	Income tax benefits	1.6				—				3.5				1.5			0.8			—			1.8			0.8			0.7		0.1		1.5		0.7

Common_Equity_Tables

Common Equity (Tables)	9 Months Ended
	Sep. 30, 2013
Stockholders' Equity Note [Abstract]	'
Common Share Activity	'
	A summary of Alliant Energy’s common stock activity was as follows:
	Shares outstanding, January 1, 2013	110,987,400
	Equity-based compensation plans (Note 5(b))	(23,374	)
	Other	(20,357	)
	Shares outstanding, September 30, 2013	110,943,669

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt Disclosure [Line Items]	'
Other Short-Term Borrowings	'
	Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
IPL [Member]	'
Debt Disclosure [Line Items]	'
Other Short-Term Borrowings	'
	Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.
WPL [Member]	'
Debt Disclosure [Line Items]	'
Other Short-Term Borrowings	'
	Information regarding commercial paper classified as short-term debt and back-stopped by Alliant Energy’s, IPL’s and WPL’s credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	September 30, 2013	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$237.30		$93.90	$—		$143.40
	Weighted average remaining maturity	1 day		2 days	N/A		1 day
	Weighted average interest rates	0.20%		0.20%	N/A		0.10%
	Available credit facility capacity (a)	$697.70		$206.10	$235.00		$256.60
		Alliant Energy						IPL						WPL
	Three Months Ended September 30	2013			2012			2013			2012			2013			2012
	Maximum amount outstanding		$284.10			$185.30			$—			$19.50			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$228.80			$133.00			$—			$1.30			$140.90			$11.90
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	N/A			0.4		%	0.2		%	0.3		%
	Nine Months Ended September 30
	Maximum amount outstanding		$284.10			$185.30			$26.30			$35.40			$165.40			$35.60
	(based on daily outstanding balances)
	Average amount outstanding		$197.20			$100.20			$1.70			$7.20			$113.40			$13.30
	(based on daily outstanding balances)
	Weighted average interest rates	0.2		%	0.4		%	0.4		%	0.4		%	0.2		%	0.3		%
	(a)	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at September 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at September 30, 2013 classified as long-term debt on Alliant Energy’s and IPL’s Condensed Consolidated Balance Sheets.

Investments_Tables

Investments (Tables)	9 Months Ended
	Sep. 30, 2013
Schedule of Investments [Line Items]	'
Unconsolidated Equity Investments	'
	Equity (income) loss from Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy												WPL
		Three Months						Nine Months						Three Months						Nine Months
		2013			2012			2013			2012			2013			2012			2013			2012
	ATC		($10.8	)		($10.4	)		($31.7	)		($30.6	)		($10.8	)		($10.4	)		($31.7	)		($30.6	)
	Other	(0.3		)	—			(1.0		)	0.2			(0.3		)	(0.1		)	(1.0		)	(0.6		)
			($11.1	)		($10.4	)		($32.7	)		($30.4	)		($11.1	)		($10.5	)		($32.7	)		($31.2	)
Summary Financial Information	'
	Summary financial information from the unaudited financial statements of ATC for the three and nine months ended September 30 was as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013			2012
	Operating revenues		$160.40			$150.30			$464.30			$450.10
	Operating income	82.9			81.5			247.1			240
	Net income	62.7			60.5			184.5			177.9
WPL [Member]	'
Schedule of Investments [Line Items]	'
Unconsolidated Equity Investments	'
	Equity (income) loss from Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions):
		Alliant Energy												WPL
		Three Months						Nine Months						Three Months						Nine Months
		2013			2012			2013			2012			2013			2012			2013			2012
	ATC		($10.8	)		($10.4	)		($31.7	)		($30.6	)		($10.8	)		($10.4	)		($31.7	)		($30.6	)
	Other	(0.3		)	—			(1.0		)	0.2			(0.3		)	(0.1		)	(1.0		)	(0.6		)
			($11.1	)		($10.4	)		($32.7	)		($30.4	)		($11.1	)		($10.5	)		($32.7	)		($31.2	)
Summary Financial Information	'
	Summary financial information from the unaudited financial statements of ATC for the three and nine months ended September 30 was as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013			2012
	Operating revenues		$160.40			$150.30			$464.30			$450.10
	Operating income	82.9			81.5			247.1			240
	Net income	62.7			60.5			184.5			177.9

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Carrying Amount and Fair Value Of Financial Instruments	'
	Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
Fair Value Measurements	'
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
	Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
	Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
	WPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
	Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
	Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Fair Value Measurements Using Significant Unobservable Inputs	'
	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
	Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
	Transfers out of Level 3 (c)	—			9.3			—		—
	Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
	Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
	Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
	Purchases	50.9			35.8			—		—
	Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
	Transfers into Level 3 (b)	(0.1		)	—			—		—
	Transfers out of Level 3 (c)	—			7.4			—		—
	Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
	Transfers into Level 3 (b)	—			(1.1		)	—		—
	Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
	Purchases	46.1			26.8			—		—
	Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended September 30	2013			2012
	Beginning balance, July 1		$1.90			$4.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
	Transfers into Level 3 (b)	(9.8		)	(0.4		)
	Transfers out of Level 3 (c)	—			1.9
	Settlements	(1.6		)	(2.0		)
	Ending balance, September 30		($11.4	)		$2.10
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Nine Months Ended September 30	2013			2012
	Beginning balance, January 1		($0.6	)		($5.2	)
	Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
	Transfers into Level 3 (b)	(0.4		)	(0.6		)
	Transfers out of Level 3 (c)	1			5.9
	Purchases	4.8			9
	Settlements	(6.4		)	(3.5		)
	Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
IPL [Member]	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Carrying Amount and Fair Value Of Financial Instruments	'
	Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
Fair Value Measurements	'
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
	Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
	Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
	WPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
	Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
	Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Fair Value Measurements Using Significant Unobservable Inputs	'
	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
	Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
	Transfers out of Level 3 (c)	—			9.3			—		—
	Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
	Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
	Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
	Purchases	50.9			35.8			—		—
	Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
	Transfers into Level 3 (b)	(0.1		)	—			—		—
	Transfers out of Level 3 (c)	—			7.4			—		—
	Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
	Transfers into Level 3 (b)	—			(1.1		)	—		—
	Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
	Purchases	46.1			26.8			—		—
	Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended September 30	2013			2012
	Beginning balance, July 1		$1.90			$4.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
	Transfers into Level 3 (b)	(9.8		)	(0.4		)
	Transfers out of Level 3 (c)	—			1.9
	Settlements	(1.6		)	(2.0		)
	Ending balance, September 30		($11.4	)		$2.10
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Nine Months Ended September 30	2013			2012
	Beginning balance, January 1		($0.6	)		($5.2	)
	Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
	Transfers into Level 3 (b)	(0.4		)	(0.6		)
	Transfers out of Level 3 (c)	1			5.9
	Purchases	4.8			9
	Settlements	(6.4		)	(3.5		)
	Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
WPL [Member]	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Carrying Amount and Fair Value Of Financial Instruments	'
	Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
		Alliant Energy						IPL				WPL
	September 30, 2013	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$36.80			$36.80			$31.50		$31.50		$5.30		$5.30
	Deferred proceeds (sales of receivables) (Note 3(a))	86.9			86.9			86.9		86.9		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,153.20			3,553.60			1,374.80		1,553.80		1,332.00		1,541.90
	Cumulative preferred stock (Note 7)	200			169.5			200		169.5		—		—
	Derivative liabilities (Note 11)	27.1			27.1			6.7		6.7		20.4		20.4
		Alliant Energy						IPL				WPL
	December 31, 2012	Carrying			Fair			Carrying		Fair		Carrying		Fair
		Amount			Value			Amount		Value		Amount		Value
	Assets:
	Derivative assets (Note 11)		$26.20			$26.20			$17.50		$17.50		$8.70		$8.70
	Deferred proceeds (sales of receivables) (Note 3(a))	66.8			66.8			66.8		66.8		—		—
	Capitalization and liabilities:
	Long-term debt (including current maturities) (Note 8(b))	3,138.10			3,860.50			1,359.50		1,679.90		1,331.50		1,713.30
	Cumulative preferred stock (Note 7)	205.1			212.6			145.1		151.8		60		60.8
	Derivative liabilities (Note 11)	40.4			40.4			16.1		16.1		24.3		24.3
Fair Value Measurements	'
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$36.80			$—			$3.20		$33.60		$26.20		$—		$4.80		$21.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,553.60			—			3,553.20		0.4		3,860.50		—		3,860.00		0.5
	Cumulative preferred stock	169.5			169.5			—		—		212.6		162.3		50.3		—
	Derivatives - commodity contracts	27.1			—			10.7		16.4		40.4		—		30.9		9.5
	IPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$31.50			$—			$1.90		$29.60		$17.50		$—		$3.10		$14.40
	Deferred proceeds	86.9			—			—		86.9		66.8		—		—		66.8
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,553.80			—			1,553.80		—		1,679.90		—		1,679.90		—
	Cumulative preferred stock	169.5			169.5			—		—		151.8		151.8		—		—
	Derivatives - commodity contracts	6.7			—			5.7		1		16.1		—		14.2		1.9
	WPL	September 30, 2013										December 31, 2012
		Fair			Level			Level		Level		Fair		Level		Level		Level
		Value			1			2		3		Value		1		2		3
	Assets:
	Derivatives - commodity contracts		$5.30			$—			$1.30		$4.00		$8.70		$—		$1.70		$7.00
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,541.90			—			1,541.90		—		1,713.30		—		1,713.30		—
	Cumulative preferred stock	—			—			—		—		60.8		10.5		50.3		—
	Derivatives - commodity contracts	20.4			—			5		15.4		24.3		—		16.7		7.6
Fair Value Measurements Using Significant Unobservable Inputs	'
	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$42.50			$18.80			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	0.1			(2.3		)	—		—
	Transfers into Level 3 (b)	(9.9		)	(0.4		)	—		—
	Transfers out of Level 3 (c)	—			9.3			—		—
	Settlements (d)	(15.5		)	(7.8		)	17.6		72.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$0.10			($0.7	)		$—		$—
	Alliant Energy	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$11.90			($0.9	)		$66.80		$53.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(8.3		)	(8.3		)	—		—
	Transfers into Level 3 (b)	(0.4		)	(1.7		)	—		—
	Transfers out of Level 3 (c)	(0.5		)	8.3			—		—
	Purchases	50.9			35.8			—		—
	Settlements (d)	(36.4		)	(15.6		)	20.1		100.2
	Ending balance, September 30		$17.20			$17.60			$86.90		$153.90
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($8.3	)		($4.4	)		$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended September 30	2013			2012			2013		2012
	Beginning balance, July 1		$40.60			$14.10			$69.30		$81.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	2			(0.2		)	—		—
	Transfers into Level 3 (b)	(0.1		)	—			—		—
	Transfers out of Level 3 (c)	—			7.4			—		—
	Settlements (d)	(13.9		)	(5.8		)	17.6		72.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 (a)		$2.00			$1.40			$—		$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Nine Months Ended September 30	2013			2012			2013		2012
	Beginning balance, January 1		$12.50			$4.30			$66.80		$53.70
	Total net gains (losses) (realized/unrealized) included in changes in net assets (a)	1.5			(4.8		)	—		—
	Transfers into Level 3 (b)	—			(1.1		)	—		—
	Transfers out of Level 3 (c)	(1.5		)	2.4			—		—
	Purchases	46.1			26.8			—		—
	Settlements (d)	(30.0		)	(12.1		)	20.1		100.2
	Ending balance, September 30		$28.60			$15.50			$86.90		$153.90
	The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 (a)		$1.50			($0.7	)		$—		$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended September 30	2013			2012
	Beginning balance, July 1		$1.90			$4.70
	Total net losses (realized/unrealized) included in changes in net assets (a)	(1.9		)	(2.1		)
	Transfers into Level 3 (b)	(9.8		)	(0.4		)
	Transfers out of Level 3 (c)	—			1.9
	Settlements	(1.6		)	(2.0		)
	Ending balance, September 30		($11.4	)		$2.10
	The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($1.9	)		($2.1	)
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Nine Months Ended September 30	2013			2012
	Beginning balance, January 1		($0.6	)		($5.2	)
	Total net losses (realized/unrealized) included in changes in net assets (a)	(9.8		)	(3.5		)
	Transfers into Level 3 (b)	(0.4		)	(0.6		)
	Transfers out of Level 3 (c)	1			5.9
	Purchases	4.8			9
	Settlements	(6.4		)	(3.5		)
	Ending balance, September 30		($11.4	)		$2.10
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 (a)		($9.8	)		($3.7	)
(a)	Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b)	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c)	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d)	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.

Derivative_Instruments_Tables

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative [Line Items]	'
Notional Amounts Of Derivative Instruments	'
	As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
Fair Value Of Financial Instruments	'
	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments	'
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
Balance Sheet Offsetting	'
	Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4
IPL [Member]	'
Derivative [Line Items]	'
Notional Amounts Of Derivative Instruments	'
	As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
Fair Value Of Financial Instruments	'
	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments	'
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
Balance Sheet Offsetting	'
	Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4
WPL [Member]	'
Derivative [Line Items]	'
Notional Amounts Of Derivative Instruments	'
	As of September 30, 2013, notional amounts by delivery year related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands):
		2013			2014			2015		2016		2017			2018			Total
	Alliant Energy
	Electricity (MWhs)	1,460			5,625			2,190		1,318		1,314			1,314			13,221
	FTRs (MWs)	13			22			—		—		—			—			35
	Natural gas (Dths)	30,852			32,518			7,544		1,639		—			—			72,553
	Coal (tons)	239			1,591			936		955		868			714			5,303
	IPL
	Electricity (MWhs)	835			1,923			—		—		—			—			2,758
	FTRs (MWs)	8			14			—		—		—			—			22
	Natural gas (Dths)	23,908			24,001			6,419		1,639		—			—			55,967
	Coal (tons)	15			270			—		216		129			184			814
	WPL
	Electricity (MWhs)	625			3,702			2,190		1,318		1,314			1,314			10,463
	FTRs (MWs)	5			8			—		—		—			—			13
	Natural gas (Dths)	6,944			8,517			1,125		—		—			—			16,586
	Coal (tons)	224			1,321			936		739		739			530			4,489
Fair Value Of Financial Instruments	'
	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other long-term liabilities and deferred credits” on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
	Commodity contracts	September 30,				December 31,			September 30,			December 31,				September 30,			December 31,
		2013				2012			2013			2012				2013			2012
	Current derivative assets		$34.70				$23.50			$29.90			$17.00				$4.80			$6.50
	Non-current derivative assets	2.1				2.7			1.6			0.5				0.5			2.2
	Current derivative liabilities	11.8				31.1			4.9			14.1				6.9			17
	Non-current derivative liabilities	15.3				9.3			1.8			2				13.5			7.3
Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments	'
	Changes in unrealized gains (losses) from commodity derivative instruments not designated as hedging instruments were recorded with offsets to regulatory assets or regulatory liabilities on the Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		2013				2012			2013			2012				2013			2012
	Three Months Ended September 30
	Regulatory assets		$2.20				($6.3	)		($0.4	)		($0.1	)			$2.60			($6.2	)
	Regulatory liabilities	(1.0		)		15.8			3.6			6.9				(4.6		)	8.9
	Nine Months Ended September 30
	Regulatory assets	(14.2		)		(38.3		)	(4.6		)	(17.3		)		(9.6		)	(21.0		)
	Regulatory liabilities	16.6				21.3			9.9			11.3				6.7			10
Balance Sheet Offsetting	'
	Alliant Energy, IPL and WPL do not net the fair value amounts of derivative instruments subject to a master netting arrangement by counterparty on the Condensed Consolidated Balance Sheets. Alliant Energy, IPL and WPL also do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. However, if Alliant Energy, IPL and WPL did net the fair value amounts of derivative instruments and related cash collateral by counterparty, derivative assets and derivative liabilities related to commodity contracts would have been presented on their Condensed Consolidated Balance Sheets as follows (in millions):
		Alliant Energy							IPL							WPL
		Gross							Gross							Gross
		(as reported)				Net			(as reported)			Net				(as reported)			Net
	September 30, 2013
	Derivative assets		$36.80				$32.30			$31.50			$29.20				$5.30			$3.10
	Derivative liabilities	27.1				23.5			6.7			5.3				20.4			18.2
	31-Dec-12
	Derivative assets	26.2				19.3			17.5			14.5				8.7			4.8
	Derivative liabilities	40.4				33			16.1			12.6				24.3			20.4

Commitments_And_Contingencies_

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2013
Long-term Purchase Commitment [Line Items]	'
Operating Expense Purchase Obligations	'
	At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.
IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Operating Expense Purchase Obligations	'
	At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.
WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Operating Expense Purchase Obligations	'
	At September 30, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy		IPL		WPL
	Purchased power (a):
	DAEC (IPL) (b)		$1,698		$1,698		$—
	Kewaunee (WPL)	18		—		18
	Other (c)	259		1		258
		1,975		1,699		276
	Natural gas	336		203		133
	Coal (d)	328		151		177
	SO2 emission allowances	34		34		—
	Other (e)	19		9		6
			$2,692		$2,096		$592
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
	(c)	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.
	(d)	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2013 regarding expected future usage, which is subject to change.
	(e)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2013.

Segments_Of_Business_Tables

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting Information [Line Items]	'
Schedule Of Segments Of Business	'
	Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations.
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$798.10		$39.80			$17.40			$855.30		$11.30			$866.60
	Operating income (loss)	199.6		(3.4		)	(0.3		)	195.9		5.5			201.4
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									171.3		(12.4		)	158.9
	Loss from discontinued operations, net of tax									—		(1.3		)	(1.3		)
	Net income (loss) attributable to Alliant Energy common shareowners									171.3		(13.7		)	157.6
	Three Months Ended September 30, 2012
	Operating revenues		$815.30		$46.80			$12.20			$874.30		$13.30			$887.60
	Operating income	203.1		0.8			1.5			205.4		8.3			213.7
	Amounts attributable to Alliant Energy common shareowners:
	Income (loss) from continuing operations, net of tax									159.2		(10.2		)	149
	Income from discontinued operations, net of tax									—		1.7			1.7
	Net income (loss) attributable to Alliant Energy common shareowners									159.2		(8.5		)	150.7
		Utility										Non-Regulated,			Alliant Energy
		Electric		Gas			Other			Total		Parent and Other			Consolidated
		(in millions)
	Nine Months Ended September 30, 2013
	Operating revenues		$2,043.40		$310.50			$52.40			$2,406.30		$37.90			$2,444.20
	Operating income	359.1		39.5			5.5			404.1		21.2			425.3
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									292.8		4.9			297.7
	Loss from discontinued operations, net of tax									—		(4.9		)	(4.9		)
	Net income attributable to Alliant Energy common shareowners									292.8		—			292.8
	Nine Months Ended September 30, 2012
	Operating revenues		$2,000.30		$263.90			$39.70			$2,303.90		$39.70			$2,343.60
	Operating income	354		32.1			4.7			390.8		27.3			418.1
	Amounts attributable to Alliant Energy common shareowners:
	Income from continuing operations, net of tax									237.4		16.4			253.8
	Loss from discontinued operations, net of tax									—		(2.3		)	(2.3		)
	Net income attributable to Alliant Energy common shareowners									237.4		14.1			251.5
IPL [Member]	'
Segment Reporting Information [Line Items]	'
Schedule Of Segments Of Business	'
	Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$457.60		$24.60			$12.20			$494.40
	Operating income (loss)	99.6		(0.7		)	1.1			100
	Earnings available for common stock									110
	Three Months Ended September 30, 2012
	Operating revenues		$456.60		$29.60			$11.50			$497.70
	Operating income	109.5		0.6			1.9			112
	Earnings available for common stock									103.3
	Nine Months Ended September 30, 2013
	Operating revenues		$1,137.40		$180.90			$37.40			$1,355.70
	Operating income	146.2		22.6			7			175.8
	Earnings available for common stock									155.1
	Nine Months Ended September 30, 2012
	Operating revenues		$1,070.70		$149.20			$37.20			$1,257.10
	Operating income	149.3		15.6			6.4			171.3
	Earnings available for common stock									115.2
WPL [Member]	'
Segment Reporting Information [Line Items]	'
Schedule Of Segments Of Business	'
	Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations.
		Electric		Gas			Other			Total
		(in millions)
	Three Months Ended September 30, 2013
	Operating revenues		$340.50		$15.20			$5.20			$360.90
	Operating income (loss)	100		(2.7		)	(1.4		)	95.9
	Earnings available for common stock									61.3
	Three Months Ended September 30, 2012
	Operating revenues		$358.70		$17.20			$0.70			$376.60
	Operating income (loss)	93.6		0.2			(0.4		)	93.4
	Earnings available for common stock									55.9
	Nine Months Ended September 30, 2013
	Operating revenues		$906.00		$129.60			$15.00			$1,050.60
	Operating income (loss)	212.9		16.9			(1.5		)	228.3
	Earnings available for common stock									137.7
	Nine Months Ended September 30, 2012
	Operating revenues		$929.60		$114.70			$2.50			$1,046.80
	Operating income (loss)	204.7		16.5			(1.7		)	219.5
	Earnings available for common stock									122.2

Discontinued_Operations_And_As1

Discontinued Operations And Assets And Liabilities Held For Sale (Tables)	9 Months Ended
	Sep. 30, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Components Of Discontinued Operations In Condensed Consolidated Statements Of Income	'
	A summary of the components of discontinued operations in Alliant Energy’s Condensed Consolidated Statements of Income for the three and nine months ended September 30 was as follows (in millions):
		Three Months					Nine Months
		2013			2012		2013			2012
	Operating revenues		$—			$94.50		$0.90			$243.00
	Operating expenses	2.1			91.7		8.6			246.6
	Interest expense and other	—			0.2		—			0.4
	Income (loss) before income taxes	(2.1		)	2.6		(7.7		)	(4.0		)
	Income tax expense (benefit)	(0.8		)	0.9		(2.8		)	(1.7		)
	Income (loss) from discontinued operations, net of tax		($1.3	)		$1.70		($4.9	)		($2.3	)
Components Of Assets And Liabilities Held For Sale In Condensed Consolidated Balance Sheets	'
	As of December 31, 2012, Alliant Energy’s Condensed Consolidated Balance Sheet included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
	Current assets		$27.90
	Current liabilities	31.4
	Net liabilities held for sale		($3.5	)

Asset_Retirement_Obligations_A1

Asset Retirement Obligations (AROs) (Tables)	9 Months Ended
	Sep. 30, 2013
Schedule of Asset Retirement Obligations [Line Items]	'
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	'
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.
IPL [Member]	'
Schedule of Asset Retirement Obligations [Line Items]	'
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	'
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.
WPL [Member]	'
Schedule of Asset Retirement Obligations [Line Items]	'
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	'
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2013			2012			2013			2012			2013			2012
	Balance, January 1		$101.50			$91.10			$45.50			$56.20			$46.90			$34.90
	Revisions in estimated cash flows (a)	3.4			(9.9		)	0.8			(9.2		)	2.6			(0.7		)
	Liabilities settled	(0.9		)	(2.6		)	(0.1		)	(2.5		)	(0.8		)	(0.1		)
	Liabilities incurred (b)	—			16			—			—			—			7.6
	Accretion expense	2.8			2.6			1.3			1.4			1.2			1.2
	Balance, September 30		$106.80			$97.20			$47.50			$45.90			$49.90			$42.90
	(a)	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
	(b)	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

Related_Parties_Tables

Related Parties (Tables)	9 Months Ended
	Sep. 30, 2013
Related Party Transaction [Line Items]	'
Sales Credited And Purchases Billed	'
	The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
Corporate Services Billings	'
	The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
Net Intercompany Payables	'
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
Related Amounts Billed Between Parties	'
	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013		2012
	ATC billings to WPL		$24			$22			$72		$67
	WPL billings to ATC	2			3			9		7
IPL [Member]	'
Related Party Transaction [Line Items]	'
Sales Credited And Purchases Billed	'
	The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
Corporate Services Billings	'
	The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
Net Intercompany Payables	'
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
WPL [Member]	'
Related Party Transaction [Line Items]	'
Sales Credited And Purchases Billed	'
	The sales credited to and purchases billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Sales credited		$2			$3			$5		$7		$3		$4		$10		$10
	Purchases billed	108			87			260		237		16		13		44		50
Corporate Services Billings	'
	The amounts billed to IPL and WPL for the three and nine months ended September 30 were as follows (in millions):
		IPL										WPL
		Three Months						Nine Months				Three Months				Nine Months
		2013			2012			2013		2012		2013		2012		2013		2012
	Corporate Services billings		$39			$34			$107		$97		$28		$26		$77		$76
Net Intercompany Payables	'
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		September 30, 2013		December 31, 2012	September 30, 2013		December 31, 2012
	Net payables to Corporate Services	$95		$72	$46		$40
Related Amounts Billed Between Parties	'
	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions):
		Three Months						Nine Months
		2013			2012			2013		2012
	ATC billings to WPL		$24			$22			$72		$67
	WPL billings to ATC	2			3			9		7

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Weighted Average Common Shares Outstanding	'
	A reconciliation of the weighted average common shares outstanding used in the basic and diluted EPS calculation for the three and nine months ended September 30 was as follows (in thousands):
		Three Months		Nine Months
		2013	2012	2013	2012
	Weighted average common shares outstanding:
	Basic EPS calculation	110,783	110,768	110,775	110,747
	Effect of dilutive share-based awards	2	11	5	16
	Diluted EPS calculation	110,785	110,779	110,780	110,763

Summary_Of_Significant_Account3

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	($74.90)	$5
Increase in regulatory assets	14.4	73.5
Wholesale power supply agreement termination notice minimum term (in years)	'5 years	'
Wholesale power supply agreement minimum term (in years)	'10 years	'
Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	67	'
IPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	-68.3	-27.5
Increase in regulatory assets	9.8	57.7
IPL [Member] | Electric tax benefit rider [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	59	'
IPL [Member] | Gas tax benefit rider [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	8	'
WPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Regulatory liabilities utilized	-6.6	32.5
Increase in regulatory assets	4.6	15.8
Wpl's Edgewater Unit 5 Purchase [Member] | WPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Jointly owned utility plant, proportionate ownership share	25.00%	'
2013 and 2014 Test Period Retail Electric And Gas Final Order [Member] | Alliant Energy and WPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Increase in regulatory assets	'	5
Credit to utility other operation and maintenance	'	5
IPL FERC Authorized Return On Common Equity [Member] | IPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Return on common equity wholesale electric rate	10.97%	'
Scenario, Forecast [Member] | IPL [Member]	'	'
Public Utility, Property, Plant and Equipment [Line Items]	'	'
Expected proceeds from asset sales	$128	'

Summary_Of_Significant_Account4

Summary Of Significant Accounting Policies (Regulatory Assets) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Regulatory Assets [Line Items]	'	'
Regulatory assets	$1,596.20	$1,612.40
Tax-related [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	813.6	770.7
Pension and other postretirement benefits costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	525.2	549.2
AROs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	66.9	62.4
Emission allowances [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	30	30
Derivatives [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	26.8	40.2
Environmental-related costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	26	34.9
Other [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	107.7	125
IPL [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	1,216	1,217.90
IPL [Member] | Tax-related [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	783.6	746.2
IPL [Member] | Pension and other postretirement benefits costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	267.9	279.3
IPL [Member] | AROs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	38.8	38.6
IPL [Member] | Emission allowances [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	30	30
IPL [Member] | Derivatives [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	6.9	16.3
IPL [Member] | Environmental-related costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	21.8	30.3
IPL [Member] | Other [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	67	77.2
WPL [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	380.2	394.5
WPL [Member] | Tax-related [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	30	24.5
WPL [Member] | Pension and other postretirement benefits costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	257.3	269.9
WPL [Member] | AROs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	28.1	23.8
WPL [Member] | Emission allowances [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	0	0
WPL [Member] | Derivatives [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	19.9	23.9
WPL [Member] | Environmental-related costs [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	4.2	4.6
WPL [Member] | Other [Member]	'	'
Regulatory Assets [Line Items]	'	'
Regulatory assets	$40.70	$47.80

Summary_Of_Significant_Account5

Summary Of Significant Accounting Policies (Regulatory Liabilities) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	$837.60	$916.10
Cost of removal obligations [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	415.7	408.7
IPL's tax benefit riders [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	288.8	355.8
Energy conservation cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	58.1	55.1
IPL's electric transmission assets sale [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	24.3	32.5
Commodity cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	7	17.7
Other [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	43.7	46.3
IPL [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	630.4	701.4
IPL [Member] | Cost of removal obligations [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	275.8	268
IPL [Member] | IPL's tax benefit riders [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	288.8	355.8
IPL [Member] | Energy conservation cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	12.6	10
IPL [Member] | IPL's electric transmission assets sale [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	24.3	32.5
IPL [Member] | Commodity cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	1.1	5.2
IPL [Member] | Other [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	27.8	29.9
WPL [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	207.2	214.7
WPL [Member] | Cost of removal obligations [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	139.9	140.7
WPL [Member] | IPL's tax benefit riders [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	0	0
WPL [Member] | Energy conservation cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	45.5	45.1
WPL [Member] | IPL's electric transmission assets sale [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	0	0
WPL [Member] | Commodity cost recovery [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	5.9	12.5
WPL [Member] | Other [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory liabilities	$15.90	$16.40

Utility_Rate_Cases_Narrative_D

Utility Rate Cases (Narrative) (Details) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Jul. 31, 2012

Jul. 31, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Jun. 30, 2012

31-May-12

Nov. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2013

2012 Test Year Retail Electric Fuel Related, Request [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

Alliant Energy and IPL [Member]

Alliant Energy and IPL [Member]

Scenario, Forecast [Member]

2013/2014 Test Period Retail Electric And Gas, Request [Member]

2014 Test Year Retail Electric Fuel Related, Request [Member]

2013 Test Year Retail Electric Fuel Related, Final Order [Member]

2013 Test Year Retail Electric Fuel Related, Request [Member]

2012 Test Year Retail Electric Fuel Related, Request [Member]

2012 Test Year Retail Electric Fuel Related, Request [Member]

Gas tax benefit rider [Member]

2011 Test Year Retail Gas IA, Request [Member]

2011 Test Year Retail Gas IA, Request [Member]

2011 Test Year Retail Gas IA, Settlement [Member]

Revenue Requirement Adjustment [Member]

Revenue Requirement Adjustment [Member]

IPL [Member]

Gas tax benefit rider [Member]

Revenue Requirement Adjustment [Member]

Utility Rate Cases [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reduction in annual rates for its customers, amount

'

'

'

'

'

'

'

'

'

$13

'

$29

'

'

'

'

'

'

'

'

'

$36

'

'

'

'

Proposed gas tax benefit rider, term

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

Increase in interim rates for its customers, amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9

'

'

'

'

'

Increase in interim rates for its customers, percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

'

Increase in annual rates for its customers, amount

'

'

'

'

'

'

'

'

'

'

31

'

'

'

'

'

'

'

'

'

'

'

11

'

'

'

Increase in annual rates for its customers, percentage

'

'

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

'

'

'

'

'

'

'

4.00%

'

'

'

Revenue requirement adjustment

'

'

74.9

-5

'

'

'

6.6

-32.5

'

'

'

'

'

'

'

'

68.3

27.5

-8

'

'

'

'

'

24

Electric revenue

798.1

815.3

2,043.40

2,000.30

'

340.5

358.7

906

929.6

'

'

'

'

'

'

457.6

456.6

1,137.40

1,070.70

'

'

'

'

7

18

'

Reduction in annual rates for its customers, percentage

'

'

'

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Rate at which fuel costs will be monitored

'

'

'

'

'

'

'

'

'

'

'

'

2.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

Over-collection of fuel-related costs

'

'

'

'

17

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collected outside the approved range for 2012

'

'

'

'

'

'

'

'

'

'

'

'

'

'

11

'

'

'

'

'

'

'

'

'

'

'

Refunds to customers, including interest

'

'

'

'

'

'

'

'

'

'

'

'

'

$12

'

'

'

'

'

'

'

'

'

'

'

'

Receivables_Narrative_Details

Receivables (Narrative) (Details) (USD $)	9 Months Ended				1 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Oct. 31, 2013
			IPL [Member]	IPL [Member]	Senior Debentures [Member]
					4.7% senior debentures [Domain]
					Subsequent Event [Member]
					IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'	'
Receivables sold	'	'	$229.80	$198.40	'
Proceeds from issuance of long-term debt	0	75	'	'	250
Proceeds from Franklin County wind project cash grant	$62.40	$0	'	'	'

Receivables_Maximum_And_Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) (IPL [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Costs incurred	$0.30	$0.40	$1	$1.10
Maximum [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Outstanding aggregate cash proceeds (based on daily outstanding balances)	155	150	170	160
Average [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$132.70	$95	$132.50	$124.20

Receivables_Receivables_Sold_U

Receivables (Receivables Sold Under The Agreement) (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Fair value of deferred proceeds	$86.90		$66.80
IPL [Member]	'		'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'		'
Customer accounts receivable	158.8		118.2
Unbilled utility revenues	70.9		77.4
Other receivables	0.1		2.8
Receivables sold	229.8		198.4
Less: cash proceeds	140	[1]	130	[1]
Deferred proceeds	89.8		68.4
Less: allowance for doubtful accounts	2.9		1.6
Fair value of deferred proceeds	86.9		66.8
Outstanding receivables past due	$22		$16.10
[1]	Changes in cash proceeds are presented in bSales of accounts receivableb in operating activities in Alliant Energybs and IPLbs Condensed Consolidated Statements of Cash Flows.

Receivables_Additional_Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
IPL [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Collections reinvested in receivables	$481.10	$522.90	$1,407.40	$1,334.70
Credit losses, net of recoveries	$3.90	$3	$7.80	$7.30

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)

9 Months Ended

3 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Mar. 31, 2012

Mar. 31, 2012

Mar. 31, 2012

wind_projects

Deferred income tax assets [Member]

IPL [Member]

IPL [Member]

IPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

State Apportionment [Member]

State Apportionment [Member]

State Apportionment [Member]

Whispering Willow - East Wind Project [Member]

Cedar Ridge Wind Project [Member]

Bent Tree - Phase I Wind Project [Member]

Deferred income tax assets [Member]

IPL [Member]

WPL [Member]

MW

MW

MW

Income Tax [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Wind projects generating production tax credits (in wind projects)

3

'

'

'

'

'

'

'

'

'

'

'

'

Electric capacity of wind projects generating production tax credits (in megawatts)

'

'

'

'

'

200

'

68

200

'

'

'

'

Deferred income tax expense

'

'

'

'

'

'

'

'

'

'

$15

$8

$7

Increase (decrease) current deferred tax assets

-75.4

-90.5

-39

-71

-88.9

'

'

'

'

-40.7

'

'

'

Increase (decrease) non-current deferred tax liabilities

$129.70

'

'

$73.70

'

'

$41.30

'

'

'

'

'

'

Income_Taxes_Schedule_Of_Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Effective Tax Rate [Line Items]	'	'	'	'
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	-12.90%	-10.30%	-12.60%	-11.00%
Production tax credits	-7.70%	-5.50%	-7.70%	-6.00%
Effect of rate-making on property-related differences	-6.20%	-4.70%	-5.90%	-4.30%
Other items, net	1.60%	5.90%	2.60%	6.00%
Overall income tax rate	9.80%	20.40%	11.40%	24.00%
IPL [Member]	'	'	'	'
Effective Tax Rate [Line Items]	'	'	'	'
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	-38.90%	-34.20%	-37.80%	-34.50%
Production tax credits	-10.60%	-8.60%	-10.40%	-8.60%
Effect of rate-making on property-related differences	-16.50%	-11.20%	-16.10%	-10.60%
Other items, net	0.40%	6.40%	0.80%	6.20%
Overall income tax rate	-30.60%	-12.60%	-28.50%	-5.60%
WPL [Member]	'	'	'	'
Effective Tax Rate [Line Items]	'	'	'	'
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	0.00%	0.00%	0.00%	0.00%
Production tax credits	-6.60%	-4.30%	-6.90%	-5.50%
Effect of rate-making on property-related differences	-1.40%	-1.10%	-0.80%	-1.50%
Other items, net	3.70%	5.90%	4.40%	6.20%
Overall income tax rate	30.70%	35.50%	31.70%	37.70%
State Apportionment [Member]	'	'	'	'
Effective Tax Rate [Line Items]	'	'	'	'
State apportionment change due to planned sale of RMT	'	'	0.00%	4.30%
State Apportionment [Member] | IPL [Member]	'	'	'	'
Effective Tax Rate [Line Items]	'	'	'	'
State apportionment change due to planned sale of RMT	'	'	0.00%	6.90%
State Apportionment [Member] | WPL [Member]	'	'	'	'
Effective Tax Rate [Line Items]	'	'	'	'
State apportionment change due to planned sale of RMT	'	'	0.00%	3.50%

Income_Taxes_Production_Tax_Cr

Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Production Tax Credits [Line Items]	'	'	'	'
Production tax credits (net of state tax impacts)	$5.10	$4.50	$22.40	$17.70
WPL [Member]	'	'	'	'
Production Tax Credits [Line Items]	'	'	'	'
Production tax credits (net of state tax impacts)	2.8	2.5	12.1	9
Cedar Ridge Wind Project [Member] | WPL [Member]	'	'	'	'
Production Tax Credits [Line Items]	'	'	'	'
Production tax credits (net of state tax impacts)	0.6	0.7	2.9	3
Bent Tree - Phase I Wind Project [Member] | WPL [Member]	'	'	'	'
Production Tax Credits [Line Items]	'	'	'	'
Production tax credits (net of state tax impacts)	2.2	1.8	9.2	6
Whispering Willow - East Wind Project [Member] | IPL [Member]	'	'	'	'
Production Tax Credits [Line Items]	'	'	'	'
Production tax credits (net of state tax impacts)	$2.30	$2	$10.30	$8.70

Income_Taxes_Summary_Of_Tax_Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Operating Loss Carryforwards [Line Items]	'
Net operating losses, deferred tax assets	$464
IPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, deferred tax assets	176
WPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, deferred tax assets	172
Federal [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	775
Net operating losses, deferred tax assets	266
Tax credits, carryforward amount	161
Tax credits, deferred tax asset	159
Federal [Member] | IPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	344
Net operating losses, deferred tax assets	118
Tax credits, carryforward amount	49
Tax credits, deferred tax asset	48
Federal [Member] | WPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	321
Net operating losses, deferred tax assets	110
Tax credits, carryforward amount	54
Tax credits, deferred tax asset	53
State [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	753
Net operating losses, deferred tax assets	39
State [Member] | IPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	189
Net operating losses, deferred tax assets	10
State [Member] | WPL [Member]	'
Operating Loss Carryforwards [Line Items]	'
Net operating losses, carryforward amount	177
Net operating losses, deferred tax assets	$9

Benefit_Plans_Narrative_Detail

Benefit Plans (Narrative) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Benefit Plans [Line Items]	'
Unrecognized compensation cost	7.2
Minimum [Member]	'
Benefit Plans [Line Items]	'
Unrecognized compensation cost recognized over a weighted average period	'1 year
Maximum [Member]	'
Benefit Plans [Line Items]	'
Unrecognized compensation cost recognized over a weighted average period	'2 years

Benefit_Plans_Defined_Benefit_

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined benefit pension plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	$3.90	$3.30	$11.80	$10
Interest cost	12.3	13	36.8	38.9
Expected return on plan assets	-18.5	-17.2	-55.5	-51.6
Amortization of prior service cost (credit)	0.1	0.1	0.2	0.2
Amortization of actuarial loss	9	8.3	27.1	24.9
Total	6.8	7.5	20.4	22.4
Other Postretirement Benefits Plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	1.5	1.7	4.7	5.2
Interest cost	2.1	2.6	6.3	7.7
Expected return on plan assets	-2	-1.9	-6	-5.7
Amortization of prior service cost (credit)	-3	-3	-8.9	-9
Amortization of actuarial loss	1.3	1.6	3.7	4.7
Total	-0.1	1	-0.2	2.9
IPL [Member] | Defined benefit pension plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	2.2	1.8	6.5	5.6
Interest cost	5.7	6.1	17.1	18.1
Expected return on plan assets	-8.8	-8.2	-26.4	-24.5
Amortization of prior service cost (credit)	0	0	0.1	0.1
Amortization of actuarial loss	3.8	3.6	11.4	10.6
Total	2.9	3.3	8.7	9.9
IPL [Member] | Other Postretirement Benefits Plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	0.8	0.7	2.2	2.2
Interest cost	0.9	1.1	2.7	3.3
Expected return on plan assets	-1.4	-1.3	-4.2	-3.9
Amortization of prior service cost (credit)	-1.6	-1.5	-4.7	-4.7
Amortization of actuarial loss	0.6	0.9	2	2.7
Total	-0.7	-0.1	-2	-0.4
WPL [Member] | Defined benefit pension plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	1.5	1.3	4.4	3.9
Interest cost	5.2	5.4	15.5	16.2
Expected return on plan assets	-8	-7.5	-23.9	-22.3
Amortization of prior service cost (credit)	0.1	0.2	0.3	0.3
Amortization of actuarial loss	4.2	3.9	12.8	11.8
Total	3	3.3	9.1	9.9
WPL [Member] | Other Postretirement Benefits Plans [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	0.6	0.7	1.8	2.1
Interest cost	0.8	1	2.5	3.1
Expected return on plan assets	-0.4	-0.3	-1	-1
Amortization of prior service cost (credit)	-0.9	-1	-2.9	-2.9
Amortization of actuarial loss	0.5	0.6	1.5	1.7
Total	$0.60	$1	$1.90	$3

Benefit_Plans_Schedule_Of_Qual

Benefit Plans (Schedule Of Qualified and Non-qualified Pension And Other Postretirement Benefits Costs (Credits)) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined benefit pension plans [Member] | IPL [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Benefits costs (credits) associated with Corporate Services employees	$0.40	$0.40	$1.40	$1.40
Defined benefit pension plans [Member] | WPL [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Benefits costs (credits) associated with Corporate Services employees	0.4	0.4	1.1	1
Other Postretirement Benefits Costs (Credits) [Member] | IPL [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Benefits costs (credits) associated with Corporate Services employees	-0.1	0	-0.2	0.1
Other Postretirement Benefits Costs (Credits) [Member] | WPL [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Benefits costs (credits) associated with Corporate Services employees	($0.10)	$0.10	($0.20)	$0.10

Benefit_Plans_Estimated_Future

Benefit Plans (Estimated Future And Actual Employer Contributions) (Details) (USD $)

9 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Other postretirement benefits plans [Member]

Other postretirement benefits plans [Member]

Other postretirement benefits plans [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

IPL [Member]

WPL [Member]

IPL [Member]

WPL [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Other postretirement benefits plans [Member]

Other postretirement benefits plans [Member]

Other postretirement benefits plans [Member]

IPL [Member]

WPL [Member]

IPL [Member]

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Estimated for Calendar Year 2013

'

'

'

'

'

'

$2.30

[1]

$0.80

[1]

$0.20

[1]

$3

$0

$3

Actual Through September 30, 2013

$2

[1]

$0.70

[1]

$0.20

[1]

$2

$0

$2

'

'

'

'

'

'

[1]

Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Benefit_Plans_Employees_Partic

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
401(k) costs	$4.70		$4.40		$14.70		$14.10
IPL [Member]	'		'		'		'
401(k) costs	2.4	[1]	2.4	[1]	7.6	[1]	7.4	[1]
WPL [Member]	'		'		'		'
401(k) costs	$2.10	[1]	$2	[1]	$6.50	[1]	$6.20	[1]
[1]	IPLbs and WPLbs amounts include allocated costs associated with Corporate Services employees.

Benefit_Plans_Recognized_Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Compensation expense	$4	$0.10	$8.60	$3.80
Income tax benefits	1.6	0	3.5	1.5
IPL [Member]	'	'	'	'
Compensation expense	2	0.1	4.4	2
Income tax benefits	0.8	0	1.8	0.8
WPL [Member]	'	'	'	'
Compensation expense	1.7	0.1	3.7	1.7
Income tax benefits	$0.70	$0.10	$1.50	$0.70

Benefit_Plans_Summary_Of_Perfo

Benefit Plans (Summary Of Performance Shares Activity) (Details) (Performance Shares [Member], USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Performance Shares [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'
Nonvested, January 1 (in shares/awards)	145,277	[1]	236,979	[1]
Granted (in shares)	49,093	[1]	45,612	[1]
Vested (in shares)	-54,430	[1],[2]	-111,980	[1],[2]
Forfeited (in shares)	0	[1]	-25,334	[1]
Nonvested, September 30 (in shares/awards)	139,940	[1]	145,277	[1]
Actual number of shares paid out upon vesting, minimum percentage of target shares	0.00%		'
Actual number of shares paid out upon vesting, maximum percentage of target shares	200.00%		'
Stock payout value	$4.80		$8
Vested percentage of the target	197.50%		162.50%
Common stock shares from vested performance shares (in shares)	4,177		6,399
[1]	Share amounts represent the target number of performance shares. Each performance sharebs value is based on the price of one share of Alliant Energybs common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.
[2]	In 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). In 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares).

Benefit_Plans_Summary_Of_Perfo1

Benefit Plans (Summary Of Performance Unit Activity) (Details) (Performance Units [Member], USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Performance Units [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'
Nonvested, January 1 (in shares/awards)	64,969	[1]	42,996	[1]
Granted (in shares)	22,201	[1]	24,686	[1]
Vested (in shares)	-19,760	[1],[2]	0	[1],[2]
Forfeited (in shares)	-1,498	[1]	-878	[1]
Nonvested, September 30 (in shares/awards)	65,912	[1]	66,804	[1]
Performance multiplier range, lower	0.00%		'
Performance multiplier range, upper	200.00%		'
Vested percentage of the target	197.50%		'
Stock payout value	$1.30		'
[1]	Unit amounts represent the target number of performance units. Each performance unitbs value is based on the closing price of one share of Alliant Energybs common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.
[2]	In 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.

Benefit_Plans_Fair_Values_Of_N

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Performance Shares [Member]

Performance Shares [Member]

Performance Shares [Member]

Performance Shares [Member]

Performance Units [Member]

Performance Units [Member]

Performance Units [Member]

Performance Units [Member]

2013 Grant [Member]

2013 Grant [Member]

2012 Grant [Member]

2012 Grant [Member]

2011 Grant [Member]

2011 Grant [Member]

Performance Shares [Member]

Performance Units [Member]

Performance Shares [Member]

Performance Units [Member]

Performance Shares [Member]

Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Nonvested awards (in shares)

139,940

[1]

145,277

[1]

145,277

[1]

236,979

[1]

65,912

[2]

64,969

[2]

66,804

[2]

42,996

[2]

49,093

21,935

45,612

23,226

45,235

20,751

Alliant Energy common stock closing price on September 30, 2013 (in dollars per share)

'

'

'

'

'

'

'

'

$49.55

'

$49.55

'

$49.55

'

Alliant Energy common stock closing price on grant date (in dollars per share)

'

'

'

'

'

'

'

'

'

$47.58

'

$43.05

'

$38.75

Estimated payout percentage based on performance criteria

'

'

'

'

'

'

'

'

103.00%

103.00%

100.00%

100.00%

130.00%

130.00%

Fair values of each nonvested award (in dollars per share)

'

'

'

'

'

'

'

'

$51.04

$49.01

$49.55

$43.05

$64.42

$50.38

[1]

Share amounts represent the target number of performance shares. Each performance sharebs value is based on the price of one share of Alliant Energybs common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.

[2]

Unit amounts represent the target number of performance units. Each performance unitbs value is based on the closing price of one share of Alliant Energybs common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.

Benefit_Plans_Summary_Of_Restr

Benefit Plans (Summary Of Restricted Stock Activity) (Details) (Performance Contingent Restricted Stock [Member], USD $)	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'
Nonvested, January 1 (in shares/awards)	211,651		301,738
Nonvested shares, January 1, weighted average fair value (in dollars per share)	$32.42		$32.60
Granted (in shares)	49,093		45,612
Granted, weighted average fair value (in dollars per share)	$47.58		$43.05
Vested (in shares)	0	[1]	-65,172	[1]
Vested, weighted average fair value (in dollars per share)	$0	[1]	$32.56	[1]
Forfeited (in shares)	-101,822	[2]	-70,527	[2]
Forfeited, weighted average fair value (in dollars per share)	$23.67	[2]	$39.93	[2]
Nonvested, September 30 (in shares/awards)	158,922		211,651
Nonvested shares, September 30, weighted average fair value (in dollars per share)	$42.71		$32.42
Performance Criteria Not Met [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'
Forfeited (in shares)	-101,822		-65,516
[1]	In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.
[2]	In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.

Benefit_Plans_Summary_Of_Perfo2

Benefit Plans (Summary Of Performance Contingent Cash Awards Activity) (Details) (Performance Contingent Cash Awards [Member], USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Performance Contingent Cash Awards [Member]	'		'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]	'		'
Nonvested, January 1 (in shares/awards)	59,639		46,676
Granted (in awards)	39,530		36,936
Vested (in awards)	0	[1]	-21,605	[1]
Forfeited (in awards)	-1,413		-1,533
Nonvested, September 30 (in shares/awards)	97,756		60,474
Cash payout value	'		$0.90
[1]	In 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.

Common_Equity_Narrative_Detail

Common Equity (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
IPL [Member]	'	'
Common Equity [Line Items]	'	'
Retained earnings free of dividend restrictions	$507,000,000	'
Restricted net assets of subsidiaries	1,200,000,000	'
Capital contributions from parent	90,000,000	80,000,000
Common stock dividends to parent	95,700,000	'
WPL [Member]	'	'
Common Equity [Line Items]	'	'
Retained earnings free of dividend restrictions	32,000,000	'
Restricted net assets of subsidiaries	1,600,000,000	'
Common stock dividends to parent	$87,200,000	'

Common_Equity_Common_Share_Act

Common Equity (Common Share Activity) (Details)	9 Months Ended
	Sep. 30, 2013
Common Stock Oustanding [Roll Forward]	'
Shares outstanding, January 1 (in shares)	110,987,400
Equity-based compensation plans (in shares)	-23,374
Other (in shares)	-20,357
Shares outstanding, September 30 (in shares)	110,943,669

Redeemable_Preferred_Stock_Det

Redeemable Preferred Stock (Details) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

In Millions, except Share data, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Mar. 31, 2013

Sep. 30, 2013

Mar. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Mar. 31, 2013

Mar. 31, 2013

Mar. 31, 2013

Sep. 30, 2013

Mar. 31, 2013

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

Alliant Energy and IPL [Member]

Alliant Energy and IPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

Alliant Energy and WPL [Member]

Long-term Debt [Member]

Q

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

Redeemable Preferred Stock [Member]

IPL [Member]

board_member

5.1% [Member]

5.1% [Member]

8.375% [Member]

5.1% [Member]

8.375% [Member]

4.40% [Member]

6.50% [Member]

4.40% through 6.50% [Member]

4.40% through 6.50% [Member]

Redeemable Preferred Stock [Member]

5.1% [Member]

Temporary Equity [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock issued during period (in shares)

'

'

'

'

'

'

'

'

'

8,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock series

'

'

'

'

'

'

5.10%

'

8.38%

5.10%

5.10%

8.38%

'

'

'

'

'

'

4.50%

4.40%

6.50%

'

'

'

Preferred stock issued during period, value

'

'

'

'

'

'

'

'

'

$200

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reduction in commercial paper

'

'

34.8

17.6

'

'

-11.3

42.9

'

'

'

'

'

'

'

'

56.8

-25.7

'

'

'

'

'

40

Preferred stock issuance costs

'

'

'

'

'

'

'

'

'

'

'

'

5

'

'

'

'

'

'

'

'

'

'

'

Preferred stock redemption terms

'

'

'

'

'

'

'

'

'

'On or after March 15, 2018

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock redemption price (in dollars per share)

'

'

'

'

'

'

'

'

'

'

$25

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of board members to be elected (in members)

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of quarterly dividend requirements (in quarters)

'

'

'

'

'

'

6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock redeemed during period (in shares)

'

'

'

'

'

'

'

'

'

'

'

6,000,000

'

'

'

'

'

'

'

'

'

1,049,225

'

'

Stock redeemed during period, value

'

'

'

'

'

'

'

'

'

'

'

150

'

'

'

'

'

'

'

'

'

61

'

'

Preferred stock issuance charge

$2.60

$4

$15.30

$11.90

$2.60

$3.20

$13.70

$9.40

'

'

'

'

'

$5

$0

$0.80

$1.60

$2.50

'

'

'

'

$1

'

Debt_Narrative_Details

Debt (Narrative) (Details) (USD $)	9 Months Ended			9 Months Ended			1 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Oct. 31, 2013
				Alliant Energy and IPL [Member]	IPL [Member]	IPL [Member]	4.7% senior debentures due 2043
				Long-term Debt [Member]			Subsequent Event [Member]
							IPL [Member]
							Senior Debentures [Member]
Debt Instrument [Line Items]	'	'	'	'	'	'	'
Commercial paper	$237.30	'	$217.50	$65	$0	$26.30	'
Remaining maturity (in days)	'	'	'	'2 days	'	'	'
Weighted average interest rate	'	'	'	0.25%	'	'	4.70%
Proceeds from issuance of long-term debt	$0	$75	'	'	'	'	$250

Debt_Credit_Facilities_Details

Debt (Credit Facilities) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Commercial paper:	'		'
Amount outstanding	$237.30		$217.50
Weighted average remaining maturity (in days)	'1 day		'
Weighted average interest rates	0.20%		'
Available credit facility capacity	697.7	[1]	'
Parent Company [Member]	'		'
Commercial paper:	'		'
Amount outstanding	93.9		'
Weighted average remaining maturity (in days)	'2 days		'
Weighted average interest rates	0.20%		'
Available credit facility capacity	206.1	[1]	'
IPL [Member]	'		'
Commercial paper:	'		'
Amount outstanding	0		26.3
Available credit facility capacity	235	[1]	'
WPL [Member]	'		'
Commercial paper:	'		'
Amount outstanding	143.4		86.6
Weighted average remaining maturity (in days)	'1 day		'
Weighted average interest rates	0.10%		'
Available credit facility capacity	$256.60	[1]	'
[1]	Alliant Energybs and IPLbs available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at SeptemberB 30, 2013. Refer to Note 8(b) for further discussion of $65 million of commercial paper outstanding at SeptemberB 30, 2013 classified as long-term debt on Alliant Energybs and IPLbs Condensed Consolidated Balance Sheets.

Debt_Other_ShortTerm_Borrowing

Debt (Other Short-Term Borrowings) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Debt Instrument [Line Items]	'	'	'	'
Maximum amount outstanding (based on daily outstanding balances)	$284.10	$185.30	$284.10	$185.30
Average amount outstanding (based on daily outstanding balances)	228.8	133	197.2	100.2
Weighted average interest rates	0.20%	0.40%	0.20%	0.40%
IPL [Member]	'	'	'	'
Debt Instrument [Line Items]	'	'	'	'
Maximum amount outstanding (based on daily outstanding balances)	0	19.5	26.3	35.4
Average amount outstanding (based on daily outstanding balances)	0	1.3	1.7	7.2
Weighted average interest rates	'	0.40%	0.40%	0.40%
WPL [Member]	'	'	'	'
Debt Instrument [Line Items]	'	'	'	'
Maximum amount outstanding (based on daily outstanding balances)	165.4	35.6	165.4	35.6
Average amount outstanding (based on daily outstanding balances)	$140.90	$11.90	$113.40	$13.30
Weighted average interest rates	0.20%	0.30%	0.20%	0.30%

Investments_Unconsolidated_Equ

Investments (Unconsolidated Equity Investments) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	($11.10)	($10.40)	($32.70)	($30.40)
WPL [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-11.1	-10.5	-32.7	-31.2
ATC [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-10.8	-10.4	-31.7	-30.6
ATC [Member] | WPL [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-10.8	-10.4	-31.7	-30.6
Other [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-0.3	0	-1	0.2
Other [Member] | WPL [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-0.3	-0.1	-1	-0.6
Totals [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	-11.1	-10.4	-32.7	-30.4
Totals [Member] | WPL [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Equity (income) loss from unconsolidated investments, net	($11.10)	($10.50)	($32.70)	($31.20)

Investments_Summary_Financial_

Investments (Summary Financial Information) (Details) (ATC [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
ATC [Member]	'	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'	'
Operating revenues	$160.40	$150.30	$464.30	$450.10
Operating income	82.9	81.5	247.1	240
Net income	$62.70	$60.50	$184.50	$177.90

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)

9 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Jun. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Dec. 31, 2011

Sep. 30, 2013

Jun. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Dec. 31, 2011

Sep. 30, 2013

Jun. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Dec. 31, 2011

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

IPL [Member]

IPL [Member]

WPL [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Excluding Financial Transmission Rights [Member]

Excluding Financial Transmission Rights [Member]

Excluding Financial Transmission Rights [Member]

Financial Transmission Rights [Member]

Financial Transmission Rights [Member]

Financial Transmission Rights [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

IPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

WPL [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

Commodity Contracts [Member]

IPL [Member]

WPL [Member]

IPL [Member]

WPL [Member]

Cumulative preferred stock rate

5.10%

8.38%

4.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value, net derivative liabilities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$12.50

'

$14

'

'

'

Fair value, net derivative assets

'

'

'

$17.20

$42.50

$11.90

$17.60

$18.80

($0.90)

$28.60

$40.60

$12.50

$15.50

$14.10

$4.30

($11.40)

$1.90

($0.60)

$2.10

$4.70

($5.20)

'

$1.50

'

$29.70

$27.10

$2.60

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets:	'	'
Derivative assets	$36.80	$26.20
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	3,553.60	3,860.50
Cumulative preferred stock	200	145.1
Cumulative preferred stock	169.5	'
Cumulative preferred stock	0	60
Cumulative preferred stock	'	212.6
Derivative liabilities	27.1	40.4
IPL [Member]	'	'
Assets:	'	'
Derivative assets	31.5	17.5
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,553.80	1,679.90
Cumulative preferred stock	200	145.1
Cumulative preferred stock	169.5	151.8
Derivative liabilities	6.7	16.1
WPL [Member]	'	'
Assets:	'	'
Derivative assets	5.3	8.7
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,541.90	1,713.30
Cumulative preferred stock	0	60
Cumulative preferred stock	0	60.8
Derivative liabilities	20.4	24.3
Carrying Amount [Member]	'	'
Assets:	'	'
Derivative assets	36.8	26.2
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	3,153.20	3,138.10
Cumulative preferred stock	200	'
Cumulative preferred stock	'	205.1
Derivative liabilities	27.1	40.4
Carrying Amount [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	31.5	17.5
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,374.80	1,359.50
Cumulative preferred stock	200	145.1
Derivative liabilities	6.7	16.1
Carrying Amount [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	5.3	8.7
Deferred proceeds (sales of receivables)	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,332	1,331.50
Cumulative preferred stock	0	60
Derivative liabilities	20.4	24.3
Fair Value [Member]	'	'
Assets:	'	'
Derivative assets	36.8	26.2
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	3,553.60	3,860.50
Cumulative preferred stock	169.5	'
Cumulative preferred stock	'	212.6
Derivative liabilities	27.1	40.4
Fair Value [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	31.5	17.5
Deferred proceeds (sales of receivables)	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,553.80	1,679.90
Cumulative preferred stock	169.5	151.8
Derivative liabilities	6.7	16.1
Fair Value [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	5.3	8.7
Deferred proceeds (sales of receivables)	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,541.90	1,713.30
Cumulative preferred stock	0	60.8
Derivative liabilities	$20.40	$24.30

Fair_Value_Measurements_Fair_V1

Fair Value Measurements (Fair Value Measurements) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets:	'	'
Derivative assets	$32.30	$19.30
Deferred proceeds	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	3,553.60	3,860.50
Cumulative preferred stock	'	212.6
Cumulative preferred stock	169.5	'
Derivative liabilities	23.5	33
IPL [Member]	'	'
Assets:	'	'
Derivative assets	29.2	14.5
Deferred proceeds	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,553.80	1,679.90
Cumulative preferred stock	169.5	151.8
Derivative liabilities	5.3	12.6
WPL [Member]	'	'
Assets:	'	'
Derivative assets	3.1	4.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,541.90	1,713.30
Cumulative preferred stock	0	60.8
Derivative liabilities	18.2	20.4
Commodity Contracts [Member]	'	'
Assets:	'	'
Derivative assets	36.8	26.2
Capitalization and liabilities:	'	'
Derivative liabilities	27.1	40.4
Commodity Contracts [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	31.5	17.5
Capitalization and liabilities:	'	'
Derivative liabilities	6.7	16.1
Commodity Contracts [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	5.3	8.7
Capitalization and liabilities:	'	'
Derivative liabilities	20.4	24.3
Level 1 [Member]	'	'
Assets:	'	'
Deferred proceeds	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	'	162.3
Cumulative preferred stock	169.5	'
Level 1 [Member] | IPL [Member]	'	'
Assets:	'	'
Deferred proceeds	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	169.5	151.8
Level 1 [Member] | WPL [Member]	'	'
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	0	10.5
Level 1 [Member] | Commodity Contracts [Member]	'	'
Assets:	'	'
Derivative assets	0	0
Capitalization and liabilities:	'	'
Derivative liabilities	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	0	0
Capitalization and liabilities:	'	'
Derivative liabilities	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	0	0
Capitalization and liabilities:	'	'
Derivative liabilities	0	0
Level 2 [Member]	'	'
Assets:	'	'
Deferred proceeds	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	3,553.20	3,860
Cumulative preferred stock	'	50.3
Cumulative preferred stock	0	'
Level 2 [Member] | IPL [Member]	'	'
Assets:	'	'
Deferred proceeds	0	0
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,553.80	1,679.90
Cumulative preferred stock	0	0
Level 2 [Member] | WPL [Member]	'	'
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	1,541.90	1,713.30
Cumulative preferred stock	0	50.3
Level 2 [Member] | Commodity Contracts [Member]	'	'
Assets:	'	'
Derivative assets	3.2	4.8
Capitalization and liabilities:	'	'
Derivative liabilities	10.7	30.9
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	1.9	3.1
Capitalization and liabilities:	'	'
Derivative liabilities	5.7	14.2
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	1.3	1.7
Capitalization and liabilities:	'	'
Derivative liabilities	5	16.7
Level 3 [Member]	'	'
Assets:	'	'
Deferred proceeds	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0.4	0.5
Cumulative preferred stock	'	0
Cumulative preferred stock	0	'
Level 3 [Member] | IPL [Member]	'	'
Assets:	'	'
Deferred proceeds	86.9	66.8
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	0	0
Level 3 [Member] | WPL [Member]	'	'
Capitalization and liabilities:	'	'
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	0	0
Level 3 [Member] | Commodity Contracts [Member]	'	'
Assets:	'	'
Derivative assets	33.6	21.4
Capitalization and liabilities:	'	'
Derivative liabilities	16.4	9.5
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]	'	'
Assets:	'	'
Derivative assets	29.6	14.4
Capitalization and liabilities:	'	'
Derivative liabilities	1	1.9
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]	'	'
Assets:	'	'
Derivative assets	4	7
Capitalization and liabilities:	'	'
Derivative liabilities	$15.40	$7.60

Fair_Value_Measurements_Fair_V2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Commodity Contracts [Member]	'		'		'		'
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning balance	$42.50		$18.80		$11.90		($0.90)
Total net gains (losses) (realized/unrealized) included in changes in net assets	0.1	[1]	-2.3	[1]	-8.3	[1]	-8.3	[1]
Transfers into Level 3	-9.9	[2]	-0.4	[2]	-0.4	[2]	-1.7	[2]
Transfers out of Level 3	0	[3]	9.3	[3]	-0.5	[3]	8.3	[3]
Purchases	'		'		50.9		35.8
Settlements	-15.5	[4]	-7.8	[4]	-36.4	[4]	-15.6	[4]
Ending balance	17.2		17.6		17.2		17.6
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	0.1	[1]	-0.7	[1]	-8.3	[1]	-4.4	[1]
Commodity Contracts [Member] | IPL [Member]	'		'		'		'
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning balance	40.6		14.1		12.5		4.3
Total net gains (losses) (realized/unrealized) included in changes in net assets	2	[1]	-0.2	[1]	1.5	[1]	-4.8	[1]
Transfers into Level 3	-0.1	[2]	0	[2]	0	[2]	-1.1	[2]
Transfers out of Level 3	0	[3]	7.4	[3]	-1.5	[3]	2.4	[3]
Purchases	'		'		46.1		26.8
Settlements	-13.9	[4]	-5.8	[4]	-30	[4]	-12.1	[4]
Ending balance	28.6		15.5		28.6		15.5
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	2	[1]	1.4	[1]	1.5	[1]	-0.7	[1]
Commodity Contracts [Member] | WPL [Member]	'		'		'		'
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning balance	1.9		4.7		-0.6		-5.2
Total net gains (losses) (realized/unrealized) included in changes in net assets	-1.9	[1]	-2.1	[1]	-9.8	[1]	-3.5	[1]
Transfers into Level 3	-9.8	[2]	-0.4	[2]	-0.4	[2]	-0.6	[2]
Transfers out of Level 3	0	[3]	1.9	[3]	1	[3]	5.9	[3]
Purchases	'		'		4.8		9
Settlements	-1.6		-2		-6.4		-3.5
Ending balance	-11.4		2.1		-11.4		2.1
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	-1.9	[1]	-2.1	[1]	-9.8	[1]	-3.7	[1]
Deferred Proceeds [Member]	'		'		'		'
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning balance	69.3		81.7		66.8		53.7
Total net gains (losses) (realized/unrealized) included in changes in net assets	0	[1]	0	[1]	0	[1]	0	[1]
Transfers into Level 3	0	[2]	0	[2]	0	[2]	0	[2]
Transfers out of Level 3	0	[3]	0	[3]	0	[3]	0	[3]
Purchases	'		'		0		0
Settlements	17.6	[4]	72.2	[4]	20.1	[4]	100.2	[4]
Ending balance	86.9		153.9		86.9		153.9
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	0	[1]	0	[1]	0	[1]	0	[1]
Deferred Proceeds [Member] | IPL [Member]	'		'		'		'
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning balance	69.3		81.7		66.8		53.7
Total net gains (losses) (realized/unrealized) included in changes in net assets	0	[1]	0	[1]	0	[1]	0	[1]
Transfers into Level 3	0	[2]	0	[2]	0	[2]	0	[2]
Transfers out of Level 3	0	[3]	0	[3]	0	[3]	0	[3]
Purchases	'		'		0		0
Settlements	17.6	[4]	72.2	[4]	20.1	[4]	100.2	[4]
Ending balance	86.9		153.9		86.9		153.9
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	$0	[1]	$0	[1]	$0	[1]	$0	[1]
[1]	Gains and losses related to derivative assets and derivative liabilities are recorded in bRegulatory assetsb and bRegulatory liabilitiesb on the Condensed Consolidated Balance Sheets.
[2]	Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
[3]	Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
[4]	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.

Derivative_Instruments_Narrati

Derivative Instruments (Narrative) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
	counterparty
Derivative [Line Items]	'	'
Aggregate fair value of all derivatives with credit risk-related contingent features, net liability position	$27.10	'
Restrictive credit risk-related contingent features for derivative agreements, net liability position	27.1	'
IPL [Member]	'	'
Derivative [Line Items]	'	'
Aggregate fair value of all derivatives with credit risk-related contingent features, net liability position	6.7	'
Restrictive credit risk-related contingent features for derivative agreements, net liability position	6.7	'
WPL [Member]	'	'
Derivative [Line Items]	'	'
Aggregate fair value of all derivatives with credit risk-related contingent features, net liability position	20.4	'
Restrictive credit risk-related contingent features for derivative agreements, net liability position	20.4	'
Alliant Energy and IPL [Member]	'	'
Derivative [Line Items]	'	'
Cash collateral posted by counterparty	0.9	0
Number of counterparties exceeding derivative asset position (in counterparties)	1	'
Cash collateral posted by IPL	$0	$0.50

Derivative_Instruments_Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Sep. 30, 2013
	MWh
Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,221,000
Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,758,000
Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	10,463,000
FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	35,000
FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	22,000
FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,000
Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	72,553,000
Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	55,967,000
Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	16,586,000
Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,303,000
Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	814,000
Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	4,489,000
2013 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,460,000
2013 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	835,000
2013 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	625,000
2013 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,000
2013 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,000
2013 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,000
2013 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	30,852,000
2013 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	23,908,000
2013 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,944,000
2013 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	239,000
2013 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	15,000
2013 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	224,000
2014 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,625,000
2014 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,923,000
2014 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	3,702,000
2014 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	22,000
2014 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	14,000
2014 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,000
2014 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	32,518,000
2014 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	24,001,000
2014 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,517,000
2014 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,591,000
2014 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	270,000
2014 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,321,000
2015 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,190,000
2015 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,190,000
2015 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	7,544,000
2015 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,419,000
2015 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,125,000
2015 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	936,000
2015 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	936,000
2016 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,318,000
2016 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,318,000
2016 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,639,000
2016 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,639,000
2016 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	955,000
2016 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	216,000
2016 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	739,000
2017 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2017 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2017 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	868,000
2017 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	129,000
2017 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	739,000
2018 [Member] | Electricity (MWhs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2018 [Member] | Electricity (MWhs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Electricity (MWhs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2018 [Member] | FTRs (MWs) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | FTRs (MWs) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | FTRs (MWs) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Coal (Tons) [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	714,000
2018 [Member] | Coal (Tons) [Member] | IPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	184,000
2018 [Member] | Coal (Tons) [Member] | WPL [Member]	'
Notional Amount of Derivatives [Line Items]	'
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	530,000

Derivative_Instruments_Fair_Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) (Commodity Contracts [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]	'	'
Current derivative assets	$34.70	$23.50
Non-current derivative assets	2.1	2.7
Current derivative liabilities	11.8	31.1
Non-current derivative liabilities	15.3	9.3
IPL [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Current derivative assets	29.9	17
Non-current derivative assets	1.6	0.5
Current derivative liabilities	4.9	14.1
Non-current derivative liabilities	1.8	2
WPL [Member]	'	'
Derivatives, Fair Value [Line Items]	'	'
Current derivative assets	4.8	6.5
Non-current derivative assets	0.5	2.2
Current derivative liabilities	6.9	17
Non-current derivative liabilities	$13.50	$7.30

Derivative_Instruments_Gains_A

Derivative Instruments (Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Regulatory Assets [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	$2.20	($6.30)	($14.20)	($38.30)
Regulatory Assets [Member] | IPL [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	-0.4	-0.1	-4.6	-17.3
Regulatory Assets [Member] | WPL [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	2.6	-6.2	-9.6	-21
Regulatory Liabilities [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	-1	15.8	16.6	21.3
Regulatory Liabilities [Member] | IPL [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	3.6	6.9	9.9	11.3
Regulatory Liabilities [Member] | WPL [Member]	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Gains (losses) from commodity derivative instruments not designated as hedging instruments	($4.60)	$8.90	$6.70	$10

Derivative_Instruments_Derivat

Derivative Instruments Derivative Instruments (Balance Sheet Offsetting) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Derivative assets, Gross (as reported)	$36.80	$26.20
Derivative assets, Net	32.3	19.3
Derivative liabilities, Gross (as reported)	27.1	40.4
Derivative liabilities, Net	23.5	33
IPL [Member]	'	'
Derivative [Line Items]	'	'
Derivative assets, Gross (as reported)	31.5	17.5
Derivative assets, Net	29.2	14.5
Derivative liabilities, Gross (as reported)	6.7	16.1
Derivative liabilities, Net	5.3	12.6
WPL [Member]	'	'
Derivative [Line Items]	'	'
Derivative assets, Gross (as reported)	5.3	8.7
Derivative assets, Net	3.1	4.8
Derivative liabilities, Gross (as reported)	20.4	24.3
Derivative liabilities, Net	$18.20	$20.40

Commitments_And_Contingencies_1

Commitments And Contingencies (Narrative) (Details) (USD $)

1 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Jul. 31, 2012

Dec. 31, 2010

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Dec. 31, 2011

Feb. 28, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

subclass

IPL [Member]

WPL [Member]

Manufactured Gas Plant Sites [Member]

Manufactured Gas Plant Sites [Member]

Manufactured Gas Plant Sites [Member]

Indemnifications [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Defined benefit pension plans [Member]

Performance guarantees outstanding, 2013 [Member]

Performance guarantees outstanding, 2014 [Member]

Performance guarantees outstanding, 2015 [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Scenario, Forecast [Member]

Civil Penalty [Member]

Environmental Issue [Member]

Minimum [Member]

Maximum [Member]

site

site

IPL [Member]

WPL [Member]

RMT [Member]

Cash Balance Plan [Member]

Cash Balance Plan [Member]

IPL [Member]

WPL [Member]

Capital Purchase Obligation [Member]

Capital Purchase Obligation [Member]

Capital Purchase Obligation [Member]

WPL [Member]

WPL [Member]

IPL [Member]

WPL [Member]

Long-term Purchase Commitment [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Minimum future commitments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$2,692

$2,096

$592

$64

$21

$43

'

'

'

'

Interest crediting rate

'

8.20%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate additional payments to certain plan participants

'

'

'

'

'

'

'

'

'

'

'

10

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of new subclasses certified as a result of court opinion and order (in subclasses)

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Estimated damages from court opinion and order

'

'

'

'

'

'

'

'

'

'

18.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss contingency, damages sought, value

'

'

'

'

'

'

'

'

'

'

'

'

'

9.6

'

'

'

'

'

'

'

'

'

'

'

'

'

Damages to be paid out of common fund

'

'

'

'

'

'

'

'

'

4.3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss contingency, damages awarded, value

'

'

'

'

'

'

'

'

'

'

'

'

6.4

'

'

'

'

'

'

'

'

'

'

2

7

'

'

Stautue of limitations, lump sum distributions

'

'

'6 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss contingency, estimate of possible loss

'

'

'

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Warranty period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'12 months

'60 months

Performance guarantees outstanding

'

'

493

'

'

'

'

'

'

'

'

'

'

'

146

294

53

'

'

'

'

'

'

'

'

'

'

Present value abandonment obligation

'

'

31

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of sites monitoring and remediating (in sites)

'

'

'

27

5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Minimum remaining estimated cost incurred for investigation, remediation and monitoring

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15

13

2

'

'

'

'

'

'

'

Maximum remaining estimated cost incurred for investigation, remediation and monitoring

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

32

28

4

'

'

'

'

'

'

'

Current and non-current environmental liabilities

'

'

'

'

'

$20

$17

$3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Commitments_And_Contingencies_2

Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
	MW
Long-term Purchase Commitment [Line Items]	'
Individual commitments incurred	1
Duane Arnold Energy Center (DAEC) (IPL) [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Approved amount of electric power capacity (in megawatts)	431
Scenario, Forecast [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	2,692
Scenario, Forecast [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	2,096
Scenario, Forecast [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	592
Scenario, Forecast [Member] | Other [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	19	[1]
Scenario, Forecast [Member] | Other [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	9	[1]
Scenario, Forecast [Member] | Other [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	6	[1]
Scenario, Forecast [Member] | Natural Gas [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	336
Scenario, Forecast [Member] | Natural Gas [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	203
Scenario, Forecast [Member] | Natural Gas [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	133
Scenario, Forecast [Member] | Coal [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	328	[2]
Scenario, Forecast [Member] | Coal [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	151	[2]
Scenario, Forecast [Member] | Coal [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	177	[2]
Scenario, Forecast [Member] | SO2 emission allowances [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	34
Scenario, Forecast [Member] | SO2 emission allowances [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	34
Scenario, Forecast [Member] | SO2 emission allowances [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	0
Scenario, Forecast [Member] | Purchased Power [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	1,975	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	1,699	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	276	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	1,698	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	1,698	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Duane Arnold Energy Center (DAEC) (IPL) [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	0	[3],[4]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	18	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	0	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Kewaunee Nuclear Power Plant (Kewaunee) (WPL) [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	18	[3]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	259	[3],[5]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | IPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	1	[3],[5]
Scenario, Forecast [Member] | Purchased Power [Member] | Other [Member] | WPL [Member]	'
Long-term Purchase Commitment [Line Items]	'
Minimum future commitments	258	[3],[5]
[1]	Includes individual commitments incurred during the normal course of business that exceeded $1 million at SeptemberB 30, 2013.
[2]	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of SeptemberB 30, 2013 regarding expected future usage, which is subject to change.
[3]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
[4]	Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPLbs energy adjustment clause.
[5]	In June 2013, WPL entered into a new PPA for a term from January 1, 2014 through December 31, 2018.

Segments_Of_Business_Schedule_

Segments Of Business (Schedule Of Segment Of Business) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	$866.60	$887.60	$2,444.20	$2,343.60
Operating income (loss)	201.4	213.7	425.3	418.1
Income (loss) from continuing operations, net of tax	158.9	149	297.7	253.8
Income (loss) from discontinued operations, net of tax	-1.3	1.7	-4.9	-2.3
Net income (loss) attributable to Alliant Energy common shareowners	157.6	150.7	292.8	251.5
IPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	494.4	497.7	1,355.70	1,257.10
Operating income (loss)	100	112	175.8	171.3
Net income (loss) attributable to Alliant Energy common shareowners	110	103.3	155.1	115.2
WPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	360.9	376.6	1,050.60	1,046.80
Operating income (loss)	95.9	93.4	228.3	219.5
Net income (loss) attributable to Alliant Energy common shareowners	61.3	55.9	137.7	122.2
Electric [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	798.1	815.3	2,043.40	2,000.30
Operating income (loss)	199.6	203.1	359.1	354
Electric [Member] | IPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	457.6	456.6	1,137.40	1,070.70
Operating income (loss)	99.6	109.5	146.2	149.3
Electric [Member] | WPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	340.5	358.7	906	929.6
Operating income (loss)	100	93.6	212.9	204.7
Gas [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	39.8	46.8	310.5	263.9
Operating income (loss)	-3.4	0.8	39.5	32.1
Gas [Member] | IPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	24.6	29.6	180.9	149.2
Operating income (loss)	-0.7	0.6	22.6	15.6
Gas [Member] | WPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	15.2	17.2	129.6	114.7
Operating income (loss)	-2.7	0.2	16.9	16.5
Other Utility [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	17.4	12.2	52.4	39.7
Operating income (loss)	-0.3	1.5	5.5	4.7
Other Utility [Member] | IPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	12.2	11.5	37.4	37.2
Operating income (loss)	1.1	1.9	7	6.4
Other Utility [Member] | WPL [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	5.2	0.7	15	2.5
Operating income (loss)	-1.4	-0.4	-1.5	-1.7
Utility Business [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	855.3	874.3	2,406.30	2,303.90
Operating income (loss)	195.9	205.4	404.1	390.8
Income (loss) from continuing operations, net of tax	171.3	159.2	292.8	237.4
Income (loss) from discontinued operations, net of tax	0	0	0	0
Net income (loss) attributable to Alliant Energy common shareowners	171.3	159.2	292.8	237.4
Non-Regulated, Parent and Other [Member] | Other Segments [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Operating revenues	11.3	13.3	37.9	39.7
Operating income (loss)	5.5	8.3	21.2	27.3
Income (loss) from continuing operations, net of tax	-12.4	-10.2	4.9	16.4
Income (loss) from discontinued operations, net of tax	-1.3	1.7	-4.9	-2.3
Net income (loss) attributable to Alliant Energy common shareowners	($13.70)	($8.50)	$0	$14.10

Discontinued_Operations_And_As2

Discontinued Operations And Assets And Liabilities Held For Sale (Components Of Discontinued Operations In Condensed Consolidated Statements Of Income) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'	'
Operating revenues	$0	$94.50	$0.90	$243
Operating expenses	2.1	91.7	8.6	246.6
Interest expense and other	0	0.2	0	0.4
Income (loss) before income taxes	-2.1	2.6	-7.7	-4
Income tax expense (benefit)	-0.8	0.9	-2.8	-1.7
Income (loss) from discontinued operations, net of tax	($1.30)	$1.70	($4.90)	($2.30)

Discontinued_Operations_And_As3

Discontinued Operations And Assets And Liabilities Held For Sale (Components Of Assets And Liabilities Held For Sale In Condensed Consolidated Balance Sheets) (Details) (USD $)	Dec. 31, 2012
In Millions, unless otherwise specified
Discontinued Operations and Disposal Groups [Abstract]	'
Current assets	$27.90
Current liabilities	31.4
Net liabilities held for sale	($3.50)

Asset_Retirement_Obligations_A2

Asset Retirement Obligations (AROs) (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance, January 1	$101.50		$91.10
Revisions in estimated cash flows	3.4	[1]	-9.9	[1]
Liabilities settled	-0.9		-2.6
Liabilities incurred	0	[2]	16	[2]
Accretion expense	2.8		2.6
Balance, September 30	106.8		97.2
IPL [Member]	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance, January 1	45.5		56.2
Revisions in estimated cash flows	0.8	[1]	-9.2	[1]
Liabilities settled	-0.1		-2.5
Liabilities incurred	0	[2]	0	[2]
Accretion expense	1.3		1.4
Balance, September 30	47.5		45.9
WPL [Member]	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance, January 1	46.9		34.9
Revisions in estimated cash flows	2.6	[1]	-0.7	[1]
Liabilities settled	-0.8		-0.1
Liabilities incurred	0	[2]	7.6	[2]
Accretion expense	1.2		1.2
Balance, September 30	49.9		42.9
Sixth Street [Member] | IPL [Member]	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Revisions in estimated cash flows	'		-8.2
Franklin County Wind Project [Member] | Resources [Member]	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Liabilities incurred	'		8.4
Nelson Dewey [Member] | WPL [Member]	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Liabilities incurred	'		$7.60
[1]	For the nine months ended September 30, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.
[2]	For the nine months ended September 30, 2012, Resources recorded AROs of $8.4 million related to its Franklin County wind project and WPL recorded AROs of $7.6 million related to Nelson Dewey.

Related_Parties_Narrative_Deta

Related Parties (Narrative) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
WPL Owed ATC [Member]	'	'
Related Party Transaction [Line Items]	'	'
Net amounts owed	$7	$6
IPL [Member]	'	'
Related Party Transaction [Line Items]	'	'
Net amounts owed	95	72
WPL [Member]	'	'
Related Party Transaction [Line Items]	'	'
Net amounts owed	$46	$40

Related_Parties_Sales_Credited

Related Parties (Sales Credited And Purchases Billed) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
SCOA Sales Credited [Member] | IPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	$2	$3	$5	$7
SCOA Sales Credited [Member] | WPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	3	4	10	10
SCOA Purchases Billed [Member] | IPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	108	87	260	237
SCOA Purchases Billed [Member] | WPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	$16	$13	$44	$50

Related_Parties_Corporate_Serv

Related Parties (Corporate Services Billings) (Details) (Corporate Service Billings [Member], USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
IPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Corporate Services billings	$39	$34	$107	$97
WPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Corporate Services billings	$28	$26	$77	$76

Related_Parties_Net_Intercompa

Related Parties (Net Intercompany Payables) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
IPL [Member]	'	'
Related Party Transaction [Line Items]	'	'
Net payables to Corporate Services	$95	$72
WPL [Member]	'	'
Related Party Transaction [Line Items]	'	'
Net payables to Corporate Services	$46	$40

Related_Parties_Related_Amount

Related Parties (Related Amounts Billed Between Parties) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
ATC Billings To WPL [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	$24	$22	$72	$67
WPL Billings To ATC [Member]	'	'	'	'
Related Party Transaction [Line Items]	'	'	'	'
Amounts billed between related parties	$2	$3	$9	$7

Earnings_Per_Share_Weighted_Av

Earnings Per Share (Weighted Average Common Shares Outstanding) (Details)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Weighted average common shares outstanding:	'	'	'	'
Basic EPS calculation (in shares)	110,783	110,768	110,775	110,747
Effect of dilutive share-based awards (in shares)	2	11	5	16
Diluted EPS calculation (in shares)	110,785	110,779	110,780	110,763