Alliant Energy (LNT) 10-Q 1 May 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	352541
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	112,977,238
IPL [Member]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	52485
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	107832
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
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Utility:
Electric	$671.30	$675.80
Gas	198.4	240.7
Other	16.4	22.8
Non-regulated	11.3	13.5
Total operating revenues	897.4	952.8
Utility:
Electric production fuel and purchased power	215.9	238.7
Electric transmission service	123.2	114.1
Cost of gas sold	130.8	161.9
Other operation and maintenance	146.6	161
Non-regulated operation and maintenance	1.3	1.3
Depreciation and amortization	100.2	95.5
Taxes other than income taxes	26.5	26.1
Total operating expenses	744.5	798.6
Operating income	152.9	154.2
Interest expense and other:
Interest expense	46.6	45.2
Equity income from unconsolidated investments, net	-6.5	-11.4
Allowance for funds used during construction	-6.8	-9.1
Interest income and other	-0.1	-1.7
Total interest expense and other	33.2	23
Income before income taxes	119.7	131.2
Income tax expense (benefit)	20.5	20.6
Net income (loss)	99.2	110.6
Preferred dividend requirements of IPL	2.6	2.6
Net income (loss) attributable to common shareowners	96.6	108
Weighted average number of common shares outstanding (basic and diluted) (in shares)	111.1	110.8
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$0.87	$0.97
Dividends declared per common share (in dollars per share)	$0.55	$0.51
IPL [Member]
Utility:
Electric	362.6	374.2
Gas	111.2	135.7
Other	15.2	19
Total operating revenues	489	528.9
Utility:
Electric production fuel and purchased power	110.1	140
Electric transmission service	83.9	83.6
Cost of gas sold	71	88.1
Other operation and maintenance	92.6	97.2
Depreciation and amortization	51.8	48.7
Taxes other than income taxes	14.1	13.8
Total operating expenses	423.5	471.4
Operating income	65.5	57.5
Interest expense and other:
Interest expense	24.1	22.5
Allowance for funds used during construction	-5.3	-6
Interest income and other	-0.1	0
Total interest expense and other	18.7	16.5
Income before income taxes	46.8	41
Income tax expense (benefit)	-3.6	-5
Net income (loss)	50.4	46
Preferred dividend requirements of IPL	2.6	2.6
Net income (loss) attributable to common shareowners	47.8	43.4
WPL [Member]
Utility:
Electric	308.7	301.6
Gas	87.2	105
Other	1.2	3.8
Total operating revenues	397.1	410.4
Utility:
Electric production fuel and purchased power	105.8	98.7
Electric transmission service	39.3	30.5
Cost of gas sold	59.8	73.8
Other operation and maintenance	54	63.8
Depreciation and amortization	46	44.7
Taxes other than income taxes	11.4	11.2
Total operating expenses	316.3	322.7
Operating income	80.8	87.7
Interest expense and other:
Interest expense	23.1	21.1
Equity income from unconsolidated investments, net	-7.8	-11.4
Allowance for funds used during construction	-1.5	-3.1
Interest income and other	0.1	0
Total interest expense and other	13.9	6.6
Income before income taxes	66.9	81.1
Income tax expense (benefit)	22.1	26.3
Net income (loss)	44.8	54.8
Net income attributable to noncontrolling interest	0.2	0
Net income (loss) attributable to common shareowners	$44.60	$54.80

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Current assets:
Cash and cash equivalents	$97.60	$56.90
Accounts receivable, less allowance for doubtful accounts	361.6	427.3
Production fuel, at weighted average cost	67.6	83.8
Materials and supplies, at weighted average cost	81.5	72.9
Gas stored underground, at weighted average cost	18.3	67.1
Regulatory assets	59	68.1
Other	227.6	267
Total current assets	913.2	1,043.10
Property, plant and equipment, net	9,050	8,938.40
Investments:
Investment in American Transmission Company LLC	288.5	286.5
Other	55.4	58.4
Total investments	343.9	344.9
Other assets:
Regulatory assets	1,731.30	1,715.60
Deferred charges and other	41.2	43.9
Total other assets	1,772.50	1,759.50
Total assets	12,079.60	12,085.90
Current liabilities:
Current maturities of long-term debt	183	183
Commercial paper	41.5	141.3
Accounts payable	356.9	427.9
Regulatory liabilities	209.4	200.1
Other	232.3	262.4
Total current liabilities	1,023.10	1,214.70
Long-term debt, net (excluding current portion)	3,606.70	3,606.70
Other liabilities:
Deferred income tax liabilities	2,366.90	2,321.10
Regulatory liabilities	606.7	621.1
Pension and other benefit obligations	417.7	421.7
Other	259.7	260.1
Total other liabilities	3,651	3,624
Commitments and contingencies (Note 13)
Common equity:
Common stock	1.1	1.1
Additional paid-in capital	1,631.60	1,509.10
Retained earnings	1,973.90	1,938
Accumulated other comprehensive loss	-0.6	-0.6
Shares in deferred compensation trust - 232,550 and 238,935 shares at a weighted average cost of $38.27 and $37.45 per share	-8.9	-8.9
Total common equity	3,597.10	3,438.70
Cumulative preferred stock of Interstate Power and Light Company	200	200
Noncontrolling interest	1.7	1.8
Total equity	3,798.80	3,640.50
Total liabilities and equity	12,079.60	12,085.90
IPL [Member]
Current assets:
Cash and cash equivalents	2.6	5.3
Accounts receivable, less allowance for doubtful accounts	158.8	216.7
Production fuel, at weighted average cost	36.2	52.7
Materials and supplies, at weighted average cost	48.1	42
Gas stored underground, at weighted average cost	5.2	30.8
Regulatory assets	31.1	38.7
Other	136.5	169.9
Total current assets	418.5	556.1
Property, plant and equipment, net	4,631.40	4,554.70
Investments:
Total investments	19.1	19.1
Other assets:
Regulatory assets	1,332.60	1,319.20
Deferred charges and other	12.9	12.7
Total other assets	1,345.50	1,331.90
Total assets	6,414.50	6,461.80
Current liabilities:
Current maturities of long-term debt	150	150
Commercial paper	0
Accounts payable	199.6	259.6
Accounts payable to associated companies	34.4	31.3
Regulatory liabilities	137.5	129.7
Other	122.7	135.3
Total current liabilities	644.2	705.9
Long-term debt, net (excluding current portion)	1,618.80	1,618.70
Other liabilities:
Deferred income tax liabilities	1,370.40	1,341.40
Regulatory liabilities	434.6	453.8
Pension and other benefit obligations	142.1	142.4
Other	177.5	185.5
Total other liabilities	2,124.60	2,123.10
Commitments and contingencies (Note 13)
Common equity:
Common stock	33.4	33.4
Additional paid-in capital	1,242.80	1,242.80
Retained earnings	550.7	537.9
Total common equity	1,826.90	1,814.10
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	2,026.90	2,014.10
Total liabilities and equity	6,414.50	6,461.80
WPL [Member]
Current assets:
Cash and cash equivalents	90.9	46.7
Accounts receivable, less allowance for doubtful accounts	188.4	185.8
Production fuel, at weighted average cost	31.4	31.1
Materials and supplies, at weighted average cost	31.5	29.2
Gas stored underground, at weighted average cost	13.1	36.3
Regulatory assets	27.9	29.4
Other	83.2	98.7
Total current assets	466.4	457.2
Property, plant and equipment, net	3,966.70	3,938.90
Investments:
Investment in American Transmission Company LLC	288.5	286.5
Other	18.7	19.5
Total investments	307.2	306
Other assets:
Regulatory assets	398.7	396.4
Deferred charges and other	27.9	29.7
Total other assets	426.6	426.1
Total assets	5,166.90	5,128.20
Current liabilities:
Current maturities of long-term debt	30.6	30.6
Commercial paper	0
Accounts payable	107.7	112.9
Accounts payable to associated companies	21.3	25.5
Regulatory liabilities	71.9	70.4
Other	82.7	70.9
Total current liabilities	314.2	310.3
Long-term debt, net (excluding current portion)	1,543.40	1,543.30
Other liabilities:
Deferred income tax liabilities	984.4	970
Regulatory liabilities	172.1	167.3
Capital lease obligations - Sheboygan Falls Energy Facility	88	89.4
Pension and other benefit obligations	179.7	180.4
Other	159.5	155.2
Total other liabilities	1,583.70	1,562.30
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	959	959
Retained earnings	691.4	678.6
Total common equity	1,716.60	1,703.80
Noncontrolling interest	9	8.5
Total equity	1,725.60	1,712.30
Total liabilities and equity	$5,166.90	$5,128.20

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
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)	112,977,238	110,935,680
Shares in deferred compensation trust (in shares)	232,550	238,935
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$38.27	$37.45
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 $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$99.20	$110.60
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	100.2	95.5
Deferred taxes and investment tax credits	29.7	35.9
Other	-0.1	5.9
Other changes in assets and liabilities:
Accounts receivable	6.6	-55.6
Sales of accounts receivable	52	46
Production fuel	16.2	34.8
Gas stored underground	49.5	28.5
Accounts payable	-32.8	25.4
Other	-5.8	-33.4
Net cash flows from operating activities	314.7	293.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	-226	-159
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	-19.8	-14
Other	-5.1	-3.8
Net cash flows used for investing activities	-250.9	-176.8
Cash flows used for financing activities:
Common stock dividends	-60.7	-56.5
Proceeds from issuance of common stock, net	122.1	0
Net change in commercial paper	-99.8	-58.1
Other	15.3	2.5
Net cash flows used for financing activities	-23.1	-112.1
Net increase (decrease) in cash and cash equivalents	40.7	4.7
Cash and cash equivalents at beginning of period	56.9	9.8
Cash and cash equivalents at end of period	97.6	14.5
Supplemental cash flows information:
Interest, net of capitalized interest	-40.2	-41.4
Income taxes, net	0.1	3.9
Significant non-cash investing and financing activities:
Accrued capital expenditures	119	85.9
IPL [Member]
Cash flows from operating activities:
Net income	50.4	46
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	51.8	48.7
Other	12.5	10.1
Other changes in assets and liabilities:
Accounts receivable	-2.2	-48.9
Sales of accounts receivable	52	46
Gas stored underground	26.4	13.3
Accounts payable	-36.1	28.8
Accounts payable to associated companies	3.1	-28.8
Other	12.2	-9.6
Net cash flows from operating activities	170.1	105.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	-150.6	-91.1
Other	-5.7	-5.5
Net cash flows used for investing activities	-156.3	-96.6
Cash flows used for financing activities:
Common stock dividends	-35	-35
Capital contributions from parent	0	30
Other	18.5	-2.6
Net cash flows used for financing activities	-16.5	-7.6
Net increase (decrease) in cash and cash equivalents	-2.7	1.4
Cash and cash equivalents at beginning of period	5.3	4.4
Cash and cash equivalents at end of period	2.6	5.8
Supplemental cash flows information:
Interest, net of capitalized interest	-18.4	-19.3
Income taxes, net	6.2	-1.5
Significant non-cash investing and financing activities:
Accrued capital expenditures	82.8	46.3
WPL [Member]
Cash flows from operating activities:
Net income	44.8	54.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	46	44.7
Deferred taxes and investment tax credits	10.4	20.8
Other	-0.9	8.7
Other changes in assets and liabilities:
Derivative assets	0.2	-19.8
Gas stored underground	23.1	15.2
Regulatory liabilities	5.1	26.1
Other	29.1	-21.8
Net cash flows from operating activities	157.8	128.7
Cash flows used for investing activities:
Utility construction and acquisition expenditures	-75.4	-67.9
Other	-3	-2.6
Net cash flows used for investing activities	-78.4	-70.5
Cash flows used for financing activities:
Common stock dividends	-31.8	-29.7
Net change in commercial paper	0	-28.2
Other	-3.4	4.1
Net cash flows used for financing activities	-35.2	-53.8
Net increase (decrease) in cash and cash equivalents	44.2	4.4
Cash and cash equivalents at beginning of period	46.7	0.5
Cash and cash equivalents at end of period	90.9	4.9
Supplemental cash flows information:
Interest, net of capitalized interest	-22.6	-23.2
Income taxes, net	9.1	0.6
Significant non-cash investing and financing activities:
Accrued capital expenditures	$32.90	$33.70

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
	(b) New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
	(b) New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
	(b) New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.

Regulatory_Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2015
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70
	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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2015, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures.
	Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):
	Electric tax benefit rider credits		$18
	Gas tax benefit rider credits	3
			$21
	Refer to Note 8 for additional details regarding IPL’s tax benefit riders.
	Utility Rate Cases -
	IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 test year rate case through 2016 and provides targeted retail electric customer billing credits beginning May 2014. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
		2015
	Billing credits to reduce retail electric customers’ bills	$6
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). The $28 million of deferred fuel-related costs is included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. Beginning in 2015, the regulatory asset accrues interest at WPL’s PSCW authorized short-term debt rate. In March 2015, WPL filed a fuel reconciliation application with the PSCW to seek recovery in 2016 of the deferred fuel-related costs, including interest. WPL anticipates a decision from the PSCW regarding its application in the third quarter of 2015.
IPL [Member]
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70
	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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2015, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures.
	Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):
	Electric tax benefit rider credits		$18
	Gas tax benefit rider credits	3
			$21
	Refer to Note 8 for additional details regarding IPL’s tax benefit riders.
	Utility Rate Cases -
	IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 test year rate case through 2016 and provides targeted retail electric customer billing credits beginning May 2014. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
		2015
	Billing credits to reduce retail electric customers’ bills	$6
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). The $28 million of deferred fuel-related costs is included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. Beginning in 2015, the regulatory asset accrues interest at WPL’s PSCW authorized short-term debt rate. In March 2015, WPL filed a fuel reconciliation application with the PSCW to seek recovery in 2016 of the deferred fuel-related costs, including interest. WPL anticipates a decision from the PSCW regarding its application in the third quarter of 2015.
WPL [Member]
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS
	Regulatory Assets and Regulatory Liabilities -
	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70
	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 for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2015, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures.
	Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities.
	IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers 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, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):
	Electric tax benefit rider credits		$18
	Gas tax benefit rider credits	3
			$21
	Refer to Note 8 for additional details regarding IPL’s tax benefit riders.
	Utility Rate Cases -
	IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 test year rate case through 2016 and provides targeted retail electric customer billing credits beginning May 2014. For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
		2015
	Billing credits to reduce retail electric customers’ bills	$6
	WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). The $28 million of deferred fuel-related costs is included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. Beginning in 2015, the regulatory asset accrues interest at WPL’s PSCW authorized short-term debt rate. In March 2015, WPL filed a fuel reconciliation application with the PSCW to seek recovery in 2016 of the deferred fuel-related costs, including interest. WPL anticipates a decision from the PSCW regarding its application in the third quarter of 2015.

Property_Plant_and_Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT
	Utility -
	Emission Controls Project -
	WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of March 31, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $110 million and AFUDC of $4 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.
	Natural Gas-Fired Generation Project -
	IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of March 31, 2015, Alliant Energy and IPL recorded capitalized expenditures of $248 million and AFUDC of $7 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets.
	Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received net proceeds of $11 million and a promissory note of $2 million. The proceeds are subject to post-closing adjustments based on the value of the net assets transferred as of the closing date, and will be used for general corporate purposes. Refer to Note 16 for details of the natural gas distribution assets, which qualified as held for sale as of March 31, 2015 and December 31, 2014.
	In April 2015, the MPUC approved the sale of IPL’s Minnesota electric distribution assets, subject to certain conditions. IPL is currently reviewing the MPUC’s decision. Pending the receipt of remaining regulatory approvals, IPL currently expects the electric transaction to be concluded in the third quarter of 2015. As of March 31, 2015, IPL’s assets and liabilities included in the electric sales agreement did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process that existed on such date.
	Non-regulated and Other -
	Corporate Services and Other - Corporate Services is implementing a new customer billing and information system for IPL and WPL, which is currently expected to be deployed in 2015. As of March 31, 2015, Alliant Energy recorded capitalized expenditures of $71 million and capitalized interest of $2 million for the system in “Property, plant and equipment, net” on its balance sheet.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT
	Utility -
	Emission Controls Project -
	WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of March 31, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $110 million and AFUDC of $4 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.
	Natural Gas-Fired Generation Project -
	IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of March 31, 2015, Alliant Energy and IPL recorded capitalized expenditures of $248 million and AFUDC of $7 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets.
	Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received net proceeds of $11 million and a promissory note of $2 million. The proceeds are subject to post-closing adjustments based on the value of the net assets transferred as of the closing date, and will be used for general corporate purposes. Refer to Note 16 for details of the natural gas distribution assets, which qualified as held for sale as of March 31, 2015 and December 31, 2014.
	In April 2015, the MPUC approved the sale of IPL’s Minnesota electric distribution assets, subject to certain conditions. IPL is currently reviewing the MPUC’s decision. Pending the receipt of remaining regulatory approvals, IPL currently expects the electric transaction to be concluded in the third quarter of 2015. As of March 31, 2015, IPL’s assets and liabilities included in the electric sales agreement did not meet the criteria to be classified as held for sale due to uncertainties in the regulatory approval process that existed on such date.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT
	Utility -
	Emission Controls Project -
	WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of March 31, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $110 million and AFUDC of $4 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.

Receivables

Receivables	3 Months Ended
	Mar. 31, 2015
Receivables [Line Items]
Receivables	RECEIVABLES
	(a) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its Iowa customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party 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. As of March 31, 2015, IPL sold $197.5 million of receivables to the third party, received $74.0 million in cash proceeds and recorded deferred proceeds of $117.7 million.
	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):
		2015		2014
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)		$118.00		$75.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	68		27.6
	For the three months ended March 31, 2015 and 2014, IPL’s costs incurred related to the sales of accounts receivable program were not material.
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		March 31, 2015		December 31, 2014
	Customer accounts receivable		$144.80		$134.80
	Unbilled utility revenues	52.5		69.7
	Other receivables	0.2		0.1
	Receivables sold to third party	197.5		204.6
	Less: cash proceeds (a)	74		22
	Deferred proceeds	123.5		182.6
	Less: allowance for doubtful accounts	5.8		5.4
	Fair value of deferred proceeds		$117.70		$177.20
	Outstanding receivables past due		$21.70		$19.90
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):
		2015		2014
	Collections reinvested in receivables		$505.90		$541.40
	Credit losses, net of recoveries	1		2.5
	(b) Whiting Petroleum Tax Sharing Agreement - Prior to an initial public offering of Whiting Petroleum in 2003, Alliant Energy and Whiting Petroleum entered into a tax separation and indemnification agreement pursuant to which Alliant Energy and Whiting Petroleum made certain tax elections. These tax elections had the effect of increasing the tax basis of the assets of Whiting Petroleum’s consolidated tax group based on the sales price of Whiting Petroleum’s shares in the initial public offering. The increase in the tax basis of the assets was included in income in Alliant Energy’s U.S. federal income tax return for the calendar year 2003. Pursuant to the tax separation and indemnification agreement, Whiting Petroleum paid Resources the final payment of $26 million in March 2014, which represented the present value of certain future tax benefits expected to be realized by Whiting Petroleum through future tax deductions. The $26 million received by Alliant Energy is presented in operating activities in its cash flows statement for the three months ended March 31, 2014.
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES
	(a) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its Iowa customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party 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. As of March 31, 2015, IPL sold $197.5 million of receivables to the third party, received $74.0 million in cash proceeds and recorded deferred proceeds of $117.7 million.
	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):
		2015		2014
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)		$118.00		$75.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	68		27.6
	For the three months ended March 31, 2015 and 2014, IPL’s costs incurred related to the sales of accounts receivable program were not material.
	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		March 31, 2015		December 31, 2014
	Customer accounts receivable		$144.80		$134.80
	Unbilled utility revenues	52.5		69.7
	Other receivables	0.2		0.1
	Receivables sold to third party	197.5		204.6
	Less: cash proceeds (a)	74		22
	Deferred proceeds	123.5		182.6
	Less: allowance for doubtful accounts	5.8		5.4
	Fair value of deferred proceeds		$117.70		$177.20
	Outstanding receivables past due		$21.70		$19.90
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):
		2015		2014
	Collections reinvested in receivables		$505.90		$541.40
	Credit losses, net of recoveries	1		2.5

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Schedule of Investments [Line Items]
Investments	INVESTMENTS
	Unconsolidated Equity Investments - Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
		Alliant Energy						WPL
		2015			2014			2015			2014
	ATC		($7.8	)		($11.2	)		($7.8	)		($11.2	)
	Other	1.3			(0.2		)	—			(0.2		)
			($6.5	)		($11.4	)		($7.8	)		($11.4	)
WPL [Member]
Schedule of Investments [Line Items]
Investments	INVESTMENTS
	Unconsolidated Equity Investments - Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
		Alliant Energy						WPL
		2015			2014			2015			2014
	ATC		($7.8	)		($11.2	)		($7.8	)		($11.2	)
	Other	1.3			(0.2		)	—			(0.2		)
			($6.5	)		($11.4	)		($7.8	)		($11.4	)

Common_Equity

Common Equity	3 Months Ended
	Mar. 31, 2015
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, 2015	110,935,680
	At-the-market offering program	1,996,450
	Shareowner Direct Plan	11,193
	Equity-based compensation plans (Note 9(b))	56,378
	Other	(22,463	)
	Shares outstanding, March 31, 2015	112,977,238
	At-the-Market Offering Program - In March 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. As of March 31, 2015, Alliant Energy issued 1,996,450 shares of common stock through this program and received cash proceeds of $121 million, net of $2 million in fees and commissions. Alliant Energy also had commitments not recognized on its balance sheet at March 31, 2015 to sell 190,167 shares of common stock under sales transactions executed through this program in late March 2015. Subsequent to March 31, 2015, Alliant Energy issued shares to settle these transactions in exchange for net cash proceeds of $12 million. The proceeds from the issuances of common stock were used for general corporate purposes. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program.
	Dividend Restrictions - As of March 31, 2015, IPL’s amount of retained earnings that were free of dividend restrictions was $518 million. As of March 31, 2015, WPL’s amount of retained earnings that were free of dividend restrictions was $95 million for the remainder of 2015.
	Restricted Net Assets of Subsidiaries - As of March 31, 2015, 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 $1.3 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the three months ended March 31, 2015, IPL and WPL each paid common stock dividends of $35.0 million and $31.8 million, respectively, to its parent company.
	Comprehensive Income - For the three months ended March 31, 2015 and 2014, 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 months ended March 31, 2015 and 2014, 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]
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, 2015	110,935,680
	At-the-market offering program	1,996,450
	Shareowner Direct Plan	11,193
	Equity-based compensation plans (Note 9(b))	56,378
	Other	(22,463	)
	Shares outstanding, March 31, 2015	112,977,238
	At-the-Market Offering Program - In March 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. As of March 31, 2015, Alliant Energy issued 1,996,450 shares of common stock through this program and received cash proceeds of $121 million, net of $2 million in fees and commissions. Alliant Energy also had commitments not recognized on its balance sheet at March 31, 2015 to sell 190,167 shares of common stock under sales transactions executed through this program in late March 2015. Subsequent to March 31, 2015, Alliant Energy issued shares to settle these transactions in exchange for net cash proceeds of $12 million. The proceeds from the issuances of common stock were used for general corporate purposes. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program.
	Dividend Restrictions - As of March 31, 2015, IPL’s amount of retained earnings that were free of dividend restrictions was $518 million. As of March 31, 2015, WPL’s amount of retained earnings that were free of dividend restrictions was $95 million for the remainder of 2015.
	Restricted Net Assets of Subsidiaries - As of March 31, 2015, 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 $1.3 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the three months ended March 31, 2015, IPL and WPL each paid common stock dividends of $35.0 million and $31.8 million, respectively, to its parent company.
	Comprehensive Income - For the three months ended March 31, 2015 and 2014, 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 months ended March 31, 2015 and 2014, 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]
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, 2015	110,935,680
	At-the-market offering program	1,996,450
	Shareowner Direct Plan	11,193
	Equity-based compensation plans (Note 9(b))	56,378
	Other	(22,463	)
	Shares outstanding, March 31, 2015	112,977,238
	At-the-Market Offering Program - In March 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. As of March 31, 2015, Alliant Energy issued 1,996,450 shares of common stock through this program and received cash proceeds of $121 million, net of $2 million in fees and commissions. Alliant Energy also had commitments not recognized on its balance sheet at March 31, 2015 to sell 190,167 shares of common stock under sales transactions executed through this program in late March 2015. Subsequent to March 31, 2015, Alliant Energy issued shares to settle these transactions in exchange for net cash proceeds of $12 million. The proceeds from the issuances of common stock were used for general corporate purposes. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program.
	Dividend Restrictions - As of March 31, 2015, IPL’s amount of retained earnings that were free of dividend restrictions was $518 million. As of March 31, 2015, WPL’s amount of retained earnings that were free of dividend restrictions was $95 million for the remainder of 2015.
	Restricted Net Assets of Subsidiaries - As of March 31, 2015, 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 $1.3 billion and $1.6 billion, respectively.
	Capital Transactions with Subsidiaries - For the three months ended March 31, 2015, IPL and WPL each paid common stock dividends of $35.0 million and $31.8 million, respectively, to its parent company.
	Comprehensive Income - For the three months ended March 31, 2015 and 2014, 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 months ended March 31, 2015 and 2014, 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.

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt [Line Items]
Debt	DEBT
	Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%
IPL [Member]
Debt [Line Items]
Debt	DEBT
	Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%
WPL [Member]
Debt [Line Items]
Debt	DEBT
	Short-term Debt - Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Taxes [Line Items]
Income Taxes	INCOME TAXES
	Income Tax Rates - The provision for income taxes is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items or extraordinary items. The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
	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 IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders.
	Production tax credits - For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by the effect of rate-making principles on certain property-related differences for which deferred tax is not recognized in the income statement, substantially all of which relates to IPL. The increased benefits from property-related differences recognized during the three months ended March 31, 2015 were primarily due to additional repairs deductions.
	Deferred Tax Assets and Liabilities - For the three months ended March 31, 2015, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $45.8 million, $29.0 million and $14.4 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2015, including an increase in qualifying repairs expenditures, and utilization of federal net operating loss carryforwards.
	Carryforwards - At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES
	Income Tax Rates - The provision for income taxes is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items or extraordinary items. The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
	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 IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders.
	Production tax credits - For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by the effect of rate-making principles on certain property-related differences for which deferred tax is not recognized in the income statement, substantially all of which relates to IPL. The increased benefits from property-related differences recognized during the three months ended March 31, 2015 were primarily due to additional repairs deductions.
	Deferred Tax Assets and Liabilities - For the three months ended March 31, 2015, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $45.8 million, $29.0 million and $14.4 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2015, including an increase in qualifying repairs expenditures, and utilization of federal net operating loss carryforwards.
	Carryforwards - At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES
	Income Tax Rates - The provision for income taxes is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items or extraordinary items. The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
	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 IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders.
	Production tax credits - For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
	Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by the effect of rate-making principles on certain property-related differences for which deferred tax is not recognized in the income statement, substantially all of which relates to IPL. The increased benefits from property-related differences recognized during the three months ended March 31, 2015 were primarily due to additional repairs deductions.
	Deferred Tax Assets and Liabilities - For the three months ended March 31, 2015, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $45.8 million, $29.0 million and $14.4 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2015, including an increase in qualifying repairs expenditures, and utilization of federal net operating loss carryforwards.
	Carryforwards - At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210

Benefit_Plans

Benefit Plans	3 Months Ended
	Mar. 31, 2015
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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
	401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5
	As of March 31, 2015, total unrecognized compensation cost related to share-based compensation awards was $13.1 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 income statements.
	Performance Shares and Units -
	Performance Shares - A summary of the performance shares activity was as follows:
		2015 (a)			2014 (a)
	Nonvested shares, January 1	144,424			139,940
	Granted	45,403			51,221
	Vested	(45,612	)		(45,235	)
	Nonvested shares, March 31	144,215			145,926
	(a)	Share amounts represent the target number of performance shares.
	During the three months ended March 31, certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:
		2015				2014
		2012 Grant				2011 Grant
	Performance shares vested	45,612				45,235
	Percentage of target number of performance shares	167.5		%		147.5		%
	Aggregate payout value (in millions)		$5.10				$3.40
	Payout - cash (in millions)		$3.20				$2.90
	Payout - common stock shares issued	10,975				4,810
	Performance Units - A summary of the performance units activity was as follows:
		2015 (a)			2014 (a)
	Nonvested units, January 1	63,665			65,912
	Granted	17,837			20,422
	Vested	(22,845	)		(20,751	)
	Forfeited	(93	)		(311	)
	Nonvested units, March 31	58,564			65,272
	(a)	Unit amounts represent the target number of performance units.
During the three months ended March 31, certain performance units vested, resulting in cash payouts as follows:
	2015				2014
	2012 Grant				2011 Grant
Performance units vested	22,845				20,751
Percentage of target number of performance units	167.5		%		147.5		%
Payout value (in millions)		$1.60				$1.20
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at March 31, 2015, by year of grant, was as follows:
	Performance Shares												Performance Units
	2015 Grant				2014 Grant				2013 Grant				2015 Grant			2014 Grant			2013 Grant
Nonvested awards	45,403				49,719				49,093				17,744			19,440			21,380
Alliant Energy common stock closing price on March 31, 2015		$63.00				$63.00				$63.00
Alliant Energy common stock closing price on grant date														$65.09			$53.77			$47.58
Estimated payout percentage based on performance criteria	100		%		128		%		178		%		100		%	128		%	178		%
Fair values of each nonvested award		$63.00				$80.64				$112.14				$65.09			$68.83			$84.69
At March 31, 2015, fair values of nonvested performance shares and units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group.
Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
	2015							2014
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	98,812				$50.69			158,922				$42.71
Granted	45,403			65.09				51,221			53.77
Vested (a)	(49,093	)		47.58				(90,847	)		40.91
Forfeited	—			—				(18,982	)		38.75
Nonvested shares, March 31	95,122			59.17				100,314			50.74
(a)	In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2015			2014
Nonvested awards, January 1	78,930			96,977
Granted	41,105			42,446
Vested (a)	(37,332	)		(55,517	)
Forfeited	(469	)		(3,406	)
Nonvested awards, March 31	82,234			80,500
(a)	In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.
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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
	401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5
	As of March 31, 2015, total unrecognized compensation cost related to share-based compensation awards was $13.1 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 income statements.
	Performance Shares and Units -
	Performance Shares - A summary of the performance shares activity was as follows:
		2015 (a)			2014 (a)
	Nonvested shares, January 1	144,424			139,940
	Granted	45,403			51,221
	Vested	(45,612	)		(45,235	)
	Nonvested shares, March 31	144,215			145,926
	(a)	Share amounts represent the target number of performance shares.
	During the three months ended March 31, certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:
		2015				2014
		2012 Grant				2011 Grant
	Performance shares vested	45,612				45,235
	Percentage of target number of performance shares	167.5		%		147.5		%
	Aggregate payout value (in millions)		$5.10				$3.40
	Payout - cash (in millions)		$3.20				$2.90
	Payout - common stock shares issued	10,975				4,810
	Performance Units - A summary of the performance units activity was as follows:
		2015 (a)			2014 (a)
	Nonvested units, January 1	63,665			65,912
	Granted	17,837			20,422
	Vested	(22,845	)		(20,751	)
	Forfeited	(93	)		(311	)
	Nonvested units, March 31	58,564			65,272
	(a)	Unit amounts represent the target number of performance units.
During the three months ended March 31, certain performance units vested, resulting in cash payouts as follows:
	2015				2014
	2012 Grant				2011 Grant
Performance units vested	22,845				20,751
Percentage of target number of performance units	167.5		%		147.5		%
Payout value (in millions)		$1.60				$1.20
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at March 31, 2015, by year of grant, was as follows:
	Performance Shares												Performance Units
	2015 Grant				2014 Grant				2013 Grant				2015 Grant			2014 Grant			2013 Grant
Nonvested awards	45,403				49,719				49,093				17,744			19,440			21,380
Alliant Energy common stock closing price on March 31, 2015		$63.00				$63.00				$63.00
Alliant Energy common stock closing price on grant date														$65.09			$53.77			$47.58
Estimated payout percentage based on performance criteria	100		%		128		%		178		%		100		%	128		%	178		%
Fair values of each nonvested award		$63.00				$80.64				$112.14				$65.09			$68.83			$84.69
At March 31, 2015, fair values of nonvested performance shares and units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group.
Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
	2015							2014
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	98,812				$50.69			158,922				$42.71
Granted	45,403			65.09				51,221			53.77
Vested (a)	(49,093	)		47.58				(90,847	)		40.91
Forfeited	—			—				(18,982	)		38.75
Nonvested shares, March 31	95,122			59.17				100,314			50.74
(a)	In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2015			2014
Nonvested awards, January 1	78,930			96,977
Granted	41,105			42,446
Vested (a)	(37,332	)		(55,517	)
Forfeited	(469	)		(3,406	)
Nonvested awards, March 31	82,234			80,500
(a)	In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.
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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
	401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5
	As of March 31, 2015, total unrecognized compensation cost related to share-based compensation awards was $13.1 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 income statements.
	Performance Shares and Units -
	Performance Shares - A summary of the performance shares activity was as follows:
		2015 (a)			2014 (a)
	Nonvested shares, January 1	144,424			139,940
	Granted	45,403			51,221
	Vested	(45,612	)		(45,235	)
	Nonvested shares, March 31	144,215			145,926
	(a)	Share amounts represent the target number of performance shares.
	During the three months ended March 31, certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:
		2015				2014
		2012 Grant				2011 Grant
	Performance shares vested	45,612				45,235
	Percentage of target number of performance shares	167.5		%		147.5		%
	Aggregate payout value (in millions)		$5.10				$3.40
	Payout - cash (in millions)		$3.20				$2.90
	Payout - common stock shares issued	10,975				4,810
	Performance Units - A summary of the performance units activity was as follows:
		2015 (a)			2014 (a)
	Nonvested units, January 1	63,665			65,912
	Granted	17,837			20,422
	Vested	(22,845	)		(20,751	)
	Forfeited	(93	)		(311	)
	Nonvested units, March 31	58,564			65,272
	(a)	Unit amounts represent the target number of performance units.
During the three months ended March 31, certain performance units vested, resulting in cash payouts as follows:
	2015				2014
	2012 Grant				2011 Grant
Performance units vested	22,845				20,751
Percentage of target number of performance units	167.5		%		147.5		%
Payout value (in millions)		$1.60				$1.20
Fair Value of Awards - Information related to fair values of nonvested performance shares and units at March 31, 2015, by year of grant, was as follows:
	Performance Shares												Performance Units
	2015 Grant				2014 Grant				2013 Grant				2015 Grant			2014 Grant			2013 Grant
Nonvested awards	45,403				49,719				49,093				17,744			19,440			21,380
Alliant Energy common stock closing price on March 31, 2015		$63.00				$63.00				$63.00
Alliant Energy common stock closing price on grant date														$65.09			$53.77			$47.58
Estimated payout percentage based on performance criteria	100		%		128		%		178		%		100		%	128		%	178		%
Fair values of each nonvested award		$63.00				$80.64				$112.14				$65.09			$68.83			$84.69
At March 31, 2015, fair values of nonvested performance shares and units were calculated based on Alliant Energy’s stock price and anticipated total shareowner returns of Alliant Energy and its investor-owned utility peer group over the performance period. The portion of the fair values based on anticipated total shareowner returns was estimated using a model that incorporates the probability of meeting performance targets based on historical returns relative to the peer group.
Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows:
	2015							2014
	Shares			Weighted				Shares			Weighted
				Average							Average
				Fair Value							Fair Value
Nonvested shares, January 1	98,812				$50.69			158,922				$42.71
Granted	45,403			65.09				51,221			53.77
Vested (a)	(49,093	)		47.58				(90,847	)		40.91
Forfeited	—			—				(18,982	)		38.75
Nonvested shares, March 31	95,122			59.17				100,314			50.74
(a)	In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity was as follows:
	2015			2014
Nonvested awards, January 1	78,930			96,977
Granted	41,105			42,446
Vested (a)	(37,332	)		(55,517	)
Forfeited	(469	)		(3,406	)
Nonvested awards, March 31	82,234			80,500
(a)	In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.

Asset_Retirement_Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2015
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
	CCR Rule - In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have current and former coal-fired EGUs with existing coal ash surface impoundments, as well as active CCR company-owned landfills that are expected to be impacted by this rule. Alliant Energy, IPL and WPL are currently evaluating the final CCR Rule to determine its full impact. Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10
	Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
	CCR Rule - In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have current and former coal-fired EGUs with existing coal ash surface impoundments, as well as active CCR company-owned landfills that are expected to be impacted by this rule. Alliant Energy, IPL and WPL are currently evaluating the final CCR Rule to determine its full impact. Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10
	Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
WPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS
	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
	CCR Rule - In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is effective October 2015. IPL and WPL have current and former coal-fired EGUs with existing coal ash surface impoundments, as well as active CCR company-owned landfills that are expected to be impacted by this rule. Alliant Energy, IPL and WPL are currently evaluating the final CCR Rule to determine its full impact. Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10
	Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Measurements	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of 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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
	Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and risk policies are maintained that govern the use of such derivative instruments. 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 forward contracts (IPL and WPL)
	Fuel used to supply natural gas-fired EGUs	Natural gas swap contracts (IPL and WPL)
		Natural gas options and physical forward contracts (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired EGUs	Coal physical forward contracts (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	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. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. 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. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities.
	The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. 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 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 accounts receivable 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 4(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.
	Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
	Value			1			2			3			Value			1		2		3
Assets:
Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on 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.
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 March 31	2015			2014			2015			2014
Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
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 March 31		($16.5	)		$31.00			$—			$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2015			2014			2015			2014
Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
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 March 31		($10.7	)		$3.10			$—			$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2015			2014
Beginning balance, January 1		($1.5	)		($10.2	)
Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
Settlements	(1.0		)	(7.9		)
Ending balance, March 31		($8.1	)		$16.10
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 March 31		($5.8	)		$27.90
(a)	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 - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
	Alliant Energy						IPL						WPL
	Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of 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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
	Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and risk policies are maintained that govern the use of such derivative instruments. 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 forward contracts (IPL and WPL)
	Fuel used to supply natural gas-fired EGUs	Natural gas swap contracts (IPL and WPL)
		Natural gas options and physical forward contracts (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired EGUs	Coal physical forward contracts (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	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. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. 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. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities.
	The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. 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 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 accounts receivable 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 4(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.
	Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
	Value			1			2			3			Value			1		2		3
Assets:
Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on 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.
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 March 31	2015			2014			2015			2014
Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
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 March 31		($16.5	)		$31.00			$—			$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2015			2014			2015			2014
Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
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 March 31		($10.7	)		$3.10			$—			$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2015			2014
Beginning balance, January 1		($1.5	)		($10.2	)
Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
Settlements	(1.0		)	(7.9		)
Ending balance, March 31		($8.1	)		$16.10
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 March 31		($5.8	)		$27.90
(a)	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 - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
	Alliant Energy						IPL						WPL
	Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS
	Fair Value of Financial Instruments - The carrying amounts of 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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
	Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds.
	Valuation Techniques -
	Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs, and risk policies are maintained that govern the use of such derivative instruments. 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 forward contracts (IPL and WPL)
	Fuel used to supply natural gas-fired EGUs	Natural gas swap contracts (IPL and WPL)
		Natural gas options and physical forward contracts (WPL)
	Natural gas supplied to retail customers	Natural gas options and physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Fuel used at coal-fired EGUs	Coal physical forward contracts (IPL and WPL)
	Optimize the value of natural gas pipeline capacity	Natural gas physical forward contracts (IPL and WPL)
		Natural gas swap contracts (IPL)
	Manage transmission congestion costs	FTRs (IPL and WPL)
	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. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. 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. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities.
	The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. 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 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 accounts receivable 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 4(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.
	Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date.
	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
	Value			1			2			3			Value			1		2		3
Assets:
Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on 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.
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 March 31	2015			2014			2015			2014
Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
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 March 31		($16.5	)		$31.00			$—			$—
IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2015			2014			2015			2014
Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
Sales	(0.9		)	—			—			—
Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
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 March 31		($10.7	)		$3.10			$—			$—
WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2015			2014
Beginning balance, January 1		($1.5	)		($10.2	)
Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
Settlements	(1.0		)	(7.9		)
Ending balance, March 31		($8.1	)		$16.10
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 March 31		($5.8	)		$27.90
(a)	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 - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
	Alliant Energy						IPL						WPL
	Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3

Derivative_Instruments

Derivative Instruments	3 Months Ended
	Mar. 31, 2015
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments.
	Notional Amounts - As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
	Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets 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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
	Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
	Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8
	Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments.
	Notional Amounts - As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
	Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets 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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
	Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
	Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8
	Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS
	Commodity Derivatives -
	Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments.
	Notional Amounts - As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
	Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets 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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
	Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
	Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8
	Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Commitments_And_Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of a scrubber at Lansing Unit 4 to reduce SO2 emissions. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, and generation maintenance and performance improvements at Columbia Units 1 and 2. At March 31, 2015, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $26 million, $2 million and $24 million, respectively.
	(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
	(c) Legal Proceedings -
	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 March 31, 2015. 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 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 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 March 31, 2015, Alliant Energy had $251 million of performance guarantees outstanding, with $128 million, $48 million and $75 million currently expected to expire in 2015, 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects.
	Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of March 31, 2015. Due to the early stages of the warranty claims, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	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 March 31, 2015, the present value of the abandonment obligations is estimated at $35 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 March 31, 2015.
	(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 have, or may have in the 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 these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 25 and 5 sites, respectively. Included in IPL’s sites is a Minnesota site for which responsibility of monitoring and/or remediating the site was transferred to the buyer as part of the sale of IPL’s Minnesota natural gas distribution assets.
	Environmental liabilities related to these MGP sites are recorded 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. At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2
	WPL Consent Decree - In 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs 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 State Implementation Plan. 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 State Implementation Plan 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 U.S. District Court for the Western District of Wisconsin, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	Selective catalytic reduction system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014);
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	Selective catalytic reduction 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. In addition, WPL 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.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Clean Air Visibility Rule, MATS Rule, Industrial Boiler and Process Heater Maximum Achievable Control Technology Rule, Ozone National Ambient Air Quality Standards Rule, SO2 National Ambient Air Quality Standards Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. Some recent developments concerning these environmental matters are included below:
	Air Quality -
	MATS Rule - In March 2015, the EPA approved an extension to the MATS Rule compliance deadline from April 2015 to April 2016 for IPL’s M.L. Kapp Unit 2.
	Land and Solid Waste -
	CCR Rule - Refer to Note 10 for discussion of the final CCR Rule, including additional AROs that are expected to be recognized in the second quarter of 2015.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of a scrubber at Lansing Unit 4 to reduce SO2 emissions. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, and generation maintenance and performance improvements at Columbia Units 1 and 2. At March 31, 2015, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $26 million, $2 million and $24 million, respectively.
	(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
	(c) Legal Proceedings -
	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 March 31, 2015. 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 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 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 March 31, 2015, Alliant Energy had $251 million of performance guarantees outstanding, with $128 million, $48 million and $75 million currently expected to expire in 2015, 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects.
	Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of March 31, 2015. Due to the early stages of the warranty claims, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	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 March 31, 2015, the present value of the abandonment obligations is estimated at $35 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 March 31, 2015.
	(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 have, or may have in the 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 these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 25 and 5 sites, respectively. Included in IPL’s sites is a Minnesota site for which responsibility of monitoring and/or remediating the site was transferred to the buyer as part of the sale of IPL’s Minnesota natural gas distribution assets.
	Environmental liabilities related to these MGP sites are recorded 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. At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2
	WPL Consent Decree - In 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs 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 State Implementation Plan. 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 State Implementation Plan 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 U.S. District Court for the Western District of Wisconsin, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	Selective catalytic reduction system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014);
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	Selective catalytic reduction 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. In addition, WPL 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.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Clean Air Visibility Rule, MATS Rule, Industrial Boiler and Process Heater Maximum Achievable Control Technology Rule, Ozone National Ambient Air Quality Standards Rule, SO2 National Ambient Air Quality Standards Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. Some recent developments concerning these environmental matters are included below:
	Air Quality -
	MATS Rule - In March 2015, the EPA approved an extension to the MATS Rule compliance deadline from April 2015 to April 2016 for IPL’s M.L. Kapp Unit 2.
	Land and Solid Waste -
	CCR Rule - Refer to Note 10 for discussion of the final CCR Rule, including additional AROs that are expected to be recognized in the second quarter of 2015.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES
	(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of a scrubber at Lansing Unit 4 to reduce SO2 emissions. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, and generation maintenance and performance improvements at Columbia Units 1 and 2. At March 31, 2015, Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $26 million, $2 million and $24 million, respectively.
	(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
	(c) Legal Proceedings -
	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 March 31, 2015. 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 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 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 March 31, 2015, Alliant Energy had $251 million of performance guarantees outstanding, with $128 million, $48 million and $75 million currently expected to expire in 2015, 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects.
	Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of March 31, 2015. Due to the early stages of the warranty claims, Alliant Energy is currently unable to provide an estimate of potential loss or range of potential loss.
	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 March 31, 2015, the present value of the abandonment obligations is estimated at $35 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 March 31, 2015.
	(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 have, or may have in the 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 these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 25 and 5 sites, respectively. Included in IPL’s sites is a Minnesota site for which responsibility of monitoring and/or remediating the site was transferred to the buyer as part of the sale of IPL’s Minnesota natural gas distribution assets.
	Environmental liabilities related to these MGP sites are recorded 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. At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2
	WPL Consent Decree - In 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs 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 State Implementation Plan. 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 State Implementation Plan 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 U.S. District Court for the Western District of Wisconsin, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following emission controls systems:
	•	Selective catalytic reduction system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012);
	•	Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014);
	•	Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and
	•	Selective catalytic reduction 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. In addition, WPL 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.
	Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Clean Air Visibility Rule, MATS Rule, Industrial Boiler and Process Heater Maximum Achievable Control Technology Rule, Ozone National Ambient Air Quality Standards Rule, SO2 National Ambient Air Quality Standards Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. Some recent developments concerning these environmental matters are included below:
	Air Quality -
	MATS Rule - In March 2015, the EPA approved an extension to the MATS Rule compliance deadline from April 2015 to April 2016 for IPL’s M.L. Kapp Unit 2.
	Land and Solid Waste -
	CCR Rule - Refer to Note 10 for discussion of the final CCR Rule, including additional AROs that are expected to be recognized in the second quarter of 2015.

Segments_Of_Business

Segments Of Business	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015
	Operating revenues		$671.30		$198.40		$16.40		$886.10		$11.30		$897.40
	Operating income	104.7		36.3		5.3		146.3		6.6		152.9
	Net income attributable to Alliant Energy common shareowners							92.4		4.2		96.6
	Three Months Ended March 31, 2014
	Operating revenues		$675.80		$240.70		$22.80		$939.30		$13.50		$952.80
	Operating income	94.3		43		7.9		145.2		9		154.2
	Net income attributable to Alliant Energy common shareowners							98.2		9.8		108
	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 March 31, 2015
	Operating revenues		$362.60		$111.20		$15.20		$489.00
	Operating income	40.3		20.6		4.6		65.5
	Earnings available for common stock							47.8
	Three Months Ended March 31, 2014
	Operating revenues		$374.20		$135.70		$19.00		$528.90
	Operating income	26.5		23.3		7.7		57.5
	Earnings available for common stock							43.4
	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 March 31, 2015
	Operating revenues		$308.70		$87.20		$1.20		$397.10
	Operating income	64.4		15.7		0.7		80.8
	Earnings available for common stock							44.6
	Three Months Ended March 31, 2014
	Operating revenues		$301.60		$105.00		$3.80		$410.40
	Operating income	67.8		19.7		0.2		87.7
	Earnings available for common stock							54.8
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 March 31, 2015
	Operating revenues		$671.30		$198.40		$16.40		$886.10		$11.30		$897.40
	Operating income	104.7		36.3		5.3		146.3		6.6		152.9
	Net income attributable to Alliant Energy common shareowners							92.4		4.2		96.6
	Three Months Ended March 31, 2014
	Operating revenues		$675.80		$240.70		$22.80		$939.30		$13.50		$952.80
	Operating income	94.3		43		7.9		145.2		9		154.2
	Net income attributable to Alliant Energy common shareowners							98.2		9.8		108
	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 March 31, 2015
	Operating revenues		$362.60		$111.20		$15.20		$489.00
	Operating income	40.3		20.6		4.6		65.5
	Earnings available for common stock							47.8
	Three Months Ended March 31, 2014
	Operating revenues		$374.20		$135.70		$19.00		$528.90
	Operating income	26.5		23.3		7.7		57.5
	Earnings available for common stock							43.4
	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 March 31, 2015
	Operating revenues		$308.70		$87.20		$1.20		$397.10
	Operating income	64.4		15.7		0.7		80.8
	Earnings available for common stock							44.6
	Three Months Ended March 31, 2014
	Operating revenues		$301.60		$105.00		$3.80		$410.40
	Operating income	67.8		19.7		0.2		87.7
	Earnings available for common stock							54.8
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 March 31, 2015
	Operating revenues		$671.30		$198.40		$16.40		$886.10		$11.30		$897.40
	Operating income	104.7		36.3		5.3		146.3		6.6		152.9
	Net income attributable to Alliant Energy common shareowners							92.4		4.2		96.6
	Three Months Ended March 31, 2014
	Operating revenues		$675.80		$240.70		$22.80		$939.30		$13.50		$952.80
	Operating income	94.3		43		7.9		145.2		9		154.2
	Net income attributable to Alliant Energy common shareowners							98.2		9.8		108
	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 March 31, 2015
	Operating revenues		$362.60		$111.20		$15.20		$489.00
	Operating income	40.3		20.6		4.6		65.5
	Earnings available for common stock							47.8
	Three Months Ended March 31, 2014
	Operating revenues		$374.20		$135.70		$19.00		$528.90
	Operating income	26.5		23.3		7.7		57.5
	Earnings available for common stock							43.4
	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 March 31, 2015
	Operating revenues		$308.70		$87.20		$1.20		$397.10
	Operating income	64.4		15.7		0.7		80.8
	Earnings available for common stock							44.6
	Three Months Ended March 31, 2014
	Operating revenues		$301.60		$105.00		$3.80		$410.40
	Operating income	67.8		19.7		0.2		87.7
	Earnings available for common stock							54.8

Related_Parties

Related Parties	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES
	Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general 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. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO and PJM. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO and PJM. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
	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 months ended March 31 were as follows (in millions):
		2015			2014
	ATC billings to WPL		$25			$24
	WPL billings to ATC	2			3
	WPL owed ATC net amounts of $7 million as of March 31, 2015 and $8 million as of December 31, 2014.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES
	Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general 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. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO and PJM. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO and PJM. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES
	Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general 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. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO and PJM. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO and PJM. The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
	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 months ended March 31 were as follows (in millions):
		2015			2014
	ATC billings to WPL		$25			$24
	WPL billings to ATC	2			3
	WPL owed ATC net amounts of $7 million as of March 31, 2015 and $8 million as of December 31, 2014.

Assets_And_Liabilities_Held_Fo

Assets And Liabilities Held For Sale	3 Months Ended
	Mar. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets and Liabilities Held For Sale	ASSETS AND LIABILITIES HELD FOR SALE
	In December 2014, the MPUC issued an order approving the sale of IPL’s Minnesota natural gas distribution assets. In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets. Alliant Energy’s and IPL’s balance sheets included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
		March 31, 2015		31-Dec-14
	Assets held for sale:
	Current assets		$2.30		$1.10
	Property, plant and equipment, net	11		11
	Other assets	6.4		7
	Total assets held for sale	19.7		19.1
	Liabilities held for sale:
	Current liabilities	0.2		1
	Other liabilities	6.8		7.1
	Total liabilities held for sale	7		8.1
	Net assets held for sale		$12.70		$11.00
	Alliant Energy and IPL evaluated the sale of IPL’s Minnesota natural gas distribution assets and believe it did not represent a strategic shift that has, or will have, a major effect on their operational and financial results. As a result, the operating results of IPL’s Minnesota natural gas distribution assets have not been separately classified and reported as discontinued operations in Alliant Energy’s and IPL’s income statements. Refer to Note 3 for further discussion of IPL’s sale of its Minnesota natural gas distribution assets.
IPL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets and Liabilities Held For Sale	ASSETS AND LIABILITIES HELD FOR SALE
	In December 2014, the MPUC issued an order approving the sale of IPL’s Minnesota natural gas distribution assets. In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets. Alliant Energy’s and IPL’s balance sheets included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
		March 31, 2015		31-Dec-14
	Assets held for sale:
	Current assets		$2.30		$1.10
	Property, plant and equipment, net	11		11
	Other assets	6.4		7
	Total assets held for sale	19.7		19.1
	Liabilities held for sale:
	Current liabilities	0.2		1
	Other liabilities	6.8		7.1
	Total liabilities held for sale	7		8.1
	Net assets held for sale		$12.70		$11.00
	Alliant Energy and IPL evaluated the sale of IPL’s Minnesota natural gas distribution assets and believe it did not represent a strategic shift that has, or will have, a major effect on their operational and financial results. As a result, the operating results of IPL’s Minnesota natural gas distribution assets have not been separately classified and reported as discontinued operations in Alliant Energy’s and IPL’s income statements. Refer to Note 3 for further discussion of IPL’s sale of its Minnesota natural gas distribution assets.

Summary_Of_Significant_Account1

Summary Of Significant Accounting Policies (Policy)	3 Months Ended
	Mar. 31, 2015
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
New Accounting Pronouncements	New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
New Accounting Pronouncements	New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 the 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 three months ended March 31, 2015 are not necessarily indicative of results that may be expected for the year ending December 31, 2015. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude assets and liabilities held for sale for all periods presented.
New Accounting Pronouncements	New Accounting Pronouncements -
	Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL are currently required to adopt this standard on January 1, 2017; however, in April 2015, the Financial Accounting Standards Board proposed to defer the effective date of this standard by one year. Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations.
	Presentation of Debt Issuance Costs - In April 2015, the Financial Accounting Standards Board issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability will be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2016 and early adoption is permitted. Debt issuance costs represent less than 1% of total long-term debt.

Regulatory_Matters_Tables

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2015
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70
Tax Benefit Riders	For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):
	Electric tax benefit rider credits		$18
	Gas tax benefit rider credits	3
			$21
Customer Billing Credits	For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
		2015
	Billing credits to reduce retail electric customers’ bills	$6
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70
Tax Benefit Riders	For the three months ended March 31, 2015, Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $21 million as follows (in millions):
	Electric tax benefit rider credits		$18
	Gas tax benefit rider credits	3
			$21
Customer Billing Credits	For the three months ended March 31, IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions):
		2015
	Billing credits to reduce retail electric customers’ bills	$6
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Tax-related		$968.20		$955.30		$940.50		$928.00		$27.70		$27.30
	Pension and OPEB costs	562.9		570.2		284.8		287.9		278.1		282.3
	AROs	75.6		73.7		42.5		41.4		33.1		32.3
	Derivatives	49.6		46.9		26.4		28		23.2		18.9
	Commodity cost recovery	32.1		31.1		0.6		0.4		31.5		30.7
	Emission allowances	26.9		27.4		26.9		27.4		—		—
	Other	75		79.1		42		44.8		33		34.3
			$1,790.30		$1,783.70		$1,363.70		$1,357.90		$426.60		$425.80
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions):
		Alliant Energy				IPL				WPL
		March 31,		December 31,		March 31,		December 31,		March 31,		December 31,
		2015		2014		2015		2014		2015		2014
	Cost of removal obligations		$423.20		$421.70		$279.50		$279.10		$143.70		$142.60
	IPL’s tax benefit riders	222		243		222		243		—		—
	Energy efficiency cost recovery	62.2		64.3		1.6		—		60.6		64.3
	Commodity cost recovery	26.5		15.4		22.8		15.1		3.7		0.3
	IPL’s electric transmission cost recovery	23.2		19.4		23.2		19.4		—		—
	Other	59		57.4		23		26.9		36		30.5
			$816.10		$821.20		$572.10		$583.50		$244.00		$237.70

Receivables_Tables

Receivables (Tables)	3 Months Ended
	Mar. 31, 2015
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):
		2015		2014
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)		$118.00		$75.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	68		27.6
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		March 31, 2015		December 31, 2014
	Customer accounts receivable		$144.80		$134.80
	Unbilled utility revenues	52.5		69.7
	Other receivables	0.2		0.1
	Receivables sold to third party	197.5		204.6
	Less: cash proceeds (a)	74		22
	Deferred proceeds	123.5		182.6
	Less: allowance for doubtful accounts	5.8		5.4
	Fair value of deferred proceeds		$117.70		$177.20
	Outstanding receivables past due		$21.70		$19.90
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):
		2015		2014
	Collections reinvested in receivables		$505.90		$541.40
	Credit losses, net of recoveries	1		2.5
IPL [Member]
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three months ended March 31 were as follows (in millions):
		2015		2014
	Maximum outstanding aggregate cash proceeds (based on daily outstanding balances)		$118.00		$75.00
	Average outstanding aggregate cash proceeds (based on daily outstanding balances)	68		27.6
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
		March 31, 2015		December 31, 2014
	Customer accounts receivable		$144.80		$134.80
	Unbilled utility revenues	52.5		69.7
	Other receivables	0.2		0.1
	Receivables sold to third party	197.5		204.6
	Less: cash proceeds (a)	74		22
	Deferred proceeds	123.5		182.6
	Less: allowance for doubtful accounts	5.8		5.4
	Fair value of deferred proceeds		$117.70		$177.20
	Outstanding receivables past due		$21.70		$19.90
	(a)	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions):
		2015		2014
	Collections reinvested in receivables		$505.90		$541.40
	Credit losses, net of recoveries	1		2.5

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Schedule of Investments [Line Items]
Unconsolidated Equity Investments	Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
		Alliant Energy						WPL
		2015			2014			2015			2014
	ATC		($7.8	)		($11.2	)		($7.8	)		($11.2	)
	Other	1.3			(0.2		)	—			(0.2		)
			($6.5	)		($11.4	)		($7.8	)		($11.4	)
WPL [Member]
Schedule of Investments [Line Items]
Unconsolidated Equity Investments	Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
		Alliant Energy						WPL
		2015			2014			2015			2014
	ATC		($7.8	)		($11.2	)		($7.8	)		($11.2	)
	Other	1.3			(0.2		)	—			(0.2		)
			($6.5	)		($11.4	)		($7.8	)		($11.4	)

Common_Equity_Tables

Common Equity (Tables)	3 Months Ended
	Mar. 31, 2015
Stockholders' Equity Note [Abstract]
Common Share Activity	A summary of Alliant Energy’s common stock activity was as follows:
	Shares outstanding, January 1, 2015	110,935,680
	At-the-market offering program	1,996,450
	Shareowner Direct Plan	11,193
	Equity-based compensation plans (Note 9(b))	56,378
	Other	(22,463	)
	Shares outstanding, March 31, 2015	112,977,238

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%
IPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%
WPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions):
		Alliant Energy		Parent
	March 31, 2015	(Consolidated)		Company	IPL		WPL
	Commercial paper:
	Amount outstanding	$41.50		$41.50	$—		$—
	Weighted average remaining maturity	1 day		1 day	N/A		N/A
	Weighted average interest rates	0.50%		0.50%	N/A		N/A
	Available credit facility capacity	$958.50		$258.50	$300.00		$400.00
		Alliant Energy						IPL						WPL
	Three Months Ended March 31	2015			2014			2015			2014			2015		2014
	Maximum amount outstanding		$151.30			$316.20			$1.40			$10.00			$—		$204.70
	(based on daily outstanding balances)
	Average amount outstanding		$127.90			$275.60			$—			$0.30			$—		$173.00
	(based on daily outstanding balances)
	Weighted average interest rates	0.4		%	0.1		%	0.4		%	0.2		%	N/A		0.1		%

Income_Taxes_Tables

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2015
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
Production Tax Credits (Net Of State Tax Impacts)	For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
Summary Of Tax Credit Carryforwards	At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
Production Tax Credits (Net Of State Tax Impacts)	For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
Summary Of Tax Credit Carryforwards	At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
		Alliant Energy						IPL					WPL
	Three Months Ended March 31	2015			2014			2015			2014		2015		2014
	Statutory federal income tax rate	35	%		35	%		35	%		35	%	35	%	35	%
	IPL’s tax benefit riders	(9.9	)		(11.9	)		(25.2	)		(31.2	)	—		—
	Production tax credits	(6.2	)		(6.7	)		(7.3	)		(8.3	)	(6.0	)	(6.4	)
	Effect of rate-making on property-related differences	(6.1	)		(5.3	)		(14.6	)		(12.4	)	(0.6	)	(1.0	)
	Other items, net	4.3			4.6			4.4			4.7		4.6		4.8
	Overall income tax rate	17.1	%		15.7	%		(7.7	%)		(12.2	%)	33	%	32.4	%
Production Tax Credits (Net Of State Tax Impacts)	For the three months ended March 31, details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
		End of Production		Nameplate
		Tax Credit Generation		Capacity in MW			2015				2014
	Cedar Ridge (WPL)	Dec-18		68				$1.20				$1.20
	Bent Tree - Phase I (WPL)	Feb-21		201			3.9				4.2
	Subtotal (WPL)						5.1				5.4
	Whispering Willow - East (IPL)	Dec-19		200			4.3				4.6
								$9.40				$10.00
Summary Of Tax Credit Carryforwards	At March 31, 2015, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
	Alliant Energy	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$894				$306			2029
	State net operating losses	853				44				2018
	Federal tax credits	214				210				2022
							$560
	IPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$424				$145			2029
	State net operating losses	260				13				2018
	Federal tax credits	73				72				2022
							$230
	WPL	Tax Carryforwards				Deferred				Earliest
						Tax Assets				Expiration Date
	Federal net operating losses		$355				$122			2029
	State net operating losses	166				8				2018
	Federal tax credits	82				80				2022
							$210

Benefit_Plans_Tables

Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
Employees Participate In Defined Contribution Retirement Plans	For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5
Schedule Of Equity-based Compensation Plans Activity	Information related to fair values of nonvested performance shares and units at March 31, 2015, by year of grant, was as follows:
		Performance Shares												Performance Units
		2015 Grant				2014 Grant				2013 Grant				2015 Grant			2014 Grant			2013 Grant
	Nonvested awards	45,403				49,719				49,093				17,744			19,440			21,380
	Alliant Energy common stock closing price on March 31, 2015		$63.00				$63.00				$63.00
	Alliant Energy common stock closing price on grant date														$65.09			$53.77			$47.58
	Estimated payout percentage based on performance criteria	100		%		128		%		178		%		100		%	128		%	178		%
	Fair values of each nonvested award		$63.00				$80.64				$112.14				$65.09			$68.83			$84.69
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance shares activity was as follows:
		2015 (a)			2014 (a)
	Nonvested shares, January 1	144,424			139,940
	Granted	45,403			51,221
	Vested	(45,612	)		(45,235	)
	Nonvested shares, March 31	144,215			145,926
	(a)	Share amounts represent the target number of performance shares.
	During the three months ended March 31, certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:
		2015				2014
		2012 Grant				2011 Grant
	Performance shares vested	45,612				45,235
	Percentage of target number of performance shares	167.5		%		147.5		%
	Aggregate payout value (in millions)		$5.10				$3.40
	Payout - cash (in millions)		$3.20				$2.90
	Payout - common stock shares issued	10,975				4,810
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance units activity was as follows:
		2015 (a)			2014 (a)
	Nonvested units, January 1	63,665			65,912
	Granted	17,837			20,422
	Vested	(22,845	)		(20,751	)
	Forfeited	(93	)		(311	)
	Nonvested units, March 31	58,564			65,272
	(a)	Unit amounts represent the target number of performance units.
	During the three months ended March 31, certain performance units vested, resulting in cash payouts as follows:
		2015				2014
		2012 Grant				2011 Grant
	Performance units vested	22,845				20,751
	Percentage of target number of performance units	167.5		%		147.5		%
	Payout value (in millions)		$1.60				$1.20
Performance Contingent Restricted Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance contingent restricted stock activity was as follows:
		2015							2014
		Shares			Weighted				Shares			Weighted
					Average							Average
					Fair Value							Fair Value
	Nonvested shares, January 1	98,812				$50.69			158,922				$42.71
	Granted	45,403			65.09				51,221			53.77
	Vested (a)	(49,093	)		47.58				(90,847	)		40.91
	Forfeited	—			—				(18,982	)		38.75
	Nonvested shares, March 31	95,122			59.17				100,314			50.74
	(a)	In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
Performance Contingent Cash Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance contingent cash awards activity was as follows:
		2015			2014
	Nonvested awards, January 1	78,930			96,977
	Granted	41,105			42,446
	Vested (a)	(37,332	)		(55,517	)
	Forfeited	(469	)		(3,406	)
	Nonvested awards, March 31	82,234			80,500
	(a)	In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.
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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
Employees Participate In Defined Contribution Retirement Plans	For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5
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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 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 their 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 OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.
		Defined Benefit Pension Plans								OPEB Plans
	Alliant Energy	2015				2014				2015				2014
	Service cost		$4.00				$3.30				$1.40				$1.30
	Interest cost	13.4				13.5				2.2				2.4
	Expected return on plan assets	(18.7		)		(18.7		)		(2.1		)		(2.1		)
	Amortization of prior service credit	(0.1		)		—				(2.8		)		(3.0		)
	Amortization of actuarial loss	8.8				4.8				1.2				0.6
	Additional benefit costs	0.2				—				—				—
			$7.60				$2.90				($0.1	)			($0.8	)
		Defined Benefit Pension Plans								OPEB Plans
	IPL	2015				2014				2015				2014
	Service cost		$2.20				$1.80				$0.60				$0.60
	Interest cost	6.2				6.3				0.9				1
	Expected return on plan assets	(8.9		)		(9.0		)		(1.4		)		(1.5		)
	Amortization of prior service credit	—				—				(1.5		)		(1.6		)
	Amortization of actuarial loss	3.8				2				0.6				0.3
			$3.30				$1.10				($0.8	)			($1.2	)
		Defined Benefit Pension Plans								OPEB Plans
	WPL	2015				2014				2015				2014
	Service cost		$1.40				$1.20				$0.60				$0.50
	Interest cost	5.6				5.7				0.9				1
	Expected return on plan assets	(8.1		)		(8.1		)		(0.4		)		(0.3		)
	Amortization of prior service cost (credit)	0.1				0.1				(0.9		)		(1.0		)
	Amortization of actuarial loss	4.2				2.3				0.6				0.3
	Additional benefit costs	0.2				—				—				—
			$3.40				$1.20				$0.80				$0.50
Employees Participate In Defined Contribution Retirement Plans	For the three months ended March 31, costs related to the 401(k) savings plans, which are partially based on the participants’ contributions, were as follows (in millions):
		Alliant Energy								IPL (a)							WPL (a)
		2015				2014				2015				2014			2015			2014
	401(k) costs		$6.70				$5.90				$3.40				$3.10			$2.90			$2.60
	(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 (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
		Alliant Energy								IPL							WPL
		2015				2014				2015				2014			2015			2014
	Compensation expense		$3.20				$3.10				$1.70				$1.70			$1.40			$1.30
	Income tax benefits	1.3				1.3				0.7				0.7			0.6			0.5

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2015
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
Asset Retirement Obligations Expected To Be Recognized [Table Text Block]	Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
Asset Retirement Obligations Expected To Be Recognized [Table Text Block]	Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
		Alliant Energy						IPL						WPL
		2015			2014			2015			2014			2015		2014
	Balance, January 1		$114.00			$109.70			$51.80			$47.90			$52.40		$52.40
	Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
	Liabilities incurred	—			16.5			—			16.3			—		0.2
	Accretion expense	1			1			0.4			0.5			0.4		0.4
	Balance, March 31		$112.80			$126.70			$50.00			$64.40			$52.80		$52.80
Asset Retirement Obligations Expected To Be Recognized [Table Text Block]	Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):
		Alliant Energy		IPL	WPL
	Estimated ARO increase not to exceed	$85		$75	$10

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Statement [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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
Fair Value Measurements	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
	Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
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 March 31	2015			2014			2015			2014
	Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
	Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
	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 March 31		($16.5	)		$31.00			$—			$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended March 31	2015			2014			2015			2014
	Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
	Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
	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 March 31		($10.7	)		$3.10			$—			$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended March 31	2015			2014
	Beginning balance, January 1		($1.5	)		($10.2	)
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
	Settlements	(1.0		)	(7.9		)
	Ending balance, March 31		($8.1	)		$16.10
	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 March 31		($5.8	)		$27.90
	(a)	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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
		Alliant Energy						IPL						WPL
		Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
	March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
	31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3
IPL [Member]
Statement [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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
Fair Value Measurements	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
	Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
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 March 31	2015			2014			2015			2014
	Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
	Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
	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 March 31		($16.5	)		$31.00			$—			$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended March 31	2015			2014			2015			2014
	Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
	Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
	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 March 31		($10.7	)		$3.10			$—			$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended March 31	2015			2014
	Beginning balance, January 1		($1.5	)		($10.2	)
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
	Settlements	(1.0		)	(7.9		)
	Ending balance, March 31		($8.1	)		$16.10
	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 March 31		($5.8	)		$27.90
	(a)	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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
		Alliant Energy						IPL						WPL
		Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
	March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
	31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3
WPL [Member]
Statement [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
	March 31, 2015	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$16.90			$16.90			$6.50			$6.50			$10.40			$10.40
	Deferred proceeds (sales of receivables) (Note 4(a))	117.7			117.7			117.7			117.7			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,490.40			1,768.80			2,092.90			1,574.00			1,938.90
	Cumulative preferred stock	200			203.7			200			203.7			—			—
	Derivative liabilities (Note 12)	42.7			42.7			20			20			22.7			22.7
		Alliant Energy						IPL						WPL
	December 31, 2014	Carrying			Fair			Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value			Amount			Value
	Assets:
	Derivative assets (Note 12)		$38.60			$38.60			$28.00			$28.00			$10.60			$10.60
	Deferred proceeds (sales of receivables) (Note 4(a))	177.2			177.2			177.2			177.2			—			—
	Capitalization and liabilities:
	Long-term debt (including current maturities)	3,789.70			4,418.20			1,768.70			2,053.00			1,573.90			1,908.90
	Cumulative preferred stock	200			200.2			200			200.2			—			—
	Derivative liabilities (Note 12)	37.6			37.6			19.5			19.5			18.1			18.1
Fair Value Measurements	Items subject to fair value measurement disclosure requirements were as follows (in millions):
	Alliant Energy	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$16.90			$—			$2.20			$14.70			$38.60			$—		$2.60		$36.00
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	4,490.40			—			4,487.40			3			4,418.20			—		4,414.90		3.3
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	42.7			—			14.9			27.8			37.6			—		19.5		18.1
	IPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$6.50			$—			$1.70			$4.80			$28.00			$—		$2.40		$25.60
	Deferred proceeds	117.7			—			—			117.7			177.2			—		—		177.2
	Capitalization and liabilities:
	Long-term debt (including current maturities)	2,092.90			—			2,092.90			—			2,053.00			—		2,053.00		—
	Cumulative preferred stock	203.7			203.7			—			—			200.2			200.2		—		—
	Derivatives - commodity contracts	20			—			10.2			9.8			19.5			—		13.3		6.2
	WPL	March 31, 2015												December 31, 2014
		Fair			Level			Level			Level			Fair			Level		Level		Level
		Value			1			2			3			Value			1		2		3
	Assets:
	Derivatives - commodity contracts		$10.40			$—			$0.50			$9.90			$10.60			$—		$0.20		$10.40
	Capitalization and liabilities:
	Long-term debt (including current maturities)	1,938.90			—			1,938.90			—			1,908.90			—		1,908.90		—
	Derivatives - commodity contracts	22.7			—			4.7			18			18.1			—		6.2		11.9
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 March 31	2015			2014			2015			2014
	Beginning balance, January 1		$17.90			$4.40			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(18.1		)	38.4			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(12.0		)	(18.9		)	(59.5		)	(32.7		)
	Ending balance, March 31		($13.1	)		$23.90			$117.70			$170.80
	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 March 31		($16.5	)		$31.00			$—			$—
	IPL	Commodity Contract Derivative
		Assets and (Liabilities), net						Deferred Proceeds
	Three Months Ended March 31	2015			2014			2015			2014
	Beginning balance, January 1		$19.40			$14.60			$177.20			$203.50
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(12.5		)	4.2			—			—
	Sales	(0.9		)	—			—			—
	Settlements (a)	(11.0		)	(11.0		)	(59.5		)	(32.7		)
	Ending balance, March 31		($5.0	)		$7.80			$117.70			$170.80
	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 March 31		($10.7	)		$3.10			$—			$—
	WPL	Commodity Contract Derivative
		Assets and (Liabilities), net
	Three Months Ended March 31	2015			2014
	Beginning balance, January 1		($1.5	)		($10.2	)
	Total net gains (losses) (realized/unrealized) included in changes in net assets	(5.6		)	34.2
	Settlements	(1.0		)	(7.9		)
	Ending balance, March 31		($8.1	)		$16.10
	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 March 31		($5.8	)		$27.90
	(a)	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.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
		Alliant Energy						IPL						WPL
		Excluding FTRs			FTRs			Excluding FTRs			FTRs			Excluding FTRs			FTRs
	March 31, 2015		($17.2	)		$4.10			($8.5	)		$3.50			($8.7	)		$0.60
	31-Dec-14	(7.0		)	24.9			(3.2		)	22.6			(3.8		)	2.3

Derivative_Instruments_Tables

Derivative Instruments (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
Gains And Losses From Derivative Instruments	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
Credit Risk-related Contingent Features	The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
Balance Sheet Offsetting	The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
Gains And Losses From Derivative Instruments	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
Credit Risk-related Contingent Features	The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
Balance Sheet Offsetting	The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 2015, gross 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):
		2015			2016			2017		2018		Total
	Alliant Energy
	Electricity (MWhs)	3,530			2,870			1,314		1,314		9,028
	FTRs (MWhs)	3,478			—			—		—		3,478
	Natural gas (Dths)	42,989			27,423			7,126		—		77,538
	Coal (tons)	1,118			2,044			1,073		1,113		5,348
	IPL
	Electricity (MWhs)	1,612			439			—		—		2,051
	FTRs (MWhs)	2,041			—			—		—		2,041
	Natural gas (Dths)	26,967			13,176			2,758		—		42,901
	Coal (tons)	56			830			274		387		1,547
	WPL
	Electricity (MWhs)	1,918			2,431			1,314		1,314		6,977
	FTRs (MWhs)	1,437			—			—		—		1,437
	Natural gas (Dths)	16,022			14,247			4,368		—		34,637
	Coal (tons)	1,062			1,214			799		726		3,801
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 liabilities” on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Commodity contracts	March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Current derivative assets		$9.10				$30.50			$5.60			$27.40		$3.50			$3.10
	Non-current derivative assets	7.8				8.1			0.9			0.6		6.9			7.5
	Current derivative liabilities	24.4				28.1			13.8			16.4		10.6			11.7
	Non-current derivative liabilities	18.3				9.5			6.2			3.1		12.1			6.4
Gains And Losses From Derivative Instruments	Changes in unrealized gains (losses) from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
	Three Months Ended March 31	2015				2014			2015			2014		2015			2014
	Regulatory assets		($20.9	)			$10.10			($11.7	)		$5.50		($9.2	)		$4.60
	Regulatory liabilities	2.2				48.1			(1.4		)	12.1		3.6			36
Credit Risk-related Contingent Features	The aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position, as well as amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered, were as follows (in millions):
		Alliant Energy							IPL					WPL
		March 31,				December 31,			March 31,			December 31,		March 31,			December 31,
		2015				2014			2015			2014		2015			2014
	Aggregate fair value		$42.70				$37.60			$20.00			$19.50		$22.70			$18.10
	Credit support to be posted if triggered	42.2				37.4			20			19.5		22.2			17.9
Balance Sheet Offsetting	The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):
		Alliant Energy							IPL					WPL
		Gross							Gross					Gross
		(as reported)				Net			(as reported)			Net		(as reported)			Net
	March 31, 2015
	Derivative assets		$16.90				$10.30			$6.50			$5.10		$10.40			$5.20
	Derivative liabilities	42.7				36.1			20			18.6		22.7			17.5
	31-Dec-14
	Derivative assets	38.6				33			28			24.7		10.6			8.3
	Derivative liabilities	37.6				32			19.5			16.2		18.1			15.8

Commitments_And_Contingencies_

Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2
IPL [Member]
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2
WPL [Member]
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At March 31, 2015, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
		Alliant Energy			IPL				WPL
	Purchased power (a):
	DAEC (IPL)		$1,510			$1,510				$—
	Other	220			1				219
		1,730			1,511				219
	Natural gas	228			120				108
	Coal (b)	264			113				151
	SO2 emission allowances	22			22				—
	Other (c)	39			29				10
			$2,283			$1,795				$488
	(a)	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
	(b)	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 March 31, 2015 regarding expected future usage, which is subject to change.
	(c)	Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 2015, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions):
		Alliant Energy					IPL					WPL
	Range of estimated future costs		$14	-	$34			$13		-	$31		$1	-	$3
	Current and non-current environmental liabilities	16					14					2

Segments_Of_Business_Tables

Segments Of Business (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015
	Operating revenues		$671.30		$198.40		$16.40		$886.10		$11.30		$897.40
	Operating income	104.7		36.3		5.3		146.3		6.6		152.9
	Net income attributable to Alliant Energy common shareowners							92.4		4.2		96.6
	Three Months Ended March 31, 2014
	Operating revenues		$675.80		$240.70		$22.80		$939.30		$13.50		$952.80
	Operating income	94.3		43		7.9		145.2		9		154.2
	Net income attributable to Alliant Energy common shareowners							98.2		9.8		108
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 March 31, 2015
	Operating revenues		$362.60		$111.20		$15.20		$489.00
	Operating income	40.3		20.6		4.6		65.5
	Earnings available for common stock							47.8
	Three Months Ended March 31, 2014
	Operating revenues		$374.20		$135.70		$19.00		$528.90
	Operating income	26.5		23.3		7.7		57.5
	Earnings available for common stock							43.4
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 March 31, 2015
	Operating revenues		$308.70		$87.20		$1.20		$397.10
	Operating income	64.4		15.7		0.7		80.8
	Earnings available for common stock							44.6
	Three Months Ended March 31, 2014
	Operating revenues		$301.60		$105.00		$3.80		$410.40
	Operating income	67.8		19.7		0.2		87.7
	Earnings available for common stock							54.8

Related_Parties_Tables

Related Parties (Tables)	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):
		2015			2014
	ATC billings to WPL		$25			$24
	WPL billings to ATC	2			3
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions):
		IPL						WPL
		2015			2014			2015		2014
	Corporate Services billings		$36			$33			$28		$28
	Sales credited	4			2			6		(1		)
	Purchases billed	79			99			14		30
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions):
		IPL			WPL
		March 31, 2015		December 31, 2014	March 31, 2015		December 31, 2014
	Net payables to Corporate Services	$85		$84	$52		$58
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions):
		2015			2014
	ATC billings to WPL		$25			$24
	WPL billings to ATC	2			3

Recovered_Sheet1

Assets And Liabilities Held for Sale (Tables)	3 Months Ended
	Mar. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets And Liabilities Held For Sale on Balance Sheets	Alliant Energy’s and IPL’s balance sheets included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
		March 31, 2015		31-Dec-14
	Assets held for sale:
	Current assets		$2.30		$1.10
	Property, plant and equipment, net	11		11
	Other assets	6.4		7
	Total assets held for sale	19.7		19.1
	Liabilities held for sale:
	Current liabilities	0.2		1
	Other liabilities	6.8		7.1
	Total liabilities held for sale	7		8.1
	Net assets held for sale		$12.70		$11.00
IPL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets And Liabilities Held For Sale on Balance Sheets	Alliant Energy’s and IPL’s balance sheets included assets held for sale recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions):
		March 31, 2015		31-Dec-14
	Assets held for sale:
	Current assets		$2.30		$1.10
	Property, plant and equipment, net	11		11
	Other assets	6.4		7
	Total assets held for sale	19.7		19.1
	Liabilities held for sale:
	Current liabilities	0.2		1
	Other liabilities	6.8		7.1
	Total liabilities held for sale	7		8.1
	Net assets held for sale		$12.70		$11.00

Summary_Of_Significant_Account2

Summary Of Significant Accounting Policies (Narrative) (Details) (Minimum [Member])	Mar. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs percentage, on total long-term debt	1.00%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs percentage, on total long-term debt	1.00%
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs percentage, on total long-term debt	1.00%

Regulatory_Matters_Narrative_D

Regulatory Matters (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Alliant Energy and IPL [Member] | Tax benefit riders [Member]
Regulatory Matters [Line Items]
Decrease in regulatory liabilities	$21
WPL [Member]
Regulatory Matters [Line Items]
Decrease in regulatory liabilities	5.1	26.1
2014 Test Year Retail Electric Fuel Related Request [Member] | WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs			2.00%
2014 Test Year Retail Electric Fuel Related Request [Member] | Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Under-collection of retail fuel-related costs			33
Fuel-related costs	$28

Regulatory_Matters_Regulatory_

Regulatory Matters (Regulatory Assets) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Regulatory Assets [Line Items]
Regulatory assets	$1,790.30	$1,783.70
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	968.2	955.3
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	562.9	570.2
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	75.6	73.7
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	49.6	46.9
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	32.1	31.1
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.9	27.4
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	75	79.1
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,363.70	1,357.90
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	940.5	928
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	284.8	287.9
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	42.5	41.4
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.4	28
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	0.6	0.4
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.9	27.4
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	44.8
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	426.6	425.8
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	27.7	27.3
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	278.1	282.3
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	33.1	32.3
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	23.2	18.9
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	31.5	30.7
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$33	$34.30

Regulatory_Matters_Regulatory_1

Regulatory Matters (Regulatory Liabilities) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]
Regulatory liabilities	$816.10	$821.20
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	423.2	421.7
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	222	243
Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62.2	64.3
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26.5	15.4
IPL's electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23.2	19.4
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	59	57.4
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	572.1	583.5
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	279.5	279.1
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	222	243
IPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1.6	0
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22.8	15.1
IPL [Member] | IPL's electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23.2	19.4
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23	26.9
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	244	237.7
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	143.7	142.6
WPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	60.6	64.3
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.7	0.3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$36	$30.50

Regulatory_Matters_Tax_Benefit

Regulatory Matters (Tax Benefit Riders) (Details) (Alliant Energy and IPL [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Electric tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	$18
Gas tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	3
Tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Decrease in regulatory liabilities	$21

Regulatory_Matters_Customer_Bi

Regulatory Matters (Customer Billing Credits) (Details) (IPL [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
IPL [Member]
Regulatory Liabilities [Line Items]
Customer billing credits	$6

Property_Plant_and_Equipment_N

Property, Plant and Equipment (Narrative) (Details) (USD $)	3 Months Ended		1 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Apr. 30, 2015
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$6.80	$9.10
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	5.3	6
Edgewater Unit 5 [Member] | Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress	110
Allowance for funds used during construction	4
Marshalltown [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts)	650
Marshalltown [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress	248
Allowance for funds used during construction	7
Customer Billing And Information System [Member]
Property, Plant and Equipment [Line Items]
Capitalized expenditures	71
Capitalized interest	2
Subsequent Event [Member] | Gas distribution assets [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Expected proceeds from asset sales			11
Expected receipt of promissory note			$2

Receivables_Narrative_Details

Receivables (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2015		Dec. 31, 2014
Receivables [Line Items]
Deferred proceeds		$117.70		$177.20
IPL [Member]
Receivables [Line Items]
Receivables sold to third party		197.5
Deferred proceeds		117.7		177.2
Whiting Petroleum Corporation [Member]
Receivables [Line Items]
Final payment of certain future tax benefits expected to be realized	26
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Receivables sold to third party		197.5		204.6
Cash proceeds of receivables sold		74	[1]	22	[1]
Deferred proceeds		$117.70		$177.20
[1]	Changes in cash proceeds are presented in bSales of accounts receivableb in operating activities in Alliant Energybs and IPLbs cash flows statements.

Receivables_Maximum_And_Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) (IPL [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$68	$27.60
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$118	$75

Receivables_Receivables_Sold_U

Receivables (Receivables Sold Under The Agreement) (Details) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Millions, unless otherwise specified
Receivables [Line Items]
Fair value of deferred proceeds	$117.70		$177.20
IPL [Member]
Receivables [Line Items]
Receivables sold to third party	197.5
Fair value of deferred proceeds	117.7		177.2
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	144.8		134.8
Unbilled utility revenues	52.5		69.7
Other receivables	0.2		0.1
Receivables sold to third party	197.5		204.6
Less: cash proceeds	74	[1]	22	[1]
Deferred proceeds	123.5		182.6
Less: allowance for doubtful accounts	5.8		5.4
Fair value of deferred proceeds	117.7		177.2
Outstanding receivables past due	$21.70		$19.90
[1]	Changes in cash proceeds are presented in bSales of accounts receivableb in operating activities in Alliant Energybs and IPLbs cash flows statements.

Receivables_Additional_Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
IPL [Member]
Receivables [Line Items]
Collections reinvested in receivables	$505.90	$541.40
Credit losses, net of recoveries	$1	$2.50

Investments_Unconsolidated_Equ

Investments (Unconsolidated Equity Investments) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	($6.50)	($11.40)
WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	-7.8	-11.4
ATC [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	-7.8	-11.2
ATC [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	-7.8	-11.2
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	1.3	-0.2
Other [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$0	($0.20)

Common_Equity_Narrative_Detail

Common Equity (Narrative) (Details) (USD $)	3 Months Ended		1 Months Ended	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 30, 2015	Dec. 31, 2015
Common Equity [Line Items]
Proceeds from issuance of common stock, net	$122,100,000	$0
Other comprehensive income	0	0
IPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	518,000,000
Restricted net assets of subsidiaries	1,300,000,000
Common stock dividends to parent	35,000,000
Other comprehensive income	0	0
WPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	95,000,000
Restricted net assets of subsidiaries	1,600,000,000
Common stock dividends to parent	31,800,000
Other comprehensive income	0	0
At The Market Offering Program [Member]
Common Equity [Line Items]
New shares of common stock issued, At-the-market offering program (in shares)	1,996,450
Proceeds from issuance of common stock, net	121,000,000
Fees and commissions from issuance of common stock	2,000,000
At The Market Offering Program [Member] | Subsequent Event [Member]
Common Equity [Line Items]
Maximum aggregate gross sales price of common stock that can be offered and sold				150,000,000
New shares of common stock issued, At-the-market offering program (in shares)			190,167
Proceeds from issuance of common stock, net			$12,000,000

Common_Equity_Common_Share_Act

Common Equity (Common Share Activity) (Details)	3 Months Ended
	Mar. 31, 2015
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2015 (in shares)	110,935,680
New shares of stock issued, Shareowner Direct Plan (in shares)	11,193
Equity-based compensation plans (in shares)	56,378
Other (in shares)	-22,463
Shares outstanding, March 31, 2015 (in shares)	112,977,238
At The Market Offering Program [Member]
Common Stock Oustanding [Roll Forward]
New shares of common stock issued, At-the-market offering program (in shares)	1,996,450

Debt_Credit_Facilities_Details

Debt (Credit Facilities) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Commercial paper:
Amount outstanding	$41.50	$141.30
Weighted average remaining maturity (in days)	1 day
Weighted average interest rates	0.50%
Available credit facility capacity	958.5
Parent Company [Member]
Commercial paper:
Amount outstanding	41.5
Weighted average remaining maturity (in days)	1 day
Weighted average interest rates	0.50%
Available credit facility capacity	258.5
IPL [Member]
Commercial paper:
Amount outstanding	0
Available credit facility capacity	300
WPL [Member]
Commercial paper:
Amount outstanding	0
Available credit facility capacity	$400

Debt_Other_ShortTerm_Borrowing

Debt (Other Short-Term Borrowings) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$151.30	$316.20
Average amount outstanding (based on daily outstanding balances)	127.9	275.6
Weighted average interest rates	0.40%	0.10%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	1.4	10
Average amount outstanding (based on daily outstanding balances)	0	0.3
Weighted average interest rates	0.40%	0.20%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	0	204.7
Average amount outstanding (based on daily outstanding balances)	$0	$173
Weighted average interest rates		0.10%

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$45.80
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	29
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$14.40

Income_Taxes_Schedule_Of_Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	-9.90%	-11.90%
Production tax credits	-6.20%	-6.70%
Effect of rate-making on property-related differences	-6.10%	-5.30%
Other items, net	4.30%	4.60%
Overall income tax rate	17.10%	15.70%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
IPL's tax benefit riders	-25.20%	-31.20%
Production tax credits	-7.30%	-8.30%
Effect of rate-making on property-related differences	-14.60%	-12.40%
Other items, net	4.40%	4.70%
Overall income tax rate	-7.70%	-12.20%
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%
Production tax credits	-6.00%	-6.40%
Effect of rate-making on property-related differences	-0.60%	-1.00%
Other items, net	4.60%	4.80%
Overall income tax rate	33.00%	32.40%

Income_Taxes_Production_Tax_Cr

Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Production Tax Credits [Line Items]
Production tax credits	$9.40	$10
WPL [Member]
Production Tax Credits [Line Items]
Production tax credits	5.1	5.4
Cedar Ridge Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)	68
Production tax credits	1.2	1.2
Bent Tree - Phase I Wind Project [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)	201
Production tax credits	3.9	4.2
Whispering Willow - East Wind Project [Member] | IPL [Member]
Production Tax Credits [Line Items]
Nameplate Capacity (in megawatts)	200
Production tax credits	$4.30	$4.60

Income_Taxes_Summary_Of_Tax_Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$560
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	230
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	210
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	894
Net operating losses, deferred tax assets	306
Tax credits, carryforward amount	214
Tax credits, deferred tax assets	210
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	424
Net operating losses, deferred tax assets	145
Tax credits, carryforward amount	73
Tax credits, deferred tax assets	72
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	355
Net operating losses, deferred tax assets	122
Tax credits, carryforward amount	82
Tax credits, deferred tax assets	80
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	853
Net operating losses, deferred tax assets	44
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	260
Net operating losses, deferred tax assets	13
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	166
Net operating losses, deferred tax assets	$8

Benefit_Plans_Narrative_Detail

Benefit Plans (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	13.1
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Maximum [Member]
Defined Benefit Plan Disclosure [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
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$4	$3.30
Interest cost	13.4	13.5
Expected return on plan assets	-18.7	-18.7
Amortization of prior service cost (credit)	-0.1	0
Amortization of actuarial loss	8.8	4.8
Additional benefit costs	0.2	0
Total	7.6	2.9
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.4	1.3
Interest cost	2.2	2.4
Expected return on plan assets	-2.1	-2.1
Amortization of prior service cost (credit)	-2.8	-3
Amortization of actuarial loss	1.2	0.6
Additional benefit costs	0	0
Total	-0.1	-0.8
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.2	1.8
Interest cost	6.2	6.3
Expected return on plan assets	-8.9	-9
Amortization of prior service cost (credit)	0	0
Amortization of actuarial loss	3.8	2
Total	3.3	1.1
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.6
Interest cost	0.9	1
Expected return on plan assets	-1.4	-1.5
Amortization of prior service cost (credit)	-1.5	-1.6
Amortization of actuarial loss	0.6	0.3
Total	-0.8	-1.2
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.4	1.2
Interest cost	5.6	5.7
Expected return on plan assets	-8.1	-8.1
Amortization of prior service cost (credit)	0.1	0.1
Amortization of actuarial loss	4.2	2.3
Additional benefit costs	0.2	0
Total	3.4	1.2
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.5
Interest cost	0.9	1
Expected return on plan assets	-0.4	-0.3
Amortization of prior service cost (credit)	-0.9	-1
Amortization of actuarial loss	0.6	0.3
Additional benefit costs	0	0
Total	$0.80	$0.50

Benefit_Plans_Defined_Contribu

Benefit Plans (Defined Contribution Retirement Plans) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
401(k) costs	$6.70		$5.90
IPL [Member]
401(k) costs	3.4	[1]	3.1	[1]
WPL [Member]
401(k) costs	$2.90	[1]	$2.60	[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
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Compensation expense	$3.20	$3.10
Income tax benefits	1.3	1.3
IPL [Member]
Compensation expense	1.7	1.7
Income tax benefits	0.7	0.7
WPL [Member]
Compensation expense	1.4	1.3
Income tax benefits	$0.60	$0.50

Benefit_Plans_Summary_Of_Perfo

Benefit Plans (Summary Of Performance Shares Activity) (Details) (Performance Shares [Member], USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	144,424	[1]	139,940	[1]
Granted (in shares/awards)	45,403	[1]	51,221	[1]
Vested (in shares/awards)	-45,612	[1]	-45,235	[1]
Nonvested, March 31 (in shares/awards)	144,215	[1]	145,926	[1]
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	-45,612
Vested percentage of the target	167.50%
Aggregate payout value	5.1
Payout - cash	3.2
Payout - common stock shares issued (in shares)	10,975
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-45,235
Vested percentage of the target			147.50%
Aggregate payout value			3.4
Payout - cash			2.9
Payout - common stock shares issued (in shares)			4,810
[1]	Share amounts represent the target number of performance shares.

Benefit_Plans_Summary_Of_Perfo1

Benefit Plans (Summary Of Performance Unit Activity) (Details) (Performance Units [Member], USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	63,665	[1]	65,912	[1]
Granted (in shares/awards)	17,837	[1]	20,422	[1]
Vested (in shares/awards)	-22,845	[1]	-20,751	[1]
Forfeited (in shares/awards)	-93	[1]	-311	[1]
Nonvested, March 31 (in shares/awards)	58,564	[1]	65,272	[1]
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	-22,845
Vested percentage of the target	167.50%
Aggregate payout value	1.6
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-20,751
Vested percentage of the target			147.50%
Aggregate payout value			1.2
[1]	Unit amounts represent the target number of performance units.

Benefit_Plans_Fair_Values_Of_N

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014		Dec. 31, 2013
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	144,215	[1]	144,424	[1]	145,926	[1]	139,940	[1]
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	58,564	[2]	63,665	[2]	65,272	[2]	65,912	[2]
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	45,403
Alliant Energy common stock closing price on March 31, 2015 (in dollars per share)	$63
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$63
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	17,744
Alliant Energy common stock closing price on grant date (in dollars per share)	$65.09
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$65.09
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	49,719
Alliant Energy common stock closing price on March 31, 2015 (in dollars per share)	$63
Estimated payout percentage based on performance criteria	128.00%
Fair values of each nonvested award (in dollars per share)	$80.64
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	19,440
Alliant Energy common stock closing price on grant date (in dollars per share)	$53.77
Estimated payout percentage based on performance criteria	128.00%
Fair values of each nonvested award (in dollars per share)	$68.83
2013 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	49,093
Alliant Energy common stock closing price on March 31, 2015 (in dollars per share)	$63
Estimated payout percentage based on performance criteria	178.00%
Fair values of each nonvested award (in dollars per share)	$112.14
2013 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	21,380
Alliant Energy common stock closing price on grant date (in dollars per share)	$47.58
Estimated payout percentage based on performance criteria	178.00%
Fair values of each nonvested award (in dollars per share)	$84.69
[1]	Share amounts represent the target number of performance shares.
[2]	Unit amounts represent the target number of performance units.

Benefit_Plans_Summary_Of_Restr

Benefit Plans (Summary Of Restricted Stock Activity) (Details) (Performance Contingent Restricted Stock [Member], USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	98,812		158,922
Nonvested shares, January 1, weighted average fair value (in dollars per share)	$50.69		$42.71
Granted (in shares/awards)	45,403		51,221
Granted, weighted average fair value (in dollars per share)	$65.09		$53.77
Vested (in shares/awards)	-49,093	[1]	-90,847	[1]
Vested, weighted average fair value (in dollars per share)	$47.58	[1]	$40.91	[1]
Forfeited (in shares/awards)	0		-18,982
Forfeited, weighted average fair value (in dollars per share)	$0		$38.75
Nonvested, March 31 (in shares/awards)	95,122		100,314
Nonvested shares, March 31, weighted average fair value (in dollars per share)	$59.17		$50.74
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	-49,093	[1]
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-45,612	[1]
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-45,235	[1]
[1]	In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.

Benefit_Plans_Summary_Of_Perfo2

Benefit Plans (Summary Of Performance Contingent Cash Awards Activity) (Details) (Performance Contingent Cash Awards [Member], USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	78,930		96,977
Granted (in shares/awards)	41,105		42,446
Vested (in shares/awards)	-37,332	[1]	-55,517	[1]
Forfeited (in shares/awards)	-469		-3,406
Nonvested, March 31 (in shares/awards)	82,234		80,500
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	-37,332	[1]
Cash payout value	2.4	[1]
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-34,766	[1]
Cash payout value			1.9	[1]
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			-20,751	[1]
Cash payout value			1.1	[1]
[1]	In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.

Asset_Retirement_Obligations_R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$114	$109.70
Liabilities settled	-2.2	-0.5
Liabilities incurred	0	16.5
Accretion expense	1	1
Balance, March 31	112.8	126.7
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	51.8	47.9
Liabilities settled	-2.2	-0.3
Liabilities incurred	0	16.3
Accretion expense	0.4	0.5
Balance, March 31	50	64.4
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	52.4	52.4
Liabilities settled	0	-0.2
Liabilities incurred	0	0.2
Accretion expense	0.4	0.4
Balance, March 31	$52.80	$52.80

Asset_Retirement_Obligations_A

Asset Retirement Obligations (Asset Retirement Obligations Expected To Be Recognized) (Details) (Scenario, Forecast [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2015
Asset Retirement Obligations [Line Items]
Expected ARO increase not to exceed	$85
IPL [Member]
Asset Retirement Obligations [Line Items]
Expected ARO increase not to exceed	75
WPL [Member]
Asset Retirement Obligations [Line Items]
Expected ARO increase not to exceed	$10

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (IPL [Member])	3 Months Ended
	Mar. 31, 2015
IPL [Member]
Cumulative preferred stock rate	5.10%

Fair_Value_Measurements_Fair_V

Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Assets:
Derivative assets	$16.90	$38.60
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	4,490.40	4,418.20
Cumulative preferred stock	203.7	200.2
Derivative liabilities	42.7	37.6
IPL [Member]
Assets:
Derivative assets	6.5	28
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	2,092.90	2,053
Cumulative preferred stock	203.7	200.2
Derivative liabilities	20	19.5
WPL [Member]
Assets:
Derivative assets	10.4	10.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90	1,908.90
Derivative liabilities	22.7	18.1
Carrying Value [Member]
Assets:
Derivative assets	16.9	38.6
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	3,789.70	3,789.70
Cumulative preferred stock	200	200
Derivative liabilities	42.7	37.6
Carrying Value [Member] | IPL [Member]
Assets:
Derivative assets	6.5	28
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	1,768.80	1,768.70
Cumulative preferred stock	200	200
Derivative liabilities	20	19.5
Carrying Value [Member] | WPL [Member]
Assets:
Derivative assets	10.4	10.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,574	1,573.90
Derivative liabilities	22.7	18.1
Fair Value [Member]
Assets:
Derivative assets	16.9	38.6
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	4,490.40	4,418.20
Cumulative preferred stock	203.7	200.2
Derivative liabilities	42.7	37.6
Fair Value [Member] | IPL [Member]
Assets:
Derivative assets	6.5	28
Deferred proceeds (sales of receivables)	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	2,092.90	2,053
Cumulative preferred stock	203.7	200.2
Derivative liabilities	20	19.5
Fair Value [Member] | WPL [Member]
Assets:
Derivative assets	10.4	10.6
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90	1,908.90
Derivative liabilities	$22.70	$18.10

Fair_Value_Measurements_Fair_V1

Fair Value Measurements (Fair Value Measurements) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Assets:
Derivative assets	$10.30	$33
Deferred proceeds	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	4,490.40	4,418.20
Cumulative preferred stock	203.7	200.2
Derivative liabilities	36.1	32
IPL [Member]
Assets:
Derivative assets	5.1	24.7
Deferred proceeds	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	2,092.90	2,053
Cumulative preferred stock	203.7	200.2
Derivative liabilities	18.6	16.2
WPL [Member]
Assets:
Derivative assets	5.2	8.3
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90	1,908.90
Derivative liabilities	17.5	15.8
Commodity Contracts [Member]
Assets:
Derivative assets	16.9	38.6
Capitalization and liabilities:
Derivative liabilities	42.7	37.6
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivative assets	6.5	28
Capitalization and liabilities:
Derivative liabilities	20	19.5
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivative assets	10.4	10.6
Capitalization and liabilities:
Derivative liabilities	22.7	18.1
Level 1 [Member]
Assets:
Deferred proceeds	0	0
Capitalization and liabilities:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	203.7	200.2
Level 1 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Capitalization and liabilities:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock	203.7	200.2
Level 1 [Member] | WPL [Member]
Capitalization and liabilities:
Long-term debt (including current maturities)	0	0
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)	4,487.40	4,414.90
Cumulative preferred stock	0	0
Level 2 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Capitalization and liabilities:
Long-term debt (including current maturities)	2,092.90	2,053
Cumulative preferred stock	0	0
Level 2 [Member] | WPL [Member]
Capitalization and liabilities:
Long-term debt (including current maturities)	1,938.90	1,908.90
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivative assets	2.2	2.6
Capitalization and liabilities:
Derivative liabilities	14.9	19.5
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivative assets	1.7	2.4
Capitalization and liabilities:
Derivative liabilities	10.2	13.3
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivative assets	0.5	0.2
Capitalization and liabilities:
Derivative liabilities	4.7	6.2
Level 3 [Member]
Assets:
Deferred proceeds	117.7	177.2
Capitalization and liabilities:
Long-term debt (including current maturities)	3	3.3
Cumulative preferred stock	0	0
Level 3 [Member] | IPL [Member]
Assets:
Deferred proceeds	117.7	177.2
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
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivative assets	14.7	36
Capitalization and liabilities:
Derivative liabilities	27.8	18.1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivative assets	4.8	25.6
Capitalization and liabilities:
Derivative liabilities	9.8	6.2
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivative assets	9.9	10.4
Capitalization and liabilities:
Derivative liabilities	$18	$11.90

Fair_Value_Measurements_Fair_V2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$17.90		$4.40
Total net gains (losses) (realized/unrealized) included in changes in net assets	-18.1		38.4
Sales	-0.9		0
Settlements	-12	[1]	-18.9	[1]
Ending balance	-13.1		23.9
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 March 31	-16.5		31
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	19.4		14.6
Total net gains (losses) (realized/unrealized) included in changes in net assets	-12.5		4.2
Sales	-0.9		0
Settlements	-11	[1]	-11	[1]
Ending balance	-5		7.8
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 March 31	-10.7		3.1
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	-1.5		-10.2
Total net gains (losses) (realized/unrealized) included in changes in net assets	-5.6		34.2
Settlements	-1		-7.9
Ending balance	-8.1		16.1
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 March 31	-5.8		27.9
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	177.2		203.5
Total net gains (losses) (realized/unrealized) included in changes in net assets	0		0
Sales	0		0
Settlements	-59.5	[1]	-32.7	[1]
Ending balance	117.7		170.8
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 March 31	0		0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	177.2		203.5
Total net gains (losses) (realized/unrealized) included in changes in net assets	0		0
Sales	0		0
Settlements	-59.5	[1]	-32.7	[1]
Ending balance	117.7		170.8
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 March 31	$0		$0
[1]	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.

Fair_Value_Measurements_Fair_V3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) (Commodity Contracts [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	($13.10)	$17.90	$23.90	$4.40
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	-17.2	-7
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	4.1	24.9
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	-5	19.4	7.8	14.6
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	-8.5	-3.2
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	3.5	22.6
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	-8.1	-1.5	16.1	-10.2
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	-8.7	-3.8
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$0.60	$2.30

Derivative_Instruments_Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Mar. 31, 2015
	MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	9,028,000
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,051,000
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	6,977,000
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	3,478,000
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,041,000
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,437,000
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	77,538,000
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	42,901,000
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	34,637,000
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	5,348,000
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,547,000
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	3,801,000
2015 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	3,530,000
2015 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,612,000
2015 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,918,000
2015 [Member] | FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	3,478,000
2015 [Member] | FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,041,000
2015 [Member] | FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,437,000
2015 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	42,989,000
2015 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	26,967,000
2015 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	16,022,000
2015 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,118,000
2015 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	56,000
2015 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,062,000
2016 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,870,000
2016 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	439,000
2016 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,431,000
2016 [Member] | FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2016 [Member] | FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2016 [Member] | FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2016 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	27,423,000
2016 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	13,176,000
2016 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	14,247,000
2016 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,044,000
2016 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	830,000
2016 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,214,000
2017 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/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/Dths/Tons)	0
2017 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,314,000
2017 [Member] | FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2017 [Member] | FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2017 [Member] | FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	7,126,000
2017 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	2,758,000
2017 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	4,368,000
2017 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,073,000
2017 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	274,000
2017 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	799,000
2018 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/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/Dths/Tons)	0
2018 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,314,000
2018 [Member] | FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	0
2018 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	1,113,000
2018 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	387,000
2018 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/Tons)	726,000

Derivative_Instruments_Fair_Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) (Commodity Contracts [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]
Current derivative assets	$9.10	$30.50
Non-current derivative assets	7.8	8.1
Current derivative liabilities	24.4	28.1
Non-current derivative liabilities	18.3	9.5
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	5.6	27.4
Non-current derivative assets	0.9	0.6
Current derivative liabilities	13.8	16.4
Non-current derivative liabilities	6.2	3.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	3.5	3.1
Non-current derivative assets	6.9	7.5
Current derivative liabilities	10.6	11.7
Non-current derivative liabilities	$12.10	$6.40

Derivative_Instruments_Gains_A

Derivative Instruments (Gains And Losses From Derivative Instruments) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Regulatory Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	($20.90)	$10.10
Regulatory Assets [Member] | IPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	-11.7	5.5
Regulatory Assets [Member] | WPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	-9.2	4.6
Regulatory Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	2.2	48.1
Regulatory Liabilities [Member] | IPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	-1.4	12.1
Regulatory Liabilities [Member] | WPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from commodity derivative instruments	$3.60	$36

Derivative_Instruments_Credit_

Derivative Instruments (Credit Risk-related Contingent Features) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Derivative Instruments [Line Items]
Aggregate fair value	$42.70	$37.60
Credit support to be posted if triggered	42.2	37.4
IPL [Member]
Derivative Instruments [Line Items]
Aggregate fair value	20	19.5
Credit support to be posted if triggered	20	19.5
WPL [Member]
Derivative Instruments [Line Items]
Aggregate fair value	22.7	18.1
Credit support to be posted if triggered	$22.20	$17.90

Derivative_Instruments_Balance

Derivative Instruments (Balance Sheet Offsetting) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$16.90	$38.60
Derivative assets, Net	10.3	33
Derivative liabilities, Gross (as reported)	42.7	37.6
Derivative liabilities, Net	36.1	32
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	6.5	28
Derivative assets, Net	5.1	24.7
Derivative liabilities, Gross (as reported)	20	19.5
Derivative liabilities, Net	18.6	16.2
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	10.4	10.6
Derivative assets, Net	5.2	8.3
Derivative liabilities, Gross (as reported)	22.7	18.1
Derivative liabilities, Net	$17.50	$15.80

Commitments_And_Contingencies_1

Commitments And Contingencies (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Commitments and Contingencies [Line Items]
Minimum future commitments	$2,283
Performance guarantees outstanding	251
Present value abandonment obligation	35
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,795
Number of sites monitoring and remediating (in sites)	25
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	488
Number of sites monitoring and remediating (in sites)	5
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	26
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	2
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	24
Performance guarantees outstanding, 2015 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	128
Performance guarantees outstanding, 2016 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	48
Performance guarantees outstanding, 2017 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	75
Environmental Issue [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	$7
Minimum [Member]
Commitments and Contingencies [Line Items]
Warranty period	12 months
Maximum [Member]
Commitments and Contingencies [Line Items]
Warranty period	60 months

Commitments_And_Contingencies_2

Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Commitments and Contingencies [Line Items]
Minimum future commitments	$2,283
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,795
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	488
DAEC (IPL) [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,510	[1]
DAEC (IPL) [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,510	[1]
DAEC (IPL) [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	0	[1]
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	220	[1]
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1	[1]
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	219	[1]
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,730	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,511	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	219	[1]
Natural Gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	228
Natural Gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	120
Natural Gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	108
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	264	[2]
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	113	[2]
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	151	[2]
SO2 emission allowances [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	22
SO2 emission allowances [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	22
SO2 emission allowances [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	0
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	39	[3]
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	29	[3]
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$10	[3]
[1]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
[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 MarchB 31, 2015 regarding expected future usage, which is subject to change.
[3]	Includes individual commitments incurred during the normal course of business that exceeded $1 million at MarchB 31, 2015.

Commitments_And_Contingencies_3

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) (Manufactured Gas Plant Sites [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	$14
Maximum range of estimated future costs	34
Current and non-current environmental liabilities	16
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	13
Maximum range of estimated future costs	31
Current and non-current environmental liabilities	14
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	1
Maximum range of estimated future costs	3
Current and non-current environmental liabilities	$2

Segments_Of_Business_Schedule_

Segments Of Business (Schedule Of Segments Of Business) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$897.40	$952.80
Operating income (loss)	152.9	154.2
Net income (loss) attributable to common shareowners	96.6	108
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	489	528.9
Operating income (loss)	65.5	57.5
Net income (loss) attributable to common shareowners	47.8	43.4
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	397.1	410.4
Operating income (loss)	80.8	87.7
Net income (loss) attributable to common shareowners	44.6	54.8
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	671.3	675.8
Operating income (loss)	104.7	94.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	362.6	374.2
Operating income (loss)	40.3	26.5
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	308.7	301.6
Operating income (loss)	64.4	67.8
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	198.4	240.7
Operating income (loss)	36.3	43
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	111.2	135.7
Operating income (loss)	20.6	23.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	87.2	105
Operating income (loss)	15.7	19.7
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	16.4	22.8
Operating income (loss)	5.3	7.9
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	15.2	19
Operating income (loss)	4.6	7.7
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	1.2	3.8
Operating income (loss)	0.7	0.2
Utilities Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	886.1	939.3
Operating income (loss)	146.3	145.2
Net income (loss) attributable to common shareowners	92.4	98.2
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	11.3	13.5
Operating income (loss)	6.6	9
Net income (loss) attributable to common shareowners	$4.20	$9.80

Related_Parties_Narrative_Deta

Related Parties (Narrative) (Details) (WPL [Member], WPL Owed ATC [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
WPL [Member] | WPL Owed ATC [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	($7)	($8)

Related_Parties_Service_Agreem

Related Parties (Service Agreements) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$36	$33
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	28	28
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	4	2
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	6	-1
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	79	99
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$14	$30

Related_Parties_Net_Intercompa

Related Parties (Net Intercompany Payables) (Details) (Corporate Services Billings [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
IPL [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	($85)	($84)
WPL [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	($52)	($58)

Related_Parties_Amounts_Billed

Related Parties (Amounts Billed Between Parties) (Details) (WPL [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$25	$24
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$2	$3

Assets_And_Liabilities_Held_Fo1

Assets And Liabilities Held For Sale (Components Of Assets And Liabilities Held For Sale In Consolidated Balance Sheets) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Current assets	$2.30	$1.10
Property, plant and equipment, net	11	11
Other assets	6.4	7
Total assets held for sale	19.7	19.1
Current liabilities	0.2	1
Other liabilities	6.8	7.1
Total liabilities held for sale	7	8.1
Net assets held for sale	$12.70	$11