Alliant Energy (LNT) 10-Q 10 Aug 20 2020 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	6 Months Ended
	Jun. 30, 2020shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	0000352541
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	1-9894
Entity Tax Identification Number	39-1380265
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	LNT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	249,644,352
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
IPL [Member]
Entity Information [Line Items]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Incorporation, State or Country Code	IA
Entity Address, Address Line One	Alliant Energy Tower
Entity Address, City or Town	Cedar Rapids
Entity Address, State or Province	IA
Entity Address, Postal Zip Code	52401
City Area Code	319
Local Phone Number	786-4411
Entity File Number	1-4117
Entity Tax Identification Number	42-0331370
Title of 12(b) Security	5.100% Series D Cumulative Perpetual Preferred Stock, $0.01 Par Value
Trading Symbol	IPLDP
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Information [Line Items]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	0-337
Entity Tax Identification Number	39-0714890
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Electric utility	$ 675.2	$ 691.2	$ 1,405.5	$ 1,434.6
Gas utility	58.9	65.2	211.1	281
Other utility	10.1	10.9	21.7	22
Non-utility	18.9	22.9	40.5	39.8
Total revenues	763.1	790.2	1,678.8	1,777.4
Operating expenses:
Electric production fuel and purchased power	163.5	164.8	347.6	383.2
Electric transmission service	71.6	112.4	193.8	235.4
Cost of gas sold	20.9	20.4	105.9	142
Other operation and maintenance	159.8	172.3	322	353.5
Depreciation and amortization	152.1	142.9	298.4	279.8
Taxes other than income taxes	27.1	27.6	54.7	56.9
Total operating expenses	595	640.4	1,322.4	1,450.8
Operating income	168.1	149.8	356.4	326.6
Other (income) and deductions:
Interest expense	69.6	69.2	138.5	135.5
Equity income from unconsolidated investments, net	(17.4)	(12.7)	(30.8)	(23.6)
Allowance for funds used during construction	(15.2)	(18.3)	(38.2)	(43.7)
Other	2.5	3.3	4.4	7.3
Total other (income) and deductions	39.5	41.5	73.9	75.5
Income before income taxes	128.6	108.3	282.5	251.1
Income tax expense (benefit)	(8.3)	11.2	(27)	26.3
Net income	136.9	97.1	309.5	224.8
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	$ 134.4	$ 94.6	$ 304.4	$ 219.7
Weighted average number of common shares outstanding:
Basic (in shares)	249.6	237.5	247	237
Diluted (in shares)	249.8	238.1	247.2	237.3
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.54	$ 0.40	$ 1.23	$ 0.93
IPL [Member]
Revenues:
Electric utility	$ 388.4	$ 392.3	$ 813.2	$ 812.1
Gas utility	33.9	38.4	116.9	163
Other utility	9.6	10.5	20.7	21.2
Total revenues	431.9	441.2	950.8	996.3
Operating expenses:
Electric production fuel and purchased power	96	83.3	202.2	212.2
Electric transmission service	34	77.4	118.5	165.1
Cost of gas sold	12.4	10.8	56.6	74.1
Other operation and maintenance	97.5	97.4	184.1	205.4
Depreciation and amortization	88.7	82.6	174.6	159.7
Taxes other than income taxes	14.6	15.2	29.4	31.8
Total operating expenses	343.2	366.7	765.4	848.3
Operating income	88.7	74.5	185.4	148
Other (income) and deductions:
Interest expense	34.8	31.5	69.3	60.9
Allowance for funds used during construction	(5.6)	(7.9)	(15.4)	(23.7)
Other	1	1.5	1.9	3.4
Total other (income) and deductions	30.2	25.1	55.8	40.6
Income before income taxes	58.5	49.4	129.6	107.4
Income tax expense (benefit)	(3.8)	1.9	(17.9)	4
Net income	62.3	47.5	147.5	103.4
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	59.8	45	142.4	98.3
WPL [Member]
Revenues:
Electric utility	286.8	298.9	592.3	622.5
Gas utility	25	26.8	94.2	118
Other utility	0.5	0.4	1	0.8
Total revenues	312.3	326.1	687.5	741.3
Operating expenses:
Electric production fuel and purchased power	67.5	81.5	145.4	171
Electric transmission service	37.6	35	75.3	70.3
Cost of gas sold	8.5	9.6	49.3	67.9
Other operation and maintenance	53.2	62.4	107.4	125.9
Depreciation and amortization	62	59.1	121.1	117.7
Taxes other than income taxes	11.8	11.5	23.5	23.4
Total operating expenses	240.6	259.1	522	576.2
Operating income	71.7	67	165.5	165.1
Other (income) and deductions:
Interest expense	27.3	26.1	52.4	51.9
Allowance for funds used during construction	(9.5)	(10.4)	(22.7)	(20)
Other	0.8	1.6	1.3	3.2
Total other (income) and deductions	18.6	17.3	31	35.1
Income before income taxes	53.1	49.7	134.5	130
Income tax expense (benefit)	(4.5)	7.7	(12.7)	22.3
Net income	$ 57.6	$ 42	$ 147.2	$ 107.7

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 208.1	$ 16.3
Accounts receivable, less allowance for expected credit losses	386.5	402.1
Production fuel, at weighted average cost	78	77.7
Gas stored underground, at weighted average cost	36.8	49.1
Materials and supplies, at weighted average cost	107	100.5
Regulatory assets	94.5	86.4
Other	133.4	143.4
Total current assets	1,044.3	875.5
Property, plant and equipment, net	13,936.4	13,527.1
Investments:
ATC Holdings	326.1	320.1
Other	147.1	147.7
Total investments	473.2	467.8
Other assets:
Regulatory assets	1,748.5	1,758.3
Deferred charges and other	67.3	72
Total other assets	1,815.8	1,830.3
Total assets	17,269.7	16,700.7
Current liabilities:
Current maturities of long-term debt	7.4	657.2
Commercial paper	185.4	337.4
Accounts payable	429.9	422.3
Regulatory liabilities	211.4	212
Other	386.8	425.2
Total current liabilities	1,220.9	2,054.1
Long-term debt, net (excluding current portion)	6,572.4	5,533
Other liabilities:
Deferred tax liabilities	1,761.3	1,714
Regulatory liabilities	1,159.6	1,211.6
Pension and other benefit obligations	450.2	484
Other	357	298.9
Total other liabilities	3,728.1	3,708.5
Commitments and contingencies (Note 13)
Common equity:
Common stock	2.5	2.5
Additional paid-in capital	2,683.1	2,445.9
Retained earnings	2,873.5	2,765.4
Accumulated other comprehensive income (loss)	(0.6)	1.3
Shares in deferred compensation trust - 367,493 and 381,232 shares at a weighted average cost of $27.86 and $26.24 per share	(10.2)	(10)
Total common equity	5,548.3	5,205.1
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	5,748.3	5,405.1
Total liabilities and equity	17,269.7	16,700.7
IPL [Member]
Current assets:
Cash and cash equivalents	203.5	9.3
Accounts receivable, less allowance for expected credit losses	208.9	202.8
Production fuel, at weighted average cost	54.8	47.1
Gas stored underground, at weighted average cost	10.4	21.7
Materials and supplies, at weighted average cost	60.4	55
Regulatory assets	54	43.5
Other	32.5	30
Total current assets	624.5	409.4
Property, plant and equipment, net	7,666.3	7,480.7
Other assets:
Regulatory assets	1,350.9	1,355.8
Deferred charges and other	37.9	31.6
Total other assets	1,388.8	1,387.4
Total assets	9,679.6	9,277.5
Current liabilities:
Current maturities of long-term debt	0	200
Accounts payable	207.3	207
Regulatory liabilities	131.1	115.9
Other	293.8	307.6
Total current liabilities	632.2	830.5
Long-term debt, net (excluding current portion)	3,343.5	2,947.3
Other liabilities:
Deferred tax liabilities	1,012.7	1,008
Regulatory liabilities	586.8	598.8
Pension and other benefit obligations	160.1	167.7
Other	273.2	253.4
Total other liabilities	2,032.8	2,027.9
Commitments and contingencies (Note 13)
Common equity:
Common stock	33.4	33.4
Additional paid-in capital	2,522.8	2,347.8
Retained earnings	914.9	890.6
Total common equity	3,471.1	3,271.8
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,671.1	3,471.8
Total liabilities and equity	9,679.6	9,277.5
WPL [Member]
Current assets:
Cash and cash equivalents	3.2	4.4
Accounts receivable, less allowance for expected credit losses	166.9	190.9
Production fuel, at weighted average cost	23.1	30.6
Gas stored underground, at weighted average cost	26.4	27.4
Materials and supplies, at weighted average cost	44.3	43.1
Regulatory assets	40.5	42.9
Other	52.1	103.4
Total current assets	356.5	442.7
Property, plant and equipment, net	5,867.2	5,638.3
Other assets:
Regulatory assets	397.6	402.5
Deferred charges and other	27.1	23
Total other assets	424.7	425.5
Total assets	6,648.4	6,506.5
Current liabilities:
Current maturities of long-term debt	0	150
Commercial paper	37.9	168.2
Accounts payable	183	159.9
Accounts payable to associated companies	28.9	41.8
Regulatory liabilities	80.3	96.1
Other	79.5	74.3
Total current liabilities	409.6	690.3
Long-term debt, net (excluding current portion)	2,129.4	1,782.7
Other liabilities:
Deferred tax liabilities	667.4	626.2
Regulatory liabilities	572.8	612.8
Finance lease obligations - Sheboygan Falls Energy Facility	46.7	51.4
Pension and other benefit obligations	201.8	210.8
Other	168.9	168.7
Total other liabilities	1,657.6	1,669.9
Commitments and contingencies (Note 13)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,459	1,434
Retained earnings	926.6	863.4
Total common equity	2,451.8	2,363.6
Total equity	2,451.8	2,363.6
Total liabilities and equity	$ 6,648.4	$ 6,506.5

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	249,644,352	245,022,800
Shares in deferred compensation trust (in shares)	367,493	381,232
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 27.86	$ 26.24
IPL [Member]
Common stock, par value (in dollars per share)	$ 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 (in dollars per share)	$ 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 Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 309.5	$ 224.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	298.4	279.8
Deferred tax expense (benefit) and tax credits	(28.8)	19.9
Equity component of allowance for funds used during construction	(26.8)	(30.8)
Other	26.6	13.5
Other changes in assets and liabilities:
Accounts receivable	(197.9)	(199.7)
Accounts payable	8.3	(33.1)
Regulatory liabilities	(63.4)	(26.1)
Pension and other benefit obligations	(33.8)	(21.7)
Deferred income taxes	81.9	34.3
Other	(54.3)	16
Net cash flows from operating activities	319.7	276.9
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(584)	(652.5)
Other construction and acquisition expenditures	(24.3)	(54.1)
Cash receipts on sold receivables	209.9	125.5
Other	6.1	(25.9)
Net cash flows used for investing activities	(392.3)	(607)
Cash flows from financing activities:
Common stock dividends	(187.6)	(167.8)
Proceeds from issuance of common stock, net	234.8	60.6
Proceeds from issuance of long-term debt	1,050	650
Payments to retire long-term debt	(653.7)	(3.4)
Net change in commercial paper	(152)	(50.7)
Other	(27.2)	(9.9)
Net cash flows from financing activities	264.3	478.8
Net increase (decrease) in cash, cash equivalents and restricted cash	191.7	148.7
Cash, cash equivalents and restricted cash at beginning of period	17.7	25.5
Cash, cash equivalents and restricted cash at end of period	209.4	174.2
Supplemental cash flows information:
Interest	(138.1)	(132.7)
Income taxes, net	(5)	2.5
Significant non-cash investing and financing activities:
Accrued capital expenditures	208.3	187.4
Beneficial interest obtained in exchange for securitized accounts receivable	194.1	214.6
IPL [Member]
Cash flows from operating activities:
Net income	147.5	103.4
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	174.6	159.7
Deferred tax expense (benefit) and tax credits	(20.9)	(11.7)
Other	(5.8)	(14.9)
Other changes in assets and liabilities:
Accounts receivable	(218.7)	(209.3)
Accounts payable	26.1	(17)
Deferred income taxes	25.6	25.3
Other	(51.2)	53.5
Net cash flows from operating activities	77.2	89
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(309.6)	(449.5)
Cash receipts on sold receivables	209.9	125.5
Other	(25.5)	(30.5)
Net cash flows used for investing activities	(125.2)	(354.5)
Cash flows from financing activities:
Common stock dividends	(118.1)	(83.9)
Capital contributions from parent	175	100
Proceeds from issuance of long-term debt	400	300
Payments to retire long-term debt	(200)	0
Net change in commercial paper	0	(50.4)
Other	(14.7)	(6.2)
Net cash flows from financing activities	242.2	259.5
Net increase (decrease) in cash, cash equivalents and restricted cash	194.2	(6)
Cash, cash equivalents and restricted cash at beginning of period	9.3	12.4
Cash, cash equivalents and restricted cash at end of period	203.5	6.4
Supplemental cash flows information:
Interest	(71.6)	(58.3)
Income taxes, net	7.3	12.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	93.8	117.4
Beneficial interest obtained in exchange for securitized accounts receivable	194.1	214.6
WPL [Member]
Cash flows from operating activities:
Net income	147.2	107.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	121.1	117.7
Other	(18.9)	17
Other changes in assets and liabilities:
Accounts receivable	23.1	7.6
Regulatory liabilities	(63.3)	(18.4)
Deferred income taxes	53.2	11.2
Other	(6.1)	(34.6)
Net cash flows from operating activities	256.3	208.2
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(274.4)	(203)
Other	14.6	(15)
Net cash flows used for investing activities	(259.8)	(218)
Cash flows from financing activities:
Common stock dividends	(84)	(72)
Capital contributions from parent	25	0
Proceeds from issuance of long-term debt	350	350
Payments to retire long-term debt	(150)	0
Net change in commercial paper	(130.3)	(105.5)
Other	(8.4)	(7.4)
Net cash flows from financing activities	2.3	165.1
Net increase (decrease) in cash, cash equivalents and restricted cash	(1.2)	155.3
Cash, cash equivalents and restricted cash at beginning of period	4.4	9.2
Cash, cash equivalents and restricted cash at end of period	3.2	164.5
Supplemental cash flows information:
Interest	(49.7)	(51.7)
Income taxes, net	1.1	(6.5)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 113.7	$ 66.4

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. 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 . NOTE 1(b) Cash and Cash Equivalents - At June 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $198.3 million and $198.3 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. 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 . NOTE 1(b) Cash and Cash Equivalents - At June 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $198.3 million and $198.3 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 . In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities. 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 . NOTE 1(b) Cash and Cash Equivalents - At June 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $198.3 million and $198.3 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively. NOTE 1(c) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts. NOTE 1(d) New Accounting Standards - Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .

Regulatory Matters

Regulatory Matters	6 Months Ended
	Jun. 30, 2020
Public Utilities, General Disclosures [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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the six months ended June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the three and six months ended June 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in the second quarter of 2020 related to MISO transmission owner return on equity complaints.
IPL [Member]
Public Utilities, General Disclosures [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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the six months ended June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the three and six months ended June 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in the second quarter of 2020 related to MISO transmission owner return on equity complaints.
WPL [Member]
Public Utilities, General Disclosures [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 June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9 Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the six months ended June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily from returning a portion of these excess deferred tax benefits back to customers. Electric transmission cost recovery - In the second quarter of 2020, pursuant to a June 2020 IUB order, IPL issued $42 million of credits to its retail electric customers through its transmission cost rider for amounts previously collected in rates, which resulted in a corresponding reduction to “Electric transmission service” expense in Alliant Energy’s and IPL’s income statements for the three and six months ended June 30, 2020 . Refer to Note 13(f) for discussion of refunds received by IPL and WPL in the second quarter of 2020 related to MISO transmission owner return on equity complaints.

Receivables

Receivables	6 Months Ended
	Jun. 30, 2020
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9 Note 3(b) Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its 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 June 30, 2020 , IPL had $89 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $65.0 $25.0 $96.0 $108.0 Average outstanding aggregate cash proceeds 11.1 2.6 17.3 41.6 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2020 December 31, 2019 Customer accounts receivable $113.5 $124.7 Unbilled utility revenues 92.3 95.5 Other receivables 0.4 0.9 Receivables sold to third party 206.2 221.1 Less: cash proceeds 1.0 27.0 Deferred proceeds 205.2 194.1 Less: allowance for expected credit losses 11.1 6.4 Fair value of deferred proceeds $194.1 $187.7 As of June 30, 2020 , outstanding receivables past due under the Receivables Agreement were $25.1 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Collections $453.0 $487.7 $994.4 $1,043.5 Write-offs, net of recoveries 1.2 2.6 3.3 8.1
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9 Note 3(b) Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its 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 June 30, 2020 , IPL had $89 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $65.0 $25.0 $96.0 $108.0 Average outstanding aggregate cash proceeds 11.1 2.6 17.3 41.6 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2020 December 31, 2019 Customer accounts receivable $113.5 $124.7 Unbilled utility revenues 92.3 95.5 Other receivables 0.4 0.9 Receivables sold to third party 206.2 221.1 Less: cash proceeds 1.0 27.0 Deferred proceeds 205.2 194.1 Less: allowance for expected credit losses 11.1 6.4 Fair value of deferred proceeds $194.1 $187.7 As of June 30, 2020 , outstanding receivables past due under the Receivables Agreement were $25.1 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Collections $453.0 $487.7 $994.4 $1,043.5 Write-offs, net of recoveries 1.2 2.6 3.3 8.1
WPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Note 3(a) Accounts Receivable - Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9

Investments

Investments	6 Months Ended
	Jun. 30, 2020
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and six months ended June 30 was as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC Holdings ($13.5 ) ($10.0 ) ($24.5 ) ($19.5 ) Non-utility wind farm in Oklahoma (1.9 ) (1.3 ) (4.1 ) (2.4 ) Other (2.0 ) (1.4 ) (2.2 ) (1.7 ) ($17.4 ) ($12.7 ) ($30.8 ) ($23.6 )

Common Equity

Common Equity	6 Months Ended
	Jun. 30, 2020
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 248,220 Equity-based compensation plans 98,205 Shares outstanding, June 30, 2020 249,644,352 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 248,220 Equity-based compensation plans 98,205 Shares outstanding, June 30, 2020 249,644,352 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2
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, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 248,220 Equity-based compensation plans 98,205 Shares outstanding, June 30, 2020 249,644,352 Equity Forward Agreements - In November 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. The initial forward sale price of $52.235 per share was subject to daily adjustment based on a floating interest rate factor, and decreased by other fixed amounts specified in the forward sale agreements. In the first quarter of 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2

Debt

Debt	6 Months Ended
	Jun. 30, 2020
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of June 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of June 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5% NOTE 6(b) Long-term Debt - In March 2020, AEF entered into a $300 million variable rate ( 1% as of June 30, 2020 ) term loan credit agreement (with Alliant Energy as guarantor) and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that would have expired in April 2020. AEF’s current term loan credit agreement expires in March 2022 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement. In April 2020, WPL issued $350 million of 3.65% debentures due 2050. The net proceeds from the issuance were used by WPL to reduce borrowings under the single credit facility and for general corporate purposes. In June 2020, WPL retired its $150 million 4.6% debentures. In June 2020, IPL issued $400 million of 2.3% senior debentures due 2030. The net proceeds from the issuance were used by IPL to retire its $200 million 3.65% senior debentures that would have matured in September 2020 and for general corporate purposes.

Revenues

Revenues	6 Months Ended
	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	REVENUES Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2020
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2% Deferred Tax Assets and Liabilities - Carryforwards - At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170

Benefit Plans

Benefit Plans	6 Months Ended
	Jun. 30, 2020
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9 As of June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $9.9 million , $5.5 million and $4.1 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9 As of June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $9.9 million , $5.5 million and $4.1 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy. NOTE 9(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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9 As of June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $9.9 million , $5.5 million and $4.1 million , respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years . For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49

Asset Retirement Obligations

Asset Retirement Obligations	6 Months Ended
	Jun. 30, 2020
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the six months ended June 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196.3 $133.9 Revisions in estimated cash flows 0.9 — Liabilities settled (3.5 ) (2.8 ) Liabilities incurred (a) 27.6 27.6 Accretion expense 3.5 2.5 Balance, June 30 $224.8 $161.2 (a) During the six months ended June 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the six months ended June 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196.3 $133.9 Revisions in estimated cash flows 0.9 — Liabilities settled (3.5 ) (2.8 ) Liabilities incurred (a) 27.6 27.6 Accretion expense 3.5 2.5 Balance, June 30 $224.8 $161.2 (a) During the six months ended June 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 30, 2020
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1 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. At June 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than 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. 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at June 30, 2020 and December 31, 2019 . 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 - Notional Amounts - As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1 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. At June 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than 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. 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at June 30, 2020 and December 31, 2019 . 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 - Notional Amounts - As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1 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. At June 30, 2020 and December 31, 2019 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than 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. 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, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at June 30, 2020 and December 31, 2019 . 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.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
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 related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $14.2 $0.4 $188.0 $178.3 Total net gains (losses) included in changes in net assets (realized/unrealized) 12.0 (0.1 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.1 ) — — — Settlements (a) (3.7 ) (4.8 ) 6.1 36.3 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.9 $— $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $21.2 $12.2 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 9.0 (5.7 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (7.6 ) (10.8 ) 6.4 95.2 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $9.0 ($2.6 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $13.5 $0.6 $188.0 $178.3 Total net gains included in changes in net assets (realized/unrealized) 11.0 0.4 — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.1 ) — — — Settlements (a) (2.7 ) (3.7 ) 6.1 36.3 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.0 $0.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $18.7 $9.0 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.8 (2.8 ) — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.2 ) (0.1 ) — — Settlements (a) (5.6 ) (8.8 ) 6.4 95.2 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $8.8 ($0.9 ) $— $— (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 amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5
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 related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $14.2 $0.4 $188.0 $178.3 Total net gains (losses) included in changes in net assets (realized/unrealized) 12.0 (0.1 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.1 ) — — — Settlements (a) (3.7 ) (4.8 ) 6.1 36.3 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.9 $— $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $21.2 $12.2 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 9.0 (5.7 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (7.6 ) (10.8 ) 6.4 95.2 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $9.0 ($2.6 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $13.5 $0.6 $188.0 $178.3 Total net gains included in changes in net assets (realized/unrealized) 11.0 0.4 — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.1 ) — — — Settlements (a) (2.7 ) (3.7 ) 6.1 36.3 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.0 $0.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $18.7 $9.0 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.8 (2.8 ) — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.2 ) (0.1 ) — — Settlements (a) (5.6 ) (8.8 ) 6.4 95.2 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $8.8 ($0.9 ) $— $— (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 amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5
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 related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2 Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $14.2 $0.4 $188.0 $178.3 Total net gains (losses) included in changes in net assets (realized/unrealized) 12.0 (0.1 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.1 ) — — — Settlements (a) (3.7 ) (4.8 ) 6.1 36.3 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.9 $— $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $21.2 $12.2 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 9.0 (5.7 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (7.6 ) (10.8 ) 6.4 95.2 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $9.0 ($2.6 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $13.5 $0.6 $188.0 $178.3 Total net gains included in changes in net assets (realized/unrealized) 11.0 0.4 — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.1 ) — — — Settlements (a) (2.7 ) (3.7 ) 6.1 36.3 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.0 $0.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $18.7 $9.0 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.8 (2.8 ) — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.2 ) (0.1 ) — — Settlements (a) (5.6 ) (8.8 ) 6.4 95.2 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $8.8 ($0.9 ) $— $— (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 amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5

Commitments And Contingencies

Commitments And Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the expansion of wind generation. WPL’s projects include the expansion of wind and solar generation. At June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $60 million , $8 million and $52 million , respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 . NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships and currently known obligations include costs associated with the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC’s guarantees, which do not include a maximum limit, apply to the Whiting Petroleum affiliate’s obligations and to the other partners. Alliant Energy Resources, LLC may be required to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 30, 2020 , the currently known partnership obligations are the abandonment obligations. The Whiting Petroleum affiliate’s share of these abandonment obligations on an undiscounted basis is estimated at $63 million as of June 30, 2020 based on information made available to Alliant Energy by Whiting Petroleum, and this represents Alliant Energy’s best estimate of the contingent obligations for potential future payments. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. As a result of Whiting Petroleum’s deterioration in credit worthiness since January 1, 2020 likely from significantly depressed oil and gas prices and general market conditions, Alliant Energy currently expects credit exposure related to the guarantees and has recognized a $20 million credit loss liability as of June 30, 2020 related to the contingent obligations, which is recorded in “Other liabilities” on Alliant Energy’s balance sheet. The incremental pre-tax change in the liability, $8 million , was recorded as a credit loss expense within Alliant Energy’s “Other operation and maintenance” expenses for the six months ended June 30, 2020 . There was no incremental pre-tax change in the liability recorded for the three months ended June 30, 2020 . Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $82 million as of June 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of June 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of June 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(d) Environmental Matters - Manufactured Gas Plant (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. At June 30, 2020 , 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, which are not discounted, were as follows (in millions). At June 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $10 - $24 Current and non-current environmental liabilities 16 13 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Burlington by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. 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: Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) Collective Bargaining Agreements - At June 30, 2020 , employees covered by collective bargaining agreements represented 53% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On August 31, 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 44% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are unable to predict the outcome. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. In the second quarter of 2020, IPL and WPL received $10 million and $3 million , respectively, in refunds related to the November 2019 FERC order. Additional refunds are currently expected to be issued; however, as a result of the May 2020 FERC order, timing is uncertain. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the expansion of wind generation. WPL’s projects include the expansion of wind and solar generation. At June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $60 million , $8 million and $52 million , respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 . NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships and currently known obligations include costs associated with the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC’s guarantees, which do not include a maximum limit, apply to the Whiting Petroleum affiliate’s obligations and to the other partners. Alliant Energy Resources, LLC may be required to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 30, 2020 , the currently known partnership obligations are the abandonment obligations. The Whiting Petroleum affiliate’s share of these abandonment obligations on an undiscounted basis is estimated at $63 million as of June 30, 2020 based on information made available to Alliant Energy by Whiting Petroleum, and this represents Alliant Energy’s best estimate of the contingent obligations for potential future payments. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. As a result of Whiting Petroleum’s deterioration in credit worthiness since January 1, 2020 likely from significantly depressed oil and gas prices and general market conditions, Alliant Energy currently expects credit exposure related to the guarantees and has recognized a $20 million credit loss liability as of June 30, 2020 related to the contingent obligations, which is recorded in “Other liabilities” on Alliant Energy’s balance sheet. The incremental pre-tax change in the liability, $8 million , was recorded as a credit loss expense within Alliant Energy’s “Other operation and maintenance” expenses for the six months ended June 30, 2020 . There was no incremental pre-tax change in the liability recorded for the three months ended June 30, 2020 . Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $82 million as of June 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of June 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of June 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(d) Environmental Matters - Manufactured Gas Plant (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. At June 30, 2020 , 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, which are not discounted, were as follows (in millions). At June 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $10 - $24 Current and non-current environmental liabilities 16 13 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Burlington by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. 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: Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) Collective Bargaining Agreements - At June 30, 2020 , employees covered by collective bargaining agreements represented 53% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On August 31, 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 44% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are unable to predict the outcome. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. In the second quarter of 2020, IPL and WPL received $10 million and $3 million , respectively, in refunds related to the November 2019 FERC order. Additional refunds are currently expected to be issued; however, as a result of the May 2020 FERC order, timing is uncertain. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the expansion of wind generation. WPL’s projects include the expansion of wind and solar generation. At June 30, 2020 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $60 million , $8 million and $52 million , respectively. NOTE 13(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 . NOTE 13(c) Guarantees and Indemnifications - Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships and currently known obligations include costs associated with the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC’s guarantees, which do not include a maximum limit, apply to the Whiting Petroleum affiliate’s obligations and to the other partners. Alliant Energy Resources, LLC may be required to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. As of June 30, 2020 , the currently known partnership obligations are the abandonment obligations. The Whiting Petroleum affiliate’s share of these abandonment obligations on an undiscounted basis is estimated at $63 million as of June 30, 2020 based on information made available to Alliant Energy by Whiting Petroleum, and this represents Alliant Energy’s best estimate of the contingent obligations for potential future payments. Alliant Energy is not aware of any material liabilities related to these guarantees that it is probable that it will be obligated to pay; however, the new credit loss accounting standard adopted on January 1, 2020 requires recognition of a liability for expected credit losses related to the contingent obligations that are in the scope of these guarantees. With the adoption of this standard, Alliant Energy recorded a pre-tax $12 million cumulative effect adjustment to decrease the opening balance of retained earnings as of January 1, 2020. As a result of Whiting Petroleum’s deterioration in credit worthiness since January 1, 2020 likely from significantly depressed oil and gas prices and general market conditions, Alliant Energy currently expects credit exposure related to the guarantees and has recognized a $20 million credit loss liability as of June 30, 2020 related to the contingent obligations, which is recorded in “Other liabilities” on Alliant Energy’s balance sheet. The incremental pre-tax change in the liability, $8 million , was recorded as a credit loss expense within Alliant Energy’s “Other operation and maintenance” expenses for the six months ended June 30, 2020 . There was no incremental pre-tax change in the liability recorded for the three months ended June 30, 2020 . Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $82 million as of June 30, 2020 and will reduce annually until expiring in July 2047 . Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031 , subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of June 30, 2020 and December 31, 2019 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of June 30, 2020 and December 31, 2019 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(d) Environmental Matters - Manufactured Gas Plant (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. At June 30, 2020 , 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, which are not discounted, were as follows (in millions). At June 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $10 - $24 Current and non-current environmental liabilities 16 13 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Burlington by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers. 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: Effluent Limitation Guidelines, Coal Combustion Residuals Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 13(e) Collective Bargaining Agreements - At June 30, 2020 , employees covered by collective bargaining agreements represented 53% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On August 31, 2020, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 44% of total employees of Alliant Energy and IPL, respectively. While the process to renew the agreement is underway and a tentative agreement has been reached, Alliant Energy and IPL are unable to predict the outcome. NOTE 13(f) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed complaints with FERC requesting a reduction to the base return on equity used by MISO transmission owners, including ITC Midwest LLC and ATC. The first complaint covered the period from November 12, 2013 through February 11, 2015. In 2017, IPL and WPL received refunds related to the first complaint period, which were subsequently refunded to their retail and wholesale customers. The second complaint covered the period from February 12, 2015 through May 11, 2016. In November 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity used by the MISO transmission owners to 9.88% effective for the first complaint period and subsequent to September 28, 2016. The November 2019 FERC order also dismissed the second complaint; therefore, FERC did not direct refunds to be made for that complaint. In May 2020, FERC issued an order in response to various rehearing requests and increased the base return on equity used by the MISO transmission owners from 9.88% to 10.02% for the first complaint period and subsequent to September 28, 2016, which reduces the refunds originally anticipated to be received by IPL and WPL as a result of FERC’s November 2019 order. In the second quarter of 2020, IPL and WPL received $10 million and $3 million , respectively, in refunds related to the November 2019 FERC order. Additional refunds are currently expected to be issued; however, as a result of the May 2020 FERC order, timing is uncertain. IPL currently expects that all refunds will be returned to its retail electric customers after refund amounts and timing are known and a refund plan is approved by the IUB. WPL proposed to retain the refunds as part of WPL’s application with the PSCW to maintain its current retail electric base rates through the end of 2021. WPL currently expects that any refunds not utilized to maintain base rates would be returned to its customers in WPL’s next retail electric rate review proceeding . Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs.

Segments Of Business

Segments Of Business	6 Months Ended
	Jun. 30, 2020
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7

Related Parties

Related Parties	6 Months Ended
	Jun. 30, 2020
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, 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. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC billings to WPL $25 $27 $53 $54 WPL billings to ATC 3 3 6 7 WPL owed ATC net amounts of $9 million as of June 30, 2020 and $9 million as of December 31, 2019 . In the second quarter of 2020, WPL received $46 million from ATC related to construction deposits WPL previously provided ATC for transmission network upgrades for the West Riverside Energy Center, which is recorded in “Other” in AEC’s and WPL’s cash flows from investing activities.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, 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. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, 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. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC billings to WPL $25 $27 $53 $54 WPL billings to ATC 3 3 6 7 WPL owed ATC net amounts of $9 million as of June 30, 2020 and $9 million as of December 31, 2019 . In the second quarter of 2020, WPL received $46 million from ATC related to construction deposits WPL previously provided ATC for transmission network upgrades for the West Riverside Energy Center, which is recorded in “Other” in AEC’s and WPL’s cash flows from investing activities.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	6 Months Ended
	Jun. 30, 2020
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 . 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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
General, Use of Estimates	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 .
Cash and Cash Equivalents	At June 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $198.3 million and $198.3 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively.
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .
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 . 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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
General, Use of Estimates	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 .
Cash and Cash Equivalents	At June 30, 2020 , Alliant Energy’s and IPL’s cash and cash equivalents included $198.3 million and $198.3 million of money market fund investments, with weighted average interest rates of 0.1% and 0.1% , respectively.
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .
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 . 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 six months ended June 30, 2020 are not necessarily indicative of results that may be expected for the year ending December 31, 2020 .
General, COVID-19	In March 2020, COVID-19 was declared a global pandemic, which has resulted in widespread travel restrictions and closures of commercial spaces and industrial facilities in Alliant Energy’s service territories. For the three and six months ended June 30 , 2020, Alliant Energy, IPL and WPL considered the impact of COVID-19 on their overall business operations, financial condition, results of operations and cash flows, along with assumptions and estimates used. While the total expected impact of COVID-19 on future sales is currently unknown, Alliant Energy, IPL and WPL have experienced higher electric residential sales and lower electric commercial and industrial sales since the outset of the pandemic. The degree to which the COVID-19 pandemic may impact Alliant Energy, IPL and WPL in the future is currently unknown and will depend on future developments of the pandemic as well as possible additional actions by government and regulatory authorities.
General, Use of Estimates	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 .
Current Expected Credit Losses Estimates	Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as impacts related to COVID-19 and related regulatory actions, and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
New Accounting Standards	Credit Losses - In June 2016, the Financial Accounting Standards Board issued an accounting standard requiring use of a current expected credit loss model rather than an incurred loss method, which is intended to result in more timely recognition of credit losses on trade receivables, certain other assets and off-balance sheet credit exposures. Alliant Energy, IPL and WPL adopted this standard on January 1, 2020 using a modified retrospective method of adoption, which required cumulative effect adjustments to retained earnings on January 1, 2020. IPL and WPL did not record a cumulative effect adjustment to retained earnings and Alliant Energy recorded a pre-tax $12 million (after-tax $8.7 million ) cumulative effect adjustment to decrease retained earnings related to Alliant Energy’s guarantees in the partnership obligations of an affiliate of Whiting Petroleum (refer to Note 13(c) for further discussion). This adjustment is included in “Adoption of new accounting standard” in Alliant Energy’s summary of changes in shareowners’ equity in Note 5 for the six months ended June 30, 2020 .

Regulatory Matters (Tables)

Regulatory Matters (Tables)	6 Months Ended
	Jun. 30, 2020
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $842.5 $817.6 $797.4 $776.8 $45.1 $40.8 Pension and OPEB costs 501.2 524.0 251.3 262.5 249.9 261.5 Assets retired early 122.9 134.0 81.8 87.9 41.1 46.1 Asset retirement obligations 114.0 111.8 78.2 76.2 35.8 35.6 IPL’s DAEC PPA amendment 109.4 108.2 109.4 108.2 — — Derivatives 47.0 39.5 20.5 18.3 26.5 21.2 Emission allowances 19.8 21.1 19.8 21.1 — — Other 86.2 88.5 46.5 48.3 39.7 40.2 $1,843.0 $1,844.7 $1,404.9 $1,399.3 $438.1 $445.4
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Tax-related $779.0 $835.6 $343.6 $350.9 $435.4 $484.7 Cost of removal obligations 385.8 387.7 256.4 257.0 129.4 130.7 Electric transmission cost recovery 66.3 88.6 30.7 51.3 35.6 37.3 Commodity cost recovery 30.1 24.2 14.0 8.8 16.1 15.4 Derivatives 28.8 19.9 26.3 17.4 2.5 2.5 WPL’s earnings sharing mechanism 20.4 21.9 — — 20.4 21.9 Other 60.6 45.7 46.9 29.3 13.7 16.4 $1,371.0 $1,423.6 $717.9 $714.7 $653.1 $708.9

Receivables (Tables)

Receivables (Tables)	6 Months Ended
	Jun. 30, 2020
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $65.0 $25.0 $96.0 $108.0 Average outstanding aggregate cash proceeds 11.1 2.6 17.3 41.6
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2020 December 31, 2019 Customer accounts receivable $113.5 $124.7 Unbilled utility revenues 92.3 95.5 Other receivables 0.4 0.9 Receivables sold to third party 206.2 221.1 Less: cash proceeds 1.0 27.0 Deferred proceeds 205.2 194.1 Less: allowance for expected credit losses 11.1 6.4 Fair value of deferred proceeds $194.1 $187.7
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Collections $453.0 $487.7 $994.4 $1,043.5 Write-offs, net of recoveries 1.2 2.6 3.3 8.1
IPL [Member]
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Maximum outstanding aggregate cash proceeds $65.0 $25.0 $96.0 $108.0 Average outstanding aggregate cash proceeds 11.1 2.6 17.3 41.6
Schedule of Sales Of Accounts Receivable Sold Under Agreement Table Text Block	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): June 30, 2020 December 31, 2019 Customer accounts receivable $113.5 $124.7 Unbilled utility revenues 92.3 95.5 Other receivables 0.4 0.9 Receivables sold to third party 206.2 221.1 Less: cash proceeds 1.0 27.0 Deferred proceeds 205.2 194.1 Less: allowance for expected credit losses 11.1 6.4 Fair value of deferred proceeds $194.1 $187.7
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 Collections $453.0 $487.7 $994.4 $1,043.5 Write-offs, net of recoveries 1.2 2.6 3.3 8.1
WPL [Member]
Receivables [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets were as follows (in millions): Alliant Energy IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Customer $92.7 $91.6 $— $— $82.4 $83.5 Unbilled utility revenues 68.2 82.1 — — 68.2 82.1 Deferred proceeds 194.1 187.7 194.1 187.7 — — Other 41.5 48.0 16.5 16.3 24.5 31.4 Allowance for expected credit losses (10.0 ) (7.3 ) (1.7 ) (1.2 ) (8.2 ) (6.1 ) $386.5 $402.1 $208.9 $202.8 $166.9 $190.9

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Equity Method Investments [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and six months ended June 30 was as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC Holdings ($13.5 ) ($10.0 ) ($24.5 ) ($19.5 ) Non-utility wind farm in Oklahoma (1.9 ) (1.3 ) (4.1 ) (2.4 ) Other (2.0 ) (1.4 ) (2.2 ) (1.7 ) ($17.4 ) ($12.7 ) ($30.8 ) ($23.6 )

Common Equity (Tables)

Common Equity (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Capitalization, Equity [Line Items]
Common Share Activity	A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2020 245,022,800 Equity forward agreements 4,275,127 Shareowner Direct Plan 248,220 Equity-based compensation plans 98,205 Shares outstanding, June 30, 2020 249,644,352
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2
IPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2
WPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $2.5 $2,674.1 $2,833.7 $2.0 ($9.9 ) $200.0 $5,702.4 Net income attributable to Alliant Energy common shareowners 134.4 134.4 Common stock dividends ($0.38 per share) (94.6 ) (94.6 ) Shareowner Direct Plan issuances 6.4 6.4 Equity-based compensation plans and other 2.6 (0.3 ) 2.3 Other comprehensive loss, net of tax (2.6 ) (2.6 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Net income attributable to Alliant Energy common shareowners 94.6 94.6 Common stock dividends ($0.355 per share) (84.1 ) (84.1 ) Shareowner Direct Plan issuances 6.0 6.0 Equity-based compensation plans and other 2.4 (0.3 ) 2.1 Other comprehensive loss, net of tax (1.4 ) (1.4 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Alliant Energy Total Alliant Energy Common Equity Accumulated Shares in Cumulative Additional Other Deferred Preferred Common Paid-In Retained Comprehensive Compensation Stock Total Stock Capital Earnings Income (Loss) Trust of IPL Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $2.5 $2,445.9 $2,765.4 $1.3 ($10.0 ) $200.0 $5,405.1 Net income attributable to Alliant Energy common shareowners 304.4 304.4 Common stock dividends ($0.76 per share) (187.6 ) (187.6 ) Equity forward settlements and Shareowner Direct Plan issuances 234.8 234.8 Equity-based compensation plans and other 2.4 (0.2 ) 2.2 Adoption of new accounting standard, net of tax (refer to Note 1(d) ) (8.7 ) (8.7 ) Other comprehensive loss, net of tax (1.9 ) (1.9 ) Ending balance, June 30, 2020 $2.5 $2,683.1 $2,873.5 ($0.6 ) ($10.2 ) $200.0 $5,748.3 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $2.4 $2,045.5 $2,545.9 $1.7 ($9.8 ) $200.0 $4,785.7 Net income attributable to Alliant Energy common shareowners 219.7 219.7 Common stock dividends ($0.71 per share) (167.8 ) (167.8 ) Equity forward settlements and Shareowner Direct Plan issuances 60.6 60.6 Equity-based compensation plans and other 2.3 (0.2 ) 2.1 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, June 30, 2019 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $33.4 $2,447.8 $914.2 $200.0 $3,595.4 Net income available for common stock 59.8 59.8 Common stock dividends (59.1 ) (59.1 ) Capital contributions from parent 75.0 75.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Net income available for common stock 45.0 45.0 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $33.4 $2,347.8 $890.6 $200.0 $3,471.8 Net income available for common stock 142.4 142.4 Common stock dividends (118.1 ) (118.1 ) Capital contributions from parent 175.0 175.0 Ending balance, June 30, 2020 $33.4 $2,522.8 $914.9 $200.0 $3,671.1 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Net income available for common stock 98.3 98.3 Common stock dividends (83.9 ) (83.9 ) Capital contributions from parent 100.0 100.0 Ending balance, June 30, 2019 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended June 30, 2020 Beginning balance, March 31, 2020 $66.2 $1,459.0 $910.9 $2,436.1 Net income 57.6 57.6 Common stock dividends (41.9 ) (41.9 ) Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Three Months Ended June 30, 2019 Beginning balance, March 31, 2019 $66.2 $1,309.0 $804.0 $2,179.2 Net income 42.0 42.0 Common stock dividends (36.0 ) (36.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Six Months Ended June 30, 2020 Beginning balance, December 31, 2019 $66.2 $1,434.0 $863.4 $2,363.6 Net income 147.2 147.2 Common stock dividends (84.0 ) (84.0 ) Capital contributions from parent 25.0 25.0 Ending balance, June 30, 2020 $66.2 $1,459.0 $926.6 $2,451.8 Six Months Ended June 30, 2019 Beginning balance, December 31, 2018 $66.2 $1,309.0 $774.3 $2,149.5 Net income 107.7 107.7 Common stock dividends (72.0 ) (72.0 ) Ending balance, June 30, 2019 $66.2 $1,309.0 $810.0 $2,185.2

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions): June 30, 2020 Alliant Energy IPL WPL Amount outstanding $185.4 $— $37.9 Weighted average interest rates 0.3% N/A 0.2% Available credit facility capacity $814.6 $250.0 $262.1 Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Maximum amount outstanding (based on daily outstanding balances) $270.5 $590.2 $8.4 $— $182.0 $193.3 Average amount outstanding (based on daily outstanding balances) $121.2 $531.7 $0.4 $— $8.7 $141.6 Weighted average interest rates 0.5% 2.7% 0.5% N/A 0.5% 2.5% Six Months Ended June 30 Maximum amount outstanding (based on daily outstanding balances) $462.5 $600.6 $8.4 $50.4 $212.0 $195.1 Average amount outstanding (based on daily outstanding balances) $251.8 $515.4 $0.2 $0.3 $87.9 $139.8 Weighted average interest rates 1.5% 2.7% 0.5% 2.8% 1.7% 2.5%

Revenues (Tables)

Revenues (Tables)	6 Months Ended
	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $249.7 $233.3 $135.3 $125.9 $114.4 $107.4 Retail - commercial 164.0 171.3 109.0 111.4 55.0 59.9 Retail - industrial 197.3 214.2 114.3 118.4 83.0 95.8 Wholesale 39.1 41.0 13.0 14.6 26.1 26.4 Bulk power and other 25.1 31.4 16.8 22.0 8.3 9.4 Total Electric Utility 675.2 691.2 388.4 392.3 286.8 298.9 Gas Utility: Retail - residential 33.6 35.2 18.5 20.0 15.1 15.2 Retail - commercial 14.7 16.1 8.3 8.8 6.4 7.3 Retail - industrial 1.7 2.0 1.3 1.6 0.4 0.4 Transportation/other 8.9 11.9 5.8 8.0 3.1 3.9 Total Gas Utility 58.9 65.2 33.9 38.4 25.0 26.8 Other Utility: Steam 8.6 9.2 8.6 9.2 — — Other utility 1.5 1.7 1.0 1.3 0.5 0.4 Total Other Utility 10.1 10.9 9.6 10.5 0.5 0.4 Non-Utility and Other: Transportation and other 18.9 22.9 — — — — Total Non-Utility and Other 18.9 22.9 — — — — Total revenues $763.1 $790.2 $431.9 $441.2 $312.3 $326.1 Alliant Energy IPL WPL Six Months Ended June 30 2020 2019 2020 2019 2020 2019 Electric Utility: Retail - residential $516.5 $508.0 $282.7 $273.4 $233.8 $234.6 Retail - commercial 346.3 352.4 228.7 228.0 117.6 124.4 Retail - industrial 407.2 422.9 235.5 234.5 171.7 188.4 Wholesale 80.0 87.5 27.4 31.5 52.6 56.0 Bulk power and other 55.5 63.8 38.9 44.7 16.6 19.1 Total Electric Utility 1,405.5 1,434.6 813.2 812.1 592.3 622.5 Gas Utility: Retail - residential 124.1 167.0 67.3 97.9 56.8 69.1 Retail - commercial 60.4 79.7 32.4 43.6 28.0 36.1 Retail - industrial 5.9 7.4 3.6 4.8 2.3 2.6 Transportation/other 20.7 26.9 13.6 16.7 7.1 10.2 Total Gas Utility 211.1 281.0 116.9 163.0 94.2 118.0 Other Utility: Steam 18.6 17.6 18.6 17.6 — — Other utility 3.1 4.4 2.1 3.6 1.0 0.8 Total Other Utility 21.7 22.0 20.7 21.2 1.0 0.8 Non-Utility and Other: Transportation and other 40.5 39.8 — — — — Total Non-Utility and Other 40.5 39.8 — — — — Total revenues $1,678.8 $1,777.4 $950.8 $996.3 $687.5 $741.3

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2020
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2%
Summary Of Tax Credit Carryforwards	At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2%
Summary Of Tax Credit Carryforwards	At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The decreases in overall effective income tax rates for the three and six months ended June 30 , 2020 compared to the same periods in 2019 were primarily due to increases in production tax credits as a result of increased wind production in 2020 and increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2020 increased revenue requirements. Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Overall income tax rate (6.5%) 10.3% (9.6%) 10.5% (6.5%) 3.8% (13.8%) 3.7% (8.5%) 15.5% (9.4%) 17.2%
Summary Of Tax Credit Carryforwards	At June 30, 2020 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2037 $299 $276 $3 State net operating losses 2020-2040 595 9 2 Federal tax credits 2022-2040 403 212 170

Benefit Plans (Tables)

Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included below (in millions). For IPL and WPL, amounts represent those for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months Alliant Energy 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $2.7 $2.4 $5.4 $4.8 $0.9 $0.9 $1.7 $1.7 Interest cost 10.8 12.4 21.6 24.9 1.7 2.1 3.5 4.2 Expected return on plan assets (17.5 ) (15.0 ) (34.9 ) (30.0 ) (1.4 ) (1.3 ) (2.7 ) (2.5 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.3 ) (0.3 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 8.6 9.1 17.2 18.2 0.9 0.8 1.7 1.6 Settlement losses (a) — — 4.2 — — — — — $4.5 $8.8 $13.2 $17.6 $2.1 $2.4 $4.2 $4.9 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months IPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $1.7 $1.5 $3.4 $3.0 $0.4 $0.4 $0.7 $0.7 Interest cost 5.0 5.7 10.0 11.4 0.7 0.9 1.4 1.7 Expected return on plan assets (8.2 ) (7.1 ) (16.3 ) (14.1 ) (0.9 ) (0.9 ) (1.9 ) (1.8 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — — — Amortization of actuarial loss 3.7 4.0 7.4 7.9 0.2 0.3 0.5 0.7 $2.2 $4.1 $4.4 $8.1 $0.4 $0.7 $0.7 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Six Months Three Months Six Months WPL 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $0.9 $0.8 $1.9 $1.7 $0.3 $0.3 $0.6 $0.6 Interest cost 4.7 5.4 9.4 10.8 0.7 0.9 1.4 1.7 Expected return on plan assets (7.6 ) (6.6 ) (15.2 ) (13.1 ) (0.1 ) (0.2 ) (0.3 ) (0.3 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — (0.1 ) — (0.1 ) Amortization of actuarial loss 4.1 4.4 8.2 8.8 0.5 0.4 1.0 0.8 $2.1 $4.0 $4.2 $8.1 $1.4 $1.3 $2.7 $2.7 (a) Settlement losses related to payments made to retired executives of Alliant Energy.
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 and six months ended June 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Six Months Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 2020 2019 Compensation expense $2.7 $3.4 $5.4 $8.1 $1.5 $1.9 $2.9 $4.5 $1.2 $1.4 $2.3 $3.2 Income tax benefits 0.8 1.0 1.5 2.3 0.4 0.5 0.8 1.3 0.3 0.4 0.6 0.9
Schedule Of Equity-based Compensation Plans Activity	For the six months ended June 30 , 2020 , performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. As of June 30, 2020 , 228,207 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Weighted Average Grants Grant Date Fair Value Performance shares 55,303 $64.04 Performance restricted stock units 55,303 59.47 Restricted stock units 60,284 59.49

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the six months ended June 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196.3 $133.9 Revisions in estimated cash flows 0.9 — Liabilities settled (3.5 ) (2.8 ) Liabilities incurred (a) 27.6 27.6 Accretion expense 3.5 2.5 Balance, June 30 $224.8 $161.2 (a) During the six months ended June 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in asset retirement obligations associated with long-lived assets for the six months ended June 30, 2020 is as follows (in millions): Alliant Energy IPL Balance, January 1 $196.3 $133.9 Revisions in estimated cash flows 0.9 — Liabilities settled (3.5 ) (2.8 ) Liabilities incurred (a) 27.6 27.6 Accretion expense 3.5 2.5 Balance, June 30 $224.8 $161.2 (a) During the six months ended June 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of June 30, 2020 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): FTRs Natural Gas Coal Diesel Fuel MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 21,455 2020-2021 234,304 2020-2028 4,482 2020-2021 6,804 2020-2022 IPL 8,978 2020-2021 123,308 2020-2028 1,834 2020-2021 — — WPL 12,477 2020-2021 110,996 2020-2027 2,648 2020-2021 6,804 2020-2022
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL June 30, December 31, June 30, December 31, June 30, December 31, Current derivative assets $27.9 $15.8 $22.5 $12.1 $5.4 $3.7 Non-current derivative assets 14.5 11.0 14.5 10.2 — 0.8 Current derivative liabilities 20.0 19.0 8.5 8.9 11.5 10.1 Non-current derivative liabilities 26.2 18.6 11.8 8.5 14.4 10.1

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $14.2 $0.4 $188.0 $178.3 Total net gains (losses) included in changes in net assets (realized/unrealized) 12.0 (0.1 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.1 ) — — — Settlements (a) (3.7 ) (4.8 ) 6.1 36.3 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.9 $— $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $21.2 $12.2 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 9.0 (5.7 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (7.6 ) (10.8 ) 6.4 95.2 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $9.0 ($2.6 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $13.5 $0.6 $188.0 $178.3 Total net gains included in changes in net assets (realized/unrealized) 11.0 0.4 — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.1 ) — — — Settlements (a) (2.7 ) (3.7 ) 6.1 36.3 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.0 $0.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $18.7 $9.0 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.8 (2.8 ) — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.2 ) (0.1 ) — — Settlements (a) (5.6 ) (8.8 ) 6.4 95.2 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $8.8 ($0.9 ) $— $— (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 amounts received from the receivables sold.
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5
IPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2
Fair Value Measurements Using Significant Unobservable Inputs	Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material. Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $14.2 $0.4 $188.0 $178.3 Total net gains (losses) included in changes in net assets (realized/unrealized) 12.0 (0.1 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.1 ) — — — Settlements (a) (3.7 ) (4.8 ) 6.1 36.3 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.9 $— $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $21.2 $12.2 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 9.0 (5.7 ) — — Transfers out of Level 3 — 3.9 — — Purchases 14.0 13.8 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (7.6 ) (10.8 ) 6.4 95.2 Ending balance, June 30 $36.4 $13.2 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $9.0 ($2.6 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended June 30 2020 2019 2020 2019 Beginning balance, April 1 $13.5 $0.6 $188.0 $178.3 Total net gains included in changes in net assets (realized/unrealized) 11.0 0.4 — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.1 ) — — — Settlements (a) (2.7 ) (3.7 ) 6.1 36.3 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at June 30 $11.0 $0.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Six Months Ended June 30 2020 2019 2020 2019 Beginning balance, January 1 $18.7 $9.0 $187.7 $119.4 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.8 (2.8 ) — — Transfers out of Level 3 — 2.5 — — Purchases 10.7 9.5 — — Sales (0.2 ) (0.1 ) — — Settlements (a) (5.6 ) (8.8 ) 6.4 95.2 Ending balance, June 30 $32.4 $9.3 $194.1 $214.6 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30 $8.8 ($0.9 ) $— $— (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 amounts received from the receivables sold.
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5
WPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 42.4 — 4.6 37.8 42.4 26.8 — 4.8 22.0 26.8 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 46.2 — 44.8 1.4 46.2 37.6 — 36.8 0.8 37.6 Long-term debt (incl. current maturities) 6,579.8 — 7,768.1 1.7 7,769.8 6,190.2 — 6,917.9 2.0 6,919.9 IPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $198.3 $198.3 $— $— $198.3 $5.4 $5.4 $— $— $5.4 Derivatives 37.0 — 3.3 33.7 37.0 22.3 — 2.8 19.5 22.3 Deferred proceeds 194.1 — — 194.1 194.1 187.7 — — 187.7 187.7 Liabilities: Derivatives 20.3 — 19.0 1.3 20.3 17.4 — 16.6 0.8 17.4 Long-term debt (incl. current maturities) 3,343.5 — 3,924.7 — 3,924.7 3,147.3 — 3,489.1 — 3,489.1 WPL June 30, 2020 December 31, 2019 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.4 $— $1.3 $4.1 $5.4 $4.5 $— $2.0 $2.5 $4.5 Liabilities: Derivatives 25.9 — 25.8 0.1 25.9 20.2 — 20.2 — 20.2 Long-term debt (incl. current maturities) 2,129.4 — 2,657.2 — 2,657.2 1,932.7 — 2,268.2 — 2,268.2
Fair Value Of Net Derivative Assets	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs June 30, 2020 $19.3 $17.1 $18.6 $13.8 $0.7 $3.3 December 31, 2019 14.6 6.6 13.6 5.1 1.0 1.5

Commitments And Contingencies (

Commitments And Contingencies (Tables)	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 .
MGP Site Estimated Future Costs And Recorded Liabilities	At June 30, 2020 , 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, which are not discounted, were as follows (in millions). At June 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $10 - $24 Current and non-current environmental liabilities 16 13
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 .
MGP Site Estimated Future Costs And Recorded Liabilities	At June 30, 2020 , 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, which are not discounted, were as follows (in millions). At June 30, 2020 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $12 - $29 $10 - $24 Current and non-current environmental liabilities 16 13
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At June 30, 2020 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $39 $38 $1 Natural gas 1,017 536 481 Coal (b) 101 62 39 Other (c) 113 54 28 $1,270 $690 $549 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million . (b) Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 .

Segments Of Business (Tables)

Segments Of Business (Tables)	6 Months Ended
	Jun. 30, 2020
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended June 30, 2020 Revenues $675.2 $58.9 $10.1 $744.2 $18.9 $763.1 Operating income 152.1 7.1 1.2 160.4 7.7 168.1 Net income attributable to Alliant Energy common shareowners 117.4 17.0 134.4 Three Months Ended June 30, 2019 Revenues $691.2 $65.2 $10.9 $767.3 $22.9 $790.2 Operating income 132.9 7.2 1.4 141.5 8.3 149.8 Net income attributable to Alliant Energy common shareowners 87.0 7.6 94.6 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Six Months Ended June 30, 2020 Revenues $1,405.5 $211.1 $21.7 $1,638.3 $40.5 $1,678.8 Operating income 298.3 48.7 3.9 350.9 5.5 356.4 Net income attributable to Alliant Energy common shareowners 289.6 14.8 304.4 Six Months Ended June 30, 2019 Revenues $1,434.6 $281.0 $22.0 $1,737.6 $39.8 $1,777.4 Operating income 259.3 52.4 1.4 313.1 13.5 326.6 Net income attributable to Alliant Energy common shareowners 206.0 13.7 219.7 IPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $388.4 $33.9 $9.6 $431.9 Operating income 82.1 5.2 1.4 88.7 Net income available for common stock 59.8 Three Months Ended June 30, 2019 Revenues $392.3 $38.4 $10.5 $441.2 Operating income 68.9 4.2 1.4 74.5 Net income available for common stock 45.0 Six Months Ended June 30, 2020 Revenues $813.2 $116.9 $20.7 $950.8 Operating income 149.1 32.5 3.8 185.4 Net income available for common stock 142.4 Six Months Ended June 30, 2019 Revenues $812.1 $163.0 $21.2 $996.3 Operating income 115.7 30.5 1.8 148.0 Net income available for common stock 98.3 WPL Electric Gas Other Total (in millions) Three Months Ended June 30, 2020 Revenues $286.8 $25.0 $0.5 $312.3 Operating income (loss) 70.0 1.9 (0.2 ) 71.7 Net income 57.6 Three Months Ended June 30, 2019 Revenues $298.9 $26.8 $0.4 $326.1 Operating income 64.0 3.0 — 67.0 Net income 42.0 Six Months Ended June 30, 2020 Revenues $592.3 $94.2 $1.0 $687.5 Operating income 149.2 16.2 0.1 165.5 Net income 147.2 Six Months Ended June 30, 2019 Revenues $622.5 $118.0 $0.8 $741.3 Operating income (loss) 143.6 21.9 (0.4 ) 165.1 Net income 107.7

Related Parties (Tables)

Related Parties (Tables)	6 Months Ended
	Jun. 30, 2020
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC billings to WPL $25 $27 $53 $54 WPL billings to ATC 3 3 6 7
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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85
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 and six months ended June 30 were as follows (in millions): IPL WPL Three Months Six Months Three Months Six Months 2020 2019 2020 2019 2020 2019 2020 2019 Corporate Services billings $44 $47 $81 $90 $35 $35 $67 $68 Sales credited 10 12 25 27 2 3 4 4 Purchases billed 57 74 138 158 20 29 40 59
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL June 30, 2020 December 31, 2019 June 30, 2020 December 31, 2019 Net payables to Corporate Services $93 $112 $65 $85
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and six months ended June 30 were as follows (in millions): Three Months Six Months 2020 2019 2020 2019 ATC billings to WPL $25 $27 $53 $54 WPL billings to ATC 3 3 6 7

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 198.3	$ 5.4
Money market fund investments interest rate, percentage	0.10%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 198.3	5.4
Money market fund investments interest rate, percentage	0.10%
Credit Losses ASU [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax		12
New accounting standard, cumulative effect adjustment to retained earnings, after-tax		$ 8.7

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Regulatory Matters [Line Items]
Credits issued to customers		$ (63.4)	$ (26.1)
Electric transmission cost recovery [Member] | IPL [Member]
Regulatory Matters [Line Items]
Credits issued to customers	$ 42

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory assets	$ 1,843	$ 1,844.7
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	842.5	817.6
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	501.2	524
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	122.9	134
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	114	111.8
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	109.4	108.2
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	47	39.5
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19.8	21.1
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	86.2	88.5
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,404.9	1,399.3
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	797.4	776.8
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	251.3	262.5
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	81.8	87.9
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	78.2	76.2
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	109.4	108.2
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	20.5	18.3
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19.8	21.1
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	46.5	48.3
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	438.1	445.4
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	45.1	40.8
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	249.9	261.5
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.1	46.1
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	35.8	35.6
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.5	21.2
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 39.7	$ 40.2

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,371	$ 1,423.6
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	779	835.6
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	385.8	387.7
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	66.3	88.6
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30.1	24.2
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	28.8	19.9
WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.4	21.9
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	60.6	45.7
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	717.9	714.7
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	343.6	350.9
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	256.4	257
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30.7	51.3
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	14	8.8
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26.3	17.4
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	46.9	29.3
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	653.1	708.9
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	435.4	484.7
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	129.4	130.7
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	35.6	37.3
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	16.1	15.4
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	2.5	2.5
WPL [Member] | WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.4	21.9
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 13.7	$ 16.4

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Jun. 30, 2020USD ($)
Receivables [Line Items]
Available capacity	$ 89
Outstanding receivables past due	$ 25.1

Receivables (Details of Account

Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Receivables [Line Items]
Customer	$ 92.7	$ 91.6
Unbilled utility revenues	68.2	82.1
Deferred proceeds	194.1	187.7
Other	41.5	48
Allowance for expected credit losses	(10)	(7.3)
Accounts receivable, less allowance for expected credit losses	386.5	402.1
IPL [Member]
Receivables [Line Items]
Customer	0	0
Unbilled utility revenues	0	0
Deferred proceeds	194.1	187.7
Other	16.5	16.3
Allowance for expected credit losses	(1.7)	(1.2)
Accounts receivable, less allowance for expected credit losses	208.9	202.8
WPL [Member]
Receivables [Line Items]
Customer	82.4	83.5
Unbilled utility revenues	68.2	82.1
Other	24.5	31.4
Allowance for expected credit losses	(8.2)	(6.1)
Accounts receivable, less allowance for expected credit losses	$ 166.9	$ 190.9

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 65	$ 25	$ 96	$ 108
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 11.1	$ 2.6	$ 17.3	$ 41.6

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Receivables [Line Items]
Fair value of deferred proceeds	$ 194.1	$ 187.7
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	194.1	187.7
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	113.5	124.7
Unbilled utility revenues	92.3	95.5
Other receivables	0.4	0.9
Receivables sold to third party	206.2	221.1
Less: cash proceeds	1	27
Deferred proceeds	205.2	194.1
Less: allowance for expected credit losses	11.1	6.4
Fair value of deferred proceeds	$ 194.1	$ 187.7

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Receivables [Line Items]
Collections	$ 453	$ 487.7	$ 994.4	$ 1,043.5
Write-offs, net of recoveries	$ 1.2	$ 2.6	$ 3.3	$ 8.1

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (17.4)	$ (12.7)	$ (30.8)	$ (23.6)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(13.5)	(10)	(24.5)	(19.5)
Non-utility wind farm in Oklahoma [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(1.9)	(1.3)	(4.1)	(2.4)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (2)	$ (1.4)	$ (2.2)	$ (1.7)

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Nov. 30, 2019	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Common Equity [Line Items]
Proceeds from issuance of common stock, net		$ 6.4		$ 6	$ 234.8	$ 60.6
Equity Forward Agreements [Member]
Common Equity [Line Items]
Common stock to be issued, equity forward agreements (in shares)	4,275,127
Forward sales price (in dollars per share)	$ 52.235		$ 51.98
Proceeds from issuance of common stock, net			$ 222
Common stock issued during the period, equity forward agreements (in shares)			4,275,127		4,275,127

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details) - shares	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2020
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2020 (in shares)	245,022,800	245,022,800
Shareowner Direct Plan (in shares)		248,220
Equity-based compensation plans (in shares)		98,205
Shares outstanding, June 30, 2020 (in shares)		249,644,352
Equity Forward Agreements [Member]
Common Stock Oustanding [Roll Forward]
Equity forward agreements (in shares)	4,275,127	4,275,127

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance		$ 5,205.1		$ 5,205.1
Beginning balance	$ 5,702.4	5,405.1	$ 4,882.4	5,405.1	$ 4,785.7
Net income attributable to common shareowners	134.4		94.6	304.4	219.7
Net income	136.9		97.1	309.5	224.8
Common stock dividends	(94.6)		(84.1)	(187.6)	(167.8)
Equity forward settlements and Shareowner Direct Plan issuances	6.4		6	234.8	60.6
Equity-based compensation plans and other	2.3		2.1	2.2	2.1
Adoption of new accounting standard, net of tax				(8.7)
Other comprehensive loss, net of tax	(2.6)		(1.4)	(1.9)	(0.7)
Ending balance	5,548.3			5,548.3
Ending balance	$ 5,748.3	5,702.4	$ 4,899.6	$ 5,748.3	$ 4,899.6
Common stock dividends (in dollars per share)	$ 0.38		$ 0.355	$ 0.76	$ 0.71
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 2.5	2.5	$ 2.4	$ 2.5	$ 2.4
Equity forward settlements and Shareowner Direct Plan issuances
Ending balance	2.5	2.5	2.4	2.5	2.4
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,674.1	2,445.9	2,100	2,445.9	2,045.5
Equity forward settlements and Shareowner Direct Plan issuances	6.4		6	234.8	60.6
Equity-based compensation plans and other	2.6		2.4	2.4	2.3
Ending balance	2,683.1	2,674.1	2,108.4	2,683.1	2,108.4
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,833.7	2,765.4	2,587.3	2,765.4	2,545.9
Net income attributable to common shareowners	134.4		94.6	304.4	219.7
Common stock dividends	(94.6)		(84.1)	(187.6)	(167.8)
Ending balance	2,873.5	2,833.7	2,597.8	2,873.5	2,597.8
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2	1.3	2.4	1.3	1.7
Other comprehensive loss, net of tax	(2.6)		(1.4)	(1.9)	(0.7)
Ending balance	(0.6)	2	1	(0.6)	1
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(9.9)	(10)	(9.7)	(10)	(9.8)
Equity-based compensation plans and other	(0.3)		(0.3)	(0.2)	(0.2)
Ending balance	(10.2)	(9.9)	(10)	(10.2)	(10)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200	200
Ending balance	200	200	200	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance		3,271.8		3,271.8
Beginning balance	3,595.4	3,471.8	3,342	3,471.8	3,230.7
Net income attributable to common shareowners	59.8		45	142.4	98.3
Net income	62.3		47.5	147.5	103.4
Common stock dividends	(59.1)		(41.9)	(118.1)	(83.9)
Capital contributions from parent	75			175	100
Ending balance	3,471.1			3,471.1
Ending balance	3,671.1	3,595.4	3,345.1	3,671.1	3,345.1
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33.4	33.4	33.4	33.4	33.4
Ending balance	33.4	33.4	33.4	33.4	33.4
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,447.8	2,347.8	2,322.8	2,347.8	2,222.8
Capital contributions from parent	75			175	100
Ending balance	2,522.8	2,447.8	2,322.8	2,522.8	2,322.8
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	914.2	890.6	785.8	890.6	774.5
Net income attributable to common shareowners	59.8		45	142.4	98.3
Common stock dividends	(59.1)		(41.9)	(118.1)	(83.9)
Ending balance	914.9	914.2	788.9	914.9	788.9
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200	200
Ending balance	200	200	200	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance		2,363.6		2,363.6
Beginning balance	2,436.1	2,363.6	2,179.2	2,363.6	2,149.5
Net income	57.6		42	147.2	107.7
Common stock dividends	(41.9)		(36)	(84)	(72)
Capital contributions from parent				25	0
Ending balance	2,451.8			2,451.8
Ending balance	2,451.8	2,436.1	2,185.2	2,451.8	2,185.2
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66.2	66.2	66.2	66.2	66.2
Ending balance	66.2	66.2	66.2	66.2	66.2
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,459	1,434	1,309	1,434	1,309
Capital contributions from parent				25
Ending balance	1,459	1,459	1,309	1,459	1,309
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	910.9	863.4	804	863.4	774.3
Net income	57.6		42	147.2	107.7
Common stock dividends	(41.9)		(36)	(84)	(72)
Ending balance	$ 926.6	$ 910.9	$ 810	926.6	$ 810
Credit Losses ASU [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax				$ (8.7)

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended			6 Months Ended
	Jun. 30, 2020	Apr. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019
Debt [Line Items]
Payments to retire long-term debt				$ 653.7	$ 3.4
IPL [Member]
Debt [Line Items]
Payments to retire long-term debt				200	0
WPL [Member]
Debt [Line Items]
Payments to retire long-term debt				$ 150	$ 0
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through March 2022 [Member] | Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt			$ 300
Interest rate, percent	1.00%			1.00%
Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through April 2020 [Member] | Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Payments to retire long-term debt			$ 300
Debentures [Member] | 3.65% debenture, due 2050 [Member] | WPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt		$ 350
Interest rate, percent		3.65%
Debentures [Member] | 4.6% debenture, due 2020 [Member] | WPL [Member]
Debt [Line Items]
Interest rate, percent	4.60%			4.60%
Payments to retire long-term debt	$ 150
Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member] | IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 400
Interest rate, percent	2.30%			2.30%
Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member] | IPL [Member]
Debt [Line Items]
Interest rate, percent	3.65%			3.65%
Payments to retire long-term debt	$ 200

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Jun. 30, 2020USD ($)
Debt [Line Items]
Amount outstanding	$ 185.4
Weighted average interest rates	0.30%
Available credit facility capacity	$ 814.6
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 37.9
Weighted average interest rates	0.20%
Available credit facility capacity	$ 262.1

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 270.5	$ 590.2	$ 462.5	$ 600.6
Average amount outstanding (based on daily outstanding balances)	$ 121.2	$ 531.7	$ 251.8	$ 515.4
Weighted average interest rates	0.50%	2.70%	1.50%	2.70%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 8.4	$ 0	$ 8.4	$ 50.4
Average amount outstanding (based on daily outstanding balances)	$ 0.4	0	$ 0.2	$ 0.3
Weighted average interest rates	0.50%		0.50%	2.80%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 182	193.3	$ 212	$ 195.1
Average amount outstanding (based on daily outstanding balances)	$ 8.7	$ 141.6	$ 87.9	$ 139.8
Weighted average interest rates	0.50%	2.50%	1.70%	2.50%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 763.1	$ 790.2	$ 1,678.8	$ 1,777.4
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	675.2	691.2	1,405.5	1,434.6
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	249.7	233.3	516.5	508
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	164	171.3	346.3	352.4
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	197.3	214.2	407.2	422.9
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39.1	41	80	87.5
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25.1	31.4	55.5	63.8
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	58.9	65.2	211.1	281
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	33.6	35.2	124.1	167
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14.7	16.1	60.4	79.7
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.7	2	5.9	7.4
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.9	11.9	20.7	26.9
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10.1	10.9	21.7	22
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.6	9.2	18.6	17.6
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.5	1.7	3.1	4.4
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18.9	22.9	40.5	39.8
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18.9	22.9	40.5	39.8
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	431.9	441.2	950.8	996.3
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	388.4	392.3	813.2	812.1
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	135.3	125.9	282.7	273.4
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	109	111.4	228.7	228
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	114.3	118.4	235.5	234.5
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14.6	27.4	31.5
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.8	22	38.9	44.7
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	33.9	38.4	116.9	163
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18.5	20	67.3	97.9
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.3	8.8	32.4	43.6
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.3	1.6	3.6	4.8
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5.8	8	13.6	16.7
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9.6	10.5	20.7	21.2
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.6	9.2	18.6	17.6
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1.3	2.1	3.6
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	312.3	326.1	687.5	741.3
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	286.8	298.9	592.3	622.5
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	114.4	107.4	233.8	234.6
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	59.9	117.6	124.4
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	83	95.8	171.7	188.4
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	26.1	26.4	52.6	56
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.3	9.4	16.6	19.1
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	25	26.8	94.2	118
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15.1	15.2	56.8	69.1
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6.4	7.3	28	36.1
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.4	0.4	2.3	2.6
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3.1	3.9	7.1	10.2
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.5	0.4	1	0.8
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0.5	$ 0.4	$ 1	$ 0.8

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Effective Tax Rate [Line Items]
Overall income tax rate	(6.50%)	10.30%	(9.60%)	10.50%
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(6.50%)	3.80%	(13.80%)	3.70%
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(8.50%)	15.50%	(9.40%)	17.20%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2020USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 299
Tax credits, carryforward amount	403
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	276
Tax credits, carryforward amount	212
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Tax credits, carryforward amount	170
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	595
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	9
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 9.9
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
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 5.5
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 4.1
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	228,207

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 2.7	$ 2.4	$ 5.4	$ 4.8
Interest cost		10.8	12.4	21.6	24.9
Expected return on plan assets		(17.5)	(15)	(34.9)	(30)
Amortization of prior service credit		(0.1)	(0.1)	(0.3)	(0.3)
Amortization of actuarial loss		8.6	9.1	17.2	18.2
Settlement losses	[1]	0	0	4.2	0
Total		4.5	8.8	13.2	17.6
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.9	0.9	1.7	1.7
Interest cost		1.7	2.1	3.5	4.2
Expected return on plan assets		(1.4)	(1.3)	(2.7)	(2.5)
Amortization of prior service credit		0	(0.1)	0	(0.1)
Amortization of actuarial loss		0.9	0.8	1.7	1.6
Settlement losses		0	0	0	0
Total		2.1	2.4	4.2	4.9
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		1.7	1.5	3.4	3
Interest cost		5	5.7	10	11.4
Expected return on plan assets		(8.2)	(7.1)	(16.3)	(14.1)
Amortization of prior service credit		0	0	(0.1)	(0.1)
Amortization of actuarial loss		3.7	4	7.4	7.9
Total		2.2	4.1	4.4	8.1
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.4	0.4	0.7	0.7
Interest cost		0.7	0.9	1.4	1.7
Expected return on plan assets		(0.9)	(0.9)	(1.9)	(1.8)
Amortization of prior service credit		0	0	0	0
Amortization of actuarial loss		0.2	0.3	0.5	0.7
Total		0.4	0.7	0.7	1.3
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.9	0.8	1.9	1.7
Interest cost		4.7	5.4	9.4	10.8
Expected return on plan assets		(7.6)	(6.6)	(15.2)	(13.1)
Amortization of prior service credit		0	0	(0.1)	(0.1)
Amortization of actuarial loss		4.1	4.4	8.2	8.8
Total		2.1	4	4.2	8.1
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.3	0.3	0.6	0.6
Interest cost		0.7	0.9	1.4	1.7
Expected return on plan assets		(0.1)	(0.2)	(0.3)	(0.3)
Amortization of prior service credit		0	(0.1)	0	(0.1)
Amortization of actuarial loss		0.5	0.4	1	0.8
Total		$ 1.4	$ 1.3	$ 2.7	$ 2.7
[1]	Settlement losses related to payments made to retired executives of Alliant Energy.

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Compensation expense	$ 2.7	$ 3.4	$ 5.4	$ 8.1
Income tax benefits	0.8	1	1.5	2.3
IPL [Member]
Compensation expense	1.5	1.9	2.9	4.5
Income tax benefits	0.4	0.5	0.8	1.3
WPL [Member]
Compensation expense	1.2	1.4	2.3	3.2
Income tax benefits	$ 0.3	$ 0.4	$ 0.6	$ 0.9

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	55,303
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 64.04
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	55,303
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 59.47
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	60,284
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 59.49

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 196.3
Revisions in estimated cash flows	0.9
Liabilities settled	(3.5)
Liabilities incurred	27.6	[1]
Accretion expense	3.5
Balance, June 30	224.8
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	133.9
Revisions in estimated cash flows	0
Liabilities settled	(2.8)
Liabilities incurred	27.6	[1]
Accretion expense	2.5
Balance, June 30	$ 161.2
[1]	During the six months ended June 30 , 2020, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Whispering Willow North and Golden Plains wind sites. The increases in asset retirement obligations resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands, T in Thousands, MWh in Thousands, Dekatherms in Thousands	6 Months Ended
	Jun. 30, 2020DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	21,455
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	8,978
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	12,477
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	234,304
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	123,308
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	110,996
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,482
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	1,834
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	2,648
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	6,804
Diesel Fuel (Gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	0
Diesel Fuel (Gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	6,804

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 27.9	$ 15.8
Non-current derivative assets	14.5	11
Current derivative liabilities	20	19
Non-current derivative liabilities	26.2	18.6
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	22.5	12.1
Non-current derivative assets	14.5	10.2
Current derivative liabilities	8.5	8.9
Non-current derivative liabilities	11.8	8.5
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	5.4	3.7
Non-current derivative assets	0	0.8
Current derivative liabilities	11.5	10.1
Non-current derivative liabilities	$ 14.4	$ 10.1

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets:
Money market fund investments	$ 198.3	$ 5.4
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	7,769.8	6,919.9
IPL [Member]
Assets:
Money market fund investments	198.3	5.4
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	3,924.7	3,489.1
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,657.2	2,268.2
Commodity Contracts [Member]
Assets:
Derivatives	42.4	26.8
Liabilities:
Derivatives	46.2	37.6
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	37	22.3
Liabilities:
Derivatives	20.3	17.4
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	5.4	4.5
Liabilities:
Derivatives	25.9	20.2
Level 1 [Member]
Assets:
Money market fund investments	198.3	5.4
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	198.3	5.4
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	7,768.1	6,917.9
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,924.7	3,489.1
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,657.2	2,268.2
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	4.6	4.8
Liabilities:
Derivatives	44.8	36.8
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	3.3	2.8
Liabilities:
Derivatives	19	16.6
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	1.3	2
Liabilities:
Derivatives	25.8	20.2
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	1.7	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	37.8	22
Liabilities:
Derivatives	1.4	0.8
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	33.7	19.5
Liabilities:
Derivatives	1.3	0.8
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	4.1	2.5
Liabilities:
Derivatives	0.1	0
Carrying Amount [Member]
Assets:
Money market fund investments	198.3	5.4
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	6,579.8	6,190.2
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	198.3	5.4
Deferred proceeds	194.1	187.7
Liabilities:
Long-term debt (incl. current maturities)	3,343.5	3,147.3
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,129.4	1,932.7
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	42.4	26.8
Liabilities:
Derivatives	46.2	37.6
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	37	22.3
Liabilities:
Derivatives	20.3	17.4
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	5.4	4.5
Liabilities:
Derivatives	$ 25.9	$ 20.2

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 14.2	$ 0.4	$ 21.2	$ 12.2
Total net gains (losses) included in changes in net assets (realized/unrealized)		12	(0.1)	9	(5.7)
Transfers out of Level 3		0	3.9	0	3.9
Purchases		14	13.8	14	13.8
Sales		(0.1)	0	(0.2)	(0.2)
Settlements		(3.7)	(4.8)	(7.6)	(10.8)
Ending balance		36.4	13.2	36.4	13.2
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 June 30		11.9	0	9	(2.6)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		13.5	0.6	18.7	9
Total net gains (losses) included in changes in net assets (realized/unrealized)		11	0.4	8.8	(2.8)
Transfers out of Level 3		0	2.5	0	2.5
Purchases		10.7	9.5	10.7	9.5
Sales		(0.1)	0	(0.2)	(0.1)
Settlements		(2.7)	(3.7)	(5.6)	(8.8)
Ending balance		32.4	9.3	32.4	9.3
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 June 30		11	0.5	8.8	(0.9)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		188	178.3	187.7	119.4
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0	0	0
Transfers out of Level 3		0	0	0	0
Purchases		0	0	0	0
Sales		0	0	0	0
Settlements	[1]	6.1	36.3	6.4	95.2
Ending balance		194.1	214.6	194.1	214.6
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30		0	0	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		188	178.3	187.7	119.4
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0	0	0
Transfers out of Level 3		0	0	0	0
Purchases		0	0	0	0
Sales		0	0	0	0
Settlements	[1]	6.1	36.3	6.4	95.2
Ending balance		194.1	214.6	194.1	214.6
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at June 30		$ 0	$ 0	$ 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 amounts received from the receivables sold.

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 36.4	$ 14.2	$ 21.2	$ 13.2	$ 0.4	$ 12.2
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	19.3		14.6
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	17.1		6.6
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	32.4	$ 13.5	18.7	$ 9.3	$ 0.6	$ 9
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	18.6		13.6
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	13.8		5.1
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	0.7		1
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 3.3		$ 1.5

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
		May 31, 2020	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Commitments and Contingencies [Line Items]
Minimum future commitments				$ 1,270
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				690
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				549
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				60
Capital Purchase Commitment [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				8
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				52
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			39
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			38
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			1
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			$ 82	82
Indemnification Agreement [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			17	17
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			17	$ 17
Workforce Subject to Collective Bargaining Arrangements [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement				53.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement				60.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement				82.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement				18.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement				44.00%
Credit Losses ASU [Member]
Commitments and Contingencies [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax					$ 12
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent				6.00%
Obligations, maximum			63	$ 63
Credit loss liability			20	20
Credit loss expense			0	$ 8
Whiting Petroleum Affiliate [Member] | Credit Losses ASU [Member]
Commitments and Contingencies [Line Items]
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax					$ 12
FederalEnergyRegulatoryCommission [Member]
Commitments and Contingencies [Line Items]
MISO base return on equity, percentage		10.02%			9.88%
FederalEnergyRegulatoryCommission [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Refunds related to MISO base return on equity complaints			10
FederalEnergyRegulatoryCommission [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Refunds related to MISO base return on equity complaints			$ 3
[1]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million .

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) - USD ($) $ in Millions		1 Months Ended	6 Months Ended
		Sep. 30, 2020	Jun. 30, 2020
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,270
Individual commitments incurred			1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			690
Individual commitments incurred			1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			549
Individual commitments incurred			1
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		39
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		38
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			1,017
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			536
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			481
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		101
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		62
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		39
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		113
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		54
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		$ 28
Forecast [Member] | DAEC PPA [Member]
Commitments and Contingencies [Line Items]
Buyout payment		$ 110
[1]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million .
[2]	Corporate Services has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of June 30, 2020 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 June 30, 2020 .

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 16
IPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	13
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	12
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	10
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	29
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 24

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 763.1	$ 790.2	$ 1,678.8	$ 1,777.4
Operating income (loss)	168.1	149.8	356.4	326.6
Net income attributable to common shareowners	134.4	94.6	304.4	219.7
Net income	136.9	97.1	309.5	224.8
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	431.9	441.2	950.8	996.3
Operating income (loss)	88.7	74.5	185.4	148
Net income attributable to common shareowners	59.8	45	142.4	98.3
Net income	62.3	47.5	147.5	103.4
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	312.3	326.1	687.5	741.3
Operating income (loss)	71.7	67	165.5	165.1
Net income	57.6	42	147.2	107.7
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	675.2	691.2	1,405.5	1,434.6
Operating income (loss)	152.1	132.9	298.3	259.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	388.4	392.3	813.2	812.1
Operating income (loss)	82.1	68.9	149.1	115.7
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	286.8	298.9	592.3	622.5
Operating income (loss)	70	64	149.2	143.6
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	58.9	65.2	211.1	281
Operating income (loss)	7.1	7.2	48.7	52.4
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	33.9	38.4	116.9	163
Operating income (loss)	5.2	4.2	32.5	30.5
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	25	26.8	94.2	118
Operating income (loss)	1.9	3	16.2	21.9
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10.1	10.9	21.7	22
Operating income (loss)	1.2	1.4	3.9	1.4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	9.6	10.5	20.7	21.2
Operating income (loss)	1.4	1.4	3.8	1.8
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.5	0.4	1	0.8
Operating income (loss)	(0.2)	0	0.1	(0.4)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	744.2	767.3	1,638.3	1,737.6
Operating income (loss)	160.4	141.5	350.9	313.1
Net income attributable to common shareowners	117.4	87	289.6	206
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	18.9	22.9	40.5	39.8
Operating income (loss)	7.7	8.3	5.5	13.5
Net income attributable to common shareowners	$ 17	$ 7.6	$ 14.8	$ 13.7

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
WPL Owed ATC LLC [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 9	$ 9
WPL [Member]
Related Party Transactions [Line Items]
Receipt of construction deposits	$ 46

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 44	$ 47	$ 81	$ 90
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	35	35	67	68
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	10	12	25	27
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	2	3	4	4
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	57	74	138	158
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 20	$ 29	$ 40	$ 59

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 93	$ 112
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 65	$ 85

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 25	$ 27	$ 53	$ 54
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 3	$ 3	$ 6	$ 7