Wisconsin Power & Light 10-Q 7 Nov 19 2019 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2019shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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	240,342,949
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Electric utility	$ 915.9	$ 861.2	$ 2,350.5	$ 2,296.2
Gas utility	41.5	44.8	322.5	299
Other utility	11.2	12.3	33.2	36.2
Non-utility	21.6	10.3	61.4	29.6
Total revenues	990.2	928.6	2,767.6	2,661
Operating expenses:
Electric production fuel and purchased power	218.5	227.8	601.7	639.5
Electric transmission service	127.5	129.1	362.9	375.2
Cost of gas sold	9.1	11.3	151.1	150
Other operation and maintenance	173.7	148.4	527.2	468.8
Depreciation and amortization	143.8	129	423.6	376.4
Taxes other than income taxes	27.4	26.9	84.3	78.1
Total operating expenses	700	672.5	2,150.8	2,088
Operating income	290.2	256.1	616.8	573
Other (income) and deductions:
Interest expense	68.3	63.3	203.8	183.8
Equity income from unconsolidated investments, net	(11.6)	(9.8)	(35.2)	(41.6)
Allowance for funds used during construction	(21.9)	(18.8)	(65.6)	(51.8)
Other	3.7	1.6	11	6
Total other (income) and deductions	38.5	36.3	114	96.4
Income before income taxes	251.7	219.8	502.8	476.6
Income tax expense (benefit)	23.1	11.7	49.4	42.1
Net income	228.6	208.1	453.4	434.5
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	$ 226	$ 205.5	$ 445.7	$ 426.8
Weighted average number of common shares outstanding (basic) (in shares)	239.1	235.2	237.7	232.9
Weighted average number of common shares outstanding (diluted) (in shares)	239.9	235.2	238.2	232.9
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic) (in dollars per share)	$ 0.95	$ 0.87	$ 1.88	$ 1.83
Earnings per weighted average common share attributable to Alliant Energy common shareowners (diluted) (in dollars per share)	$ 0.94	$ 0.87	$ 1.87	$ 1.83
IPL [Member]
Revenues:
Electric utility	$ 560.9	$ 509.2	$ 1,373	$ 1,337
Gas utility	24.8	26.7	187.8	177
Other utility	10.8	11.7	32	34.2
Total revenues	596.5	547.6	1,592.8	1,548.2
Operating expenses:
Electric production fuel and purchased power	126.8	122.5	339	354
Electric transmission service	91.8	92.8	256.9	268
Cost of gas sold	5.9	6.4	80	83.8
Other operation and maintenance	100.2	94.6	305.6	297.1
Depreciation and amortization	83.7	73.9	243.4	209.2
Taxes other than income taxes	14.6	14.3	46.4	39.7
Total operating expenses	423	404.5	1,271.3	1,251.8
Operating income	173.5	143.1	321.5	296.4
Other (income) and deductions:
Interest expense	31.7	30.4	92.6	90.6
Allowance for funds used during construction	(10.8)	(11)	(34.5)	(28.3)
Other	2	0.5	5.4	2
Total other (income) and deductions	22.9	19.9	63.5	64.3
Income before income taxes	150.6	123.2	258	232.1
Income tax expense (benefit)	6.9	(5.9)	10.9	(0.5)
Net income	143.7	129.1	247.1	232.6
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
WPL [Member]
Revenues:
Electric utility	355	352	977.5	959.2
Gas utility	16.7	18.1	134.7	122
Other utility	0.4	0.6	1.2	2
Total revenues	372.1	370.7	1,113.4	1,083.2
Operating expenses:
Electric production fuel and purchased power	91.7	105.3	262.7	285.5
Electric transmission service	35.7	36.3	106	107.2
Cost of gas sold	3.2	4.9	71.1	66.2
Other operation and maintenance	62.3	54.2	188.2	172.8
Depreciation and amortization	58.9	54.1	176.6	164.2
Taxes other than income taxes	12	11.7	35.4	35.7
Total operating expenses	263.8	266.5	840	831.6
Operating income	108.3	104.2	273.4	251.6
Other (income) and deductions:
Interest expense	25.4	24.2	77.3	73.5
Allowance for funds used during construction	(11.1)	(7.8)	(31.1)	(23.5)
Other	1.4	1.3	4.6	3.4
Total other (income) and deductions	15.7	17.7	50.8	53.4
Income before income taxes	92.6	86.5	222.6	198.2
Income tax expense (benefit)	17.1	10.2	39.4	28.1
Net income			183.2	170.1
Net income attributable to common shareowners	$ 75.5	$ 76.3	$ 183.2	$ 170.1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 193.7	$ 20.9
Accounts receivable, less allowance for doubtful accounts	451.5	350.4
Production fuel, at weighted average cost	71.1	61.4
Gas stored underground, at weighted average cost	46.1	49
Materials and supplies, at weighted average cost	106.9	101.4
Regulatory assets	76.3	79.8
Prepaid gross receipts tax	30.3	42.2
Other	137.1	80
Total current assets	1,113	785.1
Property, plant and equipment, net	13,131.1	12,462.4
Investments:
ATC Holdings	309.1	293.6
Other	143.9	137.7
Total investments	453	431.3
Other assets:
Regulatory assets	1,763.7	1,657.5
Deferred charges and other	72.6	89.7
Total other assets	1,836.3	1,747.2
Total assets	16,533.4	15,426
Current liabilities:
Current maturities of long-term debt	656.8	256.5
Commercial paper	349.6	441.2
Accounts payable	497.7	543.3
Regulatory liabilities	188.9	142.7
Other	389.1	260.4
Total current liabilities	2,082.1	1,644.1
Long-term debt, net (excluding current portion)	5,535.1	5,246.3
Other liabilities:
Deferred tax liabilities	1,703	1,603.1
Regulatory liabilities	1,262.1	1,350.5
Pension and other benefit obligations	476.3	509.1
Other	305.6	287.2
Total other liabilities	3,747	3,749.9
Commitments and contingencies (Note 14)
Common equity:
Common stock	2.4	2.4
Additional paid-in capital	2,236.9	2,045.5
Retained earnings	2,739.1	2,545.9
Accumulated other comprehensive income	1	1.7
Shares in deferred compensation trust - 385,343 and 384,580 shares at a weighted average cost of $26.52 and $25.60 per share	(10.2)	(9.8)
Total common equity	4,969.2	4,585.7
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	5,169.2	4,785.7
Total liabilities and equity	16,533.4	15,426
IPL [Member]
Current assets:
Cash and cash equivalents	184	9.7
Accounts receivable, less allowance for doubtful accounts	258.3	153.5
Production fuel, at weighted average cost	40.3	44.8
Gas stored underground, at weighted average cost	21.6	26.1
Materials and supplies, at weighted average cost	60.3	55.4
Regulatory assets	34.6	39.2
Other	22.1	43.1
Total current assets	621.2	371.8
Property, plant and equipment, net	7,283.9	6,781.5
Other assets:
Regulatory assets	1,369.4	1,239.8
Deferred charges and other	28.1	18.3
Total other assets	1,397.5	1,258.1
Total assets	9,302.6	8,411.4
Current liabilities:
Current maturities of long-term debt	200	0
Commercial paper	0	50.4
Accounts payable	290	304.9
Accounts payable to associated companies	40.7	28.8
Regulatory liabilities	95.5	90
Accrued taxes	58.7	45.8
Other	197.7	87.2
Total current liabilities	882.6	607.1
Long-term debt, net (excluding current portion)	2,946.8	2,552.3
Other liabilities:
Deferred tax liabilities	974.9	957.3
Regulatory liabilities	638.1	664.9
Pension and other benefit obligations	165.1	178.4
Other	251	220.7
Total other liabilities	2,029.1	2,021.3
Commitments and contingencies (Note 14)
Common equity:
Common stock	33.4	33.4
Additional paid-in capital	2,322.8	2,222.8
Retained earnings	887.9	774.5
Total common equity	3,244.1	3,030.7
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,444.1	3,230.7
Total liabilities and equity	9,302.6	8,411.4
WPL [Member]
Current assets:
Cash and cash equivalents	8.3	8.7
Accounts receivable, less allowance for doubtful accounts	184.3	190.1
Production fuel, at weighted average cost	30.8	16.6
Gas stored underground, at weighted average cost	24.5	22.9
Materials and supplies, at weighted average cost	43.7	42.9
Regulatory assets	41.7	40.6
Prepaid gross receipts tax	30.3	42.2
Other	86.6	20.6
Total current assets	450.2	384.6
Property, plant and equipment, net	5,449.7	5,287.3
Other assets:
Regulatory assets	394.3	417.7
Deferred charges and other	19.5	62.9
Total other assets	413.8	480.6
Total assets	6,313.7	6,152.5
Current liabilities:
Current maturities of long-term debt	150	250
Commercial paper	0	105.5
Accounts payable	151.1	180.9
Regulatory liabilities	93.4	52.7
Other	113.6	105.5
Total current liabilities	508.1	694.6
Long-term debt, net (excluding current portion)	1,782.3	1,584.9
Other liabilities:
Deferred tax liabilities	652.6	582
Regulatory liabilities	624	685.6
Finance lease obligations - Sheboygan Falls Energy Facility	53.6	60
Pension and other benefit obligations	203.5	217.7
Other	164.8	178.2
Total other liabilities	1,698.5	1,723.5
Commitments and contingencies (Note 14)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,409	1,309
Retained earnings	849.6	774.3
Total common equity	2,324.8	2,149.5
Total equity	2,324.8	2,149.5
Total liabilities and equity	$ 6,313.7	$ 6,152.5

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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)	240,342,949	236,063,279
Shares in deferred compensation trust (in shares)	385,343	384,580
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 26.52	$ 25.60
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	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 453.4	$ 434.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	423.6	376.4
Deferred tax expense and tax credits	53.2	62.5
Equity component of allowance for funds used during construction	(46.3)	(35.5)
Other	17.1	2.1
Other changes in assets and liabilities:
Accounts receivable	(359.2)	(325.2)
Accounts payable	(27.9)	(47.3)
Deferred income taxes	45.4	32.7
Other	(50.1)	(58)
Net cash flows from operating activities	509.2	442.2
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(1,003.9)	(1,080.2)
Other construction and acquisition expenditures	(71.4)	(47.8)
Cash receipts on sold receivables	255.9	337.2
Other	(41.7)	(24.9)
Net cash flows used for investing activities	(861.1)	(815.7)
Cash flows from (used for) financing activities:
Common stock dividends	(252.5)	(233.3)
Proceeds from issuance of common stock, net	185.4	191.3
Proceeds from issuance of long-term debt	950	1,500
Payments to retire long-term debt	(253.5)	(603.1)
Net change in commercial paper and other short-term borrowings	(91.6)	(278.4)
Other	(11.7)	10.9
Net cash flows from (used for) financing activities	526.1	587.4
Net increase (decrease) in cash, cash equivalents and restricted cash	174.2	213.9
Cash, cash equivalents and restricted cash at beginning of period	25.5	33.9
Cash, cash equivalents and restricted cash at end of period	199.7	247.8
Supplemental cash flows information:
Interest	(194.7)	(171.6)
Income taxes, net	0.8	(5)
Significant non-cash investing and financing activities:
Accrued capital expenditures	254.2	236.2
Beneficial interest obtained in exchange for securitized accounts receivable	237	243.7
IPL [Member]
Cash flows from operating activities:
Net income	247.1	232.6
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	243.4	209.2
Equity component of allowance for funds used during construction	(24.6)	(19.3)
Other	(13.2)	0.7
Other changes in assets and liabilities:
Accounts receivable	(365)	(353.2)
Accounts payable	(14)	(34.5)
Deferred income taxes	31.5	22.9
Other	33.3	(19.5)
Net cash flows from operating activities	138.5	38.9
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(696.3)	(635.2)
Cash receipts on sold receivables	255.9	337.2
Other	(43.7)	(30.9)
Net cash flows used for investing activities	(484.1)	(328.9)
Cash flows from (used for) financing activities:
Common stock dividends	(126)	(125.9)
Capital contributions from parent	100	230
Proceeds from issuance of long-term debt	600	500
Payments to retire long-term debt	0	(100)
Net change in commercial paper and other short-term borrowings	(50.4)	0
Other	(5.1)	15
Net cash flows from (used for) financing activities	518.5	519.1
Net increase (decrease) in cash, cash equivalents and restricted cash	172.9	229.1
Cash, cash equivalents and restricted cash at beginning of period	12.4	7.2
Cash, cash equivalents and restricted cash at end of period	185.3	236.3
Supplemental cash flows information:
Interest	(93.9)	(89.1)
Income taxes, net	8.2	(2.4)
Significant non-cash investing and financing activities:
Accrued capital expenditures	180.2	142.4
Beneficial interest obtained in exchange for securitized accounts receivable	237	243.7
WPL [Member]
Cash flows from operating activities:
Net income	183.2	170.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	176.6	164.2
Deferred tax expense and tax credits	54.6	50.3
Other	(7.8)	(12)
Other changes in assets and liabilities:
Accounts receivable	3.8	29.7
Regulatory liabilities	(28.6)	7.2
Other	(22.2)	(64)
Net cash flows from operating activities	359.6	345.5
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(307.6)	(445)
Other	(27.3)	(23.7)
Net cash flows used for investing activities	(334.9)	(468.7)
Cash flows from (used for) financing activities:
Common stock dividends	(107.9)	(105)
Capital contributions from parent	100	200
Proceeds from issuance of long-term debt	350	0
Payments to retire long-term debt	(250)	0
Net change in commercial paper and other short-term borrowings	(105.5)	13.4
Other	(10.9)	(1.7)
Net cash flows from (used for) financing activities	(24.3)	106.7
Net increase (decrease) in cash, cash equivalents and restricted cash	0.4	(16.5)
Cash, cash equivalents and restricted cash at beginning of period	9.2	24.2
Cash, cash equivalents and restricted cash at end of period	9.6	7.7
Supplemental cash flows information:
Interest	(73.9)	(68.5)
Income taxes, net	(7)	(11.2)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 70.3	$ 86.2

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019 . 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 September 30, 2019 , Alliant Energy’s and IPL’s cash and cash equivalents included $174.4 million and $173.7 million of money market fund investments, with interest rates of 2.0% and 2.0% , respectively. NOTE 1(c) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term. 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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.
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 nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019 . 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 September 30, 2019 , Alliant Energy’s and IPL’s cash and cash equivalents included $174.4 million and $173.7 million of money market fund investments, with interest rates of 2.0% and 2.0% , respectively. NOTE 1(c) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term. 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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.
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 nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019 . 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 September 30, 2019 , Alliant Energy’s and IPL’s cash and cash equivalents included $174.4 million and $173.7 million of money market fund investments, with interest rates of 2.0% and 2.0% , respectively. NOTE 1(c) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term. 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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2019
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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3 Assets Retired Early - Upon completion of the phased installation of advanced metering infrastructure, IPL retired certain analog electric meters in September 2019 and reclassified the $36 million remaining net book value of these meters from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Recovery of these retired meters is included in the settlement agreement for IPL’s current retail electric base rate increase, and the IUB will decide on the recovery of these assets with the current retail electric rate review decision. IPL’s DAEC PPA Amendment - In January 2019, IPL incurred an obligation to make a September 2020 buyout payment of $110 million in exchange for shortening the term of IPL’s DAEC nuclear generation PPA by 5 years. The IUB approved placing the buyout payment in a regulatory asset account, which will be recovered from IPL’s retail customers over a 5 -year period following the payment. The offsetting obligation has been discounted and is recorded in “Other current liabilities” on Alliant Energy’s and IPL’s balance sheets. Utility Rate Reviews IPL’s Retail Electric Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers based on a 2020 forward-looking Test Period. The key drivers for IPL’s request included recovery of capital projects, including new wind generation. IPL concurrently filed for interim retail electric rates based on 2018 historical data as adjusted for certain known and measurable changes occurring in the first quarter of 2019. An interim retail electric base rate increase of $90 million , on an annual basis, was implemented effective April 1, 2019. Implementing interim rates does not require regulatory approval; however, interim rates are subject to refund pending the IUB’s final rate review decision. In October 2019, IPL reached a partial, non-unanimous settlement agreement with intervenor groups for an annual retail electric base rate increase of $127 million . The agreement includes both the recovery of and a return on IPL’s early retired EGUs, and the recovery of IPL’s retired analog electric meters. The settlement agreement also includes IPL providing billing credits over a 12 -month period beginning with final rates, including $27 million of excess deferred taxes resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform and $8 million from a partial refund of interim rates implemented in 2019. The IUB generally must decide on requests for retail rate changes within 10 months of the date of the application for which changes are filed. IPL currently expects a final decision, including a decision on the settlement agreement, from the IUB in the fourth quarter of 2019 with final rates effective in the first quarter of 2020. IPL’s Retail Gas Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers based on a 2020 forward-looking Test Period. The key drivers for IPL’s request included recovery of capital projects. In October 2019, IPL reached a unanimous settlement agreement with intervenor groups for an annual retail gas base rate increase of $12 million . IPL currently expects a decision, including a decision on the settlement agreement, from the IUB in the fourth quarter of 2019 with final rates effective in the first quarter of 2020.
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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3 Assets Retired Early - Upon completion of the phased installation of advanced metering infrastructure, IPL retired certain analog electric meters in September 2019 and reclassified the $36 million remaining net book value of these meters from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Recovery of these retired meters is included in the settlement agreement for IPL’s current retail electric base rate increase, and the IUB will decide on the recovery of these assets with the current retail electric rate review decision. IPL’s DAEC PPA Amendment - In January 2019, IPL incurred an obligation to make a September 2020 buyout payment of $110 million in exchange for shortening the term of IPL’s DAEC nuclear generation PPA by 5 years. The IUB approved placing the buyout payment in a regulatory asset account, which will be recovered from IPL’s retail customers over a 5 -year period following the payment. The offsetting obligation has been discounted and is recorded in “Other current liabilities” on Alliant Energy’s and IPL’s balance sheets. Utility Rate Reviews IPL’s Retail Electric Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers based on a 2020 forward-looking Test Period. The key drivers for IPL’s request included recovery of capital projects, including new wind generation. IPL concurrently filed for interim retail electric rates based on 2018 historical data as adjusted for certain known and measurable changes occurring in the first quarter of 2019. An interim retail electric base rate increase of $90 million , on an annual basis, was implemented effective April 1, 2019. Implementing interim rates does not require regulatory approval; however, interim rates are subject to refund pending the IUB’s final rate review decision. In October 2019, IPL reached a partial, non-unanimous settlement agreement with intervenor groups for an annual retail electric base rate increase of $127 million . The agreement includes both the recovery of and a return on IPL’s early retired EGUs, and the recovery of IPL’s retired analog electric meters. The settlement agreement also includes IPL providing billing credits over a 12 -month period beginning with final rates, including $27 million of excess deferred taxes resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform and $8 million from a partial refund of interim rates implemented in 2019. The IUB generally must decide on requests for retail rate changes within 10 months of the date of the application for which changes are filed. IPL currently expects a final decision, including a decision on the settlement agreement, from the IUB in the fourth quarter of 2019 with final rates effective in the first quarter of 2020. IPL’s Retail Gas Rate Review (2020 Forward-looking Test Period) - In March 2019, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers based on a 2020 forward-looking Test Period. The key drivers for IPL’s request included recovery of capital projects. In October 2019, IPL reached a unanimous settlement agreement with intervenor groups for an annual retail gas base rate increase of $12 million . IPL currently expects a decision, including a decision on the settlement agreement, from the IUB in the fourth quarter of 2019 with final rates effective in the first quarter of 2020.
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 September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3

Receivables

Receivables	9 Months Ended
	Sep. 30, 2019
Receivables [Line Items]
Receivables	RECEIVABLES 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 September 30, 2019 , IPL had $109 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 nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Maximum outstanding aggregate cash proceeds $103.0 $110.0 $108.0 $116.0 Average outstanding aggregate cash proceeds 45.4 36.4 42.9 49.8 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2019 December 31, 2018 Customer accounts receivable $154.2 $140.1 Unbilled utility revenues 92.1 97.1 Other receivables 0.4 0.1 Receivables sold to third party 246.7 237.3 Less: cash proceeds 1.0 108.0 Deferred proceeds 245.7 129.3 Less: allowance for doubtful accounts 8.7 9.9 Fair value of deferred proceeds $237.0 $119.4 As of September 30, 2019 , outstanding receivables past due under the Receivables Agreement were $26.6 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Collections $592.2 $549.5 $1,635.7 $1,550.2 Write-offs, net of recoveries 3.2 4.9 11.3 12.9
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES 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 September 30, 2019 , IPL had $109 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 nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Maximum outstanding aggregate cash proceeds $103.0 $110.0 $108.0 $116.0 Average outstanding aggregate cash proceeds 45.4 36.4 42.9 49.8 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2019 December 31, 2018 Customer accounts receivable $154.2 $140.1 Unbilled utility revenues 92.1 97.1 Other receivables 0.4 0.1 Receivables sold to third party 246.7 237.3 Less: cash proceeds 1.0 108.0 Deferred proceeds 245.7 129.3 Less: allowance for doubtful accounts 8.7 9.9 Fair value of deferred proceeds $237.0 $119.4 As of September 30, 2019 , outstanding receivables past due under the Receivables Agreement were $26.6 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Collections $592.2 $549.5 $1,635.7 $1,550.2 Write-offs, net of recoveries 3.2 4.9 11.3 12.9

Investments and Acquisitions

Investments and Acquisitions	9 Months Ended
	Sep. 30, 2019
Schedule of Investments [Line Items]
Investments and Acquisitions	INVESTMENTS AND ACQUISITIONS Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC Holdings ($10.5 ) ($8.9 ) ($30.0 ) ($25.4 ) Non-utility wind farm in Oklahoma (0.4 ) 0.1 (2.8 ) (14.5 ) Other (0.7 ) (1.0 ) (2.4 ) (1.7 ) ($11.6 ) ($9.8 ) ($35.2 ) ($41.6 ) Non-utility Transportation Acquisitions - In the first quarter of 2019, Alliant Energy, through its wholly-owned non-utility subsidiaries, completed acquisitions of freight management companies located in Cedar Rapids, Iowa and Stoughton, Wisconsin. These acquisitions were purchased for $21 million , including contingent consideration of $8 million , which is expected to be paid within two years . The purchase price was largely allocated to intangibles and the remainder was allocated to working capital and property.

Common Equity

Common Equity	9 Months Ended
	Sep. 30, 2019
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, 2019 236,063,279 Equity forward agreements 3,790,300 Shareowner Direct Plan 390,630 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, September 30, 2019 240,342,949 Equity Forward Agreements - In December 2018, Alliant Energy entered into forward sale agreements with various counterparties in connection with a public offering of 8,358,973 shares of Alliant Energy common stock. The initial forward sale price of $44.33 per share is subject to daily adjustment based on a floating interest rate factor, and will decrease by other fixed amounts specified in the forward sale agreements. In 2019, Alliant Energy settled $167 million under the forward sale agreements by delivering 3,790,300 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $43.99 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. As of September 30, 2019 , 671,237 incremental shares were included in the calculation of diluted EPS related to the remaining securities under the forward sale agreements. 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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 Comprehensive Income - For the three and nine months ended September 30, 2019 and 2018 , Alliant Energy’s other comprehensive income was not material; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2019 and 2018 , IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2019 236,063,279 Equity forward agreements 3,790,300 Shareowner Direct Plan 390,630 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, September 30, 2019 240,342,949 Equity Forward Agreements - In December 2018, Alliant Energy entered into forward sale agreements with various counterparties in connection with a public offering of 8,358,973 shares of Alliant Energy common stock. The initial forward sale price of $44.33 per share is subject to daily adjustment based on a floating interest rate factor, and will decrease by other fixed amounts specified in the forward sale agreements. In 2019, Alliant Energy settled $167 million under the forward sale agreements by delivering 3,790,300 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $43.99 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. As of September 30, 2019 , 671,237 incremental shares were included in the calculation of diluted EPS related to the remaining securities under the forward sale agreements. 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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 Comprehensive Income - For the three and nine months ended September 30, 2019 and 2018 , Alliant Energy’s other comprehensive income was not material; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2019 and 2018 , IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2019 236,063,279 Equity forward agreements 3,790,300 Shareowner Direct Plan 390,630 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, September 30, 2019 240,342,949 Equity Forward Agreements - In December 2018, Alliant Energy entered into forward sale agreements with various counterparties in connection with a public offering of 8,358,973 shares of Alliant Energy common stock. The initial forward sale price of $44.33 per share is subject to daily adjustment based on a floating interest rate factor, and will decrease by other fixed amounts specified in the forward sale agreements. In 2019, Alliant Energy settled $167 million under the forward sale agreements by delivering 3,790,300 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $43.99 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. As of September 30, 2019 , 671,237 incremental shares were included in the calculation of diluted EPS related to the remaining securities under the forward sale agreements. 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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 Comprehensive Income - For the three and nine months ended September 30, 2019 and 2018 , Alliant Energy’s other comprehensive income was not material; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2019 and 2018 , IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - In March 2019, Alliant Energy, IPL and WPL extended their single credit facility agreement by one year , which currently expires in August 2023. As of September 30, 2019 , the short-term borrowing capacity under the agreement totaled $1 billion ( $450 million for Alliant Energy at the parent company, $250 million for IPL and $300 million for WPL). Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9% NOTE 6(b) Long-term Debt - In April 2019, IPL issued $300 million of 3.60% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.50% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds have been or will be allocated for the construction and development of IPL’s wind projects. In June 2019, WPL issued $350 million of 3.00% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - In March 2019, Alliant Energy, IPL and WPL extended their single credit facility agreement by one year , which currently expires in August 2023. As of September 30, 2019 , the short-term borrowing capacity under the agreement totaled $1 billion ( $450 million for Alliant Energy at the parent company, $250 million for IPL and $300 million for WPL). Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9% NOTE 6(b) Long-term Debt - In April 2019, IPL issued $300 million of 3.60% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.50% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds have been or will be allocated for the construction and development of IPL’s wind projects. In June 2019, WPL issued $350 million of 3.00% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 6(a) Short-term Debt - In March 2019, Alliant Energy, IPL and WPL extended their single credit facility agreement by one year , which currently expires in August 2023. As of September 30, 2019 , the short-term borrowing capacity under the agreement totaled $1 billion ( $450 million for Alliant Energy at the parent company, $250 million for IPL and $300 million for WPL). Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9% NOTE 6(b) Long-term Debt - In April 2019, IPL issued $300 million of 3.60% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.50% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds have been or will be allocated for the construction and development of IPL’s wind projects. In June 2019, WPL issued $350 million of 3.00% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Line Items]
Operating Leases	LEASES Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $— Finance Lease - WPL’s finance lease is an agreement for WPL to lease the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business through 2025, the initial lease term. WPL is responsible for the operation of the EGU and has exclusive rights to its output. This finance lease contains two lease renewal periods, which are not included in the finance lease obligation, as well as an option to purchase the facility at the end of the initial lease term. WPL’s retail and wholesale rates include recovery of the Sheboygan Falls Energy Facility lease payments. WPL’s finance lease details are as follows (dollars in millions): September 30, 2019 Property, plant and equipment, net $34 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 54 Total finance lease liabilities $62 Remaining lease term 6 years Discount rate 11 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Depreciation expense $1 $4 Interest expense 1 5 Total finance lease expense $2 $9 Expected Maturities - As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62 Prior period amounts have not been restated to reflect the adoption of the new lease accounting standard and continue to be reported under the accounting standards in effect for those periods. As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
IPL [Member]
Leases [Line Items]
Operating Leases	LEASES Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $— Finance Lease - WPL’s finance lease is an agreement for WPL to lease the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business through 2025, the initial lease term. WPL is responsible for the operation of the EGU and has exclusive rights to its output. This finance lease contains two lease renewal periods, which are not included in the finance lease obligation, as well as an option to purchase the facility at the end of the initial lease term. WPL’s retail and wholesale rates include recovery of the Sheboygan Falls Energy Facility lease payments. WPL’s finance lease details are as follows (dollars in millions): September 30, 2019 Property, plant and equipment, net $34 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 54 Total finance lease liabilities $62 Remaining lease term 6 years Discount rate 11 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Depreciation expense $1 $4 Interest expense 1 5 Total finance lease expense $2 $9 Expected Maturities - As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62 Prior period amounts have not been restated to reflect the adoption of the new lease accounting standard and continue to be reported under the accounting standards in effect for those periods. As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
WPL [Member]
Leases [Line Items]
Operating Leases	LEASES Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $— Finance Lease - WPL’s finance lease is an agreement for WPL to lease the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business through 2025, the initial lease term. WPL is responsible for the operation of the EGU and has exclusive rights to its output. This finance lease contains two lease renewal periods, which are not included in the finance lease obligation, as well as an option to purchase the facility at the end of the initial lease term. WPL’s retail and wholesale rates include recovery of the Sheboygan Falls Energy Facility lease payments. WPL’s finance lease details are as follows (dollars in millions): September 30, 2019 Property, plant and equipment, net $34 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 54 Total finance lease liabilities $62 Remaining lease term 6 years Discount rate 11 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Depreciation expense $1 $4 Interest expense 1 5 Total finance lease expense $2 $9 Expected Maturities - As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62 Prior period amounts have not been restated to reflect the adoption of the new lease accounting standard and continue to be reported under the accounting standards in effect for those periods. As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
Finance Leases	LEASES Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $— Finance Lease - WPL’s finance lease is an agreement for WPL to lease the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business through 2025, the initial lease term. WPL is responsible for the operation of the EGU and has exclusive rights to its output. This finance lease contains two lease renewal periods, which are not included in the finance lease obligation, as well as an option to purchase the facility at the end of the initial lease term. WPL’s retail and wholesale rates include recovery of the Sheboygan Falls Energy Facility lease payments. WPL’s finance lease details are as follows (dollars in millions): September 30, 2019 Property, plant and equipment, net $34 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 54 Total finance lease liabilities $62 Remaining lease term 6 years Discount rate 11 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Depreciation expense $1 $4 Interest expense 1 5 Total finance lease expense $2 $9 Expected Maturities - As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62 Prior period amounts have not been restated to reflect the adoption of the new lease accounting standard and continue to be reported under the accounting standards in effect for those periods. As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68

Revenues

Revenues	9 Months Ended
	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer	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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 % Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 % Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 % Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2019
Benefit Plans	BENEFIT PLANS NOTE 10(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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4 NOTE 10(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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4 As of September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7.2 million , $4.0 million and $2.9 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. For the nine months ended September 30 , 2019, performance shares, performance restricted stock units and restricted stock units were granted to key employees and will be paid out in shares, and are therefore accounted for as equity awards. The 2019 performance shares contain a market condition based on total shareowner return relative to an investor-owned utility peer group. The fair value of each performance share is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a 3 -year performance period. For the nine months ended September 30 , 2019, 91,816 performance shares were granted with a weighted average grant date fair value of $47.23 . The 2019 performance restricted stock units will vest based on the achievement of certain targets (specified growth of consolidated net income from continuing operations) during a 3 -year performance period. The actual number of performance shares and performance restricted units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares or units, as applicable. The 2019 restricted stock units will vest based on the expiration of a 3 -year time-vesting period. For the nine months ended September 30 , 2019, 91,816 performance restricted stock units were granted with a weighted average grant date fair value of $46.10 , and 105,348 restricted stock units were granted with a weighted average grant date fair value of $45.98 , which is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. As of September 30, 2019 , 122,720 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4 NOTE 10(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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4 As of September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7.2 million , $4.0 million and $2.9 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. For the nine months ended September 30 , 2019, performance shares, performance restricted stock units and restricted stock units were granted to key employees and will be paid out in shares, and are therefore accounted for as equity awards. The 2019 performance shares contain a market condition based on total shareowner return relative to an investor-owned utility peer group. The fair value of each performance share is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a 3 -year performance period. For the nine months ended September 30 , 2019, 91,816 performance shares were granted with a weighted average grant date fair value of $47.23 . The 2019 performance restricted stock units will vest based on the achievement of certain targets (specified growth of consolidated net income from continuing operations) during a 3 -year performance period. The actual number of performance shares and performance restricted units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares or units, as applicable. The 2019 restricted stock units will vest based on the expiration of a 3 -year time-vesting period. For the nine months ended September 30 , 2019, 91,816 performance restricted stock units were granted with a weighted average grant date fair value of $46.10 , and 105,348 restricted stock units were granted with a weighted average grant date fair value of $45.98 , which is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. As of September 30, 2019 , 122,720 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(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 nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4 NOTE 10(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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4 As of September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $7.2 million , $4.0 million and $2.9 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. For the nine months ended September 30 , 2019, performance shares, performance restricted stock units and restricted stock units were granted to key employees and will be paid out in shares, and are therefore accounted for as equity awards. The 2019 performance shares contain a market condition based on total shareowner return relative to an investor-owned utility peer group. The fair value of each performance share is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a 3 -year performance period. For the nine months ended September 30 , 2019, 91,816 performance shares were granted with a weighted average grant date fair value of $47.23 . The 2019 performance restricted stock units will vest based on the achievement of certain targets (specified growth of consolidated net income from continuing operations) during a 3 -year performance period. The actual number of performance shares and performance restricted units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares or units, as applicable. The 2019 restricted stock units will vest based on the expiration of a 3 -year time-vesting period. For the nine months ended September 30 , 2019, 91,816 performance restricted stock units were granted with a weighted average grant date fair value of $46.10 , and 105,348 restricted stock units were granted with a weighted average grant date fair value of $45.98 , which is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. As of September 30, 2019 , 122,720 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Revisions in estimated cash flows (5.8 ) (7.0 ) Liabilities settled (5.9 ) (5.6 ) Liabilities incurred (a) 26.2 26.2 Accretion expense 5.3 3.5 Balance, September 30 $197.3 $135.4 (a) During the nine months ended September 30 , 2019, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Upland Prairie and English Farms 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 nine months ended September 30, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Revisions in estimated cash flows (5.8 ) (7.0 ) Liabilities settled (5.9 ) (5.6 ) Liabilities incurred (a) 26.2 26.2 Accretion expense 5.3 3.5 Balance, September 30 $197.3 $135.4 (a) During the nine months ended September 30 , 2019, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Upland Prairie and English Farms 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	9 Months Ended
	Sep. 30, 2019
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6 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 September 30, 2019 and December 31, 2018 , 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 September 30, 2019 and December 31, 2018 . 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 September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6 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 September 30, 2019 and December 31, 2018 , 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 September 30, 2019 and December 31, 2018 . 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 September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021 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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6 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 September 30, 2019 and December 31, 2018 , 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 September 30, 2019 and December 31, 2018 . 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	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8
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 September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8
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 September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s and WPL’s projects include the expansion of wind generation, and WPL’s projects also include the West Riverside Energy Center. At September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $124 million , $79 million and $45 million , respectively. NOTE 14(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 September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 . NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. 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 general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2019 , the present value of the abandonment obligations is estimated at $38 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Alliant Energy Resources, LLC will be obligated to pay and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2019 and December 31, 2018 . Non-utility Wind Farm in Oklahoma - In July 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 September 30, 2019 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 September 30, 2019 and December 31, 2018 . 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 September 30, 2019 and December 31, 2018 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 14(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 September 30, 2019 , 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 September 30, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $31 $12 - $25 Current and non-current environmental liabilities 19 16 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. Clean Air Act Section 111(d) - In July 2019, the EPA published the final Affordable Clean Energy rule, which repeals the Clean Power Plan effective September 6, 2019. The final rule establishes emission guidelines for states to develop plans by July 2022 to reduce carbon dioxide emissions from existing coal-fired EGUs, and is subject to legal challenges. Alliant Energy, IPL and WPL are currently unable to predict with certainty the final outcome or impact of these matters. NOTE 14(e) Collective Bargaining Agreements - At September 30, 2019 , employees covered by collective bargaining agreements represented 54% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On May 31, 2019, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expired, representing 27% and 82% of total employees of Alliant Energy and WPL, respectively. In November 2019, the parties reached a new agreement, which expires May 31, 2022.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s and WPL’s projects include the expansion of wind generation, and WPL’s projects also include the West Riverside Energy Center. At September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $124 million , $79 million and $45 million , respectively. NOTE 14(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 September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 . NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. 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 general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2019 , the present value of the abandonment obligations is estimated at $38 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Alliant Energy Resources, LLC will be obligated to pay and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2019 and December 31, 2018 . Non-utility Wind Farm in Oklahoma - In July 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 September 30, 2019 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 September 30, 2019 and December 31, 2018 . 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 September 30, 2019 and December 31, 2018 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 14(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 September 30, 2019 , 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 September 30, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $31 $12 - $25 Current and non-current environmental liabilities 19 16 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. Clean Air Act Section 111(d) - In July 2019, the EPA published the final Affordable Clean Energy rule, which repeals the Clean Power Plan effective September 6, 2019. The final rule establishes emission guidelines for states to develop plans by July 2022 to reduce carbon dioxide emissions from existing coal-fired EGUs, and is subject to legal challenges. Alliant Energy, IPL and WPL are currently unable to predict with certainty the final outcome or impact of these matters. NOTE 14(e) Collective Bargaining Agreements - At September 30, 2019 , employees covered by collective bargaining agreements represented 54% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On May 31, 2019, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expired, representing 27% and 82% of total employees of Alliant Energy and WPL, respectively. In November 2019, the parties reached a new agreement, which expires May 31, 2022.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s and WPL’s projects include the expansion of wind generation, and WPL’s projects also include the West Riverside Energy Center. At September 30, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $124 million , $79 million and $45 million , respectively. NOTE 14(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 September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 . NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. 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 general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2019 , the present value of the abandonment obligations is estimated at $38 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Alliant Energy Resources, LLC will be obligated to pay and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2019 and December 31, 2018 . Non-utility Wind Farm in Oklahoma - In July 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 September 30, 2019 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 September 30, 2019 and December 31, 2018 . 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 September 30, 2019 and December 31, 2018 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 14(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 September 30, 2019 , 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 September 30, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $31 $12 - $25 Current and non-current environmental liabilities 19 16 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. Clean Air Act Section 111(d) - In July 2019, the EPA published the final Affordable Clean Energy rule, which repeals the Clean Power Plan effective September 6, 2019. The final rule establishes emission guidelines for states to develop plans by July 2022 to reduce carbon dioxide emissions from existing coal-fired EGUs, and is subject to legal challenges. Alliant Energy, IPL and WPL are currently unable to predict with certainty the final outcome or impact of these matters. NOTE 14(e) Collective Bargaining Agreements - At September 30, 2019 , employees covered by collective bargaining agreements represented 54% , 60% and 82% of total employees of Alliant Energy, IPL and WPL, respectively. On May 31, 2019, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expired, representing 27% and 82% of total employees of Alliant Energy and WPL, respectively. In November 2019, the parties reached a new agreement, which expires May 31, 2022.

Segments Of Business

Segments Of Business	9 Months Ended
	Sep. 30, 2019
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2019 Revenues $915.9 $41.5 $11.2 $968.6 $21.6 $990.2 Operating income (loss) 283.7 (4.7 ) 2.8 281.8 8.4 290.2 Net income attributable to Alliant Energy common shareowners 216.6 9.4 226.0 Three Months Ended September 30, 2018 Revenues $861.2 $44.8 $12.3 $918.3 $10.3 $928.6 Operating income (loss) 248.7 (2.0 ) 0.6 247.3 8.8 256.1 Net income attributable to Alliant Energy common shareowners 202.8 2.7 205.5 ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2019 Revenues $2,350.5 $322.5 $33.2 $2,706.2 $61.4 $2,767.6 Operating income 543.0 47.7 4.2 594.9 21.9 616.8 Net income attributable to Alliant Energy common shareowners 422.6 23.1 445.7 Nine Months Ended September 30, 2018 Revenues $2,296.2 $299.0 $36.2 $2,631.4 $29.6 $2,661.0 Operating income 510.2 34.9 2.9 548.0 25.0 573.0 Net income attributable to Alliant Energy common shareowners 395.0 31.8 426.8 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $560.9 $24.8 $10.8 $596.5 Operating income (loss) 175.1 (4.2 ) 2.6 173.5 Earnings available for common stock 141.1 Three Months Ended September 30, 2018 Revenues $509.2 $26.7 $11.7 $547.6 Operating income (loss) 144.7 (3.1 ) 1.5 143.1 Earnings available for common stock 126.5 Nine Months Ended September 30, 2019 Revenues $1,373.0 $187.8 $32.0 $1,592.8 Operating income 290.8 26.3 4.4 321.5 Earnings available for common stock 239.4 Nine Months Ended September 30, 2018 Revenues $1,337.0 $177.0 $34.2 $1,548.2 Operating income 275.7 16.3 4.4 296.4 Earnings available for common stock 224.9 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $355.0 $16.7 $0.4 $372.1 Operating income (loss) 108.6 (0.5 ) 0.2 108.3 Earnings available for common stock 75.5 Three Months Ended September 30, 2018 Revenues $352.0 $18.1 $0.6 $370.7 Operating income (loss) 104.0 1.1 (0.9 ) 104.2 Earnings available for common stock 76.3 Nine Months Ended September 30, 2019 Revenues $977.5 $134.7 $1.2 $1,113.4 Operating income (loss) 252.2 21.4 (0.2 ) 273.4 Earnings available for common stock 183.2 Nine Months Ended September 30, 2018 Revenues $959.2 $122.0 $2.0 $1,083.2 Operating income (loss) 234.5 18.6 (1.5 ) 251.6 Earnings available for common stock 170.1
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2019 Revenues $915.9 $41.5 $11.2 $968.6 $21.6 $990.2 Operating income (loss) 283.7 (4.7 ) 2.8 281.8 8.4 290.2 Net income attributable to Alliant Energy common shareowners 216.6 9.4 226.0 Three Months Ended September 30, 2018 Revenues $861.2 $44.8 $12.3 $918.3 $10.3 $928.6 Operating income (loss) 248.7 (2.0 ) 0.6 247.3 8.8 256.1 Net income attributable to Alliant Energy common shareowners 202.8 2.7 205.5 ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2019 Revenues $2,350.5 $322.5 $33.2 $2,706.2 $61.4 $2,767.6 Operating income 543.0 47.7 4.2 594.9 21.9 616.8 Net income attributable to Alliant Energy common shareowners 422.6 23.1 445.7 Nine Months Ended September 30, 2018 Revenues $2,296.2 $299.0 $36.2 $2,631.4 $29.6 $2,661.0 Operating income 510.2 34.9 2.9 548.0 25.0 573.0 Net income attributable to Alliant Energy common shareowners 395.0 31.8 426.8 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $560.9 $24.8 $10.8 $596.5 Operating income (loss) 175.1 (4.2 ) 2.6 173.5 Earnings available for common stock 141.1 Three Months Ended September 30, 2018 Revenues $509.2 $26.7 $11.7 $547.6 Operating income (loss) 144.7 (3.1 ) 1.5 143.1 Earnings available for common stock 126.5 Nine Months Ended September 30, 2019 Revenues $1,373.0 $187.8 $32.0 $1,592.8 Operating income 290.8 26.3 4.4 321.5 Earnings available for common stock 239.4 Nine Months Ended September 30, 2018 Revenues $1,337.0 $177.0 $34.2 $1,548.2 Operating income 275.7 16.3 4.4 296.4 Earnings available for common stock 224.9 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $355.0 $16.7 $0.4 $372.1 Operating income (loss) 108.6 (0.5 ) 0.2 108.3 Earnings available for common stock 75.5 Three Months Ended September 30, 2018 Revenues $352.0 $18.1 $0.6 $370.7 Operating income (loss) 104.0 1.1 (0.9 ) 104.2 Earnings available for common stock 76.3 Nine Months Ended September 30, 2019 Revenues $977.5 $134.7 $1.2 $1,113.4 Operating income (loss) 252.2 21.4 (0.2 ) 273.4 Earnings available for common stock 183.2 Nine Months Ended September 30, 2018 Revenues $959.2 $122.0 $2.0 $1,083.2 Operating income (loss) 234.5 18.6 (1.5 ) 251.6 Earnings available for common stock 170.1
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2019 Revenues $915.9 $41.5 $11.2 $968.6 $21.6 $990.2 Operating income (loss) 283.7 (4.7 ) 2.8 281.8 8.4 290.2 Net income attributable to Alliant Energy common shareowners 216.6 9.4 226.0 Three Months Ended September 30, 2018 Revenues $861.2 $44.8 $12.3 $918.3 $10.3 $928.6 Operating income (loss) 248.7 (2.0 ) 0.6 247.3 8.8 256.1 Net income attributable to Alliant Energy common shareowners 202.8 2.7 205.5 ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2019 Revenues $2,350.5 $322.5 $33.2 $2,706.2 $61.4 $2,767.6 Operating income 543.0 47.7 4.2 594.9 21.9 616.8 Net income attributable to Alliant Energy common shareowners 422.6 23.1 445.7 Nine Months Ended September 30, 2018 Revenues $2,296.2 $299.0 $36.2 $2,631.4 $29.6 $2,661.0 Operating income 510.2 34.9 2.9 548.0 25.0 573.0 Net income attributable to Alliant Energy common shareowners 395.0 31.8 426.8 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $560.9 $24.8 $10.8 $596.5 Operating income (loss) 175.1 (4.2 ) 2.6 173.5 Earnings available for common stock 141.1 Three Months Ended September 30, 2018 Revenues $509.2 $26.7 $11.7 $547.6 Operating income (loss) 144.7 (3.1 ) 1.5 143.1 Earnings available for common stock 126.5 Nine Months Ended September 30, 2019 Revenues $1,373.0 $187.8 $32.0 $1,592.8 Operating income 290.8 26.3 4.4 321.5 Earnings available for common stock 239.4 Nine Months Ended September 30, 2018 Revenues $1,337.0 $177.0 $34.2 $1,548.2 Operating income 275.7 16.3 4.4 296.4 Earnings available for common stock 224.9 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $355.0 $16.7 $0.4 $372.1 Operating income (loss) 108.6 (0.5 ) 0.2 108.3 Earnings available for common stock 75.5 Three Months Ended September 30, 2018 Revenues $352.0 $18.1 $0.6 $370.7 Operating income (loss) 104.0 1.1 (0.9 ) 104.2 Earnings available for common stock 76.3 Nine Months Ended September 30, 2019 Revenues $977.5 $134.7 $1.2 $1,113.4 Operating income (loss) 252.2 21.4 (0.2 ) 273.4 Earnings available for common stock 183.2 Nine Months Ended September 30, 2018 Revenues $959.2 $122.0 $2.0 $1,083.2 Operating income (loss) 234.5 18.6 (1.5 ) 251.6 Earnings available for common stock 170.1

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC billings to WPL $28 $26 $82 $79 WPL billings to ATC 3 3 10 8 WPL owed ATC net amounts of $9 million as of September 30, 2019 and $8 million as of December 31, 2018 . WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 7 for discussion of WPL’s Sheboygan Falls Energy Facility lease.
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC billings to WPL $28 $26 $82 $79 WPL billings to ATC 3 3 10 8 WPL owed ATC net amounts of $9 million as of September 30, 2019 and $8 million as of December 31, 2018 . WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 7 for discussion of WPL’s Sheboygan Falls Energy Facility lease.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2019
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K .
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019
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	Cash and Cash Equivalents - At September 30, 2019 , Alliant Energy’s and IPL’s cash and cash equivalents included $174.4 million and $173.7 million of money market fund investments, with interest rates of 2.0% and 2.0% , respectively.
Leases	Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
New Accounting Standards	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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K .
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019
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	Cash and Cash Equivalents - At September 30, 2019 , Alliant Energy’s and IPL’s cash and cash equivalents included $174.4 million and $173.7 million of money market fund investments, with interest rates of 2.0% and 2.0% , respectively.
Leases	Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
New Accounting Standards	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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K .
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2019 are not necessarily indicative of results that may be expected for the year ending December 31, 2019
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.
Leases	Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and interest expenses. Finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
New Accounting Standards	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 and certain other assets. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 using the modified retrospective method of adoption, which requires cumulative effect adjustments to retained earnings on January 1, 2020 upon adoption. Alliant Energy, IPL and WPL will continue to evaluate the impact of this standard and do not currently expect a material change to their financial condition or results of operations as a result of adopting this standard. Cloud Computing Arrangements - In August 2018, the Financial Accounting Standards Board issued an accounting standard that clarifies capitalization and presentation requirements of implementation costs incurred in cloud computing arrangements. Alliant Energy, IPL and WPL will adopt this standard on January 1, 2020 and are currently evaluating the impact of this standard on their financial statements. Leases - In February 2016, the Financial Accounting Standards Board issued an accounting standard requiring lease assets and lease liabilities, including operating leases, to be recognized on the balance sheet. The accounting for capital leases, now referred to as finance leases, remains unchanged with the adoption of this standard. Alliant Energy, IPL and WPL adopted this standard on January 1, 2019 using an optional transition approach and there was no cumulative effect adjustment to the balance sheets as of January 1, 2019. Prior period amounts have not been restated to reflect the adoption of this standard and continue to be reported under the accounting standards in effect for those periods. Upon transition to the new standard, Alliant Energy, IPL and WPL elected the land easement transition practical expedient, for which existing land easements that were not previously accounted for as leases under the original accounting standards did not need to be evaluated under the new accounting standard. In addition, Alliant Energy, IPL and WPL evaluated land easements that were previously accounted for as leases and determined that the majority of these land easements relate to joint-use land sites, and do not meet the criteria for leases under the new accounting standard. Therefore, these land easement arrangements are no longer reflected as operating leases effective January 1, 2019. Refer to Note 7 for further discussion of leases.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2019
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $825.2 $820.6 $787.2 $783.1 $38.0 $37.5 Pension and OPEB costs 513.1 542.3 260.0 274.0 253.1 268.3 Assets retired early 138.7 111.6 90.1 55.4 48.6 56.2 Asset retirement obligations 110.7 110.8 75.2 76.3 35.5 34.5 IPL’s DAEC PPA amendment 107.7 — 107.7 — — — Derivatives 34.0 28.0 15.0 15.1 19.0 12.9 Emission allowances 21.7 23.6 21.7 23.6 — — Other 88.9 100.4 47.1 51.5 41.8 48.9 $1,840.0 $1,737.3 $1,404.0 $1,279.0 $436.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $851.4 $890.6 $365.0 $390.1 $486.4 $500.5 Cost of removal obligations 390.9 401.2 261.0 273.3 129.9 127.9 Electric transmission cost recovery 89.8 104.0 48.0 47.7 41.8 56.3 Commodity cost recovery 29.1 16.8 16.7 11.9 12.4 4.9 WPL’s earnings sharing mechanism 21.8 25.4 — — 21.8 25.4 Derivatives 20.8 18.5 16.9 10.2 3.9 8.3 Other 47.2 36.7 26.0 21.7 21.2 15.0 $1,451.0 $1,493.2 $733.6 $754.9 $717.4 $738.3

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 2019
Receivables [Line Items]
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 nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Maximum outstanding aggregate cash proceeds $103.0 $110.0 $108.0 $116.0 Average outstanding aggregate cash proceeds 45.4 36.4 42.9 49.8
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2019 December 31, 2018 Customer accounts receivable $154.2 $140.1 Unbilled utility revenues 92.1 97.1 Other receivables 0.4 0.1 Receivables sold to third party 246.7 237.3 Less: cash proceeds 1.0 108.0 Deferred proceeds 245.7 129.3 Less: allowance for doubtful accounts 8.7 9.9 Fair value of deferred proceeds $237.0 $119.4
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Collections $592.2 $549.5 $1,635.7 $1,550.2 Write-offs, net of recoveries 3.2 4.9 11.3 12.9
IPL [Member]
Receivables [Line Items]
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 nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Maximum outstanding aggregate cash proceeds $103.0 $110.0 $108.0 $116.0 Average outstanding aggregate cash proceeds 45.4 36.4 42.9 49.8
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2019 December 31, 2018 Customer accounts receivable $154.2 $140.1 Unbilled utility revenues 92.1 97.1 Other receivables 0.4 0.1 Receivables sold to third party 246.7 237.3 Less: cash proceeds 1.0 108.0 Deferred proceeds 245.7 129.3 Less: allowance for doubtful accounts 8.7 9.9 Fair value of deferred proceeds $237.0 $119.4
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 Collections $592.2 $549.5 $1,635.7 $1,550.2 Write-offs, net of recoveries 3.2 4.9 11.3 12.9

Investments and Acquisitions (T

Investments and Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2019
Schedule of 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 nine months ended September 30 was as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC Holdings ($10.5 ) ($8.9 ) ($30.0 ) ($25.4 ) Non-utility wind farm in Oklahoma (0.4 ) 0.1 (2.8 ) (14.5 ) Other (0.7 ) (1.0 ) (2.4 ) (1.7 ) ($11.6 ) ($9.8 ) ($35.2 ) ($41.6 )

Common Equity (Tables)

Common Equity (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 236,063,279 Equity forward agreements 3,790,300 Shareowner Direct Plan 390,630 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, September 30, 2019 240,342,949
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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6
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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6
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 September 30, 2019 Beginning balance, July 1 $2.4 $2,108.4 $2,597.8 $1.0 ($10.0 ) $200.0 $4,899.6 Net income attributable to Alliant Energy common shareowners 226.0 226.0 Common stock dividends ($0.355 per share) (84.7 ) (84.7 ) Equity forward settlements and Shareowner Direct Plan issuances 124.8 124.8 Equity-based compensation plans and other 3.7 (0.2 ) 3.5 Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Three Months Ended September 30, 2018 Beginning balance, July 1 $2.3 $1,947.2 $2,412.5 $0.1 ($11.4 ) $200.0 $4,550.7 Net income attributable to Alliant Energy common shareowners 205.5 205.5 Common stock dividends ($0.335 per share) (78.5 ) (78.5 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 91.1 91.2 Equity-based compensation plans and other (0.1 ) 1.9 1.8 Other comprehensive loss, net of tax (0.3 ) (0.3 ) Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 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 Nine Months Ended September 30, 2019 Beginning balance, January 1 $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 445.7 445.7 Common stock dividends ($1.065 per share) (252.5 ) (252.5 ) Equity forward settlements and Shareowner Direct Plan issuances 185.4 185.4 Equity-based compensation plans and other 6.0 (0.4 ) 5.6 Other comprehensive loss, net of tax (0.7 ) (0.7 ) Ending balance, September 30 $2.4 $2,236.9 $2,739.1 $1.0 ($10.2 ) $200.0 $5,169.2 Nine Months Ended September 30, 2018 Beginning balance, January 1 $2.3 $1,845.5 $2,346.0 ($0.5 ) ($11.1 ) $200.0 $4,382.2 Net income attributable to Alliant Energy common shareowners 426.8 426.8 Common stock dividends ($1.005 per share) (233.3 ) (233.3 ) At-the-market offering program and Shareowner Direct Plan issuances 0.1 191.2 191.3 Equity-based compensation plans and other 1.5 1.6 3.1 Other comprehensive income, net of tax 0.3 0.3 Ending balance, September 30 $2.4 $2,038.2 $2,539.5 ($0.2 ) ($9.5 ) $200.0 $4,770.4 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $33.4 $2,322.8 $788.9 $200.0 $3,345.1 Earnings available for common stock 141.1 141.1 Common stock dividends (42.1 ) (42.1 ) Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Three Months Ended September 30, 2018 Beginning balance, July 1 $33.4 $1,927.8 $692.9 $200.0 $2,854.1 Earnings available for common stock 126.5 126.5 Common stock dividends (41.9 ) (41.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 239.4 239.4 Common stock dividends (126.0 ) (126.0 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $33.4 $2,322.8 $887.9 $200.0 $3,444.1 Nine Months Ended September 30, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 224.9 224.9 Common stock dividends (125.9 ) (125.9 ) Capital contributions from parent 230.0 230.0 Ending balance, September 30 $33.4 $2,027.8 $777.5 $200.0 $3,038.7 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2019 Beginning balance, July 1 $66.2 $1,309.0 $810.0 $2,185.2 Earnings available for common stock 75.5 75.5 Common stock dividends (35.9 ) (35.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Three Months Ended September 30, 2018 Beginning balance, July 1 $66.2 $1,259.0 $730.0 $2,055.2 Earnings available for common stock 76.3 76.3 Common stock dividends (34.9 ) (34.9 ) Capital contributions from parent 50.0 50.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 183.2 183.2 Common stock dividends (107.9 ) (107.9 ) Capital contributions from parent 100.0 100.0 Ending balance, September 30 $66.2 $1,409.0 $849.6 $2,324.8 Nine Months Ended September 30, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 170.1 170.1 Common stock dividends (105.0 ) (105.0 ) Capital contributions from parent 200.0 200.0 Ending balance, September 30 $66.2 $1,309.0 $771.4 $2,146.6

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Commercial paper outstanding $349.6 $— $— Commercial paper weighted average interest rates 2.3% N/A N/A Available credit facility capacity $650.4 $250.0 $300.0 Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $471.7 $153.3 $— $— $89.7 $75.4 Average amount outstanding (based on daily outstanding balances) $399.5 $80.8 $— $— $27.0 $23.1 Weighted average interest rates 2.5% 2.2% N/A N/A 2.3% 2.0% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $600.6 $446.5 $50.4 $31.4 $195.1 $109.4 Average amount outstanding (based on daily outstanding balances) $476.3 $207.6 $0.2 $1.7 $101.8 $26.6 Weighted average interest rates 2.6% 2.1% 2.8% 2.3% 2.5% 1.9%

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $—
Schedule of Operating Lease Liability Maturities	As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62
Schedule of Future Minimum Payments for Operating Leases	As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
IPL [Member]
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $—
Schedule of Operating Lease Liability Maturities	As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62
Schedule of Future Minimum Payments for Operating Leases	As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
WPL [Member]
Leases [Line Items]
Schedule of Lease Details	WPL’s finance lease details are as follows (dollars in millions): September 30, 2019 Property, plant and equipment, net $34 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 54 Total finance lease liabilities $62 Remaining lease term 6 years Discount rate 11 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Depreciation expense $1 $4 Interest expense 1 5 Total finance lease expense $2 $9 September 30, 2019 Alliant Energy IPL WPL Property, plant and equipment, net $17 $10 $7 Other current liabilities $2 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $17 $10 $7 Weighted average remaining lease term 11 years 12 years 10 years Weighted average discount rate 4 % 4 % 4 % Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Alliant Energy IPL WPL Alliant Energy IPL WPL Operating lease cost $1 $1 $— $2 $1 $—
Schedule of Operating Lease Liability Maturities	As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62
Schedule of Finance Lease Liability Maturities	As of September 30, 2019 , expected maturities of lease liabilities were as follows (in millions): Remainder of 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $— $2 $2 $2 $2 $13 $21 $4 $17 IPL — 1 1 1 1 9 13 3 10 WPL — 1 1 1 1 4 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 4 15 15 15 15 20 84 22 62
Schedule of Future Minimum Payments for Operating Leases	As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68
Schedule of Future Minimum Payments for Capital Leases	As of December 31, 2018 , future minimum operating (excluding contingent rentals) and capital lease payments were as follows (in millions): 2019 2020 2021 2022 2023 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Operating Leases: Alliant Energy $5 $5 $3 $3 $2 $12 $30 IPL 3 2 2 2 2 12 23 WPL 2 3 1 — — — 6 WPL’s Capital Lease: Sheboygan Falls Energy Facility $15 $15 $15 $15 $15 $19 $94 $26 $68

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2
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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2
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 September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $331.6 $312.9 $196.0 $180.1 $135.6 $132.8 Retail - commercial 230.9 215.4 158.4 146.0 72.5 69.4 Retail - industrial 263.4 247.8 157.5 141.4 105.9 106.4 Wholesale 49.8 50.0 17.7 18.2 32.1 31.8 Bulk power and other 40.2 35.1 31.3 23.5 8.9 11.6 Total Electric Utility 915.9 861.2 560.9 509.2 355.0 352.0 Gas Utility: Retail - residential 20.4 21.8 11.7 12.6 8.7 9.2 Retail - commercial 10.0 11.0 5.9 6.4 4.1 4.6 Retail - industrial 2.3 3.0 1.9 2.0 0.4 1.0 Transportation/other 8.8 9.0 5.3 5.7 3.5 3.3 Total Gas Utility 41.5 44.8 24.8 26.7 16.7 18.1 Other Utility: Steam 9.1 8.7 9.1 8.7 — — Other utility 2.1 3.6 1.7 3.0 0.4 0.6 Total Other Utility 11.2 12.3 10.8 11.7 0.4 0.6 Non-Utility and Other: Transportation and other 21.6 10.3 — — — — Total Non-Utility and Other 21.6 10.3 — — — — Total revenues $990.2 $928.6 $596.5 $547.6 $372.1 $370.7 Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $839.6 $820.6 $469.4 $461.6 $370.2 $359.0 Retail - commercial 583.3 561.7 386.4 371.8 196.9 189.9 Retail - industrial 686.3 675.1 392.0 385.0 294.3 290.1 Wholesale 137.3 146.9 49.2 56.4 88.1 90.5 Bulk power and other 104.0 91.9 76.0 62.2 28.0 29.7 Total Electric Utility 2,350.5 2,296.2 1,373.0 1,337.0 977.5 959.2 Gas Utility: Retail - residential 187.4 170.1 109.6 100.9 77.8 69.2 Retail - commercial 89.7 87.3 49.5 49.8 40.2 37.5 Retail - industrial 9.7 11.4 6.7 6.1 3.0 5.3 Transportation/other 35.7 30.2 22.0 20.2 13.7 10.0 Total Gas Utility 322.5 299.0 187.8 177.0 134.7 122.0 Other Utility: Steam 26.7 26.5 26.7 26.5 — — Other utility 6.5 9.7 5.3 7.7 1.2 2.0 Total Other Utility 33.2 36.2 32.0 34.2 1.2 2.0 Non-Utility and Other: Transportation and other 61.4 29.6 — — — — Total Non-Utility and Other 61.4 29.6 — — — — Total revenues $2,767.6 $2,661.0 $1,592.8 $1,548.2 $1,113.4 $1,083.2

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2019
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 %
Summary Of Tax Credit Carryforwards	At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 %
Summary Of Tax Credit Carryforwards	At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income taxes by income before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.0 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.3 ) (5.4 ) (14.7 ) (5.5 ) (4.4 ) (6.4 ) Effect of rate-making on property-related differences (5.6 ) (6.3 ) (9.0 ) (11.5 ) (2.8 ) (2.1 ) Amortization of excess deferred taxes (1.1 ) (0.1 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (1.8 ) (5.7 ) 1.3 (10.2 ) 0.4 — IPL’s tax benefit riders (0.8 ) (2.3 ) (1.5 ) (4.8 ) — — Federal Tax Reform adjustments — (2.5 ) — (0.9 ) — (6.4 ) Other items, net (0.2 ) (0.3 ) (0.3 ) (0.6 ) (0.2 ) (0.4 ) Overall income tax rate 9.2 % 5.3 % 4.6 % (4.8 %) 18.5 % 11.8 % Alliant Energy IPL WPL Nine Months Ended September 30 2019 2018 2019 2018 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefits 7.1 6.9 8.1 7.7 6.2 6.2 Production tax credits (9.1 ) (5.4 ) (14.3 ) (5.4 ) (4.5 ) (6.6 ) Effect of rate-making on property-related differences (5.7 ) (6.7 ) (9.3 ) (12.0 ) (2.6 ) (2.3 ) Amortization of excess deferred taxes (1.1 ) (0.3 ) (0.3 ) — (1.7 ) (0.1 ) Adjustment for prior period taxes (0.7 ) (2.6 ) 0.6 (5.4 ) (0.3 ) — IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.6 ) — — Federal Tax Reform adjustments — (1.2 ) — (0.5 ) — (2.8 ) Other items, net (1.0 ) (0.7 ) (0.1 ) (1.0 ) (0.4 ) (1.2 ) Overall income tax rate 9.8 % 8.8 % 4.2 % (0.2 %) 17.7 % 14.2 %
Summary Of Tax Credit Carryforwards	At September 30, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2037 $611 $522 $41 State net operating losses 2019-2039 677 12 2 Federal tax credits 2022-2039 337 162 156

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4
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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4
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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts represent their current and former employees covered under plans they sponsor, as well as amounts directly assigned to them related to their current and former employees who are participants in the Alliant Energy and Corporate Services sponsored plans. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $2.5 $3.1 $7.3 $9.1 $0.8 $1.0 $2.5 $3.1 Interest cost 12.5 11.7 37.4 35.1 2.2 2.0 6.4 5.8 Expected return on plan assets (15.1 ) (17.4 ) (45.1 ) (52.3 ) (1.2 ) (1.5 ) (3.7 ) (4.5 ) Amortization of prior service credit (0.2 ) (0.2 ) (0.5 ) (0.5 ) (0.1 ) — (0.2 ) (0.1 ) Amortization of actuarial loss 9.1 8.8 27.3 26.4 0.8 0.8 2.4 2.5 $8.8 $6.0 $26.4 $17.8 $2.5 $2.3 $7.4 $6.8 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $1.6 $1.8 $4.6 $5.5 $0.3 $0.4 $1.0 $1.3 Interest cost 5.6 5.3 17.0 16.0 0.8 0.7 2.5 2.3 Expected return on plan assets (7.0 ) (8.1 ) (21.1 ) (24.4 ) (0.9 ) (1.1 ) (2.7 ) (3.3 ) Amortization of prior service credit (0.1 ) — (0.2 ) (0.1 ) — — — — Amortization of actuarial loss 3.9 3.7 11.8 11.2 0.4 0.4 1.1 1.0 $4.0 $2.7 $12.1 $8.2 $0.6 $0.4 $1.9 $1.3 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $0.9 $1.1 $2.6 $3.3 $0.3 $0.4 $0.9 $1.2 Interest cost 5.3 5.0 16.1 15.1 0.9 0.8 2.6 2.3 Expected return on plan assets (6.5 ) (7.6 ) (19.6 ) (22.8 ) (0.2 ) (0.2 ) (0.5 ) (0.5 ) Amortization of prior service credit — — (0.1 ) (0.1 ) — — (0.1 ) (0.1 ) Amortization of actuarial loss 4.4 4.3 13.2 12.9 0.4 0.5 1.2 1.5 $4.1 $2.8 $12.2 $8.4 $1.4 $1.5 $4.1 $4.4
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 nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 2019 2018 Compensation expense $7.5 $4.2 $15.6 $12.6 $4.2 $2.4 $8.7 $7.0 $3.0 $1.7 $6.2 $5.1 Income tax benefits 2.1 1.2 4.4 3.6 1.2 0.7 2.5 2.1 0.8 0.5 1.7 1.4

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Revisions in estimated cash flows (5.8 ) (7.0 ) Liabilities settled (5.9 ) (5.6 ) Liabilities incurred (a) 26.2 26.2 Accretion expense 5.3 3.5 Balance, September 30 $197.3 $135.4 (a) During the nine months ended September 30 , 2019, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Upland Prairie and English Farms 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 nine months ended September 30, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Revisions in estimated cash flows (5.8 ) (7.0 ) Liabilities settled (5.9 ) (5.6 ) Liabilities incurred (a) 26.2 26.2 Accretion expense 5.3 3.5 Balance, September 30 $197.3 $135.4 (a) During the nine months ended September 30 , 2019, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Upland Prairie and English Farms 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)	9 Months Ended
	Sep. 30, 2019
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021
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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021
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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2019 , 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 18,141 2019-2020 184,007 2019-2026 7,620 2019-2021 5,796 2019-2021 IPL 8,630 2019-2020 101,579 2019-2026 3,311 2019-2021 — — WPL 9,511 2019-2020 82,428 2019-2026 4,309 2019-2021 5,796 2019-2021
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 September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $18.6 $24.6 $12.8 $16.1 $5.8 $8.5 Non-current derivative assets 11.7 3.7 10.5 1.6 1.2 2.1 Current derivative liabilities 13.4 5.6 5.6 3.1 7.8 2.5 Non-current derivative liabilities 18.4 17.7 7.8 8.1 10.6 9.6

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 (Liabilities)	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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8
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 September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 (Liabilities)	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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8
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 September 30, 2019 December 31, 2018 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 $174.4 $174.4 $— $— $174.4 $— $— $— $— $— Derivatives 30.3 — 8.1 22.2 30.3 28.3 — 8.9 19.4 28.3 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 31.8 — 31.3 0.5 31.8 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 6,191.9 — 7,016.4 2.0 7,018.4 5,502.8 — 5,858.4 2.4 5,860.8 IPL September 30, 2019 December 31, 2018 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 $173.7 $173.7 $— $— $173.7 $— $— $— $— $— Derivatives 23.3 — 4.8 18.5 23.3 17.7 — 4.0 13.7 17.7 Deferred proceeds 237.0 — — 237.0 237.0 119.4 — — 119.4 119.4 Liabilities: Derivatives 13.4 — 12.9 0.5 13.4 11.2 — 6.5 4.7 11.2 Long-term debt (incl. current maturities) 3,146.8 — 3,537.0 — 3,537.0 2,552.3 — 2,691.2 — 2,691.2 WPL September 30, 2019 December 31, 2018 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $7.0 $— $3.3 $3.7 $7.0 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 18.4 — 18.4 — 18.4 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,932.3 — 2,314.1 — 2,314.1 1,834.9 — 2,043.7 — 2,043.7
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $13.2 ($10.7 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 12.7 25.7 — — Transfers out of Level 3 (1.2 ) 15.6 — — Sales — (0.2 ) — — Settlements (a) (3.0 ) (6.2 ) 22.4 35.4 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $12.7 $26.1 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 6.9 15.7 — — Transfers out of Level 3 2.8 15.6 — — Purchases 13.8 26.7 — — Sales (0.2 ) (0.2 ) — — Settlements (a) (13.8 ) (21.4 ) 117.6 21.6 Ending balance, September 30 $21.7 $24.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.1 $16.5 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2019 2018 2019 2018 Beginning balance, July 1 $9.3 ($4.1 ) $214.6 $208.3 Total net gains included in changes in net assets (realized/unrealized) 11.5 16.8 — — Transfers out of Level 3 (0.6 ) 10.5 — — Sales — (0.1 ) — — Settlements (a) (2.2 ) (4.9 ) 22.4 35.4 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $11.5 $16.8 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net gains included in changes in net assets (realized/unrealized) 8.6 7.6 — — Transfers out of Level 3 2.0 10.5 — — Purchases 9.5 19.3 — — Sales (0.1 ) (0.1 ) — — Settlements (a) (11.0 ) (17.7 ) 117.6 21.6 Ending balance, September 30 $18.0 $18.2 $237.0 $243.7 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $10.5 $7.9 $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2019 2018 Beginning balance, July 1 $3.9 ($6.6 ) Total net gains included in changes in net assets (realized/unrealized) 1.2 8.9 Transfers out of Level 3 (0.6 ) 5.1 Sales — (0.1 ) Settlements (0.8 ) (1.3 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $1.2 $9.3 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (1.7 ) 8.1 Transfers out of Level 3 0.8 5.1 Purchases 4.3 7.4 Sales (0.1 ) (0.1 ) Settlements (2.8 ) (3.7 ) Ending balance, September 30 $3.7 $6.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 ($0.4 ) $8.6 (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 (Liabilities)	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 September 30, 2019 $13.1 $8.6 $12.5 $5.5 $0.6 $3.1 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8

Commitments And Contingencies (

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2019 , 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 September 30, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $31 $12 - $25 Current and non-current environmental liabilities 19 16
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2019 , 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 September 30, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $31 $12 - $25 Current and non-current environmental liabilities 19 16
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $145 $144 $1 Natural gas 892 460 432 Coal (b) 117 76 41 Other (c) 76 43 24 $1,230 $723 $498 (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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 .

Segments Of Business (Tables)

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2019 Revenues $915.9 $41.5 $11.2 $968.6 $21.6 $990.2 Operating income (loss) 283.7 (4.7 ) 2.8 281.8 8.4 290.2 Net income attributable to Alliant Energy common shareowners 216.6 9.4 226.0 Three Months Ended September 30, 2018 Revenues $861.2 $44.8 $12.3 $918.3 $10.3 $928.6 Operating income (loss) 248.7 (2.0 ) 0.6 247.3 8.8 256.1 Net income attributable to Alliant Energy common shareowners 202.8 2.7 205.5 ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2019 Revenues $2,350.5 $322.5 $33.2 $2,706.2 $61.4 $2,767.6 Operating income 543.0 47.7 4.2 594.9 21.9 616.8 Net income attributable to Alliant Energy common shareowners 422.6 23.1 445.7 Nine Months Ended September 30, 2018 Revenues $2,296.2 $299.0 $36.2 $2,631.4 $29.6 $2,661.0 Operating income 510.2 34.9 2.9 548.0 25.0 573.0 Net income attributable to Alliant Energy common shareowners 395.0 31.8 426.8
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $560.9 $24.8 $10.8 $596.5 Operating income (loss) 175.1 (4.2 ) 2.6 173.5 Earnings available for common stock 141.1 Three Months Ended September 30, 2018 Revenues $509.2 $26.7 $11.7 $547.6 Operating income (loss) 144.7 (3.1 ) 1.5 143.1 Earnings available for common stock 126.5 Nine Months Ended September 30, 2019 Revenues $1,373.0 $187.8 $32.0 $1,592.8 Operating income 290.8 26.3 4.4 321.5 Earnings available for common stock 239.4 Nine Months Ended September 30, 2018 Revenues $1,337.0 $177.0 $34.2 $1,548.2 Operating income 275.7 16.3 4.4 296.4 Earnings available for common stock 224.9
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2019 Revenues $355.0 $16.7 $0.4 $372.1 Operating income (loss) 108.6 (0.5 ) 0.2 108.3 Earnings available for common stock 75.5 Three Months Ended September 30, 2018 Revenues $352.0 $18.1 $0.6 $370.7 Operating income (loss) 104.0 1.1 (0.9 ) 104.2 Earnings available for common stock 76.3 Nine Months Ended September 30, 2019 Revenues $977.5 $134.7 $1.2 $1,113.4 Operating income (loss) 252.2 21.4 (0.2 ) 273.4 Earnings available for common stock 183.2 Nine Months Ended September 30, 2018 Revenues $959.2 $122.0 $2.0 $1,083.2 Operating income (loss) 234.5 18.6 (1.5 ) 251.6 Earnings available for common stock 170.1

Related Parties (Tables)

Related Parties (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC billings to WPL $28 $26 $82 $79 WPL billings to ATC 3 3 10 8
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71
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 nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2019 2018 2019 2018 2019 2018 2019 2018 Corporate Services billings $47 $43 $137 $128 $36 $33 $104 $100 Sales credited 23 11 50 34 2 7 6 16 Purchases billed 93 95 251 268 32 19 91 56
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2019 December 31, 2018 September 30, 2019 December 31, 2018 Net payables to Corporate Services $108 $95 $75 $71
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2019 2018 2019 2018 ATC billings to WPL $28 $26 $82 $79 WPL billings to ATC 3 3 10 8

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 174.4	$ 0
Money market fund investments interest rate, percentage	2.00%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market fund investments	$ 173.7	$ 0
Money market fund investments interest rate, percentage	2.00%

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2018
Regulatory Matters [Line Items]
Regulatory assets		$ 1,840		$ 1,737.3
Regulatory liabilities		1,451		1,493.2
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets		1,404		1,279
Regulatory liabilities		733.6		$ 754.9
2020 Forward-looking Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Interim rate annual increase, amount		90
Forecast [Member] | 2020 Forward-looking Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Requested rate annual increase, amount			$ 127
Billing credit, period			12 months
Forecast [Member] | 2020 Forward-looking Test Period Retail Gas [Member] | IPL [Member]
Regulatory Matters [Line Items]
Requested rate annual increase, amount			$ 12
Tax-related [Member] | 2020 Forward-looking Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		27
Revenue Subject to Refund [Member] | 2020 Forward-looking Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		8
Analog Electric Meters [Member] | Alliant Energy And IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets		$ 36
DAEC PPA [Member]
Regulatory Matters [Line Items]
PPA term amendment		5 years
Recovery period, authorized		5 years
DAEC PPA [Member] | Forecast [Member]
Regulatory Matters [Line Items]
Buyout payment	$ 110

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory assets	$ 1,840	$ 1,737.3
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	825.2	820.6
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	513.1	542.3
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	138.7	111.6
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	110.7	110.8
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	107.7	0
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	34	28
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	21.7	23.6
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	88.9	100.4
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,404	1,279
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	787.2	783.1
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	260	274
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	90.1	55.4
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	75.2	76.3
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	107.7	0
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	15	15.1
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	21.7	23.6
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	47.1	51.5
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	436	458.3
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	38	37.5
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	253.1	268.3
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	48.6	56.2
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	35.5	34.5
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	19	12.9
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 41.8	$ 48.9

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,451	$ 1,493.2
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	851.4	890.6
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	390.9	401.2
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	89.8	104
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	29.1	16.8
WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.8	25.4
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.8	18.5
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	47.2	36.7
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	733.6	754.9
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	365	390.1
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	261	273.3
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48	47.7
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	16.7	11.9
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	16.9	10.2
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26	21.7
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	717.4	738.3
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	486.4	500.5
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	129.9	127.9
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	41.8	56.3
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12.4	4.9
WPL [Member] | WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.8	25.4
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.9	8.3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 21.2	$ 15

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Sep. 30, 2019USD ($)
Receivables [Line Items]
Available capacity	$ 109
Outstanding receivables past due	$ 26.6

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 103	$ 110	$ 108	$ 116
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 45.4	$ 36.4	$ 42.9	$ 49.8

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Receivables [Line Items]
Fair value of deferred proceeds	$ 237	$ 119.4
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	237	119.4
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	154.2	140.1
Unbilled utility revenues	92.1	97.1
Other receivables	0.4	0.1
Receivables sold to third party	246.7	237.3
Less: cash proceeds	1	108
Deferred proceeds	245.7	129.3
Less: allowance for doubtful accounts	8.7	9.9
Fair value of deferred proceeds	$ 237	$ 119.4

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Receivables [Line Items]
Collections	$ 592.2	$ 549.5	$ 1,635.7	$ 1,550.2
Write-offs, net of recoveries	$ 3.2	$ 4.9	$ 11.3	$ 12.9

Investments and Acquisitions (N

Investments and Acquisitions (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Schedule of Investments [Line Items]
Acquisitions of freight management companies	$ 21
Contingent consideration	$ 8
Contingent consideration, expected payment timing	2 years

Investments and Acquisitions (U

Investments and Acquisitions (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (11.6)	$ (9.8)	$ (35.2)	$ (41.6)
ATC Holdings [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(10.5)	(8.9)	(30)	(25.4)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.4)	0.1	(2.8)	(14.5)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.7)	$ (1)	$ (2.4)	$ (1.7)

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Common Equity [Line Items]
Proceeds from issuance of common stock, net	$ 124.8	$ 91.2	$ 185.4	$ 191.3
Comprehensive income (loss)		(0.3)	(0.7)	0.3
IPL [Member]
Common Equity [Line Items]
Comprehensive income (loss)	0	0	0	0
WPL [Member]
Common Equity [Line Items]
Comprehensive income (loss)	$ 0	$ 0	$ 0	$ 0
Equity Forward Agreements [Member]
Common Equity [Line Items]
Common stock issued during the period, equity forward agreements (in shares)			3,790,300
Forward sales price (in dollars per share)	$ 43.99		$ 43.99			$ 44.33
Proceeds from issuance of common stock, net			$ 167
Shares included in diluted earnings per share (in shares)			671,237
Forecast [Member] | Equity Forward Agreements [Member]
Common Equity [Line Items]
Common stock issued during the period, equity forward agreements (in shares)					8,358,973

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	9 Months Ended
	Sep. 30, 2019shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2019 (in shares)	236,063,279
Shareowner Direct Plan (in shares)	390,630
Equity-based compensation plans (in shares)	101,478
Other (in shares)	(2,738)
Shares outstanding, September 30, 2019 (in shares)	240,342,949
Equity Forward Agreements [Member]
Common Stock Oustanding [Roll Forward]
Equity forward agreements (in shares)	3,790,300

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 4,585.7
Beginning balance	$ 4,899.6	$ 4,550.7	4,785.7	$ 4,382.2
Net income attributable to common shareowners	226	205.5	445.7	426.8
Common stock dividends	(84.7)	(78.5)	(252.5)	(233.3)
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances	124.8	91.2	185.4	191.3
Equity-based compensation plans and other	3.5	1.8	5.6	3.1
Other comprehensive income (loss), net of tax		(0.3)	(0.7)	0.3
Ending balance	4,969.2		4,969.2
Ending balance	$ 5,169.2	$ 4,770.4	$ 5,169.2	$ 4,770.4
Common stock dividends (in dollars per share)	$ 0.355	$ 0.335	$ 1.065	$ 1.005
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 2.4	$ 2.3	$ 2.4	$ 2.3
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances		0.1		0.1
Ending balance	2.4	2.4	2.4	2.4
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,108.4	1,947.2	2,045.5	1,845.5
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances	124.8	91.1	185.4	191.2
Equity-based compensation plans and other	3.7	(0.1)	6	1.5
Ending balance	2,236.9	2,038.2	2,236.9	2,038.2
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,597.8	2,412.5	2,545.9	2,346
Net income attributable to common shareowners	226	205.5	445.7	426.8
Common stock dividends	(84.7)	(78.5)	(252.5)	(233.3)
Ending balance	2,739.1	2,539.5	2,739.1	2,539.5
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1	0.1	1.7	(0.5)
Other comprehensive income (loss), net of tax		(0.3)	(0.7)	0.3
Ending balance	1	(0.2)	1	(0.2)
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(10)	(11.4)	(9.8)	(11.1)
Equity-based compensation plans and other	(0.2)	1.9	(0.4)	1.6
Ending balance	(10.2)	(9.5)	(10.2)	(9.5)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,030.7
Beginning balance	3,345.1	2,854.1	3,230.7	2,709.7
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
Common stock dividends	(42.1)	(41.9)	(126)	(125.9)
Capital contributions from parent		100	100	230
Other comprehensive income (loss), net of tax	0	0	0	0
Ending balance	3,244.1		3,244.1
Ending balance	3,444.1	3,038.7	3,444.1	3,038.7
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33.4	33.4	33.4	33.4
Ending balance	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	2,322.8	1,927.8	2,222.8	1,797.8
Capital contributions from parent		100	100	230
Ending balance	2,322.8	2,027.8	2,322.8	2,027.8
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	788.9	692.9	774.5	678.5
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
Common stock dividends	(42.1)	(41.9)	(126)	(125.9)
Ending balance	887.9	777.5	887.9	777.5
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			2,149.5
Beginning balance	2,185.2	2,055.2	2,149.5	1,881.5
Net income attributable to common shareowners	75.5	76.3	183.2	170.1
Common stock dividends	(35.9)	(34.9)	(107.9)	(105)
Capital contributions from parent	100	50	100	200
Other comprehensive income (loss), net of tax	0	0	0	0
Ending balance	2,324.8		2,324.8
Ending balance	2,324.8	2,146.6	2,324.8	2,146.6
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66.2	66.2	66.2	66.2
Ending balance	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	1,309	1,259	1,309	1,109
Capital contributions from parent	100	50	100	200
Ending balance	1,409	1,309	1,409	1,309
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	810	730	774.3	706.3
Net income attributable to common shareowners	75.5	76.3	183.2	170.1
Common stock dividends	(35.9)	(34.9)	(107.9)	(105)
Ending balance	$ 849.6	$ 771.4	$ 849.6	$ 771.4

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	1 Months Ended				9 Months Ended
	Sep. 30, 2019	Jul. 31, 2019	Jun. 30, 2019	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Debt [Line Items]
Credit facility agreement, extension					1 year
Line of credit facility, current borrowing capacity	$ 1,000,000,000				$ 1,000,000,000
Payments to retire long-term debt					253,500,000	$ 603,100,000
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	250,000,000				250,000,000
Payments to retire long-term debt					0	100,000,000
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 300,000,000				300,000,000
Payments to retire long-term debt					$ 250,000,000	$ 0
Senior Debentures [Member] | 3.6% senior debentures due 2029 [Member] | IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt				$ 300,000,000
Interest rate, percent	3.60%				3.60%
Senior Debentures [Member] | 3.5% senior debentures due 2049 [Member] | IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 300,000,000
Interest rate, percent	3.50%				3.50%
Debentures [Member] | 3% debentures due 2029 [Member] | WPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt			$ 350,000,000
Interest rate, percent	3.00%				3.00%
Debentures [Member] | 5% debentures due 2019 [Member] | WPL [Member]
Debt [Line Items]
Interest rate, percent			5.00%
Payments to retire long-term debt		$ 250,000,000
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 450,000,000				$ 450,000,000

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt [Line Items]
Commercial paper outstanding	$ 349.6	$ 441.2
Commercial paper weighted average interest rates	2.30%
Available credit facility capacity	$ 650.4
IPL [Member]
Debt [Line Items]
Commercial paper outstanding	0	50.4
Available credit facility capacity	250
WPL [Member]
Debt [Line Items]
Commercial paper outstanding	0	$ 105.5
Available credit facility capacity	$ 300

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 471.7	$ 153.3	$ 600.6	$ 446.5
Average amount outstanding (based on daily outstanding balances)	$ 399.5	$ 80.8	$ 476.3	$ 207.6
Weighted average interest rates	2.50%	2.20%	2.60%	2.10%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 0	$ 50.4	$ 31.4
Average amount outstanding (based on daily outstanding balances)	0	0	$ 0.2	$ 1.7
Weighted average interest rates			2.80%	2.30%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	89.7	75.4	$ 195.1	$ 109.4
Average amount outstanding (based on daily outstanding balances)	$ 27	$ 23.1	$ 101.8	$ 26.6
Weighted average interest rates	2.30%	2.00%	2.50%	1.90%

Leases (Narrative) (Details)

Leases (Narrative) (Details)	12 Months Ended
	Dec. 31, 2005lease_renewal_period_option
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Finance leases, renewal options (in number of renewal periods)	2

Leases (Operating Leases) (Deta

Leases (Operating Leases) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 17	$ 17
Operating leases liabilities, Other current liabilities	2	2
Operating leases liabilities, Other liabilities	15	15
Operating leases liabilities, Total	$ 17	$ 17
Operating Lease, Weighted average remaining lease term	11 years	11 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%
Operating leases, Cost	$ 1	$ 2
IPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	10	10
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	9	9
Operating leases liabilities, Total	$ 10	$ 10
Operating Lease, Weighted average remaining lease term	12 years	12 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%
Operating leases, Cost	$ 1	$ 1
WPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	7	7
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	6	6
Operating leases liabilities, Total	$ 7	$ 7
Operating Lease, Weighted average remaining lease term	10 years	10 years
Operating leases, Weighted average discount rate, percent	4.00%	4.00%
Operating leases, Cost	$ 0	$ 0

Leases (Finance Lease) (Details

Leases (Finance Lease) (Details) - WPL [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Leases [Line Items]
Finance lease liabilities, Sheboygan Falls Energy Facility	$ 53.6	$ 53.6	$ 60
Sheboygan Falls Energy Facility [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	34	34
Finance lease liabilities, Other current liabilities	8	8
Finance lease liabilities, Sheboygan Falls Energy Facility	54	54
Finance lease liabilities, Total	$ 62	$ 62
Finance Lease, Remaining lease term	6 years	6 years
Finance lease, Discount rate, percent	11.00%	11.00%
Finance lease, Depreciation expense	$ 1	$ 4
Finance lease, Interest expense	1	5
Finance lease, Total expense	$ 2	$ 9

Leases (Expected Maturities of

Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) $ in Millions	Sep. 30, 2019USD ($)
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	$ 0
Operating Leases Liability, 2020	2
Operating Leases Liability, 2021	2
Operating Leases Liability, 2022	2
Operating Leases Liability, 2023	2
Operating Leases Liability, Thereafter	13
Operating Leases Liability, Total	21
Operating Leases Liability, Less: amount representing interest	4
Operating Leases Liability, Present value of minimum lease payments	17
IPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	0
Operating Leases Liability, 2020	1
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, Thereafter	9
Operating Leases Liability, Total	13
Operating Leases Liability, Less: amount representing interest	3
Operating Leases Liability, Present value of minimum lease payments	10
WPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	0
Operating Leases Liability, 2020	1
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, Thereafter	4
Operating Leases Liability, Total	8
Operating Leases Liability, Less: amount representing interest	1
Operating Leases Liability, Present value of minimum lease payments	7
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Finance Lease Liability, Remainder of 2019	4
Finance Lease Liability, 2020	15
Finance Lease Liability, 2021	15
Finance Lease Liability, 2022	15
Finance Lease Liability, 2023	15
Finance Lease Liability, Thereafter	20
Finance Lease Liability, Total	84
Finance Lease Liability, Less: amount representing interest	22
Finance Lease Liability, Present value of minimum lease payments	$ 62

Leases (Future Minimum Operatin

Leases (Future Minimum Operating and Capital Lease Payments) (Details) $ in Millions	Dec. 31, 2018USD ($)
Leases [Line Items]
Operating Leases, 2019	$ 5
Operating Leases, 2020	5
Operating Leases, 2021	3
Operating Leases, 2022	3
Operating Leases, 2023	2
Operating Leases, Thereafter	12
Operating Leases, Total	30
IPL [Member]
Leases [Line Items]
Operating Leases, 2019	3
Operating Leases, 2020	2
Operating Leases, 2021	2
Operating Leases, 2022	2
Operating Leases, 2023	2
Operating Leases, Thereafter	12
Operating Leases, Total	23
WPL [Member]
Leases [Line Items]
Operating Leases, 2019	2
Operating Leases, 2020	3
Operating Leases, 2021	1
Operating Leases, 2022	0
Operating Leases, 2023	0
Operating Leases, Thereafter	0
Operating Leases, Total	6
WPL [Member] | Sheboygan Falls Energy Facility [Member]
Leases [Line Items]
Capital Leases, 2019	15
Capital Leases, 2020	15
Capital Leases, 2021	15
Capital Leases, 2022	15
Capital Leases, 2023	15
Capital Leases, Thereafter	19
Capital Leases, Total	94
Capital Leases, Less: amount representing interest	26
Capital Leases, Present value of minimum capital lease payments	$ 68

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 990.2	$ 928.6	$ 2,767.6	$ 2,661
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	915.9	861.2	2,350.5	2,296.2
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	331.6	312.9	839.6	820.6
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	230.9	215.4	583.3	561.7
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	263.4	247.8	686.3	675.1
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49.8	50	137.3	146.9
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	40.2	35.1	104	91.9
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	41.5	44.8	322.5	299
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	20.4	21.8	187.4	170.1
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	11	89.7	87.3
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.3	3	9.7	11.4
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.8	9	35.7	30.2
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.2	12.3	33.2	36.2
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9.1	8.7	26.7	26.5
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.1	3.6	6.5	9.7
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21.6	10.3	61.4	29.6
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21.6	10.3	61.4	29.6
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	596.5	547.6	1,592.8	1,548.2
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	560.9	509.2	1,373	1,337
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	196	180.1	469.4	461.6
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	158.4	146	386.4	371.8
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	157.5	141.4	392	385
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17.7	18.2	49.2	56.4
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31.3	23.5	76	62.2
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24.8	26.7	187.8	177
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.7	12.6	109.6	100.9
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5.9	6.4	49.5	49.8
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.9	2	6.7	6.1
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5.3	5.7	22	20.2
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10.8	11.7	32	34.2
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9.1	8.7	26.7	26.5
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.7	3	5.3	7.7
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	372.1	370.7	1,113.4	1,083.2
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	355	352	977.5	959.2
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	135.6	132.8	370.2	359
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72.5	69.4	196.9	189.9
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	105.9	106.4	294.3	290.1
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32.1	31.8	88.1	90.5
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.9	11.6	28	29.7
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.7	18.1	134.7	122
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.7	9.2	77.8	69.2
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4.1	4.6	40.2	37.5
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.4	1	3	5.3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3.5	3.3	13.7	10
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.4	0.6	1.2	2
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0.4	$ 0.6	$ 1.2	$ 2

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefits	7.00%	6.90%	7.10%	6.90%
Production tax credits	(9.30%)	(5.40%)	(9.10%)	(5.40%)
Effect of rate-making on property-related differences	(5.60%)	(6.30%)	(5.70%)	(6.70%)
Amortization of excess deferred taxes	(1.10%)	(0.10%)	(1.10%)	(0.30%)
Adjustment for prior period taxes	(1.80%)	(5.70%)	(0.70%)	(2.60%)
IPL's tax benefit riders	(0.80%)	(2.30%)	(0.70%)	(2.20%)
Federal Tax Reform adjustments	0.00%	(2.50%)	0.00%	(1.20%)
Other items, net	(0.20%)	(0.30%)	(1.00%)	(0.70%)
Overall income tax rate	9.20%	5.30%	9.80%	8.80%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefits	8.10%	7.70%	8.10%	7.70%
Production tax credits	(14.70%)	(5.50%)	(14.30%)	(5.40%)
Effect of rate-making on property-related differences	(9.00%)	(11.50%)	(9.30%)	(12.00%)
Amortization of excess deferred taxes	(0.30%)	0.00%	(0.30%)	0.00%
Adjustment for prior period taxes	1.30%	(10.20%)	0.60%	(5.40%)
IPL's tax benefit riders	(1.50%)	(4.80%)	(1.50%)	(4.60%)
Federal Tax Reform adjustments	0.00%	(0.90%)	0.00%	(0.50%)
Other items, net	(0.30%)	(0.60%)	(0.10%)	(1.00%)
Overall income tax rate	4.60%	(4.80%)	4.20%	(0.20%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefits	6.20%	6.20%	6.20%	6.20%
Production tax credits	(4.40%)	(6.40%)	(4.50%)	(6.60%)
Effect of rate-making on property-related differences	(2.80%)	(2.10%)	(2.60%)	(2.30%)
Amortization of excess deferred taxes	(1.70%)	(0.10%)	(1.70%)	(0.10%)
Adjustment for prior period taxes	0.40%	0.00%	(0.30%)	0.00%
Federal Tax Reform adjustments	0.00%	(6.40%)	0.00%	(2.80%)
Other items, net	(0.20%)	(0.40%)	(0.40%)	(1.20%)
Overall income tax rate	18.50%	11.80%	17.70%	14.20%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2019USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 611
Tax credits, carryforward amount	337
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	522
Tax credits, carryforward amount	162
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	41
Tax credits, carryforward amount	156
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	677
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	12
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)$ / sharesshares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost | $	$ 7.2
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 | $	$ 4
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost | $	$ 2.9
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	91,816
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 47.23
Shares included in diluted earnings per share (in shares)	122,720
Performance Shares [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0.00%
Performance Shares [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200.00%
Performance Restricted Stock Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	91,816
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 46.10
Instrument valuation based on shares of common stock, number of shares	1
Performance Restricted Stock Unit [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0.00%
Performance Restricted Stock Unit [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200.00%
Restricted Stock Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	105,348
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 45.98
Instrument valuation based on shares of common stock, number of shares	1

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.5	$ 3.1	$ 7.3	$ 9.1
Interest cost	12.5	11.7	37.4	35.1
Expected return on plan assets	(15.1)	(17.4)	(45.1)	(52.3)
Amortization of prior service credit	(0.2)	(0.2)	(0.5)	(0.5)
Amortization of actuarial loss	9.1	8.8	27.3	26.4
Total	8.8	6	26.4	17.8
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	1	2.5	3.1
Interest cost	2.2	2	6.4	5.8
Expected return on plan assets	(1.2)	(1.5)	(3.7)	(4.5)
Amortization of prior service credit	(0.1)	0	(0.2)	(0.1)
Amortization of actuarial loss	0.8	0.8	2.4	2.5
Total	2.5	2.3	7.4	6.8
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.6	1.8	4.6	5.5
Interest cost	5.6	5.3	17	16
Expected return on plan assets	(7)	(8.1)	(21.1)	(24.4)
Amortization of prior service credit	(0.1)	0	(0.2)	(0.1)
Amortization of actuarial loss	3.9	3.7	11.8	11.2
Total	4	2.7	12.1	8.2
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4	1	1.3
Interest cost	0.8	0.7	2.5	2.3
Expected return on plan assets	(0.9)	(1.1)	(2.7)	(3.3)
Amortization of prior service credit	0	0	0	0
Amortization of actuarial loss	0.4	0.4	1.1	1
Total	0.6	0.4	1.9	1.3
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	1.1	2.6	3.3
Interest cost	5.3	5	16.1	15.1
Expected return on plan assets	(6.5)	(7.6)	(19.6)	(22.8)
Amortization of prior service credit	0	0	(0.1)	(0.1)
Amortization of actuarial loss	4.4	4.3	13.2	12.9
Total	4.1	2.8	12.2	8.4
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4	0.9	1.2
Interest cost	0.9	0.8	2.6	2.3
Expected return on plan assets	(0.2)	(0.2)	(0.5)	(0.5)
Amortization of prior service credit	0	0	(0.1)	(0.1)
Amortization of actuarial loss	0.4	0.5	1.2	1.5
Total	$ 1.4	$ 1.5	$ 4.1	$ 4.4

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Compensation expense	$ 7.5	$ 4.2	$ 15.6	$ 12.6
Income tax benefits	2.1	1.2	4.4	3.6
IPL [Member]
Compensation expense	4.2	2.4	8.7	7
Income tax benefits	1.2	0.7	2.5	2.1
WPL [Member]
Compensation expense	3	1.7	6.2	5.1
Income tax benefits	$ 0.8	$ 0.5	$ 1.7	$ 1.4

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 177.5
Revisions in estimated cash flows	(5.8)
Liabilities settled	(5.9)
Liabilities incurred	26.2	[1]
Accretion expense	5.3
Balance, September 30	197.3
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	118.3
Revisions in estimated cash flows	(7)
Liabilities settled	(5.6)
Liabilities incurred	26.2	[1]
Accretion expense	3.5
Balance, September 30	$ 135.4
[1]	During the nine months ended September 30 , 2019, Alliant Energy and IPL recognized additional asset retirement obligations related to IPL’s newly constructed Upland Prairie and English Farms 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	9 Months Ended
	Sep. 30, 2019DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	18,141
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	8,630
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	9,511
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	184,007
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	101,579
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	82,428
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	7,620
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	3,311
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,309
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	5,796
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	5,796

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 18.6	$ 24.6
Non-current derivative assets	11.7	3.7
Current derivative liabilities	13.4	5.6
Non-current derivative liabilities	18.4	17.7
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	12.8	16.1
Non-current derivative assets	10.5	1.6
Current derivative liabilities	5.6	3.1
Non-current derivative liabilities	7.8	8.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	5.8	8.5
Non-current derivative assets	1.2	2.1
Current derivative liabilities	7.8	2.5
Non-current derivative liabilities	$ 10.6	$ 9.6

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Assets:
Money market fund investments	$ 174.4	$ 0
Deferred proceeds	237	119.4
Liabilities:
Long-term debt (incl. current maturities)	7,018.4	5,860.8
IPL [Member]
Assets:
Money market fund investments	173.7	0
Deferred proceeds	237	119.4
Liabilities:
Long-term debt (incl. current maturities)	3,537	2,691.2
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,314.1	2,043.7
Commodity Contracts [Member]
Assets:
Derivatives	30.3	28.3
Liabilities:
Derivatives	31.8	23.3
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	23.3	17.7
Liabilities:
Derivatives	13.4	11.2
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	7	10.6
Liabilities:
Derivatives	18.4	12.1
Level 1 [Member]
Assets:
Money market fund investments	174.4	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	173.7	0
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)	7,016.4	5,858.4
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,537	2,691.2
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,314.1	2,043.7
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	8.1	8.9
Liabilities:
Derivatives	31.3	16.1
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	4.8	4
Liabilities:
Derivatives	12.9	6.5
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	3.3	4.9
Liabilities:
Derivatives	18.4	9.6
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	237	119.4
Liabilities:
Long-term debt (incl. current maturities)	2	2.4
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	237	119.4
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	22.2	19.4
Liabilities:
Derivatives	0.5	7.2
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	18.5	13.7
Liabilities:
Derivatives	0.5	4.7
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	3.7	5.7
Liabilities:
Derivatives	0	2.5
Carrying Amount [Member]
Assets:
Money market fund investments	174.4	0
Deferred proceeds	237	119.4
Liabilities:
Long-term debt (incl. current maturities)	6,191.9	5,502.8
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	173.7	0
Deferred proceeds	237	119.4
Liabilities:
Long-term debt (incl. current maturities)	3,146.8	2,552.3
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	1,932.3	1,834.9
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	30.3	28.3
Liabilities:
Derivatives	31.8	23.3
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	23.3	17.7
Liabilities:
Derivatives	13.4	11.2
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	7	10.6
Liabilities:
Derivatives	$ 18.4	$ 12.1

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 13.2	$ (10.7)	$ 12.2	$ (12.2)
Total net gains (losses) included in changes in net assets (realized/unrealized)		12.7	25.7	6.9	15.7
Transfers out of Level 3		(1.2)	15.6	2.8	15.6
Purchases				13.8	26.7
Sales		0	(0.2)	(0.2)	(0.2)
Settlements		(3)	(6.2)	(13.8)	(21.4)
Ending balance		21.7	24.2	21.7	24.2
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 September 30		12.7	26.1	10.1	16.5
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		9.3	(4.1)	9	(1.4)
Total net gains (losses) included in changes in net assets (realized/unrealized)		11.5	16.8	8.6	7.6
Transfers out of Level 3		(0.6)	10.5	2	10.5
Purchases				9.5	19.3
Sales		0	(0.1)	(0.1)	(0.1)
Settlements		(2.2)	(4.9)	(11)	(17.7)
Ending balance		18	18.2	18	18.2
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 September 30		11.5	16.8	10.5	7.9
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		3.9	(6.6)	3.2	(10.8)
Total net gains (losses) included in changes in net assets (realized/unrealized)		1.2	8.9	(1.7)	8.1
Transfers out of Level 3		(0.6)	5.1	0.8	5.1
Purchases				4.3	7.4
Sales		0	(0.1)	(0.1)	(0.1)
Settlements		(0.8)	(1.3)	(2.8)	(3.7)
Ending balance		3.7	6	3.7	6
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		1.2	9.3	(0.4)	8.6
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		214.6	208.3	119.4	222.1
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
Sales		0	0	0	0
Settlements	[1]	22.4	35.4	117.6	21.6
Ending balance		237	243.7	237	243.7
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		0	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		214.6	208.3	119.4	222.1
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
Sales		0	0	0	0
Settlements	[1]	22.4	35.4	117.6	21.6
Ending balance		237	243.7	237	243.7
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		$ 0	$ 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	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 21.7	$ 13.2	$ 12.2	$ 24.2	$ (10.7)	$ (12.2)
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	13.1		3.2
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	8.6		9
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	18	9.3	9	18.2	(4.1)	(1.4)
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	12.5		1.8
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	5.5		7.2
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	3.7	$ 3.9	3.2	$ 6	$ (6.6)	$ (10.8)
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	0.6		1.4
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 3.1		$ 1.8

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,230
Present value abandonment obligation	38
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	723
Indemnification obligations, maximum	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	498
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	124
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	79
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	45
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	145	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	144	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1	[1]
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Indemnification obligations, maximum	82
Indemnification Agreement [Member] | Purchased Power [Member]
Commitments and Contingencies [Line Items]
Indemnification obligations, maximum	$ 17
Workforce Subject to Collective Bargaining Arrangements [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement	54.00%
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	27.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement	82.00%
[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	9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,230
Individual commitments incurred			1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			723
Individual commitments incurred			1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			498
Individual commitments incurred			1
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		145
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		144
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			892
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			460
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			432
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		117
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		76
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		41
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		76
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		43
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		$ 24
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 entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2019 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 September 30, 2019 .

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 19
IPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	16
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	14
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	12
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	31
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 25

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 990.2	$ 928.6	$ 2,767.6	$ 2,661
Operating income (loss)	290.2	256.1	616.8	573
Net income attributable to common shareowners	226	205.5	445.7	426.8
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	596.5	547.6	1,592.8	1,548.2
Operating income (loss)	173.5	143.1	321.5	296.4
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	372.1	370.7	1,113.4	1,083.2
Operating income (loss)	108.3	104.2	273.4	251.6
Net income attributable to common shareowners	75.5	76.3	183.2	170.1
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	915.9	861.2	2,350.5	2,296.2
Operating income (loss)	283.7	248.7	543	510.2
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	560.9	509.2	1,373	1,337
Operating income (loss)	175.1	144.7	290.8	275.7
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	355	352	977.5	959.2
Operating income (loss)	108.6	104	252.2	234.5
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	41.5	44.8	322.5	299
Operating income (loss)	(4.7)	(2)	47.7	34.9
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	24.8	26.7	187.8	177
Operating income (loss)	(4.2)	(3.1)	26.3	16.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	16.7	18.1	134.7	122
Operating income (loss)	(0.5)	1.1	21.4	18.6
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	11.2	12.3	33.2	36.2
Operating income (loss)	2.8	0.6	4.2	2.9
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10.8	11.7	32	34.2
Operating income (loss)	2.6	1.5	4.4	4.4
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.4	0.6	1.2	2
Operating income (loss)	0.2	(0.9)	(0.2)	(1.5)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	968.6	918.3	2,706.2	2,631.4
Operating income (loss)	281.8	247.3	594.9	548
Net income attributable to common shareowners	216.6	202.8	422.6	395
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	21.6	10.3	61.4	29.6
Operating income (loss)	8.4	8.8	21.9	25
Net income attributable to common shareowners	$ 9.4	$ 2.7	$ 23.1	$ 31.8

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
ATC [Member] | WPL Owed ATC LLC [Member] | Equity Method Investee [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 9	$ 8

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 47	$ 43	$ 137	$ 128
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	36	33	104	100
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	23	11	50	34
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	2	7	6	16
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	93	95	251	268
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 32	$ 19	$ 91	$ 56

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 108	$ 95
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 75	$ 71

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 28	$ 26	$ 82	$ 79
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 3	$ 3	$ 10	$ 8