Alliant Energy (LNT) 10-Q 3 May 19 2019 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	3 Months Ended
	Mar. 31, 2019shares
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	0000352541
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	237,394,409
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
IPL [Member]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	0000052485
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	13,370,788
WPL [Member]
Entity Registrant Name	WISCONSIN POWER & LIGHT CO
Entity Central Index Key	0000107832
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Electric utility	$ 743.4	$ 708.7
Gas utility	215.8	185.6
Other utility	11.1	13.2
Non-utility	16.9	8.8
Total revenues	987.2	916.3
Operating expenses:
Electric production fuel and purchased power	218.4	203.2
Electric transmission service	123	126.4
Cost of gas sold	121.6	111.2
Other operation and maintenance	181.2	162.4
Depreciation and amortization	136.9	120.4
Taxes other than income taxes	29.3	27
Total operating expenses	810.4	750.6
Operating income	176.8	165.7
Other (income) and deductions:
Interest expense	66.3	59.2
Equity income from unconsolidated investments, net	(10.9)	(21.3)
Allowance for funds used during construction	(25.4)	(14.9)
Other	4	2.4
Total other (income) and deductions	34	25.4
Income before income taxes	142.8	140.3
Income taxes	15.1	16.8
Net income	127.7	123.5
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	$ 125.1	$ 120.9
Weighted average number of common shares outstanding (basic) (in shares)	236.5	231.4
Weighted average number of common shares outstanding (diluted) (in shares)	236.6	231.4
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.53	$ 0.52
IPL [Member]
Revenues:
Electric utility	$ 419.8	$ 405.7
Gas utility	124.6	108.1
Other utility	10.7	12
Total revenues	555.1	525.8
Operating expenses:
Electric production fuel and purchased power	128.9	114.6
Electric transmission service	87.7	90.8
Cost of gas sold	63.3	60.6
Other operation and maintenance	108	105.5
Depreciation and amortization	77.1	64.8
Taxes other than income taxes	16.6	13.9
Total operating expenses	481.6	450.2
Operating income	73.5	75.6
Other (income) and deductions:
Interest expense	29.4	29.8
Allowance for funds used during construction	(15.8)	(7.4)
Other	1.9	0.8
Total other (income) and deductions	15.5	23.2
Income before income taxes	58	52.4
Income taxes	2.1	3.1
Net income	55.9	49.3
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	53.3	46.7
WPL [Member]
Revenues:
Electric utility	323.6	303
Gas utility	91.2	77.5
Other utility	0.4	1.2
Total revenues	415.2	381.7
Operating expenses:
Electric production fuel and purchased power	89.5	88.6
Electric transmission service	35.3	35.6
Cost of gas sold	58.3	50.6
Other operation and maintenance	63.5	56.3
Depreciation and amortization	58.6	54.6
Taxes other than income taxes	11.9	12
Total operating expenses	317.1	297.7
Operating income	98.1	84
Other (income) and deductions:
Interest expense	25.8	24.7
Allowance for funds used during construction	(9.6)	(7.5)
Other	1.6	1.1
Total other (income) and deductions	17.8	18.3
Income before income taxes	80.3	65.7
Income taxes	14.6	11.7
Net income	65.7	54
Net income attributable to common shareowners	$ 65.7	$ 54

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 10.1	$ 20.9
Accounts receivable, less allowance for doubtful accounts	417.9	350.4
Production fuel, at weighted average cost	47	61.4
Gas stored underground, at weighted average cost	15.9	49
Materials and supplies, at weighted average cost	105.1	101.4
Regulatory assets	65.8	79.8
Other	153.4	122.2
Total current assets	815.2	785.1
Property, plant and equipment, net	12,665.2	12,462.4
Investments:
ATC Holdings	295	293.6
Other	138.6	137.7
Total investments	433.6	431.3
Other assets:
Regulatory assets	1,726.6	1,657.5
Deferred charges and other	72.8	89.7
Total other assets	1,799.4	1,747.2
Total assets	15,713.4	15,426
Current liabilities:
Current maturities of long-term debt	256.5	256.5
Commercial paper	514.7	441.2
Accounts payable	387.7	543.3
Regulatory liabilities	179.8	142.7
Other	249	260.4
Total current liabilities	1,587.7	1,644.1
Long-term debt, net (excluding current portion)	5,362.2	5,246.3
Other liabilities:
Deferred tax liabilities	1,642	1,603.1
Regulatory liabilities	1,302.6	1,350.5
Pension and other benefit obligations	493.6	509.1
Other	442.9	287.2
Total other liabilities	3,881.1	3,749.9
Commitments and contingencies (Note 14)
Common equity:
Common stock	2.4	2.4
Additional paid-in capital	2,100	2,045.5
Retained earnings	2,587.3	2,545.9
Accumulated other comprehensive income	2.4	1.7
Shares in deferred compensation trust - 375,542 and 384,580 shares at a weighted average cost of $25.93 and $25.60 per share	(9.7)	(9.8)
Total common equity	4,682.4	4,585.7
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	4,882.4	4,785.7
Total liabilities and equity	15,713.4	15,426
IPL [Member]
Current assets:
Cash and cash equivalents	3.9	9.7
Accounts receivable, less allowance for doubtful accounts	209.5	153.5
Production fuel, at weighted average cost	31.2	44.8
Gas stored underground, at weighted average cost	5.4	26.1
Materials and supplies, at weighted average cost	56.9	55.4
Regulatory assets	27	39.2
Other	21.3	43.1
Total current assets	355.2	371.8
Property, plant and equipment, net	6,947.9	6,781.5
Other assets:
Regulatory assets	1,324.4	1,239.8
Deferred charges and other	19.5	18.3
Total other assets	1,343.9	1,258.1
Total assets	8,647	8,411.4
Current liabilities:
Commercial paper	0	50.4
Accounts payable	227.3	304.9
Regulatory liabilities	107.3	90
Other	150.3	161.8
Total current liabilities	484.9	607.1
Long-term debt, net (excluding current portion)	2,667.8	2,552.3
Other liabilities:
Deferred tax liabilities	970.9	957.3
Regulatory liabilities	641.5	664.9
Pension and other benefit obligations	174.6	178.4
Other	365.3	220.7
Total other liabilities	2,152.3	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	785.8	774.5
Total common equity	3,142	3,030.7
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	3,342	3,230.7
Total liabilities and equity	8,647	8,411.4
WPL [Member]
Current assets:
Cash and cash equivalents	3.4	8.7
Accounts receivable, less allowance for doubtful accounts	198.7	190.1
Production fuel, at weighted average cost	15.8	16.6
Gas stored underground, at weighted average cost	10.5	22.9
Materials and supplies, at weighted average cost	45.3	42.9
Regulatory assets	38.8	40.6
Other	103.5	62.8
Total current assets	416	384.6
Property, plant and equipment, net	5,322.8	5,287.3
Other assets:
Regulatory assets	402.2	417.7
Deferred charges and other	24	62.9
Total other assets	426.2	480.6
Total assets	6,165	6,152.5
Current liabilities:
Current maturities of long-term debt	250	250
Commercial paper	138.4	105.5
Accounts payable	104.5	180.9
Regulatory liabilities	72.5	52.7
Other	112.5	105.5
Total current liabilities	677.9	694.6
Long-term debt, net (excluding current portion)	1,585.4	1,584.9
Other liabilities:
Deferred tax liabilities	601	582
Regulatory liabilities	661.1	685.6
Finance lease obligations - Sheboygan Falls Energy Facility	57.9	60
Pension and other benefit obligations	214.2	217.7
Other	188.3	178.2
Total other liabilities	1,722.5	1,723.5
Commitments and contingencies (Note 14)
Common equity:
Common stock	66.2	66.2
Additional paid-in capital	1,309	1,309
Retained earnings	804	774.3
Total common equity	2,179.2	2,149.5
Total equity	2,179.2	2,149.5
Total liabilities and equity	$ 6,165	$ 6,152.5

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	237,394,409	236,063,279
Shares in deferred compensation trust (in shares)	375,542	384,580
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 25.93	$ 25.60
IPL [Member]
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Common stock, par value	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed Consolidated Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 127.7	$ 123.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	136.9	120.4
Deferred tax expense and tax credits	21.7	17.6
Other	(10.1)	(14.8)
Other changes in assets and liabilities:
Accounts receivable	(121.6)	(80.6)
Gas stored underground	33.1	28.2
Accounts payable	(42.7)	(59.6)
Regulatory liabilities	14.1	34.2
Other	22	(12.6)
Net cash flows from operating activities	181.1	156.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(374)	(335.2)
Other construction and acquisition expenditures	(32.1)	(20.3)
Cash receipts on sold receivables	53.4	217.3
Other	(12.1)	(14)
Net cash flows used for investing activities	(364.8)	(152.2)
Cash flows from (used for) financing activities:
Common stock dividends	(83.7)	(77.5)
Proceeds from issuance of common stock, net	54.6	6.3
Net change in commercial paper	188.5	62.1
Other	16.6	(0.7)
Net cash flows from (used for) financing activities	176	(9.8)
Net decrease in cash, cash equivalents and restricted cash	(7.7)	(5.7)
Cash, cash equivalents and restricted cash at beginning of period	25.5	33.9
Cash, cash equivalents and restricted cash at end of period	17.8	28.2
Supplemental cash flows information:
Interest, net of capitalized interest	(62.9)	(54.2)
Income taxes, net	6.8	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	167.5	144.9
Beneficial interest obtained in exchange for securitized accounts receivable	178.3	120.9
IPL [Member]
Cash flows from operating activities:
Net income	55.9	49.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	77.1	64.8
Other	(10.1)	0
Other changes in assets and liabilities:
Accounts receivable	(112.6)	(99.7)
Gas stored underground	20.7	16.7
Accounts payable	(15)	(34.3)
Regulatory liabilities	17.4	21.7
Other	43.3	(16.7)
Net cash flows from operating activities	76.7	1.8
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(261.3)	(218.2)
Cash receipts on sold receivables	53.4	217.3
Other	(13.9)	(10.5)
Net cash flows used for investing activities	(221.8)	(11.4)
Cash flows from (used for) financing activities:
Common stock dividends	(42)	(41.9)
Capital contributions from parent	100	0
Net change in commercial paper	64.6	45.9
Other	17	4.9
Net cash flows from (used for) financing activities	139.6	8.9
Net decrease in cash, cash equivalents and restricted cash	(5.5)	(0.7)
Cash, cash equivalents and restricted cash at beginning of period	12.4	7.2
Cash, cash equivalents and restricted cash at end of period	6.9	6.5
Supplemental cash flows information:
Interest, net of capitalized interest	(36)	(28.2)
Income taxes, net	6.8	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	106.6	68.3
Beneficial interest obtained in exchange for securitized accounts receivable	178.3	120.9
WPL [Member]
Cash flows from operating activities:
Net income	65.7	54
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	58.6	54.6
Deferred tax expense and tax credits	14.8	6.7
Other	(2)	(4.7)
Other changes in assets and liabilities:
Accounts receivable	(10.3)	18.7
Accounts payable	(28.7)	(23)
Other	24.1	35.4
Net cash flows from operating activities	122.2	141.7
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(112.7)	(117)
Other	(7.6)	(11.7)
Net cash flows used for investing activities	(120.3)	(128.7)
Cash flows from (used for) financing activities:
Common stock dividends	(36)	(35)
Net change in commercial paper	32.9	5.6
Other	(3.3)	(1.9)
Net cash flows from (used for) financing activities	(6.4)	(31.3)
Net decrease in cash, cash equivalents and restricted cash	(4.5)	(18.3)
Cash, cash equivalents and restricted cash at beginning of period	9.2	24.2
Cash, cash equivalents and restricted cash at end of period	4.7	5.9
Supplemental cash flows information:
Interest, net of capitalized interest	(22.5)	(21.5)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 57.3	$ 73.9

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 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 three months ended March 31, 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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) . NOTE 1(b) 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(c) New Accounting Standards - 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. Cash Flows Statements - On January 1, 2018, Alliant Energy and IPL adopted an accounting standard that requires classification of the consideration received for the beneficial interest obtained for transferring accounts receivable from IPL’s sales of accounts receivable program as an investing activity, instead of an operating activity. Alliant Energy and IPL currently use a method of presentation that allocates cash flows between operating and investing activities based on daily transactional activity. For the three months ended March 31, 2018, Alliant Energy and IPL initially utilized a method of presentation that allocated cash flows between operating and investing activities based on monthly transactional activity. The change in method of presentation to daily transactional activity increases Alliant Energy’s operating cash flows by $67.0 million to $156.3 million and increases IPL’s operating cash flows by $67.0 million to $1.8 million for the three months ended March 31, 2018.
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 three months ended March 31, 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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) . NOTE 1(b) 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(c) New Accounting Standards - 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. Cash Flows Statements - On January 1, 2018, Alliant Energy and IPL adopted an accounting standard that requires classification of the consideration received for the beneficial interest obtained for transferring accounts receivable from IPL’s sales of accounts receivable program as an investing activity, instead of an operating activity. Alliant Energy and IPL currently use a method of presentation that allocates cash flows between operating and investing activities based on daily transactional activity. For the three months ended March 31, 2018, Alliant Energy and IPL initially utilized a method of presentation that allocated cash flows between operating and investing activities based on monthly transactional activity. The change in method of presentation to daily transactional activity increases Alliant Energy’s operating cash flows by $67.0 million to $156.3 million and increases IPL’s operating cash flows by $67.0 million to $1.8 million for the three months ended March 31, 2018.
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 three months ended March 31, 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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) . NOTE 1(b) 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(c) New Accounting Standards - 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. Cash Flows Statements - On January 1, 2018, Alliant Energy and IPL adopted an accounting standard that requires classification of the consideration received for the beneficial interest obtained for transferring accounts receivable from IPL’s sales of accounts receivable program as an investing activity, instead of an operating activity. Alliant Energy and IPL currently use a method of presentation that allocates cash flows between operating and investing activities based on daily transactional activity. For the three months ended March 31, 2018, Alliant Energy and IPL initially utilized a method of presentation that allocated cash flows between operating and investing activities based on monthly transactional activity. The change in method of presentation to daily transactional activity increases Alliant Energy’s operating cash flows by $67.0 million to $156.3 million and increases IPL’s operating cash flows by $67.0 million to $1.8 million for the three months ended March 31, 2018.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 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 March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3 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 five years. The IUB approved recovery of the buyout payment from IPL’s retail customers over a five -year period following the payment. The offsetting obligation has been discounted and is recorded in “Other liabilities” on Alliant Energy’s and IPL’s balance sheets. Utility Rate Reviews IPL’s Retail Electric Rate Review (2020 Forward Test Period) - In March 2019, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers by $204 million , based on a 2020 forward-looking Test Period. IPL currently expects the proposed retail electric base rate increase to be largely offset by cost reductions in non-base rate factors, including lower electric transmission, fuel-related and energy efficiency costs. 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 rate base 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. Interveners have challenged, among other issues, the return on common equity percentage used in interim rates, and IPL expects that the IUB will address this issue in its final decision. 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 from the IUB in the fourth quarter of 2019 on the interim rate increase, as well as the remaining $114 million of final rates, which would be effective in the first quarter of 2020. The key drivers for IPL’s request included recovery of capital projects, including new wind generation. IPL’s Retail Gas Rate Review (2020 Forward Test Period) - In March 2019, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers by $21 million , based on a 2020 forward-looking Test Period. IPL currently expects the proposed retail gas base rate increase will be more than offset by cost reductions in non-base rate factors, including lower cost of gas sold and energy efficiency costs. The key drivers for IPL’s request included recovery of capital projects. IPL currently expects a decision 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 March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3 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 five years. The IUB approved recovery of the buyout payment from IPL’s retail customers over a five -year period following the payment. The offsetting obligation has been discounted and is recorded in “Other liabilities” on Alliant Energy’s and IPL’s balance sheets. Utility Rate Reviews IPL’s Retail Electric Rate Review (2020 Forward Test Period) - In March 2019, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers by $204 million , based on a 2020 forward-looking Test Period. IPL currently expects the proposed retail electric base rate increase to be largely offset by cost reductions in non-base rate factors, including lower electric transmission, fuel-related and energy efficiency costs. 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 rate base 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. Interveners have challenged, among other issues, the return on common equity percentage used in interim rates, and IPL expects that the IUB will address this issue in its final decision. 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 from the IUB in the fourth quarter of 2019 on the interim rate increase, as well as the remaining $114 million of final rates, which would be effective in the first quarter of 2020. The key drivers for IPL’s request included recovery of capital projects, including new wind generation. IPL’s Retail Gas Rate Review (2020 Forward Test Period) - In March 2019, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers by $21 million , based on a 2020 forward-looking Test Period. IPL currently expects the proposed retail gas base rate increase will be more than offset by cost reductions in non-base rate factors, including lower cost of gas sold and energy efficiency costs. The key drivers for IPL’s request included recovery of capital projects. IPL currently expects a decision 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 March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3

Receivables

Receivables	3 Months Ended
	Mar. 31, 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 March 31, 2019 , IPL had $21.0 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 months ended March 31 were as follows (in millions): 2019 2018 Maximum outstanding aggregate cash proceeds $108.0 $116.0 Average outstanding aggregate cash proceeds 81.0 61.1 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2019 December 31, 2018 Customer accounts receivable $169.9 $140.1 Unbilled utility revenues 86.8 97.1 Other receivables 0.1 0.1 Receivables sold to third party 256.8 237.3 Less: cash proceeds 69.0 108.0 Deferred proceeds 187.8 129.3 Less: allowance for doubtful accounts 9.5 9.9 Fair value of deferred proceeds $178.3 $119.4 As of March 31, 2019 , outstanding receivables past due under the Receivables Agreement were $38.8 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2019 2018 Collections $555.8 $517.0 Write-offs, net of recoveries 5.5 6.1
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 March 31, 2019 , IPL had $21.0 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 months ended March 31 were as follows (in millions): 2019 2018 Maximum outstanding aggregate cash proceeds $108.0 $116.0 Average outstanding aggregate cash proceeds 81.0 61.1 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2019 December 31, 2018 Customer accounts receivable $169.9 $140.1 Unbilled utility revenues 86.8 97.1 Other receivables 0.1 0.1 Receivables sold to third party 256.8 237.3 Less: cash proceeds 69.0 108.0 Deferred proceeds 187.8 129.3 Less: allowance for doubtful accounts 9.5 9.9 Fair value of deferred proceeds $178.3 $119.4 As of March 31, 2019 , outstanding receivables past due under the Receivables Agreement were $38.8 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three months ended March 31 were as follows (in millions): 2019 2018 Collections $555.8 $517.0 Write-offs, net of recoveries 5.5 6.1

Investments and Acquisitions

Investments and Acquisitions	3 Months Ended
	Mar. 31, 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 months ended March 31 was as follows (in millions): 2019 2018 ATC Holdings ($9.5 ) ($8.7 ) Non-utility wind farm in Oklahoma (1.1 ) (12.1 ) Other (0.3 ) (0.5 ) ($10.9 ) ($21.3 ) 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	3 Months Ended
	Mar. 31, 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 1,090,300 Shareowner Direct Plan issuances 142,090 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, March 31, 2019 237,394,409 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 the first quarter of 2019, Alliant Energy settled $48 million under the forward sale agreements by delivering 1,090,300 shares of newly issued Alliant Energy common stock at a forward sale price of $44.13 per share. Alliant Energy used the net proceeds from the settlement for general corporate purposes. As of March 31, 2019 , 96,261 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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5 Comprehensive Income - For the three months ended March 31, 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 months ended March 31, 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 1,090,300 Shareowner Direct Plan issuances 142,090 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, March 31, 2019 237,394,409 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 the first quarter of 2019, Alliant Energy settled $48 million under the forward sale agreements by delivering 1,090,300 shares of newly issued Alliant Energy common stock at a forward sale price of $44.13 per share. Alliant Energy used the net proceeds from the settlement for general corporate purposes. As of March 31, 2019 , 96,261 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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5 Comprehensive Income - For the three months ended March 31, 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 months ended March 31, 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 1,090,300 Shareowner Direct Plan issuances 142,090 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, March 31, 2019 237,394,409 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 the first quarter of 2019, Alliant Energy settled $48 million under the forward sale agreements by delivering 1,090,300 shares of newly issued Alliant Energy common stock at a forward sale price of $44.13 per share. Alliant Energy used the net proceeds from the settlement for general corporate purposes. As of March 31, 2019 , 96,261 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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5 Comprehensive Income - For the three months ended March 31, 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 months ended March 31, 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	3 Months Ended
	Mar. 31, 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 March 31, 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): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 . NOTE 6(b) Long-term Debt - As of March 31, 2019 , $115.0 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s balance sheets due to the existence of a long-term credit facility that back-stops this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis. As of March 31, 2019 , this commercial paper balance had a 2.7% interest rate. In April 2019, IPL issued $300 million of 3.6% senior debentures due 2029. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of IPL’s wind projects.
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 March 31, 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): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 . NOTE 6(b) Long-term Debt - As of March 31, 2019 , $115.0 million of commercial paper was recorded in “Long-term debt, net” on Alliant Energy’s and IPL’s balance sheets due to the existence of a long-term credit facility that back-stops this commercial paper balance, along with Alliant Energy’s and IPL’s intent and ability to refinance these balances on a long-term basis. As of March 31, 2019 , this commercial paper balance had a 2.7% interest rate. In April 2019, IPL issued $300 million of 3.6% senior debentures due 2029. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of IPL’s wind projects.
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 March 31, 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): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 .

Leases

Leases	3 Months Ended
	Mar. 31, 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): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 % 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): March 31, 2019 Property, plant and equipment, net $37 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 58 Total finance lease liabilities $66 Three Months Ended March 31, 2019 Depreciation expense $1 Interest expense 2 Total finance lease expense $3 Remaining lease term 6 years Discount rate 11 % Expected Maturities - As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66 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): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 % 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): March 31, 2019 Property, plant and equipment, net $37 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 58 Total finance lease liabilities $66 Three Months Ended March 31, 2019 Depreciation expense $1 Interest expense 2 Total finance lease expense $3 Remaining lease term 6 years Discount rate 11 % Expected Maturities - As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66 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): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 % 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): March 31, 2019 Property, plant and equipment, net $37 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 58 Total finance lease liabilities $66 Three Months Ended March 31, 2019 Depreciation expense $1 Interest expense 2 Total finance lease expense $3 Remaining lease term 6 years Discount rate 11 % Expected Maturities - As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66 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): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 % 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): March 31, 2019 Property, plant and equipment, net $37 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 58 Total finance lease liabilities $66 Three Months Ended March 31, 2019 Depreciation expense $1 Interest expense 2 Total finance lease expense $3 Remaining lease term 6 years Discount rate 11 % Expected Maturities - As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66 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	3 Months Ended
	Mar. 31, 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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7
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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7
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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 % Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151
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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 % Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151
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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 % Deferred Tax Assets and Liabilities - Carryforwards - At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151

Benefit Plans

Benefit Plans	3 Months Ended
	Mar. 31, 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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5 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 months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4 As of March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13.7 million , $7.6 million and $5.6 million , respectively, which is expected to be recognized over a weighted average period of between one and two years. In the first quarter of 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 three -year performance period. In the first quarter of 2019, 80,837 performance shares were granted with a grant date fair value of $46.35 . 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 three -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 three -year time-vesting period. In the first quarter of 2019, 80,837 performance restricted stock units and 95,938 restricted stock units were granted with a grant date fair value of $45.63 , 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 March 31, 2019 , an immaterial amount of shares was 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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5 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 months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4 As of March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13.7 million , $7.6 million and $5.6 million , respectively, which is expected to be recognized over a weighted average period of between one and two years. In the first quarter of 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 three -year performance period. In the first quarter of 2019, 80,837 performance shares were granted with a grant date fair value of $46.35 . 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 three -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 three -year time-vesting period. In the first quarter of 2019, 80,837 performance restricted stock units and 95,938 restricted stock units were granted with a grant date fair value of $45.63 , 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 March 31, 2019 , an immaterial amount of shares was 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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5 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 months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4 As of March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $13.7 million , $7.6 million and $5.6 million , respectively, which is expected to be recognized over a weighted average period of between one and two years. In the first quarter of 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 three -year performance period. In the first quarter of 2019, 80,837 performance shares were granted with a grant date fair value of $46.35 . 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 three -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 three -year time-vesting period. In the first quarter of 2019, 80,837 performance restricted stock units and 95,938 restricted stock units were granted with a grant date fair value of $45.63 , 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 March 31, 2019 , an immaterial amount of shares was included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 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 three months ended March 31, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Liabilities settled (0.7 ) (0.6 ) Liabilities incurred (a) 25.9 25.9 Accretion expense 1.6 1.0 Balance, March 31 $204.3 $144.6 (a) During the three months ended March 31 , 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 three months ended March 31, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Liabilities settled (0.7 ) (0.6 ) Liabilities incurred (a) 25.9 25.9 Accretion expense 1.6 1.0 Balance, March 31 $204.3 $144.6 (a) During the three months ended March 31 , 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	3 Months Ended
	Mar. 31, 2019
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019 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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 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 March 31, 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 March 31, 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 March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019 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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 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 March 31, 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 March 31, 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 March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019 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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 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 March 31, 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 March 31, 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	3 Months Ended
	Mar. 31, 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8

Commitments And Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 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 projects include the expansion of wind generation. WPL’s projects include the West Riverside Energy Center. At March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $65 million , $33 million and $32 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 March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 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 March 31, 2019 , the present value of the abandonment obligations is estimated at $37 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 March 31, 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 $90 million as of March 31, 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 March 31, 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 March 31, 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 March 31, 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 March 31, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $15 - $31 $12 - $26 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. NOTE 14(e) Collective Bargaining Agreements - At March 31, 2019 , employees covered by collective bargaining agreements represented 55% , 62% 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 expires, representing 26% and 82% of total employees of Alliant Energy and WPL, respectively. While negotiations to renew the agreement are underway, Alliant Energy and WPL are currently unable to predict the outcome.
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 projects include the expansion of wind generation. WPL’s projects include the West Riverside Energy Center. At March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $65 million , $33 million and $32 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 March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 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 March 31, 2019 , the present value of the abandonment obligations is estimated at $37 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 March 31, 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 $90 million as of March 31, 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 March 31, 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 March 31, 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 March 31, 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 March 31, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $15 - $31 $12 - $26 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. NOTE 14(e) Collective Bargaining Agreements - At March 31, 2019 , employees covered by collective bargaining agreements represented 55% , 62% 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 expires, representing 26% and 82% of total employees of Alliant Energy and WPL, respectively. While negotiations to renew the agreement are underway, Alliant Energy and WPL are currently unable to predict the outcome.
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 projects include the expansion of wind generation. WPL’s projects include the West Riverside Energy Center. At March 31, 2019 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $65 million , $33 million and $32 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 March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 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 March 31, 2019 , the present value of the abandonment obligations is estimated at $37 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 March 31, 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 $90 million as of March 31, 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 March 31, 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 March 31, 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 March 31, 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 March 31, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $15 - $31 $12 - $26 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. NOTE 14(e) Collective Bargaining Agreements - At March 31, 2019 , employees covered by collective bargaining agreements represented 55% , 62% 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 expires, representing 26% and 82% of total employees of Alliant Energy and WPL, respectively. While negotiations to renew the agreement are underway, Alliant Energy and WPL are currently unable to predict the outcome.

Segments Of Business

Segments Of Business	3 Months Ended
	Mar. 31, 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 March 31, 2019 Revenues $743.4 $215.8 $11.1 $970.3 $16.9 $987.2 Operating income 126.4 45.2 — 171.6 5.2 176.8 Net income attributable to Alliant Energy common shareowners 119.0 6.1 125.1 Three Months Ended March 31, 2018 Revenues $708.7 $185.6 $13.2 $907.5 $8.8 $916.3 Operating income 126.7 31.5 1.4 159.6 6.1 165.7 Net income attributable to Alliant Energy common shareowners 100.7 20.2 120.9 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $419.8 $124.6 $10.7 $555.1 Operating income 46.8 26.3 0.4 73.5 Earnings available for common stock 53.3 Three Months Ended March 31, 2018 Revenues $405.7 $108.1 $12.0 $525.8 Operating income 57.5 16.9 1.2 75.6 Earnings available for common stock 46.7 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $323.6 $91.2 $0.4 $415.2 Operating income (loss) 79.6 18.9 (0.4 ) 98.1 Earnings available for common stock 65.7 Three Months Ended March 31, 2018 Revenues $303.0 $77.5 $1.2 $381.7 Operating income 69.2 14.6 0.2 84.0 Earnings available for common stock 54.0
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 March 31, 2019 Revenues $743.4 $215.8 $11.1 $970.3 $16.9 $987.2 Operating income 126.4 45.2 — 171.6 5.2 176.8 Net income attributable to Alliant Energy common shareowners 119.0 6.1 125.1 Three Months Ended March 31, 2018 Revenues $708.7 $185.6 $13.2 $907.5 $8.8 $916.3 Operating income 126.7 31.5 1.4 159.6 6.1 165.7 Net income attributable to Alliant Energy common shareowners 100.7 20.2 120.9 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $419.8 $124.6 $10.7 $555.1 Operating income 46.8 26.3 0.4 73.5 Earnings available for common stock 53.3 Three Months Ended March 31, 2018 Revenues $405.7 $108.1 $12.0 $525.8 Operating income 57.5 16.9 1.2 75.6 Earnings available for common stock 46.7 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $323.6 $91.2 $0.4 $415.2 Operating income (loss) 79.6 18.9 (0.4 ) 98.1 Earnings available for common stock 65.7 Three Months Ended March 31, 2018 Revenues $303.0 $77.5 $1.2 $381.7 Operating income 69.2 14.6 0.2 84.0 Earnings available for common stock 54.0
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 March 31, 2019 Revenues $743.4 $215.8 $11.1 $970.3 $16.9 $987.2 Operating income 126.4 45.2 — 171.6 5.2 176.8 Net income attributable to Alliant Energy common shareowners 119.0 6.1 125.1 Three Months Ended March 31, 2018 Revenues $708.7 $185.6 $13.2 $907.5 $8.8 $916.3 Operating income 126.7 31.5 1.4 159.6 6.1 165.7 Net income attributable to Alliant Energy common shareowners 100.7 20.2 120.9 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $419.8 $124.6 $10.7 $555.1 Operating income 46.8 26.3 0.4 73.5 Earnings available for common stock 53.3 Three Months Ended March 31, 2018 Revenues $405.7 $108.1 $12.0 $525.8 Operating income 57.5 16.9 1.2 75.6 Earnings available for common stock 46.7 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $323.6 $91.2 $0.4 $415.2 Operating income (loss) 79.6 18.9 (0.4 ) 98.1 Earnings available for common stock 65.7 Three Months Ended March 31, 2018 Revenues $303.0 $77.5 $1.2 $381.7 Operating income 69.2 14.6 0.2 84.0 Earnings available for common stock 54.0

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 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 months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $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 months ended March 31 were as follows (in millions): Three Months 2019 2018 ATC billings to WPL $27 $27 WPL billings to ATC 4 2 WPL owed ATC net amounts of $7 million as of March 31, 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 months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $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 months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $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 months ended March 31 were as follows (in millions): Three Months 2019 2018 ATC billings to WPL $27 $27 WPL billings to ATC 4 2 WPL owed ATC net amounts of $7 million as of March 31, 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)	3 Months Ended
	Mar. 31, 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 three months ended March 31, 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.
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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) .
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 - 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. Cash Flows Statements - On January 1, 2018, Alliant Energy and IPL adopted an accounting standard that requires classification of the consideration received for the beneficial interest obtained for transferring accounts receivable from IPL’s sales of accounts receivable program as an investing activity, instead of an operating activity. Alliant Energy and IPL currently use a method of presentation that allocates cash flows between operating and investing activities based on daily transactional activity. For the three months ended March 31, 2018, Alliant Energy and IPL initially utilized a method of presentation that allocated cash flows between operating and investing activities based on monthly transactional activity. The change in method of presentation to daily transactional activity increases Alliant Energy’s operating cash flows by $67.0 million to $156.3 million and increases IPL’s operating cash flows by $67.0 million to $1.8 million for the three months ended March 31, 2018.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K.
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 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.
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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) .
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 - 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. Cash Flows Statements - On January 1, 2018, Alliant Energy and IPL adopted an accounting standard that requires classification of the consideration received for the beneficial interest obtained for transferring accounts receivable from IPL’s sales of accounts receivable program as an investing activity, instead of an operating activity. Alliant Energy and IPL currently use a method of presentation that allocates cash flows between operating and investing activities based on daily transactional activity. For the three months ended March 31, 2018, Alliant Energy and IPL initially utilized a method of presentation that allocated cash flows between operating and investing activities based on monthly transactional activity. The change in method of presentation to daily transactional activity increases Alliant Energy’s operating cash flows by $67.0 million to $156.3 million and increases IPL’s operating cash flows by $67.0 million to $1.8 million for the three months ended March 31, 2018.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K.
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the three months ended March 31, 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.
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, including modifications to the presentation of cash receipts on sold receivables in the cash flows statements as discussed in Note 1(c) .
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 - 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)	3 Months Ended
	Mar. 31, 2019
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $802.9 $820.6 $770.2 $783.1 $32.7 $37.5 Pension and OPEB costs 532.6 542.3 269.3 274.0 263.3 268.3 Asset retirement obligations 112.1 110.8 77.5 76.3 34.6 34.5 EGUs retired early 107.3 111.6 53.6 55.4 53.7 56.2 IPL’s DAEC PPA amendment 106.5 — 106.5 — — — Emission allowances 23.0 23.6 23.0 23.6 — — Derivatives 16.9 28.0 8.0 15.1 8.9 12.9 Other 91.1 100.4 43.3 51.5 47.8 48.9 $1,792.4 $1,737.3 $1,351.4 $1,279.0 $441.0 $458.3
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL March 31, December 31, March 31, December 31, March 31, December 31, Tax-related $858.1 $890.6 $366.2 $390.1 $491.9 $500.5 Cost of removal obligations 402.7 401.2 273.4 273.3 129.3 127.9 Electric transmission cost recovery 104.8 104.0 53.0 47.7 51.8 56.3 Commodity cost recovery 43.2 16.8 32.2 11.9 11.0 4.9 WPL’s earnings sharing mechanism 25.0 25.4 — — 25.0 25.4 Other 48.6 55.2 24.0 31.9 24.6 23.3 $1,482.4 $1,493.2 $748.8 $754.9 $733.6 $738.3

Receivables (Tables)

Receivables (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31 were as follows (in millions): 2019 2018 Maximum outstanding aggregate cash proceeds $108.0 $116.0 Average outstanding aggregate cash proceeds 81.0 61.1
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2019 December 31, 2018 Customer accounts receivable $169.9 $140.1 Unbilled utility revenues 86.8 97.1 Other receivables 0.1 0.1 Receivables sold to third party 256.8 237.3 Less: cash proceeds 69.0 108.0 Deferred proceeds 187.8 129.3 Less: allowance for doubtful accounts 9.5 9.9 Fair value of deferred proceeds $178.3 $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 months ended March 31 were as follows (in millions): 2019 2018 Collections $555.8 $517.0 Write-offs, net of recoveries 5.5 6.1
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 months ended March 31 were as follows (in millions): 2019 2018 Maximum outstanding aggregate cash proceeds $108.0 $116.0 Average outstanding aggregate cash proceeds 81.0 61.1
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): March 31, 2019 December 31, 2018 Customer accounts receivable $169.9 $140.1 Unbilled utility revenues 86.8 97.1 Other receivables 0.1 0.1 Receivables sold to third party 256.8 237.3 Less: cash proceeds 69.0 108.0 Deferred proceeds 187.8 129.3 Less: allowance for doubtful accounts 9.5 9.9 Fair value of deferred proceeds $178.3 $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 months ended March 31 were as follows (in millions): 2019 2018 Collections $555.8 $517.0 Write-offs, net of recoveries 5.5 6.1

Investments and Acquisitions (T

Investments and Acquisitions (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31 was as follows (in millions): 2019 2018 ATC Holdings ($9.5 ) ($8.7 ) Non-utility wind farm in Oklahoma (1.1 ) (12.1 ) Other (0.3 ) (0.5 ) ($10.9 ) ($21.3 )

Common Equity (Tables)

Common Equity (Tables)	3 Months Ended
	Mar. 31, 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 1,090,300 Shareowner Direct Plan issuances 142,090 Equity-based compensation plans 101,478 Other (2,738 ) Shares outstanding, March 31, 2019 237,394,409
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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5
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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5
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 March 31, 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 125.1 125.1 Common stock dividends ($0.355 per share) (83.7 ) (83.7 ) Equity forward settlements and Shareowner Direct Plan issuances 54.6 54.6 Equity-based compensation plans and other (0.1 ) 0.1 — Other comprehensive income, net of tax 0.7 0.7 Ending balance, March 31 $2.4 $2,100.0 $2,587.3 $2.4 ($9.7 ) $200.0 $4,882.4 Three Months Ended March 31, 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 120.9 120.9 Common stock dividends ($0.335 per share) (77.5 ) (77.5 ) Shareowner Direct Plan issuances 6.3 6.3 Equity-based compensation plans (0.4 ) (0.4 ) Ending balance, March 31 $2.3 $1,851.4 $2,389.4 ($0.5 ) ($11.1 ) $200.0 $4,431.5 IPL Total IPL Common Equity Additional Cumulative Common Paid-In Retained Preferred Total Stock Capital Earnings Stock Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $33.4 $2,222.8 $774.5 $200.0 $3,230.7 Earnings available for common stock 53.3 53.3 Common stock dividends (42.0 ) (42.0 ) Capital contribution from parent 100.0 100.0 Ending balance, March 31 $33.4 $2,322.8 $785.8 $200.0 $3,342.0 Three Months Ended March 31, 2018 Beginning balance, January 1 $33.4 $1,797.8 $678.5 $200.0 $2,709.7 Earnings available for common stock 46.7 46.7 Common stock dividends (41.9 ) (41.9 ) Ending balance, March 31 $33.4 $1,797.8 $683.3 $200.0 $2,714.5 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended March 31, 2019 Beginning balance, January 1 $66.2 $1,309.0 $774.3 $2,149.5 Earnings available for common stock 65.7 65.7 Common stock dividends (36.0 ) (36.0 ) Ending balance, March 31 $66.2 $1,309.0 $804.0 $2,179.2 Three Months Ended March 31, 2018 Beginning balance, January 1 $66.2 $1,109.0 $706.3 $1,881.5 Earnings available for common stock 54.0 54.0 Common stock dividends (35.0 ) (35.0 ) Ending balance, March 31 $66.2 $1,109.0 $725.3 $1,900.5

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 .
IPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 .
WPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): March 31, 2019 Alliant Energy IPL WPL Commercial paper outstanding $514.7 $— $138.4 Commercial paper weighted average interest rates 2.6% N/A 2.5% Available credit facility capacity (a) $370.3 $135.0 $161.6 Alliant Energy IPL WPL Three Months Ended March 31 2019 2018 2019 2018 2019 2018 Maximum amount outstanding (based on daily outstanding balances) $600.6 $336.4 $50.4 $3.0 $195.1 $36.7 Average amount outstanding (based on daily outstanding balances) $498.8 $310.1 $0.6 $— $138.1 $11.5 Weighted average interest rates 2.7% 1.9% 2.8% 1.8% 2.5% 1.6% (a) Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019 .

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 %
Schedule of Operating Lease Liability Maturities	As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66
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): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 %
Schedule of Operating Lease Liability Maturities	As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66
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): March 31, 2019 Property, plant and equipment, net $37 Other current liabilities $8 Finance lease obligations - Sheboygan Falls Energy Facility 58 Total finance lease liabilities $66 Three Months Ended March 31, 2019 Depreciation expense $1 Interest expense 2 Total finance lease expense $3 Remaining lease term 6 years Discount rate 11 % Operating lease details are as follows (dollars in millions): Alliant Energy IPL WPL March 31, 2019 Property, plant and equipment, net $18 $10 $7 Other current liabilities $3 $1 $1 Other liabilities 15 9 6 Total operating lease liabilities $18 $10 $7 Three Months Ended March 31, 2019 Operating lease cost $1 $— $— Weighted average remaining lease term 12 years 13 years 10 years Weighted average discount rate 4 % 4 % 4 %
Schedule of Operating Lease Liability Maturities	As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66
Schedule of Finance Lease Liability Maturities	As of March 31, 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 $2 $13 $23 $5 $18 IPL 1 1 1 1 1 9 14 4 10 WPL 1 1 1 1 1 3 8 1 7 WPL’s Finance Lease: Sheboygan Falls Energy Facility 11 15 15 15 15 20 91 25 66
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)	3 Months Ended
	Mar. 31, 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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7
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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7
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 March 31 2019 2018 2019 2018 2019 2018 Electric Utility: Retail - residential $274.7 $259.4 $147.5 $142.2 $127.2 $117.2 Retail - commercial 181.1 174.0 116.6 111.6 64.5 62.4 Retail - industrial 208.7 201.9 116.1 114.8 92.6 87.1 Wholesale 46.5 53.8 16.9 24.3 29.6 29.5 Bulk power and other 32.4 19.6 22.7 12.8 9.7 6.8 Total Electric Utility 743.4 708.7 419.8 405.7 323.6 303.0 Gas Utility: Retail - residential 131.8 110.6 77.9 65.5 53.9 45.1 Retail - commercial 63.6 57.0 34.8 31.6 28.8 25.4 Retail - industrial 5.4 5.8 3.2 2.7 2.2 3.1 Transportation/other 15.0 12.2 8.7 8.3 6.3 3.9 Total Gas Utility 215.8 185.6 124.6 108.1 91.2 77.5 Other Utility: Steam 8.4 9.4 8.4 9.4 — — Other utility 2.7 3.8 2.3 2.6 0.4 1.2 Total Other Utility 11.1 13.2 10.7 12.0 0.4 1.2 Non-Utility and Other: Transportation and other 16.9 8.8 — — — — Total Non-Utility and Other 16.9 8.8 — — — — Total revenues $987.2 $916.3 $555.1 $525.8 $415.2 $381.7

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 %
Summary Of Tax Credit Carryforwards	At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151
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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 %
Summary Of Tax Credit Carryforwards	At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151
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 March 31 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 6.7 7.5 7.2 8.5 6.2 6.2 Production tax credits (9.2 ) (5.5 ) (14.0 ) (5.4 ) (4.9 ) (6.7 ) Effect of rate-making on property-related differences (5.6 ) (7.4 ) (9.2 ) (13.5 ) (2.3 ) (2.4 ) Amortization of excess deferred taxes (0.9 ) (0.4 ) (0.2 ) — (1.4 ) (0.1 ) IPL’s tax benefit riders (0.7 ) (2.2 ) (1.5 ) (4.7 ) — — Other items, net (0.7 ) (1.0 ) 0.3 — (0.4 ) (0.2 ) Overall income tax rate 10.6 % 12.0 % 3.6 % 5.9 % 18.2 % 17.8 %
Summary Of Tax Credit Carryforwards	At March 31, 2019 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2031-2039 $776 $551 $129 State net operating losses 2019-2039 785 13 2 Federal tax credits 2022-2039 307 138 151

Benefit Plans (Tables)

Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4
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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4
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 months ended March 31 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 Alliant Energy 2019 2018 2019 2018 Service cost $2.4 $3.0 $0.8 $1.1 Interest cost 12.5 11.7 2.1 1.9 Expected return on plan assets (15.0 ) (17.4 ) (1.2 ) (1.5 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Amortization of actuarial loss 9.1 8.8 0.8 0.8 $8.8 $5.9 $2.5 $2.3 Defined Benefit Pension Plans OPEB Plans IPL 2019 2018 2019 2018 Service cost $1.5 $1.8 $0.3 $0.4 Interest cost 5.7 5.3 0.8 0.8 Expected return on plan assets (7.0 ) (8.1 ) (0.9 ) (1.1 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 3.9 3.7 0.4 0.3 $4.0 $2.7 $0.6 $0.4 Defined Benefit Pension Plans OPEB Plans WPL 2019 2018 2019 2018 Service cost $0.9 $1.1 $0.3 $0.4 Interest cost 5.4 5.0 0.8 0.8 Expected return on plan assets (6.5 ) (7.6 ) (0.1 ) (0.2 ) Amortization of prior service credit (0.1 ) — — — Amortization of actuarial loss 4.4 4.3 0.4 0.5 $4.1 $2.8 $1.4 $1.5
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions): Alliant Energy IPL WPL 2019 2018 2019 2018 2019 2018 Compensation expense $4.7 $3.3 $2.6 $1.8 $1.8 $1.3 Income tax benefits 1.3 0.9 0.8 0.5 0.5 0.4

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 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 three months ended March 31, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Liabilities settled (0.7 ) (0.6 ) Liabilities incurred (a) 25.9 25.9 Accretion expense 1.6 1.0 Balance, March 31 $204.3 $144.6 (a) During the three months ended March 31 , 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 three months ended March 31, 2019 is as follows (in millions): Alliant Energy IPL Balance, January 1 $177.5 $118.3 Liabilities settled (0.7 ) (0.6 ) Liabilities incurred (a) 25.9 25.9 Accretion expense 1.6 1.0 Balance, March 31 $204.3 $144.6 (a) During the three months ended March 31 , 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)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019
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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 9.6
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019
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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 9.6
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of March 31, 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 3,903 2019 158,337 2019-2026 10,042 2019-2021 2,268 2019 IPL 2,378 2019 68,345 2019-2026 4,429 2019-2021 — — WPL 1,525 2019 89,992 2019-2026 5,613 2019-2021 2,268 2019
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 March 31, December 31, March 31, December 31, March 31, December 31, Current derivative assets $15.8 $24.6 $9.0 $16.1 $6.8 $8.5 Non-current derivative assets 5.9 3.7 2.9 1.6 3.0 2.1 Current derivative liabilities 3.6 5.6 2.1 3.1 1.5 2.5 Non-current derivative liabilities 12.1 17.7 5.0 8.1 7.1 9.6

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 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 March 31, 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 $21.7 $— $15.9 $5.8 $21.7 $28.3 $— $8.9 $19.4 $28.3 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 15.7 — 10.3 5.4 15.7 23.3 — 16.1 7.2 23.3 Long-term debt (incl. current maturities) 5,618.7 — 6,071.6 2.1 6,073.7 5,502.8 — 5,858.4 2.4 5,860.8 IPL March 31, 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 $11.9 $— $7.7 $4.2 $11.9 $17.7 $— $4.0 $13.7 $17.7 Deferred proceeds 178.3 — — 178.3 178.3 119.4 — — 119.4 119.4 Liabilities: Derivatives 7.1 — 3.5 3.6 7.1 11.2 — 6.5 4.7 11.2 Long-term debt 2,667.8 — 2,852.4 — 2,852.4 2,552.3 — 2,691.2 — 2,691.2 WPL March 31, 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 $9.8 $— $8.2 $1.6 $9.8 $10.6 $— $4.9 $5.7 $10.6 Liabilities: Derivatives 8.6 — 6.8 1.8 8.6 12.1 — 9.6 2.5 12.1 Long-term debt (incl. current maturities) 1,835.4 — 2,080.0 — 2,080.0 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 March 31 2019 2018 2019 2018 Beginning balance, January 1 $12.2 ($12.2 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (5.6 ) (9.8 ) — — Sales (0.2 ) — — — Settlements (a) (6.0 ) (7.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.4 ($29.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($2.6 ) ($9.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended March 31 2019 2018 2019 2018 Beginning balance, January 1 $9.0 ($1.4 ) $119.4 $222.1 Total net losses included in changes in net assets (realized/unrealized) (3.2 ) (7.6 ) — — Sales (0.1 ) — — — Settlements (a) (5.1 ) (6.4 ) 58.9 (101.2 ) Ending balance, March 31 $0.6 ($15.4 ) $178.3 $120.9 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.4 ) ($7.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended March 31 2019 2018 Beginning balance, January 1 $3.2 ($10.8 ) Total net losses included in changes in net assets (realized/unrealized) (2.4 ) (2.2 ) Sales (0.1 ) — Settlements (0.9 ) (1.0 ) Ending balance, March 31 ($0.2 ) ($14.0 ) The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 ($1.2 ) ($2.1 ) (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 (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs March 31, 2019 ($3.3 ) $3.7 ($2.4 ) $3.0 ($0.9 ) $0.7 December 31, 2018 3.2 9.0 1.8 7.2 1.4 1.8

Commitments And Contingencies (

Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies [Line Items]
Other Purchase Obligations	At March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 2019 .
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 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 March 31, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $15 - $31 $12 - $26 Current and non-current environmental liabilities 19 16
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Obligations	At March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 2019 .
MGP Site Estimated Future Costs And Recorded Liabilities	At March 31, 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 March 31, 2019 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $15 - $31 $12 - $26 Current and non-current environmental liabilities 19 16
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Obligations	At March 31, 2019 , the related minimum future commitments were as follows (in millions): Alliant Energy IPL WPL Purchased power (a) $221 $219 $2 Natural gas 879 388 491 Coal (b) 163 96 67 Other (c) 88 49 26 $1,351 $752 $586 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 2019 .

Segments Of Business (Tables)

Segments Of Business (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 Revenues $743.4 $215.8 $11.1 $970.3 $16.9 $987.2 Operating income 126.4 45.2 — 171.6 5.2 176.8 Net income attributable to Alliant Energy common shareowners 119.0 6.1 125.1 Three Months Ended March 31, 2018 Revenues $708.7 $185.6 $13.2 $907.5 $8.8 $916.3 Operating income 126.7 31.5 1.4 159.6 6.1 165.7 Net income attributable to Alliant Energy common shareowners 100.7 20.2 120.9
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $419.8 $124.6 $10.7 $555.1 Operating income 46.8 26.3 0.4 73.5 Earnings available for common stock 53.3 Three Months Ended March 31, 2018 Revenues $405.7 $108.1 $12.0 $525.8 Operating income 57.5 16.9 1.2 75.6 Earnings available for common stock 46.7
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended March 31, 2019 Revenues $323.6 $91.2 $0.4 $415.2 Operating income (loss) 79.6 18.9 (0.4 ) 98.1 Earnings available for common stock 65.7 Three Months Ended March 31, 2018 Revenues $303.0 $77.5 $1.2 $381.7 Operating income 69.2 14.6 0.2 84.0 Earnings available for common stock 54.0

Related Parties (Tables)

Related Parties (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $71
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): Three Months 2019 2018 ATC billings to WPL $27 $27 WPL billings to ATC 4 2
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $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 months ended March 31 were as follows (in millions): IPL WPL 2019 2018 2019 2018 Corporate Services billings $43 $41 $33 $33 Sales credited 15 5 1 1 Purchases billed 84 93 30 17
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 Net payables to Corporate Services $98 $95 $73 $71
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three months ended March 31 were as follows (in millions): Three Months 2019 2018 ATC billings to WPL $27 $27 WPL billings to ATC 4 2

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in operating cash flows from change in method of presentation to daily transactional activity		$ 67
Net cash flows from operating activities	$ 181.1	156.3
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in operating cash flows from change in method of presentation to daily transactional activity		67
Net cash flows from operating activities	$ 76.7	$ 1.8

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Mar. 31, 2019	Dec. 31, 2020
2020 Forward Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Requested rate annual increase, amount		$ 204
Interim rate annual increase, amount		90
2020 Forward Test Period Retail Gas [Member] | IPL [Member]
Regulatory Matters [Line Items]
Requested rate annual increase, amount		$ 21
Scenario, Forecast [Member] | 2020 Forward Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Requested rate annual increase, amount			$ 114
DAEC PPA [Member]
Regulatory Matters [Line Items]
PPA term amendment		5 years
Recovery period, authorized		5 years
DAEC PPA [Member] | Scenario, Forecast [Member]
Regulatory Matters [Line Items]
Buyout payment	$ 110

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory assets	$ 1,792.4	$ 1,737.3
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	802.9	820.6
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	532.6	542.3
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	112.1	110.8
EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	107.3	111.6
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	106.5	0
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	23	23.6
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	16.9	28
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	91.1	100.4
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,351.4	1,279
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	770.2	783.1
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	269.3	274
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	77.5	76.3
IPL [Member] | EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	53.6	55.4
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	106.5	0
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	23	23.6
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	8	15.1
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	43.3	51.5
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	441	458.3
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	32.7	37.5
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	263.3	268.3
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	34.6	34.5
WPL [Member] | EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	53.7	56.2
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	8.9	12.9
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 47.8	$ 48.9

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,482.4	$ 1,493.2
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	858.1	890.6
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	402.7	401.2
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	104.8	104
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	43.2	16.8
WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	25.4
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48.6	55.2
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	748.8	754.9
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	366.2	390.1
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	273.4	273.3
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	53	47.7
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32.2	11.9
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24	31.9
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	733.6	738.3
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	491.9	500.5
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	129.3	127.9
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	51.8	56.3
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	11	4.9
WPL [Member] | WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	25.4
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 24.6	$ 23.3

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Mar. 31, 2019USD ($)
Receivables [Line Items]
Available capacity	$ 21
Outstanding receivables past due	$ 38.8

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 81	$ 61.1
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 108	$ 116

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Receivables [Line Items]
Fair value of deferred proceeds	$ 178.3	$ 119.4
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	178.3	119.4
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	169.9	140.1
Unbilled utility revenues	86.8	97.1
Other receivables	0.1	0.1
Receivables sold to third party	256.8	237.3
Less: cash proceeds	69	108
Deferred proceeds	187.8	129.3
Less: allowance for doubtful accounts	9.5	9.9
Fair value of deferred proceeds	$ 178.3	$ 119.4

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Receivables [Line Items]
Collections	$ 555.8	$ 517
Write-offs, net of recoveries	$ 5.5	$ 6.1

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
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (10.9)	$ (21.3)
ATC Holdings [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(9.5)	(8.7)
Non-utility wind farm In Oklahoma [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(1.1)	(12.1)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.3)	$ (0.5)

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Common Equity [Line Items]
Proceeds from issuance of common stock, net	$ 54.6	$ 6.3
Comprehensive income	0.7
IPL [Member]
Common Equity [Line Items]
Comprehensive income	0	0
WPL [Member]
Common Equity [Line Items]
Comprehensive income	$ 0	$ 0
Equity Forward Agreements [Member]
Common Equity [Line Items]
Common stock issued during the period, equity forward agreements (in shares)	1,090,300
Forward sales price (in dollars per share)	$ 44.13			$ 44.33
Proceeds from issuance of common stock, net	$ 48
Shares included in diluted earnings per share (in shares)	96,261
Scenario, 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)	3 Months Ended
	Mar. 31, 2019shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2019 (in shares)	236,063,279
Shareowner Direct Plan issuances (in shares)	142,090
Equity-based compensation plans (in shares)	101,478
Other (in shares)	(2,738)
Shares outstanding, March 31, 2019 (in shares)	237,394,409
Equity Forward Agreements [Member]
Common Stock Oustanding [Roll Forward]
Equity forward agreements (in shares)	1,090,300

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 4,585.7
Beginning balance	4,785.7	$ 4,382.2
Net income attributable to common shareowners	125.1	120.9
Common stock dividends	(83.7)	(77.5)
Equity forward settlements and Shareowner Direct Plan issuances	54.6	6.3
Equity-based compensation plans and other	0	(0.4)
Other comprehensive income, net of tax	0.7
Ending balance	4,682.4
Ending balance	$ 4,882.4	$ 4,431.5
Common stock dividends (in dollars per share)	$ 0.355	$ 0.335
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 2.4	$ 2.3
Ending balance	2.4	2.3
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,045.5	1,845.5
Equity forward settlements and Shareowner Direct Plan issuances	54.6	6.3
Equity-based compensation plans and other	(0.1)	(0.4)
Ending balance	2,100	1,851.4
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,545.9	2,346
Net income attributable to common shareowners	125.1	120.9
Common stock dividends	(83.7)	(77.5)
Ending balance	2,587.3	2,389.4
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1.7	(0.5)
Other comprehensive income, net of tax	0.7
Ending balance	2.4	(0.5)
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(9.8)	(11.1)
Equity-based compensation plans and other	0.1
Ending balance	(9.7)	(11.1)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200
Ending balance	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,030.7
Beginning balance	3,230.7	2,709.7
Net income attributable to common shareowners	53.3	46.7
Common stock dividends	(42)	(41.9)
Capital contributions from parent	100	0
Other comprehensive income, net of tax	0	0
Ending balance	3,142
Ending balance	3,342	2,714.5
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33.4	33.4
Ending balance	33.4	33.4
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,222.8	1,797.8
Capital contributions from parent	100
Ending balance	2,322.8	1,797.8
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	774.5	678.5
Net income attributable to common shareowners	53.3	46.7
Common stock dividends	(42)	(41.9)
Ending balance	785.8	683.3
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200
Ending balance	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,149.5
Beginning balance	2,149.5	1,881.5
Net income attributable to common shareowners	65.7	54
Common stock dividends	(36)	(35)
Other comprehensive income, net of tax	0	0
Ending balance	2,179.2
Ending balance	2,179.2	1,900.5
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66.2	66.2
Ending balance	66.2	66.2
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,309	1,109
Ending balance	1,309	1,109
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	774.3	706.3
Net income attributable to common shareowners	65.7	54
Common stock dividends	(36)	(35)
Ending balance	$ 804	$ 725.3

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019
Debt [Line Items]
Credit facility agreement, extension		1 year
Line of credit facility, current borrowing capacity		$ 1,000,000,000
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		250,000,000
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		300,000,000
Alliant Energy and IPL [Member]
Debt [Line Items]
Commercial paper, long-term		$ 115,000,000
Commercial paper, long-term, interest rate percent		2.70%
Senior Debentures [Member] | Subsequent Event [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%
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity		$ 450,000,000

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Debt [Line Items]
Commercial paper outstanding		$ 514.7	$ 441.2
Commercial paper weighted average interest rates		2.60%
Available credit facility capacity	[1]	$ 370.3
IPL [Member]
Debt [Line Items]
Commercial paper outstanding		0	50.4
Available credit facility capacity	[1]	135
WPL [Member]
Debt [Line Items]
Commercial paper outstanding		$ 138.4	$ 105.5
Commercial paper weighted average interest rates		2.50%
Available credit facility capacity		$ 161.6
[1]	Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at March 31, 2019.

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 600.6	$ 336.4
Average amount outstanding (based on daily outstanding balances)	$ 498.8	$ 310.1
Weighted average interest rates	2.70%	1.90%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 50.4	$ 3
Average amount outstanding (based on daily outstanding balances)	$ 0.6	$ 0
Weighted average interest rates	2.80%	1.80%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 195.1	$ 36.7
Average amount outstanding (based on daily outstanding balances)	$ 138.1	$ 11.5
Weighted average interest rates	2.50%	1.60%

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
	Mar. 31, 2019USD ($)
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 18
Operating leases liabilities, Other current liabilities	3
Operating leases liabilities, Other liabilities	15
Operating leases liabilities, Total	18
Operating leases, Cost	$ 1
Operating leases, Weighted average remaining lease term	12 years
Operating leases, Weighted average discount rate, percent	4.00%
IPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 10
Operating leases liabilities, Other current liabilities	1
Operating leases liabilities, Other liabilities	9
Operating leases liabilities, Total	10
Operating leases, Cost	$ 0
Operating leases, Weighted average remaining lease term	13 years
Operating leases, Weighted average discount rate, percent	4.00%
WPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 7
Operating leases liabilities, Other current liabilities	1
Operating leases liabilities, Other liabilities	6
Operating leases liabilities, Total	7
Operating leases, Cost	$ 0
Operating leases, Weighted average remaining lease term	10 years
Operating leases, Weighted average discount rate, percent	4.00%

Leases (Finance Lease) (Details

Leases (Finance Lease) (Details) - WPL [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Leases [Line Items]
Finance lease liabilities, Sheboygan Falls Energy Facility	$ 57.9	$ 60
Sheboygan Falls Energy Facility [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	37
Finance lease liabilities, Other current liabilities	8
Finance lease liabilities, Sheboygan Falls Energy Facility	58
Finance lease liabilities, Total	66
Finance lease, Depreciation expense	1
Finance lease, Interest expense	2
Finance lease, Total expense	$ 3
Finance lease, Remaining lease term	6 years
Finance lease, Discount rate, percent	11.00%

Leases (Expected Maturities of

Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) $ in Millions	Mar. 31, 2019USD ($)
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	$ 2
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	23
Operating Leases Liability, Less: amount representing interest	5
Operating Leases Liability, Present value of minimum lease payments	18
IPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	1
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	14
Operating Leases Liability, Less: amount representing interest	4
Operating Leases Liability, Present value of minimum lease payments	10
WPL [Member]
Leases [Line Items]
Operating Leases Liability, Remainder of 2019	1
Operating Leases Liability, 2020	1
Operating Leases Liability, 2021	1
Operating Leases Liability, 2022	1
Operating Leases Liability, 2023	1
Operating Leases Liability, Thereafter	3
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	11
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	91
Finance Lease Liability, Less: amount representing interest	25
Finance Lease Liability, Present value of minimum lease payments	$ 66

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
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 987.2	$ 916.3
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	743.4	708.7
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	274.7	259.4
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	181.1	174
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	208.7	201.9
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	46.5	53.8
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32.4	19.6
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	215.8	185.6
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	131.8	110.6
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	63.6	57
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5.4	5.8
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	12.2
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11.1	13.2
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.4	9.4
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.7	3.8
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.9	8.8
Non-utility and Other [Member] | Transportation and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.9	8.8
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	555.1	525.8
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	419.8	405.7
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	147.5	142.2
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116.6	111.6
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116.1	114.8
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16.9	24.3
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22.7	12.8
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	124.6	108.1
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	77.9	65.5
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34.8	31.6
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3.2	2.7
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.7	8.3
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10.7	12
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8.4	9.4
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.3	2.6
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	415.2	381.7
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	323.6	303
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	127.2	117.2
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	64.5	62.4
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	92.6	87.1
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29.6	29.5
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9.7	6.8
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	91.2	77.5
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	53.9	45.1
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	28.8	25.4
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2.2	3.1
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6.3	3.9
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.4	1.2
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0.4	$ 1.2

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%
State income taxes, net of federal benefits	6.70%	7.50%
Production tax credits	(9.20%)	(5.50%)
Effect of rate-making on property-related differences	(5.60%)	(7.40%)
Amortization of excess deferred taxes	(0.90%)	(0.40%)
IPL's tax benefit riders	(0.70%)	(2.20%)
Other items, net	(0.70%)	(1.00%)
Overall income tax rate	10.60%	12.00%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%
State income taxes, net of federal benefits	7.20%	8.50%
Production tax credits	(14.00%)	(5.40%)
Effect of rate-making on property-related differences	(9.20%)	(13.50%)
Amortization of excess deferred taxes	(0.20%)	0.00%
IPL's tax benefit riders	(1.50%)	(4.70%)
Other items, net	0.30%	0.00%
Overall income tax rate	3.60%	5.90%
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21.00%	21.00%
State income taxes, net of federal benefits	6.20%	6.20%
Production tax credits	(4.90%)	(6.70%)
Effect of rate-making on property-related differences	(2.30%)	(2.40%)
Amortization of excess deferred taxes	(1.40%)	(0.10%)
Other items, net	(0.40%)	(0.20%)
Overall income tax rate	18.20%	17.80%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2019USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 776
Tax credits, carryforward amount	307
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	551
Tax credits, carryforward amount	138
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	129
Tax credits, carryforward amount	151
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	785
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	13
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	3 Months Ended
	Mar. 31, 2019USD ($)$ / sharesshares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost | $	$ 13.7
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 | $	$ 7.6
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost | $	$ 5.6
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	80,837
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 46.35
Actual number of shares paid out upon vesting, minimum percentage of target shares	0.00%
Actual number of shares paid out upon vesting, maximum percentage of target shares	200.00%
Performance Restricted Stock Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	80,837
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 45.63
Actual number of shares paid out upon vesting, minimum percentage of target shares	0.00%
Actual number of shares paid out upon vesting, maximum percentage of target shares	200.00%
Instrument valuation based on shares of common stock, number of shares	1
Restricted Stock Units (RSUs) [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period	3 years
Granted (in shares/awards)	95,938
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 45.63
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
	Mar. 31, 2019	Mar. 31, 2018
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.4	$ 3
Interest cost	12.5	11.7
Expected return on plan assets	(15)	(17.4)
Amortization of prior service credit	(0.2)	(0.2)
Amortization of actuarial loss	9.1	8.8
Total	8.8	5.9
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	1.1
Interest cost	2.1	1.9
Expected return on plan assets	(1.2)	(1.5)
Amortization of prior service credit	0	0
Amortization of actuarial loss	0.8	0.8
Total	2.5	2.3
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.5	1.8
Interest cost	5.7	5.3
Expected return on plan assets	(7)	(8.1)
Amortization of prior service credit	(0.1)	0
Amortization of actuarial loss	3.9	3.7
Total	4	2.7
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4
Interest cost	0.8	0.8
Expected return on plan assets	(0.9)	(1.1)
Amortization of prior service credit	0	0
Amortization of actuarial loss	0.4	0.3
Total	0.6	0.4
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	1.1
Interest cost	5.4	5
Expected return on plan assets	(6.5)	(7.6)
Amortization of prior service credit	(0.1)	0
Amortization of actuarial loss	4.4	4.3
Total	4.1	2.8
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.4
Interest cost	0.8	0.8
Expected return on plan assets	(0.1)	(0.2)
Amortization of prior service credit	0	0
Amortization of actuarial loss	0.4	0.5
Total	$ 1.4	$ 1.5

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Compensation expense	$ 4.7	$ 3.3
Income tax benefits	1.3	0.9
IPL [Member]
Compensation expense	2.6	1.8
Income tax benefits	0.8	0.5
WPL [Member]
Compensation expense	1.8	1.3
Income tax benefits	$ 0.5	$ 0.4

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 177.5
Liabilities settled	(0.7)
Liabilities incurred	25.9	[1]
Accretion expense	1.6
Balance, March 31	204.3
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	118.3
Liabilities settled	(0.6)
Liabilities incurred	25.9	[1]
Accretion expense	1
Balance, March 31	$ 144.6
[1]	During the three months ended March 31, 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	3 Months Ended
	Mar. 31, 2019DekathermsMWhTgal
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	3,903
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	2,378
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs) | MWh	1,525
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	158,337
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	68,345
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	89,992
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	10,042
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,429
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	5,613
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	2,268
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	2,268

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 15.8	$ 24.6
Non-current derivative assets	5.9	3.7
Current derivative liabilities	3.6	5.6
Non-current derivative liabilities	12.1	17.7
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	9	16.1
Non-current derivative assets	2.9	1.6
Current derivative liabilities	2.1	3.1
Non-current derivative liabilities	5	8.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	6.8	8.5
Non-current derivative assets	3	2.1
Current derivative liabilities	1.5	2.5
Non-current derivative liabilities	$ 7.1	$ 9.6

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Deferred proceeds	$ 178.3	$ 119.4
Liabilities:
Long-term debt (incl. current maturities)	6,073.7	5,860.8
IPL [Member]
Assets:
Deferred proceeds	178.3	119.4
Liabilities:
Long-term debt (incl. current maturities)	2,852.4	2,691.2
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,080	2,043.7
Commodity Contracts [Member]
Assets:
Derivatives	21.7	28.3
Liabilities:
Derivatives	15.7	23.3
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	11.9	17.7
Liabilities:
Derivatives	7.1	11.2
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9.8	10.6
Liabilities:
Derivatives	8.6	12.1
Level 1 [Member]
Assets:
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
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:
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	6,071.6	5,858.4
Level 2 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	2,852.4	2,691.2
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,080	2,043.7
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	15.9	8.9
Liabilities:
Derivatives	10.3	16.1
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	7.7	4
Liabilities:
Derivatives	3.5	6.5
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	8.2	4.9
Liabilities:
Derivatives	6.8	9.6
Level 3 [Member]
Assets:
Deferred proceeds	178.3	119.4
Liabilities:
Long-term debt (incl. current maturities)	2.1	2.4
Level 3 [Member] | IPL [Member]
Assets:
Deferred proceeds	178.3	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	5.8	19.4
Liabilities:
Derivatives	5.4	7.2
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	4.2	13.7
Liabilities:
Derivatives	3.6	4.7
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	1.6	5.7
Liabilities:
Derivatives	1.8	2.5
Carrying Amount [Member]
Assets:
Deferred proceeds	178.3	119.4
Liabilities:
Long-term debt (incl. current maturities)	5,618.7	5,502.8
Carrying Amount [Member] | IPL [Member]
Assets:
Deferred proceeds	178.3	119.4
Liabilities:
Long-term debt (incl. current maturities)	2,667.8	2,552.3
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	1,835.4	1,834.9
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	21.7	28.3
Liabilities:
Derivatives	15.7	23.3
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	11.9	17.7
Liabilities:
Derivatives	7.1	11.2
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9.8	10.6
Liabilities:
Derivatives	$ 8.6	$ 12.1

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 12.2	$ (12.2)
Total net losses included in changes in net assets (realized/unrealized)		(5.6)	(9.8)
Sales		(0.2)	0
Settlements		(6)	(7.4)
Ending balance		0.4	(29.4)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		(2.6)	(9.4)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		9	(1.4)
Total net losses included in changes in net assets (realized/unrealized)		(3.2)	(7.6)
Sales		(0.1)	0
Settlements		(5.1)	(6.4)
Ending balance		0.6	(15.4)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		(1.4)	(7.3)
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		3.2	(10.8)
Total net losses included in changes in net assets (realized/unrealized)		(2.4)	(2.2)
Sales		(0.1)	0
Settlements		(0.9)	(1)
Ending balance		(0.2)	(14)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		(1.2)	(2.1)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		119.4	222.1
Total net losses included in changes in net assets (realized/unrealized)		0	0
Sales		0	0
Settlements	[1]	58.9	(101.2)
Ending balance		178.3	120.9
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		119.4	222.1
Total net losses included in changes in net assets (realized/unrealized)		0	0
Sales		0	0
Settlements	[1]	58.9	(101.2)
Ending balance		178.3	120.9
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		$ 0	$ 0
[1]	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash 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	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 0.4	$ 12.2	$ (29.4)	$ (12.2)
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	3.3
Fair value, net derivative assets		3.2
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	3.7	9
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	0.6	9	(15.4)	(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 liabilities	2.4
Fair value, net derivative assets		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	3	7.2
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	(0.2)	3.2	$ (14)	$ (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 liabilities	0.9
Fair value, net derivative assets		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	$ 0.7	$ 1.8

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1,351
Present value abandonment obligation	37
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	752
Indemnification obligations, maximum	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	586
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	65
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	33
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	32
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	221	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	219	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	2	[1]
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Indemnification obligations, maximum	90
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	55.00%
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Employees covered by collective bargaining agreement	62.00%
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	26.00%
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 amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 Obligations) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended
		Sep. 30, 2020	Mar. 31, 2019
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,351
Individual commitments incurred			1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			752
Individual commitments incurred			1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			586
Individual commitments incurred			1
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		221
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		219
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		2
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			879
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			388
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			491
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		163
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		96
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		67
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		88
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		49
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		$ 26
Scenario, 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 amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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 March 31, 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 March 31, 2019.

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Manufactured Gas Plant Sites [Member] $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	$ 15
Maximum range of estimated future costs	31
Current and non-current environmental liabilities	19
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	12
Maximum range of estimated future costs	26
Current and non-current environmental liabilities	$ 16

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 987.2	$ 916.3
Operating income (loss)	176.8	165.7
Net income attributable to common shareowners	125.1	120.9
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	555.1	525.8
Operating income (loss)	73.5	75.6
Net income attributable to common shareowners	53.3	46.7
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	415.2	381.7
Operating income (loss)	98.1	84
Net income attributable to common shareowners	65.7	54
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	743.4	708.7
Operating income (loss)	126.4	126.7
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	419.8	405.7
Operating income (loss)	46.8	57.5
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	323.6	303
Operating income (loss)	79.6	69.2
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	215.8	185.6
Operating income (loss)	45.2	31.5
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	124.6	108.1
Operating income (loss)	26.3	16.9
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	91.2	77.5
Operating income (loss)	18.9	14.6
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	11.1	13.2
Operating income (loss)	0	1.4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10.7	12
Operating income (loss)	0.4	1.2
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.4	1.2
Operating income (loss)	(0.4)	0.2
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	970.3	907.5
Operating income (loss)	171.6	159.6
Net income attributable to common shareowners	119	100.7
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	16.9	8.8
Operating income (loss)	5.2	6.1
Net income attributable to common shareowners	$ 6.1	$ 20.2

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
ATC [Member] | WPL Owed ATC LLC [Member] | Equity Method Investee [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 7	$ 8

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 43	$ 41
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	33	33
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	15	5
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	1	1
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	84	93
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 30	$ 17

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 98	$ 95
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 73	$ 71

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 27	$ 27
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 4	$ 2