Wisconsin Power & Light 10-Q 4 Nov 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2016shares
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	352,541
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	227,500,428
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
IPL [Member]
Entity Registrant Name	INTERSTATE POWER & LIGHT CO
Entity Central Index Key	52,485
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	107,832
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		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating revenues:
Electric utility		$ 864.3	$ 835.8	$ 2,209.1	$ 2,147.5
Gas utility		39.5	38	248.7	288.1
Other utility		9.4	13.4	35	44.6
Non-regulated		11.4	11.7	30.2	33.3
Total operating revenues		924.6	898.9	2,523	2,513.5
Operating expenses:
Electric production fuel and purchased power		245.9	245.8	646.3	646.9
Electric transmission service		138.6	127.6	396.8	367.7
Cost of gas sold		12.5	13.6	132.3	166.3
Asset valuation charges for Franklin County wind farm		86.4	0	86.4	0
Other operation and maintenance		148.6	151.1	438.2	456.3
Depreciation and amortization		104.1	99.3	308.7	299.9
Taxes other than income taxes		25.9	25.6	77.2	78.6
Total operating expenses		762	663	2,085.9	2,015.7
Operating income		162.6	235.9	437.1	497.8
Interest expense and other:
Interest expense		48.8	46.4	144.8	139.5
Equity income from unconsolidated investments, net		(9.2)	(11.1)	(28.8)	(28.9)
Allowance for funds used during construction		(15.8)	(9.7)	(44.3)	(25.1)
Interest income and other		(0.1)	(0.1)	(0.3)	(0.4)
Total interest expense and other		23.7	25.5	71.4	85.1
Income from continuing operations before income taxes		138.9	210.4	365.7	412.7
Income tax expense (benefit)		7.5	27.8	47.2	59.5
Income from continuing operations, net of tax		131.4	182.6	318.5	353.2
Loss from discontinued operations, net of tax		(0.4)	(0.1)	(2)	(1.4)
Net income		131	182.5	316.5	351.8
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners		$ 128.4	$ 179.9	$ 308.8	$ 344.1
Weighted average number of common shares outstanding (basic and diluted) (in shares)	[1]	227.2	226.4	227	225
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax (in dollars per share)	[1]	$ 0.57	$ 0.79	$ 1.37	$ 1.54
Loss from discontinued operations, net of tax (in dollars per share)	[1]	0	0	(0.01)	(0.01)
Net income (in dollars per share)	[1]	$ 0.57	$ 0.79	$ 1.36	$ 1.53
Amounts attributable to common shareowners:
Income from continuing operations, net of tax		$ 128.8	$ 180	$ 310.8	$ 345.5
Loss from discontinued operations, net of tax		(0.4)	(0.1)	(2)	(1.4)
Net income (loss) attributable to common shareowners		$ 128.4	$ 179.9	$ 308.8	$ 344.1
Dividends declared per common share (in dollars per share)	[1]	$ 0.29375	$ 0.275	$ 0.88125	$ 0.825
IPL [Member]
Operating revenues:
Electric utility		$ 483.2	$ 468.6	$ 1,209.2	$ 1,170.6
Gas utility		23.9	23.1	142.6	164.1
Other utility		9.1	12.9	34.1	41.1
Total operating revenues		516.2	504.6	1,385.9	1,375.8
Operating expenses:
Electric production fuel and purchased power		125	131.4	324.8	332
Electric transmission service		95.9	87.5	270.7	249.3
Cost of gas sold		8	9.4	76.3	93.4
Other operation and maintenance		94.8	94.3	279.8	287.5
Depreciation and amortization		52.7	51.2	157.8	155.1
Taxes other than income taxes		13.9	13.8	40.6	42.2
Total operating expenses		390.3	387.6	1,150	1,159.5
Operating income		125.9	117	235.9	216.3
Interest expense and other:
Interest expense		25.5	23.8	75.4	71.8
Allowance for funds used during construction		(13.8)	(7.3)	(36.2)	(19.3)
Interest income and other		0	0.1	(0.1)	0
Total interest expense and other		11.7	16.6	39.1	52.5
Income from continuing operations before income taxes		114.2	100.4	196.8	163.8
Income tax expense (benefit)		(2.5)	(18.7)	(2.5)	(24.4)
Net income		116.7	119.1	199.3	188.2
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners		114.1	116.5	191.6	180.5
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners		114.1	116.5	191.6	180.5
WPL [Member]
Operating revenues:
Electric utility		381.1	367.2	999.9	976.9
Gas utility		15.6	14.9	106.1	124
Other utility		0.3	0.5	0.9	3.5
Total operating revenues		397	382.6	1,106.9	1,104.4
Operating expenses:
Electric production fuel and purchased power		120.9	114.4	321.5	314.9
Electric transmission service		42.7	40.1	126.1	118.4
Cost of gas sold		4.5	4.2	56	72.9
Other operation and maintenance		54.2	57	157.2	167.7
Depreciation and amortization		48.7	45.7	143.5	137.5
Taxes other than income taxes		11	10.9	33.8	33.6
Total operating expenses		282	272.3	838.1	845
Operating income		115	110.3	268.8	259.4
Interest expense and other:
Interest expense		22.9	23.1	68.7	69.5
Equity income from unconsolidated investments, net		(9.3)	(11.1)	(29)	(30.2)
Allowance for funds used during construction		(2)	(2.4)	(8.1)	(5.8)
Interest income and other		0.1	(0.3)	(0.2)	(0.3)
Total interest expense and other		11.7	9.3	31.4	33.2
Income from continuing operations before income taxes		103.3	101	237.4	226.2
Income tax expense (benefit)		33.7	32.6	77.1	73
Net income		69.6	68.4	160.3	153.2
Net income attributable to noncontrolling interest		0.6	0.4	1.6	1.1
Net income (loss) attributable to common shareowners		69	68	158.7	152.1
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners		$ 69	$ 68	$ 158.7	$ 152.1
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents		$ 84.7	$ 5.8
Accounts receivable, less allowance for doubtful accounts		491.5	397.6
Production fuel, at weighted average cost		92.6	98.8
Gas stored underground, at weighted average cost		37.8	43.3
Materials and supplies, at weighted average cost		89.5	81.4
Regulatory assets		63.1	120.2
Other		98.9	79.7
Total current assets		958.1	826.8
Property, plant and equipment, net		9,920.4	9,519.1
Investments:
Investment in American Transmission Company LLC		309.9	293.3
Other		19.7	53
Total investments		329.6	346.3
Other assets:
Regulatory assets		1,811.7	1,788.4
Deferred charges and other		9.4	14.6
Total other assets		1,821.1	1,803
Total assets		13,029.2	12,495.2
Current liabilities:
Current maturities of long-term debt		314	313.4
Commercial paper		238.3	159.8
Accounts payable		365.1	402.4
Regulatory liabilities		178.4	187.1
Other		273.9	296.6
Total current liabilities		1,369.7	1,359.3
Long-term debt, net (excluding current portion)		3,816.9	3,522.2
Other liabilities:
Deferred tax liabilities		2,530.6	2,381.2
Regulatory liabilities		497.4	550.6
Pension and other benefit obligations		455.3	451.8
Other		300.2	306
Total other liabilities		3,783.5	3,689.6
Commitments and contingencies (Note 13)
Common equity:
Common stock	[1]	2.3	2.3
Additional paid-in capital		1,686	1,661.8
Retained earnings		2,181	2,068.9
Accumulated other comprehensive loss		(0.4)	(0.4)
Shares in deferred compensation trust - 432,619 and 430,186 shares at a weighted average cost of $22.54 and $19.84 per share	[1]	(9.8)	(8.5)
Total common equity		3,859.1	3,724.1
Cumulative preferred stock of Interstate Power and Light Company		200	200
Total equity		4,059.1	3,924.1
Total liabilities and equity		13,029.2	12,495.2
IPL [Member]
Current assets:
Cash and cash equivalents		77.7	4.5
Accounts receivable, less allowance for doubtful accounts		266.8	200
Production fuel, at weighted average cost		70	60.2
Gas stored underground, at weighted average cost		17.4	18.2
Materials and supplies, at weighted average cost		50	45.7
Regulatory assets		15	39.6
Other		37.2	28.2
Total current assets		534.1	396.4
Property, plant and equipment, net		5,220.1	4,925.1
Investments:
Total investments		0.8	19.6
Other assets:
Regulatory assets		1,402.2	1,363
Deferred charges and other		3.8	5
Total other assets		1,406	1,368
Total assets		7,161	6,709.1
Current liabilities:
Commercial paper		0
Accounts payable		172.6	197.2
Accounts payable to associated companies		55	37.7
Regulatory liabilities		132.5	130.9
Accrued taxes		41.2	67.6
Other		85.9	97.7
Total current liabilities		487.2	531.1
Long-term debt, net (excluding current portion)		2,153.1	1,856.9
Other liabilities:
Deferred tax liabilities		1,493.6	1,378
Regulatory liabilities		298.9	358.3
Pension and other benefit obligations		161.2	160.2
Other		229.1	229.3
Total other liabilities		2,182.8	2,125.8
Commitments and contingencies (Note 13)
Common equity:
Common stock		33.4	33.4
Additional paid-in capital		1,472.8	1,407.8
Retained earnings		631.7	554.1
Total common equity		2,137.9	1,995.3
Cumulative preferred stock of Interstate Power and Light Company		200	200
Total equity		2,337.9	2,195.3
Total liabilities and equity		7,161	6,709.1
WPL [Member]
Current assets:
Cash and cash equivalents		5.6	0.4
Accounts receivable, less allowance for doubtful accounts		190.7	185.4
Production fuel, at weighted average cost		22.6	38.6
Gas stored underground, at weighted average cost		20.4	25.1
Materials and supplies, at weighted average cost		35.7	33.5
Regulatory assets		48.1	80.6
Other		53.9	59.9
Total current assets		377	423.5
Property, plant and equipment, net		4,289.1	4,103.7
Investments:
Investment in American Transmission Company LLC		309.9	293.3
Other		13.4	15.4
Total investments		323.3	308.7
Other assets:
Regulatory assets		409.5	425.4
Deferred charges and other		6.9	9.1
Total other assets		416.4	434.5
Total assets		5,405.8	5,270.4
Current liabilities:
Commercial paper		11.8	19.9
Accounts payable		122.3	136
Accounts payable to associated companies		32.8	21.6
Regulatory liabilities		45.9	56.2
Other		91	103.2
Total current liabilities		303.8	336.9
Long-term debt, net (excluding current portion)		1,534.9	1,533.9
Other liabilities:
Deferred tax liabilities		1,108.8	1,005.4
Regulatory liabilities		198.5	192.3
Capital lease obligations - Sheboygan Falls Energy Facility		78.9	83.6
Pension and other benefit obligations		186.2	188.7
Other		162.4	162
Total other liabilities		1,734.8	1,632
Commitments and contingencies (Note 13)
Common equity:
Common stock		66.2	66.2
Additional paid-in capital		959	959
Retained earnings		788.6	731.1
Total common equity		1,813.8	1,756.3
Noncontrolling interest		18.5	11.3
Total equity		1,832.3	1,767.6
Total liabilities and equity		$ 5,405.8	$ 5,270.4
[1]	Share and per share amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Condensed Consolidated Balance4

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares		Sep. 30, 2016	Dec. 31, 2015
Common stock, par value	[1]	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	[1]	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	[1]	227,500,428	226,918,432
Shares in deferred compensation trust (in shares)	[1]	432,619	430,186
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	[1]	$ 22.54	$ 19.84
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
[1]	Share and per share amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Condensed Consolidated Stateme5

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 316.5	$ 351.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	308.7	299.9
Deferred tax expense and investment tax credits	76.7	101
Asset valuation charges for Franklin County wind farm	86.4	0
Other	(44)	(2.5)
Other changes in assets and liabilities:
Accounts receivable	(101)	11.7
Sales of accounts receivable	(4)	(21)
Regulatory assets	36.6	(51.3)
Regulatory liabilities	(66.5)	(61.5)
Deferred income taxes	71.8	74.1
Other	(27.2)	(6.9)
Net cash flows from operating activities	654	695.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(743.6)	(678.9)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(43.3)	(47.5)
Proceeds from Minnesota electric and natural gas distribution asset sales	0	138.1
Other	15.1	(24.7)
Net cash flows used for investing activities	(771.8)	(613)
Cash flows from (used for) financing activities:
Common stock dividends	(199.8)	(185.1)
Proceeds from issuance of common stock, net	20.4	145.4
Proceeds from issuance of long-term debt	300	250.7
Payments to retire long-term debt	(1.9)	(182)
Net change in commercial paper	78.5	(32.2)
Other	(0.5)	3.2
Net cash flows from (used for) financing activities	196.7	0
Net increase (decrease) in cash and cash equivalents	78.9	82.3
Cash and cash equivalents at beginning of period	5.8	56.9
Cash and cash equivalents at end of period	84.7	139.2
Supplemental cash flows information:
Interest, net of capitalized interest	(140.7)	(133.9)
Income taxes, net	(8.3)	0
Significant non-cash investing and financing activities:
Accrued capital expenditures	99.9	180
IPL [Member]
Cash flows from operating activities:
Net income	199.3	188.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	157.8	155.1
Other	24.3	32.3
Other changes in assets and liabilities:
Accounts receivable	(66.5)	(8.3)
Sales of accounts receivable	(4)	(21)
Regulatory assets	(14.1)	(38.1)
Regulatory liabilities	(64.5)	(63.1)
Deferred income taxes	67.7	72
Other	(43.5)	0.9
Net cash flows from operating activities	256.5	318
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(436.5)	(432.6)
Proceeds from Minnesota electric and natural gas distribution asset sales	0	138.1
Other	1.1	(24.9)
Net cash flows used for investing activities	(435.4)	(319.4)
Cash flows from (used for) financing activities:
Common stock dividends	(114)	(105)
Capital contributions from parent	65	100
Proceeds from issuance of long-term debt	300	250
Payments to retire long-term debt	0	(150)
Other	1.1	0.5
Net cash flows from (used for) financing activities	252.1	95.5
Net increase (decrease) in cash and cash equivalents	73.2	94.1
Cash and cash equivalents at beginning of period	4.5	5.3
Cash and cash equivalents at end of period	77.7	99.4
Supplemental cash flows information:
Interest, net of capitalized interest	(72.5)	(66.7)
Income taxes, net	0.7	31.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	44.5	115.5
WPL [Member]
Cash flows from operating activities:
Net income	160.3	153.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	143.5	137.5
Deferred tax expense and investment tax credits	97.9	60
Other	(20.3)	(8.3)
Other changes in assets and liabilities:
Regulatory assets	50.7	(13.2)
Derivative liabilities	(13.3)	19
Other	20.5	27.7
Net cash flows from operating activities	439.3	375.9
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(307.1)	(246.3)
Other	(19.6)	(13.3)
Net cash flows used for investing activities	(326.7)	(259.6)
Cash flows from (used for) financing activities:
Common stock dividends	(101.2)	(95.3)
Payments to retire long-term debt	0	(30.6)
Other	(6.2)	(1.4)
Net cash flows from (used for) financing activities	(107.4)	(127.3)
Net increase (decrease) in cash and cash equivalents	5.2	(11)
Cash and cash equivalents at beginning of period	0.4	46.7
Cash and cash equivalents at end of period	5.6	35.7
Supplemental cash flows information:
Interest, net of capitalized interest	(67.7)	(69.2)
Income taxes, net	19.6	(10)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 50.8	$ 57.2

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2016
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split. NOTE 1(b) New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted. NOTE 1(c) Property, Plant and Equipment - Utility Plant - Depreciation - In September 2016, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2017 as a result of a recently completed depreciation study. WPL estimates the new average rates of depreciation for its electric generation, electric distribution and gas properties will be approximately 3.2% , 2.6% and 2.3% , respectively, during 2017.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split. NOTE 1(b) New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split. NOTE 1(b) New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted. NOTE 1(c) Property, Plant and Equipment - Utility Plant - Depreciation - In September 2016, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2017 as a result of a recently completed depreciation study. WPL estimates the new average rates of depreciation for its electric generation, electric distribution and gas properties will be approximately 3.2% , 2.6% and 2.3% , respectively, during 2017.

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2016
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5 Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $56 million as follows (in millions): Electric tax benefit rider credits $47 Gas tax benefit rider credits 9 $56 Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate case with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million , or approximately 1% , increase in annual rates for WPL’s retail electric customers. The net requested increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflected a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million , or approximately 13% , increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate case filing in the fourth quarter of 2016. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three and nine months ended September 30 , IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Billing credits to reduce retail electric customers’ bills $3 $7 $7 $19 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - Pursuant to a 2015 PSCW order, WPL’s 2016 fuel-related costs will be subject to deferral if they are outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through September 30, 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of September 30, 2016, fuel-related costs outside of the approved range were $9 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. Pursuant to an August 2016 PSCW order, WPL will refund $ 10 million , including interest, to its retail electric customers in the fourth quarter of 2016 for these over-collections.
IPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5 Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $56 million as follows (in millions): Electric tax benefit rider credits $47 Gas tax benefit rider credits 9 $56 Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate case with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million , or approximately 1% , increase in annual rates for WPL’s retail electric customers. The net requested increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflected a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million , or approximately 13% , increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate case filing in the fourth quarter of 2016. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three and nine months ended September 30 , IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Billing credits to reduce retail electric customers’ bills $3 $7 $7 $19 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - Pursuant to a 2015 PSCW order, WPL’s 2016 fuel-related costs will be subject to deferral if they are outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through September 30, 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of September 30, 2016, fuel-related costs outside of the approved range were $9 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. Pursuant to an August 2016 PSCW order, WPL will refund $ 10 million , including interest, to its retail electric customers in the fourth quarter of 2016 for these over-collections.
WPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0 Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5 Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Derivatives - Refer to Note 12 for discussion of derivative assets and derivative liabilities. IPL’s tax benefit riders - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. For the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $56 million as follows (in millions): Electric tax benefit rider credits $47 Gas tax benefit rider credits 9 $56 Refer to Note 8 for additional details regarding IPL’s tax benefit riders. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In May 2016, WPL filed a retail base rate case with the PSCW based on a forward-looking test period that includes 2017 and 2018. WPL’s filing was based on a stipulated agreement reached between PSCW staff, intervener groups and WPL. The filing requested approval for WPL to implement a $13 million , or approximately 1% , increase in annual rates for WPL’s retail electric customers. The net requested increase for 2017 compared to WPL’s retail electric rate case for the 2015/2016 Test Period reflected a $65 million increase in base rates, partially offset by a $52 million reduction in fuel-related costs, using a preliminary estimate for 2017 fuel-related costs. The filing also requested approval for WPL to implement a $9 million , or approximately 13% , increase in annual base rates for WPL’s retail gas customers. Any rate changes granted from this request are expected to be effective January 1, 2017 and extend through the end of 2018. WPL currently expects a decision from the PSCW regarding this base rate case filing in the fourth quarter of 2016. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits. For the three and nine months ended September 30 , IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Billing credits to reduce retail electric customers’ bills $3 $7 $7 $19 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - Pursuant to a 2015 PSCW order, WPL’s 2016 fuel-related costs will be subject to deferral if they are outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through September 30, 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of September 30, 2016, fuel-related costs outside of the approved range were $9 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - Pursuant to a 2014 PSCW order, WPL’s 2015 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL in 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. Pursuant to an August 2016 PSCW order, WPL will refund $ 10 million , including interest, to its retail electric customers in the fourth quarter of 2016 for these over-collections.

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of September 30, 2016 , Alliant Energy and WPL recorded capitalized expenditures of $223 million and AFUDC of $12 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in the second quarter of 2017. As of September 30, 2016 , Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $600 million and AFUDC of $56 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million and a promissory note of $2 million . In 2015, IPL completed the sale of its Minnesota electric distribution assets and received proceeds of $129 million . The proceeds from the natural gas distribution assets were used for general corporate purposes and the proceeds from the electric distribution assets were used to reduce cash amounts received from IPL’s sales of accounts receivable program. The premium received over the book value of the property, plant and equipment sold was more than offset by a reduction in tax-related regulatory assets associated with the distribution assets. As a result, Alliant Energy and IPL recorded pre-tax charges of $9 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements for the nine months ended September 30, 2015 . Non-regulated and Other - Non-regulated Generation - Franklin County Wind Farm - Based on an evaluation of the strategic options for the Franklin County wind farm performed in the third quarter of 2016, Alliant Energy concluded, as of September 30, 2016, it was probable the Franklin County wind farm will be transferred to IPL. As a result, Alliant Energy performed an impairment analysis of such assets in the third quarter of 2016. The impairment analysis evaluated the value of the assets and a reasonable estimate of the amount of costs associated with the Franklin County wind farm that would be allowed for recovery for IPL’s electric rate-making purposes. Based on various analyses, including discounted cash flows projected from the Franklin County wind farm, recently executed purchased power agreements associated with wind generating facilities located near the Franklin County wind farm, and the cost of new wind farms identified through IPL’s planned wind expansion, the current value of the Franklin County wind farm assets as of September 30, 2016 was determined to be approximately $33 million , subject to working capital adjustments. Alliant Energy concluded such value represents a reasonable estimate of the amount IPL will be allowed for recovery for IPL’s electric rate-making purposes. As a result, the carrying amount of the Franklin County wind farm was reduced to its current value, resulting in non-cash, pre-tax asset valuation charges of $86 million (after-tax charges of $51 million , or $0.23 per share) in the third quarter of 2016. Alliant Energy recorded such charges as a reduction to “Property, plant and equipment, net” on its balance sheet in 2016 and charges to “Asset valuation charges for Franklin County wind farm” in its income statements for the three and nine months ended September 30, 2016. IPL currently anticipates requesting approval from FERC in the fourth quarter of 2016 to transfer the Franklin County wind farm to IPL and expects to complete such transfer in the first quarter of 2017. The final amount to be recovered for IPL’s electric rate-making purposes will be determined by the IUB as part of IPL’s Iowa retail electric rate case for the 2016 Test Year, currently anticipated to be filed in the second quarter of 2017, and therefore the final asset valuation charges are subject to change.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of September 30, 2016 , Alliant Energy and WPL recorded capitalized expenditures of $223 million and AFUDC of $12 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in the second quarter of 2017. As of September 30, 2016 , Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $600 million and AFUDC of $56 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million and a promissory note of $2 million . In 2015, IPL completed the sale of its Minnesota electric distribution assets and received proceeds of $129 million . The proceeds from the natural gas distribution assets were used for general corporate purposes and the proceeds from the electric distribution assets were used to reduce cash amounts received from IPL’s sales of accounts receivable program. The premium received over the book value of the property, plant and equipment sold was more than offset by a reduction in tax-related regulatory assets associated with the distribution assets. As a result, Alliant Energy and IPL recorded pre-tax charges of $9 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements for the nine months ended September 30, 2015 . Non-regulated and Other - Non-regulated Generation - Franklin County Wind Farm - Based on an evaluation of the strategic options for the Franklin County wind farm performed in the third quarter of 2016, Alliant Energy concluded, as of September 30, 2016, it was probable the Franklin County wind farm will be transferred to IPL. As a result, Alliant Energy performed an impairment analysis of such assets in the third quarter of 2016. The impairment analysis evaluated the value of the assets and a reasonable estimate of the amount of costs associated with the Franklin County wind farm that would be allowed for recovery for IPL’s electric rate-making purposes. Based on various analyses, including discounted cash flows projected from the Franklin County wind farm, recently executed purchased power agreements associated with wind generating facilities located near the Franklin County wind farm, and the cost of new wind farms identified through IPL’s planned wind expansion, the current value of the Franklin County wind farm assets as of September 30, 2016 was determined to be approximately $33 million , subject to working capital adjustments. Alliant Energy concluded such value represents a reasonable estimate of the amount IPL will be allowed for recovery for IPL’s electric rate-making purposes. As a result, the carrying amount of the Franklin County wind farm was reduced to its current value, resulting in non-cash, pre-tax asset valuation charges of $86 million (after-tax charges of $51 million , or $0.23 per share) in the third quarter of 2016. Alliant Energy recorded such charges as a reduction to “Property, plant and equipment, net” on its balance sheet in 2016 and charges to “Asset valuation charges for Franklin County wind farm” in its income statements for the three and nine months ended September 30, 2016. IPL currently anticipates requesting approval from FERC in the fourth quarter of 2016 to transfer the Franklin County wind farm to IPL and expects to complete such transfer in the first quarter of 2017. The final amount to be recovered for IPL’s electric rate-making purposes will be determined by the IUB as part of IPL’s Iowa retail electric rate case for the 2016 Test Year, currently anticipated to be filed in the second quarter of 2017, and therefore the final asset valuation charges are subject to change.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of September 30, 2016 , Alliant Energy and WPL recorded capitalized expenditures of $223 million and AFUDC of $12 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.

Receivables

Receivables	9 Months Ended
	Sep. 30, 2016
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2016, IPL extended through March 2018 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of September 30, 2016 , IPL sold $252.9 million of receivables to the third party, received $1.0 million in cash proceeds and recorded deferred proceeds of $239.7 million . IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $172.0 $137.0 $172.0 $137.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 112.3 41.2 91.5 62.1 For the three and nine months ended September 30 , 2016 and 2015 , IPL’s costs incurred related to the sales of accounts receivable program were not material. The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2016 December 31, 2015 Customer accounts receivable $172.9 $109.7 Unbilled utility revenues 79.8 71.3 Other receivables 0.2 0.1 Receivables sold to third party 252.9 181.1 Less: cash proceeds (a) 1.0 5.0 Deferred proceeds 251.9 176.1 Less: allowance for doubtful accounts 12.2 4.1 Fair value of deferred proceeds $239.7 $172.0 (a) Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements. As of September 30, 2016 , outstanding receivables past due under the Receivables Agreement were $64.5 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Collections reinvested in receivables $499.7 $480.1 $1,362.1 $1,403.1 Write-offs (recoveries), net (0.3 ) 3.3 (0.6 ) 6.8 In connection with the implementation of IPL’s new customer billing and information system in the first quarter of 2016, IPL postponed the write-off of customer bills, resulting in lower write-offs for the three and nine months ended September 30, 2016.
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2016, IPL extended through March 2018 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. As of September 30, 2016 , IPL sold $252.9 million of receivables to the third party, received $1.0 million in cash proceeds and recorded deferred proceeds of $239.7 million . IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $172.0 $137.0 $172.0 $137.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 112.3 41.2 91.5 62.1 For the three and nine months ended September 30 , 2016 and 2015 , IPL’s costs incurred related to the sales of accounts receivable program were not material. The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2016 December 31, 2015 Customer accounts receivable $172.9 $109.7 Unbilled utility revenues 79.8 71.3 Other receivables 0.2 0.1 Receivables sold to third party 252.9 181.1 Less: cash proceeds (a) 1.0 5.0 Deferred proceeds 251.9 176.1 Less: allowance for doubtful accounts 12.2 4.1 Fair value of deferred proceeds $239.7 $172.0 (a) Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements. As of September 30, 2016 , outstanding receivables past due under the Receivables Agreement were $64.5 million . Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Collections reinvested in receivables $499.7 $480.1 $1,362.1 $1,403.1 Write-offs (recoveries), net (0.3 ) 3.3 (0.6 ) 6.8 In connection with the implementation of IPL’s new customer billing and information system in the first quarter of 2016, IPL postponed the write-off of customer bills, resulting in lower write-offs for the three and nine months ended September 30, 2016.

Investments

Investments	9 Months Ended
	Sep. 30, 2016
Schedule of Investments [Line Items]
Investments	INVESTMENTS NOTE 5(a) Unconsolidated Equity Investments - Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Alliant Energy WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 ATC ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) Other (0.1 ) (0.2 ) (0.2 ) 0.7 (0.2 ) (0.2 ) (0.4 ) (0.6 ) ($9.2 ) ($11.1 ) ($28.8 ) ($28.9 ) ($9.3 ) ($11.1 ) ($29.0 ) ($30.2 ) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed two complaints with FERC requesting a reduction of the base return on equity used by MISO transmission owners, including ATC. In September 2016, FERC issued an order on the first complaint to reduce the base return on equity for the refund period from November 12, 2013 through February 11, 2015. In June 2016, a FERC administrative law judge issued an initial decision regarding the second complaint recommending a reduction of the base return on equity for the refund period from February 12, 2015 through May 11, 2016. A final decision on the second complaint from FERC is currently expected in the first half of 2017. Alliant Energy and WPL have realized a cumulative $24 million of reductions in the amount of equity income from ATC as a result of the two complaints through September 30, 2016, including $9 million during the nine months ended September 30, 2016. NOTE 5(b) Cash Surrender Value of Life Insurance Policies - During the nine months ended September 30 , 2016, certain of Alliant Energy’s and IPL’s company-owned life insurance policies were liquidated. The related proceeds of $31 million and $19 million were recorded in investing activities in Alliant Energy’s and IPL’s cash flows statements, respectively.
IPL [Member]
Schedule of Investments [Line Items]
Investments	INVESTMENTS NOTE 5(a) Unconsolidated Equity Investments - Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Alliant Energy WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 ATC ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) Other (0.1 ) (0.2 ) (0.2 ) 0.7 (0.2 ) (0.2 ) (0.4 ) (0.6 ) ($9.2 ) ($11.1 ) ($28.8 ) ($28.9 ) ($9.3 ) ($11.1 ) ($29.0 ) ($30.2 ) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed two complaints with FERC requesting a reduction of the base return on equity used by MISO transmission owners, including ATC. In September 2016, FERC issued an order on the first complaint to reduce the base return on equity for the refund period from November 12, 2013 through February 11, 2015. In June 2016, a FERC administrative law judge issued an initial decision regarding the second complaint recommending a reduction of the base return on equity for the refund period from February 12, 2015 through May 11, 2016. A final decision on the second complaint from FERC is currently expected in the first half of 2017. Alliant Energy and WPL have realized a cumulative $24 million of reductions in the amount of equity income from ATC as a result of the two complaints through September 30, 2016, including $9 million during the nine months ended September 30, 2016. NOTE 5(b) Cash Surrender Value of Life Insurance Policies - During the nine months ended September 30 , 2016, certain of Alliant Energy’s and IPL’s company-owned life insurance policies were liquidated. The related proceeds of $31 million and $19 million were recorded in investing activities in Alliant Energy’s and IPL’s cash flows statements, respectively.
WPL [Member]
Schedule of Investments [Line Items]
Investments	INVESTMENTS NOTE 5(a) Unconsolidated Equity Investments - Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Alliant Energy WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 ATC ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) Other (0.1 ) (0.2 ) (0.2 ) 0.7 (0.2 ) (0.2 ) (0.4 ) (0.6 ) ($9.2 ) ($11.1 ) ($28.8 ) ($28.9 ) ($9.3 ) ($11.1 ) ($29.0 ) ($30.2 ) MISO Transmission Owner Return on Equity Complaints - A group of MISO cooperative and municipal utilities previously filed two complaints with FERC requesting a reduction of the base return on equity used by MISO transmission owners, including ATC. In September 2016, FERC issued an order on the first complaint to reduce the base return on equity for the refund period from November 12, 2013 through February 11, 2015. In June 2016, a FERC administrative law judge issued an initial decision regarding the second complaint recommending a reduction of the base return on equity for the refund period from February 12, 2015 through May 11, 2016. A final decision on the second complaint from FERC is currently expected in the first half of 2017. Alliant Energy and WPL have realized a cumulative $24 million of reductions in the amount of equity income from ATC as a result of the two complaints through September 30, 2016, including $9 million during the nine months ended September 30, 2016.

Common Equity

Common Equity	9 Months Ended
	Sep. 30, 2016
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, 2016 226,918,432 Shareowner Direct Plan issuances 559,588 Equity-based compensation plans ( Note 9(b) ) 22,408 Shares outstanding, September 30, 2016 227,500,428 At-the-Market Offering Program - During the nine months ended September 30 , 2015 , Alliant Energy issued 4,373,234 shares of common stock through an at-the-market offering program and received cash proceeds of $133 million , net of $2 million in fees and commissions. The proceeds from the issuances of common stock were used for general corporate purposes. Common Stock Split - On April 20, 2016, Alliant Energy’s Board of Directors approved a two -for-one common stock split and a proportionate increase in the number of authorized shares of common stock of Alliant Energy from 240 million shares to 480 million shares to implement the stock split. Alliant Energy shareowners of record at the close of business on May 4, 2016 received one additional share of Alliant Energy common stock for each share held on that date. The proportionate interest that a shareowner owns in Alliant Energy did not change as a result of the stock split. The additional shares were distributed on May 19, 2016 and post-split trading began on May 20, 2016. All Alliant Energy share and per share amounts in this report have been reflected on a post-split basis. Dividend Restrictions - As of September 30, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $632 million . As of September 30, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $34 million for the remainder of 2016 . Restricted Net Assets of Subsidiaries - As of September 30, 2016 , the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.5 billion and $1.8 billion , respectively. Capital Transactions with Subsidiaries - For the nine months ended September 30 , 2016 , IPL received capital contributions of $65.0 million from its parent company. For the nine months ended September 30 , 2016 , IPL and WPL paid common stock dividends of $114.0 million and $101.2 million , respectively, to their parent company. Comprehensive Income - For the three and nine months ended September 30, 2016 and 2015 , Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2016 and 2015 , 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, 2016 226,918,432 Shareowner Direct Plan issuances 559,588 Equity-based compensation plans ( Note 9(b) ) 22,408 Shares outstanding, September 30, 2016 227,500,428 At-the-Market Offering Program - During the nine months ended September 30 , 2015 , Alliant Energy issued 4,373,234 shares of common stock through an at-the-market offering program and received cash proceeds of $133 million , net of $2 million in fees and commissions. The proceeds from the issuances of common stock were used for general corporate purposes. Common Stock Split - On April 20, 2016, Alliant Energy’s Board of Directors approved a two -for-one common stock split and a proportionate increase in the number of authorized shares of common stock of Alliant Energy from 240 million shares to 480 million shares to implement the stock split. Alliant Energy shareowners of record at the close of business on May 4, 2016 received one additional share of Alliant Energy common stock for each share held on that date. The proportionate interest that a shareowner owns in Alliant Energy did not change as a result of the stock split. The additional shares were distributed on May 19, 2016 and post-split trading began on May 20, 2016. All Alliant Energy share and per share amounts in this report have been reflected on a post-split basis. Dividend Restrictions - As of September 30, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $632 million . As of September 30, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $34 million for the remainder of 2016 . Restricted Net Assets of Subsidiaries - As of September 30, 2016 , the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.5 billion and $1.8 billion , respectively. Capital Transactions with Subsidiaries - For the nine months ended September 30 , 2016 , IPL received capital contributions of $65.0 million from its parent company. For the nine months ended September 30 , 2016 , IPL and WPL paid common stock dividends of $114.0 million and $101.2 million , respectively, to their parent company. Comprehensive Income - For the three and nine months ended September 30, 2016 and 2015 , Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2016 and 2015 , 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, 2016 226,918,432 Shareowner Direct Plan issuances 559,588 Equity-based compensation plans ( Note 9(b) ) 22,408 Shares outstanding, September 30, 2016 227,500,428 At-the-Market Offering Program - During the nine months ended September 30 , 2015 , Alliant Energy issued 4,373,234 shares of common stock through an at-the-market offering program and received cash proceeds of $133 million , net of $2 million in fees and commissions. The proceeds from the issuances of common stock were used for general corporate purposes. Common Stock Split - On April 20, 2016, Alliant Energy’s Board of Directors approved a two -for-one common stock split and a proportionate increase in the number of authorized shares of common stock of Alliant Energy from 240 million shares to 480 million shares to implement the stock split. Alliant Energy shareowners of record at the close of business on May 4, 2016 received one additional share of Alliant Energy common stock for each share held on that date. The proportionate interest that a shareowner owns in Alliant Energy did not change as a result of the stock split. The additional shares were distributed on May 19, 2016 and post-split trading began on May 20, 2016. All Alliant Energy share and per share amounts in this report have been reflected on a post-split basis. Dividend Restrictions - As of September 30, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $632 million . As of September 30, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $34 million for the remainder of 2016 . Restricted Net Assets of Subsidiaries - As of September 30, 2016 , the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was $1.5 billion and $1.8 billion , respectively. Capital Transactions with Subsidiaries - For the nine months ended September 30 , 2016 , IPL received capital contributions of $65.0 million from its parent company. For the nine months ended September 30 , 2016 , IPL and WPL paid common stock dividends of $114.0 million and $101.2 million , respectively, to their parent company. Comprehensive Income - For the three and nine months ended September 30, 2016 and 2015 , Alliant Energy had no other comprehensive income; therefore, its comprehensive income was equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was equal to its net income attributable to Alliant Energy common shareowners for such periods. For the three and nine months ended September 30, 2016 and 2015 , IPL and WPL had no other comprehensive income; therefore, their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

Debt

Debt	9 Months Ended
	Sep. 30, 2016
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A NOTE 7(b) Long-term Debt - In September 2016, IPL issued $300 million of 3.7% senior debentures due 2046. The proceeds from the issuance were used by IPL to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $100 million and for general corporate purposes. In October 2016, AEF entered into a $500 million variable-rate ( 1.3% at October 31, 2016) term loan credit agreement and used the proceeds from borrowings under this agreement to retire borrowings under Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper and for general corporate purposes. AEF’s term loan credit agreement expires in October 2018 and includes substantially the same financial covenants that are included in Alliant Energy’s credit facility agreement.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A NOTE 7(b) Long-term Debt - In September 2016, IPL issued $300 million of 3.7% senior debentures due 2046. The proceeds from the issuance were used by IPL to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $100 million and for general corporate purposes.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
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 tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the nine months ended September 30 , 2016 , Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $149.4 million , $115.6 million and $103.4 million , respectively. These increases in deferred tax liabilities were primarily due to property-related differences recorded during the nine months ended September 30 , 2016 . Carryforwards - At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192
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 tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the nine months ended September 30 , 2016 , Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $149.4 million , $115.6 million and $103.4 million , respectively. These increases in deferred tax liabilities were primarily due to property-related differences recorded during the nine months ended September 30 , 2016 . Carryforwards - At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192
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 tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the nine months ended September 30 , 2016 , Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $149.4 million , $115.6 million and $103.4 million , respectively. These increases in deferred tax liabilities were primarily due to property-related differences recorded during the nine months ended September 30 , 2016 . Carryforwards - At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2016
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3 401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4 Voluntary Employee Separation Charges - In the third quarter of 2015, Alliant Energy offered certain employees a voluntary separation package. Approximately 2% of total Alliant Energy employees accepted this package, which resulted in Alliant Energy, IPL and WPL recording charges of $8 million , $5 million and $3 million , respectively, in the third quarter of 2015. NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 6 . A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0 As of September 30, 2016 , total unrecognized compensation cost related to share-based compensation awards was $8.2 million , which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows: Performance Shares Performance Units 2016 2015 2016 2015 Nonvested awards, January 1 288,430 288,848 116,412 127,330 Granted 68,585 90,806 23,918 35,674 Vested (98,186 ) (91,224 ) (42,760 ) (45,690 ) Forfeited (1,230 ) — (4,250 ) (902 ) Nonvested awards, September 30 257,599 288,430 93,320 116,412 Granted Awards - For performance units granted in 2016, the final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Vested Awards - During the nine months ended September 30 , certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows: Performance Shares Performance Units 2016 2015 2016 2015 2013 Grant 2012 Grant 2013 Grant 2012 Grant Performance awards vested 98,186 91,224 42,760 45,690 Percentage of target number of performance awards 165.0 % 167.5 % 165.0 % 167.5 % Aggregate payout value (in millions) $5.1 $5.1 $1.7 $1.6 Payout - cash (in millions) $2.9 $3.2 $1.7 $1.6 Payout - common stock shares issued 22,408 21,950 N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at September 30, 2016 , by year of grant, was as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on September 30, 2016 $38.31 $38.31 $38.31 $38.31 N/A N/A Alliant Energy common stock closing price on grant date N/A N/A N/A N/A $32.55 $26.89 Estimated payout percentage based on performance criteria 125 % 168 % 175 % 125 % 168 % 175 % Fair values of each nonvested award $47.89 $64.36 $67.04 $47.89 $54.68 $47.05 Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows: 2016 2015 Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 Granted — — 90,806 32.55 Vested (a) — — (98,186 ) 23.79 Nonvested shares, September 30 190,244 29.59 190,244 29.59 (a) In 2015, 98,186 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three -year performance period. The actual number of 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 units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2016 Units Weighted Average Grant Date Fair Value Granted 68,585 $33.96 Forfeited (1,230 ) 33.90 Nonvested units, September 30 67,355 33.96 Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 23,918 Forfeited (1,261 ) Nonvested units, September 30 22,657 Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 45,056 Forfeited (2,016 ) Nonvested units, September 30 43,040 Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three -year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows: 2016 Restricted Stock Units Restricted Units Granted 58,790 20,502 Forfeited (1,054 ) (1,082 ) Nonvested units, September 30 57,736 19,420 Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows: 2016 2015 Nonvested awards, January 1 163,752 157,860 Granted — 82,210 Vested (a) — (74,664 ) Forfeited (3,652 ) (1,654 ) Nonvested awards, September 30 160,100 163,752 (a) In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million .
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3 401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4 Voluntary Employee Separation Charges - In the third quarter of 2015, Alliant Energy offered certain employees a voluntary separation package. Approximately 2% of total Alliant Energy employees accepted this package, which resulted in Alliant Energy, IPL and WPL recording charges of $8 million , $5 million and $3 million , respectively, in the third quarter of 2015. NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 6 . A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0 As of September 30, 2016 , total unrecognized compensation cost related to share-based compensation awards was $8.2 million , which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows: Performance Shares Performance Units 2016 2015 2016 2015 Nonvested awards, January 1 288,430 288,848 116,412 127,330 Granted 68,585 90,806 23,918 35,674 Vested (98,186 ) (91,224 ) (42,760 ) (45,690 ) Forfeited (1,230 ) — (4,250 ) (902 ) Nonvested awards, September 30 257,599 288,430 93,320 116,412 Granted Awards - For performance units granted in 2016, the final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Vested Awards - During the nine months ended September 30 , certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows: Performance Shares Performance Units 2016 2015 2016 2015 2013 Grant 2012 Grant 2013 Grant 2012 Grant Performance awards vested 98,186 91,224 42,760 45,690 Percentage of target number of performance awards 165.0 % 167.5 % 165.0 % 167.5 % Aggregate payout value (in millions) $5.1 $5.1 $1.7 $1.6 Payout - cash (in millions) $2.9 $3.2 $1.7 $1.6 Payout - common stock shares issued 22,408 21,950 N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at September 30, 2016 , by year of grant, was as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on September 30, 2016 $38.31 $38.31 $38.31 $38.31 N/A N/A Alliant Energy common stock closing price on grant date N/A N/A N/A N/A $32.55 $26.89 Estimated payout percentage based on performance criteria 125 % 168 % 175 % 125 % 168 % 175 % Fair values of each nonvested award $47.89 $64.36 $67.04 $47.89 $54.68 $47.05 Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows: 2016 2015 Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 Granted — — 90,806 32.55 Vested (a) — — (98,186 ) 23.79 Nonvested shares, September 30 190,244 29.59 190,244 29.59 (a) In 2015, 98,186 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three -year performance period. The actual number of 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 units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2016 Units Weighted Average Grant Date Fair Value Granted 68,585 $33.96 Forfeited (1,230 ) 33.90 Nonvested units, September 30 67,355 33.96 Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 23,918 Forfeited (1,261 ) Nonvested units, September 30 22,657 Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 45,056 Forfeited (2,016 ) Nonvested units, September 30 43,040 Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three -year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows: 2016 Restricted Stock Units Restricted Units Granted 58,790 20,502 Forfeited (1,054 ) (1,082 ) Nonvested units, September 30 57,736 19,420 Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows: 2016 2015 Nonvested awards, January 1 163,752 157,860 Granted — 82,210 Vested (a) — (74,664 ) Forfeited (3,652 ) (1,654 ) Nonvested awards, September 30 160,100 163,752 (a) In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million .
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 9(a) Pension and Other Postretirement Benefits Plans - Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3 401(k) Savings Plan - A significant number of employees participate in a defined contribution retirement plan (401(k) savings plan). For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4 Voluntary Employee Separation Charges - In the third quarter of 2015, Alliant Energy offered certain employees a voluntary separation package. Approximately 2% of total Alliant Energy employees accepted this package, which resulted in Alliant Energy, IPL and WPL recording charges of $8 million , $5 million and $3 million , respectively, in the third quarter of 2015. NOTE 9(b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 6 . A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0 As of September 30, 2016 , total unrecognized compensation cost related to share-based compensation awards was $8.2 million , which is expected to be recognized over a weighted average period of between one and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows: Performance Shares Performance Units 2016 2015 2016 2015 Nonvested awards, January 1 288,430 288,848 116,412 127,330 Granted 68,585 90,806 23,918 35,674 Vested (98,186 ) (91,224 ) (42,760 ) (45,690 ) Forfeited (1,230 ) — (4,250 ) (902 ) Nonvested awards, September 30 257,599 288,430 93,320 116,412 Granted Awards - For performance units granted in 2016, the final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Vested Awards - During the nine months ended September 30 , certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows: Performance Shares Performance Units 2016 2015 2016 2015 2013 Grant 2012 Grant 2013 Grant 2012 Grant Performance awards vested 98,186 91,224 42,760 45,690 Percentage of target number of performance awards 165.0 % 167.5 % 165.0 % 167.5 % Aggregate payout value (in millions) $5.1 $5.1 $1.7 $1.6 Payout - cash (in millions) $2.9 $3.2 $1.7 $1.6 Payout - common stock shares issued 22,408 21,950 N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at September 30, 2016 , by year of grant, was as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on September 30, 2016 $38.31 $38.31 $38.31 $38.31 N/A N/A Alliant Energy common stock closing price on grant date N/A N/A N/A N/A $32.55 $26.89 Estimated payout percentage based on performance criteria 125 % 168 % 175 % 125 % 168 % 175 % Fair values of each nonvested award $47.89 $64.36 $67.04 $47.89 $54.68 $47.05 Performance Contingent Restricted Stock - A summary of the performance contingent restricted stock activity was as follows: 2016 2015 Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 Granted — — 90,806 32.55 Vested (a) — — (98,186 ) 23.79 Nonvested shares, September 30 190,244 29.59 190,244 29.59 (a) In 2015, 98,186 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. Performance Restricted Stock Units and Performance Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as performance restricted stock units, performance restricted units and key employee performance restricted units. Payouts of these units are based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations) during the three -year performance period. The actual number of 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 units. If performance targets are not met during the performance period, these units are forfeited. Subject to achievement of the performance criteria, payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the performance period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Subject to achievement of the performance criteria, payouts of units to participants who terminate employment after the first year of the performance period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the performance period. Performance Restricted Stock Units - Performance restricted stock units must be paid out in shares and are accounted for as equity awards. Each performance restricted stock unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2016 Units Weighted Average Grant Date Fair Value Granted 68,585 $33.96 Forfeited (1,230 ) 33.90 Nonvested units, September 30 67,355 33.96 Performance Restricted Units - Performance restricted units must be paid out in cash and are accounted for as liability awards. Each performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 23,918 Forfeited (1,261 ) Nonvested units, September 30 22,657 Key Employee Performance Restricted Units - Key employee performance restricted units must be paid out in cash and are accounted for as liability awards. Each key employee performance restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 45,056 Forfeited (2,016 ) Nonvested units, September 30 43,040 Restricted Stock Units and Restricted Units - Alliant Energy granted new types of share-based compensation awards to key employees in the first quarter of 2016 referred to as restricted stock units and restricted units. Payouts of these units are based on the expiration of a three -year time-vesting period. Payouts of nonvested units are prorated in the event of retirement, death or disability during the first year of the time-vesting period based on time worked during the first year of the period, and are prorated upon involuntary termination without cause based on time worked during the entire period. Upon expiration of the time-vesting period, payouts of units to participants who terminate employment after the first year of the period due to retirement, death or disability are not prorated. Participants’ nonvested units are forfeited if the participant voluntarily leaves Alliant Energy or is terminated for cause during the time-vesting period. Each restricted stock unit’s and restricted unit’s final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the time-vesting period. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Restricted stock units can be paid out in shares of Alliant Energy common stock, cash or a combination of cash and stock. Restricted units must be paid out in cash. Alliant Energy assumes it will make future payouts of its restricted stock units and restricted units in cash; therefore, restricted stock units and restricted units are accounted for as liability awards. A summary of the restricted stock units and restricted units activity was as follows: 2016 Restricted Stock Units Restricted Units Granted 58,790 20,502 Forfeited (1,054 ) (1,082 ) Nonvested units, September 30 57,736 19,420 Performance-Contingent Cash Awards - A summary of the performance-contingent cash awards activity was as follows: 2016 2015 Nonvested awards, January 1 163,752 157,860 Granted — 82,210 Vested (a) — (74,664 ) Forfeited (3,652 ) (1,654 ) Nonvested awards, September 30 160,100 163,752 (a) In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million .

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2016
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs 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 AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
WPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2016
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and rail transportation costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Manage rail transportation costs Diesel fuel swap contracts (WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 4 for additional information regarding deferred proceeds. Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 7(b) for additional information regarding long-term debt. Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and rail transportation costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Manage rail transportation costs Diesel fuel swap contracts (WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 4 for additional information regarding deferred proceeds. Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 7(b) for additional information regarding long-term debt. Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments, and Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and rail transportation costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Manage rail transportation costs Diesel fuel swap contracts (WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 12 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 4 for additional information regarding deferred proceeds. Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on quoted market prices for similar liabilities at each reporting date or on a discounted cash flow methodology, which utilizes assumptions of current market pricing curves at each reporting date. Refer to Note 7(b) for additional information regarding long-term debt. Cumulative preferred stock - The fair value of IPL’s 5.1% cumulative preferred stock was based on its closing market price quoted by the New York Stock Exchange at each reporting date. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2016
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments. Notional Amounts - As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 11 for further discussion. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2016 and December 31, 2015 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2016 and December 31, 2015 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments. Notional Amounts - As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 11 for further discussion. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2016 and December 31, 2015 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2016 and December 31, 2015 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 11 for detailed discussion of derivative instruments. Notional Amounts - As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities. The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 11 for further discussion. Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided in the form of letters of credit or cash collateral up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At September 30, 2016 and December 31, 2015 , the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, amounts would not be materially different from gross amounts of derivative assets and derivative liabilities at September 30, 2016 and December 31, 2015 . Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU, and generation maintenance and performance improvements at Columbia Units 1 and 2. At September 30, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $27 million , $1 million and $26 million , respectively. NOTE 13(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 . NOTE 13(c) Legal Proceedings - Flood Damage Claims - In 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In February 2016, the Iowa District Court for Linn County ruled in favor of Alliant Energy and CRANDIC and dismissed all claims against them, resulting in no loss. In August 2016, the Iowa District Court for Linn County dismissed all claims against the remaining defendants. In September 2016, plaintiffs filed a notice of appeal with the Supreme Court of Iowa. Alliant Energy does not currently believe any material losses for this complaint are both probable and reasonably estimated, and therefore has not recognized any material loss contingency amounts as of September 30, 2016 . NOTE 13(d) Guarantees and Indemnifications - RMT - In 2013, Alliant Energy sold RMT. RMT provided renewable energy services, including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The contractual warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016. Limited warranties may be extended in certain cases for warranty work performed. Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2016 , Alliant Energy had $123 million of performance guarantees outstanding, with $48 million and $75 million currently expected to expire in 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects. Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of September 30, 2016 . Alliant Energy does not currently believe that the range of future potential loss from any warranty claims will be material. Refer to Note 16 for further discussion of RMT, including amounts Alliant Energy recorded to “Operating expenses” during the nine months ended September 30, 2016 and 2015 related to certain warranty claims. Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Resources, as the successor to a predecessor entity that owned Whiting Petroleum, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2016 , the present value of the abandonment obligations is estimated at $30 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Resources will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2016 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the July 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2016 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(e) Environmental Matters - MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 23 and 5 sites, respectively. Environmental liabilities related to the MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3 WPL Consent Decree - In 2013, the U.S. District Court for the Western District of Wisconsin approved a Consent Decree that WPL, along with the other owners of Edgewater and Columbia, entered into with the EPA and the Sierra Club, thereby resolving claims against WPL. Such claims included allegations that the owners of Edgewater, Nelson Dewey and Columbia violated the Prevention of Significant Deterioration program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin State Implementation Plan designed to implement the CAA. WPL has completed various requirements under the Consent Decree. WPL’s remaining requirements include installing an SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia and Edgewater. WPL is in the process of completing approximately $7 million in environmental mitigation projects. Alliant Energy and WPL currently expect to recover material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. The recovery of such costs will be decided by the PSCW in future rate cases or other proceedings. 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 CAA 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 installing an SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019; fuel switching or retiring Prairie Creek Unit 4 by June 1, 2018, the Burlington Generating Station by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025; and either installing combined cycle technology at, or retiring, the Dubuque and Sutherland Generating Stations by June 1, 2019. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits with varying averaging times for the Burlington, Lansing, M.L. Kapp, Ottumwa and Prairie Creek Generating Stations. In addition, the Consent Decree includes calendar-year SO2 and NOx emission caps for the Prairie Creek Generating Station, and calendar-year SO2 and NOx emission caps in aggregate for the Burlington, Dubuque, Lansing, M.L. Kapp, Ottumwa, Prairie Creek and Sutherland Generating Stations. IPL will also complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Ozone NAAQS Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU, and generation maintenance and performance improvements at Columbia Units 1 and 2. At September 30, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $27 million , $1 million and $26 million , respectively. NOTE 13(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 . NOTE 13(c) Legal Proceedings - Flood Damage Claims - In 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In February 2016, the Iowa District Court for Linn County ruled in favor of Alliant Energy and CRANDIC and dismissed all claims against them, resulting in no loss. In August 2016, the Iowa District Court for Linn County dismissed all claims against the remaining defendants. In September 2016, plaintiffs filed a notice of appeal with the Supreme Court of Iowa. Alliant Energy does not currently believe any material losses for this complaint are both probable and reasonably estimated, and therefore has not recognized any material loss contingency amounts as of September 30, 2016 . NOTE 13(d) Guarantees and Indemnifications - RMT - In 2013, Alliant Energy sold RMT. RMT provided renewable energy services, including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The contractual warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016. Limited warranties may be extended in certain cases for warranty work performed. Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2016 , Alliant Energy had $123 million of performance guarantees outstanding, with $48 million and $75 million currently expected to expire in 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects. Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of September 30, 2016 . Alliant Energy does not currently believe that the range of future potential loss from any warranty claims will be material. Refer to Note 16 for further discussion of RMT, including amounts Alliant Energy recorded to “Operating expenses” during the nine months ended September 30, 2016 and 2015 related to certain warranty claims. Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Resources, as the successor to a predecessor entity that owned Whiting Petroleum, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2016 , the present value of the abandonment obligations is estimated at $30 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Resources will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2016 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the July 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2016 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(e) Environmental Matters - MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 23 and 5 sites, respectively. Environmental liabilities related to the MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3 WPL Consent Decree - In 2013, the U.S. District Court for the Western District of Wisconsin approved a Consent Decree that WPL, along with the other owners of Edgewater and Columbia, entered into with the EPA and the Sierra Club, thereby resolving claims against WPL. Such claims included allegations that the owners of Edgewater, Nelson Dewey and Columbia violated the Prevention of Significant Deterioration program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin State Implementation Plan designed to implement the CAA. WPL has completed various requirements under the Consent Decree. WPL’s remaining requirements include installing an SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia and Edgewater. WPL is in the process of completing approximately $7 million in environmental mitigation projects. Alliant Energy and WPL currently expect to recover material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. The recovery of such costs will be decided by the PSCW in future rate cases or other proceedings. 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 CAA 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 installing an SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019; fuel switching or retiring Prairie Creek Unit 4 by June 1, 2018, the Burlington Generating Station by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025; and either installing combined cycle technology at, or retiring, the Dubuque and Sutherland Generating Stations by June 1, 2019. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits with varying averaging times for the Burlington, Lansing, M.L. Kapp, Ottumwa and Prairie Creek Generating Stations. In addition, the Consent Decree includes calendar-year SO2 and NOx emission caps for the Prairie Creek Generating Station, and calendar-year SO2 and NOx emission caps in aggregate for the Burlington, Dubuque, Lansing, M.L. Kapp, Ottumwa, Prairie Creek and Sutherland Generating Stations. IPL will also complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Ozone NAAQS Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 13(a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU, and generation maintenance and performance improvements at Columbia Units 1 and 2. At September 30, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $27 million , $1 million and $26 million , respectively. NOTE 13(b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 . NOTE 13(c) Legal Proceedings - Flood Damage Claims - In 2013, several plaintiffs purporting to represent a class of residential and commercial property owners filed a complaint against CRANDIC, Alliant Energy and various other defendants in the Iowa District Court for Linn County. Plaintiffs assert claims of negligence and strict liability based on their allegations that CRANDIC (along with other defendants) caused or exacerbated flooding of the Cedar River in June 2008. In February 2016, the Iowa District Court for Linn County ruled in favor of Alliant Energy and CRANDIC and dismissed all claims against them, resulting in no loss. In August 2016, the Iowa District Court for Linn County dismissed all claims against the remaining defendants. In September 2016, plaintiffs filed a notice of appeal with the Supreme Court of Iowa. Alliant Energy does not currently believe any material losses for this complaint are both probable and reasonably estimated, and therefore has not recognized any material loss contingency amounts as of September 30, 2016 . NOTE 13(d) Guarantees and Indemnifications - RMT - In 2013, Alliant Energy sold RMT. RMT provided renewable energy services, including construction and high voltage connection services for wind and solar projects. As part of the sale, Alliant Energy indemnified the buyer for any claims, including claims of warranty under the project obligations that were commenced or are based on actions that occurred prior to the sale, except for liabilities already accounted for through adjustments to the purchase price. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The contractual warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016. Limited warranties may be extended in certain cases for warranty work performed. Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of September 30, 2016 , Alliant Energy had $123 million of performance guarantees outstanding, with $48 million and $75 million currently expected to expire in 2016 and 2017, respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects. Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of September 30, 2016 . Alliant Energy does not currently believe that the range of future potential loss from any warranty claims will be material. Refer to Note 16 for further discussion of RMT, including amounts Alliant Energy recorded to “Operating expenses” during the nine months ended September 30, 2016 and 2015 related to certain warranty claims. Whiting Petroleum - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Whiting Petroleum is an independent oil and gas company. Resources, as the successor to a predecessor entity that owned Whiting Petroleum, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of September 30, 2016 , the present value of the abandonment obligations is estimated at $30 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Resources will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2016 . IPL’s Minnesota Electric Distribution Assets - IPL provided indemnifications associated with the July 2015 sale of its Minnesota electric distribution assets for losses resulting from potential breach of IPL’s representations, warranties and obligations under the sale agreement. Alliant Energy and IPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. IPL has not recorded any material liabilities related to these indemnifications as of September 30, 2016 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . NOTE 13(e) Environmental Matters - MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 23 and 5 sites, respectively. Environmental liabilities related to the MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3 WPL Consent Decree - In 2013, the U.S. District Court for the Western District of Wisconsin approved a Consent Decree that WPL, along with the other owners of Edgewater and Columbia, entered into with the EPA and the Sierra Club, thereby resolving claims against WPL. Such claims included allegations that the owners of Edgewater, Nelson Dewey and Columbia violated the Prevention of Significant Deterioration program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin State Implementation Plan designed to implement the CAA. WPL has completed various requirements under the Consent Decree. WPL’s remaining requirements include installing an SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia and Edgewater. WPL is in the process of completing approximately $7 million in environmental mitigation projects. Alliant Energy and WPL currently expect to recover material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. The recovery of such costs will be decided by the PSCW in future rate cases or other proceedings. 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 CAA 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 installing an SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019; fuel switching or retiring Prairie Creek Unit 4 by June 1, 2018, the Burlington Generating Station by December 31, 2021 and Prairie Creek Units 1 and 3 by December 31, 2025; and either installing combined cycle technology at, or retiring, the Dubuque and Sutherland Generating Stations by June 1, 2019. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits with varying averaging times for the Burlington, Lansing, M.L. Kapp, Ottumwa and Prairie Creek Generating Stations. In addition, the Consent Decree includes calendar-year SO2 and NOx emission caps for the Prairie Creek Generating Station, and calendar-year SO2 and NOx emission caps in aggregate for the Burlington, Dubuque, Lansing, M.L. Kapp, Ottumwa, Prairie Creek and Sutherland Generating Stations. IPL will also complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however future capital investments and/or modifications to EGUs to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: Cross-State Air Pollution Rule, Ozone NAAQS Rule, Federal Clean Water Act including Section 316(b), Effluent Limitation Guidelines, Hydroelectric Fish Passage Device, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs.

Segments Of Business

Segments Of Business	9 Months Ended
	Sep. 30, 2016
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. Refer to Note 3 for discussion of asset valuation charges recorded in the third quarter of 2016 related to the Franklin County wind farm, which decreased the assets for “Non-Regulated, Parent and Other.” Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2016 Operating revenues $864.3 $39.5 $9.4 $913.2 $11.4 $924.6 Operating income (loss) 244.2 (3.7 ) 0.4 240.9 (78.3 ) 162.6 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 183.1 (54.3 ) 128.8 Loss from discontinued operations, net of tax — (0.4 ) (0.4 ) Net income (loss) 183.1 (54.7 ) 128.4 Three Months Ended September 30, 2015 Operating revenues $835.8 $38.0 $13.4 $887.2 $11.7 $898.9 Operating income (loss) 232.8 (5.7 ) 0.2 227.3 8.6 235.9 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 184.5 (4.5 ) 180.0 Loss from discontinued operations, net of tax — (0.1 ) (0.1 ) Net income (loss) 184.5 (4.6 ) 179.9 Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2016 Operating revenues $2,209.1 $248.7 $35.0 $2,492.8 $30.2 $2,523.0 Operating income (loss) 473.3 27.0 4.4 504.7 (67.6 ) 437.1 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 350.3 (39.5 ) 310.8 Loss from discontinued operations, net of tax — (2.0 ) (2.0 ) Net income (loss) 350.3 (41.5 ) 308.8 Nine Months Ended September 30, 2015 Operating revenues $2,147.5 $288.1 $44.6 $2,480.2 $33.3 $2,513.5 Operating income 438.4 28.6 8.7 475.7 22.1 497.8 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 332.6 12.9 345.5 Loss from discontinued operations, net of tax — (1.4 ) (1.4 ) Net income 332.6 11.5 344.1 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $483.2 $23.9 $9.1 $516.2 Operating income (loss) 125.9 (1.4 ) 1.4 125.9 Earnings available for common stock 114.1 Three Months Ended September 30, 2015 Operating revenues $468.6 $23.1 $12.9 $504.6 Operating income (loss) 119.4 (2.9 ) 0.5 117.0 Earnings available for common stock 116.5 Nine Months Ended September 30, 2016 Operating revenues $1,209.2 $142.6 $34.1 $1,385.9 Operating income 213.8 15.3 6.8 235.9 Earnings available for common stock 191.6 Nine Months Ended September 30, 2015 Operating revenues $1,170.6 $164.1 $41.1 $1,375.8 Operating income 193.6 15.3 7.4 216.3 Earnings available for common stock 180.5 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $381.1 $15.6 $0.3 $397.0 Operating income (loss) 118.3 (2.3 ) (1.0 ) 115.0 Earnings available for common stock 69.0 Three Months Ended September 30, 2015 Operating revenues $367.2 $14.9 $0.5 $382.6 Operating income (loss) 113.4 (2.8 ) (0.3 ) 110.3 Earnings available for common stock 68.0 Nine Months Ended September 30, 2016 Operating revenues $999.9 $106.1 $0.9 $1,106.9 Operating income (loss) 259.5 11.7 (2.4 ) 268.8 Earnings available for common stock 158.7 Nine Months Ended September 30, 2015 Operating revenues $976.9 $124.0 $3.5 $1,104.4 Operating income 244.8 13.3 1.3 259.4 Earnings available for common stock 152.1
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. Refer to Note 3 for discussion of asset valuation charges recorded in the third quarter of 2016 related to the Franklin County wind farm, which decreased the assets for “Non-Regulated, Parent and Other.” Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2016 Operating revenues $864.3 $39.5 $9.4 $913.2 $11.4 $924.6 Operating income (loss) 244.2 (3.7 ) 0.4 240.9 (78.3 ) 162.6 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 183.1 (54.3 ) 128.8 Loss from discontinued operations, net of tax — (0.4 ) (0.4 ) Net income (loss) 183.1 (54.7 ) 128.4 Three Months Ended September 30, 2015 Operating revenues $835.8 $38.0 $13.4 $887.2 $11.7 $898.9 Operating income (loss) 232.8 (5.7 ) 0.2 227.3 8.6 235.9 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 184.5 (4.5 ) 180.0 Loss from discontinued operations, net of tax — (0.1 ) (0.1 ) Net income (loss) 184.5 (4.6 ) 179.9 Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2016 Operating revenues $2,209.1 $248.7 $35.0 $2,492.8 $30.2 $2,523.0 Operating income (loss) 473.3 27.0 4.4 504.7 (67.6 ) 437.1 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 350.3 (39.5 ) 310.8 Loss from discontinued operations, net of tax — (2.0 ) (2.0 ) Net income (loss) 350.3 (41.5 ) 308.8 Nine Months Ended September 30, 2015 Operating revenues $2,147.5 $288.1 $44.6 $2,480.2 $33.3 $2,513.5 Operating income 438.4 28.6 8.7 475.7 22.1 497.8 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 332.6 12.9 345.5 Loss from discontinued operations, net of tax — (1.4 ) (1.4 ) Net income 332.6 11.5 344.1 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $483.2 $23.9 $9.1 $516.2 Operating income (loss) 125.9 (1.4 ) 1.4 125.9 Earnings available for common stock 114.1 Three Months Ended September 30, 2015 Operating revenues $468.6 $23.1 $12.9 $504.6 Operating income (loss) 119.4 (2.9 ) 0.5 117.0 Earnings available for common stock 116.5 Nine Months Ended September 30, 2016 Operating revenues $1,209.2 $142.6 $34.1 $1,385.9 Operating income 213.8 15.3 6.8 235.9 Earnings available for common stock 191.6 Nine Months Ended September 30, 2015 Operating revenues $1,170.6 $164.1 $41.1 $1,375.8 Operating income 193.6 15.3 7.4 216.3 Earnings available for common stock 180.5 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $381.1 $15.6 $0.3 $397.0 Operating income (loss) 118.3 (2.3 ) (1.0 ) 115.0 Earnings available for common stock 69.0 Three Months Ended September 30, 2015 Operating revenues $367.2 $14.9 $0.5 $382.6 Operating income (loss) 113.4 (2.8 ) (0.3 ) 110.3 Earnings available for common stock 68.0 Nine Months Ended September 30, 2016 Operating revenues $999.9 $106.1 $0.9 $1,106.9 Operating income (loss) 259.5 11.7 (2.4 ) 268.8 Earnings available for common stock 158.7 Nine Months Ended September 30, 2015 Operating revenues $976.9 $124.0 $3.5 $1,104.4 Operating income 244.8 13.3 1.3 259.4 Earnings available for common stock 152.1
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Certain financial information relating to Alliant Energy’s business segments is as follows. Intersegment revenues were not material to Alliant Energy’s operations. Refer to Note 3 for discussion of asset valuation charges recorded in the third quarter of 2016 related to the Franklin County wind farm, which decreased the assets for “Non-Regulated, Parent and Other.” Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2016 Operating revenues $864.3 $39.5 $9.4 $913.2 $11.4 $924.6 Operating income (loss) 244.2 (3.7 ) 0.4 240.9 (78.3 ) 162.6 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 183.1 (54.3 ) 128.8 Loss from discontinued operations, net of tax — (0.4 ) (0.4 ) Net income (loss) 183.1 (54.7 ) 128.4 Three Months Ended September 30, 2015 Operating revenues $835.8 $38.0 $13.4 $887.2 $11.7 $898.9 Operating income (loss) 232.8 (5.7 ) 0.2 227.3 8.6 235.9 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 184.5 (4.5 ) 180.0 Loss from discontinued operations, net of tax — (0.1 ) (0.1 ) Net income (loss) 184.5 (4.6 ) 179.9 Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2016 Operating revenues $2,209.1 $248.7 $35.0 $2,492.8 $30.2 $2,523.0 Operating income (loss) 473.3 27.0 4.4 504.7 (67.6 ) 437.1 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 350.3 (39.5 ) 310.8 Loss from discontinued operations, net of tax — (2.0 ) (2.0 ) Net income (loss) 350.3 (41.5 ) 308.8 Nine Months Ended September 30, 2015 Operating revenues $2,147.5 $288.1 $44.6 $2,480.2 $33.3 $2,513.5 Operating income 438.4 28.6 8.7 475.7 22.1 497.8 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 332.6 12.9 345.5 Loss from discontinued operations, net of tax — (1.4 ) (1.4 ) Net income 332.6 11.5 344.1 IPL - Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $483.2 $23.9 $9.1 $516.2 Operating income (loss) 125.9 (1.4 ) 1.4 125.9 Earnings available for common stock 114.1 Three Months Ended September 30, 2015 Operating revenues $468.6 $23.1 $12.9 $504.6 Operating income (loss) 119.4 (2.9 ) 0.5 117.0 Earnings available for common stock 116.5 Nine Months Ended September 30, 2016 Operating revenues $1,209.2 $142.6 $34.1 $1,385.9 Operating income 213.8 15.3 6.8 235.9 Earnings available for common stock 191.6 Nine Months Ended September 30, 2015 Operating revenues $1,170.6 $164.1 $41.1 $1,375.8 Operating income 193.6 15.3 7.4 216.3 Earnings available for common stock 180.5 WPL - Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $381.1 $15.6 $0.3 $397.0 Operating income (loss) 118.3 (2.3 ) (1.0 ) 115.0 Earnings available for common stock 69.0 Three Months Ended September 30, 2015 Operating revenues $367.2 $14.9 $0.5 $382.6 Operating income (loss) 113.4 (2.8 ) (0.3 ) 110.3 Earnings available for common stock 68.0 Nine Months Ended September 30, 2016 Operating revenues $999.9 $106.1 $0.9 $1,106.9 Operating income (loss) 259.5 11.7 (2.4 ) 268.8 Earnings available for common stock 158.7 Nine Months Ended September 30, 2015 Operating revenues $976.9 $124.0 $3.5 $1,104.4 Operating income 244.8 13.3 1.3 259.4 Earnings available for common stock 152.1

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2016
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 ATC billings to WPL $28 $25 $82 $75 WPL billings to ATC 4 4 10 9 WPL owed ATC net amounts of $9 million as of September 30, 2016 and $8 million as of December 31, 2015 . Franklin County Wind Farm - Refer to Note 3 for discussion of IPL’s anticipated filing with FERC in the fourth quarter of 2016 requesting approval to transfer the Franklin County wind farm assets from AEF to IPL in 2017.
IPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 ATC billings to WPL $28 $25 $82 $75 WPL billings to ATC 4 4 10 9 WPL owed ATC net amounts of $9 million as of September 30, 2016 and $8 million as of December 31, 2015 . Franklin County Wind Farm - Refer to Note 3 for discussion of IPL’s anticipated filing with FERC in the fourth quarter of 2016 requesting approval to transfer the Franklin County wind farm assets from AEF to IPL in 2017.
WPL [Member]
Related Party Transactions [Line Items]
Related Parties	RELATED PARTIES Service Agreements - IPL and WPL are parties to service agreements with an affiliate, Corporate Services. Pursuant to these service agreements, IPL and WPL receive various administrative and general services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54 ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 ATC billings to WPL $28 $25 $82 $75 WPL billings to ATC 4 4 10 9 WPL owed ATC net amounts of $9 million as of September 30, 2016 and $8 million as of December 31, 2015 .

Discontinued Operations

Discontinued Operations	9 Months Ended
	Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations and Assets and Liabilities Held For Sale	DISCONTINUED OPERATIONS In 2013, Alliant Energy sold RMT to narrow its strategic focus and risk profile. The operating results of RMT have been separately classified and reported as discontinued operations in Alliant Energy’s income statements. A summary of the components of discontinued operations in Alliant Energy’s income statements for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Operating expenses $0.6 $0.3 $3.3 $2.3 Loss before income taxes (0.6 ) (0.3 ) (3.3 ) (2.3 ) Income tax benefit (0.2 ) (0.2 ) (1.3 ) (0.9 ) Loss from discontinued operations, net of tax ($0.4 ) ($0.1 ) ($2.0 ) ($1.4 ) Refer to Note 13(d) for further discussion of warranty claims associated with RMT that have resulted in operating expenses subsequent to the sale.

Summary Of Significant Accoun22

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2016
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K.
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split.
New Accounting Standards	New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted.
Depreciation	Property, Plant and Equipment - Utility Plant - Depreciation - In September 2016, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2017 as a result of a recently completed depreciation study. WPL estimates the new average rates of depreciation for its electric generation, electric distribution and gas properties will be approximately 3.2% , 2.6% and 2.3% , respectively, during 2017.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K.
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split.
New Accounting Standards	New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the latest combined Annual Report on Form 10-K.
General, Use of Estimates	In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2016 are not necessarily indicative of results that may be expected for the year ending December 31, 2016 . A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification	Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. Unless otherwise noted, the Notes herein exclude discontinued operations for all periods presented. In the fourth quarter of 2015, IPL and WPL implemented a change in method of recording income taxes that impacts the separate financial statements of IPL and WPL. As discussed in Note 6 , all Alliant Energy share and per share amounts have been adjusted to reflect a two -for-one common stock split distributed in May 2016. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect the tax method change and common stock split.
New Accounting Standards	New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are evaluating the impact of this standard on their financial condition and results of operations. 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 for all leases with terms longer than 12 months. The standard also requires disclosure of key information about leasing arrangements. Alliant Energy, IPL and WPL are required to adopt this standard on January 1, 2019 and are currently evaluating the impact of this standard on their financial condition and results of operations. Early adoption of this standard is permitted.
Depreciation	Property, Plant and Equipment - Utility Plant - Depreciation - In September 2016, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2017 as a result of a recently completed depreciation study. WPL estimates the new average rates of depreciation for its electric generation, electric distribution and gas properties will be approximately 3.2% , 2.6% and 2.3% , respectively, during 2017.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2016
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5
Tax Benefit Riders	For the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $56 million as follows (in millions): Electric tax benefit rider credits $47 Gas tax benefit rider credits 9 $56
Customer Billing Credits	For the three and nine months ended September 30 , IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Billing credits to reduce retail electric customers’ bills $3 $7 $7 $19
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5
Tax Benefit Riders	For the nine months ended September 30 , 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $56 million as follows (in millions): Electric tax benefit rider credits $47 Gas tax benefit rider credits 9 $56
Customer Billing Credits	For the three and nine months ended September 30 , IPL recorded billing credits to reduce retail electric customers’ bills as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Billing credits to reduce retail electric customers’ bills $3 $7 $7 $19
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,033.5 $987.7 $1,000.7 $958.2 $32.8 $29.5 Pension and OPEB costs 551.0 579.5 284.7 298.1 266.3 281.4 AROs 103.9 92.4 61.5 50.8 42.4 41.6 WPL’s EGUs retired early 43.1 45.0 — — 43.1 45.0 Derivatives 39.0 70.6 10.6 28.2 28.4 42.4 Emission allowances 26.3 26.9 26.3 26.9 — — Commodity cost recovery 10.1 35.9 0.4 2.8 9.7 33.1 Other 67.9 70.6 33.0 37.6 34.9 33.0 $1,874.8 $1,908.6 $1,417.2 $1,402.6 $457.6 $506.0
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Cost of removal obligations $410.6 $406.0 $267.2 $260.4 $143.4 $145.6 IPL’s tax benefit riders 103.1 159.2 103.1 159.2 — — Electric transmission cost recovery 54.5 43.5 25.0 21.9 29.5 21.6 Commodity cost recovery 39.1 37.6 15.1 23.5 24.0 14.1 Energy efficiency cost recovery 28.0 48.3 — — 28.0 48.3 Other 40.5 43.1 21.0 24.2 19.5 18.9 $675.8 $737.7 $431.4 $489.2 $244.4 $248.5

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 2016
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $172.0 $137.0 $172.0 $137.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 112.3 41.2 91.5 62.1
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2016 December 31, 2015 Customer accounts receivable $172.9 $109.7 Unbilled utility revenues 79.8 71.3 Other receivables 0.2 0.1 Receivables sold to third party 252.9 181.1 Less: cash proceeds (a) 1.0 5.0 Deferred proceeds 251.9 176.1 Less: allowance for doubtful accounts 12.2 4.1 Fair value of deferred proceeds $239.7 $172.0 (a) Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Collections reinvested in receivables $499.7 $480.1 $1,362.1 $1,403.1 Write-offs (recoveries), net (0.3 ) 3.3 (0.6 ) 6.8
IPL [Member]
Receivables [Line Items]
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $172.0 $137.0 $172.0 $137.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 112.3 41.2 91.5 62.1
Receivables Sold Under The Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2016 December 31, 2015 Customer accounts receivable $172.9 $109.7 Unbilled utility revenues 79.8 71.3 Other receivables 0.2 0.1 Receivables sold to third party 252.9 181.1 Less: cash proceeds (a) 1.0 5.0 Deferred proceeds 251.9 176.1 Less: allowance for doubtful accounts 12.2 4.1 Fair value of deferred proceeds $239.7 $172.0 (a) Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Collections reinvested in receivables $499.7 $480.1 $1,362.1 $1,403.1 Write-offs (recoveries), net (0.3 ) 3.3 (0.6 ) 6.8

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2016
Schedule of Investments [Line Items]
Unconsolidated Equity Investments	Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Alliant Energy WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 ATC ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) Other (0.1 ) (0.2 ) (0.2 ) 0.7 (0.2 ) (0.2 ) (0.4 ) (0.6 ) ($9.2 ) ($11.1 ) ($28.8 ) ($28.9 ) ($9.3 ) ($11.1 ) ($29.0 ) ($30.2 )
WPL [Member]
Schedule of Investments [Line Items]
Unconsolidated Equity Investments	Equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Alliant Energy WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 ATC ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) ($9.1 ) ($10.9 ) ($28.6 ) ($29.6 ) Other (0.1 ) (0.2 ) (0.2 ) 0.7 (0.2 ) (0.2 ) (0.4 ) (0.6 ) ($9.2 ) ($11.1 ) ($28.8 ) ($28.9 ) ($9.3 ) ($11.1 ) ($29.0 ) ($30.2 )

Common Equity (Tables)

Common Equity (Tables)	9 Months Ended
	Sep. 30, 2016
Stockholders' Equity Note [Abstract]
Common Share Activity	A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2016 226,918,432 Shareowner Direct Plan issuances 559,588 Equity-based compensation plans ( Note 9(b) ) 22,408 Shares outstanding, September 30, 2016 227,500,428

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A
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): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A
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): Alliant Energy Parent September 30, 2016 (Consolidated) Company IPL WPL Commercial paper: Amount outstanding $238.3 $226.5 $— $11.8 Weighted average remaining maturity 4 days 4 days N/A 3 days Weighted average interest rates 0.6% 0.7% N/A 0.4% Available credit facility capacity $761.7 $73.5 $300.0 $388.2 Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $55.4 $— Average amount outstanding (based on daily outstanding balances) $220.1 $122.4 $0.1 $0.5 $36.4 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $248.0 $181.2 $3.1 $18.4 $62.9 $— Average amount outstanding (based on daily outstanding balances) $210.7 $114.5 $— $0.2 $33.2 $— Weighted average interest rates 0.6 % 0.4 % 0.6 % 0.4 % 0.4% N/A

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2016
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 %
Summary Of Tax Credit Carryforwards	At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 %
Summary Of Tax Credit Carryforwards	At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes. Alliant Energy IPL WPL Three Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (13.1 ) (11.0 ) (20.1 ) (30.0 ) — — Effect of rate-making on property-related differences (11.9 ) (7.1 ) (16.5 ) (18.7 ) (0.7 ) (0.7 ) Production tax credits (9.0 ) (6.7 ) (6.0 ) (8.6 ) (5.7 ) (6.1 ) Other items, net 4.4 3.0 5.4 3.7 4.0 4.1 Overall income tax rate 5.4 % 13.2 % (2.2 %) (18.6 %) 32.6 % 32.3 % Alliant Energy IPL WPL Nine Months Ended September 30 2016 2015 2016 2015 2016 2015 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % IPL’s tax benefit riders (10.2 ) (10.6 ) (19.6 ) (28.2 ) — — Effect of rate-making on property-related differences (8.2 ) (7.1 ) (14.8 ) (17.9 ) (0.8 ) (0.6 ) Production tax credits (7.2 ) (6.6 ) (6.1 ) (8.0 ) (6.1 ) (6.3 ) Other items, net 3.5 3.7 4.2 4.2 4.4 4.2 Overall income tax rate 12.9 % 14.4 % (1.3 %) (14.9 %) 32.5 % 32.3 %
Summary Of Tax Credit Carryforwards	At September 30, 2016 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions): Alliant Energy IPL WPL Earliest Expiration Date Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Tax Carryforwards Deferred Tax Assets Federal net operating losses 2030 $587 $201 $255 $86 $242 $85 State net operating losses 2018 674 35 15 1 3 — Federal tax credits 2022 264 260 95 91 108 107 $496 $178 $192

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3
Employees Participate In Defined Contribution Retirement Plans	For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0
Performance Shares and Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows: Performance Shares Performance Units 2016 2015 2016 2015 Nonvested awards, January 1 288,430 288,848 116,412 127,330 Granted 68,585 90,806 23,918 35,674 Vested (98,186 ) (91,224 ) (42,760 ) (45,690 ) Forfeited (1,230 ) — (4,250 ) (902 ) Nonvested awards, September 30 257,599 288,430 93,320 116,412 Granted Awards - For performance units granted in 2016, the final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period. Vested Awards - During the nine months ended September 30 , certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows: Performance Shares Performance Units 2016 2015 2016 2015 2013 Grant 2012 Grant 2013 Grant 2012 Grant Performance awards vested 98,186 91,224 42,760 45,690 Percentage of target number of performance awards 165.0 % 167.5 % 165.0 % 167.5 % Aggregate payout value (in millions) $5.1 $5.1 $1.7 $1.6 Payout - cash (in millions) $2.9 $3.2 $1.7 $1.6 Payout - common stock shares issued 22,408 21,950 N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at September 30, 2016 , by year of grant, was as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on September 30, 2016 $38.31 $38.31 $38.31 $38.31 N/A N/A Alliant Energy common stock closing price on grant date N/A N/A N/A N/A $32.55 $26.89 Estimated payout percentage based on performance criteria 125 % 168 % 175 % 125 % 168 % 175 % Fair values of each nonvested award $47.89 $64.36 $67.04 $47.89 $54.68 $47.05
Performance Contingent Restricted Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance contingent restricted stock activity was as follows: 2016 2015 Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 Granted — — 90,806 32.55 Vested (a) — — (98,186 ) 23.79 Nonvested shares, September 30 190,244 29.59 190,244 29.59 (a) In 2015, 98,186 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.
Performance Restricted Stock Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2016 Units Weighted Average Grant Date Fair Value Granted 68,585 $33.96 Forfeited (1,230 ) 33.90 Nonvested units, September 30 67,355 33.96
Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 23,918 Forfeited (1,261 ) Nonvested units, September 30 22,657
Key Employee Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows: 2016 Granted 45,056 Forfeited (2,016 ) Nonvested units, September 30 43,040
Restricted Stock Unit And Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the restricted stock units and restricted units activity was as follows: 2016 Restricted Stock Units Restricted Units Granted 58,790 20,502 Forfeited (1,054 ) (1,082 ) Nonvested units, September 30 57,736 19,420
Performance Contingent Cash Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance-contingent cash awards activity was as follows: 2016 2015 Nonvested awards, January 1 163,752 157,860 Granted — 82,210 Vested (a) — (74,664 ) Forfeited (3,652 ) (1,654 ) Nonvested awards, September 30 160,100 163,752 (a) In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million .
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3
Employees Participate In Defined Contribution Retirement Plans	For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Pension And Other Postretirement Benefits Plans	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $3.2 $4.0 $9.5 $11.9 $1.4 $1.3 $4.0 $4.1 Interest cost 13.2 13.5 39.7 40.3 2.3 2.3 7.0 6.8 Expected return on plan assets (16.3 ) (18.7 ) (49.1 ) (56.2 ) (1.6 ) (2.1 ) (4.6 ) (6.3 ) Amortization of prior service credit (0.1 ) (0.1 ) (0.2 ) (0.2 ) (1.0 ) (2.8 ) (3.1 ) (8.4 ) Amortization of actuarial loss 9.3 8.8 28.0 26.5 1.2 1.2 3.6 3.6 Additional benefit costs — 0.1 — 0.4 — — — — $9.3 $7.6 $27.9 $22.7 $2.3 ($0.1 ) $6.9 ($0.2 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.8 $2.2 $5.6 $6.6 $0.5 $0.6 $1.7 $1.8 Interest cost 6.1 6.2 18.4 18.7 1.0 0.9 2.9 2.8 Expected return on plan assets (7.7 ) (8.9 ) (23.2 ) (26.8 ) (1.0 ) (1.4 ) (3.2 ) (4.2 ) Amortization of prior service credit — — (0.1 ) (0.1 ) (0.7 ) (1.5 ) (2.0 ) (4.6 ) Amortization of actuarial loss 4.2 3.8 12.4 11.5 0.7 0.6 2.0 1.7 $4.4 $3.3 $13.1 $9.9 $0.5 ($0.8 ) $1.4 ($2.5 ) Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2016 2015 2016 2015 2016 2015 2016 2015 Service cost $1.3 $1.4 $3.7 $4.3 $0.5 $0.5 $1.5 $1.6 Interest cost 5.5 5.6 16.7 16.9 0.9 0.9 2.8 2.7 Expected return on plan assets (7.0 ) (8.1 ) (21.2 ) (24.3 ) (0.2 ) (0.3 ) (0.6 ) (1.1 ) Amortization of prior service cost (credit) — 0.1 0.1 0.2 (0.3 ) (0.9 ) (0.7 ) (2.6 ) Amortization of actuarial loss 4.4 4.2 13.2 12.6 0.5 0.6 1.4 1.7 Additional benefit costs — 0.1 — 0.4 — — — — $4.2 $3.3 $12.5 $10.1 $1.4 $0.8 $4.4 $2.3
Employees Participate In Defined Contribution Retirement Plans	For the three and nine months ended September 30 , costs related to the 401(k) savings plan, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 401(k) costs $5.6 $6.4 $17.5 $18.7 $2.8 $3.3 $8.8 $9.6 $2.6 $2.9 $8.0 $8.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 2016 2015 Compensation expense $4.4 $0.3 $16.8 $5.8 $2.4 $0.2 $8.9 $3.1 $1.9 $0.1 $7.3 $2.5 Income tax benefits 1.7 0.2 6.8 2.4 1.0 0.1 3.7 1.3 0.7 — 2.9 1.0

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2016
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs 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 AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Balance, January 1 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 Revisions in estimated cash flows (a) 3.9 8.9 4.2 11.9 (0.3 ) (1.9 ) Liabilities settled (11.2 ) (7.1 ) (5.0 ) (3.1 ) (6.2 ) (4.0 ) Liabilities incurred (a) 2.6 76.1 0.7 59.9 1.9 16.2 Accretion expense 4.8 3.4 2.8 1.6 1.7 1.4 Balance, September 30 $214.1 $195.3 $135.6 $122.1 $69.0 $64.1 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million , $57 million and $17 million , respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2016
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
IPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
WPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $27.8 $— $1.9 $25.9 $27.8 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 36.9 — 3.1 33.8 36.9 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,130.9 — 4,868.3 3.3 4,871.6 3,835.6 — 4,332.4 3.7 4,336.1 Cumulative preferred stock of IPL 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 IPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $22.2 $— $1.2 $21.0 $22.2 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 239.7 — — 239.7 239.7 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 9.0 — 1.4 7.6 9.0 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.1 — 2,495.8 — 2,495.8 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 215.4 — — 215.4 200.0 206.6 — — 206.6 WPL September 30, 2016 December 31, 2015 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $5.6 $— $0.7 $4.9 $5.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 27.9 — 1.7 26.2 27.9 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,534.9 — 1,920.4 — 1,920.4 1,533.9 — 1,793.0 — 1,793.0
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $0.6 $0.6 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (5.1 ) (21.1 ) — — Transfers out of Level 3 0.8 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.0 ) (3.7 ) 165.3 122.1 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($5.0 ) ($18.4 ) $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($32.7 ) $17.9 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 8.0 (58.2 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.6 — — Purchases 22.0 36.9 — — Sales (0.9 ) (1.7 ) — — Settlements (a) (6.4 ) (20.1 ) 67.7 18.3 Ending balance, September 30 ($7.9 ) ($24.6 ) $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $9.7 ($52.2 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2016 2015 2016 2015 Beginning balance, July 1 $18.3 $18.3 $74.4 $73.4 Total net losses included in changes in net assets (realized/unrealized) (0.4 ) (8.6 ) — — Transfers out of Level 3 0.3 — — — Sales (0.2 ) (0.4 ) — — Settlements (a) (4.6 ) (5.5 ) 165.3 122.1 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 ($0.4 ) ($8.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2016 2015 2016 2015 Beginning balance, January 1 ($1.9 ) $19.4 $172.0 $177.2 Total net gains (losses) included in changes in net assets (realized/unrealized) 4.8 (26.0 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (0.9 ) (1.6 ) — — Settlements (a) (9.9 ) (21.1 ) 67.7 18.3 Ending balance, September 30 $13.4 $3.8 $239.7 $195.5 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $5.7 ($21.2 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2016 2015 Beginning balance, July 1 ($17.7 ) ($17.7 ) Total net losses included in changes in net assets (realized/unrealized) (4.7 ) (12.5 ) Transfers out of Level 3 0.5 — Settlements 0.6 1.8 Ending balance, September 30 ($21.3 ) ($28.4 ) 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 September 30 ($4.6 ) ($10.4 ) WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 3.2 (32.2 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.6 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.5 1.0 Ending balance, September 30 ($21.3 ) ($28.4 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 $4.0 ($31.0 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2016 ($26.3 ) $18.4 ($3.5 ) $16.9 ($22.8 ) $1.5 December 31, 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2016
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017
Fair Value Of Financial Instruments	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017
Fair Value Of Financial Instruments	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2016 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs, coal contracts and diesel fuel contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal Diesel Fuel MWhs Years MWhs Years Dths Years Tons Years Gallons Years Alliant Energy 3,427 2016-2018 14,437 2016-2017 82,277 2016-2020 4,640 2016-2019 3,780 2016-2017 IPL 187 2016 8,865 2016-2017 47,141 2016-2020 2,202 2016-2019 — — WPL 3,240 2016-2018 5,572 2016-2017 35,136 2016-2020 2,438 2016-2018 3,780 2016-2017
Fair Value Of Financial Instruments	The fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL Commodity contracts September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $25.1 $15.1 $20.5 $13.8 $4.6 $1.3 Non-current derivative assets 2.7 3.3 1.7 1.7 1.0 1.6 Current derivative liabilities 21.2 47.3 5.4 18.5 15.8 28.8 Non-current derivative liabilities 15.7 17.3 3.6 4.9 12.1 12.4

Commitments And Contingencies (

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3
IPL [Member]
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3
WPL [Member]
Commitments and Contingencies [Line Items]
Operating Expense Purchase Obligations	At September 30, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy IPL WPL Purchased power (a): DAEC (IPL) $1,320 $1,320 $— Other 139 1 138 1,459 1,321 138 Natural gas 557 231 326 Coal (b) 193 85 108 SO2 emission allowances 8 8 — Other (c) 21 4 1 $2,238 $1,649 $573 (a) Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change. (c) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016 .
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2016 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $27 $9 - $23 $2 - $4 Current and non-current environmental liabilities 15 12 3

Segments Of Business (Tables)

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 2016
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. Refer to Note 3 for discussion of asset valuation charges recorded in the third quarter of 2016 related to the Franklin County wind farm, which decreased the assets for “Non-Regulated, Parent and Other.” Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2016 Operating revenues $864.3 $39.5 $9.4 $913.2 $11.4 $924.6 Operating income (loss) 244.2 (3.7 ) 0.4 240.9 (78.3 ) 162.6 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 183.1 (54.3 ) 128.8 Loss from discontinued operations, net of tax — (0.4 ) (0.4 ) Net income (loss) 183.1 (54.7 ) 128.4 Three Months Ended September 30, 2015 Operating revenues $835.8 $38.0 $13.4 $887.2 $11.7 $898.9 Operating income (loss) 232.8 (5.7 ) 0.2 227.3 8.6 235.9 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 184.5 (4.5 ) 180.0 Loss from discontinued operations, net of tax — (0.1 ) (0.1 ) Net income (loss) 184.5 (4.6 ) 179.9 Utility Non-Regulated, Alliant Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2016 Operating revenues $2,209.1 $248.7 $35.0 $2,492.8 $30.2 $2,523.0 Operating income (loss) 473.3 27.0 4.4 504.7 (67.6 ) 437.1 Amounts attributable to Alliant Energy common shareowners: Income (loss) from continuing operations, net of tax 350.3 (39.5 ) 310.8 Loss from discontinued operations, net of tax — (2.0 ) (2.0 ) Net income (loss) 350.3 (41.5 ) 308.8 Nine Months Ended September 30, 2015 Operating revenues $2,147.5 $288.1 $44.6 $2,480.2 $33.3 $2,513.5 Operating income 438.4 28.6 8.7 475.7 22.1 497.8 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 332.6 12.9 345.5 Loss from discontinued operations, net of tax — (1.4 ) (1.4 ) Net income 332.6 11.5 344.1
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to IPL’s business segments is as follows. Intersegment revenues were not material to IPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $483.2 $23.9 $9.1 $516.2 Operating income (loss) 125.9 (1.4 ) 1.4 125.9 Earnings available for common stock 114.1 Three Months Ended September 30, 2015 Operating revenues $468.6 $23.1 $12.9 $504.6 Operating income (loss) 119.4 (2.9 ) 0.5 117.0 Earnings available for common stock 116.5 Nine Months Ended September 30, 2016 Operating revenues $1,209.2 $142.6 $34.1 $1,385.9 Operating income 213.8 15.3 6.8 235.9 Earnings available for common stock 191.6 Nine Months Ended September 30, 2015 Operating revenues $1,170.6 $164.1 $41.1 $1,375.8 Operating income 193.6 15.3 7.4 216.3 Earnings available for common stock 180.5
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to WPL’s business segments is as follows. Intersegment revenues were not material to WPL’s operations. Electric Gas Other Total (in millions) Three Months Ended September 30, 2016 Operating revenues $381.1 $15.6 $0.3 $397.0 Operating income (loss) 118.3 (2.3 ) (1.0 ) 115.0 Earnings available for common stock 69.0 Three Months Ended September 30, 2015 Operating revenues $367.2 $14.9 $0.5 $382.6 Operating income (loss) 113.4 (2.8 ) (0.3 ) 110.3 Earnings available for common stock 68.0 Nine Months Ended September 30, 2016 Operating revenues $999.9 $106.1 $0.9 $1,106.9 Operating income (loss) 259.5 11.7 (2.4 ) 268.8 Earnings available for common stock 158.7 Nine Months Ended September 30, 2015 Operating revenues $976.9 $124.0 $3.5 $1,104.4 Operating income 244.8 13.3 1.3 259.4 Earnings available for common stock 152.1

Related Parties (Tables)

Related Parties (Tables)	9 Months Ended
	Sep. 30, 2016
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 ATC billings to WPL $28 $25 $82 $75 WPL billings to ATC 4 4 10 9
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2016 2015 2016 2015 2016 2015 2016 2015 Corporate Services billings $41 $38 $124 $114 $33 $30 $103 $90 Sales credited 4 2 7 8 3 9 6 21 Purchases billed 126 110 324 278 23 16 65 49
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2016 December 31, 2015 September 30, 2016 December 31, 2015 Net payables to Corporate Services $114 $93 $68 $54
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 ATC billings to WPL $28 $25 $82 $75 WPL billings to ATC 4 4 10 9

Discontinued Operations (Tables

Discontinued Operations (Tables)	9 Months Ended
	Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations in Income Statement	A summary of the components of discontinued operations in Alliant Energy’s income statements for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2016 2015 2016 2015 Operating expenses $0.6 $0.3 $3.3 $2.3 Loss before income taxes (0.6 ) (0.3 ) (3.3 ) (2.3 ) Income tax benefit (0.2 ) (0.2 ) (1.3 ) (0.9 ) Loss from discontinued operations, net of tax ($0.4 ) ($0.1 ) ($2.0 ) ($1.4 )

Summary Of Significant Accoun37

Summary Of Significant Accounting Policies (Narrative) (Details)	Apr. 20, 2016	Dec. 31, 2017
Summary of Significant Accounting Policies [Line Items]
Common stock split conversion ratio (2:1)	2
Scenario, Forecast [Member] | Electric Generation [Member] | WPL [Member]
Summary of Significant Accounting Policies [Line Items]
Average rate of depreciation		3.20%
Scenario, Forecast [Member] | Electric Distribution [Member] | WPL [Member]
Summary of Significant Accounting Policies [Line Items]
Average rate of depreciation		2.60%
Scenario, Forecast [Member] | Gas Transmission [Member] | WPL [Member]
Summary of Significant Accounting Policies [Line Items]
Average rate of depreciation		2.30%

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2015
2016 Test Year Retail Electric Fuel-Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs		2.00%
2016 Test Year Retail Electric Fuel-Related [Member] | Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 9
2015 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs				2.00%
Scenario, Forecast [Member] | 2017/2018 Test Period Retail Electric [Member] | WPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount			$ 13
Requested rate increase (decrease), percentage			1.00%
Scenario, Forecast [Member] | 2017 Test Period Retail Electric Base Rate [Member] | WPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount			$ 65
Scenario, Forecast [Member] | 2017 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount			(52)
Scenario, Forecast [Member] | 2017/2018 Test Period Retail Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Requested rate increase (decrease), amount			$ 9
Requested rate increase (decrease), percentage			13.00%
Scenario, Forecast [Member] | 2015 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized refund to customers, including interest	$ 10

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory assets	$ 1,874.8	$ 1,908.6
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,033.5	987.7
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	551	579.5
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	103.9	92.4
WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	43.1	45
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	39	70.6
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.3	26.9
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	10.1	35.9
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.9	70.6
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,417.2	1,402.6
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,000.7	958.2
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	284.7	298.1
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	61.5	50.8
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	10.6	28.2
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.3	26.9
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	0.4	2.8
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	33	37.6
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	457.6	506
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	32.8	29.5
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	266.3	281.4
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	42.4	41.6
WPL [Member] | WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	43.1	45
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	28.4	42.4
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	9.7	33.1
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 34.9	$ 33

Regulatory Matters (Regulator40

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 675.8	$ 737.7
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	410.6	406
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	103.1	159.2
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	54.5	43.5
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	39.1	37.6
Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	28	48.3
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40.5	43.1
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	431.4	489.2
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	267.2	260.4
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	103.1	159.2
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	25	21.9
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	15.1	23.5
IPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21	24.2
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	244.4	248.5
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	143.4	145.6
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	29.5	21.6
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24	14.1
WPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	28	48.3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 19.5	$ 18.9

Regulatory Matters (Tax Benefit

Regulatory Matters (Tax Benefit Riders) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (66.5)	$ (61.5)
Alliant Energy and IPL [Member] | Electric tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(47)
Alliant Energy and IPL [Member] | Gas tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(9)
Alliant Energy and IPL [Member] | Tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (56)

Regulatory Matters (Customer Bi

Regulatory Matters (Customer Billing Credits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
IPL [Member]
Regulatory Liabilities [Line Items]
Billings credits to reduce retail electric customers' bills	$ 3	$ 7	$ 7	$ 19

Property, Plant and Equipment (

Property, Plant and Equipment (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016USD ($)$ / shares	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)$ / sharesMW	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ (15.8)	$ (9.7)	$ (44.3)	$ (25.1)
Current value of Franklin County wind farm assets	33		33
Asset valuation charges for Franklin County wind farm, pre-tax	86.4	0	86.4	0
Asset valuation charges for Franklin County wind farm, after tax	$ 51		$ 51
Asset valuation charges for Franklin County wind farm, after tax (in dollars per share) | $ / shares	$ 0.23		$ 0.23
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ (13.8)	$ (7.3)	$ (36.2)	(19.3)
Edgewater Unit 5 [Member] | Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Plant in service	223		223
Allowance for funds used during construction			(12)
Marshalltown [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction			(56)
Construction work in progress	$ 600		$ 600
Marshalltown [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) | MW			650
Gas Distribution Equipment [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets				3
Gas Distribution Equipment [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from sale of property, plant, and equipment					$ 11
Receipt of promissory note					2
Electric Distribution [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets				$ 9
Electric Distribution [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from sale of property, plant, and equipment					$ 129

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Receivables [Line Items]
Deferred proceeds		$ 239.7	$ 172
IPL [Member]
Receivables [Line Items]
Deferred proceeds		239.7	172
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Receivables sold to third party		252.9	181.1
Cash proceeds of receivables sold	[1]	1	5
Deferred proceeds		239.7	$ 172
Outstanding receivables past due		$ 64.5
[1]	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 112.3	$ 41.2	$ 91.5	$ 62.1
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 172	$ 137	$ 172	$ 137

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Receivables [Line Items]
Fair value of deferred proceeds		$ 239.7	$ 172
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds		239.7	172
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable		172.9	109.7
Unbilled utility revenues		79.8	71.3
Other receivables		0.2	0.1
Receivables sold to third party		252.9	181.1
Less: cash proceeds	[1]	1	5
Deferred proceeds		251.9	176.1
Less: allowance for doubtful accounts		12.2	4.1
Fair value of deferred proceeds		$ 239.7	$ 172
[1]	Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Receivables [Line Items]
Collections reinvested in receivables	$ 499.7	$ 480.1	$ 1,362.1	$ 1,403.1
Write-offs (recoveries), net	$ (0.3)	$ 3.3	$ (0.6)	$ 6.8

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended	35 Months Ended
	Sep. 30, 2016	Sep. 30, 2016
Schedule of Investments [Line Items]
Proceeds from liquidation of company-owned life insurance policies	$ 31
IPL [Member]
Schedule of Investments [Line Items]
Proceeds from liquidation of company-owned life insurance policies	19
ATC [Member] | Alliant Energy and WPL [Member]
Schedule of Investments [Line Items]
Reduction in equity income from ATC	$ 9	$ 24

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (9.2)	$ (11.1)	$ (28.8)	$ (28.9)
WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(9.3)	(11.1)	(29)	(30.2)
ATC [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(9.1)	(10.9)	(28.6)	(29.6)
ATC [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(9.1)	(10.9)	(28.6)	(29.6)
Other [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(0.1)	(0.2)	(0.2)	0.7
Other [Member] | WPL [Member]
Schedule of Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (0.2)	$ (0.2)	$ (0.4)	$ (0.6)

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) $ in Millions	Apr. 20, 2016shares	Sep. 30, 2016USD ($)shares		Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)shares		Sep. 30, 2015USD ($)shares	Dec. 31, 2015shares
Common Equity [Line Items]
Proceeds from issuance of common stock, net					$ 20.4		$ 145.4
Common stock split conversion ratio (2:1)	2
Common stock, shares authorized (in shares) | shares	240,000,000	480,000,000	[1]		480,000,000	[1]		480,000,000	[1]
Other comprehensive income		$ 0		$ 0	$ 0		0
IPL [Member]
Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares		24,000,000			24,000,000			24,000,000
Retained earnings free of dividend restrictions		$ 632			$ 632
Restricted net assets of subsidiaries		1,500			1,500
Capital contributions from parent					65		100
Common stock dividends to parent					114
Other comprehensive income		$ 0		0	$ 0		0
WPL [Member]
Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares		18,000,000			18,000,000			18,000,000
Retained earnings free of dividend restrictions		$ 34			$ 34
Restricted net assets of subsidiaries		1,800			1,800
Common stock dividends to parent					101.2
Other comprehensive income		$ 0		$ 0	$ 0		$ 0
At-the-market Offering Program [Member]
Common Equity [Line Items]
Common stock issued during the period, At-the-market offering program (in shares) | shares							4,373,234
Proceeds from issuance of common stock, net							$ 133
Fees and commissions from issuance of common stock							$ 2
[1]	Share and per share amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	9 Months Ended
	Sep. 30, 2016shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2016 (in shares)	226,918,432	[1]
Shareowner Direct Plan issuances (in shares)	559,588
Equity-based compensation plans (in shares)	22,408
Shares outstanding, September 30, 2016 (in shares)	227,500,428	[1]
[1]	Share and per share amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended		9 Months Ended
	Oct. 31, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Debt [Line Items]
Long-term debt issued			$ 300	$ 250.7
IPL [Member]
Debt [Line Items]
Long-term debt issued			300	$ 250
Repayments of commercial paper			$ 100
Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt issued		$ 300
Interest rate		3.70%	3.70%
Subsequent Event [Member] | Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through 2018, 1% at September 30, 2016 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt issued	$ 500
Interest rate	1.30%

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Commercial paper:
Amount outstanding	$ 238.3	$ 159.8
Weighted average remaining maturity (in days)	4 days
Weighted average interest rates	0.60%
Available credit facility capacity	$ 761.7
Parent Company [Member]
Commercial paper:
Amount outstanding	$ 226.5
Weighted average remaining maturity (in days)	4 days
Weighted average interest rates	0.70%
Available credit facility capacity	$ 73.5
IPL [Member]
Commercial paper:
Amount outstanding	0
Available credit facility capacity	300
WPL [Member]
Commercial paper:
Amount outstanding	$ 11.8	$ 19.9
Weighted average remaining maturity (in days)	3 days
Weighted average interest rates	0.40%
Available credit facility capacity	$ 388.2

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 248	$ 181.2	$ 248	$ 181.2
Average amount outstanding (based on daily outstanding balances)	$ 220.1	$ 122.4	$ 210.7	$ 114.5
Weighted average interest rates	0.60%	0.40%	0.60%	0.40%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 3.1	$ 18.4	$ 3.1	$ 18.4
Average amount outstanding (based on daily outstanding balances)	$ 0.1	$ 0.5	$ 0	$ 0.2
Weighted average interest rates	0.60%	0.40%	0.60%	0.40%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 55.4	$ 0	$ 62.9	$ 0
Average amount outstanding (based on daily outstanding balances)	$ 36.4	$ 0	$ 33.2	$ 0
Weighted average interest rates	0.40%		0.40%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	$ 149.4
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	115.6
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	$ 103.4

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	(13.10%)	(11.00%)	(10.20%)	(10.60%)
Effect of rate-making on property-related differences	(11.90%)	(7.10%)	(8.20%)	(7.10%)
Production tax credits	(9.00%)	(6.70%)	(7.20%)	(6.60%)
Other items, net	4.40%	3.00%	3.50%	3.70%
Overall income tax rate	5.40%	13.20%	12.90%	14.40%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
IPL's tax benefit riders	(20.10%)	(30.00%)	(19.60%)	(28.20%)
Effect of rate-making on property-related differences	(16.50%)	(18.70%)	(14.80%)	(17.90%)
Production tax credits	(6.00%)	(8.60%)	(6.10%)	(8.00%)
Other items, net	5.40%	3.70%	4.20%	4.20%
Overall income tax rate	(2.20%)	(18.60%)	(1.30%)	(14.90%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
Effect of rate-making on property-related differences	(0.70%)	(0.70%)	(0.80%)	(0.60%)
Production tax credits	(5.70%)	(6.10%)	(6.10%)	(6.30%)
Other items, net	4.00%	4.10%	4.40%	4.20%
Overall income tax rate	32.60%	32.30%	32.50%	32.30%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2016USD ($)
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 496
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	178
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	192
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	587
Net operating losses, deferred tax assets	201
Tax credits, carryforward amount	264
Tax credits, deferred tax assets	260
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	255
Net operating losses, deferred tax assets	86
Tax credits, carryforward amount	95
Tax credits, deferred tax assets	91
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	242
Net operating losses, deferred tax assets	85
Tax credits, carryforward amount	108
Tax credits, deferred tax assets	107
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	674
Net operating losses, deferred tax assets	35
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	15
Net operating losses, deferred tax assets	1
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Net operating losses, deferred tax assets	$ 0

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees accepting voluntary separation package	2.00%
Voluntary employee separation charges	$ 8
Unrecognized compensation cost		$ 8.2
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period		1 year
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period		2 years
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Voluntary employee separation charges	5
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Voluntary employee separation charges	$ 3
Performance Restricted Stock Unit And Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period		3 years
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 Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance Restricted Stock Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Key Employee Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Restricted Stock Unit And Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance period		3 years

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.2	$ 4	$ 9.5	$ 11.9
Interest cost	13.2	13.5	39.7	40.3
Expected return on plan assets	(16.3)	(18.7)	(49.1)	(56.2)
Amortization of prior service cost (credit)	(0.1)	(0.1)	(0.2)	(0.2)
Amortization of actuarial loss	9.3	8.8	28	26.5
Additional benefit costs	0	0.1	0	0.4
Total	9.3	7.6	27.9	22.7
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.4	1.3	4	4.1
Interest cost	2.3	2.3	7	6.8
Expected return on plan assets	(1.6)	(2.1)	(4.6)	(6.3)
Amortization of prior service cost (credit)	(1)	(2.8)	(3.1)	(8.4)
Amortization of actuarial loss	1.2	1.2	3.6	3.6
Additional benefit costs	0	0	0	0
Total	2.3	(0.1)	6.9	(0.2)
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.8	2.2	5.6	6.6
Interest cost	6.1	6.2	18.4	18.7
Expected return on plan assets	(7.7)	(8.9)	(23.2)	(26.8)
Amortization of prior service cost (credit)	0	0	(0.1)	(0.1)
Amortization of actuarial loss	4.2	3.8	12.4	11.5
Total	4.4	3.3	13.1	9.9
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.6	1.7	1.8
Interest cost	1	0.9	2.9	2.8
Expected return on plan assets	(1)	(1.4)	(3.2)	(4.2)
Amortization of prior service cost (credit)	(0.7)	(1.5)	(2)	(4.6)
Amortization of actuarial loss	0.7	0.6	2	1.7
Total	0.5	(0.8)	1.4	(2.5)
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.3	1.4	3.7	4.3
Interest cost	5.5	5.6	16.7	16.9
Expected return on plan assets	(7)	(8.1)	(21.2)	(24.3)
Amortization of prior service cost (credit)	0	0.1	0.1	0.2
Amortization of actuarial loss	4.4	4.2	13.2	12.6
Additional benefit costs	0	0.1	0	0.4
Total	4.2	3.3	12.5	10.1
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.5	1.5	1.6
Interest cost	0.9	0.9	2.8	2.7
Expected return on plan assets	(0.2)	(0.3)	(0.6)	(1.1)
Amortization of prior service cost (credit)	(0.3)	(0.9)	(0.7)	(2.6)
Amortization of actuarial loss	0.5	0.6	1.4	1.7
Additional benefit costs	0	0	0	0
Total	$ 1.4	$ 0.8	$ 4.4	$ 2.3

Benefit Plans (Defined Contribu

Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
401(k) costs	$ 5.6	$ 6.4	$ 17.5	$ 18.7
IPL [Member]
401(k) costs	2.8	3.3	8.8	9.6
WPL [Member]
401(k) costs	$ 2.6	$ 2.9	$ 8	$ 8.4

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Compensation expense	$ 4.4	$ 0.3	$ 16.8	$ 5.8
Income tax benefits	1.7	0.2	6.8	2.4
IPL [Member]
Compensation expense	2.4	0.2	8.9	3.1
Income tax benefits	1	0.1	3.7	1.3
WPL [Member]
Compensation expense	1.9	0.1	7.3	2.5
Income tax benefits	$ 0.7	$ 0	$ 2.9	$ 1

Benefit Plans (Summary Of Perfo

Benefit Plans (Summary Of Performance Shares and Performance Units Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	288,430	288,848
Granted (in shares/awards)	68,585	90,806
Vested (in shares/awards)	(98,186)	(91,224)
Forfeited (in shares/awards)	(1,230)	0
Nonvested, September 30 (in shares/awards)	257,599	288,430
Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	116,412	127,330
Granted (in shares/awards)	23,918	35,674
Vested (in shares/awards)	(42,760)	(45,690)
Forfeited (in shares/awards)	(4,250)	(902)
Nonvested, September 30 (in shares/awards)	93,320	116,412
2013 Grant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	(98,186)
Vested percentage of the target	165.00%
Aggregate payout value	$ 5.1
Payout - cash	$ 2.9
Payout - common stock shares issued (in shares)	22,408
2013 Grant [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	(42,760)
Vested percentage of the target	165.00%
Aggregate payout value	$ 1.7
Payout - cash	$ 1.7
2012 Grant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(91,224)
Vested percentage of the target		167.50%
Aggregate payout value		$ 5.1
Payout - cash		$ 3.2
Payout - common stock shares issued (in shares)		21,950
2012 Grant [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(45,690)
Vested percentage of the target		167.50%
Aggregate payout value		$ 1.6
Payout - cash		$ 1.6

Benefit Plans (Fair Values Of N

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	257,599	288,430	288,430	288,848
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	93,320	116,412	116,412	127,330
2016 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	67,355
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 47.89
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	22,657
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 47.89
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	90,806
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	168.00%
Fair values of each nonvested award (in dollars per share)	$ 64.36
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	33,268
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 32.55
Estimated payout percentage based on performance criteria	168.00%
Fair values of each nonvested award (in dollars per share)	$ 54.68
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	99,438
Alliant Energy common stock closing price on September 30, 2016 (in dollars per share)	$ 38.31
Estimated payout percentage based on performance criteria	175.00%
Fair values of each nonvested award (in dollars per share)	$ 67.04
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	37,395
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 26.89
Estimated payout percentage based on performance criteria	175.00%
Fair values of each nonvested award (in dollars per share)	$ 47.05

Benefit Plans (Summary Of Restr

Benefit Plans (Summary Of Restricted Stock and Units Activity) (Details) - $ / shares		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015
Performance Contingent Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		190,244	197,624
Nonvested, January 1, weighted average grant date fair value (in dollars per share)		$ 29.59	$ 25.35
Granted (in shares/awards)		0	90,806
Granted, weighted average grant date fair value (in dollars per share)		$ 0	$ 32.55
Vested (in shares/awards)	[1]	0	(98,186)
Vested, weighted average grant date fair value (in dollars per share)	[1]	$ 0	$ 23.79
Nonvested, September 30 (in shares/awards)		190,244	190,244
Nonvested, September 30, weighted average grant date fair value (in dollars per share)		$ 29.59	$ 29.59
Performance Restricted Stock Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards)		68,585
Granted, weighted average grant date fair value (in dollars per share)		$ 33.96
Forfeited (in shares/awards)		(1,230)
Forfeited, weighted average grant date fair value (in dollars per share)		$ 33.90
Nonvested, September 30 (in shares/awards)		67,355
Nonvested, September 30, weighted average grant date fair value (in dollars per share)		$ 33.96
Performance Restricted Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards)		23,918
Forfeited (in shares/awards)		(1,261)
Nonvested, September 30 (in shares/awards)		22,657
Key Employee Performance Restricted Unit [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards)		45,056
Forfeited (in shares/awards)		(2,016)
Nonvested, September 30 (in shares/awards)		43,040
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards)		58,790
Forfeited (in shares/awards)		(1,054)
Nonvested, September 30 (in shares/awards)		57,736
Restricted Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards)		20,502
Forfeited (in shares/awards)		(1,082)
Nonvested, September 30 (in shares/awards)		19,420
2013 Grant [Member] | Performance Contingent Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	[1]		(98,186)
[1]	In 2015, 98,186 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.

Benefit Plans (Summary Of Per65

Benefit Plans (Summary Of Performance Contingent Cash Awards Activity) (Details) - Performance Contingent Cash Awards [Member] - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		163,752	157,860
Granted (in shares/awards)		0	82,210
Vested (in shares/awards)	[1]	0	(74,664)
Forfeited (in shares/awards)		(3,652)	(1,654)
Nonvested, September 30 (in shares/awards)		160,100	163,752
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	[1]		(74,664)
Cash payout value	[1]		$ 2.4
[1]	In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million.

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions		3 Months Ended	9 Months Ended
		Jun. 30, 2015USD ($)	Sep. 30, 2016USD ($)		Sep. 30, 2015USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 214		$ 114
Revisions in estimated cash flows	[1]		3.9		8.9
Liabilities settled			(11.2)		(7.1)
Liabilities incurred		$ 74	2.6	[1]	76.1	[1]
Accretion expense			4.8		3.4
Balance, September 30			214.1		195.3
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			132.9		51.8
Revisions in estimated cash flows	[1]		4.2		11.9
Liabilities settled			(5)		(3.1)
Liabilities incurred		57	0.7	[1]	59.9	[1]
Accretion expense			2.8		1.6
Balance, September 30			$ 135.6		122.1
Electric generating units with coal ash ponds (in number of electric generating units)			9
Active coal combustion residuals landfills (in number of landfills)			4
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 71.9		52.4
Revisions in estimated cash flows	[1]		(0.3)		(1.9)
Liabilities settled			(6.2)		(4)
Liabilities incurred		$ 17	1.9	[1]	16.2	[1]
Accretion expense			1.7		1.4
Balance, September 30			$ 69		$ 64.1
Electric generating units with coal ash ponds (in number of electric generating units)			3
Active coal combustion residuals landfills (in number of landfills)			2
[1]	In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and was effective October 2015. IPL and WPL have nine and three coal-fired EGUs, respectively, with coal ash ponds that are impacted by this rule. In addition, IPL and WPL have four and two active CCR landfills, respectively, that are impacted by this rule. During the nine months ended September 30, 2015, Alliant Energy, IPL and WPL recognized additional AROs of $74 million, $57 million and $17 million, respectively, as a result of the final CCR Rule. The increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details)	9 Months Ended
	Sep. 30, 2016
IPL [Member]
Cumulative preferred stock rate	5.10%

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Assets:
Deferred proceeds	$ 239.7	$ 172
Liabilities and Equity:
Long-term debt (including current maturities)	4,871.6	4,336.1
Cumulative preferred stock of IPL	215.4	206.6
IPL [Member]
Assets:
Deferred proceeds	239.7	172
Liabilities and Equity:
Long-term debt (including current maturities)	2,495.8	2,092.7
Cumulative preferred stock of IPL	215.4	206.6
WPL [Member]
Liabilities and Equity:
Long-term debt (including current maturities)	1,920.4	1,793
Commodity Contracts [Member]
Assets:
Derivatives	27.8	18.4
Liabilities and Equity:
Derivatives	36.9	64.6
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	22.2	15.5
Liabilities and Equity:
Derivatives	9	23.4
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	5.6	2.9
Liabilities and Equity:
Derivatives	27.9	41.2
Level 1 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and Equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	215.4	206.6
Level 1 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Liabilities and Equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	215.4	206.6
Level 1 [Member] | WPL [Member]
Liabilities and Equity:
Long-term debt (including current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and Equity:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities and Equity:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities and Equity:
Derivatives	0	0
Level 2 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and Equity:
Long-term debt (including current maturities)	4,868.3	4,332.4
Cumulative preferred stock of IPL	0	0
Level 2 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Liabilities and Equity:
Long-term debt (including current maturities)	2,495.8	2,092.7
Cumulative preferred stock of IPL	0	0
Level 2 [Member] | WPL [Member]
Liabilities and Equity:
Long-term debt (including current maturities)	1,920.4	1,793
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	1.9	2.5
Liabilities and Equity:
Derivatives	3.1	16
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	1.2	2
Liabilities and Equity:
Derivatives	1.4	8
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0.7	0.5
Liabilities and Equity:
Derivatives	1.7	8
Level 3 [Member]
Assets:
Deferred proceeds	239.7	172
Liabilities and Equity:
Long-term debt (including current maturities)	3.3	3.7
Cumulative preferred stock of IPL	0	0
Level 3 [Member] | IPL [Member]
Assets:
Deferred proceeds	239.7	172
Liabilities and Equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	0	0
Level 3 [Member] | WPL [Member]
Liabilities and Equity:
Long-term debt (including current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	25.9	15.9
Liabilities and Equity:
Derivatives	33.8	48.6
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	21	13.5
Liabilities and Equity:
Derivatives	7.6	15.4
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	4.9	2.4
Liabilities and Equity:
Derivatives	26.2	33.2
Carrying Amount [Member]
Assets:
Deferred proceeds	239.7	172
Liabilities and Equity:
Long-term debt (including current maturities)	4,130.9	3,835.6
Cumulative preferred stock of IPL	200	200
Carrying Amount [Member] | IPL [Member]
Assets:
Deferred proceeds	239.7	172
Liabilities and Equity:
Long-term debt (including current maturities)	2,153.1	1,856.9
Cumulative preferred stock of IPL	200	200
Carrying Amount [Member] | WPL [Member]
Liabilities and Equity:
Long-term debt (including current maturities)	1,534.9	1,533.9
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	27.8	18.4
Liabilities and Equity:
Derivatives	36.9	64.6
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	22.2	15.5
Liabilities and Equity:
Derivatives	9	23.4
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	5.6	2.9
Liabilities and Equity:
Derivatives	$ 27.9	$ 41.2

Fair Value Measurements (Fair69

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 0.6	$ 0.6	$ (32.7)	$ 17.9
Total net gains (losses) included in changes in net assets (realized/unrealized)		(5.1)	(21.1)	8	(58.2)
Transfers into Level 3				0.9	0
Transfers out of Level 3		0.8	0	1.2	0.6
Purchases				22	36.9
Sales		(0.2)	(0.4)	(0.9)	(1.7)
Settlements	[1]	(4)	(3.7)	(6.4)	(20.1)
Ending balance		(7.9)	(24.6)	(7.9)	(24.6)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		(5)	(18.4)	9.7	(52.2)
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		18.3	18.3	(1.9)	19.4
Total net gains (losses) included in changes in net assets (realized/unrealized)		(0.4)	(8.6)	4.8	(26)
Transfers into Level 3				0.5	0
Transfers out of Level 3		0.3	0	0.2	0
Purchases				20.6	33.1
Sales		(0.2)	(0.4)	(0.9)	(1.6)
Settlements	[1]	(4.6)	(5.5)	(9.9)	(21.1)
Ending balance		13.4	3.8	13.4	3.8
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		(0.4)	(8)	5.7	(21.2)
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		(17.7)	(17.7)	(30.8)	(1.5)
Total net gains (losses) included in changes in net assets (realized/unrealized)		(4.7)	(12.5)	3.2	(32.2)
Transfers into Level 3				0.4	0
Transfers out of Level 3		0.5	0	1	0.6
Purchases				1.4	3.8
Sales				0	(0.1)
Settlements		0.6	1.8	3.5	1
Ending balance		(21.3)	(28.4)	(21.3)	(28.4)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		(4.6)	(10.4)	4	(31)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		74.4	73.4	172	177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0	0	0
Transfers into Level 3				0	0
Transfers out of Level 3		0	0	0	0
Purchases				0	0
Sales		0	0	0	0
Settlements	[1]	165.3	122.1	67.7	18.3
Ending balance		239.7	195.5	239.7	195.5
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		0	0	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		74.4	73.4	172	177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0	0	0
Transfers into Level 3				0	0
Transfers out of Level 3		0	0	0	0
Purchases				0	0
Sales		0	0	0	0
Settlements	[1]	165.3	122.1	67.7	18.3
Ending balance		239.7	195.5	239.7	195.5
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30		$ 0	$ 0	$ 0	$ 0
[1]	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.

Fair Value Measurements (Fair70

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ (7.9)	$ 0.6	$ (32.7)	$ (24.6)	$ 0.6	$ 17.9
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	(26.3)		(43.1)
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	18.4		10.4
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	13.4	18.3	(1.9)	3.8	18.3	19.4
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	(3.5)		(12.3)
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	16.9		10.4
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	(21.3)	$ (17.7)	(30.8)	$ (28.4)	$ (17.7)	$ (1.5)
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	(22.8)		(30.8)
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 1.5		$ 0

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands, T in Thousands, MWh in Thousands, Dekatherms in Thousands	9 Months Ended
	Sep. 30, 2016DekathermsMWhTgal
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	3,427
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	187
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	3,240
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	14,437
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	8,865
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	5,572
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	82,277
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	47,141
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	35,136
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	4,640
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	2,202
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Tons) | T	2,438
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,780
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	3,780

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 25.1	$ 15.1
Non-current derivative assets	2.7	3.3
Current derivative liabilities	21.2	47.3
Non-current derivative liabilities	15.7	17.3
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	20.5	13.8
Non-current derivative assets	1.7	1.7
Current derivative liabilities	5.4	18.5
Non-current derivative liabilities	3.6	4.9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	4.6	1.3
Non-current derivative assets	1	1.6
Current derivative liabilities	15.8	28.8
Non-current derivative liabilities	$ 12.1	$ 12.4

Commitments And Contingencies73

Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)site
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,238
Performance guarantees outstanding	123
Present value abandonment obligation	30
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,649
Maximum indemnification limit	$ 17
Number of sites monitoring and remediating (in sites) | site	23
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 573
Number of sites monitoring and remediating (in sites) | site	5
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 27
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	26
Performance guarantees outstanding, 2016 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	48
Performance guarantees outstanding, 2017 [Member]
Commitments and Contingencies [Line Items]
Performance guarantees outstanding	75
Environmental Issue [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	6
Environmental Issue [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	$ 7
Minimum [Member]
Commitments and Contingencies [Line Items]
Warranty period	12 months
Maximum [Member]
Commitments and Contingencies [Line Items]
Warranty period	60 months

Commitments And Contingencies74

Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,238
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,649
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	573
Individual commitments incurred	1
DAEC (IPL) [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,320	[1]
DAEC (IPL) [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,320	[1]
DAEC (IPL) [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	0	[1]
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	139	[1]
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1	[1]
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	138	[1]
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,459	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,321	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	138	[1]
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	557
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	231
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	326
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	193	[2]
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	85	[2]
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	108	[2]
SO2 emission allowances [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	8
SO2 emission allowances [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	8
SO2 emission allowances [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	0
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	21	[3]
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	4	[3]
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 1	[3]
[1]	Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased.
[2]	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2016 regarding expected future usage, which is subject to change.
[3]	Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2016.

Commitments And Contingencies75

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Manufactured Gas Plant Sites [Member] $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	$ 11
Maximum range of estimated future costs	27
Current and non-current environmental liabilities	15
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	9
Maximum range of estimated future costs	23
Current and non-current environmental liabilities	12
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	2
Maximum range of estimated future costs	4
Current and non-current environmental liabilities	$ 3

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 924.6	$ 898.9	$ 2,523	$ 2,513.5
Operating income (loss)	162.6	235.9	437.1	497.8
Income (loss) from continuing operations, net of tax	128.8	180	310.8	345.5
Loss from discontinued operations, net of tax	(0.4)	(0.1)	(2)	(1.4)
Net income (loss) attributable to common shareowners	128.4	179.9	308.8	344.1
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	516.2	504.6	1,385.9	1,375.8
Operating income (loss)	125.9	117	235.9	216.3
Net income (loss) attributable to common shareowners	114.1	116.5	191.6	180.5
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	397	382.6	1,106.9	1,104.4
Operating income (loss)	115	110.3	268.8	259.4
Net income (loss) attributable to common shareowners	69	68	158.7	152.1
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	864.3	835.8	2,209.1	2,147.5
Operating income (loss)	244.2	232.8	473.3	438.4
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	483.2	468.6	1,209.2	1,170.6
Operating income (loss)	125.9	119.4	213.8	193.6
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	381.1	367.2	999.9	976.9
Operating income (loss)	118.3	113.4	259.5	244.8
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	39.5	38	248.7	288.1
Operating income (loss)	(3.7)	(5.7)	27	28.6
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	23.9	23.1	142.6	164.1
Operating income (loss)	(1.4)	(2.9)	15.3	15.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	15.6	14.9	106.1	124
Operating income (loss)	(2.3)	(2.8)	11.7	13.3
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.4	13.4	35	44.6
Operating income (loss)	0.4	0.2	4.4	8.7
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.1	12.9	34.1	41.1
Operating income (loss)	1.4	0.5	6.8	7.4
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.3	0.5	0.9	3.5
Operating income (loss)	(1)	(0.3)	(2.4)	1.3
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	913.2	887.2	2,492.8	2,480.2
Operating income (loss)	240.9	227.3	504.7	475.7
Income (loss) from continuing operations, net of tax	183.1	184.5	350.3	332.6
Loss from discontinued operations, net of tax	0	0	0	0
Net income (loss) attributable to common shareowners	183.1	184.5	350.3	332.6
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	11.4	11.7	30.2	33.3
Operating income (loss)	(78.3)	8.6	(67.6)	22.1
Income (loss) from continuing operations, net of tax	(54.3)	(4.5)	(39.5)	12.9
Loss from discontinued operations, net of tax	(0.4)	(0.1)	(2)	(1.4)
Net income (loss) attributable to common shareowners	$ (54.7)	$ (4.6)	$ (41.5)	$ 11.5

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
WPL [Member] | WPL Owed ATC [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	$ (9)	$ (8)

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 41	$ 38	$ 124	$ 114
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	33	30	103	90
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	4	2	7	8
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	3	9	6	21
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	126	110	324	278
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 23	$ 16	$ 65	$ 49

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Subsidiary of Common Parent [Member] - Corporate Services [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
IPL [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	$ (114)	$ (93)
WPL [Member]
Related Party Transactions [Line Items]
Net amounts due from (to) related party	$ (68)	$ (54)

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC [Member] - WPL [Member] - Equity Method Investment [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 28	$ 25	$ 82	$ 75
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 4	$ 4	$ 10	$ 9

Discontinued Operations (Compon

Discontinued Operations (Components Of Discontinued Operations In Consolidated Statements Of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Discontinued Operations and Disposal Groups [Abstract]
Operating expenses	$ 0.6	$ 0.3	$ 3.3	$ 2.3
Loss before income taxes	(0.6)	(0.3)	(3.3)	(2.3)
Income tax benefit	(0.2)	(0.2)	(1.3)	(0.9)
Loss from discontinued operations, net of tax	$ (0.4)	$ (0.1)	$ (2)	$ (1.4)