Interstate Power & Light (IPLDP) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2017	Jun. 30, 2016
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
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		227,687,330
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 9
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

Consolidated Statements Of Inco

Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues:
Electric utility		$ 2,875.5	$ 2,770.5	$ 2,713.6
Gas utility		355.4	381.2	517.5
Other utility		48.6	57.9	66.1
Non-regulated		40.5	44	53.1
Total operating revenues		3,320	3,253.6	3,350.3
Operating expenses:
Electric production fuel and purchased power		854	837.7	877.2
Electric transmission service		527.9	485.3	447.5
Cost of gas sold		194.3	219.1	327.8
Asset valuation charges for Franklin County wind farm		86.4	0	0
Other operation and maintenance		606.5	629.5	665
Depreciation and amortization		411.6	401.3	388.1
Taxes other than income taxes		102.3	103.7	101.1
Total operating expenses		2,783	2,676.6	2,806.7
Operating income (loss)		537	577	543.6
Interest expense and other:
Interest expense		196.2	187.1	180.6
Equity (income) loss from unconsolidated investments, net		(39.6)	(33.8)	(40.4)
Allowance for funds used during construction		(62.5)	(36.9)	(34.8)
Interest income and other		(0.5)	(0.7)	(1.8)
Total interest expense and other		93.6	115.7	103.6
Income from continuing operations before income taxes		443.4	461.3	440
Income tax expense (benefit)		59.4	70.4	44.3
Income from continuing operations, net of tax		384	390.9	395.7
Loss from discontinued operations, net of tax		(2.3)	(2.5)	(2.4)
Net income		381.7	388.4	393.3
Preferred dividend requirements of Interstate Power and Light Company		10.2	10.2	10.2
Net income attributable to common shareowners		$ 371.5	$ 378.2	$ 383.1
Weighted average number of common shares outstanding (basic and diluted) (in shares)	[1]	227.1	225.4	221.7
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]	$ 1.65	$ 1.69	$ 1.74
Loss from discontinued operations, net of tax (in dollars per share)	[1]	(0.01)	(0.01)	(0.01)
Net income (in dollars per share)	[1]	$ 1.64	$ 1.68	$ 1.73
Amounts attributable to common shareowners:
Income from continuing operations, net of tax		$ 373.8	$ 380.7	$ 385.5
Loss from discontinued operations, net of tax		(2.3)	(2.5)	(2.4)
Net income		371.5	378.2	383.1
IPL [Member]
Operating revenues:
Electric utility		1,569.7	1,503.8	1,493.3
Gas utility		204	217.3	296.5
Other utility		46.7	53.4	58.3
Total operating revenues		1,820.4	1,774.5	1,848.1
Operating expenses:
Electric production fuel and purchased power		430.5	428.4	497.3
Electric transmission service		359.7	328.2	323.4
Cost of gas sold		111	123.3	185.5
Other operation and maintenance		383.7	389.9	381.1
Depreciation and amortization		210.8	207.2	197.5
Taxes other than income taxes		53.9	55.6	54.1
Total operating expenses		1,549.6	1,532.6	1,638.9
Operating income (loss)		270.8	241.9	209.2
Interest expense and other:
Interest expense		103.2	96.8	89.9
Allowance for funds used during construction		(52)	(28.2)	(25.9)
Interest income and other		(0.3)	(0.2)	2.3
Total interest expense and other		50.9	68.4	66.3
Income from continuing operations before income taxes		219.9	173.5	142.9
Income tax expense (benefit)		(5.9)	(22.7)	(48.9)
Net income		225.8	196.2	191.8
Preferred dividend requirements of Interstate Power and Light Company		10.2	10.2	10.2
Net income attributable to common shareowners		215.6	186	181.6
Amounts attributable to common shareowners:
Net income		215.6	186	181.6
WPL [Member]
Operating revenues:
Electric utility		1,305.8	1,266.7	1,220.3
Gas utility		151.4	163.9	221
Other utility		1.9	4.5	7.8
Total operating revenues		1,459.1	1,435.1	1,449.1
Operating expenses:
Electric production fuel and purchased power		423.5	409.3	379.9
Electric transmission service		168.2	157.1	124.1
Cost of gas sold		83.3	95.8	142.3
Other operation and maintenance		219.8	235.4	277.2
Depreciation and amortization		192.5	184.3	181.2
Taxes other than income taxes		44.8	44.5	43.4
Total operating expenses		1,132.1	1,126.4	1,148.1
Operating income (loss)		327	308.7	301
Interest expense and other:
Interest expense		91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net		(39.8)	(35.1)	(42.8)
Allowance for funds used during construction		(10.5)	(8.7)	(8.9)
Interest income and other		(0.2)	(0.4)	(0.1)
Total interest expense and other		40.9	48.2	34.6
Income from continuing operations before income taxes		286.1	260.5	266.4
Income tax expense (benefit)		93.3	82.9	85.3
Net income		192.8	177.6	181.1
Net income attributable to noncontrolling interest		2.4	1.3	0.7
Net income attributable to common shareowners		190.4	176.3	180.4
Amounts attributable to common shareowners:
Net income		$ 190.4	$ 176.3	$ 180.4
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents		$ 8.2	$ 5.8
Accounts receivable, less allowance for doubtful accounts		493.3	397.6
Production fuel, at weighted average cost		98.1	98.8
Gas stored underground, at weighted average cost		37.6	43.3
Materials and supplies, at weighted average cost		86.6	81.4
Regulatory assets		57.8	120.2
Other		95.5	79.7
Total current assets		877.1	826.8
Property, plant and equipment, net		10,279.2	9,519.1
Investments:
Investment in American Transmission Company LLC		317.6	293.3
Other		20	53
Total investments		337.6	346.3
Other assets:
Regulatory assets		1,857.3	1,788.4
Deferred charges and other		22.6	14.6
Total other assets		1,879.9	1,803
Total assets		13,373.8	12,495.2
Current liabilities:
Current maturities of long-term debt		4.6	313.4
Commercial paper		244.1	159.8
Accounts payable		445.3	402.4
Regulatory liabilities		186.2	187.1
Accrued taxes		59.5	53.2
Other		222.3	243.4
Total current liabilities		1,162	1,359.3
Long-term debt, net (excluding current portion)	[1]	4,315.6	3,522.2
Other liabilities:
Deferred tax liabilities		2,570.2	2,381.2
Regulatory liabilities		494.8	550.6
Pension and other benefit obligations		489.9	451.8
Other		279.3	306
Total other liabilities		3,834.2	3,689.6
Commitments and contingencies (Note 16)
Common equity:
Common stock	[2]	2.3	2.3
Additional paid-in capital	[2]	1,693.1	1,661.8
Retained earnings		2,177	2,068.9
Accumulated other comprehensive loss		(0.4)	(0.4)
Shares in deferred compensation trust - 441,695 and 430,186 shares at a weighted average cost of $22.71 and $19.84 per share	[2]	(10)	(8.5)
Total common equity		3,862	3,724.1	[3]
Cumulative preferred stock of Interstate Power and Light Company		200	200
Total equity		4,062	3,924.1
Total liabilities and equity		13,373.8	12,495.2
IPL [Member]
Current assets:
Cash and cash equivalents		3.3	4.5
Accounts receivable, less allowance for doubtful accounts		240.7	200
Production fuel, at weighted average cost		70.3	60.2
Gas stored underground, at weighted average cost		16.3	18.2
Materials and supplies, at weighted average cost		46.5	45.7
Regulatory assets		17.7	39.6
Other		27.7	28.2
Total current assets		422.5	396.4
Property, plant and equipment, net		5,435.6	4,925.1
Investments:
Total investments		0.8	19.6
Other assets:
Regulatory assets		1,441.1	1,363
Deferred charges and other		4.7	5
Total other assets		1,445.8	1,368
Total assets		7,304.7	6,709.1
Current liabilities:
Current maturities of long-term debt		0	0
Commercial paper		0	0
Accounts payable		186.3	197.2
Accounts payable to associated companies		43.3	37.7
Regulatory liabilities		149.6	130.9
Accrued taxes		53.8	67.6
Accrued interest		31.6	28.2
Other		57.2	69.5
Total current liabilities		521.8	531.1
Long-term debt, net (excluding current portion)	[1]	2,153.5	1,856.9
Other liabilities:
Deferred tax liabilities		1,511.8	1,378
Regulatory liabilities		281.2	358.3
Pension and other benefit obligations		173.2	160.2
Other		214.2	229.3
Total other liabilities		2,180.4	2,125.8
Commitments and contingencies (Note 16)
Common equity:
Common stock		33.4	33.4
Additional paid-in capital		1,597.8	1,407.8
Retained earnings		617.8	554.1
Total common equity		2,249	1,995.3
Cumulative preferred stock of Interstate Power and Light Company		200	200
Total equity		2,449	2,195.3
Total liabilities and equity		7,304.7	6,709.1
WPL [Member]
Current assets:
Cash and cash equivalents		4.2	0.4
Accounts receivable, less allowance for doubtful accounts		226.3	185.4
Production fuel, at weighted average cost		27.8	38.6
Gas stored underground, at weighted average cost		21.3	25.1
Materials and supplies, at weighted average cost		36.3	33.5
Regulatory assets		40.1	80.6
Prepaid gross receipts tax		39.8	39.2
Other		20.7	20.7
Total current assets		416.5	423.5
Property, plant and equipment, net		4,426.7	4,103.7
Investments:
Investment in American Transmission Company LLC		0	293.3
Other		13.7	15.4
Total investments		13.7	308.7
Other assets:
Regulatory assets		416.2	425.4
Deferred charges and other		17.2	9.1
Total other assets		433.4	434.5
Total assets		5,290.3	5,270.4
Current liabilities:
Current maturities of long-term debt		0	0
Commercial paper		52.3	19.9
Accounts payable		192.9	136
Accounts payable to associated companies		34.6	21.6
Regulatory liabilities		36.6	56.2
Accrued interest		23.6	23.7
Other		54.7	79.5
Total current liabilities		394.7	336.9
Long-term debt, net (excluding current portion)	[1]	1,535.2	1,533.9
Other liabilities:
Deferred tax liabilities		971.6	1,005.4
Regulatory liabilities		213.6	192.3
Capital lease obligations - Sheboygan Falls Energy Facility		77.2	83.6
Pension and other benefit obligations		207.8	188.7
Other		159.4	162
Total other liabilities		1,629.6	1,632
Commitments and contingencies (Note 16)
Common equity:
Common stock		66.2	66.2
Additional paid-in capital		1,019	959
Retained earnings		645.6	731.1
Total common equity		1,730.8	1,756.3
Noncontrolling interest		0	11.3
Total equity		1,730.8	1,767.6
Total liabilities and equity		$ 5,290.3	$ 5,270.4
[1]	There were no significant sinking fund requirements related to the outstanding long-term debt.
[2]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.
[3]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares		Dec. 31, 2016	Dec. 31, 2015
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	[1]	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	[1]	227,673,654	226,918,432
Shares in deferred compensation trust (in shares)	[1]	441,695	430,186
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	[1]	$ 22.71	$ 19.84
IPL [Member]
Common stock, par value (in dollars per share)		$ 2.50	$ 2.50
Common stock, shares authorized (in shares)		24,000,000	24,000,000
Common stock, shares outstanding (in shares)		13,370,788	13,370,788
WPL [Member]
Common stock, par value (in dollars per share)		$ 5	$ 5
Common stock, shares authorized (in shares)		18,000,000	18,000,000
Common stock, shares outstanding (in shares)		13,236,601	13,236,601
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 381.7	$ 388.4		$ 393.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	411.6	401.3		388.1
Other amortizations	(4.8)	12.4		54.2
Deferred tax expense (benefit) and tax credits	84.6	114.2		55.2
Equity (income) loss from unconsolidated investments, net	(39.6)	(33.8)		(40.4)
Distributions from equity method investments	28.3	30.6		36.4
Equity component of allowance for funds used during construction	(42.3)	(24.4)		(23.1)
Asset valuation charges for Franklin County wind farm	86.4	0		0
Other	0.8	15.7		2
Other changes in assets and liabilities:
Accounts receivable	(121.4)	36.8		48.7
Sales of accounts receivable	16	(17)		(7)
Regulatory assets	(3.6)	(104.5)		(439.8)
Regulatory liabilities	(63)	(67.8)		10.8
Deferred income taxes	102.4	94.6		138.4
Pension and other benefit obligations	38.1	30.1		215.1
Other	(15.6)	(5.4)		59.7
Net cash flows from operating activities	859.6	871.2		891.6
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(1,142.7)	(963.6)		(838.9)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(54.1)	(70.7)		(63.9)
Proceeds from Minnesota electric and natural gas distribution asset sales	0	139.9		0
Other	10.3	(24.8)		(14.9)
Net cash flows from (used for) investing activities	(1,186.5)	(919.2)		(917.7)
Cash flows from (used for) financing activities:
Common stock dividends	(266.5)	(247.3)		(225.8)
Proceeds from issuance of common stock, net	26.6	151.2	[1]	0
Proceeds from issuance of long-term debt	800	250.7		812.9
Payments to retire long-term debt	(313.4)	(183)		(358.5)
Net change in commercial paper	84.3	18.5		(138.1)
Other	(1.7)	6.8		(17.3)
Net cash flows from (used for) financing activities	329.3	(3.1)		73.2
Net increase (decrease) in cash and cash equivalents	2.4	(51.1)		47.1
Cash and cash equivalents at beginning of period	5.8	56.9		9.8
Cash and cash equivalents at end of period	8.2	5.8		56.9
Supplemental cash flows information:
Interest, net of capitalized interest	(192.4)	(184.8)		(180.8)
Income taxes, net	(9.8)	0		5.3
Significant non-cash investing and financing activities:
Accrued capital expenditures	154.4	148.3		160.3
IPL [Member]
Cash flows from operating activities:
Net income	225.8	196.2		191.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	210.8	207.2		197.5
Deferred tax expense (benefit) and tax credits	35.6	28.9		(11.5)
Equity component of allowance for funds used during construction	(35.2)	(18.6)		(17.1)
Other	2.9	19.5		11.3
Other changes in assets and liabilities:
Accounts receivable	(59.7)	20.4		43.3
Sales of accounts receivable	16	(17)		(7)
Regulatory assets	(54.7)	(76.3)		(272.9)
Accounts payable	8	(42.7)		18.8
Regulatory liabilities	(67.3)	(75.5)		(18.9)
Deferred income taxes	97.7	82.1		140.4
Pension and other benefit obligations	13.1	17.8		93.8
Other	(31.1)	43		36.6
Net cash flows from operating activities	361.9	385		406.1
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(689.7)	(619.3)		(526)
Proceeds from Minnesota electric and natural gas distribution asset sales	0	139.9		0
Other	(3.9)	(32.5)		(26.7)
Net cash flows from (used for) investing activities	(693.6)	(511.9)		(552.7)
Cash flows from (used for) financing activities:
Common stock dividends	(151.9)	(140)		(140)
Capital contributions from parent	190	165		90
Proceeds from issuance of long-term debt	300	250		250
Payments to retire long-term debt	0	(150)		(38.4)
Other	(7.6)	1.1		(14.1)
Net cash flows from (used for) financing activities	330.5	126.1		147.5
Net increase (decrease) in cash and cash equivalents	(1.2)	(0.8)		0.9
Cash and cash equivalents at beginning of period	4.5	5.3		4.4
Cash and cash equivalents at end of period	3.3	4.5		5.3
Supplemental cash flows information:
Interest, net of capitalized interest	(99.7)	(93.9)		(89.8)
Income taxes, net	(11.1)	19.3		20.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	53.8	77		113.2
WPL [Member]
Cash flows from operating activities:
Net income	192.8	177.6		181.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	192.5	184.3		181.2
Other amortizations	(8.7)	5.3		47.3
Deferred tax expense (benefit) and tax credits	114.5	77.6		82.6
Equity (income) loss from unconsolidated investments, net	(39.8)	(35.1)		(42.8)
Distributions from equity method investments	28.3	30.6		36.4
Other	(6.3)	(5.7)		(7.2)
Other changes in assets and liabilities:
Accounts receivable	(47.6)	3.7		2.2
Regulatory assets	51.1	(28.2)		(166.9)
Pension and other benefit obligations	19.1	8.3		92
Other	25.5	31.4		18.5
Net cash flows from operating activities	521.4	449.8		424.4
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(453)	(344.3)		(312.9)
Other	(25.9)	(13.9)		(7.2)
Net cash flows from (used for) investing activities	(478.9)	(358.2)		(320.1)
Cash flows from (used for) financing activities:
Common stock dividends	(135)	(126.9)		(118.7)
Capital contributions from parent	60	0		0
Proceeds from issuance of long-term debt	0	0		250
Net change in commercial paper	32.4	19.9		(183.7)
Other	3.9	(30.9)		(5.7)
Net cash flows from (used for) financing activities	(38.7)	(137.9)		(58.1)
Net increase (decrease) in cash and cash equivalents	3.8	(46.3)		46.2
Cash and cash equivalents at beginning of period	0.4	46.7		0.5
Cash and cash equivalents at end of period	4.2	0.4		46.7
Supplemental cash flows information:
Interest, net of capitalized interest	(91.5)	(93.1)		(84.6)
Income taxes, net	27.8	(7.4)		(12.2)
Significant non-cash investing and financing activities:
Accrued capital expenditures	93.1	55.2		38.4
Transfer of investment in ATC and tax liability to ATI	$ (163.6)	$ 0		$ 0
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Consolidated Statements of Comm

Consolidated Statements of Common Equity - USD ($) $ in Millions		Total		IPL [Member]	WPL [Member]	Common Stock [Member]		Common Stock [Member]IPL [Member]	Common Stock [Member]WPL [Member]	Additional Paid-in Capital [Member]		Additional Paid-in Capital [Member]IPL [Member]	Additional Paid-in Capital [Member]WPL [Member]	Retained Earnings [Member]		Retained Earnings [Member]IPL [Member]	Retained Earnings [Member]WPL [Member]	Accumulated Other Comprehensive Income (Loss) [Member]		Shares in Deferred Compensation Trust [Member]		Noncontrolling Interest [Member]WPL [Member]
Beginning balance at Dec. 31, 2013		$ 3,281.4	[1]	$ 1,648.1		$ 2.2	[1]	$ 33.4	$ 66.2	$ 1,506.7	[1]	$ 1,152.8	$ 959	$ 1,780.7	[1]	$ 461.9	$ 622.2	$ (0.2)	[1]	$ (8)	[1]	$ 0
Beginning balance at Dec. 31, 2013					$ 1,647.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners		383.1		181.6	180.4									383.1		181.6	180.4					0.7
Net income		393.3		191.8	181.1
Common stock dividends		(225.8)	[1]	(140)	(118.7)									(225.8)	[1]	(140)	(118.7)
Common stock issued, net		0
Capital contributions from parent				90	0							90
Contributions from noncontrolling interest					8.6																	8.6
Distributions to noncontrolling interest					(0.8)																	(0.8)
Transfer of investment in ATC to ATI					0
Other		0.4		4.6	(2.2)					1.3						4.6	(2.2)			(0.9)
Other comprehensive income (loss), net of tax		(0.4)		0	0													(0.4)
Ending balance at Dec. 31, 2014		3,438.7	[1]	1,784.3		2.2	[1]	33.4	66.2	1,508	[1]	1,242.8	959	1,938	[1]	508.1	681.7	(0.6)	[1]	(8.9)	[1]	8.5
Ending balance at Dec. 31, 2014					1,715.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners		378.2		186	176.3									378.2		186	176.3					1.3
Net income		388.4		196.2	177.6
Common stock dividends		(247.3)	[1]	(140)	(126.9)									(247.3)	[1]	(140)	(126.9)
Common stock issued, net	[1]	151.2				0.1				151.1
Capital contributions from parent				165	0							165
Contributions from noncontrolling interest					3.4																	3.4
Distributions to noncontrolling interest					(1.9)																	(1.9)
Transfer of investment in ATC to ATI					0
Other		3.1								2.7										0.4
Other comprehensive income (loss), net of tax		0.2		0	0													0.2
Ending balance at Dec. 31, 2015		3,724.1	[1]	1,995.3	1,756.3	2.3	[1]	33.4	66.2	1,661.8	[1]	1,407.8	959	2,068.9	[1]	554.1	731.1	(0.4)	[1]	(8.5)	[1]	11.3
Ending balance at Dec. 31, 2015		3,924.1		2,195.3	1,767.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners		371.5		215.6	190.4									371.5		215.6	190.4					2.4
Net income		381.7		225.8	192.8
Common stock dividends		(266.5)	[1]	(151.9)	(135)									(266.5)	[1]	(151.9)	(135)
Common stock issued, net		26.6								26.6
Capital contributions from parent				190	60							190	60
Contributions from noncontrolling interest					11.5																	11.5
Distributions to noncontrolling interest					(2.5)																	(2.5)
Transfer of investment in ATC to ATI					(163.6)												(140.9)					(22.7)
Other		6.3								4.7				3.1						(1.5)
Other comprehensive income (loss), net of tax		0		0	0
Ending balance at Dec. 31, 2016		3,862		2,249	1,730.8	$ 2.3		$ 33.4	$ 66.2	$ 1,693.1		$ 1,597.8	$ 1,019	$ 2,177		$ 617.8	$ 645.6	$ (0.4)		$ (10)		$ 0
Ending balance at Dec. 31, 2016		$ 4,062		$ 2,449	$ 1,730.8
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Consolidated Statements of Com7

Consolidated Statements of Common Equity (Parenthetical) - $ / shares		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in dollars per share)	[1]	$ 1.175	$ 1.10	$ 1.02
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (a) General - Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is an investor-owned public utility holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services. IPL’s financial statements include the accounts of IPL and its consolidated subsidiary, IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which held Alliant Energy’s investment in ATC until December 31, 2016. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin. AEF is comprised of Transportation, Non-regulated Generation, ATI and other non-regulated investments. Transportation includes a short-line railway that provides freight service between Cedar Rapids, Iowa and Iowa City, Iowa; barge terminal and hauling services on the Mississippi River; and other transfer and storage services. Non-regulated Generation owns Sheboygan Falls, a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is leased to WPL for an initial period of 20 years ending in 2025. In addition, Non-regulated Generation currently owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. In February 2017, FERC issued an order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017. ATI, a wholly-owned subsidiary of AEF, held a partial interest in WPL Transco until December 31, 2016. As of December 31, 2016, ATI holds all of Alliant Energy’s investment in ATC. Refer to Note 6(a) for further discussion of the transfer of WPL’s ATC investment to ATI. Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries. Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction. 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. As discussed in Note 7 , 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 common stock split. Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. (b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates. Refer to Note 2 for additional discussion of regulatory assets and regulatory liabilities. (c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 . (d) Cash and Cash Equivalents - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. (e) Property, Plant and Equipment - Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion. Non-utility Property - General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements. (f) Operating Revenues - Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues. Revenue Recognition - Refer to Note 1(o) for discussion of a new accounting standard issued by the Financial Accounting Standards Board in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Refer to Note 2 for additional information regarding these utility cost recovery mechanisms. (h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on IPL’s and WPL’s derivative instruments. Refer to Notes 14 , 15 and 16(f) for further discussion of derivatives and related credit risk. (i) Asset Impairments - Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value. Refer to Note 6(a) for additional discussion of investments accounted for under the equity method of accounting. (j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for additional discussion of AROs. (k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early. Refer to Note 2 for information on regulatory assets related to IPL’s and WPL’s debt retired early or refinanced. (l) Allowance for Doubtful Accounts - Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories. Refer to Note 5(a) for details of allowance for doubtful accounts. (m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis. (n) Cash Flows Presentation - Alliant Energy presents cash flows from continuing operations together with cash flows from discontinued operations in its
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (a) General - Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is an investor-owned public utility holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services. IPL’s financial statements include the accounts of IPL and its consolidated subsidiary, IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which held Alliant Energy’s investment in ATC until December 31, 2016. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin. AEF is comprised of Transportation, Non-regulated Generation, ATI and other non-regulated investments. Transportation includes a short-line railway that provides freight service between Cedar Rapids, Iowa and Iowa City, Iowa; barge terminal and hauling services on the Mississippi River; and other transfer and storage services. Non-regulated Generation owns Sheboygan Falls, a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is leased to WPL for an initial period of 20 years ending in 2025. In addition, Non-regulated Generation currently owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. In February 2017, FERC issued an order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017. ATI, a wholly-owned subsidiary of AEF, held a partial interest in WPL Transco until December 31, 2016. As of December 31, 2016, ATI holds all of Alliant Energy’s investment in ATC. Refer to Note 6(a) for further discussion of the transfer of WPL’s ATC investment to ATI. Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries. Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction. 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. As discussed in Note 7 , 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 common stock split. Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. (b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates. Refer to Note 2 for additional discussion of regulatory assets and regulatory liabilities. (c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 . (d) Cash and Cash Equivalents - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. (e) Property, Plant and Equipment - Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion. Non-utility Property - General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements. (f) Operating Revenues - Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues. Revenue Recognition - Refer to Note 1(o) for discussion of a new accounting standard issued by the Financial Accounting Standards Board in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Refer to Note 2 for additional information regarding these utility cost recovery mechanisms. (h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on IPL’s and WPL’s derivative instruments. Refer to Notes 14 , 15 and 16(f) for further discussion of derivatives and related credit risk. (i) Asset Impairments - Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value. Refer to Note 6(a) for additional discussion of investments accounted for under the equity method of accounting. (j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for additional discussion of AROs. (k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early. Refer to Note 2 for information on regulatory assets related to IPL’s and WPL’s debt retired early or refinanced. (l) Allowance for Doubtful Accounts - Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories. Refer to Note 5(a) for details of allowance for doubtful accounts. (m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis. (o) New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing princ
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (a) General - Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is an investor-owned public utility holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services. IPL’s financial statements include the accounts of IPL and its consolidated subsidiary, IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which held Alliant Energy’s investment in ATC until December 31, 2016. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin. AEF is comprised of Transportation, Non-regulated Generation, ATI and other non-regulated investments. Transportation includes a short-line railway that provides freight service between Cedar Rapids, Iowa and Iowa City, Iowa; barge terminal and hauling services on the Mississippi River; and other transfer and storage services. Non-regulated Generation owns Sheboygan Falls, a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is leased to WPL for an initial period of 20 years ending in 2025. In addition, Non-regulated Generation currently owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. In February 2017, FERC issued an order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017. ATI, a wholly-owned subsidiary of AEF, held a partial interest in WPL Transco until December 31, 2016. As of December 31, 2016, ATI holds all of Alliant Energy’s investment in ATC. Refer to Note 6(a) for further discussion of the transfer of WPL’s ATC investment to ATI. Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries. Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction. 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. As discussed in Note 7 , 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 common stock split. Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. (b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates. Refer to Note 2 for additional discussion of regulatory assets and regulatory liabilities. (c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 . (d) Cash and Cash Equivalents - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. (e) Property, Plant and Equipment - Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion. Non-utility Property - General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements. (f) Operating Revenues - Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues. Revenue Recognition - Refer to Note 1(o) for discussion of a new accounting standard issued by the Financial Accounting Standards Board in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Refer to Note 2 for additional information regarding these utility cost recovery mechanisms. (h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on IPL’s and WPL’s derivative instruments. Refer to Notes 14 , 15 and 16(f) for further discussion of derivatives and related credit risk. (i) Asset Impairments - Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value. Refer to Note 6(a) for additional discussion of investments accounted for under the equity method of accounting. (j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for additional discussion of AROs. (k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early. Refer to Note 2 for information on regulatory assets related to IPL’s and WPL’s debt retired early or refinanced. (l) Allowance for Doubtful Accounts - Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories. Refer to Note 5(a) for details of allowance for doubtful accounts. (m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis. (o) New Accounting Standards - Revenue Recognition - In May 2014, the Financial Accounting Standards Board issued an accounting standard providing princ

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2016
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets, but not the respective carrying costs of these regulatory assets, are expected to be recovered from customers in future rates. At December 31, 2016 , IPL and WPL had $44 million and $9 million , respectively, of regulatory assets representing past expenditures that were not earning a return. IPL’s regulatory assets that were not earning a return consisted primarily of emission allowances, debt redemption costs, and costs for clean air compliance and wind generation expansion projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the wholesale portion of under-collected fuel-related costs, which is discussed in Note 1(g) , and environmental-related costs. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost. Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current tax expense during the last part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates. During 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Pension and other postretirement benefits costs - The IUB and the PSCW have authorized IPL and WPL to record the retail portion of their respective previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of AOCL on the balance sheets, as these amounts are expected to be recovered in future rates. IPL and WPL also recognize the wholesale portion of their previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets on the balance sheets because these amounts are expected to be recovered in rates in future periods under the formula rate structure. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s customers. The recoverable costs included in customers’ rates are based upon pension and OPEB costs determined in accordance with GAAP and are calculated using different methods for IPL’s and WPL’s respective regulatory jurisdictions. The IUB authorized IPL in its 2009 Test Year Iowa retail electric rate case order to recover from its retail electric customers in Iowa an allocated portion of annual costs equal to a two -year simple average of actual costs incurred during its 2009 Test Year and an estimate of costs for its forward-looking post-Test Year (2010). The PSCW has authorized WPL to recover from its retail electric and gas customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during each test period. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year through FERC-approved formula rates. Refer to Note 12(a) for additional details regarding pension and OPEB costs. AROs - Alliant Energy, IPL and WPL believe it is probable that any differences between expenses accrued for legal AROs related to their regulated operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for additional details of AROs. WPL’s electric generating units retired early - In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3. WPL received approval from the PSCW and FERC to reclassify the remaining net book value of these EGUs from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets. The remaining net book value is included in WPL’s rate base and WPL is earning a return on the outstanding balance. WPL is currently recovering the remaining net book value of these EGUs from both its retail and wholesale customers over a 10 -year period beginning January 1, 2013 pursuant to PSCW and FERC orders. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 15 for additional details of derivative assets and derivative liabilities. Emission allowances - IPL entered into forward contracts in 2007 to purchase SO2 emission allowances with vintage years of 2014 through 2017 from various counterparties to meet future CAIR emission reduction standards. Any SO2 emission allowances acquired under these forward contracts could be used to meet requirements under the existing Acid Rain program regulations or the more stringent CAIR emission reduction standards but are not eligible to be used for compliance requirements under CSAPR. In 2011, the EPA issued CSAPR to replace CAIR with an anticipated effective date in 2012. As a result of the issuance of CSAPR, Alliant Energy and IPL concluded in 2011 that the allowances to be acquired under these forward contracts would not be needed by IPL to comply with expected environmental regulations in the future. Alliant Energy and IPL have recorded a regulatory asset for amounts paid under the forward contracts, as well as for the remaining obligation under the forward contracts as a result of concluding the amount is probable of recovery from IPL’s customers. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. Other - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2016 in the above table are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense in the period the likelihood of future recovery is less than probable. Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5 Regulatory liabilities related to cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities are not used to reduce rate base in the revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated legal AROs. Alliant Energy, IPL and WPL record a regulatory liability for the estimated amounts they have collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. IPL’s tax benefit riders - The IUB has approved electric and gas tax benefit riders proposed by IPL, which 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. Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to such customers, resulting in no impact to their net income from the electric and gas tax benefit riders. The tax benefit riders 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. In 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions): Electric tax benefit rider credits $64 Gas tax benefit rider credits 12 $76 In December 2016, the IUB authorized $68 million and $7 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric and gas customers’ bills in 2017 through the electric and gas tax benefit riders, respectively. Any remaining tax benefit rider regulatory liabilities are currently expected to be credited to IPL’s retail electric and gas customers’ bills in the future, subject to final review by the IUB. Electric tax benefit rider - Details for IPL’s electric tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage) $64 $72 $85 Income tax benefit resulting from decreased taxable income caused by credits 27 30 35 Income tax benefit representing tax benefits realized from electric tax benefit rider 37 42 50 The IUB authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills for 2013 through 2016 to recognize the revenue requirement impact of the changes in tax accounting methods related to tangible property and mixed service costs. The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions): 2016 2015 2014 Revenue requirement adjustment $14 $14 $15 Gas tax benefit rider - Details for IPL’s gas tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day) $12 $12 $12 Income tax benefit resulting from decreased taxable income caused by credits 5 5 5 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Electric transmission cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s electric transmission service cost recovery mechanisms. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s commodity cost recovery mechanisms. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures they each incur for energy efficiency programs, including state mandated programs and Shared Savings programs. Differences between forecasted costs used to set rates and actual costs for these programs are deferred as a regulatory asset or regulatory liability. The PSCW’s order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized energy efficiency cost recovery amortizations for 2016, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In December 2016, WPL received an order from the PSCW authorizing WPL to implement increases in annual retail electric and gas base rates of $9 million and $9 million , respectively, effective January 1, 2017 followed by a freeze of such rates through the end of 2018. The key drivers for the electric and gas base rate increases are recovery of the costs for environmental controls projects at Edgewater and Columbia, and investments in electric and gas distribution systems, including expansion of natural gas pipeline infrastructure. The filing also included utilization of amounts that WPL previously over-recovered from its customers for energy efficiency cost recovery and electric transmission cost recovery, as well as amounts deferred under the return on common equity sharing mechanism for the 2013/2014 Test Period to reduce the requested base rate increases. The order included provisions that require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels in 2017 or 2018. WPL’s Wisconsin Retail Electric and Gas Rate Case (2015/2016 Test Period) - In July 2014, WPL received an order from the PSCW authorizing WPL to maintain retail electric base rates at their then current levels through the end of 2016. The retail electric base rate case included a return of and return of costs for environmental controls projects, generation performance and reliability improvements, other ongoing capital expenditures and an increase in electric transmission service expense. The additional revenue requirement for these cost increases was offset by the impact of changes in the amortization of regulatory liabilities associated with energy efficiency recoveries and increased sales volumes. The order also authorized WPL to implement a $5 million decrease in annual base rates for its retail gas customers effective January 1, 2015 followed by a freeze of such gas base rates through the end of 2016. The order included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels in 2015 or 2016. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2016 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - The PSCW’s order for WPL’s 2013/2014 Test Period electric and gas base rate case included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels during 2013 or 2014. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2013 and 2014 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. These deferred earnings will be returned to customers as an offset to revenue requirements in 2017 and 2018 as authorized by the PSCW. 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 extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions): 2016 2015 2014 Billing credits to reduce retail electric customers’ bills $9 $24 $72 WPL’s Retail Fuel-related Rate Filings - The PSCW authorized annual retail electric rate increases for WPL in 2014, 2015 and 2016, resulting from anticipated increases in retail electric fuel-related costs during such periods. Retail fuel-related costs incurred by WPL in 2015 and 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs, and retail fuel-related costs incurred by WPL in 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs. These fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved respective annual forecasted fuel-related costs. Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions): Retail Electric Deferral of Over (Under) Timing of Refunds To or Year Rate Increase Collected Fuel-related Costs Collections From Customers 2016 $7 1% $9 Pending 2015 39 4% 10 2016 2014 19 2% (28 ) 2016
IPL [Member]
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets, but not the respective carrying costs of these regulatory assets, are expected to be recovered from customers in future rates. At December 31, 2016 , IPL and WPL had $44 million and $9 million , respectively, of regulatory assets representing past expenditures that were not earning a return. IPL’s regulatory assets that were not earning a return consisted primarily of emission allowances, debt redemption costs, and costs for clean air compliance and wind generation expansion projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the wholesale portion of under-collected fuel-related costs, which is discussed in Note 1(g) , and environmental-related costs. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost. Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current tax expense during the last part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates. During 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Pension and other postretirement benefits costs - The IUB and the PSCW have authorized IPL and WPL to record the retail portion of their respective previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of AOCL on the balance sheets, as these amounts are expected to be recovered in future rates. IPL and WPL also recognize the wholesale portion of their previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets on the balance sheets because these amounts are expected to be recovered in rates in future periods under the formula rate structure. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s customers. The recoverable costs included in customers’ rates are based upon pension and OPEB costs determined in accordance with GAAP and are calculated using different methods for IPL’s and WPL’s respective regulatory jurisdictions. The IUB authorized IPL in its 2009 Test Year Iowa retail electric rate case order to recover from its retail electric customers in Iowa an allocated portion of annual costs equal to a two -year simple average of actual costs incurred during its 2009 Test Year and an estimate of costs for its forward-looking post-Test Year (2010). The PSCW has authorized WPL to recover from its retail electric and gas customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during each test period. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year through FERC-approved formula rates. Refer to Note 12(a) for additional details regarding pension and OPEB costs. AROs - Alliant Energy, IPL and WPL believe it is probable that any differences between expenses accrued for legal AROs related to their regulated operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for additional details of AROs. WPL’s electric generating units retired early - In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3. WPL received approval from the PSCW and FERC to reclassify the remaining net book value of these EGUs from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets. The remaining net book value is included in WPL’s rate base and WPL is earning a return on the outstanding balance. WPL is currently recovering the remaining net book value of these EGUs from both its retail and wholesale customers over a 10 -year period beginning January 1, 2013 pursuant to PSCW and FERC orders. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 15 for additional details of derivative assets and derivative liabilities. Emission allowances - IPL entered into forward contracts in 2007 to purchase SO2 emission allowances with vintage years of 2014 through 2017 from various counterparties to meet future CAIR emission reduction standards. Any SO2 emission allowances acquired under these forward contracts could be used to meet requirements under the existing Acid Rain program regulations or the more stringent CAIR emission reduction standards but are not eligible to be used for compliance requirements under CSAPR. In 2011, the EPA issued CSAPR to replace CAIR with an anticipated effective date in 2012. As a result of the issuance of CSAPR, Alliant Energy and IPL concluded in 2011 that the allowances to be acquired under these forward contracts would not be needed by IPL to comply with expected environmental regulations in the future. Alliant Energy and IPL have recorded a regulatory asset for amounts paid under the forward contracts, as well as for the remaining obligation under the forward contracts as a result of concluding the amount is probable of recovery from IPL’s customers. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. Other - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2016 in the above table are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense in the period the likelihood of future recovery is less than probable. Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5 Regulatory liabilities related to cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities are not used to reduce rate base in the revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated legal AROs. Alliant Energy, IPL and WPL record a regulatory liability for the estimated amounts they have collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. IPL’s tax benefit riders - The IUB has approved electric and gas tax benefit riders proposed by IPL, which 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. Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to such customers, resulting in no impact to their net income from the electric and gas tax benefit riders. The tax benefit riders 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. In 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions): Electric tax benefit rider credits $64 Gas tax benefit rider credits 12 $76 In December 2016, the IUB authorized $68 million and $7 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric and gas customers’ bills in 2017 through the electric and gas tax benefit riders, respectively. Any remaining tax benefit rider regulatory liabilities are currently expected to be credited to IPL’s retail electric and gas customers’ bills in the future, subject to final review by the IUB. Electric tax benefit rider - Details for IPL’s electric tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage) $64 $72 $85 Income tax benefit resulting from decreased taxable income caused by credits 27 30 35 Income tax benefit representing tax benefits realized from electric tax benefit rider 37 42 50 The IUB authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills for 2013 through 2016 to recognize the revenue requirement impact of the changes in tax accounting methods related to tangible property and mixed service costs. The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions): 2016 2015 2014 Revenue requirement adjustment $14 $14 $15 Gas tax benefit rider - Details for IPL’s gas tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day) $12 $12 $12 Income tax benefit resulting from decreased taxable income caused by credits 5 5 5 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Electric transmission cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s electric transmission service cost recovery mechanisms. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s commodity cost recovery mechanisms. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures they each incur for energy efficiency programs, including state mandated programs and Shared Savings programs. Differences between forecasted costs used to set rates and actual costs for these programs are deferred as a regulatory asset or regulatory liability. The PSCW’s order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized energy efficiency cost recovery amortizations for 2016, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In December 2016, WPL received an order from the PSCW authorizing WPL to implement increases in annual retail electric and gas base rates of $9 million and $9 million , respectively, effective January 1, 2017 followed by a freeze of such rates through the end of 2018. The key drivers for the electric and gas base rate increases are recovery of the costs for environmental controls projects at Edgewater and Columbia, and investments in electric and gas distribution systems, including expansion of natural gas pipeline infrastructure. The filing also included utilization of amounts that WPL previously over-recovered from its customers for energy efficiency cost recovery and electric transmission cost recovery, as well as amounts deferred under the return on common equity sharing mechanism for the 2013/2014 Test Period to reduce the requested base rate increases. The order included provisions that require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels in 2017 or 2018. WPL’s Wisconsin Retail Electric and Gas Rate Case (2015/2016 Test Period) - In July 2014, WPL received an order from the PSCW authorizing WPL to maintain retail electric base rates at their then current levels through the end of 2016. The retail electric base rate case included a return of and return of costs for environmental controls projects, generation performance and reliability improvements, other ongoing capital expenditures and an increase in electric transmission service expense. The additional revenue requirement for these cost increases was offset by the impact of changes in the amortization of regulatory liabilities associated with energy efficiency recoveries and increased sales volumes. The order also authorized WPL to implement a $5 million decrease in annual base rates for its retail gas customers effective January 1, 2015 followed by a freeze of such gas base rates through the end of 2016. The order included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels in 2015 or 2016. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2016 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - The PSCW’s order for WPL’s 2013/2014 Test Period electric and gas base rate case included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels during 2013 or 2014. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2013 and 2014 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. These deferred earnings will be returned to customers as an offset to revenue requirements in 2017 and 2018 as authorized by the PSCW. 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 extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions): 2016 2015 2014 Billing credits to reduce retail electric customers’ bills $9 $24 $72 WPL’s Retail Fuel-related Rate Filings - The PSCW authorized annual retail electric rate increases for WPL in 2014, 2015 and 2016, resulting from anticipated increases in retail electric fuel-related costs during such periods. Retail fuel-related costs incurred by WPL in 2015 and 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs, and retail fuel-related costs incurred by WPL in 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs. These fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved respective annual forecasted fuel-related costs. Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions): Retail Electric Deferral of Over (Under) Timing of Refunds To or Year Rate Increase Collected Fuel-related Costs Collections From Customers 2016 $7 1% $9 Pending 2015 39 4% 10 2016 2014 19 2% (28 ) 2016
WPL [Member]
Regulatory Matters [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets, but not the respective carrying costs of these regulatory assets, are expected to be recovered from customers in future rates. At December 31, 2016 , IPL and WPL had $44 million and $9 million , respectively, of regulatory assets representing past expenditures that were not earning a return. IPL’s regulatory assets that were not earning a return consisted primarily of emission allowances, debt redemption costs, and costs for clean air compliance and wind generation expansion projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the wholesale portion of under-collected fuel-related costs, which is discussed in Note 1(g) , and environmental-related costs. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost. Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current tax expense during the last part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates. During 2016 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Pension and other postretirement benefits costs - The IUB and the PSCW have authorized IPL and WPL to record the retail portion of their respective previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of AOCL on the balance sheets, as these amounts are expected to be recovered in future rates. IPL and WPL also recognize the wholesale portion of their previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets on the balance sheets because these amounts are expected to be recovered in rates in future periods under the formula rate structure. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s customers. The recoverable costs included in customers’ rates are based upon pension and OPEB costs determined in accordance with GAAP and are calculated using different methods for IPL’s and WPL’s respective regulatory jurisdictions. The IUB authorized IPL in its 2009 Test Year Iowa retail electric rate case order to recover from its retail electric customers in Iowa an allocated portion of annual costs equal to a two -year simple average of actual costs incurred during its 2009 Test Year and an estimate of costs for its forward-looking post-Test Year (2010). The PSCW has authorized WPL to recover from its retail electric and gas customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during each test period. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year through FERC-approved formula rates. Refer to Note 12(a) for additional details regarding pension and OPEB costs. AROs - Alliant Energy, IPL and WPL believe it is probable that any differences between expenses accrued for legal AROs related to their regulated operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for additional details of AROs. WPL’s electric generating units retired early - In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3. WPL received approval from the PSCW and FERC to reclassify the remaining net book value of these EGUs from property, plant and equipment to a regulatory asset on Alliant Energy’s and WPL’s balance sheets. The remaining net book value is included in WPL’s rate base and WPL is earning a return on the outstanding balance. WPL is currently recovering the remaining net book value of these EGUs from both its retail and wholesale customers over a 10 -year period beginning January 1, 2013 pursuant to PSCW and FERC orders. Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 15 for additional details of derivative assets and derivative liabilities. Emission allowances - IPL entered into forward contracts in 2007 to purchase SO2 emission allowances with vintage years of 2014 through 2017 from various counterparties to meet future CAIR emission reduction standards. Any SO2 emission allowances acquired under these forward contracts could be used to meet requirements under the existing Acid Rain program regulations or the more stringent CAIR emission reduction standards but are not eligible to be used for compliance requirements under CSAPR. In 2011, the EPA issued CSAPR to replace CAIR with an anticipated effective date in 2012. As a result of the issuance of CSAPR, Alliant Energy and IPL concluded in 2011 that the allowances to be acquired under these forward contracts would not be needed by IPL to comply with expected environmental regulations in the future. Alliant Energy and IPL have recorded a regulatory asset for amounts paid under the forward contracts, as well as for the remaining obligation under the forward contracts as a result of concluding the amount is probable of recovery from IPL’s customers. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. Other - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2016 in the above table are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense in the period the likelihood of future recovery is less than probable. Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5 Regulatory liabilities related to cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities are not used to reduce rate base in the revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated legal AROs. Alliant Energy, IPL and WPL record a regulatory liability for the estimated amounts they have collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. IPL’s tax benefit riders - The IUB has approved electric and gas tax benefit riders proposed by IPL, which 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. Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to such customers, resulting in no impact to their net income from the electric and gas tax benefit riders. The tax benefit riders 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. In 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions): Electric tax benefit rider credits $64 Gas tax benefit rider credits 12 $76 In December 2016, the IUB authorized $68 million and $7 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric and gas customers’ bills in 2017 through the electric and gas tax benefit riders, respectively. Any remaining tax benefit rider regulatory liabilities are currently expected to be credited to IPL’s retail electric and gas customers’ bills in the future, subject to final review by the IUB. Electric tax benefit rider - Details for IPL’s electric tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage) $64 $72 $85 Income tax benefit resulting from decreased taxable income caused by credits 27 30 35 Income tax benefit representing tax benefits realized from electric tax benefit rider 37 42 50 The IUB authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills for 2013 through 2016 to recognize the revenue requirement impact of the changes in tax accounting methods related to tangible property and mixed service costs. The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions): 2016 2015 2014 Revenue requirement adjustment $14 $14 $15 Gas tax benefit rider - Details for IPL’s gas tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day) $12 $12 $12 Income tax benefit resulting from decreased taxable income caused by credits 5 5 5 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Electric transmission cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s electric transmission service cost recovery mechanisms. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s commodity cost recovery mechanisms. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures they each incur for energy efficiency programs, including state mandated programs and Shared Savings programs. Differences between forecasted costs used to set rates and actual costs for these programs are deferred as a regulatory asset or regulatory liability. The PSCW’s order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized energy efficiency cost recovery amortizations for 2016, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Utility Rate Cases - WPL’s Wisconsin Retail Electric and Gas Rate Case (2017/2018 Test Period) - In December 2016, WPL received an order from the PSCW authorizing WPL to implement increases in annual retail electric and gas base rates of $9 million and $9 million , respectively, effective January 1, 2017 followed by a freeze of such rates through the end of 2018. The key drivers for the electric and gas base rate increases are recovery of the costs for environmental controls projects at Edgewater and Columbia, and investments in electric and gas distribution systems, including expansion of natural gas pipeline infrastructure. The filing also included utilization of amounts that WPL previously over-recovered from its customers for energy efficiency cost recovery and electric transmission cost recovery, as well as amounts deferred under the return on common equity sharing mechanism for the 2013/2014 Test Period to reduce the requested base rate increases. The order included provisions that require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels in 2017 or 2018. WPL’s Wisconsin Retail Electric and Gas Rate Case (2015/2016 Test Period) - In July 2014, WPL received an order from the PSCW authorizing WPL to maintain retail electric base rates at their then current levels through the end of 2016. The retail electric base rate case included a return of and return of costs for environmental controls projects, generation performance and reliability improvements, other ongoing capital expenditures and an increase in electric transmission service expense. The additional revenue requirement for these cost increases was offset by the impact of changes in the amortization of regulatory liabilities associated with energy efficiency recoveries and increased sales volumes. The order also authorized WPL to implement a $5 million decrease in annual base rates for its retail gas customers effective January 1, 2015 followed by a freeze of such gas base rates through the end of 2016. The order included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels in 2015 or 2016. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2016 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - The PSCW’s order for WPL’s 2013/2014 Test Period electric and gas base rate case included provisions that required WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeded certain levels during 2013 or 2014. As of December 31, 2016 , Alliant Energy and WPL deferred $6 million of WPL’s 2013 and 2014 earnings for these provisions, which is included in “Other” in Alliant Energy’s and WPL’s regulatory liabilities tables above. These deferred earnings will be returned to customers as an offset to revenue requirements in 2017 and 2018 as authorized by the PSCW. 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 extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions): 2016 2015 2014 Billing credits to reduce retail electric customers’ bills $9 $24 $72 WPL’s Retail Fuel-related Rate Filings - The PSCW authorized annual retail electric rate increases for WPL in 2014, 2015 and 2016, resulting from anticipated increases in retail electric fuel-related costs during such periods. Retail fuel-related costs incurred by WPL in 2015 and 2016 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs, and retail fuel-related costs incurred by WPL in 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs. These fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved respective annual forecasted fuel-related costs. Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions): Retail Electric Deferral of Over (Under) Timing of Refunds To or Year Rate Increase Collected Fuel-related Costs Collections From Customers 2016 $7 1% $9 Pending 2015 39 4% 10 2016 2014 19 2% (28 ) 2016

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - Construction of a scrubber and baghouse at Edgewater Unit 5 began in 2014 and was completed in 2016, which resulted in a transfer of the capitalized project costs from “Construction work in progress” to “Electric plant - Generation in service” in the above table for Alliant Energy and WPL in 2016. As of December 31, 2016 and 2015 , the capitalized project costs for the scrubber and baghouse consisted of capitalized expenditures of $225 million and CWIP of $190 million , and AFUDC of $12 million and $8 million , respectively, for the scrubber and baghouse. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under CSAPR. Natural Gas-Fired Generation Projects - 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 April 2017. As of December 31, 2016 and 2015 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $612 million and $453 million , and AFUDC of $68 million and $24 million , respectively, for Marshalltown in “Construction work in progress” in the above table for Alliant Energy and IPL. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is expected to be completed in early 2020. As of December 31, 2016 and 2015 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $81 million and $2 million , and AFUDC of $2 million and $0 , respectively, for the Riverside expansion in “Construction work in progress” in the above table for Alliant Energy and WPL. These capital expenditures exclude any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion. Wind Generation - IPL’s Expansion of Wind Generation - IPL currently plans to add wind generation to its resources portfolio. In 2016, IPL entered into a turbine supply agreement and made progress payments for a portion of the wind turbines in such agreement in order to qualify for the full level of production tax credits for this new wind generation. IPL anticipates placing certain of the additional wind generation in service in 2019 and 2020. As of December 31, 2016 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $102 million and AFUDC of $1 million for this expansion of wind generation in “Construction work in progress” in the above table for Alliant Energy and IPL. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) 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 (primarily related to property, plant and equipment) to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives, 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 $11 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements in 2015. The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which was approved by FERC in 2015 and became effective upon the sale of IPL’s Minnesota electric distribution assets. The wholesale power supply agreement contains a five -year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years . The agreement remains in effect indefinitely, unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97% . As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets did not have a significant impact on IPL’s generation plans or operating results. AFUDC - AFUDC represents costs to finance construction additions including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8 Non-regulated and Other - The non-regulated and other property, plant and equipment recorded on Alliant Energy’s balance sheets includes the following: Non-regulated Generation - Franklin County Wind Farm - The Franklin County wind farm was placed into service in 2012 and is depreciated using the straight-line method over a 30 -year period. Based on an evaluation of the strategic options for the Franklin County wind farm performed in 2016, Alliant Energy concluded 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 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 PPAs 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 value of the Franklin County wind farm assets 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, in 2016, the carrying amount of the Franklin County wind farm was reduced to such 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 2016, Alliant Energy recorded such charges as a reduction to “Non-regulated Generation, net” in the above table and charges to “Asset valuation charges for Franklin County wind farm” in its income statement. In February 2017, FERC issued an order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017. The final amount to be recovered for IPL’s electric rate-making purposes is expected to be determined by the IUB as part of IPL’s 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. Sheboygan Falls - Sheboygan Falls was placed into service in 2005 and is depreciated using the straight-line method over a 35 -year period. As of December 31, 2016 , Alliant Energy recorded $95 million on its balance sheet related to Sheboygan Falls. Corporate Services and Other - Property, plant and equipment related to Corporate Services includes a customer billing and information system for IPL and WPL and other computer software, and the corporate headquarters building located in Madison, Wisconsin. The customer billing and information system is amortized using the straight-line method over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. Property, plant and equipment related to Transportation includes a short-line railway in Iowa and a barge terminal on the Mississippi River. The Corporate Services and Other property, plant and equipment is depreciated using the straight-line method over periods ranging from 5 to 30 years.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - Construction of a scrubber and baghouse at Edgewater Unit 5 began in 2014 and was completed in 2016, which resulted in a transfer of the capitalized project costs from “Construction work in progress” to “Electric plant - Generation in service” in the above table for Alliant Energy and WPL in 2016. As of December 31, 2016 and 2015 , the capitalized project costs for the scrubber and baghouse consisted of capitalized expenditures of $225 million and CWIP of $190 million , and AFUDC of $12 million and $8 million , respectively, for the scrubber and baghouse. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under CSAPR. Natural Gas-Fired Generation Projects - 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 April 2017. As of December 31, 2016 and 2015 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $612 million and $453 million , and AFUDC of $68 million and $24 million , respectively, for Marshalltown in “Construction work in progress” in the above table for Alliant Energy and IPL. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is expected to be completed in early 2020. As of December 31, 2016 and 2015 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $81 million and $2 million , and AFUDC of $2 million and $0 , respectively, for the Riverside expansion in “Construction work in progress” in the above table for Alliant Energy and WPL. These capital expenditures exclude any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion. Wind Generation - IPL’s Expansion of Wind Generation - IPL currently plans to add wind generation to its resources portfolio. In 2016, IPL entered into a turbine supply agreement and made progress payments for a portion of the wind turbines in such agreement in order to qualify for the full level of production tax credits for this new wind generation. IPL anticipates placing certain of the additional wind generation in service in 2019 and 2020. As of December 31, 2016 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $102 million and AFUDC of $1 million for this expansion of wind generation in “Construction work in progress” in the above table for Alliant Energy and IPL. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) 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 (primarily related to property, plant and equipment) to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives, 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 $11 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements in 2015. The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which was approved by FERC in 2015 and became effective upon the sale of IPL’s Minnesota electric distribution assets. The wholesale power supply agreement contains a five -year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years . The agreement remains in effect indefinitely, unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97% . As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets did not have a significant impact on IPL’s generation plans or operating results. AFUDC - AFUDC represents costs to finance construction additions including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - Construction of a scrubber and baghouse at Edgewater Unit 5 began in 2014 and was completed in 2016, which resulted in a transfer of the capitalized project costs from “Construction work in progress” to “Electric plant - Generation in service” in the above table for Alliant Energy and WPL in 2016. As of December 31, 2016 and 2015 , the capitalized project costs for the scrubber and baghouse consisted of capitalized expenditures of $225 million and CWIP of $190 million , and AFUDC of $12 million and $8 million , respectively, for the scrubber and baghouse. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under CSAPR. Natural Gas-Fired Generation Projects - 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 April 2017. As of December 31, 2016 and 2015 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $612 million and $453 million , and AFUDC of $68 million and $24 million , respectively, for Marshalltown in “Construction work in progress” in the above table for Alliant Energy and IPL. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is expected to be completed in early 2020. As of December 31, 2016 and 2015 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $81 million and $2 million , and AFUDC of $2 million and $0 , respectively, for the Riverside expansion in “Construction work in progress” in the above table for Alliant Energy and WPL. These capital expenditures exclude any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion. Wind Generation - IPL’s Expansion of Wind Generation - IPL currently plans to add wind generation to its resources portfolio. In 2016, IPL entered into a turbine supply agreement and made progress payments for a portion of the wind turbines in such agreement in order to qualify for the full level of production tax credits for this new wind generation. IPL anticipates placing certain of the additional wind generation in service in 2019 and 2020. As of December 31, 2016 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $102 million and AFUDC of $1 million for this expansion of wind generation in “Construction work in progress” in the above table for Alliant Energy and IPL. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) 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 (primarily related to property, plant and equipment) to Southern Minnesota Energy Cooperative, a combined group of various neighboring electric cooperatives, 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 $11 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements in 2015. The electric distribution asset sales agreement includes a wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which was approved by FERC in 2015 and became effective upon the sale of IPL’s Minnesota electric distribution assets. The wholesale power supply agreement contains a five -year termination notice, which may not be given until the fifth anniversary of the effective date of the agreement, resulting in a minimum term of 10 years . The agreement remains in effect indefinitely, unless notice to terminate is provided by either party. This wholesale power supply agreement includes standardized pricing mechanisms that are detailed in IPL’s current tariffs accepted by FERC through wholesale rate case proceedings. IPL’s current return on common equity authorized by FERC related to its wholesale electric rates is 10.97% . As a result of IPL’s requirement to supply electricity to Southern Minnesota Energy Cooperative under the wholesale power supply agreement, the sale of the electric distribution assets did not have a significant impact on IPL’s generation plans or operating results. AFUDC - AFUDC represents costs to finance construction additions including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8

Jointly-Owned Electric Utility

Jointly-Owned Electric Utility Plant	12 Months Ended
	Dec. 31, 2016
Jointly-Owned Electric Utility Plant	JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. KWh generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8 In November 2016, WPL received an order from the PSCW approving amendments to the Columbia joint operating agreement, which allow the co-owners to forgo certain capital expenditures at Columbia (excluding capital expenditures related to the Columbia Unit 2 SCR currently being constructed), resulting in WPL incurring these additional capital expenditures in exchange for a proportional increase in its ownership share of Columbia. Based on the additional capital expenditures WPL currently expects to incur through June 1, 2020, WPL’s ownership interest in Columbia is expected to increase in the future. In December 2016, WPL filed a request with FERC for approval of these amendments to the Columbia joint operating agreement, effective January 1, 2017. WPL currently expects to receive FERC’s decision on these amendments in 2017. In November 2016, various electric cooperatives, which currently have wholesale power supply agreements with WPL, notified WPL of their intent to exercise purchase options for a partial ownership interest in the Riverside expansion. WPL currently expects the exercise of the purchase options to be effective in 2017.
IPL [Member]
Jointly-Owned Electric Utility Plant	JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. KWh generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8
WPL [Member]
Jointly-Owned Electric Utility Plant	JOINTLY-OWNED ELECTRIC UTILITY PLANT Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned coal-fired EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. KWh generation and operating expenses are primarily divided between the joint owners on the same basis as ownership. IPL’s and WPL’s shares of expenses from jointly-owned coal-fired EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in their income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8 In November 2016, WPL received an order from the PSCW approving amendments to the Columbia joint operating agreement, which allow the co-owners to forgo certain capital expenditures at Columbia (excluding capital expenditures related to the Columbia Unit 2 SCR currently being constructed), resulting in WPL incurring these additional capital expenditures in exchange for a proportional increase in its ownership share of Columbia. Based on the additional capital expenditures WPL currently expects to incur through June 1, 2020, WPL’s ownership interest in Columbia is expected to increase in the future. In December 2016, WPL filed a request with FERC for approval of these amendments to the Columbia joint operating agreement, effective January 1, 2017. WPL currently expects to receive FERC’s decision on these amendments in 2017. In November 2016, various electric cooperatives, which currently have wholesale power supply agreements with WPL, notified WPL of their intent to exercise purchase options for a partial ownership interest in the Riverside expansion. WPL currently expects the exercise of the purchase options to be effective in 2017.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables	RECEIVABLES (a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4 (b) 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. IPL pays a monthly fee to the third party that varies based on interest rates, limits on cash proceeds and cash amounts received from the third party. 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. In 2016, 2015 and 2014, IPL received cash proceeds of up to $180 million from the third party in exchange for the receivables sold. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less. The limit on cash proceeds as of December 31, 2016 was $150 million , and effective February 2017 the limit on cash proceeds is $125 million . The Receivables Agreement can be terminated by the third party if arrears or write-offs exceed certain levels. IPL was in compliance with all related covenants as of December 31, 2016. As of December 31, 2016 , IPL sold $248.1 million of receivables to the third party, received $21.0 million in cash proceeds and recorded deferred proceeds of $211.1 million . Deferred proceeds represent IPL’s interest in the receivables sold to the third party. At IPL’s request, deferred proceeds are paid to IPL from collections of receivables, after paying any required expenses incurred by the third party and the collection agent. Corporate Services acts as collection agent for the third party and receives a fee for collection services. IPL believes that the allowance for doubtful accounts related to its sales of receivables is a reasonable approximation of credit risk of the customers that generated the receivables. In 2016 , 2015 and 2014 , IPL’s costs incurred related to the sales of accounts receivable program were not material. Refer to Note 14 for discussion of the fair value of deferred proceeds. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions): Maximum Average 2016 2015 2014 2016 2015 2014 Outstanding aggregate cash proceeds $172.0 $137.0 $150.0 $73.2 $46.7 $46.4 As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 Customer accounts receivable $157.6 $109.7 Unbilled utility revenues 90.4 71.3 Other receivables 0.1 0.1 Receivables sold to third party 248.1 181.1 Less: cash proceeds (a) 21.0 5.0 Deferred proceeds 227.1 176.1 Less: allowance for doubtful accounts 16.0 4.1 Fair value of deferred proceeds $211.1 $172.0 Outstanding receivables past due $68.0 $18.0 (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 IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 2014 Collections reinvested in receivables $1,818.1 $1,812.9 $1,997.9 Write-offs, net of recoveries 4.8 8.8 11.4 In connection with the implementation of IPL’s new customer billing and information system in 2016, IPL postponed the write-off of customer bills for a portion of 2016, resulting in lower write-offs in 2016 and higher outstanding receivables past due as of December 31, 2016. (c) Whiting Petroleum Tax Sharing Agreement - Prior to an initial public offering of Whiting Petroleum in 2003, Alliant Energy and Whiting Petroleum entered into a tax separation and indemnification agreement pursuant to which Alliant Energy and Whiting Petroleum made certain tax elections. These tax elections had the effect of increasing the tax basis of the assets of Whiting Petroleum’s consolidated tax group based on the sales price of Whiting Petroleum’s shares in the initial public offering. The increase in the tax basis of the assets was included as income in Alliant Energy’s U.S. federal income tax return for the calendar year 2003. Pursuant to the tax separation and indemnification agreement, Whiting Petroleum paid Alliant Energy the final payment of $26 million in 2014, which represented the present value of certain future tax benefits expected to be realized by Whiting Petroleum through future tax deductions. The $26 million received by Alliant Energy is presented in operating activities in its cash flows statement in 2014.
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables	RECEIVABLES (a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4 (b) 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. IPL pays a monthly fee to the third party that varies based on interest rates, limits on cash proceeds and cash amounts received from the third party. 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. In 2016, 2015 and 2014, IPL received cash proceeds of up to $180 million from the third party in exchange for the receivables sold. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less. The limit on cash proceeds as of December 31, 2016 was $150 million , and effective February 2017 the limit on cash proceeds is $125 million . The Receivables Agreement can be terminated by the third party if arrears or write-offs exceed certain levels. IPL was in compliance with all related covenants as of December 31, 2016. As of December 31, 2016 , IPL sold $248.1 million of receivables to the third party, received $21.0 million in cash proceeds and recorded deferred proceeds of $211.1 million . Deferred proceeds represent IPL’s interest in the receivables sold to the third party. At IPL’s request, deferred proceeds are paid to IPL from collections of receivables, after paying any required expenses incurred by the third party and the collection agent. Corporate Services acts as collection agent for the third party and receives a fee for collection services. IPL believes that the allowance for doubtful accounts related to its sales of receivables is a reasonable approximation of credit risk of the customers that generated the receivables. In 2016 , 2015 and 2014 , IPL’s costs incurred related to the sales of accounts receivable program were not material. Refer to Note 14 for discussion of the fair value of deferred proceeds. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions): Maximum Average 2016 2015 2014 2016 2015 2014 Outstanding aggregate cash proceeds $172.0 $137.0 $150.0 $73.2 $46.7 $46.4 As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 Customer accounts receivable $157.6 $109.7 Unbilled utility revenues 90.4 71.3 Other receivables 0.1 0.1 Receivables sold to third party 248.1 181.1 Less: cash proceeds (a) 21.0 5.0 Deferred proceeds 227.1 176.1 Less: allowance for doubtful accounts 16.0 4.1 Fair value of deferred proceeds $211.1 $172.0 Outstanding receivables past due $68.0 $18.0 (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 IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 2014 Collections reinvested in receivables $1,818.1 $1,812.9 $1,997.9 Write-offs, net of recoveries 4.8 8.8 11.4 In connection with the implementation of IPL’s new customer billing and information system in 2016, IPL postponed the write-off of customer bills for a portion of 2016, resulting in lower write-offs in 2016 and higher outstanding receivables past due as of December 31, 2016.
WPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables	RECEIVABLES (a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS (a) Unconsolidated Equity Investments - Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions): Ownership Interest at Carrying Value at December 31, Equity (Income) / Loss December 31, 2016 2016 2015 2016 2015 2014 Alliant Energy ATC (a) 16% $317.6 $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Other Various 8.4 9.6 (0.5 ) 0.4 1.5 $326.0 $302.9 ($39.6 ) ($33.8 ) ($40.4 ) WPL ATC —% $— $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Wisconsin River Power Company 50% 7.7 8.7 (0.7 ) (0.9 ) (0.9 ) $7.7 $302.0 ($39.8 ) ($35.1 ) ($42.8 ) (a) Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC. Summary aggregate financial information from the financial statements of these investments is as follows (in millions): Alliant Energy WPL 2016 2015 2014 2016 2015 2014 Operating revenues $658 $624 $643 $658 $624 $643 Operating income 331 299 330 331 299 330 Net income 232 186 240 234 202 240 As of December 31: Current assets 82 88 6 87 Non-current assets 4,340 3,987 19 3,977 Current liabilities 498 332 3 332 Non-current liabilities 2,144 2,052 7 2,052 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 December 31, 2016 , including $9 million , $12 million and $3 million realized in 2016, 2015 and 2014, respectively. WPL’s Noncontrolling Interest and Investment in ATC - Prior to 2014, WPL owned 100% of WPL Transco, which held Alliant Energy’s investment in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of AEF, to become a member of WPL Transco in addition to WPL. In 2014, ATI began funding capital contributions that WPL Transco made to ATC. WPL Transco’s equity income from ATC and ATC dividends received by WPL Transco were allocated between WPL and ATI based on their respective ownership interests at the time the equity income was generated and at the time of the dividend payments. Prior to the transfer of the investment in ATC to ATI discussed below, WPL consolidated WPL Transco, and ATI’s ownership in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. In June 2016, WPL received an order from the PSCW requiring WPL to transfer its investment in ATC to Alliant Energy or an Alliant Energy subsidiary by December 31, 2022. On December 31, 2016, pursuant to the PSCW order, WPL Transco was liquidated and WPL transferred its investment in ATC to ATI. In conjunction with the transfer of the investment in ATC, a deferred intercompany tax gain recognized by WPL was assumed by ATI. The impact of WPL’s transfer of the ATC investment, including the assumption of such intercompany tax gain by ATI, was recorded as a net reduction in total equity of $163.6 million on WPL’s balance sheet. WPL’s income statement includes all of the equity earnings from ATC through December 31, 2016, the date of transfer. There were no impacts of this transfer to Alliant Energy’s consolidated financial statements. As of December 31, 2016, ATI owns Alliant Energy’s entire investment in ATC. (b) Cash Surrender Value of Life Insurance Policies - Various life insurance policies cover certain current and former employees and directors. In 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 flow statements, respectively. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4
IPL [Member]
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS (b) Cash Surrender Value of Life Insurance Policies - Various life insurance policies cover certain current and former employees and directors. In 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 flow statements, respectively. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4
WPL [Member]
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS (a) Unconsolidated Equity Investments - Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions): Ownership Interest at Carrying Value at December 31, Equity (Income) / Loss December 31, 2016 2016 2015 2016 2015 2014 Alliant Energy ATC (a) 16% $317.6 $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Other Various 8.4 9.6 (0.5 ) 0.4 1.5 $326.0 $302.9 ($39.6 ) ($33.8 ) ($40.4 ) WPL ATC —% $— $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Wisconsin River Power Company 50% 7.7 8.7 (0.7 ) (0.9 ) (0.9 ) $7.7 $302.0 ($39.8 ) ($35.1 ) ($42.8 ) (a) Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC. Summary aggregate financial information from the financial statements of these investments is as follows (in millions): Alliant Energy WPL 2016 2015 2014 2016 2015 2014 Operating revenues $658 $624 $643 $658 $624 $643 Operating income 331 299 330 331 299 330 Net income 232 186 240 234 202 240 As of December 31: Current assets 82 88 6 87 Non-current assets 4,340 3,987 19 3,977 Current liabilities 498 332 3 332 Non-current liabilities 2,144 2,052 7 2,052 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 December 31, 2016 , including $9 million , $12 million and $3 million realized in 2016, 2015 and 2014, respectively. WPL’s Noncontrolling Interest and Investment in ATC - Prior to 2014, WPL owned 100% of WPL Transco, which held Alliant Energy’s investment in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of AEF, to become a member of WPL Transco in addition to WPL. In 2014, ATI began funding capital contributions that WPL Transco made to ATC. WPL Transco’s equity income from ATC and ATC dividends received by WPL Transco were allocated between WPL and ATI based on their respective ownership interests at the time the equity income was generated and at the time of the dividend payments. Prior to the transfer of the investment in ATC to ATI discussed below, WPL consolidated WPL Transco, and ATI’s ownership in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. In June 2016, WPL received an order from the PSCW requiring WPL to transfer its investment in ATC to Alliant Energy or an Alliant Energy subsidiary by December 31, 2022. On December 31, 2016, pursuant to the PSCW order, WPL Transco was liquidated and WPL transferred its investment in ATC to ATI. In conjunction with the transfer of the investment in ATC, a deferred intercompany tax gain recognized by WPL was assumed by ATI. The impact of WPL’s transfer of the ATC investment, including the assumption of such intercompany tax gain by ATI, was recorded as a net reduction in total equity of $163.6 million on WPL’s balance sheet. WPL’s income statement includes all of the equity earnings from ATC through December 31, 2016, the date of transfer. There were no impacts of this transfer to Alliant Energy’s consolidated financial statements. As of December 31, 2016, ATI owns Alliant Energy’s entire investment in ATC. (b) Cash Surrender Value of Life Insurance Policies - Various life insurance policies cover certain current and former employees and directors. In 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 flow statements, respectively. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2016
Schedule of Common Equity [Line Items]
Common Equity	COMMON EQUITY 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. Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2016 2015 2014 Shares outstanding, January 1 226,918,432 221,871,360 221,887,338 At-the-market offering program — 4,373,234 — Shareowner Direct Plan issuances 732,814 606,010 — Equity-based compensation plans ( Note 12(b) ) 22,408 112,756 71,094 Other — (44,928 ) (87,072 ) Shares outstanding, December 31 227,673,654 226,918,432 221,871,360 At December 31, 2016 , Alliant Energy had a total of 11.3 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Program - In 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this 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. This at-the-market offering program expired in 2016. Shareowner Direct Plan - Beginning in 2015, Alliant Energy satisfied its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy has established an amended and restated Shareowner Rights Agreement. The rights under this agreement will only become exercisable if a person or group has acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. Each right will initially entitle registered shareowners to purchase from Alliant Energy one-quarter of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $55.00 per full share, subject to adjustment. If any shareowner acquires 15% or more of the outstanding common stock of Alliant Energy, each right (subject to limitations) will entitle its holder to purchase, at the right’s then current exercise price, a number of common shares of Alliant Energy or of the acquirer having a market value at the time of twice the right’s per full share exercise price. Alliant Energy’s Board of Directors is authorized to reduce the 15% ownership threshold to not less than 10% . The amended and restated Shareowner Rights Agreement expires in December 2018. Alliant Energy currently has no intention to redeem the Shareowner Rights Agreement and plans to allow it to naturally expire at the end of the term. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2016 , IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2016 . Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $618 million . If IPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with IPL’s rate cases) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $126 million in 2017 and $140 million in 2018 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 51.00% for 2017 or 2018. As of December 31, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $126 million for 2017 . Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 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 $1.6 billion for each. Comprehensive Income - In 2016 , 2015 and 2014 , Alliant Energy’s other comprehensive income (loss) was $0 , $0.2 million and ($0.4) million , respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2016 , 2015 and 2014 , IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member]
Schedule of Common Equity [Line Items]
Common Equity	COMMON EQUITY 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. Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2016 2015 2014 Shares outstanding, January 1 226,918,432 221,871,360 221,887,338 At-the-market offering program — 4,373,234 — Shareowner Direct Plan issuances 732,814 606,010 — Equity-based compensation plans ( Note 12(b) ) 22,408 112,756 71,094 Other — (44,928 ) (87,072 ) Shares outstanding, December 31 227,673,654 226,918,432 221,871,360 At December 31, 2016 , Alliant Energy had a total of 11.3 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Program - In 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this 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. This at-the-market offering program expired in 2016. Shareowner Direct Plan - Beginning in 2015, Alliant Energy satisfied its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy has established an amended and restated Shareowner Rights Agreement. The rights under this agreement will only become exercisable if a person or group has acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. Each right will initially entitle registered shareowners to purchase from Alliant Energy one-quarter of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $55.00 per full share, subject to adjustment. If any shareowner acquires 15% or more of the outstanding common stock of Alliant Energy, each right (subject to limitations) will entitle its holder to purchase, at the right’s then current exercise price, a number of common shares of Alliant Energy or of the acquirer having a market value at the time of twice the right’s per full share exercise price. Alliant Energy’s Board of Directors is authorized to reduce the 15% ownership threshold to not less than 10% . The amended and restated Shareowner Rights Agreement expires in December 2018. Alliant Energy currently has no intention to redeem the Shareowner Rights Agreement and plans to allow it to naturally expire at the end of the term. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2016 , IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2016 . Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $618 million . If IPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with IPL’s rate cases) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $126 million in 2017 and $140 million in 2018 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 51.00% for 2017 or 2018. As of December 31, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $126 million for 2017 . Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 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 $1.6 billion for each. Comprehensive Income - In 2016 , 2015 and 2014 , Alliant Energy’s other comprehensive income (loss) was $0 , $0.2 million and ($0.4) million , respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2016 , 2015 and 2014 , IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member]
Schedule of Common Equity [Line Items]
Common Equity	COMMON EQUITY 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. Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2016 2015 2014 Shares outstanding, January 1 226,918,432 221,871,360 221,887,338 At-the-market offering program — 4,373,234 — Shareowner Direct Plan issuances 732,814 606,010 — Equity-based compensation plans ( Note 12(b) ) 22,408 112,756 71,094 Other — (44,928 ) (87,072 ) Shares outstanding, December 31 227,673,654 226,918,432 221,871,360 At December 31, 2016 , Alliant Energy had a total of 11.3 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Program - In 2015, Alliant Energy filed a prospectus supplement under which it may sell up to $150 million of its common stock through an at-the-market offering program. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this 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. This at-the-market offering program expired in 2016. Shareowner Direct Plan - Beginning in 2015, Alliant Energy satisfied its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy has established an amended and restated Shareowner Rights Agreement. The rights under this agreement will only become exercisable if a person or group has acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. Each right will initially entitle registered shareowners to purchase from Alliant Energy one-quarter of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $55.00 per full share, subject to adjustment. If any shareowner acquires 15% or more of the outstanding common stock of Alliant Energy, each right (subject to limitations) will entitle its holder to purchase, at the right’s then current exercise price, a number of common shares of Alliant Energy or of the acquirer having a market value at the time of twice the right’s per full share exercise price. Alliant Energy’s Board of Directors is authorized to reduce the 15% ownership threshold to not less than 10% . The amended and restated Shareowner Rights Agreement expires in December 2018. Alliant Energy currently has no intention to redeem the Shareowner Rights Agreement and plans to allow it to naturally expire at the end of the term. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2016 , IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2016 . Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2016 , IPL’s amount of retained earnings that were free of dividend restrictions was $618 million . If IPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with IPL’s rate cases) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $126 million in 2017 and $140 million in 2018 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 51.00% for 2017 or 2018. As of December 31, 2016 , WPL’s amount of retained earnings that were free of dividend restrictions was $126 million for 2017 . Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 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 $1.6 billion for each. Comprehensive Income - In 2016 , 2015 and 2014 , Alliant Energy’s other comprehensive income (loss) was $0 , $0.2 million and ($0.4) million , respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2016 , 2015 and 2014 , IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

Redeemable Preferred Stock

Redeemable Preferred Stock	12 Months Ended
	Dec. 31, 2016
Redeemable Preferred Stock	REDEEMABLE PREFERRED STOCK IPL is authorized to issue up to 16,000,000 shares of cumulative preferred stock in aggregate. Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Series Liquidation Preference/Stated Value Shares Authorized Shares Outstanding 2016 2015 (in millions) 5.1% $25 8,000,000 8,000,000 $200.0 $200.0 On or after March 15, 2018, IPL may, at its option, redeem the 5.1% cumulative preferred stock for cash at a redemption price of $25 per share plus accrued and unpaid dividends up to the redemption date. The current articles of incorporation of IPL contain a provision that grants the holders of its cumulative preferred stock voting rights to elect two members of IPL’s Board of Directors if preferred dividends equal to six or more quarterly dividend requirements (whether or not consecutive) are in arrears. Such voting rights would not provide the holders of IPL’s preferred stock control of the decision on redemption of IPL’s preferred stock and could not force IPL to exercise its call option. Therefore, IPL’s cumulative preferred stock is presented in total equity on Alliant Energy’s and IPL’s balance sheets in a manner consistent with noncontrolling interests. Refer to Note 14 for information on the fair value of cumulative preferred stock.
IPL [Member]
Redeemable Preferred Stock	REDEEMABLE PREFERRED STOCK IPL is authorized to issue up to 16,000,000 shares of cumulative preferred stock in aggregate. Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Series Liquidation Preference/Stated Value Shares Authorized Shares Outstanding 2016 2015 (in millions) 5.1% $25 8,000,000 8,000,000 $200.0 $200.0 On or after March 15, 2018, IPL may, at its option, redeem the 5.1% cumulative preferred stock for cash at a redemption price of $25 per share plus accrued and unpaid dividends up to the redemption date. The current articles of incorporation of IPL contain a provision that grants the holders of its cumulative preferred stock voting rights to elect two members of IPL’s Board of Directors if preferred dividends equal to six or more quarterly dividend requirements (whether or not consecutive) are in arrears. Such voting rights would not provide the holders of IPL’s preferred stock control of the decision on redemption of IPL’s preferred stock and could not force IPL to exercise its call option. Therefore, IPL’s cumulative preferred stock is presented in total equity on Alliant Energy’s and IPL’s balance sheets in a manner consistent with noncontrolling interests. Refer to Note 14 for information on the fair value of cumulative preferred stock.

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Instrument [Line Items]
Debt	DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2016 , Alliant Energy’s short-term borrowing arrangements included three revolving credit facilities totaling $1 billion ( $300 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL), which expire in December 2018. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3% Financial Covenants - The credit facility agreements and AEF’s term loan credit agreement each contain a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facilities and term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49% The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Debt Maturities - At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8 Fair Value of Long-term Debt - Refer to Note 14 for information on the fair value of long-term debt outstanding.
IPL [Member]
Debt Instrument [Line Items]
Debt	DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2016 , Alliant Energy’s short-term borrowing arrangements included three revolving credit facilities totaling $1 billion ( $300 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL), which expire in December 2018. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3% Financial Covenants - The credit facility agreements and AEF’s term loan credit agreement each contain a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facilities and term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49% The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Debt Maturities - At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8 Fair Value of Long-term Debt - Refer to Note 14 for information on the fair value of long-term debt outstanding.
WPL [Member]
Debt Instrument [Line Items]
Debt	DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2016 , Alliant Energy’s short-term borrowing arrangements included three revolving credit facilities totaling $1 billion ( $300 million for Alliant Energy at the parent company level, $300 million for IPL and $400 million for WPL), which expire in December 2018. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3% Financial Covenants - The credit facility agreements and AEF’s term loan credit agreement each contain a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facilities and term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49% The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt. Five-Year Schedule of Debt Maturities - At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8 Fair Value of Long-term Debt - Refer to Note 14 for information on the fair value of long-term debt outstanding.

Leases

Leases	12 Months Ended
	Dec. 31, 2016
Leases	LEASES (a) Operating Leases - Various agreements have been entered into related to property, plant and equipment rights that are accounted for as operating leases. In 2016 , 2015 and 2014 , rental expenses associated with operating leases were not material. At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7
IPL [Member]
Leases	LEASES (a) Operating Leases - Various agreements have been entered into related to property, plant and equipment rights that are accounted for as operating leases. In 2016 , 2015 and 2014 , rental expenses associated with operating leases were not material. At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7
WPL [Member]
Leases	LEASES (a) Operating Leases - Various agreements have been entered into related to property, plant and equipment rights that are accounted for as operating leases. In 2016 , 2015 and 2014 , rental expenses associated with operating leases were not material. At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7 (b) Capital Leases - WPL - In 2005, WPL entered into a 20 -year agreement with AEF’s Non-regulated Generation business to lease Sheboygan Falls, with an option for two lease renewal periods thereafter. The lease became effective in 2005 when Sheboygan Falls began commercial operation. WPL is responsible for the operation of Sheboygan Falls and has exclusive rights to its output, and the PSCW approved this affiliated lease agreement in 2005. The capital lease asset is amortized using the straight-line method over the 20 -year lease term. WPL’s retail and wholesale rates include recovery of the Sheboygan Falls lease payments. Sheboygan Falls lease expenses were included in WPL’s income statements as follows (in millions): 2016 2015 2014 Interest expense $9.3 $9.9 $10.4 Depreciation and amortization 6.2 6.2 6.2 $15.5 $16.1 $16.6 At December 31, 2016 , WPL’s estimated future minimum capital lease payments for Sheboygan Falls were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Sheboygan Falls $15 $15 $15 $15 $15 $53 $128 $44 $84

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax [Line Items]
Income Taxes	INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 % Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ( $100 million for IPL and $200 million for WPL). Carryforwards - At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113 Uncertain Tax Positions - At December 31, 2016 , 2015 and 2014 , there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2016 , no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
IPL [Member]
Income Tax [Line Items]
Income Taxes	INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 % Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ( $100 million for IPL and $200 million for WPL). Carryforwards - At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113 Uncertain Tax Positions - At December 31, 2016 , 2015 and 2014 , there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2016 , no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
WPL [Member]
Income Tax [Line Items]
Income Taxes	INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 % Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ( $100 million for IPL and $200 million for WPL). Carryforwards - At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113 Uncertain Tax Positions - At December 31, 2016 , 2015 and 2014 , there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2016 , no material changes to unrecognized tax benefits are expected during the next 12 months. Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2016
Benefit Plans	BENEFIT PLANS (a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. In IPL’s and WPL’s tables below, the defined benefit pension plans amounts represent those respective amounts 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 amounts represent respective amounts 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. Assumptions - The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Expected rate of return on plan assets - The expected rate of return on plan assets is determined by analysis of projected asset class returns based on the target asset class allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are reviewed to support the expected rate of return on plan assets assumption. Refer to “Investment Policy and Strategy for Plan Assets” below for additional information related to investment policy, and strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption was updated to utilize mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015 and 2016. Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4 Benefit Plan Assets and Obligations - A reconciliation of the funded status of Alliant Energy’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on Alliant Energy’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $1,206.3 $1,301.5 $221.4 $231.1 Service cost 12.6 15.9 5.3 5.5 Interest cost 53.0 53.6 9.4 9.1 Plan participants’ contributions — — 2.4 3.1 Plan amendments — — — (0.3 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 48.3 (70.1 ) (0.3 ) (9.4 ) Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Net benefit obligation at December 31 1,244.3 1,206.3 220.1 221.4 Change in plan assets: Fair value of plan assets at January 1 895.0 1,018.1 106.9 121.6 Actual return on plan assets 74.3 (30.2 ) 8.2 (4.9 ) Employer contributions 2.3 2.2 6.4 4.8 Plan participants’ contributions — — 2.4 3.1 Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Fair value of plan assets at December 31 895.7 895.0 105.8 106.9 Under funded status at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.2 $3.0 Other current liabilities (6.5 ) (2.6 ) (8.6 ) (6.2 ) Pension and other benefit obligations (342.1 ) (308.7 ) (108.9 ) (111.3 ) Net amounts recognized at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: Net actuarial loss $535.1 $533.1 $52.6 $59.8 Prior service credit (6.9 ) (7.2 ) (1.5 ) (5.6 ) $528.2 $525.9 $51.1 $54.2 A reconciliation of the funded status of IPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on IPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $556.1 $603.1 $91.3 $96.4 Service cost 7.5 8.8 2.3 2.4 Interest cost 24.5 25.0 3.8 3.8 Plan participants’ contributions — — 0.9 1.0 Plan amendments — — — (0.1 ) Actuarial (gain) loss 19.1 (32.3 ) (0.7 ) (4.6 ) Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Net benefit obligation at December 31 570.4 556.1 90.1 91.3 Change in plan assets: Fair value of plan assets at January 1 422.7 484.7 69.2 78.7 Actual return on plan assets 35.3 (14.3 ) 5.3 (3.1 ) Employer contributions 0.8 0.8 0.3 0.2 Plan participants’ contributions — — 0.9 1.0 Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Fair value of plan assets at December 31 422.0 422.7 68.2 69.2 Under funded status at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $0.4 $— Other current liabilities (0.7 ) (0.8 ) (1.9 ) — Pension and other benefit obligations (147.7 ) (132.6 ) (20.4 ) (22.1 ) Net amounts recognized at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $233.6 $235.5 $25.4 $29.8 Prior service credit (2.3 ) (2.5 ) — (2.7 ) $231.3 $233.0 $25.4 $27.1 A reconciliation of the funded status of WPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on WPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $505.9 $547.6 $89.7 $94.0 Service cost 4.9 5.8 2.0 2.1 Interest cost 22.3 22.6 3.8 3.7 Plan participants’ contributions — — 1.2 1.6 Plan amendments — — — (0.2 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 25.7 (30.0 ) 0.5 (3.5 ) Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Net benefit obligation at December 31 529.2 505.9 88.9 89.7 Change in plan assets: Fair value of plan assets at January 1 386.8 440.3 18.7 21.8 Actual return on plan assets 32.4 (13.0 ) 1.2 (1.1 ) Employer contributions 0.1 0.1 5.8 4.4 Plan participants’ contributions — — 1.2 1.6 Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Fair value of plan assets at December 31 389.7 386.8 18.6 18.7 Under funded status at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $2.7 $3.0 Other current liabilities (0.1 ) (0.1 ) (6.4 ) (6.0 ) Pension and other benefit obligations (139.4 ) (119.0 ) (66.6 ) (68.0 ) Net amounts recognized at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $236.1 $232.1 $21.5 $23.3 Prior service credit (1.4 ) (1.2 ) (1.5 ) (2.4 ) $234.7 $230.9 $20.0 $20.9 Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8 Investment Policy and Strategy for Plan Assets - Investment policies and strategies employed with respect to assets of defined benefit pension and OPEB plans are to combine both preservation of principal and prudent and reasonable risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. It is recognized that risk and volatility are present with all types of investments. However, risk is mitigated at the total fund level through diversification by asset class including U.S. and international equity and fixed income exposure, global asset and risk parity strategies, the number of individual investments, and sector and industry limits. Global asset and risk parity strategies include investments in global equity, global debt, commodities and currencies. Defined Benefit Pension Plan Assets - For assets of defined benefit pension plans, the mix among asset classes is controlled by asset allocation targets. Historical performance results and future expectations suggest that equity securities will provide higher total investment returns than debt securities over a long-term investment horizon. Consistent with the goals of meeting obligations to plan participants and minimizing benefit costs over the long-term, the defined benefit pension plans have a long-term investment posture more heavily weighted towards equity holdings. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investment vehicles include, but may not be limited to, direct ownership of real estate, margin trading, oil and gas limited partnerships and securities of the managers’ firms or affiliate firms. At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30% Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. The investment policy and strategy of the 401(h) assets, except for the WPL 401(h) assets, mirrors those of the defined benefit pension plans, which are discussed above. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is controlled by allocation targets. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. Mutual funds are used to achieve the desired diversification. At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46% Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 14 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, treasury bills and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include fixed income securities consisting of corporate and government bonds and agency obligations, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included in the tables below to reconcile the fair value hierarchy to the respective total plan assets. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $30.4 $5.0 $25.4 $— $23.1 $— $23.1 $— Equity securities - domestic 183.6 183.6 — — 116.4 116.4 — — Equity securities - international 97.4 97.4 — — 93.9 93.9 — — Global asset allocation securities 53.0 53.0 — — 52.9 52.9 — — Fixed income securities 125.4 53.6 71.8 — — — — — Total assets in fair value hierarchy 489.8 $392.6 $97.2 $— 286.3 $263.2 $23.1 $— Assets measured at net asset value 405.9 608.5 Accrued investment income 1.1 0.2 Due to brokers, net (pending trades with brokers) (1.1 ) — Total pension plan assets $895.7 $895.0 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $14.4 $2.4 $12.0 $— $10.9 $— $10.9 $— Equity securities - domestic 86.5 86.5 — — 54.9 54.9 — — Equity securities - international 45.9 45.9 — — 44.4 44.4 — — Global asset allocation securities 24.9 24.9 — — 25.0 25.0 — — Fixed income securities 59.1 25.3 33.8 — — — — — Total assets in fair value hierarchy 230.8 $185.0 $45.8 $— 135.2 $124.3 $10.9 $— Assets measured at net asset value 191.2 287.4 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $422.0 $422.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $13.3 $2.2 $11.1 $— $10.0 $— $10.0 $— Equity securities - domestic 79.9 79.9 — — 50.3 50.3 — — Equity securities - international 42.4 42.4 — — 40.6 40.6 — — Global asset allocation securities 23.0 23.0 — — 22.8 22.8 — — Fixed income securities 54.5 23.3 31.2 — — — — — Total assets in fair value hierarchy 213.1 $170.8 $42.3 $— 123.7 $113.7 $10.0 $— Assets measured at net asset value 176.6 263.0 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $389.7 $386.8 At December 31, the fair values of Alliant Energy’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.5 $2.0 $1.5 $— $3.6 $— $3.6 $— Equity securities - domestic 22.5 22.5 — — 22.1 22.1 — — Equity securities - international 13.5 13.5 — — 13.4 13.4 — — Global asset allocation securities 16.5 16.5 — — 16.0 16.0 — — Fixed income securities 46.8 46.2 0.6 — 46.3 46.3 — — Total assets in fair value hierarchy 102.8 $100.7 $2.1 $— 101.4 $97.8 $3.6 $— Assets measured at net asset value 3.0 5.5 Total OPEB plan assets $105.8 $106.9 At December 31, the fair values of IPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.8 $0.8 $— $— $0.9 $— $0.9 $— Equity securities - domestic 17.0 17.0 — — 16.7 16.7 — — Equity securities - international 11.0 11.0 — — 10.8 10.8 — — Global asset allocation securities 7.0 7.0 — — 6.9 6.9 — — Fixed income securities 32.4 32.4 — — 33.3 33.3 — — Total assets in fair value hierarchy 68.2 $68.2 $— $— 68.6 $67.7 $0.9 $— Assets measured at net asset value — 0.6 Total OPEB plan assets $68.2 $69.2 At December 31, the fair values of WPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.0 $0.7 $1.3 $— $2.3 $— $2.3 $— Global asset allocation securities 5.5 5.5 — — 5.4 5.4 — — Fixed income securities 11.1 11.1 — — 11.0 11.0 — — Total OPEB plan assets $18.6 $17.3 $1.3 $— $18.7 $16.4 $2.3 $— For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2016 and 2015 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 12.6% and 11.6% of total assets in the 401(k) savings plans at December 31, 2016 and 2015 , respectively. Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5 Voluntary Employee Separation Charges - In 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 2015. (b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 7 . In 2015, Alliant Energy’s shareowners approved the Amended and Restated OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2016 , performance shares, performance-contingent restricted stock and restricted stock units (performance- and time-based) were outstanding under the Amended and Restated OIP, and 7.4 million shares of Alliant Energy’s common stock remained available for grants under the Amended and Restated OIP. Alliant Energy satisfies share payouts related to equity awards under the Amended and Restated OIP through the issuance of new shares of its common stock. Alliant Energy also has the DLIP, which permits the grant of cash-based long-term performance-based awards, including performance units, restricted cash awards and restricted units, to certain key employees. At December 31, 2016 , performance units, performance-contingent cash awards and restricted units (performance- and time-based) were outstanding under the DLIP. There is no limit to the number of grants that can be made under the DLIP and Alliant Energy satisfies all payouts under the DLIP through cash payments. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6 As of December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $5.0 million , $2.7 million and $2.2 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - Payouts of performance shares under the Amended and Restated OIP and performance units under the DLIP to key employees are contingent upon achievement over three -year periods of specified performance criteria, which currently include metrics of total shareowner return relative to an investor-owned utility peer group. Performance shares can be paid out in shares of Alliant Energy’s common stock, cash or a combination of cash and stock. Performance units must be paid out in cash. Alliant Energy assumes it will make future payouts of its performance shares and performance units in cash; therefore, performance shares and performance units are accounted for as liability awards. 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 2014 2016 2015 2014 Nonvested awards, January 1 288,430 288,848 279,880 116,412 127,330 131,824 Granted 68,585 90,806 102,442 23,918 35,674 40,844 Vested (98,186 ) (91,224 ) (90,470 ) (42,760 ) (45,690 ) (41,502 ) Forfeited (1,230 ) — (3,004 ) (4,250 ) (902 ) (3,836 ) Nonvested awards, December 31 257,599 288,430 288,848 93,320 116,412 127,330 Granted Awards - Each performance share’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2016, the value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2015 and 2014, each performance 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. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. 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 - 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 2014 2016 2015 2014 2013 Grant 2012 Grant 2011 Grant 2013 Grant 2012 Grant 2011 Grant Performance awards vested 98,186 91,224 90,470 42,760 45,690 41,502 Percentage of target number of performance awards 165.0% 167.5% 147.5% 165.0% 167.5% 147.5% Aggregate payout value (in millions) $5.1 $5.1 $3.4 $1.7 $1.6 $1.2 Payout - cash (in millions) $2.9 $3.2 $2.9 $1.7 $1.6 $1.2 Payout - common stock shares issued 22,408 21,950 9,620 N/A N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at December 31, 2016 , by year of grant, were as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards at target 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on December 30, 2016 $37.89 $37.89 $37.89 $37.89 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 135 % 155 % 148 % 135 % 155 % 148 % Fair values of each nonvested award $51.15 $58.73 $56.08 $51.15 $50.45 $39.80 Performance-Contingent Restricted Stock - Vesting of performance-contingent restricted stock grants is based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations). If performance targets are not met within the performance period, which currently ranges from two to four years, these restricted stock grants are forfeited. The fair value of performance-contingent restricted stock is based on the closing market price on the grant date. A summary of the performance-contingent restricted stock activity was as follows: 2016 2015 2014 Weighted Average Weighted Average Weighted Average Shares Grant Date Fair Value Shares Grant Date Fair Value Shares Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 317,844 $21.36 Granted — — 90,806 32.55 102,442 26.89 Vested (a) — — (98,186 ) 23.79 (181,694 ) 20.46 Forfeited (b) — — — — (40,968 ) 19.93 Nonvested shares, December 31 190,244 29.59 190,244 29.59 197,624 25.
IPL [Member]
Benefit Plans	BENEFIT PLANS (a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. In IPL’s and WPL’s tables below, the defined benefit pension plans amounts represent those respective amounts 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 amounts represent respective amounts 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. Assumptions - The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Expected rate of return on plan assets - The expected rate of return on plan assets is determined by analysis of projected asset class returns based on the target asset class allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are reviewed to support the expected rate of return on plan assets assumption. Refer to “Investment Policy and Strategy for Plan Assets” below for additional information related to investment policy, and strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption was updated to utilize mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015 and 2016. Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4 Benefit Plan Assets and Obligations - A reconciliation of the funded status of Alliant Energy’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on Alliant Energy’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $1,206.3 $1,301.5 $221.4 $231.1 Service cost 12.6 15.9 5.3 5.5 Interest cost 53.0 53.6 9.4 9.1 Plan participants’ contributions — — 2.4 3.1 Plan amendments — — — (0.3 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 48.3 (70.1 ) (0.3 ) (9.4 ) Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Net benefit obligation at December 31 1,244.3 1,206.3 220.1 221.4 Change in plan assets: Fair value of plan assets at January 1 895.0 1,018.1 106.9 121.6 Actual return on plan assets 74.3 (30.2 ) 8.2 (4.9 ) Employer contributions 2.3 2.2 6.4 4.8 Plan participants’ contributions — — 2.4 3.1 Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Fair value of plan assets at December 31 895.7 895.0 105.8 106.9 Under funded status at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.2 $3.0 Other current liabilities (6.5 ) (2.6 ) (8.6 ) (6.2 ) Pension and other benefit obligations (342.1 ) (308.7 ) (108.9 ) (111.3 ) Net amounts recognized at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: Net actuarial loss $535.1 $533.1 $52.6 $59.8 Prior service credit (6.9 ) (7.2 ) (1.5 ) (5.6 ) $528.2 $525.9 $51.1 $54.2 A reconciliation of the funded status of IPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on IPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $556.1 $603.1 $91.3 $96.4 Service cost 7.5 8.8 2.3 2.4 Interest cost 24.5 25.0 3.8 3.8 Plan participants’ contributions — — 0.9 1.0 Plan amendments — — — (0.1 ) Actuarial (gain) loss 19.1 (32.3 ) (0.7 ) (4.6 ) Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Net benefit obligation at December 31 570.4 556.1 90.1 91.3 Change in plan assets: Fair value of plan assets at January 1 422.7 484.7 69.2 78.7 Actual return on plan assets 35.3 (14.3 ) 5.3 (3.1 ) Employer contributions 0.8 0.8 0.3 0.2 Plan participants’ contributions — — 0.9 1.0 Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Fair value of plan assets at December 31 422.0 422.7 68.2 69.2 Under funded status at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $0.4 $— Other current liabilities (0.7 ) (0.8 ) (1.9 ) — Pension and other benefit obligations (147.7 ) (132.6 ) (20.4 ) (22.1 ) Net amounts recognized at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $233.6 $235.5 $25.4 $29.8 Prior service credit (2.3 ) (2.5 ) — (2.7 ) $231.3 $233.0 $25.4 $27.1 A reconciliation of the funded status of WPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on WPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $505.9 $547.6 $89.7 $94.0 Service cost 4.9 5.8 2.0 2.1 Interest cost 22.3 22.6 3.8 3.7 Plan participants’ contributions — — 1.2 1.6 Plan amendments — — — (0.2 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 25.7 (30.0 ) 0.5 (3.5 ) Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Net benefit obligation at December 31 529.2 505.9 88.9 89.7 Change in plan assets: Fair value of plan assets at January 1 386.8 440.3 18.7 21.8 Actual return on plan assets 32.4 (13.0 ) 1.2 (1.1 ) Employer contributions 0.1 0.1 5.8 4.4 Plan participants’ contributions — — 1.2 1.6 Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Fair value of plan assets at December 31 389.7 386.8 18.6 18.7 Under funded status at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $2.7 $3.0 Other current liabilities (0.1 ) (0.1 ) (6.4 ) (6.0 ) Pension and other benefit obligations (139.4 ) (119.0 ) (66.6 ) (68.0 ) Net amounts recognized at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $236.1 $232.1 $21.5 $23.3 Prior service credit (1.4 ) (1.2 ) (1.5 ) (2.4 ) $234.7 $230.9 $20.0 $20.9 Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8 Investment Policy and Strategy for Plan Assets - Investment policies and strategies employed with respect to assets of defined benefit pension and OPEB plans are to combine both preservation of principal and prudent and reasonable risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. It is recognized that risk and volatility are present with all types of investments. However, risk is mitigated at the total fund level through diversification by asset class including U.S. and international equity and fixed income exposure, global asset and risk parity strategies, the number of individual investments, and sector and industry limits. Global asset and risk parity strategies include investments in global equity, global debt, commodities and currencies. Defined Benefit Pension Plan Assets - For assets of defined benefit pension plans, the mix among asset classes is controlled by asset allocation targets. Historical performance results and future expectations suggest that equity securities will provide higher total investment returns than debt securities over a long-term investment horizon. Consistent with the goals of meeting obligations to plan participants and minimizing benefit costs over the long-term, the defined benefit pension plans have a long-term investment posture more heavily weighted towards equity holdings. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investment vehicles include, but may not be limited to, direct ownership of real estate, margin trading, oil and gas limited partnerships and securities of the managers’ firms or affiliate firms. At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30% Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. The investment policy and strategy of the 401(h) assets, except for the WPL 401(h) assets, mirrors those of the defined benefit pension plans, which are discussed above. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is controlled by allocation targets. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. Mutual funds are used to achieve the desired diversification. At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46% Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 14 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, treasury bills and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include fixed income securities consisting of corporate and government bonds and agency obligations, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included in the tables below to reconcile the fair value hierarchy to the respective total plan assets. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $30.4 $5.0 $25.4 $— $23.1 $— $23.1 $— Equity securities - domestic 183.6 183.6 — — 116.4 116.4 — — Equity securities - international 97.4 97.4 — — 93.9 93.9 — — Global asset allocation securities 53.0 53.0 — — 52.9 52.9 — — Fixed income securities 125.4 53.6 71.8 — — — — — Total assets in fair value hierarchy 489.8 $392.6 $97.2 $— 286.3 $263.2 $23.1 $— Assets measured at net asset value 405.9 608.5 Accrued investment income 1.1 0.2 Due to brokers, net (pending trades with brokers) (1.1 ) — Total pension plan assets $895.7 $895.0 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $14.4 $2.4 $12.0 $— $10.9 $— $10.9 $— Equity securities - domestic 86.5 86.5 — — 54.9 54.9 — — Equity securities - international 45.9 45.9 — — 44.4 44.4 — — Global asset allocation securities 24.9 24.9 — — 25.0 25.0 — — Fixed income securities 59.1 25.3 33.8 — — — — — Total assets in fair value hierarchy 230.8 $185.0 $45.8 $— 135.2 $124.3 $10.9 $— Assets measured at net asset value 191.2 287.4 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $422.0 $422.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $13.3 $2.2 $11.1 $— $10.0 $— $10.0 $— Equity securities - domestic 79.9 79.9 — — 50.3 50.3 — — Equity securities - international 42.4 42.4 — — 40.6 40.6 — — Global asset allocation securities 23.0 23.0 — — 22.8 22.8 — — Fixed income securities 54.5 23.3 31.2 — — — — — Total assets in fair value hierarchy 213.1 $170.8 $42.3 $— 123.7 $113.7 $10.0 $— Assets measured at net asset value 176.6 263.0 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $389.7 $386.8 At December 31, the fair values of Alliant Energy’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.5 $2.0 $1.5 $— $3.6 $— $3.6 $— Equity securities - domestic 22.5 22.5 — — 22.1 22.1 — — Equity securities - international 13.5 13.5 — — 13.4 13.4 — — Global asset allocation securities 16.5 16.5 — — 16.0 16.0 — — Fixed income securities 46.8 46.2 0.6 — 46.3 46.3 — — Total assets in fair value hierarchy 102.8 $100.7 $2.1 $— 101.4 $97.8 $3.6 $— Assets measured at net asset value 3.0 5.5 Total OPEB plan assets $105.8 $106.9 At December 31, the fair values of IPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.8 $0.8 $— $— $0.9 $— $0.9 $— Equity securities - domestic 17.0 17.0 — — 16.7 16.7 — — Equity securities - international 11.0 11.0 — — 10.8 10.8 — — Global asset allocation securities 7.0 7.0 — — 6.9 6.9 — — Fixed income securities 32.4 32.4 — — 33.3 33.3 — — Total assets in fair value hierarchy 68.2 $68.2 $— $— 68.6 $67.7 $0.9 $— Assets measured at net asset value — 0.6 Total OPEB plan assets $68.2 $69.2 At December 31, the fair values of WPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.0 $0.7 $1.3 $— $2.3 $— $2.3 $— Global asset allocation securities 5.5 5.5 — — 5.4 5.4 — — Fixed income securities 11.1 11.1 — — 11.0 11.0 — — Total OPEB plan assets $18.6 $17.3 $1.3 $— $18.7 $16.4 $2.3 $— For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2016 and 2015 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 12.6% and 11.6% of total assets in the 401(k) savings plans at December 31, 2016 and 2015 , respectively. Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5 Voluntary Employee Separation Charges - In 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 2015. (b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 7 . In 2015, Alliant Energy’s shareowners approved the Amended and Restated OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2016 , performance shares, performance-contingent restricted stock and restricted stock units (performance- and time-based) were outstanding under the Amended and Restated OIP, and 7.4 million shares of Alliant Energy’s common stock remained available for grants under the Amended and Restated OIP. Alliant Energy satisfies share payouts related to equity awards under the Amended and Restated OIP through the issuance of new shares of its common stock. Alliant Energy also has the DLIP, which permits the grant of cash-based long-term performance-based awards, including performance units, restricted cash awards and restricted units, to certain key employees. At December 31, 2016 , performance units, performance-contingent cash awards and restricted units (performance- and time-based) were outstanding under the DLIP. There is no limit to the number of grants that can be made under the DLIP and Alliant Energy satisfies all payouts under the DLIP through cash payments. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6 As of December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $5.0 million , $2.7 million and $2.2 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - Payouts of performance shares under the Amended and Restated OIP and performance units under the DLIP to key employees are contingent upon achievement over three -year periods of specified performance criteria, which currently include metrics of total shareowner return relative to an investor-owned utility peer group. Performance shares can be paid out in shares of Alliant Energy’s common stock, cash or a combination of cash and stock. Performance units must be paid out in cash. Alliant Energy assumes it will make future payouts of its performance shares and performance units in cash; therefore, performance shares and performance units are accounted for as liability awards. 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 2014 2016 2015 2014 Nonvested awards, January 1 288,430 288,848 279,880 116,412 127,330 131,824 Granted 68,585 90,806 102,442 23,918 35,674 40,844 Vested (98,186 ) (91,224 ) (90,470 ) (42,760 ) (45,690 ) (41,502 ) Forfeited (1,230 ) — (3,004 ) (4,250 ) (902 ) (3,836 ) Nonvested awards, December 31 257,599 288,430 288,848 93,320 116,412 127,330 Granted Awards - Each performance share’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2016, the value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2015 and 2014, each performance 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. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. 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 - 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 2014 2016 2015 2014 2013 Grant 2012 Grant 2011 Grant 2013 Grant 2012 Grant 2011 Grant Performance awards vested 98,186 91,224 90,470 42,760 45,690 41,502 Percentage of target number of performance awards 165.0% 167.5% 147.5% 165.0% 167.5% 147.5% Aggregate payout value (in millions) $5.1 $5.1 $3.4 $1.7 $1.6 $1.2 Payout - cash (in millions) $2.9 $3.2 $2.9 $1.7 $1.6 $1.2 Payout - common stock shares issued 22,408 21,950 9,620 N/A N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at December 31, 2016 , by year of grant, were as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards at target 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on December 30, 2016 $37.89 $37.89 $37.89 $37.89 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 135 % 155 % 148 % 135 % 155 % 148 % Fair values of each nonvested award $51.15 $58.73 $56.08 $51.15 $50.45 $39.80 Performance-Contingent Restricted Stock - Vesting of performance-contingent restricted stock grants is based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations). If performance targets are not met within the performance period, which currently ranges from two to four years, these restricted stock grants are forfeited. The fair value of performance-contingent restricted stock is based on the closing market price on the grant date. A summary of the performance-contingent restricted stock activity was as follows: 2016 2015 2014 Weighted Average Weighted Average Weighted Average Shares Grant Date Fair Value Shares Grant Date Fair Value Shares Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 317,844 $21.36 Granted — — 90,806 32.55 102,442 26.89 Vested (a) — — (98,186 ) 23.79 (181,694 ) 20.46 Forfeited (b) — — — — (40,968 ) 19.93 Nonvested shares, December 31 190,244 29.59 190,244 29.59 197,624 25.
WPL [Member]
Benefit Plans	BENEFIT PLANS (a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. In IPL’s and WPL’s tables below, the defined benefit pension plans amounts represent those respective amounts 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 amounts represent respective amounts 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. Assumptions - The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Expected rate of return on plan assets - The expected rate of return on plan assets is determined by analysis of projected asset class returns based on the target asset class allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are reviewed to support the expected rate of return on plan assets assumption. Refer to “Investment Policy and Strategy for Plan Assets” below for additional information related to investment policy, and strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption was updated to utilize mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015 and 2016. Net Periodic Benefit Costs (Credits) - The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4 Benefit Plan Assets and Obligations - A reconciliation of the funded status of Alliant Energy’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on Alliant Energy’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $1,206.3 $1,301.5 $221.4 $231.1 Service cost 12.6 15.9 5.3 5.5 Interest cost 53.0 53.6 9.4 9.1 Plan participants’ contributions — — 2.4 3.1 Plan amendments — — — (0.3 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 48.3 (70.1 ) (0.3 ) (9.4 ) Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Net benefit obligation at December 31 1,244.3 1,206.3 220.1 221.4 Change in plan assets: Fair value of plan assets at January 1 895.0 1,018.1 106.9 121.6 Actual return on plan assets 74.3 (30.2 ) 8.2 (4.9 ) Employer contributions 2.3 2.2 6.4 4.8 Plan participants’ contributions — — 2.4 3.1 Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Fair value of plan assets at December 31 895.7 895.0 105.8 106.9 Under funded status at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.2 $3.0 Other current liabilities (6.5 ) (2.6 ) (8.6 ) (6.2 ) Pension and other benefit obligations (342.1 ) (308.7 ) (108.9 ) (111.3 ) Net amounts recognized at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: Net actuarial loss $535.1 $533.1 $52.6 $59.8 Prior service credit (6.9 ) (7.2 ) (1.5 ) (5.6 ) $528.2 $525.9 $51.1 $54.2 A reconciliation of the funded status of IPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on IPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $556.1 $603.1 $91.3 $96.4 Service cost 7.5 8.8 2.3 2.4 Interest cost 24.5 25.0 3.8 3.8 Plan participants’ contributions — — 0.9 1.0 Plan amendments — — — (0.1 ) Actuarial (gain) loss 19.1 (32.3 ) (0.7 ) (4.6 ) Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Net benefit obligation at December 31 570.4 556.1 90.1 91.3 Change in plan assets: Fair value of plan assets at January 1 422.7 484.7 69.2 78.7 Actual return on plan assets 35.3 (14.3 ) 5.3 (3.1 ) Employer contributions 0.8 0.8 0.3 0.2 Plan participants’ contributions — — 0.9 1.0 Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Fair value of plan assets at December 31 422.0 422.7 68.2 69.2 Under funded status at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $0.4 $— Other current liabilities (0.7 ) (0.8 ) (1.9 ) — Pension and other benefit obligations (147.7 ) (132.6 ) (20.4 ) (22.1 ) Net amounts recognized at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $233.6 $235.5 $25.4 $29.8 Prior service credit (2.3 ) (2.5 ) — (2.7 ) $231.3 $233.0 $25.4 $27.1 A reconciliation of the funded status of WPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on WPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $505.9 $547.6 $89.7 $94.0 Service cost 4.9 5.8 2.0 2.1 Interest cost 22.3 22.6 3.8 3.7 Plan participants’ contributions — — 1.2 1.6 Plan amendments — — — (0.2 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 25.7 (30.0 ) 0.5 (3.5 ) Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Net benefit obligation at December 31 529.2 505.9 88.9 89.7 Change in plan assets: Fair value of plan assets at January 1 386.8 440.3 18.7 21.8 Actual return on plan assets 32.4 (13.0 ) 1.2 (1.1 ) Employer contributions 0.1 0.1 5.8 4.4 Plan participants’ contributions — — 1.2 1.6 Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Fair value of plan assets at December 31 389.7 386.8 18.6 18.7 Under funded status at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $2.7 $3.0 Other current liabilities (0.1 ) (0.1 ) (6.4 ) (6.0 ) Pension and other benefit obligations (139.4 ) (119.0 ) (66.6 ) (68.0 ) Net amounts recognized at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $236.1 $232.1 $21.5 $23.3 Prior service credit (1.4 ) (1.2 ) (1.5 ) (2.4 ) $234.7 $230.9 $20.0 $20.9 Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8 Investment Policy and Strategy for Plan Assets - Investment policies and strategies employed with respect to assets of defined benefit pension and OPEB plans are to combine both preservation of principal and prudent and reasonable risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. It is recognized that risk and volatility are present with all types of investments. However, risk is mitigated at the total fund level through diversification by asset class including U.S. and international equity and fixed income exposure, global asset and risk parity strategies, the number of individual investments, and sector and industry limits. Global asset and risk parity strategies include investments in global equity, global debt, commodities and currencies. Defined Benefit Pension Plan Assets - For assets of defined benefit pension plans, the mix among asset classes is controlled by asset allocation targets. Historical performance results and future expectations suggest that equity securities will provide higher total investment returns than debt securities over a long-term investment horizon. Consistent with the goals of meeting obligations to plan participants and minimizing benefit costs over the long-term, the defined benefit pension plans have a long-term investment posture more heavily weighted towards equity holdings. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investment vehicles include, but may not be limited to, direct ownership of real estate, margin trading, oil and gas limited partnerships and securities of the managers’ firms or affiliate firms. At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30% Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. The investment policy and strategy of the 401(h) assets, except for the WPL 401(h) assets, mirrors those of the defined benefit pension plans, which are discussed above. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is controlled by allocation targets. The asset allocation is monitored regularly and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. Mutual funds are used to achieve the desired diversification. At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46% Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 14 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, treasury bills and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include fixed income securities consisting of corporate and government bonds and agency obligations, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included in the tables below to reconcile the fair value hierarchy to the respective total plan assets. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $30.4 $5.0 $25.4 $— $23.1 $— $23.1 $— Equity securities - domestic 183.6 183.6 — — 116.4 116.4 — — Equity securities - international 97.4 97.4 — — 93.9 93.9 — — Global asset allocation securities 53.0 53.0 — — 52.9 52.9 — — Fixed income securities 125.4 53.6 71.8 — — — — — Total assets in fair value hierarchy 489.8 $392.6 $97.2 $— 286.3 $263.2 $23.1 $— Assets measured at net asset value 405.9 608.5 Accrued investment income 1.1 0.2 Due to brokers, net (pending trades with brokers) (1.1 ) — Total pension plan assets $895.7 $895.0 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $14.4 $2.4 $12.0 $— $10.9 $— $10.9 $— Equity securities - domestic 86.5 86.5 — — 54.9 54.9 — — Equity securities - international 45.9 45.9 — — 44.4 44.4 — — Global asset allocation securities 24.9 24.9 — — 25.0 25.0 — — Fixed income securities 59.1 25.3 33.8 — — — — — Total assets in fair value hierarchy 230.8 $185.0 $45.8 $— 135.2 $124.3 $10.9 $— Assets measured at net asset value 191.2 287.4 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $422.0 $422.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $13.3 $2.2 $11.1 $— $10.0 $— $10.0 $— Equity securities - domestic 79.9 79.9 — — 50.3 50.3 — — Equity securities - international 42.4 42.4 — — 40.6 40.6 — — Global asset allocation securities 23.0 23.0 — — 22.8 22.8 — — Fixed income securities 54.5 23.3 31.2 — — — — — Total assets in fair value hierarchy 213.1 $170.8 $42.3 $— 123.7 $113.7 $10.0 $— Assets measured at net asset value 176.6 263.0 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $389.7 $386.8 At December 31, the fair values of Alliant Energy’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.5 $2.0 $1.5 $— $3.6 $— $3.6 $— Equity securities - domestic 22.5 22.5 — — 22.1 22.1 — — Equity securities - international 13.5 13.5 — — 13.4 13.4 — — Global asset allocation securities 16.5 16.5 — — 16.0 16.0 — — Fixed income securities 46.8 46.2 0.6 — 46.3 46.3 — — Total assets in fair value hierarchy 102.8 $100.7 $2.1 $— 101.4 $97.8 $3.6 $— Assets measured at net asset value 3.0 5.5 Total OPEB plan assets $105.8 $106.9 At December 31, the fair values of IPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.8 $0.8 $— $— $0.9 $— $0.9 $— Equity securities - domestic 17.0 17.0 — — 16.7 16.7 — — Equity securities - international 11.0 11.0 — — 10.8 10.8 — — Global asset allocation securities 7.0 7.0 — — 6.9 6.9 — — Fixed income securities 32.4 32.4 — — 33.3 33.3 — — Total assets in fair value hierarchy 68.2 $68.2 $— $— 68.6 $67.7 $0.9 $— Assets measured at net asset value — 0.6 Total OPEB plan assets $68.2 $69.2 At December 31, the fair values of WPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.0 $0.7 $1.3 $— $2.3 $— $2.3 $— Global asset allocation securities 5.5 5.5 — — 5.4 5.4 — — Fixed income securities 11.1 11.1 — — 11.0 11.0 — — Total OPEB plan assets $18.6 $17.3 $1.3 $— $18.7 $16.4 $2.3 $— For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2016 and 2015 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 12.6% and 11.6% of total assets in the 401(k) savings plans at December 31, 2016 and 2015 , respectively. Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5 Voluntary Employee Separation Charges - In 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 2015. (b) Equity-based Compensation Plans - All shares, units and awards included below have been adjusted to reflect the common stock split discussed in Note 7 . In 2015, Alliant Energy’s shareowners approved the Amended and Restated OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2016 , performance shares, performance-contingent restricted stock and restricted stock units (performance- and time-based) were outstanding under the Amended and Restated OIP, and 7.4 million shares of Alliant Energy’s common stock remained available for grants under the Amended and Restated OIP. Alliant Energy satisfies share payouts related to equity awards under the Amended and Restated OIP through the issuance of new shares of its common stock. Alliant Energy also has the DLIP, which permits the grant of cash-based long-term performance-based awards, including performance units, restricted cash awards and restricted units, to certain key employees. At December 31, 2016 , performance units, performance-contingent cash awards and restricted units (performance- and time-based) were outstanding under the DLIP. There is no limit to the number of grants that can be made under the DLIP and Alliant Energy satisfies all payouts under the DLIP through cash payments. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6 As of December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $5.0 million , $2.7 million and $2.2 million , respectively, which is expected to be recognized over a weighted average period of between 1 and 2 years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is primarily recorded in “Other operation and maintenance” in the income statements. Performance Shares and Performance Units - Payouts of performance shares under the Amended and Restated OIP and performance units under the DLIP to key employees are contingent upon achievement over three -year periods of specified performance criteria, which currently include metrics of total shareowner return relative to an investor-owned utility peer group. Performance shares can be paid out in shares of Alliant Energy’s common stock, cash or a combination of cash and stock. Performance units must be paid out in cash. Alliant Energy assumes it will make future payouts of its performance shares and performance units in cash; therefore, performance shares and performance units are accounted for as liability awards. 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 2014 2016 2015 2014 Nonvested awards, January 1 288,430 288,848 279,880 116,412 127,330 131,824 Granted 68,585 90,806 102,442 23,918 35,674 40,844 Vested (98,186 ) (91,224 ) (90,470 ) (42,760 ) (45,690 ) (41,502 ) Forfeited (1,230 ) — (3,004 ) (4,250 ) (902 ) (3,836 ) Nonvested awards, December 31 257,599 288,430 288,848 93,320 116,412 127,330 Granted Awards - Each performance share’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2016, the value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2015 and 2014, each performance 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. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. 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 - 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 2014 2016 2015 2014 2013 Grant 2012 Grant 2011 Grant 2013 Grant 2012 Grant 2011 Grant Performance awards vested 98,186 91,224 90,470 42,760 45,690 41,502 Percentage of target number of performance awards 165.0% 167.5% 147.5% 165.0% 167.5% 147.5% Aggregate payout value (in millions) $5.1 $5.1 $3.4 $1.7 $1.6 $1.2 Payout - cash (in millions) $2.9 $3.2 $2.9 $1.7 $1.6 $1.2 Payout - common stock shares issued 22,408 21,950 9,620 N/A N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at December 31, 2016 , by year of grant, were as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards at target 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on December 30, 2016 $37.89 $37.89 $37.89 $37.89 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 135 % 155 % 148 % 135 % 155 % 148 % Fair values of each nonvested award $51.15 $58.73 $56.08 $51.15 $50.45 $39.80 Performance-Contingent Restricted Stock - Vesting of performance-contingent restricted stock grants is based on the achievement of certain performance targets (currently specified growth of consolidated income from continuing operations). If performance targets are not met within the performance period, which currently ranges from two to four years, these restricted stock grants are forfeited. The fair value of performance-contingent restricted stock is based on the closing market price on the grant date. A summary of the performance-contingent restricted stock activity was as follows: 2016 2015 2014 Weighted Average Weighted Average Weighted Average Shares Grant Date Fair Value Shares Grant Date Fair Value Shares Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 317,844 $21.36 Granted — — 90,806 32.55 102,442 26.89 Vested (a) — — (98,186 ) 23.79 (181,694 ) 20.46 Forfeited (b) — — — — (40,968 ) 19.93 Nonvested shares, December 31 190,244 29.59 190,244 29.59 197,624 25.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2016
Schedule of Asset Retirement Obligations [Line Items]
Asset Retirement Obligations (AROs)	ASSET RETIREMENT OBLIGATIONS Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, ash ponds, wind farms, active ash landfills, certain coal yards and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, lead-based paint and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. 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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers. In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Asset Retirement Obligations (AROs)	ASSET RETIREMENT OBLIGATIONS Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, ash ponds, wind farms, active ash landfills, certain coal yards and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, lead-based paint and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. 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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers. In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Asset Retirement Obligations (AROs)	ASSET RETIREMENT OBLIGATIONS Recognized AROs relate to legal obligations for the removal, closure or dismantlement of several assets including, but not limited to, ash ponds, wind farms, active ash landfills, certain coal yards and above ground storage tanks. Recognized AROs also include legal obligations for the management and final disposition of asbestos, lead-based paint and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. 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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers. In addition, certain AROs related to EGU assets have not been recognized. Due to an indeterminate remediation date, the fair values of the AROs for these assets cannot be currently estimated. A liability for these AROs will be recorded when fair value is determinable. Removal costs of these EGUs are being recovered in rates and are recorded in regulatory liabilities.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are 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 options (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 auction prices and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. 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 5(b) 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, and was substantially classified as Level 2. Refer to Note 9(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, and was classified as Level 1. Refer to Note 8 for additional information regarding cumulative preferred stock. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 1,533.9 — 1,793.0 — 1,793.0 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are 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 options (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 auction prices and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. 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 5(b) 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, and was substantially classified as Level 2. Refer to Note 9(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, and was classified as Level 1. Refer to Note 8 for additional information regarding cumulative preferred stock. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 1,533.9 — 1,793.0 — 1,793.0 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. Valuation Techniques - Derivative assets and derivative liabilities - Derivative instruments are 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 options (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 auction prices and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. 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 5(b) 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, and was substantially classified as Level 2. Refer to Note 9(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, and was classified as Level 1. Refer to Note 8 for additional information regarding cumulative preferred stock. Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 1,533.9 — 1,793.0 — 1,793.0 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2016
Derivative [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 14 for detailed discussion of derivative instruments. Notional Amounts - As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4 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. Refer to Note 2 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 December 31, 2016 and 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 December 31, 2016 and 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 [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 14 for detailed discussion of derivative instruments. Notional Amounts - As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4 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. Refer to Note 2 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 December 31, 2016 and 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 December 31, 2016 and 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 [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 14 for detailed discussion of derivative instruments. Notional Amounts - As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4 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. Refer to Note 2 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 December 31, 2016 and 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 December 31, 2016 and 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	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies	COMMITMENTS AND CONTINGENCIES (a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, generation maintenance and performance improvements at Columbia Units 1 and 2, and the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU. At December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $58 million , $3 million and $55 million , respectively. (b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 . Certain contracts are considered leases and are therefore not included here, but are included in Note 10 . (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 December 31, 2016 . Other - Alliant Energy, IPL and WPL are involved in other legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations. (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. In 2016, the indemnification obligations and contractual warranty periods expired; however, 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 December 31, 2016 , Alliant Energy had $75 million of performance guarantees outstanding, which are currently expected to expire in 2017. 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 December 31, 2016 . Alliant Energy does not currently believe that the range of future potential loss from any warranty claims will be material. Refer to Note 19 for further discussion of RMT, including amounts Alliant Energy recorded to “Operating expenses” in 2016, 2015 and 2014 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. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of December 31, 2016 , the present value of the abandonment obligations is estimated at $31 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Alliant Energy Resources, LLC will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 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 December 31, 2016 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . Refer to Note 3 for further discussion of the sale of IPL’s Minnesota electric distribution assets. (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites. 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. Environmental liabilities related to these MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 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). At December 31, 2016 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $27 $12 - $24 Current and non-current environmental liabilities 16 13 Refer to Note 2 for discussion of regulatory assets recorded by IPL and WPL, which reflect the probable future rate recovery of MGP expenditures. Considering the current rate treatment, and assuming no material change therein, Alliant Energy, IPL and WPL believe that the clean-up costs incurred for these MGP sites will not have a material effect on their financial condition or results of operations. 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 and fuel switching or retiring Edgewater Unit 4 by December 31, 2018. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits for Columbia Units 1 and 2, and Edgewater Units 4 and 5. In addition, the Consent Decree includes annual plant-wide SO2 and NOx emission caps 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. 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 is in the process of completing 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. 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: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in Iowa, Minnesota and Illinois for IPL and Wisconsin for WPL. The geographic concentration of these customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a diverse customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or natural gas services. Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, diversification of counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and counterparty diversification, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance. Refer to Notes 5(a) and 15 for details of allowances for doubtful accounts and credit risk-related contingent features, respectively. (g) Collective Bargaining Agreements - At December 31, 2016 , employees covered by collective bargaining agreements represented 56% , 65% and 81% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2017, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 19% and 46% of total employees of Alliant Energy and IPL, respectively.
IPL [Member]
Commitments And Contingencies	COMMITMENTS AND CONTINGENCIES (a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, generation maintenance and performance improvements at Columbia Units 1 and 2, and the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU. At December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $58 million , $3 million and $55 million , respectively. (b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 . Certain contracts are considered leases and are therefore not included here, but are included in Note 10 . (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 December 31, 2016 . Other - Alliant Energy, IPL and WPL are involved in other legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations. (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. In 2016, the indemnification obligations and contractual warranty periods expired; however, 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 December 31, 2016 , Alliant Energy had $75 million of performance guarantees outstanding, which are currently expected to expire in 2017. 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 December 31, 2016 . Alliant Energy does not currently believe that the range of future potential loss from any warranty claims will be material. Refer to Note 19 for further discussion of RMT, including amounts Alliant Energy recorded to “Operating expenses” in 2016, 2015 and 2014 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. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of December 31, 2016 , the present value of the abandonment obligations is estimated at $31 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Alliant Energy Resources, LLC will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 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 December 31, 2016 . The general terms of the indemnifications provided by IPL included a maximum limit of $17 million and expire in October 2020 . Refer to Note 3 for further discussion of the sale of IPL’s Minnesota electric distribution assets. (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites. 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. Environmental liabilities related to these MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 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). At December 31, 2016 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $27 $12 - $24 Current and non-current environmental liabilities 16 13 Refer to Note 2 for discussion of regulatory assets recorded by IPL and WPL, which reflect the probable future rate recovery of MGP expenditures. Considering the current rate treatment, and assuming no material change therein, Alliant Energy, IPL and WPL believe that the clean-up costs incurred for these MGP sites will not have a material effect on their financial condition or results of operations. 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 and fuel switching or retiring Edgewater Unit 4 by December 31, 2018. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits for Columbia Units 1 and 2, and Edgewater Units 4 and 5. In addition, the Consent Decree includes annual plant-wide SO2 and NOx emission caps 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. 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 is in the process of completing 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. 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: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in Iowa, Minnesota and Illinois for IPL and Wisconsin for WPL. The geographic concentration of these customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a diverse customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or natural gas services. Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, diversification of counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and counterparty diversification, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance. Refer to Notes 5(a) and 15 for details of allowances for doubtful accounts and credit risk-related contingent features, respectively. (g) Collective Bargaining Agreements - At December 31, 2016 , employees covered by collective bargaining agreements represented 56% , 65% and 81% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2017, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 19% and 46% of total employees of Alliant Energy and IPL, respectively.
WPL [Member]
Commitments And Contingencies	COMMITMENTS AND CONTINGENCIES (a) Capital Purchase Obligations - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects. IPL’s projects include the installation of an SCR system at Ottumwa Unit 1 to reduce NOx emissions at the EGU. WPL’s projects include the Riverside expansion, generation maintenance and performance improvements at Columbia Units 1 and 2, and the installation of an SCR system at Columbia Unit 2 to reduce NOx emissions at the EGU. At December 31, 2016 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $58 million , $3 million and $55 million , respectively. (b) Operating Expense Purchase Obligations - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. Other operating expense purchase obligations with various vendors provide other goods and services. At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 . Certain contracts are considered leases and are therefore not included here, but are included in Note 10 . (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 December 31, 2016 . Other - Alliant Energy, IPL and WPL are involved in other legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations. (e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites. 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. Environmental liabilities related to these MGP sites are recorded based upon periodic studies. Such amounts are based on the best current estimate of the remaining amount to be incurred for investigation, remediation and monitoring costs for those sites where the investigation process has been or is substantially completed, and the minimum of the estimated cost range for those sites where the investigation is in its earlier stages. There are inherent uncertainties associated with the estimated remaining costs for MGP projects primarily due to unknown site conditions and potential changes in regulatory agency requirements. It is possible that future cost estimates will be greater than current estimates as the investigation process proceeds and as additional facts become known. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 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). At December 31, 2016 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $27 $12 - $24 Current and non-current environmental liabilities 16 13 Refer to Note 2 for discussion of regulatory assets recorded by IPL and WPL, which reflect the probable future rate recovery of MGP expenditures. Considering the current rate treatment, and assuming no material change therein, Alliant Energy, IPL and WPL believe that the clean-up costs incurred for these MGP sites will not have a material effect on their financial condition or results of operations. 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 and fuel switching or retiring Edgewater Unit 4 by December 31, 2018. The Consent Decree also establishes SO2, NOx and particulate matter emission rate limits for Columbia Units 1 and 2, and Edgewater Units 4 and 5. In addition, the Consent Decree includes annual plant-wide SO2 and NOx emission caps 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. 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 is in the process of completing 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. 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: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including carbon emissions from new (CAA Section 111(b)) and existing (CAA Section 111(d)) fossil-fueled EGUs. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in Iowa, Minnesota and Illinois for IPL and Wisconsin for WPL. The geographic concentration of these customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a diverse customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or natural gas services. Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, diversification of counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and counterparty diversification, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance. Refer to Notes 5(a) and 15 for details of allowances for doubtful accounts and credit risk-related contingent features, respectively. (g) Collective Bargaining Agreements - At December 31, 2016 , employees covered by collective bargaining agreements represented 56% , 65% and 81% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2017, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 19% and 46% of total employees of Alliant Energy and IPL, respectively.

Segments Of Business

Segments Of Business	12 Months Ended
	Dec. 31, 2016
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2016 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations, which include Alliant Energy’s investment in ATC; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • Non-regulated, Parent and Other - includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF’s businesses include Transportation, Non-regulated Generation and other non-regulated investments described in Note 1(a) . Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): Utility Non-Regulated, Alliant Energy 2016 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,875.5 $355.4 $48.6 $3,279.5 $40.5 $3,320.0 Depreciation and amortization 367.0 34.2 2.1 403.3 8.3 411.6 Operating income (loss) 571.9 30.7 (4.8 ) 597.8 (60.8 ) 537.0 Interest expense 194.6 1.6 196.2 Equity (income) loss from unconsolidated investments, net (39.8 ) — — (39.8 ) 0.2 (39.6 ) Income tax expense (benefit) 87.4 (28.0 ) 59.4 Net income (loss) attributable to Alliant Energy common shareowners 406.0 (34.5 ) 371.5 Total assets 11,040.5 1,091.1 781.0 12,912.6 461.2 13,373.8 Investments in equity method subsidiaries 325.3 — — 325.3 0.7 326.0 Construction and acquisition expenditures 1,005.5 137.1 0.1 1,142.7 54.1 1,196.8 Utility Non-Regulated, Alliant Energy 2015 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,770.5 $381.2 $57.9 $3,209.6 $44.0 $3,253.6 Depreciation and amortization 358.6 31.1 1.8 391.5 9.8 401.3 Operating income 514.1 34.6 1.9 550.6 26.4 577.0 Interest expense 189.2 (2.1 ) 187.1 Equity (income) loss from unconsolidated investments, net (35.1 ) — — (35.1 ) 1.3 (33.8 ) Income taxes 60.2 10.2 70.4 Net income attributable to Alliant Energy common shareowners 362.3 15.9 378.2 Total assets 10,211.3 939.3 828.9 11,979.5 515.7 12,495.2 Investments in equity method subsidiaries 302.0 — — 302.0 0.9 302.9 Construction and acquisition expenditures 855.8 106.4 1.4 963.6 70.7 1,034.3 Utility Non-Regulated, Alliant Energy 2014 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,713.6 $517.5 $66.1 $3,297.2 $53.1 $3,350.3 Depreciation and amortization 347.0 29.9 1.8 378.7 9.4 388.1 Operating income 442.4 53.8 14.0 510.2 33.4 543.6 Interest expense 176.3 4.3 180.6 Equity income (loss) from unconsolidated investments, net (42.8 ) — — (42.8 ) 2.4 (40.4 ) Income taxes 36.4 7.9 44.3 Net income attributable to Alliant Energy common shareowners 362.0 21.1 383.1 Total assets 9,660.4 913.5 993.9 11,567.8 495.7 12,063.5 Investments in equity method subsidiaries 294.3 — — 294.3 2.3 296.6 Construction and acquisition expenditures 774.8 63.2 0.9 838.9 63.9 902.8 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,569.7 $204.0 $46.7 $1,820.4 Depreciation and amortization 189.4 19.3 2.1 210.8 Operating income 252.0 15.5 3.3 270.8 Interest expense 103.2 Income tax benefit (5.9 ) Earnings available for common stock 215.6 Total assets 6,278.2 653.3 373.2 7,304.7 Construction and acquisition expenditures 598.1 91.5 0.1 689.7 2015 Electric Gas Other Total Operating revenues $1,503.8 $217.3 $53.4 $1,774.5 Depreciation and amortization 187.9 17.5 1.8 207.2 Operating income 218.8 17.7 5.4 241.9 Interest expense 96.8 Income tax benefit (22.7 ) Earnings available for common stock 186.0 Total assets 5,754.1 548.2 406.8 6,709.1 Construction and acquisition expenditures 561.2 56.7 1.4 619.3 2014 Electric Gas Other Total Operating revenues $1,493.3 $296.5 $58.3 $1,848.1 Depreciation and amortization 178.7 17.0 1.8 197.5 Operating income 166.8 25.7 16.7 209.2 Interest expense 89.9 Income tax benefit (48.9 ) Earnings available for common stock 181.6 Total assets 5,398.3 544.1 507.8 6,450.2 Construction and acquisition expenditures 490.0 35.1 0.9 526.0 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,305.8 $151.4 $1.9 $1,459.1 Depreciation and amortization 177.6 14.9 — 192.5 Operating income (loss) 319.9 15.2 (8.1 ) 327.0 Interest expense 91.4 Equity income from unconsolidated investments (39.8 ) — — (39.8 ) Income taxes 93.3 Earnings available for common stock 190.4 Total assets 4,444.7 437.8 407.8 5,290.3 Investments in equity method subsidiaries 7.7 — — 7.7 Construction and acquisition expenditures 407.4 45.6 — 453.0 2015 Electric Gas Other Total Operating revenues $1,266.7 $163.9 $4.5 $1,435.1 Depreciation and amortization 170.7 13.6 — 184.3 Operating income (loss) 295.3 16.9 (3.5 ) 308.7 Interest expense 92.4 Equity income from unconsolidated investments (35.1 ) — — (35.1 ) Income taxes 82.9 Earnings available for common stock 176.3 Total assets 4,457.2 391.1 422.1 5,270.4 Investments in equity method subsidiaries 302.0 — — 302.0 Construction and acquisition expenditures 294.6 49.7 — 344.3 2014 Electric Gas Other Total Operating revenues $1,220.3 $221.0 $7.8 $1,449.1 Depreciation and amortization 168.3 12.9 — 181.2 Operating income (loss) 275.6 28.1 (2.7 ) 301.0 Interest expense 86.4 Equity income from unconsolidated investments (42.8 ) — — (42.8 ) Income taxes 85.3 Earnings available for common stock 180.4 Total assets 4,262.1 369.4 486.1 5,117.6 Investments in equity method subsidiaries 294.3 — — 294.3 Construction and acquisition expenditures 284.8 28.1 — 312.9
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2016 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations, which include Alliant Energy’s investment in ATC; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • Non-regulated, Parent and Other - includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF’s businesses include Transportation, Non-regulated Generation and other non-regulated investments described in Note 1(a) . Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): Utility Non-Regulated, Alliant Energy 2016 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,875.5 $355.4 $48.6 $3,279.5 $40.5 $3,320.0 Depreciation and amortization 367.0 34.2 2.1 403.3 8.3 411.6 Operating income (loss) 571.9 30.7 (4.8 ) 597.8 (60.8 ) 537.0 Interest expense 194.6 1.6 196.2 Equity (income) loss from unconsolidated investments, net (39.8 ) — — (39.8 ) 0.2 (39.6 ) Income tax expense (benefit) 87.4 (28.0 ) 59.4 Net income (loss) attributable to Alliant Energy common shareowners 406.0 (34.5 ) 371.5 Total assets 11,040.5 1,091.1 781.0 12,912.6 461.2 13,373.8 Investments in equity method subsidiaries 325.3 — — 325.3 0.7 326.0 Construction and acquisition expenditures 1,005.5 137.1 0.1 1,142.7 54.1 1,196.8 Utility Non-Regulated, Alliant Energy 2015 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,770.5 $381.2 $57.9 $3,209.6 $44.0 $3,253.6 Depreciation and amortization 358.6 31.1 1.8 391.5 9.8 401.3 Operating income 514.1 34.6 1.9 550.6 26.4 577.0 Interest expense 189.2 (2.1 ) 187.1 Equity (income) loss from unconsolidated investments, net (35.1 ) — — (35.1 ) 1.3 (33.8 ) Income taxes 60.2 10.2 70.4 Net income attributable to Alliant Energy common shareowners 362.3 15.9 378.2 Total assets 10,211.3 939.3 828.9 11,979.5 515.7 12,495.2 Investments in equity method subsidiaries 302.0 — — 302.0 0.9 302.9 Construction and acquisition expenditures 855.8 106.4 1.4 963.6 70.7 1,034.3 Utility Non-Regulated, Alliant Energy 2014 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,713.6 $517.5 $66.1 $3,297.2 $53.1 $3,350.3 Depreciation and amortization 347.0 29.9 1.8 378.7 9.4 388.1 Operating income 442.4 53.8 14.0 510.2 33.4 543.6 Interest expense 176.3 4.3 180.6 Equity income (loss) from unconsolidated investments, net (42.8 ) — — (42.8 ) 2.4 (40.4 ) Income taxes 36.4 7.9 44.3 Net income attributable to Alliant Energy common shareowners 362.0 21.1 383.1 Total assets 9,660.4 913.5 993.9 11,567.8 495.7 12,063.5 Investments in equity method subsidiaries 294.3 — — 294.3 2.3 296.6 Construction and acquisition expenditures 774.8 63.2 0.9 838.9 63.9 902.8 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,569.7 $204.0 $46.7 $1,820.4 Depreciation and amortization 189.4 19.3 2.1 210.8 Operating income 252.0 15.5 3.3 270.8 Interest expense 103.2 Income tax benefit (5.9 ) Earnings available for common stock 215.6 Total assets 6,278.2 653.3 373.2 7,304.7 Construction and acquisition expenditures 598.1 91.5 0.1 689.7 2015 Electric Gas Other Total Operating revenues $1,503.8 $217.3 $53.4 $1,774.5 Depreciation and amortization 187.9 17.5 1.8 207.2 Operating income 218.8 17.7 5.4 241.9 Interest expense 96.8 Income tax benefit (22.7 ) Earnings available for common stock 186.0 Total assets 5,754.1 548.2 406.8 6,709.1 Construction and acquisition expenditures 561.2 56.7 1.4 619.3 2014 Electric Gas Other Total Operating revenues $1,493.3 $296.5 $58.3 $1,848.1 Depreciation and amortization 178.7 17.0 1.8 197.5 Operating income 166.8 25.7 16.7 209.2 Interest expense 89.9 Income tax benefit (48.9 ) Earnings available for common stock 181.6 Total assets 5,398.3 544.1 507.8 6,450.2 Construction and acquisition expenditures 490.0 35.1 0.9 526.0 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,305.8 $151.4 $1.9 $1,459.1 Depreciation and amortization 177.6 14.9 — 192.5 Operating income (loss) 319.9 15.2 (8.1 ) 327.0 Interest expense 91.4 Equity income from unconsolidated investments (39.8 ) — — (39.8 ) Income taxes 93.3 Earnings available for common stock 190.4 Total assets 4,444.7 437.8 407.8 5,290.3 Investments in equity method subsidiaries 7.7 — — 7.7 Construction and acquisition expenditures 407.4 45.6 — 453.0 2015 Electric Gas Other Total Operating revenues $1,266.7 $163.9 $4.5 $1,435.1 Depreciation and amortization 170.7 13.6 — 184.3 Operating income (loss) 295.3 16.9 (3.5 ) 308.7 Interest expense 92.4 Equity income from unconsolidated investments (35.1 ) — — (35.1 ) Income taxes 82.9 Earnings available for common stock 176.3 Total assets 4,457.2 391.1 422.1 5,270.4 Investments in equity method subsidiaries 302.0 — — 302.0 Construction and acquisition expenditures 294.6 49.7 — 344.3 2014 Electric Gas Other Total Operating revenues $1,220.3 $221.0 $7.8 $1,449.1 Depreciation and amortization 168.3 12.9 — 181.2 Operating income (loss) 275.6 28.1 (2.7 ) 301.0 Interest expense 86.4 Equity income from unconsolidated investments (42.8 ) — — (42.8 ) Income taxes 85.3 Earnings available for common stock 180.4 Total assets 4,262.1 369.4 486.1 5,117.6 Investments in equity method subsidiaries 294.3 — — 294.3 Construction and acquisition expenditures 284.8 28.1 — 312.9
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2016 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations, which include Alliant Energy’s investment in ATC; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • Non-regulated, Parent and Other - includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF’s businesses include Transportation, Non-regulated Generation and other non-regulated investments described in Note 1(a) . Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): Utility Non-Regulated, Alliant Energy 2016 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,875.5 $355.4 $48.6 $3,279.5 $40.5 $3,320.0 Depreciation and amortization 367.0 34.2 2.1 403.3 8.3 411.6 Operating income (loss) 571.9 30.7 (4.8 ) 597.8 (60.8 ) 537.0 Interest expense 194.6 1.6 196.2 Equity (income) loss from unconsolidated investments, net (39.8 ) — — (39.8 ) 0.2 (39.6 ) Income tax expense (benefit) 87.4 (28.0 ) 59.4 Net income (loss) attributable to Alliant Energy common shareowners 406.0 (34.5 ) 371.5 Total assets 11,040.5 1,091.1 781.0 12,912.6 461.2 13,373.8 Investments in equity method subsidiaries 325.3 — — 325.3 0.7 326.0 Construction and acquisition expenditures 1,005.5 137.1 0.1 1,142.7 54.1 1,196.8 Utility Non-Regulated, Alliant Energy 2015 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,770.5 $381.2 $57.9 $3,209.6 $44.0 $3,253.6 Depreciation and amortization 358.6 31.1 1.8 391.5 9.8 401.3 Operating income 514.1 34.6 1.9 550.6 26.4 577.0 Interest expense 189.2 (2.1 ) 187.1 Equity (income) loss from unconsolidated investments, net (35.1 ) — — (35.1 ) 1.3 (33.8 ) Income taxes 60.2 10.2 70.4 Net income attributable to Alliant Energy common shareowners 362.3 15.9 378.2 Total assets 10,211.3 939.3 828.9 11,979.5 515.7 12,495.2 Investments in equity method subsidiaries 302.0 — — 302.0 0.9 302.9 Construction and acquisition expenditures 855.8 106.4 1.4 963.6 70.7 1,034.3 Utility Non-Regulated, Alliant Energy 2014 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,713.6 $517.5 $66.1 $3,297.2 $53.1 $3,350.3 Depreciation and amortization 347.0 29.9 1.8 378.7 9.4 388.1 Operating income 442.4 53.8 14.0 510.2 33.4 543.6 Interest expense 176.3 4.3 180.6 Equity income (loss) from unconsolidated investments, net (42.8 ) — — (42.8 ) 2.4 (40.4 ) Income taxes 36.4 7.9 44.3 Net income attributable to Alliant Energy common shareowners 362.0 21.1 383.1 Total assets 9,660.4 913.5 993.9 11,567.8 495.7 12,063.5 Investments in equity method subsidiaries 294.3 — — 294.3 2.3 296.6 Construction and acquisition expenditures 774.8 63.2 0.9 838.9 63.9 902.8 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,569.7 $204.0 $46.7 $1,820.4 Depreciation and amortization 189.4 19.3 2.1 210.8 Operating income 252.0 15.5 3.3 270.8 Interest expense 103.2 Income tax benefit (5.9 ) Earnings available for common stock 215.6 Total assets 6,278.2 653.3 373.2 7,304.7 Construction and acquisition expenditures 598.1 91.5 0.1 689.7 2015 Electric Gas Other Total Operating revenues $1,503.8 $217.3 $53.4 $1,774.5 Depreciation and amortization 187.9 17.5 1.8 207.2 Operating income 218.8 17.7 5.4 241.9 Interest expense 96.8 Income tax benefit (22.7 ) Earnings available for common stock 186.0 Total assets 5,754.1 548.2 406.8 6,709.1 Construction and acquisition expenditures 561.2 56.7 1.4 619.3 2014 Electric Gas Other Total Operating revenues $1,493.3 $296.5 $58.3 $1,848.1 Depreciation and amortization 178.7 17.0 1.8 197.5 Operating income 166.8 25.7 16.7 209.2 Interest expense 89.9 Income tax benefit (48.9 ) Earnings available for common stock 181.6 Total assets 5,398.3 544.1 507.8 6,450.2 Construction and acquisition expenditures 490.0 35.1 0.9 526.0 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,305.8 $151.4 $1.9 $1,459.1 Depreciation and amortization 177.6 14.9 — 192.5 Operating income (loss) 319.9 15.2 (8.1 ) 327.0 Interest expense 91.4 Equity income from unconsolidated investments (39.8 ) — — (39.8 ) Income taxes 93.3 Earnings available for common stock 190.4 Total assets 4,444.7 437.8 407.8 5,290.3 Investments in equity method subsidiaries 7.7 — — 7.7 Construction and acquisition expenditures 407.4 45.6 — 453.0 2015 Electric Gas Other Total Operating revenues $1,266.7 $163.9 $4.5 $1,435.1 Depreciation and amortization 170.7 13.6 — 184.3 Operating income (loss) 295.3 16.9 (3.5 ) 308.7 Interest expense 92.4 Equity income from unconsolidated investments (35.1 ) — — (35.1 ) Income taxes 82.9 Earnings available for common stock 176.3 Total assets 4,457.2 391.1 422.1 5,270.4 Investments in equity method subsidiaries 302.0 — — 302.0 Construction and acquisition expenditures 294.6 49.7 — 344.3 2014 Electric Gas Other Total Operating revenues $1,220.3 $221.0 $7.8 $1,449.1 Depreciation and amortization 168.3 12.9 — 181.2 Operating income (loss) 275.6 28.1 (2.7 ) 301.0 Interest expense 86.4 Equity income from unconsolidated investments (42.8 ) — — (42.8 ) Income taxes 85.3 Earnings available for common stock 180.4 Total assets 4,262.1 369.4 486.1 5,117.6 Investments in equity method subsidiaries 294.3 — — 294.3 Construction and acquisition expenditures 284.8 28.1 — 312.9

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2016
Related Party Transaction [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 were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 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 were as follows (in millions): 2016 2015 2014 ATC billings to WPL $110 $101 $96 WPL billings to ATC 13 13 9 As of December 31, 2016 and 2015 , WPL owed ATC net amounts of $8 million and $8 million , respectively. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL’s Sheboygan Falls Lease - Refer to Note 10(b) for discussion of WPL’s Sheboygan Falls lease. Franklin County Wind Farm - Refer to Note 3 for discussion of a February 2017 FERC order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017.
IPL [Member]
Related Party Transaction [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 were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 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 were as follows (in millions): 2016 2015 2014 ATC billings to WPL $110 $101 $96 WPL billings to ATC 13 13 9 As of December 31, 2016 and 2015 , WPL owed ATC net amounts of $8 million and $8 million , respectively. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL’s Sheboygan Falls Lease - Refer to Note 10(b) for discussion of WPL’s Sheboygan Falls lease. Franklin County Wind Farm - Refer to Note 3 for discussion of a February 2017 FERC order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017.
WPL [Member]
Related Party Transaction [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 were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 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 were as follows (in millions): 2016 2015 2014 ATC billings to WPL $110 $101 $96 WPL billings to ATC 13 13 9 As of December 31, 2016 and 2015 , WPL owed ATC net amounts of $8 million and $8 million , respectively. Refer to Note 6(a) for discussion of WPL’s transfer of its investment in ATC to ATI on December 31, 2016. WPL’s Sheboygan Falls Lease - Refer to Note 10(b) for discussion of WPL’s Sheboygan Falls lease. Franklin County Wind Farm - Refer to Note 3 for discussion of a February 2017 FERC order approving the transfer of the Franklin County wind farm from AEF to IPL. Alliant Energy and IPL currently expect to complete this transfer in 2017.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations	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 was as follows (in millions): 2016 2015 2014 Operating expenses $3.9 $4.0 $3.7 Loss before income taxes (3.9 ) (4.0 ) (3.7 ) Income tax benefit (1.6 ) (1.5 ) (1.3 ) Loss from discontinued operations, net of tax ($2.3 ) ($2.5 ) ($2.4 ) Refer to Note 16(d) for further discussion of warranty claims associated with RMT that have resulted in operating expenses subsequent to the sale.

Selected Consolidated Quarterly

Selected Consolidated Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Selected Consolidated Quarterly Financial Data (Unaudited)	SELECTED CONSOLIDATED QUARTERLY FINANCIAL DATA (UNAUDITED) Alliant Energy - All “per share” references refer to earnings per diluted share. Summation of the individual quarters may not equal annual totals due to rounding. Refer to Note 19 for additional information on discontinued operations. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $843.8 $754.6 $924.6 $797.0 $897.4 $717.2 $898.9 $740.1 Operating income 145.9 128.6 162.6 99.9 152.9 109.0 235.9 79.2 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 97.6 84.4 128.8 63.0 96.6 68.9 180.0 35.2 Loss from discontinued operations, net of tax (1.1 ) (0.5 ) (0.4 ) (0.3 ) — (1.3 ) (0.1 ) (1.1 ) Net income 96.5 83.9 128.4 62.7 96.6 67.6 179.9 34.1 Earnings per weighted average common share attributable to Alliant Energy common shareowners (a): Income from continuing operations, net of tax 0.43 0.37 0.57 0.28 0.43 0.31 0.79 0.16 Loss from discontinued operations, net of tax — — — — — (0.01 ) — (0.01 ) Net income 0.43 0.37 0.57 0.28 0.43 0.30 0.79 0.15 (a) Amounts reflect the effects of a two -for-one common stock split distributed in May 2016 . Refer to Note 7 for additional details. IPL - Earnings per share data is not disclosed for IPL given Alliant Energy is the sole shareowner of all shares of IPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $458.7 $411.0 $516.2 $434.5 $489.0 $382.2 $504.6 $398.7 Operating income 62.0 48.0 125.9 34.9 65.5 33.8 117.0 25.6 Net income 48.2 34.4 116.7 26.5 50.1 19.0 119.1 8.0 Earnings available for common stock 45.6 31.9 114.1 24.0 47.5 16.5 116.5 5.5 WPL - Earnings per share data is not disclosed for WPL given Alliant Energy is the sole shareowner of all shares of WPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $375.6 $334.3 $397.0 $352.2 $397.1 $324.7 $382.6 $330.7 Operating income 78.8 75.0 115.0 58.2 80.8 68.3 110.3 49.3 Net income 47.0 43.7 69.6 32.5 45.1 39.7 68.4 24.4 Earnings available for common stock 46.5 43.2 69.0 31.7 44.9 39.2 68.0 24.2
IPL [Member]
Selected Consolidated Quarterly Financial Data (Unaudited)	SELECTED CONSOLIDATED QUARTERLY FINANCIAL DATA (UNAUDITED) Alliant Energy - All “per share” references refer to earnings per diluted share. Summation of the individual quarters may not equal annual totals due to rounding. Refer to Note 19 for additional information on discontinued operations. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $843.8 $754.6 $924.6 $797.0 $897.4 $717.2 $898.9 $740.1 Operating income 145.9 128.6 162.6 99.9 152.9 109.0 235.9 79.2 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 97.6 84.4 128.8 63.0 96.6 68.9 180.0 35.2 Loss from discontinued operations, net of tax (1.1 ) (0.5 ) (0.4 ) (0.3 ) — (1.3 ) (0.1 ) (1.1 ) Net income 96.5 83.9 128.4 62.7 96.6 67.6 179.9 34.1 Earnings per weighted average common share attributable to Alliant Energy common shareowners (a): Income from continuing operations, net of tax 0.43 0.37 0.57 0.28 0.43 0.31 0.79 0.16 Loss from discontinued operations, net of tax — — — — — (0.01 ) — (0.01 ) Net income 0.43 0.37 0.57 0.28 0.43 0.30 0.79 0.15 (a) Amounts reflect the effects of a two -for-one common stock split distributed in May 2016 . Refer to Note 7 for additional details. IPL - Earnings per share data is not disclosed for IPL given Alliant Energy is the sole shareowner of all shares of IPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $458.7 $411.0 $516.2 $434.5 $489.0 $382.2 $504.6 $398.7 Operating income 62.0 48.0 125.9 34.9 65.5 33.8 117.0 25.6 Net income 48.2 34.4 116.7 26.5 50.1 19.0 119.1 8.0 Earnings available for common stock 45.6 31.9 114.1 24.0 47.5 16.5 116.5 5.5 WPL - Earnings per share data is not disclosed for WPL given Alliant Energy is the sole shareowner of all shares of WPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $375.6 $334.3 $397.0 $352.2 $397.1 $324.7 $382.6 $330.7 Operating income 78.8 75.0 115.0 58.2 80.8 68.3 110.3 49.3 Net income 47.0 43.7 69.6 32.5 45.1 39.7 68.4 24.4 Earnings available for common stock 46.5 43.2 69.0 31.7 44.9 39.2 68.0 24.2
WPL [Member]
Selected Consolidated Quarterly Financial Data (Unaudited)	SELECTED CONSOLIDATED QUARTERLY FINANCIAL DATA (UNAUDITED) Alliant Energy - All “per share” references refer to earnings per diluted share. Summation of the individual quarters may not equal annual totals due to rounding. Refer to Note 19 for additional information on discontinued operations. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $843.8 $754.6 $924.6 $797.0 $897.4 $717.2 $898.9 $740.1 Operating income 145.9 128.6 162.6 99.9 152.9 109.0 235.9 79.2 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 97.6 84.4 128.8 63.0 96.6 68.9 180.0 35.2 Loss from discontinued operations, net of tax (1.1 ) (0.5 ) (0.4 ) (0.3 ) — (1.3 ) (0.1 ) (1.1 ) Net income 96.5 83.9 128.4 62.7 96.6 67.6 179.9 34.1 Earnings per weighted average common share attributable to Alliant Energy common shareowners (a): Income from continuing operations, net of tax 0.43 0.37 0.57 0.28 0.43 0.31 0.79 0.16 Loss from discontinued operations, net of tax — — — — — (0.01 ) — (0.01 ) Net income 0.43 0.37 0.57 0.28 0.43 0.30 0.79 0.15 (a) Amounts reflect the effects of a two -for-one common stock split distributed in May 2016 . Refer to Note 7 for additional details. IPL - Earnings per share data is not disclosed for IPL given Alliant Energy is the sole shareowner of all shares of IPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $458.7 $411.0 $516.2 $434.5 $489.0 $382.2 $504.6 $398.7 Operating income 62.0 48.0 125.9 34.9 65.5 33.8 117.0 25.6 Net income 48.2 34.4 116.7 26.5 50.1 19.0 119.1 8.0 Earnings available for common stock 45.6 31.9 114.1 24.0 47.5 16.5 116.5 5.5 WPL - Earnings per share data is not disclosed for WPL given Alliant Energy is the sole shareowner of all shares of WPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $375.6 $334.3 $397.0 $352.2 $397.1 $324.7 $382.6 $330.7 Operating income 78.8 75.0 115.0 58.2 80.8 68.3 110.3 49.3 Net income 47.0 43.7 69.6 32.5 45.1 39.7 68.4 24.4 Earnings available for common stock 46.5 43.2 69.0 31.7 44.9 39.2 68.0 24.2

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Statements	SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED STATEMENTS OF INCOME Year Ended December 31, 2016 2015 2014 (in millions) Operating revenues $1 $2 $2 Operating expenses 3 3 3 Operating loss (2 ) (1 ) (1 ) Interest expense and other: Equity earnings from consolidated subsidiaries (374 ) (379 ) (388 ) Interest expense 3 3 9 Interest income (2 ) (3 ) (2 ) Total interest expense and other (373 ) (379 ) (381 ) Income before income taxes 371 378 380 Income tax benefit (1 ) (1 ) (3 ) Net income $372 $379 $383 The accompanying Notes to Condensed Financial Statements are an integral part of these statements. ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED BALANCE SHEETS December 31, 2016 2015 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $74 $93 Other 5 9 Total current assets 79 102 Investments: Investments in consolidated subsidiaries 4,211 3,999 Other 2 14 Total investments 4,213 4,013 Other assets 64 20 Total assets $4,356 $4,135 LIABILITIES AND EQUITY Current liabilities: Current maturities of long-term debt $— $250 Commercial paper 192 140 Notes payable to affiliated companies 275 — Other 12 12 Total current liabilities 479 402 Other liabilities 18 12 Common equity: Common stock and additional paid-in capital 1,695 1,664 Retained earnings 2,174 2,066 Shares in deferred compensation trust (10 ) (9 ) Total common equity 3,859 3,721 Total liabilities and equity $4,356 $4,135 The accompanying Notes to Condensed Financial Statements are an integral part of these statements. ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED STATEMENTS OF CASH FLOWS Year Ended December 31, 2016 2015 2014 (in millions) Net cash flows from operating activities $254 $262 $246 Cash flows from (used for) investing activities: Capital contributions to consolidated subsidiaries (250 ) (165 ) (90 ) Capital repayments from consolidated subsidiaries 130 — 50 Net change in notes receivable from and payable to affiliates 294 2 (23 ) Other 10 — — Net cash flows from (used for) investing activities 184 (163 ) (63 ) Cash flows used for financing activities: Common stock dividends (267 ) (247 ) (226 ) Proceeds from issuance of common stock, net 27 151 — Proceeds from issuance of long-term debt — — 250 Payments to retire long-term debt (250 ) — (250 ) Net change in commercial paper 52 (1 ) 45 Other — (2 ) (2 ) Net cash flows used for financing activities (438 ) (99 ) (183 ) Net decrease in cash and cash equivalents — — — Cash and cash equivalents at beginning of period — — — Cash and cash equivalents at end of period $— $— $— Supplemental cash flows information: Cash paid during the period for: Interest, net of capitalized interest ($3 ) ($3 ) ($11 ) Income taxes, net (37 ) (9 ) (5 ) The accompanying Notes to Condensed Financial Statements are an integral part of these statements. ALLIANT ENERGY CORPORATION (Parent Company Only) NOTES TO CONDENSED FINANCIAL STATEMENTS Pursuant to rules and regulations of the SEC, the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only) do not reflect all of the information and notes normally included with financial statements prepared in accordance with GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the Financial Statements and related Notes included in the combined 2016 Form 10-K, Part II, Item 8 , which is incorporated herein by reference. In the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only), investments in subsidiaries are accounted for using the equity method.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts And Reserves	12 Months Ended
	Dec. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation and Qualifying Accounts And Reserves	SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES Additions Balance, Charged to Charged to Other Balance, Description January 1 Expense Accounts (a) Deductions (b) December 31 (in millions) Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet From the Assets to Which They Apply: Accumulated Provision for Uncollectible Accounts: Alliant Energy (c) Year ended December 31, 2016 $4.8 $17.4 $8.8 $22.3 $8.7 Year ended December 31, 2015 5.1 8.1 3.0 11.4 4.8 Year ended December 31, 2014 4.8 11.7 4.1 15.5 5.1 IPL (c) Year ended December 31, 2016 $0.6 $17.2 $— $16.7 $1.1 Year ended December 31, 2015 0.4 8.1 — 7.9 0.6 Year ended December 31, 2014 0.7 11.5 — 11.8 0.4 WPL Year ended December 31, 2016 $3.7 $0.1 $8.8 $5.5 $7.1 Year ended December 31, 2015 4.2 — 3.0 3.5 3.7 Year ended December 31, 2014 1.7 — 4.1 1.6 4.2 Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets. Other Reserves: Accumulated Provision for Other Reserves (d): Alliant Energy Year ended December 31, 2016 $27.1 $6.1 $— $8.1 $25.1 Year ended December 31, 2015 32.6 6.5 — 12.0 27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 IPL Year ended December 31, 2016 $9.4 $1.0 $— $1.7 $8.7 Year ended December 31, 2015 10.6 2.1 — 3.3 9.4 Year ended December 31, 2014 18.1 3.9 — 11.4 10.6 WPL Year ended December 31, 2016 $11.4 $1.8 $— $5.1 $8.1 Year ended December 31, 2015 16.3 0.7 — 5.6 11.4 Year ended December 31, 2014 16.2 2.5 — 2.4 16.3 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off. (b) Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off. (c) Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program. (d) Other reserves are largely related to injury and damage claims arising in the ordinary course of business.
IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation and Qualifying Accounts And Reserves	SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES Additions Balance, Charged to Charged to Other Balance, Description January 1 Expense Accounts (a) Deductions (b) December 31 (in millions) Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet From the Assets to Which They Apply: Accumulated Provision for Uncollectible Accounts: Alliant Energy (c) Year ended December 31, 2016 $4.8 $17.4 $8.8 $22.3 $8.7 Year ended December 31, 2015 5.1 8.1 3.0 11.4 4.8 Year ended December 31, 2014 4.8 11.7 4.1 15.5 5.1 IPL (c) Year ended December 31, 2016 $0.6 $17.2 $— $16.7 $1.1 Year ended December 31, 2015 0.4 8.1 — 7.9 0.6 Year ended December 31, 2014 0.7 11.5 — 11.8 0.4 WPL Year ended December 31, 2016 $3.7 $0.1 $8.8 $5.5 $7.1 Year ended December 31, 2015 4.2 — 3.0 3.5 3.7 Year ended December 31, 2014 1.7 — 4.1 1.6 4.2 Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets. Other Reserves: Accumulated Provision for Other Reserves (d): Alliant Energy Year ended December 31, 2016 $27.1 $6.1 $— $8.1 $25.1 Year ended December 31, 2015 32.6 6.5 — 12.0 27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 IPL Year ended December 31, 2016 $9.4 $1.0 $— $1.7 $8.7 Year ended December 31, 2015 10.6 2.1 — 3.3 9.4 Year ended December 31, 2014 18.1 3.9 — 11.4 10.6 WPL Year ended December 31, 2016 $11.4 $1.8 $— $5.1 $8.1 Year ended December 31, 2015 16.3 0.7 — 5.6 11.4 Year ended December 31, 2014 16.2 2.5 — 2.4 16.3 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off. (b) Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off. (c) Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program. (d) Other reserves are largely related to injury and damage claims arising in the ordinary course of business.
WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation and Qualifying Accounts And Reserves	SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES Additions Balance, Charged to Charged to Other Balance, Description January 1 Expense Accounts (a) Deductions (b) December 31 (in millions) Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet From the Assets to Which They Apply: Accumulated Provision for Uncollectible Accounts: Alliant Energy (c) Year ended December 31, 2016 $4.8 $17.4 $8.8 $22.3 $8.7 Year ended December 31, 2015 5.1 8.1 3.0 11.4 4.8 Year ended December 31, 2014 4.8 11.7 4.1 15.5 5.1 IPL (c) Year ended December 31, 2016 $0.6 $17.2 $— $16.7 $1.1 Year ended December 31, 2015 0.4 8.1 — 7.9 0.6 Year ended December 31, 2014 0.7 11.5 — 11.8 0.4 WPL Year ended December 31, 2016 $3.7 $0.1 $8.8 $5.5 $7.1 Year ended December 31, 2015 4.2 — 3.0 3.5 3.7 Year ended December 31, 2014 1.7 — 4.1 1.6 4.2 Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets. Other Reserves: Accumulated Provision for Other Reserves (d): Alliant Energy Year ended December 31, 2016 $27.1 $6.1 $— $8.1 $25.1 Year ended December 31, 2015 32.6 6.5 — 12.0 27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 IPL Year ended December 31, 2016 $9.4 $1.0 $— $1.7 $8.7 Year ended December 31, 2015 10.6 2.1 — 3.3 9.4 Year ended December 31, 2014 18.1 3.9 — 11.4 10.6 WPL Year ended December 31, 2016 $11.4 $1.8 $— $5.1 $8.1 Year ended December 31, 2015 16.3 0.7 — 5.6 11.4 Year ended December 31, 2014 16.2 2.5 — 2.4 16.3 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off. (b) Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off. (c) Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program. (d) Other reserves are largely related to injury and damage claims arising in the ordinary course of business.

Summary Of Significant Accoun30

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
General, Basis of Presentation	The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting	The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction.
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. As discussed in Note 7 , 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 common stock split.
General, Use of Estimates	The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities	Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes	The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 .
Cash and Cash Equivalents	Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days.
Property, Plant and Equipment	Non-utility Property - General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements. Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early.
Depreciation	IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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.
AFUDC	AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion.
Operating Revenues	Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Financial Instruments	Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations	The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs	Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Allowance for Doubtful Accounts	Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories.
Variable Interest Entities	An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis.
Cash Flows Presentation	Alliant Energy presents cash flows from continuing operations together with cash flows from discontinued operations in its cash flows statements.
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. Upon adoption, the standard can be applied retrospectively to all prior reporting periods presented, or retrospectively with a cumulative effect to the opening retained earnings balance on January 1, 2018 . Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations and do not anticipate a significant change in revenue recognition for retail electric and gas sales, which represent the majority of Alliant Energy’s, IPL’s and WPL’s revenues. Alliant Energy, IPL and WPL continue to evaluate additional impacts of this standard, as well as which transition method will be utilized. 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 currently expect to adopt this standard on January 1, 2019 and are evaluating the impact of this standard on their financial condition and results of operations and expect an increase in assets and liabilities from recognizing operating leases on their balance sheets. Share-based Compensation Award Payments - In March 2016, the Financial Accounting Standards Board issued an accounting standard intended to simplify certain aspects of the accounting for share-based compensation award payments and the associated income taxes. This standard changes the accounting for excess tax benefits, whereby such benefits are recognized in the income statement instead of additional paid-in capital on the balance sheet. Alliant Energy adopted this standard on January 1, 2016, which resulted in a cumulative effect of a decrease to its deferred tax liabilities and an increase to its January 1, 2016 retained earnings balance of $3.1 million , which is included in “Other” in Alliant Energy’s common equity statement in 2016.
IPL [Member]
Property, Plant and Equipment [Line Items]
General, Basis of Presentation	The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting	The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction.
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. As discussed in Note 7 , 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 common stock split.
General, Use of Estimates	The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities	Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes	The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 .
Cash and Cash Equivalents	Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days.
Property, Plant and Equipment	Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early.
Depreciation	IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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.
AFUDC	AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion.
Operating Revenues	Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Financial Instruments	Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations	The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs	Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Allowance for Doubtful Accounts	Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories.
Variable Interest Entities	An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis.
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. Upon adoption, the standard can be applied retrospectively to all prior reporting periods presented, or retrospectively with a cumulative effect to the opening retained earnings balance on January 1, 2018 . Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations and do not anticipate a significant change in revenue recognition for retail electric and gas sales, which represent the majority of Alliant Energy’s, IPL’s and WPL’s revenues. Alliant Energy, IPL and WPL continue to evaluate additional impacts of this standard, as well as which transition method will be utilized. 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 currently expect to adopt this standard on January 1, 2019 and are evaluating the impact of this standard on their financial condition and results of operations and expect an increase in assets and liabilities from recognizing operating leases on their balance sheets.
WPL [Member]
Property, Plant and Equipment [Line Items]
General, Basis of Presentation	The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments, which Alliant Energy and WPL do not control, but have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method. Refer to Notes 1(m) and 6(a) for further discussion of VIEs and equity method investments, respectively. All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting	The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making and accounting practices of FERC and state commissions having regulatory jurisdiction.
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. As discussed in Note 7 , 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 common stock split.
General, Use of Estimates	The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities	Alliant Energy, IPL and WPL are subject to regulation by FERC and various state regulatory commissions. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-regulated entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts deferred as regulatory assets or accrued as regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes	The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not include the impact of certain deferred tax expenses (benefits) in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. Refer to Note 2 for further discussion of these tax regulatory assets and regulatory liabilities associated with property-related differences at IPL. In Wisconsin, the PSCW has allowed rate recovery of deferred tax expense on all temporary differences since 1991. Investment tax credits are deferred and amortized to income over the average lives of the related property. Other tax credits reduce income tax expense in the year claimed. Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa. Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the modified separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis). The difference in the income taxes recorded for IPL and WPL under the modified separate return method compared to the income taxes recorded on a separate return basis was not material in 2016 , 2015 and 2014 .
Cash and Cash Equivalents	Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days.
Property, Plant and Equipment	Utility Plant - General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making policies. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early.
Depreciation	IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates charged to customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0% 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.
AFUDC	AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility. In accordance with their most recent rate orders, IPL applies its AFUDC rates to 100% of applicable CWIP balances and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances. WPL may apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its most recent rate order, including the Riverside expansion.
Operating Revenues	Utility - Revenues from Alliant Energy’s utility business are primarily from electricity and natural gas sales and are recognized on an accrual basis as services are rendered or commodities are delivered to customers. Energy sales to individual customers are based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period. Amounts of energy delivered to customers since the date of the last meter reading are estimated at the end of each reporting period and the corresponding estimated unbilled revenue is recorded in such reporting period. The unbilled revenue estimate is based on daily system demand volumes, estimated customer usage by class, temperature impacts, line losses and the most recent customer rates. IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. IPL’s estimated recovery amount is recorded in the current period of service and is reflected in customer bills within two years under the provisions of approved formula rates. WPL’s estimated recovery amount is recorded in the current period of service and subject to final adjustments after a customer audit period in the subsequent year. Final settled recovery amounts are reflected in WPL’s customer bills within two years under the provisions of approved formula rates. IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. MISO requires that all load serving entities and generation owners, including IPL and WPL, submit hourly day-ahead and/or real-time bids and offers for energy and ancillary services. The MISO day-ahead and real-time transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded in “Electric utility operating revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements. Non-regulated - Revenues from Alliant Energy’s non-regulated businesses are primarily from its Transportation business and are recognized on an accrual basis as services are rendered or goods are delivered to customers. Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in operating revenues.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, electricity purchased from MISO wholesale energy markets and under PPAs, costs for allowances acquired to allow certain emissions (primarily SO2 and NOx) from their EGUs and costs for chemicals utilized to control emissions from their EGUs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements. IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s retail jurisdiction also allow recovery of prudently incurred costs for emission allowances required to comply with EPA regulations through the fuel adjustment clause. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test year periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers. IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. IPL’s and WPL’s costs for emission allowances are excluded from the fuel-related cost recovery mechanisms and are recovered from their wholesale electric customers through annual changes in base rates determined by a formula rate structure. Purchased Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain of these PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. The transmission cost rider will remain in effect until the IUB’s final decision in IPL’s next retail electric base rate case, at which time the rider will continue in its current form, continue in a modified form or be terminated. WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to the escrow accounting treatment WPL received as part of its approved retail electric rate case (2015/2016 Test Period) in 2014 from the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues in 2015 and 2016 is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. The PSCW’s December 2016 order for WPL’s retail electric rate case (2017/2018 Test Period) extends this escrow accounting treatment through 2018. IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation. Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates each month for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. Energy Efficiency Costs - Costs are incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage. The costs incurred for these programs and initiatives are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through an additional tariff called an energy efficiency cost recovery factor, which is revised annually and includes a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Energy efficiency costs incurred by WPL are recovered from retail electric and gas customers through changes in base rates determined during periodic rate proceedings. Reconciliations of any under-/over-collection of energy efficiency costs from prior periods are also addressed in WPL’s periodic rate proceedings. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Financial Instruments	Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception and are accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments	Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery will be disallowed, an impairment charge is recognized equal to the amount of the carrying value that was disallowed or is probable of being disallowed. If IPL or WPL are only allowed a partial return on the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable a full return will not be allowed, an impairment charge is recognized equal to the difference between the carrying value and the present value of the future revenues expected from their regulated property, plant and equipment. Property, Plant and Equipment of Non-regulated Operations - Property, plant and equipment of non-regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 3 for discussion of Alliant Energy’s impairment analysis of the Franklin County wind farm assets in 2016 and resulting asset valuation charges recorded by Alliant Energy in 2016. Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations	The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Accretion and depreciation expenses related to AROs for Alliant Energy’s non-regulated operations are recorded to depreciation and amortization expenses in Alliant Energy’s income statements. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs	Debt issuance costs and debt premiums or discounts are presented on the balance sheet as a direct deduction from the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by others. Alliant Energy’s non-regulated businesses and Corporate Services expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Allowance for Doubtful Accounts	Allowances for doubtful accounts are recorded for estimated losses resulting from the inability of customers to make required payments. Allowances for doubtful accounts are estimated based on historical write-offs, customer arrears and other economic factors within IPL’s and WPL’s service territories.
Variable Interest Entities	An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements did not reflect any VIEs on a consolidated basis.
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. Upon adoption, the standard can be applied retrospectively to all prior reporting periods presented, or retrospectively with a cumulative effect to the opening retained earnings balance on January 1, 2018 . Alliant Energy, IPL and WPL are currently evaluating the impact of this standard on their financial condition and results of operations and do not anticipate a significant change in revenue recognition for retail electric and gas sales, which represent the majority of Alliant Energy’s, IPL’s and WPL’s revenues. Alliant Energy, IPL and WPL continue to evaluate additional impacts of this standard, as well as which transition method will be utilized. 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 currently expect to adopt this standard on January 1, 2019 and are evaluating the impact of this standard on their financial condition and results of operations and expect an increase in assets and liabilities from recognizing operating leases on their balance sheets.

Summary Of Significant Accoun31

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Average Rates of Depreciation	The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.
IPL [Member]
Schedule of Average Rates of Depreciation	The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.
WPL [Member]
Schedule of Average Rates of Depreciation	The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows: IPL WPL 2016 2015 2014 2016 2015 2014 Electric - generation 3.5% 3.6% 3.6% 3.1% 3.2% 3.2% Electric - distribution 2.4% 2.4% 2.5% 2.6% 2.7% 2.7% Electric - other 4.2% 4.0% 4.0% 4.7% 4.5% 5.9% Gas 3.3% 3.2% 3.3% 2.5% 2.5% 2.5% Other 3.9% 3.9% 4.3% 5.9% 6.0% 6.0%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2016 2015 2014 IPL (Marshalltown CWIP) (a) 7.9% 7.9% 8.0% IPL (other CWIP) 7.7% 7.7% 7.8% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 6.7% 7.9% 4.1% (a) In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2016
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5
Tax Benefit Riders	In 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions): Electric tax benefit rider credits $64 Gas tax benefit rider credits 12 $76
Electric Tax Benefit Rider	Details for IPL’s electric tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage) $64 $72 $85 Income tax benefit resulting from decreased taxable income caused by credits 27 30 35 Income tax benefit representing tax benefits realized from electric tax benefit rider 37 42 50
Revenue Requirement Adjustment	The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions): 2016 2015 2014 Revenue requirement adjustment $14 $14 $15
Gas Tax Benefit Rider	Details for IPL’s gas tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day) $12 $12 $12 Income tax benefit resulting from decreased taxable income caused by credits 5 5 5 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7
Customer Billing Credits	The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions): 2016 2015 2014 Billing credits to reduce retail electric customers’ bills $9 $24 $72
Retail Fuel-related Rate Filings	Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions): Retail Electric Deferral of Over (Under) Timing of Refunds To or Year Rate Increase Collected Fuel-related Costs Collections From Customers 2016 $7 1% $9 Pending 2015 39 4% 10 2016 2014 19 2% (28 ) 2016
IPL [Member]
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5
Tax Benefit Riders	In 2016 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $76 million as follows (in millions): Electric tax benefit rider credits $64 Gas tax benefit rider credits 12 $76
Electric Tax Benefit Rider	Details for IPL’s electric tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues (based on customers’ KWh usage) $64 $72 $85 Income tax benefit resulting from decreased taxable income caused by credits 27 30 35 Income tax benefit representing tax benefits realized from electric tax benefit rider 37 42 50
Revenue Requirement Adjustment	The revenue requirement adjustment resulted in increases to electric revenues in Alliant Energy’s and IPL’s income statements and was recognized through the energy adjustment clause as a reduction of the credits on IPL’s Iowa retail electric customers’ bills from the electric tax benefit rider as follows (in millions): 2016 2015 2014 Revenue requirement adjustment $14 $14 $15
Gas Tax Benefit Rider	Details for IPL’s gas tax benefit rider are as follows (in millions): 2016 2015 2014 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues (based on a fixed amount per day) $12 $12 $12 Income tax benefit resulting from decreased taxable income caused by credits 5 5 5 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7
Customer Billing Credits	The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extended IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provided targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits as follows (in millions): 2016 2015 2014 Billing credits to reduce retail electric customers’ bills $9 $24 $72
WPL [Member]
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Tax-related $1,055.6 $987.7 $1,022.4 $958.2 $33.2 $29.5 Pension and OPEB costs 578.7 579.5 294.0 298.1 284.7 281.4 AROs 105.9 92.4 64.3 50.8 41.6 41.6 WPL’s EGUs retired early 41.4 45.0 — — 41.4 45.0 Derivatives 30.7 70.6 10.0 28.2 20.7 42.4 Emission allowances 26.2 26.9 26.2 26.9 — — Commodity cost recovery 6.0 35.9 0.3 2.8 5.7 33.1 Other 70.6 70.6 41.6 37.6 29.0 33.0 $1,915.1 $1,908.6 $1,458.8 $1,402.6 $456.3 $506.0
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cost of removal obligations $411.6 $406.0 $269.4 $260.4 $142.2 $145.6 IPL’s tax benefit riders 83.5 159.2 83.5 159.2 — — Electric transmission cost recovery 72.0 43.5 35.7 21.9 36.3 21.6 Derivatives 31.5 8.5 12.1 6.7 19.4 1.8 Commodity cost recovery 30.8 37.6 17.8 23.5 13.0 14.1 Energy efficiency cost recovery 20.5 48.3 — — 20.5 48.3 Other 31.1 34.6 12.3 17.5 18.8 17.1 $681.0 $737.7 $430.8 $489.2 $250.2 $248.5
Retail Fuel-related Rate Filings	Details on these rate increases, as well as amounts WPL deferred for the over-collected (included in “Commodity cost recovery” regulatory liabilities) or under-collected (included in “Commodity cost recovery” regulatory assets) fuel-related costs from its retail electric customers are as follows (dollars in millions): Retail Electric Deferral of Over (Under) Timing of Refunds To or Year Rate Increase Collected Fuel-related Costs Collections From Customers 2016 $7 1% $9 Pending 2015 39 4% 10 2016 2014 19 2% (28 ) 2016

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively.
Schedule Of Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9
Schedule Of Allowance for Funds Used During Construction By Project	AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively.
Schedule Of Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9
Schedule Of Allowance for Funds Used During Construction By Project	AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Utility: Electric plant: Generation in service $5,866.9 $5,643.7 $2,916.8 $3,011.6 $2,950.1 $2,632.1 Distribution in service 4,739.2 4,489.9 2,589.3 2,447.9 2,149.9 2,042.0 Other in service 329.1 311.3 223.5 212.2 105.6 99.1 Anticipated to be retired early (a) 108.3 — 108.3 — — — Total electric plant 11,043.5 10,444.9 5,837.9 5,671.7 5,205.6 4,773.2 Gas plant in service 1,107.6 1,018.3 556.7 513.6 550.9 504.7 Other plant in service 549.3 530.6 313.0 296.0 236.3 234.6 Accumulated depreciation (4,135.7 ) (3,939.6 ) (2,258.3 ) (2,152.8 ) (1,877.4 ) (1,786.8 ) Net plant 8,564.7 8,054.2 4,449.3 4,328.5 4,115.4 3,725.7 Leased Sheboygan Falls Energy Facility, net (b) — — — — 52.4 58.6 Construction work in progress 1,226.8 897.5 968.1 578.2 258.7 319.3 Other, net 18.4 18.5 18.2 18.4 0.2 0.1 Total utility 9,809.9 8,970.2 5,435.6 4,925.1 4,426.7 4,103.7 Non-regulated and other: Non-regulated Generation, net (c) 135.0 229.3 — — — — Corporate Services and other, net (d) 334.3 319.6 — — — — Total non-regulated and other 469.3 548.9 — — — — Total property, plant and equipment $10,279.2 $9,519.1 $5,435.6 $4,925.1 $4,426.7 $4,103.7 (a) In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017. (b) Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015 , respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (c) Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015 , respectively. (d) Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015 , respectively.
Schedule Of Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Equity $42.3 $24.4 $23.1 $35.2 $18.6 $17.1 $7.1 $5.8 $6.0 Debt 20.2 12.5 11.7 16.8 9.6 8.8 3.4 2.9 2.9 $62.5 $36.9 $34.8 $52.0 $28.2 $25.9 $10.5 $8.7 $8.9
Schedule Of Allowance for Funds Used During Construction By Project	AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2016 2015 2014 IPL: Marshalltown $43.8 $20.7 $3.7 Environmental controls - Ottumwa Unit 1 — — 10.6 Other 8.2 7.5 11.6 52.0 28.2 25.9 WPL: Environmental controls - Edgewater Unit 5 4.3 5.1 2.7 Other 6.2 3.6 6.2 10.5 8.7 8.9 Alliant Energy $62.5 $36.9 $34.8

Jointly-Owned Electric Utilit34

Jointly-Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2016
Jointly Owned Electric Utility Plant [Line Items]
Components of Jointly-Owned Electric Utility Plants	Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8
IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Components of Jointly-Owned Electric Utility Plants	Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8
WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Components of Jointly-Owned Electric Utility Plants	Information relative to IPL’s and WPL’s ownership interest in these jointly-owned coal-fired EGUs at December 31, 2016 was as follows (dollars in millions): Accumulated Construction Ownership Electric Provision for Work in Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 48.0 % $489.4 $137.3 $11.1 George Neal Unit 4 25.7 % 185.2 80.8 1.6 George Neal Unit 3 28.0 % 150.7 49.1 0.3 Louisa Unit 1 4.0 % 36.5 21.8 0.6 861.8 289.0 13.6 WPL Columbia Units 1-2 46.2 % 640.2 185.0 51.0 Edgewater Unit 4 68.2 % 99.4 58.4 0.2 739.6 243.4 51.2 Alliant Energy $1,601.4 $532.4 $64.8

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions): Maximum Average 2016 2015 2014 2016 2015 2014 Outstanding aggregate cash proceeds $172.0 $137.0 $150.0 $73.2 $46.7 $46.4
Receivables Sold Under The Agreement	As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 Customer accounts receivable $157.6 $109.7 Unbilled utility revenues 90.4 71.3 Other receivables 0.1 0.1 Receivables sold to third party 248.1 181.1 Less: cash proceeds (a) 21.0 5.0 Deferred proceeds 227.1 176.1 Less: allowance for doubtful accounts 16.0 4.1 Fair value of deferred proceeds $211.1 $172.0 Outstanding receivables past due $68.0 $18.0 (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 Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 2014 Collections reinvested in receivables $1,818.1 $1,812.9 $1,997.9 Write-offs, net of recoveries 4.8 8.8 11.4
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions): Maximum Average 2016 2015 2014 2016 2015 2014 Outstanding aggregate cash proceeds $172.0 $137.0 $150.0 $73.2 $46.7 $46.4
Receivables Sold Under The Agreement	As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 Customer accounts receivable $157.6 $109.7 Unbilled utility revenues 90.4 71.3 Other receivables 0.1 0.1 Receivables sold to third party 248.1 181.1 Less: cash proceeds (a) 21.0 5.0 Deferred proceeds 227.1 176.1 Less: allowance for doubtful accounts 16.0 4.1 Fair value of deferred proceeds $211.1 $172.0 Outstanding receivables past due $68.0 $18.0 (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 Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2016 2015 2014 Collections reinvested in receivables $1,818.1 $1,812.9 $1,997.9 Write-offs, net of recoveries 4.8 8.8 11.4
WPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable Details	Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Customer $111.7 $93.8 $— $4.6 $104.4 $81.5 Unbilled utility revenues 90.2 83.1 — 1.2 90.2 81.9 Deferred proceeds 211.1 172.0 211.1 172.0 — — Other 89.0 53.5 30.7 22.8 38.8 25.7 Allowance for doubtful accounts (8.7 ) (4.8 ) (1.1 ) (0.6 ) (7.1 ) (3.7 ) $493.3 $397.6 $240.7 $200.0 $226.3 $185.4

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investment [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions): Ownership Interest at Carrying Value at December 31, Equity (Income) / Loss December 31, 2016 2016 2015 2016 2015 2014 Alliant Energy ATC (a) 16% $317.6 $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Other Various 8.4 9.6 (0.5 ) 0.4 1.5 $326.0 $302.9 ($39.6 ) ($33.8 ) ($40.4 ) WPL ATC —% $— $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Wisconsin River Power Company 50% 7.7 8.7 (0.7 ) (0.9 ) (0.9 ) $7.7 $302.0 ($39.8 ) ($35.1 ) ($42.8 ) (a) Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC.
Summary Financial Information	Summary aggregate financial information from the financial statements of these investments is as follows (in millions): Alliant Energy WPL 2016 2015 2014 2016 2015 2014 Operating revenues $658 $624 $643 $658 $624 $643 Operating income 331 299 330 331 299 330 Net income 232 186 240 234 202 240 As of December 31: Current assets 82 88 6 87 Non-current assets 4,340 3,987 19 3,977 Current liabilities 498 332 3 332 Non-current liabilities 2,144 2,052 7 2,052
Cash Surrender Value of Life Insurance Policies	At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4
IPL [Member]
Investment [Line Items]
Cash Surrender Value of Life Insurance Policies	At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4
WPL [Member]
Investment [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s and WPL’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions): Ownership Interest at Carrying Value at December 31, Equity (Income) / Loss December 31, 2016 2016 2015 2016 2015 2014 Alliant Energy ATC (a) 16% $317.6 $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Other Various 8.4 9.6 (0.5 ) 0.4 1.5 $326.0 $302.9 ($39.6 ) ($33.8 ) ($40.4 ) WPL ATC —% $— $293.3 ($39.1 ) ($34.2 ) ($41.9 ) Wisconsin River Power Company 50% 7.7 8.7 (0.7 ) (0.9 ) (0.9 ) $7.7 $302.0 ($39.8 ) ($35.1 ) ($42.8 ) (a) Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC.
Summary Financial Information	Summary aggregate financial information from the financial statements of these investments is as follows (in millions): Alliant Energy WPL 2016 2015 2014 2016 2015 2014 Operating revenues $658 $624 $643 $658 $624 $643 Operating income 331 299 330 331 299 330 Net income 232 186 240 234 202 240 As of December 31: Current assets 82 88 6 87 Non-current assets 4,340 3,987 19 3,977 Current liabilities 498 332 3 332 Non-current liabilities 2,144 2,052 7 2,052
Cash Surrender Value of Life Insurance Policies	At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Cash surrender value $10.6 $42.3 $— $18.9 $5.8 $6.4

Common Equity (Tables)

Common Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Common Equity [Line Items]
Common Stock Activity	A summary of Alliant Energy’s common stock activity was as follows: 2016 2015 2014 Shares outstanding, January 1 226,918,432 221,871,360 221,887,338 At-the-market offering program — 4,373,234 — Shareowner Direct Plan issuances 732,814 606,010 — Equity-based compensation plans ( Note 12(b) ) 22,408 112,756 71,094 Other — (44,928 ) (87,072 ) Shares outstanding, December 31 227,673,654 226,918,432 221,871,360

Redeemable Preferred Stock (Tab

Redeemable Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2016
Class of Stock [Line Items]
Schedule of Carrying Value of Cumulative Preferred Stock	Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Series Liquidation Preference/Stated Value Shares Authorized Shares Outstanding 2016 2015 (in millions) 5.1% $25 8,000,000 8,000,000 $200.0 $200.0
IPL [Member]
Class of Stock [Line Items]
Schedule of Carrying Value of Cumulative Preferred Stock	Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Series Liquidation Preference/Stated Value Shares Authorized Shares Outstanding 2016 2015 (in millions) 5.1% $25 8,000,000 8,000,000 $200.0 $200.0

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Debt Maturities	At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8
IPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Debt Maturities	At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8
WPL [Member]
Debt Disclosure [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt and back-stopped by the credit facilities was as follows (dollars in millions): Alliant Energy IPL WPL December 31 2016 2015 2016 2015 2016 2015 Commercial paper outstanding $244.1 $159.8 $— $— $52.3 $19.9 Commercial paper weighted average interest rates 0.9% 0.7% N/A N/A 0.7% 0.4% Available credit facility capacity $755.9 $840.2 $300.0 $300.0 $347.7 $380.1 Alliant Energy IPL WPL For the year ended 2016 2015 2016 2015 2016 2015 Maximum amount outstanding (based on daily outstanding balances) $251.8 $181.2 $3.1 $18.4 $118.3 $24.7 Average amount outstanding (based on daily outstanding balances) $179.0 $119.2 $— $0.2 $38.1 $2.2 Weighted average interest rates 0.6% 0.4% 0.7% 0.4% 0.4% 0.3%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 53% 47% 49%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2016 2015 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 5.875%, due 2018 $100.0 $100.0 $— $100.0 $100.0 $— 7.25%, due 2018 250.0 250.0 — 250.0 250.0 — 3.65%, due 2020 200.0 200.0 — 200.0 200.0 — 3.25%, due 2024 250.0 250.0 — 250.0 250.0 — 3.4%, due 2025 250.0 250.0 — 250.0 250.0 — 5.5%, due 2025 50.0 50.0 — 50.0 50.0 — 6.45%, due 2033 100.0 100.0 — 100.0 100.0 — 6.3%, due 2034 125.0 125.0 — 125.0 125.0 — 6.25%, due 2039 300.0 300.0 — 300.0 300.0 — 4.7%, due 2043 250.0 250.0 — 250.0 250.0 — 3.7%, due 2046 (b) 300.0 300.0 — — — — 2,175.0 2,175.0 — 1,875.0 1,875.0 — Debentures (a): 5%, due 2019 250.0 — 250.0 250.0 — 250.0 4.6%, due 2020 150.0 — 150.0 150.0 — 150.0 2.25%, due 2022 250.0 — 250.0 250.0 — 250.0 6.25%, due 2034 100.0 — 100.0 100.0 — 100.0 6.375%, due 2037 300.0 — 300.0 300.0 — 300.0 7.6%, due 2038 250.0 — 250.0 250.0 — 250.0 4.1%, due 2044 250.0 — 250.0 250.0 — 250.0 1,550.0 — 1,550.0 1,550.0 — 1,550.0 Other: AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d) 500.0 — — — — — Corporate Services 3.45% senior notes, due 2022 (a) 75.0 — — 75.0 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a) 53.8 — — 56.8 — — Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 250.0 — — Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c) — — — 60.0 — — Other, 1% at December 31, 2016, due 2017 to 2025 3.3 — — 3.7 — — 632.1 — — 445.5 — — Subtotal 4,357.1 2,175.0 1,550.0 3,870.5 1,875.0 1,550.0 Current maturities (4.6 ) — — (313.4 ) — — Unamortized debt issuance costs (23.4 ) (13.7 ) (9.1 ) (22.3 ) (11.8 ) (9.9 ) Unamortized debt (discount) and premium, net (13.5 ) (7.8 ) (5.7 ) (12.6 ) (6.3 ) (6.2 ) Long-term debt, net (e) $4,315.6 $2,153.5 $1,535.2 $3,522.2 $1,856.9 $1,533.9 (a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption. (b) In 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. (c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes. (d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement. (e) There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Debt Maturities	At December 31, 2016 , debt maturities for 2017 through 2021 were as follows (in millions): 2017 2018 2019 2020 2021 IPL $— $350 $— $200 $— WPL — — 250 150 — AEF 5 506 6 7 8 Alliant Energy $5 $856 $256 $357 $8

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7
IPL [Member]
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7
WPL [Member]
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2016 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Alliant Energy $6 $6 $2 $2 $1 $15 $32 IPL 3 2 1 1 1 10 18 WPL 3 4 — — — — 7
WPL [Member] | Sheboygan Falls Energy Facility [Member]
Schedule of Capital Lease Expense	Sheboygan Falls lease expenses were included in WPL’s income statements as follows (in millions): 2016 2015 2014 Interest expense $9.3 $9.9 $10.4 Depreciation and amortization 6.2 6.2 6.2 $15.5 $16.1 $16.6
Schedule of Future Minimum Lease Payments for Capital Leases	At December 31, 2016 , WPL’s estimated future minimum capital lease payments for Sheboygan Falls were as follows (in millions): 2017 2018 2019 2020 2021 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Sheboygan Falls $15 $15 $15 $15 $15 $53 $128 $44 $84

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax [Line Items]
Schedule of Components of Income Tax Expense (Benefit)	The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3
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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 %
Schedule of Deferred Tax Assets and Liabilities	The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4
Summary Of Tax Credit Carryforwards	At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113
Schedule Of Open Tax Years	Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
IPL [Member]
Income Tax [Line Items]
Schedule of Components of Income Tax Expense (Benefit)	The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3
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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 %
Schedule of Deferred Tax Assets and Liabilities	The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4
Summary Of Tax Credit Carryforwards	At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113
Schedule Of Open Tax Years	Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
WPL [Member]
Income Tax [Line Items]
Schedule of Components of Income Tax Expense (Benefit)	The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Current tax expense (benefit): Federal $1.8 $2.0 $36.6 ($12.8 ) ($14.1 ) $8.9 ($22.3 ) $4.7 $2.0 State 17.2 3.2 9.3 15.5 11.5 10.4 1.1 0.6 0.8 IPL’s tax benefit riders (44.2 ) (49.0 ) (56.7 ) (44.2 ) (49.0 ) (56.7 ) — — — Deferred tax expense (benefit): Federal 112.8 120.8 83.5 59.1 40.7 10.8 112.3 76.8 81.1 State 4.9 27.9 4.6 (9.0 ) 3.3 (7.9 ) 20.8 20.2 20.0 Production tax credits (31.8 ) (33.1 ) (31.3 ) (14.0 ) (14.5 ) (13.8 ) (17.8 ) (18.6 ) (17.5 ) Investment tax credits (1.3 ) (1.4 ) (1.6 ) (0.5 ) (0.6 ) (0.6 ) (0.8 ) (0.8 ) (1.0 ) Provision recorded as a change in accrued interest — — (0.1 ) — — — — — (0.1 ) $59.4 $70.4 $44.3 ($5.9 ) ($22.7 ) ($48.9 ) $93.3 $82.9 $85.3
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 2016 2015 2014 2016 2015 2014 2016 2015 2014 Statutory federal income tax rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % State income taxes, net of federal benefits 5.4 5.2 5.4 6.4 6.2 6.1 5.1 5.1 5.1 IPL’s tax benefit riders (10.0 ) (10.6 ) (12.9 ) (20.1 ) (28.3 ) (39.6 ) — — — Effect of rate-making on property-related differences (8.5 ) (6.8 ) (7.5 ) (16.2 ) (17.2 ) (21.9 ) (0.7 ) (0.5 ) (0.7 ) Production tax credits (7.2 ) (7.2 ) (7.1 ) (6.3 ) (8.3 ) (9.6 ) (6.2 ) (7.1 ) (6.6 ) Adjustment of prior period taxes (0.8 ) 0.8 (1.3 ) (1.2 ) 0.7 (3.0 ) (0.1 ) 0.1 — Other items, net (0.5 ) (1.1 ) (1.5 ) (0.3 ) (1.2 ) (1.2 ) (0.5 ) (0.8 ) (0.8 ) Overall income tax rate 13.4 % 15.3 % 10.1 % (2.7 %) (13.1 %) (34.2 %) 32.6 % 31.8 % 32.0 %
Schedule of Deferred Tax Assets and Liabilities	The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions): Alliant Energy IPL WPL 2016 2015 2016 2015 2016 2015 Deferred tax liabilities: Property $2,919.0 $2,762.9 $1,677.0 $1,587.8 $1,124.5 $1,027.0 Investment in ATC 153.1 138.1 — — — 138.9 Other 95.3 157.3 71.4 87.8 59.1 67.9 Total deferred tax liabilities 3,167.4 3,058.3 1,748.4 1,675.6 1,183.6 1,233.8 Deferred tax assets: Federal credit carryforwards 268.4 236.4 95.9 81.7 112.9 95.5 Net operating losses carryforwards - federal 173.3 250.9 69.6 113.1 75.4 105.1 Regulatory liability - IPL’s tax benefit riders 34.7 66.1 34.7 66.1 — — Net operating losses carryforwards - state 32.9 38.3 0.6 1.1 0.1 3.6 Other 87.9 85.4 35.8 35.6 23.6 24.2 Total deferred tax assets 597.2 677.1 236.6 297.6 212.0 228.4 Total deferred tax liabilities, net $2,570.2 $2,381.2 $1,511.8 $1,378.0 $971.6 $1,005.4
Summary Of Tax Credit Carryforwards	At December 31, 2016 , carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL Federal net operating losses 2030-2034 $506 $206 $215 State net operating losses 2018-2034 673 12 2 Federal tax credits 2022-2036 274 100 113
Schedule Of Open Tax Years	Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows: Consolidated federal income tax returns (a) 2013 - 2015 Consolidated Iowa income tax returns (b) 2013 - 2015 Wisconsin combined tax returns (c) 2012 - 2015 (a) The federal tax returns for 2013 and 2014 are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b) The statute of limitations for these Iowa tax returns expires three years from each filing date. (c) The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00%
Net Periodic Benefit Costs (Credits)	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost	The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4
Funded Status Of Benefit Plans	A reconciliation of the funded status of Alliant Energy’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on Alliant Energy’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $1,206.3 $1,301.5 $221.4 $231.1 Service cost 12.6 15.9 5.3 5.5 Interest cost 53.0 53.6 9.4 9.1 Plan participants’ contributions — — 2.4 3.1 Plan amendments — — — (0.3 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 48.3 (70.1 ) (0.3 ) (9.4 ) Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Net benefit obligation at December 31 1,244.3 1,206.3 220.1 221.4 Change in plan assets: Fair value of plan assets at January 1 895.0 1,018.1 106.9 121.6 Actual return on plan assets 74.3 (30.2 ) 8.2 (4.9 ) Employer contributions 2.3 2.2 6.4 4.8 Plan participants’ contributions — — 2.4 3.1 Gross benefits paid (75.9 ) (95.1 ) (18.1 ) (17.7 ) Fair value of plan assets at December 31 895.7 895.0 105.8 106.9 Under funded status at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.2 $3.0 Other current liabilities (6.5 ) (2.6 ) (8.6 ) (6.2 ) Pension and other benefit obligations (342.1 ) (308.7 ) (108.9 ) (111.3 ) Net amounts recognized at December 31 ($348.6 ) ($311.3 ) ($114.3 ) ($114.5 ) Amounts recognized in Regulatory Assets (refer to Note 2 for details) and AOCL (refer to Alliant Energy’s common equity statements for details) consist of: Net actuarial loss $535.1 $533.1 $52.6 $59.8 Prior service credit (6.9 ) (7.2 ) (1.5 ) (5.6 ) $528.2 $525.9 $51.1 $54.2
Accumulated Benefit Obligations	Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A
Regulatory Assets	In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments	Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8
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 was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6
Carrying Value And Fair Market Value Of The Deferred Compensation Obligations	At December 31, the carrying value of the deferred compensation obligation for the company stock accounts and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust were as follows (in millions): 2016 2015 Carrying value $10.0 $8.5 Fair market value 16.7 13.4
Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts	At December 31, the carrying value of deferred compensation obligations for participants’ interest and equity accounts, which approximates fair market value, was as follows (in millions): Alliant Energy IPL 2016 2015 2016 2015 Carrying value $19.4 $18.3 $4.6 $5.0
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00%
Net Periodic Benefit Costs (Credits)	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost	The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4
Funded Status Of Benefit Plans	A reconciliation of the funded status of IPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on IPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $556.1 $603.1 $91.3 $96.4 Service cost 7.5 8.8 2.3 2.4 Interest cost 24.5 25.0 3.8 3.8 Plan participants’ contributions — — 0.9 1.0 Plan amendments — — — (0.1 ) Actuarial (gain) loss 19.1 (32.3 ) (0.7 ) (4.6 ) Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Net benefit obligation at December 31 570.4 556.1 90.1 91.3 Change in plan assets: Fair value of plan assets at January 1 422.7 484.7 69.2 78.7 Actual return on plan assets 35.3 (14.3 ) 5.3 (3.1 ) Employer contributions 0.8 0.8 0.3 0.2 Plan participants’ contributions — — 0.9 1.0 Gross benefits paid (36.8 ) (48.5 ) (7.5 ) (7.6 ) Fair value of plan assets at December 31 422.0 422.7 68.2 69.2 Under funded status at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $0.4 $— Other current liabilities (0.7 ) (0.8 ) (1.9 ) — Pension and other benefit obligations (147.7 ) (132.6 ) (20.4 ) (22.1 ) Net amounts recognized at December 31 ($148.4 ) ($133.4 ) ($21.9 ) ($22.1 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $233.6 $235.5 $25.4 $29.8 Prior service credit (2.3 ) (2.5 ) — (2.7 ) $231.3 $233.0 $25.4 $27.1
Accumulated Benefit Obligations	Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A
Regulatory Assets	In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments	Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8
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 was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6
Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts	At December 31, the carrying value of deferred compensation obligations for participants’ interest and equity accounts, which approximates fair market value, was as follows (in millions): Alliant Energy IPL 2016 2015 2016 2015 Carrying value $19.4 $18.3 $4.6 $5.0
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.19% 4.47% 4.18% 3.98% 4.30% 3.97% Discount rate for net periodic cost 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.30% 6.20% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.65 % - 4.50% 3.50 % - 4.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.22% 4.50% 4.20% 3.95% 4.28% 3.94% Discount rate for net periodic cost 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 6.60% 7.60% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2016 2015 2014 2016 2015 2014 Discount rate for benefit obligations 4.23% 4.51% 4.20% 3.96% 4.28% 3.96% Discount rate for net periodic cost 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.70% 4.60% 7.30% Rate of compensation increase 3.65% 3.65% 3.50% N/A N/A N/A Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.00% 7.25% 6.75% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00%
Net Periodic Benefit Costs (Credits)	The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $12.6 $15.9 $13.1 $5.3 $5.5 $5.2 Interest cost 53.0 53.6 54.1 9.4 9.1 9.5 Expected return on plan assets (a) (65.5 ) (75.0 ) (74.9 ) (6.1 ) (8.4 ) (8.3 ) Amortization of prior service cost (credit) (b) (0.3 ) (0.2 ) — (4.1 ) (11.3 ) (11.9 ) Amortization of actuarial loss (c) 37.4 35.4 19.5 4.7 4.8 2.4 Additional benefit costs — 0.5 — — — — $37.2 $30.2 $11.8 $9.2 ($0.3 ) ($3.1 ) IPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $7.5 $8.8 $7.2 $2.3 $2.4 $2.4 Interest cost 24.5 25.0 25.1 3.8 3.8 3.9 Expected return on plan assets (a) (30.9 ) (35.8 ) (35.7 ) (4.3 ) (5.7 ) (5.8 ) Amortization of prior service cost (credit) (b) (0.2 ) (0.1 ) — (2.6 ) (6.1 ) (6.3 ) Amortization of actuarial loss (c) 16.5 15.3 8.0 2.6 2.3 1.1 $17.4 $13.2 $4.6 $1.8 ($3.3 ) ($4.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2016 2015 2014 2016 2015 2014 Service cost $4.9 $5.8 $4.9 $2.0 $2.1 $2.0 Interest cost 22.3 22.6 22.6 3.8 3.7 3.8 Expected return on plan assets (a) (28.3 ) (32.4 ) (32.4 ) (0.8 ) (1.5 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.2 0.3 (0.9 ) (3.5 ) (3.9 ) Amortization of actuarial loss (c) 17.6 16.8 9.2 1.8 2.2 1.3 Additional benefit costs — 0.5 — — — — $16.7 $13.5 $4.6 $5.9 $3.0 $1.9 (a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost	The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2017 is as follows (in millions): Alliant Energy IPL WPL Defined Benefit Defined Benefit Defined Benefit Pension Plans OPEB Plans Pension Plans OPEB Plans Pension Plans OPEB Plans Actuarial loss $37.5 $3.8 $16.1 $2.0 $18.5 $1.6 Prior service cost (credit) (0.4 ) (0.2 ) (0.2 ) — 0.1 (0.2 ) $37.1 $3.6 $15.9 $2.0 $18.6 $1.4
Funded Status Of Benefit Plans	A reconciliation of the funded status of WPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on WPL’s balance sheets at December 31 was as follows (in millions): Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Change in benefit obligation: Net benefit obligation at January 1 $505.9 $547.6 $89.7 $94.0 Service cost 4.9 5.8 2.0 2.1 Interest cost 22.3 22.6 3.8 3.7 Plan participants’ contributions — — 1.2 1.6 Plan amendments — — — (0.2 ) Additional benefit costs — 0.5 — — Actuarial (gain) loss 25.7 (30.0 ) 0.5 (3.5 ) Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Net benefit obligation at December 31 529.2 505.9 88.9 89.7 Change in plan assets: Fair value of plan assets at January 1 386.8 440.3 18.7 21.8 Actual return on plan assets 32.4 (13.0 ) 1.2 (1.1 ) Employer contributions 0.1 0.1 5.8 4.4 Plan participants’ contributions — — 1.2 1.6 Gross benefits paid (29.6 ) (40.6 ) (8.3 ) (8.0 ) Fair value of plan assets at December 31 389.7 386.8 18.6 18.7 Under funded status at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $2.7 $3.0 Other current liabilities (0.1 ) (0.1 ) (6.4 ) (6.0 ) Pension and other benefit obligations (139.4 ) (119.0 ) (66.6 ) (68.0 ) Net amounts recognized at December 31 ($139.5 ) ($119.1 ) ($70.3 ) ($71.0 ) Amounts recognized in Regulatory Assets consist of (refer to Note 2 for details): Net actuarial loss $236.1 $232.1 $21.5 $23.3 Prior service credit (1.4 ) (1.2 ) (1.5 ) (2.4 ) $234.7 $230.9 $20.0 $20.9
Accumulated Benefit Obligations	Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions): Defined Benefit Pension Plans OPEB Plans Alliant Energy 2016 2015 2016 2015 Accumulated benefit obligations $1,201.5 $1,166.0 $220.1 $221.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,201.5 1,166.0 220.1 221.4 Fair value of plan assets 895.7 895.0 105.8 106.9 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,244.3 1,206.3 N/A N/A Fair value of plan assets 895.7 895.0 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2016 2015 2016 2015 Accumulated benefit obligations $546.7 $531.0 $90.1 $91.3 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 546.7 531.0 90.1 91.3 Fair value of plan assets 422.0 422.7 68.2 69.2 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 570.4 556.1 N/A N/A Fair value of plan assets 422.0 422.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2016 2015 2016 2015 Accumulated benefit obligations $513.2 $493.8 $88.9 $89.7 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 513.2 493.8 88.9 89.7 Fair value of plan assets 389.7 386.8 18.6 18.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 529.2 505.9 N/A N/A Fair value of plan assets 389.7 386.8 N/A N/A
Regulatory Assets	In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions): IPL WPL 2016 2015 2016 2015 Regulatory assets $37.3 $38.0 $30.0 $29.5
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2017 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $6.5 $0.7 $0.1 OPEB plans 8.7 2.0 6.4 (a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments	Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $74.8 $73.2 $75.5 $77.6 $79.9 $405.9 OPEB 18.6 18.5 18.2 17.8 17.6 82.6 $93.4 $91.7 $93.7 $95.4 $97.5 $488.5 IPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $34.0 $35.1 $35.0 $37.2 $37.9 $192.1 OPEB 7.7 7.6 7.4 7.4 7.2 34.0 $41.7 $42.7 $42.4 $44.6 $45.1 $226.1 WPL 2017 2018 2019 2020 2021 2022 - 2026 Defined benefit pension benefits $30.2 $30.9 $31.8 $32.5 $32.4 $167.1 OPEB 8.0 8.0 7.8 7.4 7.3 32.7 $38.2 $38.9 $39.6 $39.9 $39.7 $199.8
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 was as follows (in millions): Alliant Energy IPL WPL 2016 2015 2014 2016 2015 2014 2016 2015 2014 Compensation expense $18.0 $10.7 $15.3 $9.5 $5.7 $8.3 $7.9 $4.7 $6.4 Income tax benefits 7.4 4.4 6.2 4.0 2.4 3.4 3.2 1.9 2.6
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30% At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $30.4 $5.0 $25.4 $— $23.1 $— $23.1 $— Equity securities - domestic 183.6 183.6 — — 116.4 116.4 — — Equity securities - international 97.4 97.4 — — 93.9 93.9 — — Global asset allocation securities 53.0 53.0 — — 52.9 52.9 — — Fixed income securities 125.4 53.6 71.8 — — — — — Total assets in fair value hierarchy 489.8 $392.6 $97.2 $— 286.3 $263.2 $23.1 $— Assets measured at net asset value 405.9 608.5 Accrued investment income 1.1 0.2 Due to brokers, net (pending trades with brokers) (1.1 ) — Total pension plan assets $895.7 $895.0
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30% At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $14.4 $2.4 $12.0 $— $10.9 $— $10.9 $— Equity securities - domestic 86.5 86.5 — — 54.9 54.9 — — Equity securities - international 45.9 45.9 — — 44.4 44.4 — — Global asset allocation securities 24.9 24.9 — — 25.0 25.0 — — Fixed income securities 59.1 25.3 33.8 — — — — — Total assets in fair value hierarchy 230.8 $185.0 $45.8 $— 135.2 $124.3 $10.9 $— Assets measured at net asset value 191.2 287.4 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $422.0 $422.7
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $13.3 $2.2 $11.1 $— $10.0 $— $10.0 $— Equity securities - domestic 79.9 79.9 — — 50.3 50.3 — — Equity securities - international 42.4 42.4 — — 40.6 40.6 — — Global asset allocation securities 23.0 23.0 — — 22.8 22.8 — — Fixed income securities 54.5 23.3 31.2 — — — — — Total assets in fair value hierarchy 213.1 $170.8 $42.3 $— 123.7 $113.7 $10.0 $— Assets measured at net asset value 176.6 263.0 Accrued investment income 0.5 0.1 Due to brokers, net (pending trades with brokers) (0.5 ) — Total pension plan assets $389.7 $386.8 At December 31, 2016 , the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 5% 3% Equity securities - domestic 22 % - 42% 30% Equity securities - international 8 % - 28% 17% Global asset allocation securities 5 % - 15% 10% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 30%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, the fair values of Alliant Energy’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.5 $2.0 $1.5 $— $3.6 $— $3.6 $— Equity securities - domestic 22.5 22.5 — — 22.1 22.1 — — Equity securities - international 13.5 13.5 — — 13.4 13.4 — — Global asset allocation securities 16.5 16.5 — — 16.0 16.0 — — Fixed income securities 46.8 46.2 0.6 — 46.3 46.3 — — Total assets in fair value hierarchy 102.8 $100.7 $2.1 $— 101.4 $97.8 $3.6 $— Assets measured at net asset value 3.0 5.5 Total OPEB plan assets $105.8 $106.9 At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46%
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, the fair values of IPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.8 $0.8 $— $— $0.9 $— $0.9 $— Equity securities - domestic 17.0 17.0 — — 16.7 16.7 — — Equity securities - international 11.0 11.0 — — 10.8 10.8 — — Global asset allocation securities 7.0 7.0 — — 6.9 6.9 — — Fixed income securities 32.4 32.4 — — 33.3 33.3 — — Total assets in fair value hierarchy 68.2 $68.2 $— $— 68.6 $67.7 $0.9 $— Assets measured at net asset value — 0.6 Total OPEB plan assets $68.2 $69.2 At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46%
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations	At December 31, the fair values of WPL’s OPEB plan assets were as follows (in millions): 2016 2015 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.0 $0.7 $1.3 $— $2.3 $— $2.3 $— Global asset allocation securities 5.5 5.5 — — 5.4 5.4 — — Fixed income securities 11.1 11.1 — — 11.0 11.0 — — Total OPEB plan assets $18.6 $17.3 $1.3 $— $18.7 $16.4 $2.3 $— At December 31, 2016 , the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0 % - 15% 3% Equity securities - domestic 0 % - 45% 22% Equity securities - international 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 46%
401(k) Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employees Participate In Defined Contribution Retirement Plans	Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5
401(k) Savings Plan [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Employees Participate In Defined Contribution Retirement Plans	Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5
401(k) Savings Plan [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Employees Participate In Defined Contribution Retirement Plans	Costs related to the 401(k) savings plans, 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 2016 2015 2014 2016 2015 2014 2016 2015 2014 401(k) costs $23.6 $24.9 $22.5 $12.0 $12.7 $11.1 $10.7 $11.2 $10.5
Performance Shares and Performance 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 2014 2016 2015 2014 Nonvested awards, January 1 288,430 288,848 279,880 116,412 127,330 131,824 Granted 68,585 90,806 102,442 23,918 35,674 40,844 Vested (98,186 ) (91,224 ) (90,470 ) (42,760 ) (45,690 ) (41,502 ) Forfeited (1,230 ) — (3,004 ) (4,250 ) (902 ) (3,836 ) Nonvested awards, December 31 257,599 288,430 288,848 93,320 116,412 127,330 Granted Awards - Each performance share’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2016, the value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For performance units granted in 2015 and 2014, each performance 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. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. 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 - 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 2014 2016 2015 2014 2013 Grant 2012 Grant 2011 Grant 2013 Grant 2012 Grant 2011 Grant Performance awards vested 98,186 91,224 90,470 42,760 45,690 41,502 Percentage of target number of performance awards 165.0% 167.5% 147.5% 165.0% 167.5% 147.5% Aggregate payout value (in millions) $5.1 $5.1 $3.4 $1.7 $1.6 $1.2 Payout - cash (in millions) $2.9 $3.2 $2.9 $1.7 $1.6 $1.2 Payout - common stock shares issued 22,408 21,950 9,620 N/A N/A N/A Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at December 31, 2016 , by year of grant, were as follows: Performance Shares Performance Units 2016 Grant 2015 Grant 2014 Grant 2016 Grant 2015 Grant 2014 Grant Nonvested awards at target 67,355 90,806 99,438 22,657 33,268 37,395 Alliant Energy common stock closing price on December 30, 2016 $37.89 $37.89 $37.89 $37.89 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 135 % 155 % 148 % 135 % 155 % 148 % Fair values of each nonvested award $51.15 $58.73 $56.08 $51.15 $50.45 $39.80
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 2014 Weighted Average Weighted Average Weighted Average Shares Grant Date Fair Value Shares Grant Date Fair Value Shares Grant Date Fair Value Nonvested shares, January 1 190,244 $29.59 197,624 $25.35 317,844 $21.36 Granted — — 90,806 32.55 102,442 26.89 Vested (a) — — (98,186 ) 23.79 (181,694 ) 20.46 Forfeited (b) — — — — (40,968 ) 19.93 Nonvested shares, December 31 190,244 29.59 190,244 29.59 197,624 25.35 (a) In 2015, 98,186 performance-contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 91,224 and 90,470 performance-contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met. (b) The forfeitures during 2014 were primarily caused by retirements and terminations of participants.
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, December 31 67,355 33.96
Restricted Stock Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the restricted stock units activity was as follows: 2016 Granted 58,790 Forfeited (1,054 ) Nonvested units, December 31 57,736
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 2014 Nonvested awards, January 1 163,752 157,860 193,954 Granted — 82,210 84,892 Vested (a) — (74,664 ) (111,034 ) Forfeited (3,652 ) (1,654 ) (9,952 ) Nonvested awards, December 31 160,100 163,752 157,860 (a) In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million . In 2014, 69,532 and 41,502 performance-contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million , respectively.

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation Of Changes In Asset Retirement Obligations (AROs)	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) (13.3 ) 17.3 (5.8 ) 15.1 (7.5 ) 3.2 Liabilities settled (14.0 ) (8.8 ) (6.8 ) (4.3 ) (7.2 ) (4.5 ) Liabilities incurred (a) 2.6 86.6 0.7 67.8 1.9 18.8 Accretion expense 6.4 4.9 3.7 2.5 2.3 2.0 Balance, December 31 $195.7 $214.0 $124.7 $132.9 $61.4 $71.9 (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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million , $67 million and $20 million , respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —
WPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2016 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 $41.4 $— $4.6 $36.8 $41.4 $18.4 $— $2.5 $15.9 $18.4 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 28.6 — 0.5 28.1 28.6 64.6 — 16.0 48.6 64.6 Long-term debt (including current maturities) 4,320.2 — 4,795.7 3.3 4,799.0 3,835.6 — 4,332.4 3.7 4,336.1 IPL’s cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 IPL 2016 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 $20.8 $— $2.8 $18.0 $20.8 $15.5 $— $2.0 $13.5 $15.5 Deferred proceeds 211.1 — — 211.1 211.1 172.0 — — 172.0 172.0 Liabilities and equity: Derivatives 8.3 — 0.4 7.9 8.3 23.4 — 8.0 15.4 23.4 Long-term debt (including current maturities) 2,153.5 — 2,352.3 — 2,352.3 1,856.9 — 2,092.7 — 2,092.7 Cumulative preferred stock 200.0 194.8 — — 194.8 200.0 206.6 — — 206.6 WPL 2016 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 $20.6 $— $1.8 $18.8 $20.6 $2.9 $— $0.5 $2.4 $2.9 Liabilities and equity: Derivatives 20.3 — 0.1 20.2 20.3 41.2 — 8.0 33.2 41.2 Long-term debt (including current maturities) 1,535.2 — 1,807.4 — 1,807.4 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 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) 30.7 (63.5 ) — — Transfers into Level 3 0.9 — — — Transfers out of Level 3 1.2 0.3 — — Purchases 22.0 36.9 — — Sales (1.0 ) (1.9 ) — — Settlements (a) (12.4 ) (22.4 ) 39.1 (5.2 ) Ending balance, December 31 $8.7 ($32.7 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $32.7 ($56.0 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 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) 7.3 (29.6 ) — — Transfers into Level 3 0.5 — — — Transfers out of Level 3 0.2 — — — Purchases 20.6 33.1 — — Sales (1.0 ) (1.8 ) — — Settlements (a) (15.6 ) (23.0 ) 39.1 (5.2 ) Ending balance, December 31 $10.1 ($1.9 ) $211.1 $172.0 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $8.5 ($23.1 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2016 2015 Beginning balance, January 1 ($30.8 ) ($1.5 ) Total net gains (losses) included in changes in net assets (realized/unrealized) 23.4 (33.9 ) Transfers into Level 3 0.4 — Transfers out of Level 3 1.0 0.3 Purchases 1.4 3.8 Sales — (0.1 ) Settlements 3.2 0.6 Ending balance, December 31 ($1.4 ) ($30.8 ) 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 December 31 $24.2 ($32.9 ) (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2016 ($2.3 ) $11.0 $0.1 $10.0 ($2.4 ) $1.0 2015 (43.1 ) 10.4 (12.3 ) 10.4 (30.8 ) —

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018
Fair Value of Financial Instruments	At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4
IPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018
Fair Value of Financial Instruments	At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4
WPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 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 2,628 2017-2018 8,970 2017 139,865 2017-2023 4,239 2017-2019 6,552 2017-2018 IPL — — 5,465 2017 56,265 2017-2021 1,955 2017-2019 — — WPL 2,628 2017-2018 3,505 2017 83,600 2017-2023 2,284 2017-2018 6,552 2017-2018
Fair Value of Financial Instruments	At December 31, 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 2016 2015 2016 2015 2016 2015 Current derivative assets $29.4 $15.1 $19.1 $13.8 $10.3 $1.3 Non-current derivative assets 12.0 3.3 1.7 1.7 10.3 1.6 Current derivative liabilities 13.3 47.3 2.7 18.5 10.6 28.8 Non-current derivative liabilities 15.3 17.3 5.6 4.9 9.7 12.4

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 .
Schedule of Environmental Liabilities	At December 31, 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). At December 31, 2016 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $27 $12 - $24 Current and non-current environmental liabilities 16 13
IPL [Member]
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 .
Schedule of Environmental Liabilities	At December 31, 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). At December 31, 2016 , such amounts for WPL were not material. Alliant Energy IPL Range of estimated future costs $14 - $27 $12 - $24 Current and non-current environmental liabilities 16 13
WPL [Member]
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2016 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $185 $189 $159 $137 $149 $599 $1,418 Natural gas 223 142 115 98 69 124 771 Coal (b) 105 54 18 — — — 177 Other (c) 16 4 5 2 2 5 34 $529 $389 $297 $237 $220 $728 $2,400 IPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $138 $131 $144 $137 $149 $599 $1,298 Natural gas 120 74 55 39 23 71 382 Coal (b) 49 19 9 — — — 77 Other (c) 15 1 1 — — — 17 $322 $225 $209 $176 $172 $670 $1,774 WPL 2017 2018 2019 2020 2021 Thereafter Total Purchased power (a) $47 $58 $15 $— $— $— $120 Natural gas 103 68 60 59 46 53 389 Coal (b) 56 35 9 — — — 100 Other (c) — 1 1 — — — 2 $206 $162 $85 $59 $46 $53 $611 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. (b) Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016 .

Segments Of Business (Tables)

Segments Of Business (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): Utility Non-Regulated, Alliant Energy 2016 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,875.5 $355.4 $48.6 $3,279.5 $40.5 $3,320.0 Depreciation and amortization 367.0 34.2 2.1 403.3 8.3 411.6 Operating income (loss) 571.9 30.7 (4.8 ) 597.8 (60.8 ) 537.0 Interest expense 194.6 1.6 196.2 Equity (income) loss from unconsolidated investments, net (39.8 ) — — (39.8 ) 0.2 (39.6 ) Income tax expense (benefit) 87.4 (28.0 ) 59.4 Net income (loss) attributable to Alliant Energy common shareowners 406.0 (34.5 ) 371.5 Total assets 11,040.5 1,091.1 781.0 12,912.6 461.2 13,373.8 Investments in equity method subsidiaries 325.3 — — 325.3 0.7 326.0 Construction and acquisition expenditures 1,005.5 137.1 0.1 1,142.7 54.1 1,196.8 Utility Non-Regulated, Alliant Energy 2015 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,770.5 $381.2 $57.9 $3,209.6 $44.0 $3,253.6 Depreciation and amortization 358.6 31.1 1.8 391.5 9.8 401.3 Operating income 514.1 34.6 1.9 550.6 26.4 577.0 Interest expense 189.2 (2.1 ) 187.1 Equity (income) loss from unconsolidated investments, net (35.1 ) — — (35.1 ) 1.3 (33.8 ) Income taxes 60.2 10.2 70.4 Net income attributable to Alliant Energy common shareowners 362.3 15.9 378.2 Total assets 10,211.3 939.3 828.9 11,979.5 515.7 12,495.2 Investments in equity method subsidiaries 302.0 — — 302.0 0.9 302.9 Construction and acquisition expenditures 855.8 106.4 1.4 963.6 70.7 1,034.3 Utility Non-Regulated, Alliant Energy 2014 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,713.6 $517.5 $66.1 $3,297.2 $53.1 $3,350.3 Depreciation and amortization 347.0 29.9 1.8 378.7 9.4 388.1 Operating income 442.4 53.8 14.0 510.2 33.4 543.6 Interest expense 176.3 4.3 180.6 Equity income (loss) from unconsolidated investments, net (42.8 ) — — (42.8 ) 2.4 (40.4 ) Income taxes 36.4 7.9 44.3 Net income attributable to Alliant Energy common shareowners 362.0 21.1 383.1 Total assets 9,660.4 913.5 993.9 11,567.8 495.7 12,063.5 Investments in equity method subsidiaries 294.3 — — 294.3 2.3 296.6 Construction and acquisition expenditures 774.8 63.2 0.9 838.9 63.9 902.8
IPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,569.7 $204.0 $46.7 $1,820.4 Depreciation and amortization 189.4 19.3 2.1 210.8 Operating income 252.0 15.5 3.3 270.8 Interest expense 103.2 Income tax benefit (5.9 ) Earnings available for common stock 215.6 Total assets 6,278.2 653.3 373.2 7,304.7 Construction and acquisition expenditures 598.1 91.5 0.1 689.7 2015 Electric Gas Other Total Operating revenues $1,503.8 $217.3 $53.4 $1,774.5 Depreciation and amortization 187.9 17.5 1.8 207.2 Operating income 218.8 17.7 5.4 241.9 Interest expense 96.8 Income tax benefit (22.7 ) Earnings available for common stock 186.0 Total assets 5,754.1 548.2 406.8 6,709.1 Construction and acquisition expenditures 561.2 56.7 1.4 619.3 2014 Electric Gas Other Total Operating revenues $1,493.3 $296.5 $58.3 $1,848.1 Depreciation and amortization 178.7 17.0 1.8 197.5 Operating income 166.8 25.7 16.7 209.2 Interest expense 89.9 Income tax benefit (48.9 ) Earnings available for common stock 181.6 Total assets 5,398.3 544.1 507.8 6,450.2 Construction and acquisition expenditures 490.0 35.1 0.9 526.0
WPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2016 Electric Gas Other Total Operating revenues $1,305.8 $151.4 $1.9 $1,459.1 Depreciation and amortization 177.6 14.9 — 192.5 Operating income (loss) 319.9 15.2 (8.1 ) 327.0 Interest expense 91.4 Equity income from unconsolidated investments (39.8 ) — — (39.8 ) Income taxes 93.3 Earnings available for common stock 190.4 Total assets 4,444.7 437.8 407.8 5,290.3 Investments in equity method subsidiaries 7.7 — — 7.7 Construction and acquisition expenditures 407.4 45.6 — 453.0 2015 Electric Gas Other Total Operating revenues $1,266.7 $163.9 $4.5 $1,435.1 Depreciation and amortization 170.7 13.6 — 184.3 Operating income (loss) 295.3 16.9 (3.5 ) 308.7 Interest expense 92.4 Equity income from unconsolidated investments (35.1 ) — — (35.1 ) Income taxes 82.9 Earnings available for common stock 176.3 Total assets 4,457.2 391.1 422.1 5,270.4 Investments in equity method subsidiaries 302.0 — — 302.0 Construction and acquisition expenditures 294.6 49.7 — 344.3 2014 Electric Gas Other Total Operating revenues $1,220.3 $221.0 $7.8 $1,449.1 Depreciation and amortization 168.3 12.9 — 181.2 Operating income (loss) 275.6 28.1 (2.7 ) 301.0 Interest expense 86.4 Equity income from unconsolidated investments (42.8 ) — — (42.8 ) Income taxes 85.3 Earnings available for common stock 180.4 Total assets 4,262.1 369.4 486.1 5,117.6 Investments in equity method subsidiaries 294.3 — — 294.3 Construction and acquisition expenditures 284.8 28.1 — 312.9

Related Parties (Tables)

Related Parties (Tables)	12 Months Ended
	Dec. 31, 2016
Related Party Transaction [Line Items]
Services Provided, Sales Credited And Purchases Billed	The amounts billed for services provided, sales credited and purchases were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 54
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2016 2015 2014 ATC billings to WPL $110 $101 $96 WPL billings to ATC 13 13 9
IPL [Member]
Related Party Transaction [Line Items]
Services Provided, Sales Credited And Purchases Billed	The amounts billed for services provided, sales credited and purchases were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 54
WPL [Member]
Related Party Transaction [Line Items]
Services Provided, Sales Credited And Purchases Billed	The amounts billed for services provided, sales credited and purchases were as follows (in millions): IPL WPL 2016 2015 2014 2016 2015 2014 Corporate Services billings $161 $150 $148 $133 $121 $116 Sales credited 8 10 8 7 24 6 Purchases billed 433 366 422 102 66 125
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2016 2015 IPL $104 $93 WPL 72 54
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2016 2015 2014 ATC billings to WPL $110 $101 $96 WPL billings to ATC 13 13 9

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Components Of Discontinued Operations In Consolidated Statements Of Income	A summary of the components of discontinued operations in Alliant Energy’s income statements was as follows (in millions): 2016 2015 2014 Operating expenses $3.9 $4.0 $3.7 Loss before income taxes (3.9 ) (4.0 ) (3.7 ) Income tax benefit (1.6 ) (1.5 ) (1.3 ) Loss from discontinued operations, net of tax ($2.3 ) ($2.5 ) ($2.4 )

Selected Consolidated Quarter50

Selected Consolidated Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Components Of Selected Consolidated Quarterly Financial Data	All “per share” references refer to earnings per diluted share. Summation of the individual quarters may not equal annual totals due to rounding. Refer to Note 19 for additional information on discontinued operations. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $843.8 $754.6 $924.6 $797.0 $897.4 $717.2 $898.9 $740.1 Operating income 145.9 128.6 162.6 99.9 152.9 109.0 235.9 79.2 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 97.6 84.4 128.8 63.0 96.6 68.9 180.0 35.2 Loss from discontinued operations, net of tax (1.1 ) (0.5 ) (0.4 ) (0.3 ) — (1.3 ) (0.1 ) (1.1 ) Net income 96.5 83.9 128.4 62.7 96.6 67.6 179.9 34.1 Earnings per weighted average common share attributable to Alliant Energy common shareowners (a): Income from continuing operations, net of tax 0.43 0.37 0.57 0.28 0.43 0.31 0.79 0.16 Loss from discontinued operations, net of tax — — — — — (0.01 ) — (0.01 ) Net income 0.43 0.37 0.57 0.28 0.43 0.30 0.79 0.15 (a) Amounts reflect the effects of a two -for-one common stock split distributed in May 2016 . Refer to Note 7 for additional details.
IPL [Member]
Components Of Selected Consolidated Quarterly Financial Data	Earnings per share data is not disclosed for IPL given Alliant Energy is the sole shareowner of all shares of IPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $458.7 $411.0 $516.2 $434.5 $489.0 $382.2 $504.6 $398.7 Operating income 62.0 48.0 125.9 34.9 65.5 33.8 117.0 25.6 Net income 48.2 34.4 116.7 26.5 50.1 19.0 119.1 8.0 Earnings available for common stock 45.6 31.9 114.1 24.0 47.5 16.5 116.5 5.5
WPL [Member]
Components Of Selected Consolidated Quarterly Financial Data	Earnings per share data is not disclosed for WPL given Alliant Energy is the sole shareowner of all shares of WPL’s common stock outstanding during the periods presented. 2016 2015 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $375.6 $334.3 $397.0 $352.2 $397.1 $324.7 $382.6 $330.7 Operating income 78.8 75.0 115.0 58.2 80.8 68.3 110.3 49.3 Net income 47.0 43.7 69.6 32.5 45.1 39.7 68.4 24.4 Earnings available for common stock 46.5 43.2 69.0 31.7 44.9 39.2 68.0 24.2

Condensed Parent Company Fina51

Condensed Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Statements of Income	ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED STATEMENTS OF INCOME Year Ended December 31, 2016 2015 2014 (in millions) Operating revenues $1 $2 $2 Operating expenses 3 3 3 Operating loss (2 ) (1 ) (1 ) Interest expense and other: Equity earnings from consolidated subsidiaries (374 ) (379 ) (388 ) Interest expense 3 3 9 Interest income (2 ) (3 ) (2 ) Total interest expense and other (373 ) (379 ) (381 ) Income before income taxes 371 378 380 Income tax benefit (1 ) (1 ) (3 ) Net income $372 $379 $383 The accompanying Notes to Condensed Financial Statements are an integral part of these statements.
Condensed Balance Sheets	ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED BALANCE SHEETS December 31, 2016 2015 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $74 $93 Other 5 9 Total current assets 79 102 Investments: Investments in consolidated subsidiaries 4,211 3,999 Other 2 14 Total investments 4,213 4,013 Other assets 64 20 Total assets $4,356 $4,135 LIABILITIES AND EQUITY Current liabilities: Current maturities of long-term debt $— $250 Commercial paper 192 140 Notes payable to affiliated companies 275 — Other 12 12 Total current liabilities 479 402 Other liabilities 18 12 Common equity: Common stock and additional paid-in capital 1,695 1,664 Retained earnings 2,174 2,066 Shares in deferred compensation trust (10 ) (9 ) Total common equity 3,859 3,721 Total liabilities and equity $4,356 $4,135 The accompanying Notes to Condensed Financial Statements are an integral part of these statements.
Condensed Statements of Cash Flows	ALLIANT ENERGY CORPORATION (Parent Company Only) CONDENSED STATEMENTS OF CASH FLOWS Year Ended December 31, 2016 2015 2014 (in millions) Net cash flows from operating activities $254 $262 $246 Cash flows from (used for) investing activities: Capital contributions to consolidated subsidiaries (250 ) (165 ) (90 ) Capital repayments from consolidated subsidiaries 130 — 50 Net change in notes receivable from and payable to affiliates 294 2 (23 ) Other 10 — — Net cash flows from (used for) investing activities 184 (163 ) (63 ) Cash flows used for financing activities: Common stock dividends (267 ) (247 ) (226 ) Proceeds from issuance of common stock, net 27 151 — Proceeds from issuance of long-term debt — — 250 Payments to retire long-term debt (250 ) — (250 ) Net change in commercial paper 52 (1 ) 45 Other — (2 ) (2 ) Net cash flows used for financing activities (438 ) (99 ) (183 ) Net decrease in cash and cash equivalents — — — Cash and cash equivalents at beginning of period — — — Cash and cash equivalents at end of period $— $— $— Supplemental cash flows information: Cash paid during the period for: Interest, net of capitalized interest ($3 ) ($3 ) ($11 ) Income taxes, net (37 ) (9 ) (5 ) The accompanying Notes to Condensed Financial Statements are an integral part of these statements.

Summary Of Significant Accoun52

Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	Apr. 20, 2016	Dec. 31, 2017	Dec. 31, 2016USD ($)customerMW	Dec. 31, 2015	Dec. 31, 2014
General:
Common stock split conversion ratio (2:1)	2
Adjustments for New Accounting Principle, Early Adoption [Member]
New Accounting Standards:
Decrease to deferred tax liabilities due to adoption of new accounting standard | $			$ (3.1)
Increase to retained earnings due to adoption of new accounting standard | $			$ 3.1
IPL [Member]
General:
Generation and distribution of steam, number of customers served (in customers) | customer			2
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP			100.00%
Operating Revenues:
Estimated recovery of overaccrued operating revenue, reflected on customer billing, maximum period			2 years
WPL [Member]
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP			50.00%
AFUDC rates, projects with approval			100.00%
Operating Revenues:
Final settlement recovery of overaccrued operating revenue, reflected on customer billing, maximum period			2 years
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW			347
Capital lease, lease term			20 years
Franklin County Wind Farm [Member]
General:
Wind EGU capacity (in megawatts) | MW			99
Electric Generation Equipment [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.50%	3.60%	3.60%
Electric Generation Equipment [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.10%	3.20%	3.20%
Electric - distribution [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.40%	2.40%	2.50%
Electric - distribution [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.60%	2.70%	2.70%
Gas [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.30%	3.20%	3.30%
Gas [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.50%	2.50%	2.50%
Scenario, Forecast [Member] | Electric Generation Equipment [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		3.20%
Scenario, Forecast [Member] | Electric - distribution [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		2.60%
Scenario, Forecast [Member] | Gas [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		2.30%

Summary Of Significant Accoun53

Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Electric - generation [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.50%	3.60%	3.60%
Electric - generation [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.10%	3.20%	3.20%
Electric - distribution [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.40%	2.40%	2.50%
Electric - distribution [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.60%	2.70%	2.70%
Electric - other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.20%	4.00%	4.00%
Electric - other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.70%	4.50%	5.90%
Gas [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.30%	3.20%	3.30%
Gas [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.50%	2.50%	2.50%
Other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.90%	3.90%	4.30%
Other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	5.90%	6.00%	6.00%

Summary Of Significant Accoun54

Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
IPL [Member] | IPL (Marshalltown CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	[1]	7.90%	7.90%	8.00%
IPL [Member] | IPL (other CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		7.70%	7.70%	7.80%
IPL [Member] | Marshalltown Generating Station [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Return on common equity for calculation of AFUDC		10.30%
WPL [Member] | WPL (retail jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		8.20%	8.20%	8.20%
WPL [Member] | WPL (wholesale jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		6.70%	7.90%	4.10%
[1]	In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (63)	$ (67.8)	$ 10.8
Regulatory liabilities		681	737.7
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		$ 44
Period for simple average of actual costs incurred during Test Year		2 years
Increase (decrease) in regulatory liabilities		$ (67.3)	(75.5)	(18.9)
Regulatory liabilities		430.8	489.2
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		9
Regulatory liabilities		250.2	248.5
Electric [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		(64)	(72)	(85)
Electric [Member] | Scenario, Forecast [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities	$ (68)
Gas [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (12)	$ (12)	$ (12)
Gas [Member] | Scenario, Forecast [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities	(7)
Nelson Dewey Units 1 and 2 and Edgewater Unit 3 [Member] | WPL [Member]
Regulatory Matters [Line Items]
Expenditure collection period after new rate implementation		10 years
2017/2018 Test Period Retail Electric [Member] | Scenario, Forecast [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount	(9)
2017/2018 Test Period Retail Gas [Member] | Scenario, Forecast [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount	$ (9)
2015/2016 Test Period Retail Electric And Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 5
2015/2016 Test Period Retail Electric And Gas [Member] | Alliant Energy and WPL [Member] | Deferral [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		6
2013/2014 Test Period Retail Electric And Gas [Member] | Alliant Energy and WPL [Member] | Deferral [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		6
2016 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 7
Annual bandwidth for fuel-related costs		2.00%

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory assets	$ 1,915.1	$ 1,908.6
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,055.6	987.7
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	578.7	579.5
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	105.9	92.4
WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.4	45
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	30.7	70.6
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.2	26.9
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	6	35.9
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	70.6	70.6
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,458.8	1,402.6
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,022.4	958.2
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	294	298.1
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	64.3	50.8
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	10	28.2
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.2	26.9
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	0.3	2.8
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.6	37.6
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	456.3	506
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	33.2	29.5
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	284.7	281.4
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.6	41.6
WPL [Member] | WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.4	45
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	20.7	42.4
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	5.7	33.1
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 29	$ 33

Regulatory Matters (Regulator57

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 681	$ 737.7
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	411.6	406
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	83.5	159.2
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	72	43.5
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	31.5	8.5
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30.8	37.6
Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.5	48.3
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	31.1	34.6
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	430.8	489.2
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	269.4	260.4
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	83.5	159.2
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	35.7	21.9
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12.1	6.7
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	17.8	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	12.3	17.5
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	250.2	248.5
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	142.2	145.6
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36.3	21.6
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	19.4	1.8
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	13	14.1
WPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.5	48.3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 18.8	$ 17.1

Regulatory Matters (IPL's Tax B

Regulatory Matters (IPL's Tax Benefit Riders) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	$ (63)	$ (67.8)	$ 10.8
Alliant Energy and IPL [Member] | Electric tax benefit rider credits [Member]
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	(64)
Alliant Energy and IPL [Member] | Gas tax benefit rider credits [Member]
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	(12)
Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	$ (76)

Regulatory Matters (Electric Ta

Regulatory Matters (Electric Tax Benefit Rider) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (63)	$ (67.8)	$ 10.8
Income tax expense (benefit)	59.4	70.4	44.3
Alliant Energy and IPL [Member] | Electric [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(64)	(72)	(85)
Income tax expense (benefit)	(37)	(42)	(50)
Alliant Energy and IPL [Member] | Electric [Member] | Decrease In taxable income from IPL's tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Income tax expense (benefit)	$ (27)	$ (30)	$ (35)

Regulatory Matters (Revenue Req

Regulatory Matters (Revenue Requirement Adjustment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Electric revenues	$ 2,875.5	$ 2,770.5	$ 2,713.6
Alliant Energy and IPL [Member] | Revenue Requirement Adjustment [Member]
Regulatory Liabilities [Line Items]
Electric revenues	$ 14	$ 14	$ 15

Regulatory Matters (Gas Tax Ben

Regulatory Matters (Gas Tax Benefit Rider) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (63)	$ (67.8)	$ 10.8
Income tax expense (benefit)	59.4	70.4	44.3
Alliant Energy and IPL [Member] | Gas [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(12)	(12)	(12)
Income tax expense (benefit)	(7)	(7)	(7)
Alliant Energy and IPL [Member] | Gas [Member] | Decrease In taxable income from IPL's tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Income tax expense (benefit)	$ (5)	$ (5)	$ (5)

Regulatory Matters (Customer Bi

Regulatory Matters (Customer Billing Credits) (Details) - USD ($) $ in Millions	12 Months Ended			36 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
IPL [Member]
Regulatory Liabilities [Line Items]
Billing credits to reduce retail electric customers' bills	$ 9	$ 24	$ 72	$ 105

Regulatory Matters (Retail Fuel

Regulatory Matters (Retail Fuel-related Rate Filings) (Details) - WPL [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
2016 Test Year Retail Electric Fuel Related [Member]
Regulatory Liabilities [Line Items]
Authorized increase (decrease) in final rates, amount	$ 7
Authorized increase (decrease) in final rates, percent	1.00%
Retail electric fuel-related costs	$ 9
2015 Test Year Retail Electric Fuel Related [Member]
Regulatory Liabilities [Line Items]
Authorized increase (decrease) in final rates, amount		$ 39
Authorized increase (decrease) in final rates, percent		4.00%
Refund of over-collected fuel-related costs	10
2014 Test Year Retail Electric Fuel Related [Member]
Regulatory Liabilities [Line Items]
Authorized increase (decrease) in final rates, amount			$ 19
Authorized increase (decrease) in final rates, percent			2.00%
Deferral [Member] | 2014 Test Year Retail Electric Fuel Related [Member]
Regulatory Liabilities [Line Items]
Authorized increase (decrease) in final rates, amount	$ (28)

Property, Plant and Equipment64

Property, Plant and Equipment (Narrative) (Details) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2016USD ($)$ / sharesMW	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 1,226.8	$ 897.5
Allowance for funds used during construction		62.5	36.9	$ 34.8
Asset valuation charges, pre-tax		86.4	0	0
Non-regulated Generation, net	[1]	135	229.3
IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		968.1	578.2
Allowance for funds used during construction		$ 52	28.2	25.9
Wholesale power supply agreement termination notice term		5 years
Wholesale power supply agreement term		10 years
WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 258.7	319.3
Allowance for funds used during construction		$ 10.5	8.7	8.9
Corporate Services [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
Corporate Services [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		30 years
Edgewater Unit 5 [Member] | Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		$ 225
Construction work in progress			190
Allowance for funds used during construction		12	8
Marshalltown Generating Station [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction		$ 43.8	20.7	$ 3.7
Fossil-fueled EGU capacity (in megawatts) | MW		650
Marshalltown Generating Station [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 612	453
Allowance for funds used during construction		68	24
Riverside Energy Center Expansion [Member] | Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		81	2
Allowance for funds used during construction		$ 2	0
Riverside Energy Center Expansion [Member] | WPL [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) | MW		730
Expansion of Wind Generation [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 102
Allowance for funds used during construction		$ 1
IPL (FERC formula) [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Authorized return on common equity		10.97%
Gas - distribution [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from asset sales			11
Receipt of promissory note			2
Gas - distribution [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets			3
Electric - distribution [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Proceeds from asset sales			129
Electric - distribution [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Loss on sale of Minnesota distribution assets			$ 11
Franklin County Wind Farm [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		30 years
Value of Franklin County wind farm		$ 33
Asset valuation charges, pre-tax		86
Asset valuation charges, after-tax		$ 51
Asset valuation charges, after-tax (in dollars per share) | $ / shares		$ 0.23
Sheboygan Falls Energy Facility [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		35 years
Non-regulated Generation, net		$ 95
Customer Billing And Information System [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		12 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		5 years
[1]	Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015, respectively.

Property, Plant and Equipment65

Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	$ 108.3	$ 0
Total electric plant		11,043.5	10,444.9
Gas plant in service		1,107.6	1,018.3
Other plant in service		549.3	530.6
Accumulated depreciation		(4,135.7)	(3,939.6)
Net plant		8,564.7	8,054.2
Construction work in progress		1,226.8	897.5
Other, net		18.4	18.5
Total utility		9,809.9	8,970.2
Non-regulated Generation, net	[2]	135	229.3
Corporate Services and other, net	[3]	334.3	319.6
Total non-regulated and other		469.3	548.9
Total property, plant and equipment		10,279.2	9,519.1
Non-regulated Generation, accumulated depreciation		46.5	59
Corporate Services and other, accumulated depreciation		272	252.9
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		5,866.9	5,643.7
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		4,739.2	4,489.9
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		329.1	311.3
IPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	108.3	0
Total electric plant		5,837.9	5,671.7
Gas plant in service		556.7	513.6
Other plant in service		313	296
Accumulated depreciation		(2,258.3)	(2,152.8)
Net plant		4,449.3	4,328.5
Construction work in progress		968.1	578.2
Other, net		18.2	18.4
Total utility		5,435.6	4,925.1
Total property, plant and equipment		5,435.6	4,925.1
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,916.8	3,011.6
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,589.3	2,447.9
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		223.5	212.2
WPL [Member]
Property, Plant and Equipment [Line Items]
Total electric plant		5,205.6	4,773.2
Gas plant in service		550.9	504.7
Other plant in service		236.3	234.6
Accumulated depreciation		(1,877.4)	(1,786.8)
Net plant		4,115.4	3,725.7
Leased Sheboygan Falls Energy Facility, net	[4]	52.4	58.6
Construction work in progress		258.7	319.3
Other, net		0.2	0.1
Total utility		4,426.7	4,103.7
Total property, plant and equipment		4,426.7	4,103.7
Leased Sheboygan Falls Energy Facility, accumulated depreciation		71.4	65.2
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,950.1	2,632.1
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,149.9	2,042
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		$ 105.6	$ 99.1
[1]	In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017.
[2]	Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015, respectively.
[3]	Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015, respectively.
[4]	Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.

Property, Plant and Equipment66

Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 62.5	$ 36.9	$ 34.8
Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	42.3	24.4	23.1
Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	20.2	12.5	11.7
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	52	28.2	25.9
IPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	35.2	18.6	17.1
IPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	16.8	9.6	8.8
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	10.5	8.7	8.9
WPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.1	5.8	6
WPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 3.4	$ 2.9	$ 2.9

Property, Plant and Equipment67

Property, Plant and Equipment (AFUDC By Project) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 62.5	$ 36.9	$ 34.8
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	52	28.2	25.9
IPL [Member] | Marshalltown Generating Station [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	43.8	20.7	3.7
IPL [Member] | Environmental controls - Ottumwa Unit 1 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0	0	10.6
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	8.2	7.5	11.6
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	10.5	8.7	8.9
WPL [Member] | Environmental controls - Edgewater Unit 5 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	4.3	5.1	2.7
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 6.2	$ 3.6	$ 6.2

Jointly-Owned Electric Utilit68

Jointly-Owned Electric Utility Plant (Details) $ in Millions	Dec. 31, 2016USD ($)
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	$ 1,601.4
Accumulated Provision for Depreciation	532.4
Construction Work in Progress	64.8
IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	861.8
Accumulated Provision for Depreciation	289
Construction Work in Progress	13.6
WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	739.6
Accumulated Provision for Depreciation	243.4
Construction Work in Progress	$ 51.2
Ottumwa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	48.00%
Electric Plant	$ 489.4
Accumulated Provision for Depreciation	137.3
Construction Work in Progress	$ 11.1
George Neal Unit 4 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	25.70%
Electric Plant	$ 185.2
Accumulated Provision for Depreciation	80.8
Construction Work in Progress	$ 1.6
George Neal Unit 3 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	28.00%
Electric Plant	$ 150.7
Accumulated Provision for Depreciation	49.1
Construction Work in Progress	$ 0.3
Louisa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	4.00%
Electric Plant	$ 36.5
Accumulated Provision for Depreciation	21.8
Construction Work in Progress	$ 0.6
Columbia Units 1-2 [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	46.20%
Electric Plant	$ 640.2
Accumulated Provision for Depreciation	185
Construction Work in Progress	$ 51
Edgewater Unit 4 [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	68.20%
Electric Plant	$ 99.4
Accumulated Provision for Depreciation	58.4
Construction Work in Progress	$ 0.2

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 28, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of deferred proceeds of receivables sold		$ 211.1	$ 172
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party		180	180	$ 180
Receivables sold to third party		248.1
Fair value of deferred proceeds of receivables sold		211.1	172
IPL [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party		172	137	150
Limit on cash proceeds to be received from third-party		150
Whiting Petroleum Corporation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Final payment of certain future tax benefits expected to be realized				$ 26
Receivables Sold [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold to third party		248.1	181.1
Cash proceeds from receivables sold	[1]	21	5
Fair value of deferred proceeds of receivables sold		$ 211.1	$ 172
Scenario, Forecast [Member] | IPL [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Limit on cash proceeds to be received from third-party					$ 125
[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 (Details of Account

Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	$ 111.7	$ 93.8
Unbilled utility revenues	90.2	83.1
Deferred proceeds	211.1	172
Other	89	53.5
Allowance for doubtful accounts	(8.7)	(4.8)
Accounts receivable, less allowance for doubtful accounts	493.3	397.6
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	0	4.6
Unbilled utility revenues	0	1.2
Deferred proceeds	211.1	172
Other	30.7	22.8
Allowance for doubtful accounts	(1.1)	(0.6)
Accounts receivable, less allowance for doubtful accounts	240.7	200
WPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	104.4	81.5
Unbilled utility revenues	90.2	81.9
Other	38.8	25.7
Allowance for doubtful accounts	(7.1)	(3.7)
Accounts receivable, less allowance for doubtful accounts	$ 226.3	$ 185.4

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 180	$ 180	$ 180
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	172	137	150
Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 73.2	$ 46.7	$ 46.4

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of deferred proceeds		$ 211.1	$ 172
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold to third party		248.1
Fair value of deferred proceeds		211.1	172
Receivables Sold [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer accounts receivable		157.6	109.7
Unbilled utility revenues		90.4	71.3
Other receivables		0.1	0.1
Receivables sold to third party		248.1	181.1
Less: cash proceeds	[1]	21	5
Deferred proceeds		227.1	176.1
Less: allowance for doubtful accounts		16	4.1
Fair value of deferred proceeds		211.1	172
Outstanding receivables past due		$ 68	$ 18
[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	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collections reinvested in receivables	$ 1,818.1	$ 1,812.9	$ 1,997.9
Write-offs, net of recoveries	$ 4.8	$ 8.8	$ 11.4

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Millions	12 Months Ended			38 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Number of legal complaints (in number of complaints)	2
Proceeds from liquidation of company-owned life insurance policies	$ 31
Alliant Energy and WPL [Member]
Schedule of Equity Method Investments [Line Items]
Reduction in equity income from ATC	9	$ 12	$ 3	$ 24
WPL [Member]
Schedule of Equity Method Investments [Line Items]
WPL's ownership interest in WPL Transco					100.00%
Net reduction in total equity due to transfer of ATC to ATI	163.6
IPL [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from liquidation of company-owned life insurance policies	$ 19

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Carrying value		$ 326	$ 302.9	$ 296.6
Equity (income) / loss		(39.6)	(33.8)	(40.4)
WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) / loss		$ (39.8)	(35.1)	(42.8)
ATC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	[1]	16.00%
Carrying value	[1]	$ 317.6	293.3
Equity (income) / loss	[1]	$ (39.1)	(34.2)	(41.9)
ATC [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		0.00%
Carrying value		$ 0	293.3
Equity (income) / loss		$ (39.1)	(34.2)	(41.9)
Wisconsin River Power Company [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Carrying value		$ 7.7	8.7
Equity (income) / loss		(0.7)	(0.9)	(0.9)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		8.4	9.6
Equity (income) / loss		(0.5)	0.4	1.5
Totals [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		326	302.9
Equity (income) / loss		(39.6)	(33.8)	(40.4)
Totals [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		7.7	302
Equity (income) / loss		$ (39.8)	$ (35.1)	$ (42.8)
[1]	Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC.

Investments (Summary Financial

Investments (Summary Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues	$ 658	$ 624	$ 643
Operating income	331	299	330
Net income	232	186	240
Current assets	82	88
Non-current assets	4,340	3,987
Current liabilities	498	332
Non-current liabilities	2,144	2,052
WPL [Member]
Operating revenues	658	624	643
Operating income	331	299	330
Net income	234	202	$ 240
Current assets	6	87
Non-current assets	19	3,977
Current liabilities	3	332
Non-current liabilities	$ 7	$ 2,052

Investments (Cash Surrender Val

Investments (Cash Surrender Value Of Life Insurance Policies) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Cash surrender value	$ 10.6	$ 42.3
IPL [Member]
Cash surrender value	0	18.9
WPL [Member]
Cash surrender value	$ 5.8	$ 6.4

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) $ / shares in Units, $ in Millions	Apr. 20, 2016shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)$ / sharesshares		Dec. 31, 2015USD ($)shares		Dec. 31, 2014USD ($)shares
Schedule of Common Equity [Line Items]
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]
Shares available for issuance under the Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares) | shares				11,300,000
Proceeds from issuance of common stock, net				$ 26.6		$ 151.2	[2]	$ 0
Ownership percentage				15.00%
Initial right entitlement, number of shares of common stock shareholders have the option to purchase (in shares) | shares				0.25
Exercise price, rights (in dollars per share) | $ / shares				$ 55
Percentage of exercise price upon change in beneficial ownership				200.00%
Other comprehensive income (loss)				$ 0		$ 0.2		(0.4)
IPL [Member]
Schedule of Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares				24,000,000		24,000,000
Retained earnings free of dividend restrictions				$ 618
Common equity ratio, computation of ratio average, number of months				13 months
Common equity ratio				42.00%
Restricted net assets of subsidiaries				$ 1,600
Other comprehensive income (loss)				$ 0		$ 0		0
WPL [Member]
Schedule of Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares				18,000,000		18,000,000
Retained earnings free of dividend restrictions				$ 126
Common equity ratio, computation of ratio average, number of months				13 months
Restricted net assets of subsidiaries				$ 1,600
Other comprehensive income (loss)				$ 0		$ 0		$ 0
Minimum [Member]
Schedule of Common Equity [Line Items]
Ownership percentage				10.00%
At The Market Offering Program [Member]
Schedule of Common Equity [Line Items]
Maximum aggregate gross sales price of common stock that can be offered and sold						$ 150
Common stock issued during the period, At-the-market offering program (in shares) | shares				0		4,373,234		0
Proceeds from issuance of common stock, net						$ 133
Fees and commissions from issuance of common stock						$ 2
Scenario, Forecast [Member] | WPL [Member]
Schedule of Common Equity [Line Items]
Retained earnings free of dividend restrictions		$ 140	$ 126
Common equity ratio		51.00%	51.00%
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.
[2]	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) - shares	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1 (in shares)	226,918,432	[1]	221,871,360		221,887,338
Common stock issued during the period, Shareowner Direct Plan (in shares)	732,814		606,010		0
Equity-based compensation plans (in shares)	22,408		112,756		71,094
Other (in shares)	0		(44,928)		(87,072)
Shares outstanding, December 31 (in shares)	227,673,654	[1]	226,918,432	[1]	221,871,360
At The Market Offering Program [Member]
Common Stock Oustanding [Roll Forward]
Common stock issued during the period, At-the-market offering program (in shares)	0		4,373,234		0
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Redeemable Preferred Stock (Nar

Redeemable Preferred Stock (Narrative) (Details) - IPL [Member]	12 Months Ended
	Dec. 31, 2016Qboard_member$ / sharesshares
Temporary Equity [Line Items]
Number of board members to be elected (in members) | board_member	2
Number of quarterly dividend requirements (in quarters) | Q	6
Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized (in shares)	16,000,000
Redeemable Preferred Stock [Member] | 5.1% [Member]
Temporary Equity [Line Items]
Shares Authorized (in shares)	8,000,000
Cumulative preferred stock rate	5.10%
Preferred stock redemption price per share (in dollars per share) | $ / shares	$ 25

Redeemable Preferred Stock (Car

Redeemable Preferred Stock (Carrying Value Of Cumulative Preferred Stock) (Details) - IPL [Member] - Redeemable Preferred Stock [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Temporary Equity [Line Items]
Shares Authorized (in shares)	16,000,000
5.1% [Member]
Temporary Equity [Line Items]
Series	5.10%
Liquidation Preference/Stated Value (in dollars per share)	$ 25
Shares Authorized (in shares)	8,000,000
Shares Outstanding (in shares)	8,000,000
Cumulative preferred stock	$ 200	$ 200

Debt (Narrative) (Details)

Debt (Narrative) (Details)	Dec. 31, 2016USD ($)revolving_credit_facility
Debt Instrument [Line Items]
Number of revolving credit facilities included in short-term borrowing arrangements (number of facilities) | revolving_credit_facility	3
Line of credit facility, current borrowing capacity	$ 1,000,000,000
Non-recourse debt and hybrid securities consolidated capital maximum limit	15.00%
Parent Company [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 300,000,000
IPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	300,000,000
WPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 400,000,000

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Commercial paper:
Amount outstanding	$ 244.1	$ 159.8
Weighted average interest rates	0.90%	0.70%
Available credit facility capacity	$ 755.9	$ 840.2
IPL [Member]
Commercial paper:
Amount outstanding	0	0
Available credit facility capacity	300	300
WPL [Member]
Commercial paper:
Amount outstanding	$ 52.3	$ 19.9
Weighted average interest rates	0.70%	0.40%
Available credit facility capacity	$ 347.7	$ 380.1

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 251.8	$ 181.2
Average amount outstanding (based on daily outstanding balances)	$ 179	$ 119.2
Weighted average interest rates	0.60%	0.40%
IPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 3.1	$ 18.4
Average amount outstanding (based on daily outstanding balances)	$ 0	$ 0.2
Weighted average interest rates	0.70%	0.40%
WPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 118.3	$ 24.7
Average amount outstanding (based on daily outstanding balances)	$ 38.1	$ 2.2
Weighted average interest rates	0.40%	0.30%

Debt (Schedule Of Debt-To-Capit

Debt (Schedule Of Debt-To-Capital Ratios) (Details)	Dec. 31, 2016
Actual	53.00%
IPL [Member]
Actual	47.00%
WPL [Member]
Actual	49.00%
Maximum [Member]
Requirement, not to exceed	65.00%
Maximum [Member] | IPL [Member]
Requirement, not to exceed	58.00%
Maximum [Member] | WPL [Member]
Requirement, not to exceed	58.00%

Debt (Long-term Debt) (Details)

Debt (Long-term Debt) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt		$ 4,357.1	$ 3,870.5
Current maturities		(4.6)	(313.4)
Unamortized debt issuance costs		(23.4)	(22.3)
Unamortized debt (discount) and premium, net		(13.5)	(12.6)
Long-term debt, net	[1]	4,315.6	3,522.2
Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	2,175	1,875
Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		5.875%	5.875%
Senior Debentures [Member] | 7.25% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		7.25%	7.25%
Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 200	$ 200
Interest rate		3.65%	3.65%
Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		3.25%	3.25%
Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		3.40%	3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 50	$ 50
Interest rate		5.50%	5.50%
Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		6.45%	6.45%
Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 125	$ 125
Interest rate		6.30%	6.30%
Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 300	$ 300
Interest rate		6.25%	6.25%
Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		4.70%	4.70%
Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]
Debt Instrument [Line Items]
Long-term debt	[2],[3]	$ 300
Interest rate		3.70%
Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 1,550	$ 1,550
Debentures [Member] | 5% debenture, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		5.00%	5.00%
Debentures [Member] | 4.6% debenture, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 150	$ 150
Interest rate		4.60%	4.60%
Debentures [Member] | 2.25% debenture, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		2.25%	2.25%
Debentures [Member] | 6.25% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		6.25%	6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 300	$ 300
Interest rate		6.375%	6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		7.60%	7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		4.10%	4.10%
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt		$ 632.1	$ 445.5
Term Loan Credit Agreement [Member] | Term loan credit agreement retired in 2016, 1% at December 31, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt	[4]		$ 250
Interest rate			1.00%
Other [Member] | Other, 1% at December 31, 2016, due 2017 to 2025 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 3.3	$ 3.7
Interest rate		1.00%	1.00%
IPL [Member]
Debt Instrument [Line Items]
Long-term debt		$ 2,175	$ 1,875
Current maturities		0	0
Unamortized debt issuance costs		(13.7)	(11.8)
Unamortized debt (discount) and premium, net		(7.8)	(6.3)
Long-term debt, net	[1]	2,153.5	1,856.9
Repayments of commercial paper		100
IPL [Member] | Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	2,175	1,875
IPL [Member] | Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		5.875%	5.875%
IPL [Member] | Senior Debentures [Member] | 7.25% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		7.25%	7.25%
IPL [Member] | Senior Debentures [Member] | 3.65% senior debenture, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 200	$ 200
Interest rate		3.65%	3.65%
IPL [Member] | Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		3.25%	3.25%
IPL [Member] | Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		3.40%	3.40%
IPL [Member] | Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 50	$ 50
Interest rate		5.50%	5.50%
IPL [Member] | Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		6.45%	6.45%
IPL [Member] | Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 125	$ 125
Interest rate		6.30%	6.30%
IPL [Member] | Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 300	$ 300
Interest rate		6.25%	6.25%
IPL [Member] | Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		4.70%	4.70%
IPL [Member] | Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]
Debt Instrument [Line Items]
Long-term debt	[2],[3]	$ 300
Proceeds from the issuance of debt		$ 300
Interest rate		3.70%
WPL [Member]
Debt Instrument [Line Items]
Long-term debt		$ 1,550	$ 1,550
Current maturities		0	0
Unamortized debt issuance costs		(9.1)	(9.9)
Unamortized debt (discount) and premium, net		(5.7)	(6.2)
Long-term debt, net	[1]	1,535.2	1,533.9
WPL [Member] | Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	1,550	1,550
WPL [Member] | Debentures [Member] | 5% debenture, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		5.00%	5.00%
WPL [Member] | Debentures [Member] | 4.6% debenture, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 150	$ 150
Interest rate		4.60%	4.60%
WPL [Member] | Debentures [Member] | 2.25% debenture, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		2.25%	2.25%
WPL [Member] | Debentures [Member] | 6.25% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 100	$ 100
Interest rate		6.25%	6.25%
WPL [Member] | Debentures [Member] | 6.375% debenture, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 300	$ 300
Interest rate		6.375%	6.375%
WPL [Member] | Debentures [Member] | 7.6% debenture, due 2038 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		7.60%	7.60%
WPL [Member] | Debentures [Member] | 4.1% debenture, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 250	$ 250
Interest rate		4.10%	4.10%
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through 2018, 1% at December 31, 2016 [Member]
Debt Instrument [Line Items]
Long-term debt	[4],[5]	$ 500
Proceeds from the issuance of debt		$ 500
Interest rate		1.00%
Corporate Services [Member] | Senior Notes [Member] | 3.45% senior notes, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 75	$ 75
Interest rate		3.45%	3.45%
Sheboygan Power, LLC [Member] | Senior Secured Notes [Member] | 5.06% senior secured notes, due 2017 to 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	[2]	$ 53.8	$ 56.8
Interest rate		5.06%	5.06%
Franklin County Holdings LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement retired in 2016, 1% at December 31, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt	[4]		$ 60
Interest rate			1.00%
[1]	There were no significant sinking fund requirements related to the outstanding long-term debt.
[2]	Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
[3]	In 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.
[4]	In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes.
[5]	Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

Debt (Schedule Of Debt Maturiti

Debt (Schedule Of Debt Maturities) (Details) $ in Millions	Dec. 31, 2016USD ($)
2,017	$ 5
2,018	856
2,019	256
2,020	357
2,021	8
IPL [Member]
2,017	0
2,018	350
2,019	0
2,020	200
2,021	0
WPL [Member]
2,017	0
2,018	0
2,019	250
2,020	150
2,021	0
Alliant Energy Finance, LLC [Member]
2,017	5
2,018	506
2,019	6
2,020	7
2,021	$ 8

Leases (Narrative) (Details)

Leases (Narrative) (Details) - Sheboygan Falls Energy Facility [Member] - WPL [Member]	12 Months Ended
	Dec. 31, 2005lease_renewal_period_option
Leases [Line Items]
Capital lease, agreement term	20 years
Capital leases, renewal options (in number of renewal periods)	2
Capital lease asset amortization term	20 years

Leases (Future Minimum Operatin

Leases (Future Minimum Operating Lease Payments, Excluding Contingent Rentals) (Details) $ in Millions	Dec. 31, 2016USD ($)
Operating Leased Assets [Line Items]
2,017	$ 6
2,018	6
2,019	2
2,020	2
2,021	1
Thereafter	15
Total future minimum operating lease payments, excluding contingent rentals	32
IPL [Member]
Operating Leased Assets [Line Items]
2,017	3
2,018	2
2,019	1
2,020	1
2,021	1
Thereafter	10
Total future minimum operating lease payments, excluding contingent rentals	18
WPL [Member]
Operating Leased Assets [Line Items]
2,017	3
2,018	4
2,019	0
2,020	0
2,021	0
Thereafter	0
Total future minimum operating lease payments, excluding contingent rentals	$ 7

Leases (Schedule Of Lease Expen

Leases (Schedule Of Lease Expenses Included In Consolidated Statements Of Income) (Details) - WPL [Member] - Sheboygan Falls Energy Facility [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Interest expense	$ 9.3	$ 9.9	$ 10.4
Depreciation and amortization	6.2	6.2	6.2
Total lease expenses included in income statements	$ 15.5	$ 16.1	$ 16.6

Leases (Future Minimum Capital

Leases (Future Minimum Capital Lease Payments) (Details) - WPL [Member] - Sheboygan Falls Energy Facility [Member] $ in Millions	Dec. 31, 2016USD ($)
Schedule of Future Lease Payments for Capital Leases [Line Items]
2,017	$ 15
2,018	15
2,019	15
2,020	15
2,021	15
Thereafter	53
Total estimated future minimum capital lease payments	128
Less: amount representing interest	44
Present value of minimum capital lease payments	$ 84

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - Scenario, Forecast [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Income Tax [Line Items]
Deductions in income tax return	$ 350
IPL [Member]
Income Tax [Line Items]
Deductions in income tax return	100
WPL [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 200

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax expense (benefit):
Federal	$ 1.8	$ 2	$ 36.6
State	17.2	3.2	9.3
Deferred tax expense (benefit):
Federal	112.8	120.8	83.5
State	4.9	27.9	4.6
Production tax credits	(31.8)	(33.1)	(31.3)
Investment tax credits	(1.3)	(1.4)	(1.6)
Provision recorded as a change in accrued interest	0	0	(0.1)
Income tax expense (benefit)	59.4	70.4	44.3
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(44.2)	(49)	(56.7)
IPL [Member]
Current tax expense (benefit):
Federal	(12.8)	(14.1)	8.9
State	15.5	11.5	10.4
Deferred tax expense (benefit):
Federal	59.1	40.7	10.8
State	(9)	3.3	(7.9)
Production tax credits	(14)	(14.5)	(13.8)
Investment tax credits	(0.5)	(0.6)	(0.6)
Provision recorded as a change in accrued interest	0	0	0
Income tax expense (benefit)	(5.9)	(22.7)	(48.9)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(44.2)	(49)	(56.7)
WPL [Member]
Current tax expense (benefit):
Federal	(22.3)	4.7	2
State	1.1	0.6	0.8
Deferred tax expense (benefit):
Federal	112.3	76.8	81.1
State	20.8	20.2	20
Production tax credits	(17.8)	(18.6)	(17.5)
Investment tax credits	(0.8)	(0.8)	(1)
Provision recorded as a change in accrued interest	0	0	(0.1)
Income tax expense (benefit)	$ 93.3	$ 82.9	$ 85.3

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.40%	5.20%	5.40%
Effect of rate-making on property-related differences	(8.50%)	(6.80%)	(7.50%)
Production tax credits	(7.20%)	(7.20%)	(7.10%)
Adjustment of prior period taxes	(0.80%)	0.80%	(1.30%)
Other items, net	(0.50%)	(1.10%)	(1.50%)
Overall income tax rate	13.40%	15.30%	10.10%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	6.40%	6.20%	6.10%
Effect of rate-making on property-related differences	(16.20%)	(17.20%)	(21.90%)
Production tax credits	(6.30%)	(8.30%)	(9.60%)
Adjustment of prior period taxes	(1.20%)	0.70%	(3.00%)
Other items, net	(0.30%)	(1.20%)	(1.20%)
Overall income tax rate	(2.70%)	(13.10%)	(34.20%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.10%	5.10%	5.10%
Effect of rate-making on property-related differences	(0.70%)	(0.50%)	(0.70%)
Production tax credits	(6.20%)	(7.10%)	(6.60%)
Adjustment of prior period taxes	(0.10%)	0.10%	0.00%
Other items, net	(0.50%)	(0.80%)	(0.80%)
Overall income tax rate	32.60%	31.80%	32.00%
IPL's tax benefit riders [Member]
Effective Tax Rate [Line Items]
IPL’s tax benefit riders	(10.00%)	(10.60%)	(12.90%)
IPL's tax benefit riders [Member] | IPL [Member]
Effective Tax Rate [Line Items]
IPL’s tax benefit riders	(20.10%)	(28.30%)	(39.60%)

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities, property	$ 2,919	$ 2,762.9
Deferred tax liabilities, other	95.3	157.3
Total deferred tax liabilities	3,167.4	3,058.3
Deferred tax assets, federal credit carryforwards	268.4	236.4
Deferred tax assets, net operating losses carryforwards - federal	173.3	250.9
Deferred tax assets, net operating losses carryforwards - state	32.9	38.3
Deferred tax assets, other	87.9	85.4
Total deferred tax assets	597.2	677.1
Total deferred tax liabilities, net	2,570.2	2,381.2
IPL [Member]
Deferred tax liabilities, property	1,677	1,587.8
Deferred tax liabilities, other	71.4	87.8
Total deferred tax liabilities	1,748.4	1,675.6
Deferred tax assets, federal credit carryforwards	95.9	81.7
Deferred tax assets, net operating losses carryforwards - federal	69.6	113.1
Deferred tax assets, net operating losses carryforwards - state	0.6	1.1
Deferred tax assets, other	35.8	35.6
Total deferred tax assets	236.6	297.6
Total deferred tax liabilities, net	1,511.8	1,378
WPL [Member]
Deferred tax liabilities, property	1,124.5	1,027
Deferred tax liabilities, other	59.1	67.9
Total deferred tax liabilities	1,183.6	1,233.8
Deferred tax assets, federal credit carryforwards	112.9	95.5
Deferred tax assets, net operating losses carryforwards - federal	75.4	105.1
Deferred tax assets, net operating losses carryforwards - state	0.1	3.6
Deferred tax assets, other	23.6	24.2
Total deferred tax assets	212	228.4
Total deferred tax liabilities, net	971.6	1,005.4
ATC [Member]
Deferred tax liabilities, investment in ATC	153.1	138.1
ATC [Member] | WPL [Member]
Deferred tax liabilities, investment in ATC	0	138.9
IPL's tax benefit riders [Member]
Deferred tax assets, regulatory liability - IPL's tax benefit riders	34.7	66.1
IPL's tax benefit riders [Member] | IPL [Member]
Deferred tax assets, regulatory liability - IPL's tax benefit riders	$ 34.7	$ 66.1

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2016USD ($)
Federal [Member]
Tax carryforwards, net operating losses	$ 506
Tax carryforwards, tax credits	274
Federal [Member] | IPL [Member]
Tax carryforwards, net operating losses	206
Tax carryforwards, tax credits	100
Federal [Member] | WPL [Member]
Tax carryforwards, net operating losses	215
Tax carryforwards, tax credits	113
State [Member]
Tax carryforwards, net operating losses	673
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	12
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	$ 2

Income Taxes (Schedule Of Uncer

Income Taxes (Schedule Of Uncertain Tax Positions) (Details)	12 Months Ended
	Dec. 31, 2016
Statute of limitations, expiration period from extended due date of federal tax return	3 years
Statute of limitations, expiration period from extended due date of Iowa tax return	3 years
Statute of limitations, expiration period from extended due date of Wisconsin tax return	4 years

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Benefit Plans [Line Items]
Total plan assets, percentage of common stock (less than 1%)	1.00%	1.00%
Common stock percentage in assets held in 401(k) saving plans	12.60%	11.60%
Percentage of employees accepting voluntary separation package		2.00%
Voluntary employee separation charges		$ 8
Unrecognized compensation cost	$ 5
Percentage of base salary and performance-based compensation	100.00%
Performance Shares and Performance Units [Member]
Benefit Plans [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 Shares [Member]
Benefit Plans [Line Items]
Instrument valuation based on shares of common stock, number of shares	1
Performance Units [Member]
Benefit Plans [Line Items]
Instrument valuation based on shares of common stock, number of shares	1
Restricted Stock Units [Member]
Benefit Plans [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 Restricted Stock Unit [Member]
Benefit Plans [Line Items]
Instrument valuation based on shares of common stock, number of shares	1
Restricted Stock Unit And Restricted Unit [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Performance Contingent Cash Awards [Member]
Benefit Plans [Line Items]
Instrument valuation based on shares of common stock, number of shares	1
Minimum [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Minimum [Member] | Performance-Contingent Restricted Stock [Member]
Benefit Plans [Line Items]
Performance period	2 years
Minimum [Member] | Performance Contingent Cash Awards [Member]
Benefit Plans [Line Items]
Performance period	2 years
Maximum [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
Maximum [Member] | Performance-Contingent Restricted Stock [Member]
Benefit Plans [Line Items]
Performance period	4 years
Maximum [Member] | Performance Contingent Cash Awards [Member]
Benefit Plans [Line Items]
Performance period	4 years
IPL [Member]
Benefit Plans [Line Items]
Voluntary employee separation charges		5
Unrecognized compensation cost	$ 2.7
WPL [Member]
Benefit Plans [Line Items]
Voluntary employee separation charges		$ 3
Unrecognized compensation cost	2.2
Other Postretirement Benefits Plans [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5
Other Postretirement Benefits Plans [Member] | IPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5
Other Postretirement Benefits Plans [Member] | WPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	$ 5
Omnibus Incentive Plan [Member]
Benefit Plans [Line Items]
Shares available for issuance under the Amended and Restated OIP	7,400,000
2016 Grant [Member] | Performance Units [Member]
Benefit Plans [Line Items]
Instrument valuation based on shares of common stock, number of shares	1

Benefit Plans (Assumptions Used

Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.19%	4.47%	4.18%
Discount rate for net periodic cost	4.47%	4.18%	4.97%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.22%	4.50%	4.20%
Discount rate for net periodic cost	4.50%	4.20%	5.05%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.65%	3.50%
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.23%	4.51%	4.20%
Discount rate for net periodic cost	4.51%	4.20%	5.05%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.65%	3.50%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	3.98%	4.30%	3.97%
Discount rate for net periodic cost	4.30%	3.97%	4.59%
Expected rate of return on plan assets	6.30%	6.20%	7.40%
Medical cost trend on covered charges, initial trend rate (end of year)	7.00%	7.25%	6.75%
Medical cost trend on covered charges, ultimate trend rate	5.00%	5.00%	5.00%
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	3.95%	4.28%	3.94%
Discount rate for net periodic cost	4.28%	3.94%	4.55%
Expected rate of return on plan assets	6.60%	6.60%	7.60%
Medical cost trend on covered charges, initial trend rate (end of year)	7.00%	7.25%	6.75%
Medical cost trend on covered charges, ultimate trend rate	5.00%	5.00%	5.00%
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	3.96%	4.28%	3.96%
Discount rate for net periodic cost	4.28%	3.96%	4.56%
Expected rate of return on plan assets	4.70%	4.60%	7.30%
Medical cost trend on covered charges, initial trend rate (end of year)	7.00%	7.25%	6.75%
Medical cost trend on covered charges, ultimate trend rate	5.00%	5.00%	5.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.65%	3.65%	3.50%
Maximum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.50%	4.50%	4.50%

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 12.6	$ 15.9	$ 13.1
Interest cost		53	53.6	54.1
Expected return on plan assets	[1]	(65.5)	(75)	(74.9)
Amortization of prior service cost (credit)		(0.3)	(0.2)	0
Amortization of actuarial loss	[2]	37.4	35.4	19.5
Additional benefit costs		0	0.5	0
Total		37.2	30.2	11.8
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		5.3	5.5	5.2
Interest cost		9.4	9.1	9.5
Expected return on plan assets	[1]	(6.1)	(8.4)	(8.3)
Amortization of prior service cost (credit)	[3]	(4.1)	(11.3)	(11.9)
Amortization of actuarial loss	[2]	4.7	4.8	2.4
Additional benefit costs		0	0	0
Total		9.2	(0.3)	(3.1)
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		7.5	8.8	7.2
Interest cost		24.5	25	25.1
Expected return on plan assets	[1]	(30.9)	(35.8)	(35.7)
Amortization of prior service cost (credit)		(0.2)	(0.1)	0
Amortization of actuarial loss	[2]	16.5	15.3	8
Total		17.4	13.2	4.6
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2.3	2.4	2.4
Interest cost		3.8	3.8	3.9
Expected return on plan assets	[1]	(4.3)	(5.7)	(5.8)
Amortization of prior service cost (credit)	[3]	(2.6)	(6.1)	(6.3)
Amortization of actuarial loss	[2]	2.6	2.3	1.1
Total		1.8	(3.3)	(4.7)
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		4.9	5.8	4.9
Interest cost		22.3	22.6	22.6
Expected return on plan assets	[1]	(28.3)	(32.4)	(32.4)
Amortization of prior service cost (credit)		0.2	0.2	0.3
Amortization of actuarial loss	[2]	17.6	16.8	9.2
Additional benefit costs		0	0.5	0
Total		16.7	13.5	4.6
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2	2.1	2
Interest cost		3.8	3.7	3.8
Expected return on plan assets	[1]	(0.8)	(1.5)	(1.3)
Amortization of prior service cost (credit)	[3]	(0.9)	(3.5)	(3.9)
Amortization of actuarial loss	[2]	1.8	2.2	1.3
Additional benefit costs		0	0	0
Total		$ 5.9	$ 3	$ 1.9
[1]	The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
[2]	Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
[3]	Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

Benefit Plans (Estimated Amorit

Benefit Plans (Estimated Amoritization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss) (Details) - Scenario, Forecast [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	$ 37.5
Prior service cost (credit)	(0.4)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	37.1
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	16.1
Prior service cost (credit)	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	15.9
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	18.5
Prior service cost (credit)	0.1
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	18.6
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	3.8
Prior service cost (credit)	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	3.6
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	2
Prior service cost (credit)	0
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	2
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	1.6
Prior service cost (credit)	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	$ 1.4

Benefit Plans (Funded Status of

Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Change in benefit obligation:
Net benefit obligation at January 1	$ 1,206.3	$ 1,301.5
Service cost	12.6	15.9	$ 13.1
Interest cost	53	53.6	54.1
Plan participants' contributions	0	0
Plan amendments	0	0
Additional benefit costs	0	0.5
Actuarial (gain) loss	48.3	(70.1)
Gross benefits paid	(75.9)	(95.1)
Net benefit obligation at December 31	1,244.3	1,206.3	1,301.5
Change in plan assets:
Fair value of plan assets at January 1	895	1,018.1
Actual return on plan assets	74.3	(30.2)
Employer contributions	2.3	2.2
Plan participants' contributions	0	0
Gross benefits paid	(75.9)	(95.1)
Fair value of plan assets at December 31	895.7	895	1,018.1
Under funded status at December 31	(348.6)	(311.3)
Pension Plans, Defined Benefit [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	556.1	603.1
Service cost	7.5	8.8	7.2
Interest cost	24.5	25	25.1
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial (gain) loss	19.1	(32.3)
Gross benefits paid	(36.8)	(48.5)
Net benefit obligation at December 31	570.4	556.1	603.1
Change in plan assets:
Fair value of plan assets at January 1	422.7	484.7
Actual return on plan assets	35.3	(14.3)
Employer contributions	0.8	0.8
Plan participants' contributions	0	0
Gross benefits paid	(36.8)	(48.5)
Fair value of plan assets at December 31	422	422.7	484.7
Under funded status at December 31	(148.4)	(133.4)
Pension Plans, Defined Benefit [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	505.9	547.6
Service cost	4.9	5.8	4.9
Interest cost	22.3	22.6	22.6
Plan participants' contributions	0	0
Plan amendments	0	0
Additional benefit costs	0	0.5
Actuarial (gain) loss	25.7	(30)
Gross benefits paid	(29.6)	(40.6)
Net benefit obligation at December 31	529.2	505.9	547.6
Change in plan assets:
Fair value of plan assets at January 1	386.8	440.3
Actual return on plan assets	32.4	(13)
Employer contributions	0.1	0.1
Plan participants' contributions	0	0
Gross benefits paid	(29.6)	(40.6)
Fair value of plan assets at December 31	389.7	386.8	440.3
Under funded status at December 31	(139.5)	(119.1)
Other Postretirement Benefits Plans [Member]
Change in benefit obligation:
Net benefit obligation at January 1	221.4	231.1
Service cost	5.3	5.5	5.2
Interest cost	9.4	9.1	9.5
Plan participants' contributions	2.4	3.1
Plan amendments	0	(0.3)
Additional benefit costs	0	0
Actuarial (gain) loss	(0.3)	(9.4)
Gross benefits paid	(18.1)	(17.7)
Net benefit obligation at December 31	220.1	221.4	231.1
Change in plan assets:
Fair value of plan assets at January 1	106.9	121.6
Actual return on plan assets	8.2	(4.9)
Employer contributions	6.4	4.8
Plan participants' contributions	2.4	3.1
Gross benefits paid	(18.1)	(17.7)
Fair value of plan assets at December 31	105.8	106.9	121.6
Under funded status at December 31	(114.3)	(114.5)
Other Postretirement Benefits Plans [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	91.3	96.4
Service cost	2.3	2.4	2.4
Interest cost	3.8	3.8	3.9
Plan participants' contributions	0.9	1
Plan amendments	0	(0.1)
Actuarial (gain) loss	(0.7)	(4.6)
Gross benefits paid	(7.5)	(7.6)
Net benefit obligation at December 31	90.1	91.3	96.4
Change in plan assets:
Fair value of plan assets at January 1	69.2	78.7
Actual return on plan assets	5.3	(3.1)
Employer contributions	0.3	0.2
Plan participants' contributions	0.9	1
Gross benefits paid	(7.5)	(7.6)
Fair value of plan assets at December 31	68.2	69.2	78.7
Under funded status at December 31	(21.9)	(22.1)
Other Postretirement Benefits Plans [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	89.7	94
Service cost	2	2.1	2
Interest cost	3.8	3.7	3.8
Plan participants' contributions	1.2	1.6
Plan amendments	0	(0.2)
Additional benefit costs	0	0
Actuarial (gain) loss	0.5	(3.5)
Gross benefits paid	(8.3)	(8)
Net benefit obligation at December 31	88.9	89.7	94
Change in plan assets:
Fair value of plan assets at January 1	18.7	21.8
Actual return on plan assets	1.2	(1.1)
Employer contributions	5.8	4.4
Plan participants' contributions	1.2	1.6
Gross benefits paid	(8.3)	(8)
Fair value of plan assets at December 31	18.6	18.7	$ 21.8
Under funded status at December 31	$ (70.3)	$ (71)

Benefit Plans (Amounts Recogniz

Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	$ (489.9)	$ (451.8)
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0	0
Other current liabilities	(6.5)	(2.6)
Pension and other benefit obligations	(342.1)	(308.7)
Net amounts recognized at December 31	(348.6)	(311.3)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	535.1	533.1
Prior service credit	(6.9)	(7.2)
Net amount recognized at December 31	528.2	525.9
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	3.2	3
Other current liabilities	(8.6)	(6.2)
Pension and other benefit obligations	(108.9)	(111.3)
Net amounts recognized at December 31	(114.3)	(114.5)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	52.6	59.8
Prior service credit	(1.5)	(5.6)
Net amount recognized at December 31	51.1	54.2
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(173.2)	(160.2)
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0	0
Other current liabilities	(0.7)	(0.8)
Pension and other benefit obligations	(147.7)	(132.6)
Net amounts recognized at December 31	(148.4)	(133.4)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	233.6	235.5
Prior service credit	(2.3)	(2.5)
Net amount recognized at December 31	231.3	233
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0.4	0
Other current liabilities	(1.9)	0
Pension and other benefit obligations	(20.4)	(22.1)
Net amounts recognized at December 31	(21.9)	(22.1)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	25.4	29.8
Prior service credit	0	(2.7)
Net amount recognized at December 31	25.4	27.1
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(207.8)	(188.7)
WPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0	0
Other current liabilities	(0.1)	(0.1)
Pension and other benefit obligations	(139.4)	(119)
Net amounts recognized at December 31	(139.5)	(119.1)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	236.1	232.1
Prior service credit	(1.4)	(1.2)
Net amount recognized at December 31	234.7	230.9
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	2.7	3
Other current liabilities	(6.4)	(6)
Pension and other benefit obligations	(66.6)	(68)
Net amounts recognized at December 31	(70.3)	(71)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	21.5	23.3
Prior service credit	(1.5)	(2.4)
Net amount recognized at December 31	$ 20	$ 20.9

Benefit Plans (Accumulated Bene

Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 1,201.5	$ 1,166
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,201.5	1,166
Fair value of plan assets	895.7	895
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,244.3	1,206.3
Fair value of plan assets	895.7	895
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	220.1	221.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	220.1	221.4
Fair value of plan assets	105.8	106.9
Plans with projected benefit obligations in excess of plan assets:
Fair value of plan assets	102.8	101.4
IPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	546.7	531
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	546.7	531
Fair value of plan assets	422	422.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	570.4	556.1
Fair value of plan assets	422	422.7
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	90.1	91.3
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	90.1	91.3
Fair value of plan assets	68.2	69.2
Plans with projected benefit obligations in excess of plan assets:
Fair value of plan assets	68.2	68.6
WPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	513.2	493.8
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	513.2	493.8
Fair value of plan assets	389.7	386.8
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	529.2	505.9
Fair value of plan assets	389.7	386.8
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	88.9	89.7
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	88.9	89.7
Fair value of plan assets	$ 18.6	$ 18.7

Benefit Plans (Regulatory Asset

Benefit Plans (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 37.3	$ 38
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 30	$ 29.5

Benefit Plans (Estimated Future

Benefit Plans (Estimated Future Funding) (Details) - Scenario, Forecast [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	$ 6.5	[1]
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	0.7	[1]
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	0.1	[1]
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	8.7
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	2
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2017	$ 6.4
[1]	Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Benefit Plans (Expected Benefit

Benefit Plans (Expected Benefit Payments) (Details) $ in Millions	Dec. 31, 2016USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	$ 93.4
Expected benefit payments, 2018	91.7
Expected benefit payments, 2019	93.7
Expected benefit payments, 2020	95.4
Expected benefit payments, 2021	97.5
Expected benefit payments, 2022 - 2026	488.5
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	74.8
Expected benefit payments, 2018	73.2
Expected benefit payments, 2019	75.5
Expected benefit payments, 2020	77.6
Expected benefit payments, 2021	79.9
Expected benefit payments, 2022 - 2026	405.9
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	18.6
Expected benefit payments, 2018	18.5
Expected benefit payments, 2019	18.2
Expected benefit payments, 2020	17.8
Expected benefit payments, 2021	17.6
Expected benefit payments, 2022 - 2026	82.6
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	41.7
Expected benefit payments, 2018	42.7
Expected benefit payments, 2019	42.4
Expected benefit payments, 2020	44.6
Expected benefit payments, 2021	45.1
Expected benefit payments, 2022 - 2026	226.1
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	34
Expected benefit payments, 2018	35.1
Expected benefit payments, 2019	35
Expected benefit payments, 2020	37.2
Expected benefit payments, 2021	37.9
Expected benefit payments, 2022 - 2026	192.1
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	7.7
Expected benefit payments, 2018	7.6
Expected benefit payments, 2019	7.4
Expected benefit payments, 2020	7.4
Expected benefit payments, 2021	7.2
Expected benefit payments, 2022 - 2026	34
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	38.2
Expected benefit payments, 2018	38.9
Expected benefit payments, 2019	39.6
Expected benefit payments, 2020	39.9
Expected benefit payments, 2021	39.7
Expected benefit payments, 2022 - 2026	199.8
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	30.2
Expected benefit payments, 2018	30.9
Expected benefit payments, 2019	31.8
Expected benefit payments, 2020	32.5
Expected benefit payments, 2021	32.4
Expected benefit payments, 2022 - 2026	167.1
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2017	8
Expected benefit payments, 2018	8
Expected benefit payments, 2019	7.8
Expected benefit payments, 2020	7.4
Expected benefit payments, 2021	7.3
Expected benefit payments, 2022 - 2026	$ 32.7

Benefit Plans (Allocation Of Pl

Benefit Plans (Allocation Of Plan Assets) (Details)	12 Months Ended
	Dec. 31, 2016
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	5.00%
Actual allocation	3.00%
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	22.00%
Target range allocation, maximum	42.00%
Actual allocation	30.00%
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	8.00%
Target range allocation, maximum	28.00%
Actual allocation	17.00%
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	5.00%
Target range allocation, maximum	15.00%
Actual allocation	10.00%
Pension Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	5.00%
Target range allocation, maximum	15.00%
Actual allocation	10.00%
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	20.00%
Target range allocation, maximum	40.00%
Actual allocation	30.00%
Other Postretirement Benefits Plans [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	15.00%
Actual allocation	3.00%
Other Postretirement Benefits Plans [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	45.00%
Actual allocation	22.00%
Other Postretirement Benefits Plans [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	21.00%
Actual allocation	13.00%
Other Postretirement Benefits Plans [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	5.00%
Target range allocation, maximum	40.00%
Actual allocation	16.00%
Other Postretirement Benefits Plans [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	10.00%
Target range allocation, maximum	70.00%
Actual allocation	46.00%

Benefit Plans (Fair Value Of Pl

Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 895.7	$ 895	$ 1,018.1
Assets measured at net asset value	405.9	608.5
Total plan assets	895.7	895
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30.4	23.1
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	0
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25.4	23.1
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	183.6	116.4
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	183.6	116.4
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97.4	93.9
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97.4	93.9
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	52.9
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	52.9
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	125.4	0
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53.6	0
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71.8	0
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	489.8	286.3
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	392.6	263.2
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97.2	23.1
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Accrued Investment Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.1	0.2
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	422	422.7	484.7
Assets measured at net asset value	191.2	287.4
Total plan assets	422	422.7
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.4	10.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.4	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12	10.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	86.5	54.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	86.5	54.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.9	44.4
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.9	44.4
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24.9	25
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24.9	25
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	59.1	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25.3	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33.8	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	230.8	135.2
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	185	124.3
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.8	10.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Accrued Investment Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.1
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	389.7	386.8	440.3
Assets measured at net asset value	176.6	263
Total plan assets	389.7	386.8
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.3	10
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.2	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.1	10
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79.9	50.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	79.9	50.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.4	40.6
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.4	40.6
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23	22.8
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23	22.8
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	54.5	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.3	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31.2	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	213.1	123.7
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	170.8	113.7
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.3	10
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Accrued Investment Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105.8	106.9	121.6
Assets measured at net asset value	3	5.5
Total plan assets	102.8	101.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100.7	97.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.1	3.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.5	3.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.5	3.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.5	22.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.5	22.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.5	13.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.5	13.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.5	16
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.5	16
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.8	46.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.2	46.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68.2	69.2	78.7
Assets measured at net asset value	0	0.6
Total plan assets	68.2	68.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	68.2	67.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	0.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	16.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	16.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	10.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	10.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	6.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	6.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32.4	33.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32.4	33.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18.6	18.7	$ 21.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.3	16.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.3	2.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.7	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.3	2.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.5	5.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.5	5.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.1	11
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.1	11
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(1.1)	0
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.5)	0
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ (0.5)	$ 0

Benefit Plans (Employees Partic

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
401(k) costs	$ 23.6	$ 24.9	$ 22.5
IPL [Member]
401(k) costs	12	12.7	11.1
WPL [Member]
401(k) costs	$ 10.7	$ 11.2	$ 10.5

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation expense	$ 18	$ 10.7	$ 15.3
Income tax benefits	7.4	4.4	6.2
IPL [Member]
Compensation expense	9.5	5.7	8.3
Income tax benefits	4	2.4	3.4
WPL [Member]
Compensation expense	7.9	4.7	6.4
Income tax benefits	$ 3.2	$ 1.9	$ 2.6

Benefit Plans (Summary Of Perfo

Benefit Plans (Summary Of Performance Shares and Units Activity) (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	279,880
Granted (in shares/awards)	68,585	90,806	102,442
Vested (in shares/awards)	(98,186)	(91,224)	(90,470)
Forfeited (in shares/awards)	(1,230)	0	(3,004)
Nonvested, December 31 (in shares/awards)	257,599	288,430	288,848
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	131,824
Granted (in shares/awards)	23,918	35,674	40,844
Vested (in shares/awards)	(42,760)	(45,690)	(41,502)
Forfeited (in shares/awards)	(4,250)	(902)	(3,836)
Nonvested, December 31 (in shares/awards)	93,320	116,412	127,330

Benefit Plans (Summary Of Pe113

Benefit Plans (Summary Of Performance Shares and Units Vested Awards) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)	98,186	91,224	90,470
Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)	42,760	45,690	41,502
2013 Grant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)	98,186
Vested percentage of the target	165.00%
Cash and stock payout value	$ 5.1
Cash payout value	$ 2.9
Common stock shares from vested performance shares (in shares)	22,408
2013 Grant [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)	42,760
Vested percentage of the target	165.00%
Cash and stock payout value	$ 1.7
Cash payout value	$ 1.7
2012 Grant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)		91,224
Vested percentage of the target		167.50%
Cash and stock payout value		$ 5.1
Cash payout value		$ 3.2
Common stock shares from vested performance shares (in shares)		21,950
2012 Grant [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)		45,690
Vested percentage of the target		167.50%
Cash and stock payout value		$ 1.6
Cash payout value		$ 1.6
2011 Grant [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)			90,470
Vested percentage of the target			147.50%
Cash and stock payout value			$ 3.4
Cash payout value			$ 2.9
Common stock shares from vested performance shares (in shares)			9,620
2011 Grant [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares/awards)			41,502
Vested percentage of the target			147.50%
Cash and stock payout value			$ 1.2
Cash payout value			$ 1.2

Benefit Plans (Fair Values Of N

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	257,599
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	93,320
2016 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	67,355
Alliant Energy common stock closing price on December 30, 2016 (in dollars per share)	$ 37.89
Estimated payout percentage based on performance criteria	135.00%
Fair values of each nonvested award (in dollars per share)	$ 51.15
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	22,657
Alliant Energy common stock closing price on December 30, 2016 (in dollars per share)	$ 37.89
Estimated payout percentage based on performance criteria	135.00%
Fair values of each nonvested award (in dollars per share)	$ 51.15
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	90,806
Alliant Energy common stock closing price on December 30, 2016 (in dollars per share)	$ 37.89
Estimated payout percentage based on performance criteria	155.00%
Fair values of each nonvested award (in dollars per share)	$ 58.73
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	33,268
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 32.55
Estimated payout percentage based on performance criteria	155.00%
Fair values of each nonvested award (in dollars per share)	$ 50.45
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	99,438
Alliant Energy common stock closing price on December 30, 2016 (in dollars per share)	$ 37.89
Estimated payout percentage based on performance criteria	148.00%
Fair values of each nonvested award (in dollars per share)	$ 56.08
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards) | shares	37,395
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 26.89
Estimated payout percentage based on performance criteria	148.00%
Fair values of each nonvested award (in dollars per share)	$ 39.80

Benefit Plans (Summary Of Pe115

Benefit Plans (Summary Of Performance Contingent Restricted Stock Activity) (Details) - Performance-Contingent Restricted Stock [Member] - $ / shares		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		190,244	197,624	317,844
Nonvested shares, January 1, weighted average grant date fair value (in dollars per share)		$ 29.59	$ 25.35	$ 21.36
Granted (in shares/awards)		0	90,806	102,442
Granted, weighted average grant date fair value (in dollars per share)		$ 0	$ 32.55	$ 26.89
Vested (in shares/awards)	[1]	0	(98,186)	(181,694)
Vested, weighted average grant date fair value (in dollars per share)	[1]	$ 0	$ 23.79	$ 20.46
Forfeited (in shares/awards)	[2]	0	0	(40,968)
Forfeited, weighted average grant date fair value (in dollars per share)	[2]	$ 0	$ 0	$ 19.93
Nonvested, December 31 (in shares/awards)		190,244	190,244	197,624
Nonvested shares, December 31, weighted average grant date fair value (in dollars per share)		$ 29.59	$ 29.59	$ 25.35
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(98,186)
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)				(91,224)
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)				(90,470)
[1]	In 2015, 98,186 performance-contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 91,224 and 90,470 performance-contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
[2]	The forfeitures during 2014 were primarily caused by retirements and terminations of participants.

Benefit Plans Benefit Plans (Su

Benefit Plans Benefit Plans (Summary of Performance Restricted Stock Units) (Details) - Performance Restricted Stock Unit [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Granted (in shares/awards) | shares	68,585
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 33.96
Forfeited (in shares/awards) | shares	(1,230)
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares	$ 33.90
Nonvested, December 31 (in shares/awards) | shares	67,355
Nonvested shares, December 31, weighted average grant date fair value (in dollars per share) | $ / shares	$ 33.96

Benefit Plans Benefit Plans 117

Benefit Plans Benefit Plans (Summary of Restricted Stock Units and Restricted Units) (Details) - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2016shares
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, December 31 (in shares/awards)	57,736

Benefit Plans (Summary Of Pe118

Benefit Plans (Summary Of Performance Contingent Cash Awards Activity) (Details) - Performance Contingent Cash Awards [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		163,752	157,860	193,954
Granted (in shares/awards)		0	82,210	84,892
Vested (in shares/awards)	[1]	0	(74,664)	(111,034)
Forfeited (in shares/awards)		(3,652)	(1,654)	(9,952)
Nonvested, December 31 (in shares/awards)		160,100	163,752	157,860
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(74,664)
Cash payout value			$ 2.4
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)				(69,532)
Cash payout value				$ 1.9
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)				(41,502)
Cash payout value				$ 1.1
[1]	In 2015, 74,664 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 69,532 and 41,502 performance-contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.

Benefit Plans (Carrying Value A

Benefit Plans (Carrying Value And Fair Market Value Of The Deferred Compensation Obligation for Company Stock Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligation	$ 10	$ 8.5
Fair market value of deferred compensation obligation	$ 16.7	$ 13.4

Benefit Plans (Carrying Value O

Benefit Plans (Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligations	$ 19.4	$ 18.3
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligations	$ 4.6	$ 5

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) $ in Millions		3 Months Ended	12 Months Ended
		Jun. 30, 2015USD ($)	Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 214		$ 114
Revisions in estimated cash flows	[1]		(13.3)		17.3
Liabilities settled			(14)		(8.8)
Liabilities incurred		$ 87	2.6	[1]	86.6	[1]
Accretion expense			6.4		4.9
Balance, December 31			195.7		214
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			132.9		51.8
Revisions in estimated cash flows	[1]		(5.8)		15.1
Liabilities settled			(6.8)		(4.3)
Liabilities incurred		67	0.7	[1]	67.8	[1]
Accretion expense			3.7		2.5
Balance, December 31			$ 124.7		132.9
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]		(7.5)		3.2
Liabilities settled			(7.2)		(4.5)
Liabilities incurred		$ 20	1.9	[1]	18.8	[1]
Accretion expense			2.3		2
Balance, December 31			$ 61.4		$ 71.9
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. In 2015, Alliant Energy, IPL and WPL recognized additional AROs of $87 million, $67 million and $20 million, respectively, as a result of the final CCR Rule. These increases in AROs resulted in corresponding increases in property, plant and equipment, net on the respective balance sheets. Actual costs resulting from the CCR Rule may be different than the amounts recorded in 2015 due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Expenditures incurred by IPL and WPL to comply with the CCR Rule are anticipated to be recovered in rates from their customers.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016
5.1% [Member] | Redeemable Preferred Stock [Member] | IPL [Member]
Cumulative preferred stock rate	5.10%

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets:
Deferred proceeds	$ 211.1	$ 172
Liabilities and equity:
Long-term debt (including current maturities)	4,799	4,336.1
IPL's cumulative preferred stock	194.8	206.6
Commodity Contracts [Member]
Assets:
Derivatives	41.4	18.4
Liabilities and equity:
Derivatives	28.6	64.6
Level 1 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
IPL's cumulative preferred stock	194.8	206.6
Level 1 [Member] | Commodity Contracts [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)	4,795.7	4,332.4
IPL's cumulative preferred stock	0	0
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	4.6	2.5
Liabilities and equity:
Derivatives	0.5	16
Level 3 [Member]
Assets:
Deferred proceeds	211.1	172
Liabilities and equity:
Long-term debt (including current maturities)	3.3	3.7
IPL's cumulative preferred stock	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	36.8	15.9
Liabilities and equity:
Derivatives	28.1	48.6
Carrying Amount [Member]
Assets:
Deferred proceeds	211.1	172
Liabilities and equity:
Long-term debt (including current maturities)	4,320.2	3,835.6
IPL's cumulative preferred stock	200	200
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	41.4	18.4
Liabilities and equity:
Derivatives	28.6	64.6
IPL [Member]
Assets:
Deferred proceeds	211.1	172
Liabilities and equity:
Long-term debt (including current maturities)	2,352.3	2,092.7
IPL's cumulative preferred stock	194.8	206.6
IPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	20.8	15.5
Liabilities and equity:
Derivatives	8.3	23.4
IPL [Member] | Level 1 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
IPL's cumulative preferred stock	194.8	206.6
IPL [Member] | Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
IPL [Member] | Level 2 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	2,352.3	2,092.7
IPL's cumulative preferred stock	0	0
IPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	2.8	2
Liabilities and equity:
Derivatives	0.4	8
IPL [Member] | Level 3 [Member]
Assets:
Deferred proceeds	211.1	172
Liabilities and equity:
Long-term debt (including current maturities)	0	0
IPL's cumulative preferred stock	0	0
IPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	18	13.5
Liabilities and equity:
Derivatives	7.9	15.4
IPL [Member] | Carrying Amount [Member]
Assets:
Deferred proceeds	211.1	172
Liabilities and equity:
Long-term debt (including current maturities)	2,153.5	1,856.9
IPL's cumulative preferred stock	200	200
IPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	20.8	15.5
Liabilities and equity:
Derivatives	8.3	23.4
WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,807.4	1,793
WPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	20.6	2.9
Liabilities and equity:
Derivatives	20.3	41.2
WPL [Member] | Level 1 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
WPL [Member] | Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
WPL [Member] | Level 2 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,807.4	1,793
WPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	1.8	0.5
Liabilities and equity:
Derivatives	0.1	8
WPL [Member] | Level 3 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
WPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	18.8	2.4
Liabilities and equity:
Derivatives	20.2	33.2
WPL [Member] | Carrying Amount [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,535.2	1,533.9
WPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	20.6	2.9
Liabilities and equity:
Derivatives	$ 20.3	$ 41.2

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Commodity Contracts Derivative Assets and (Liabilities), net [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		$ (32.7)	$ 17.9
Total net gains (losses) included in changes in net assets (realized/unrealized)		30.7	(63.5)
Transfers into Level 3		0.9	0
Transfers out of Level 3		1.2	0.3
Purchases		22	36.9
Sales		(1)	(1.9)
Settlements		(12.4)	(22.4)
Ending balance, December 31		8.7	(32.7)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		32.7	(56)
Commodity Contracts Derivative Assets and (Liabilities), net [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		(1.9)	19.4
Total net gains (losses) included in changes in net assets (realized/unrealized)		7.3	(29.6)
Transfers into Level 3		0.5	0
Transfers out of Level 3		0.2	0
Purchases		20.6	33.1
Sales		(1)	(1.8)
Settlements		(15.6)	(23)
Ending balance, December 31		10.1	(1.9)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		8.5	(23.1)
Commodity Contracts Derivative Assets and (Liabilities), net [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		(30.8)	(1.5)
Total net gains (losses) included in changes in net assets (realized/unrealized)		23.4	(33.9)
Transfers into Level 3		0.4	0
Transfers out of Level 3		1	0.3
Purchases		1.4	3.8
Sales		0	(0.1)
Settlements		3.2	0.6
Ending balance, December 31		(1.4)	(30.8)
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 December 31		24.2	(32.9)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		172	177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Purchases		0	0
Sales		0	0
Settlements	[1]	39.1	(5.2)
Ending balance, December 31		211.1	172
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 December 31		0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		172	177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Purchases		0	0
Sales		0	0
Settlements	[1]	39.1	(5.2)
Ending balance, December 31		211.1	172
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 December 31		$ 0	$ 0
[1]	Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Measurements (Fai125

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 8.7	$ (32.7)	$ 17.9
Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities	2.3	43.1
FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	11	10.4
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	10.1	(1.9)	19.4
IPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities		12.3
Fair value, net derivative assets	0.1
IPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	10	10.4
WPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	(1.4)	(30.8)	$ (1.5)
WPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities	2.4	30.8
WPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 1	$ 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	12 Months Ended
	Dec. 31, 2016DekathermsTMWhgal
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	2,628
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	0
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	2,628
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	8,970
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,465
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	3,505
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	139,865
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	56,265
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	83,600
Coal (tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	4,239
Coal (tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	1,955
Coal (tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	2,284
Diesel Fuel (gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in gallons) | gal	6,552
Diesel Fuel (gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in gallons) | gal	0
Diesel Fuel (gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in gallons) | gal	6,552

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 29.4	$ 15.1
Non-current derivative assets	12	3.3
Current derivative liabilities	13.3	47.3
Non-current derivative liabilities	15.3	17.3
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	19.1	13.8
Non-current derivative assets	1.7	1.7
Current derivative liabilities	2.7	18.5
Non-current derivative liabilities	5.6	4.9
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	10.3	1.3
Non-current derivative assets	10.3	1.6
Current derivative liabilities	10.6	28.8
Non-current derivative liabilities	$ 9.7	$ 12.4

Commitments And Contingencie128

Commitments And Contingencies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,400
Performance guarantees outstanding	75
Present value abandonment obligation	$ 31
Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	56.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	19.00%
Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 58
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,774
Maximum indemnification limit	$ 17
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	65.00%
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	46.00%
IPL [Member] | Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 3
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 611
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	81.00%
WPL [Member] | Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 55
Environmental Issue [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Damages awarded	6
Environmental Issue [Member] | WPL [Member]
Long-term Purchase Commitment [Line Items]
Damages awarded	$ 7

Commitments And Contingencie129

Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,400
Individual commitments incurred	1
Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,418	[1]
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	771
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	177	[2]
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34	[3]
2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	529
2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	185	[1]
2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	223
2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	105	[2]
2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	16	[3]
2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	389
2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	189	[1]
2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	142
2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	54	[2]
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	4	[3]
2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	297
2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	159	[1]
2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	115
2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	18	[2]
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5	[3]
2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	237
2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	137	[1]
2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	98
2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	220
2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	149	[1]
2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	69
2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	728
Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	599	[1]
Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	124
Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5	[3]
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,774
IPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,298	[1]
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	382
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	77	[2]
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	17	[3]
IPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	322
IPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1]
IPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	120
IPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	49	[2]
IPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	15	[3]
IPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	225
IPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1]
IPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	74
IPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	19	[2]
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3]
IPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	209
IPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	144	[1]
IPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	55
IPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	9	[2]
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3]
IPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	176
IPL [Member] | 2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	137	[1]
IPL [Member] | 2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	39
IPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
IPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | 2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	172
IPL [Member] | 2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	149	[1]
IPL [Member] | 2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	23
IPL [Member] | 2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
IPL [Member] | 2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	670
IPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	599	[1]
IPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	71
IPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	611
WPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	120	[1]
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	389
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	100	[2]
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
WPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	206
WPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	47	[1]
WPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	103
WPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	56	[2]
WPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	162
WPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	58	[1]
WPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	68
WPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	35	[2]
WPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3]
WPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	85
WPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	15	[1]
WPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	60
WPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	9	[2]
WPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3]
WPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	59
WPL [Member] | 2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	59
WPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | 2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	46
WPL [Member] | 2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	46
WPL [Member] | 2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | 2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	53
WPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	53
WPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 0	[3]
[1]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
[2]	Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 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 December 31, 2016.

Commitments And Contingencie130

Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	$ 14
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	27
IPL [Member]
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	12
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	24
Manufactured Gas Plant [Member]
Total environmental liabilities	16
Manufactured Gas Plant [Member] | IPL [Member]
Total environmental liabilities	$ 13

Segments Of Business (Narrative

Segments Of Business (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016segment
Utility Business [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3
IPL [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3
WPL [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 797	$ 924.6	$ 754.6	$ 843.8	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 3,320	$ 3,253.6	$ 3,350.3
Depreciation and amortization									411.6	401.3	388.1
Operating income (loss)	99.9	162.6	128.6	145.9	79.2	235.9	109	152.9	537	577	543.6
Interest expense									196.2	187.1	180.6
Equity (income) loss from unconsolidated investments, net									(39.6)	(33.8)	(40.4)
Income tax expense (benefit)									59.4	70.4	44.3
Net income (loss) attributable to common shareowners	62.7	128.4	83.9	96.5	34.1	179.9	67.6	96.6	371.5	378.2	383.1
Total assets	13,373.8				12,495.2				13,373.8	12,495.2	12,063.5
Investments in equity method subsidiaries	326				302.9				326	302.9	296.6
Construction and acquisition expenditures									1,196.8	1,034.3	902.8
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	434.5	516.2	411	458.7	398.7	504.6	382.2	489	1,820.4	1,774.5	1,848.1
Depreciation and amortization									210.8	207.2	197.5
Operating income (loss)	34.9	125.9	48	62	25.6	117	33.8	65.5	270.8	241.9	209.2
Interest expense									103.2	96.8	89.9
Income tax expense (benefit)									(5.9)	(22.7)	(48.9)
Net income (loss) attributable to common shareowners	24	114.1	31.9	45.6	5.5	116.5	16.5	47.5	215.6	186	181.6
Total assets	7,304.7				6,709.1				7,304.7	6,709.1
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	352.2	397	334.3	375.6	330.7	382.6	324.7	397.1	1,459.1	1,435.1	1,449.1
Depreciation and amortization									192.5	184.3	181.2
Operating income (loss)	58.2	115	75	78.8	49.3	110.3	68.3	80.8	327	308.7	301
Interest expense									91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									93.3	82.9	85.3
Net income (loss) attributable to common shareowners	31.7	$ 69	$ 43.2	$ 46.5	24.2	$ 68	$ 39.2	$ 44.9	190.4	176.3	180.4
Total assets	5,290.3				5,270.4				5,290.3	5,270.4
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,875.5	2,770.5	2,713.6
Depreciation and amortization									367	358.6	347
Operating income (loss)									571.9	514.1	442.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Total assets	11,040.5				10,211.3				11,040.5	10,211.3	9,660.4
Investments in equity method subsidiaries	325.3				302				325.3	302	294.3
Construction and acquisition expenditures									1,005.5	855.8	774.8
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,569.7	1,503.8	1,493.3
Depreciation and amortization									189.4	187.9	178.7
Operating income (loss)									252	218.8	166.8
Total assets	6,278.2				5,754.1				6,278.2	5,754.1	5,398.3
Construction and acquisition expenditures									598.1	561.2	490
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,305.8	1,266.7	1,220.3
Depreciation and amortization									177.6	170.7	168.3
Operating income (loss)									319.9	295.3	275.6
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Total assets	4,444.7				4,457.2				4,444.7	4,457.2	4,262.1
Investments in equity method subsidiaries	7.7				302				7.7	302	294.3
Construction and acquisition expenditures									407.4	294.6	284.8
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									355.4	381.2	517.5
Depreciation and amortization									34.2	31.1	29.9
Operating income (loss)									30.7	34.6	53.8
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	1,091.1				939.3				1,091.1	939.3	913.5
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									137.1	106.4	63.2
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									204	217.3	296.5
Depreciation and amortization									19.3	17.5	17
Operating income (loss)									15.5	17.7	25.7
Total assets	653.3				548.2				653.3	548.2	544.1
Construction and acquisition expenditures									91.5	56.7	35.1
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									151.4	163.9	221
Depreciation and amortization									14.9	13.6	12.9
Operating income (loss)									15.2	16.9	28.1
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	437.8				391.1				437.8	391.1	369.4
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									45.6	49.7	28.1
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									48.6	57.9	66.1
Depreciation and amortization									2.1	1.8	1.8
Operating income (loss)									(4.8)	1.9	14
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	781				828.9				781	828.9	993.9
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									0.1	1.4	0.9
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									46.7	53.4	58.3
Depreciation and amortization									2.1	1.8	1.8
Operating income (loss)									3.3	5.4	16.7
Total assets	373.2				406.8				373.2	406.8	507.8
Construction and acquisition expenditures									0.1	1.4	0.9
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1.9	4.5	7.8
Depreciation and amortization									0	0	0
Operating income (loss)									(8.1)	(3.5)	(2.7)
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	407.8				422.1				407.8	422.1	486.1
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									0	0	0
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues									3,279.5	3,209.6	3,297.2
Depreciation and amortization									403.3	391.5	378.7
Operating income (loss)									597.8	550.6	510.2
Interest expense									194.6	189.2	176.3
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									87.4	60.2	36.4
Net income (loss) attributable to common shareowners									406	362.3	362
Total assets	12,912.6				11,979.5				12,912.6	11,979.5	11,567.8
Investments in equity method subsidiaries	325.3				302				325.3	302	294.3
Construction and acquisition expenditures									1,142.7	963.6	838.9
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,820.4	1,774.5	1,848.1
Depreciation and amortization									210.8	207.2	197.5
Operating income (loss)									270.8	241.9	209.2
Interest expense									103.2	96.8	89.9
Income tax expense (benefit)									(5.9)	(22.7)	(48.9)
Net income (loss) attributable to common shareowners									215.6	186	181.6
Total assets	7,304.7				6,709.1				7,304.7	6,709.1	6,450.2
Construction and acquisition expenditures									689.7	619.3	526
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,459.1	1,435.1	1,449.1
Depreciation and amortization									192.5	184.3	181.2
Operating income (loss)									327	308.7	301
Interest expense									91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									93.3	82.9	85.3
Net income (loss) attributable to common shareowners									190.4	176.3	180.4
Total assets	5,290.3				5,270.4				5,290.3	5,270.4	5,117.6
Investments in equity method subsidiaries	7.7				302				7.7	302	294.3
Construction and acquisition expenditures									453	344.3	312.9
Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues									40.5	44	53.1
Depreciation and amortization									8.3	9.8	9.4
Operating income (loss)									(60.8)	26.4	33.4
Interest expense									1.6		4.3
Interest income										(2.1)
Equity (income) loss from unconsolidated investments, net									0.2	1.3	2.4
Income tax expense (benefit)									(28)	10.2	7.9
Net income (loss) attributable to common shareowners									(34.5)	15.9	21.1
Total assets	461.2				515.7				461.2	515.7	495.7
Investments in equity method subsidiaries	$ 0.7				$ 0.9				0.7	0.9	2.3
Construction and acquisition expenditures									$ 54.1	$ 70.7	$ 63.9

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
WPL [Member] | WPL Owed ATC [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 8	$ 8

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 161	$ 150	$ 148
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	133	121	116
Transmission Sales Credited [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	8	10	8
Transmission Sales Credited [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	7	24	6
Transmission Purchases Billed [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	433	366	422
Transmission Purchases Billed [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 102	$ 66	$ 125

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
IPL [Member]
Related Party Transaction [Line Items]
Intercompany payables to Corporate Services	$ 104	$ 93
WPL [Member]
Related Party Transaction [Line Items]
Intercompany payables to Corporate Services	$ 72	$ 54

Related Parties (Related Amount

Related Parties (Related Amounts Billed Between Parties) (Details) - WPL [Member] - ATC [Member] - Equity Method Investment [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ATC Billings To WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 110	$ 101	$ 96
WPL Billings To ATC [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 13	$ 13	$ 9

Discontinued Operations (Compon

Discontinued Operations (Components Of Discontinued Operations In Consolidated Statements Of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Operating expenses	$ 3.9	$ 4	$ 3.7
Loss before income taxes	(3.9)	(4)	(3.7)
Income tax benefit	(1.6)	(1.5)	(1.3)
Loss from discontinued operations, net of tax	$ (2.3)	$ (2.5)	$ (2.4)

Selected Consolidated Quarte138

Selected Consolidated Quarterly Financial Data (Unaudited) (Details) $ / shares in Units, $ in Millions		Apr. 20, 2016	Dec. 31, 2016USD ($)$ / shares	Sep. 30, 2016USD ($)$ / shares	Jun. 30, 2016USD ($)$ / shares	Mar. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)$ / shares	Sep. 30, 2015USD ($)$ / shares	Jun. 30, 2015USD ($)$ / shares	Mar. 31, 2015USD ($)$ / shares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Operating revenues			$ 797	$ 924.6	$ 754.6	$ 843.8	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 3,320	$ 3,253.6	$ 3,350.3
Operating income			99.9	162.6	128.6	145.9	79.2	235.9	109	152.9	537	577	543.6
Income from continuing operations, net of tax			63	128.8	84.4	97.6	35.2	180	68.9	96.6	373.8	380.7	385.5
Loss from discontinued operations, net of tax			(0.3)	(0.4)	(0.5)	(1.1)	(1.1)	(0.1)	(1.3)	0	(2.3)	(2.5)	(2.4)
Net income											381.7	388.4	393.3
Net income attributable to common shareowners			$ 62.7	$ 128.4	$ 83.9	$ 96.5	$ 34.1	$ 179.9	$ 67.6	$ 96.6	371.5	378.2	383.1
Income from continuing operations, net of tax (in dollars per share) | $ / shares	[1]		$ 0.28	$ 0.57	$ 0.37	$ 0.43	$ 0.16	$ 0.79	$ 0.31	$ 0.43
Loss from discontinued operations, net of tax (in dollars per share) | $ / shares	[1]		0	0	0	0	(0.01)	0	(0.01)	0
Net income (in dollars per share) | $ / shares	[1]		$ 0.28	$ 0.57	$ 0.37	$ 0.43	$ 0.15	$ 0.79	$ 0.30	$ 0.43
Common stock split conversion ratio (2:1)		2
IPL [Member]
Operating revenues			$ 434.5	$ 516.2	$ 411	$ 458.7	$ 398.7	$ 504.6	$ 382.2	$ 489	1,820.4	1,774.5	1,848.1
Operating income			34.9	125.9	48	62	25.6	117	33.8	65.5	270.8	241.9	209.2
Net income			26.5	116.7	34.4	48.2	8	119.1	19	50.1	225.8	196.2	191.8
Net income attributable to common shareowners			24	114.1	31.9	45.6	5.5	116.5	16.5	47.5	215.6	186	181.6
WPL [Member]
Operating revenues			352.2	397	334.3	375.6	330.7	382.6	324.7	397.1	1,459.1	1,435.1	1,449.1
Operating income			58.2	115	75	78.8	49.3	110.3	68.3	80.8	327	308.7	301
Net income			32.5	69.6	43.7	47	24.4	68.4	39.7	45.1	192.8	177.6	181.1
Net income attributable to common shareowners			$ 31.7	$ 69	$ 43.2	$ 46.5	$ 24.2	$ 68	$ 39.2	$ 44.9	$ 190.4	$ 176.3	$ 180.4
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Condensed Parent Company Fin139

Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues	$ 797	$ 924.6	$ 754.6	$ 843.8	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 3,320	$ 3,253.6	$ 3,350.3
Operating expenses									2,783	2,676.6	2,806.7
Operating income (loss)	$ 99.9	$ 162.6	$ 128.6	$ 145.9	$ 79.2	$ 235.9	$ 109	$ 152.9	537	577	543.6
Interest expense and other:
Equity earnings from consolidated subsidiaries									(39.6)	(33.8)	(40.4)
Interest expense									196.2	187.1	180.6
Total interest expense and other									93.6	115.7	103.6
Income from continuing operations before income taxes									443.4	461.3	440
Income tax benefit									59.4	70.4	44.3
Net income									381.7	388.4	393.3
Parent Company [Member]
Operating revenues									1	2	2
Operating expenses									3	3	3
Operating income (loss)									(2)	(1)	(1)
Interest expense and other:
Equity earnings from consolidated subsidiaries									(374)	(379)	(388)
Interest expense									3	3	9
Interest income									(2)	(3)	(2)
Total interest expense and other									(373)	(379)	(381)
Income from continuing operations before income taxes									371	378	380
Income tax benefit									(1)	(1)	(3)
Net income									$ 372	$ 379	$ 383

Condensed Parent Company Fin140

Condensed Parent Company Financial Statements (Condensed Balance Sheet) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	[2]
Current assets:
Other		$ 95.5	$ 79.7
Total current assets		877.1	826.8
Investments:
Other		20	53
Total investments		337.6	346.3
Other assets		22.6	14.6
Total assets		13,373.8	12,495.2		$ 12,063.5
Current liabilities:
Current maturities of long-term debt		4.6	313.4
Commercial paper		244.1	159.8
Other		222.3	243.4
Total current liabilities		1,162	1,359.3
Other liabilities		279.3	306
Common Equity:
Retained earnings		2,177	2,068.9
Shares in deferred compensation trust	[1]	(10)	(8.5)
Total common equity		3,862	3,724.1	[2]	$ 3,438.7	[2]	$ 3,281.4
Total liabilities and equity		13,373.8	12,495.2
Parent Company [Member]
Current assets:
Notes receivable from affiliated companies		74	93
Other		5	9
Total current assets		79	102
Investments:
Investments in consolidated subsidiaries		4,211	3,999
Other		2	14
Total investments		4,213	4,013
Other assets		64	20
Total assets		4,356	4,135
Current liabilities:
Current maturities of long-term debt		0	250
Commercial paper		192	140
Notes payable to affiliated companies		275	0
Other		12	12
Total current liabilities		479	402
Other liabilities		18	12
Common Equity:
Common stock and additional paid-in capital		1,695	1,664
Retained earnings		2,174	2,066
Shares in deferred compensation trust		(10)	(9)
Total common equity		3,859	3,721
Total liabilities and equity		$ 4,356	$ 4,135
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.
[2]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Condensed Parent Company Fin141

Condensed Parent Company Financial Statements (Condensed Statements of Cash Flow) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Net cash flows from operating activities	$ 859.6	$ 871.2		$ 891.6
Cash flows from (used for) investing activities:
Other	10.3	(24.8)		(14.9)
Net cash flows from (used for) investing activities	(1,186.5)	(919.2)		(917.7)
Cash flows used for financing activities:
Common stock dividends	(266.5)	(247.3)		(225.8)
Proceeds from issuance of common stock, net	26.6	151.2	[1]	0
Proceeds from issuance of long-term debt	800	250.7		812.9
Payments to retire long-term debt	(313.4)	(183)		(358.5)
Net change in commercial paper	84.3	18.5		(138.1)
Other	(1.7)	6.8		(17.3)
Net cash flows from (used for) financing activities	329.3	(3.1)		73.2
Net increase (decrease) in cash and cash equivalents	2.4	(51.1)		47.1
Cash and cash equivalents at beginning of period	5.8	56.9		9.8
Cash and cash equivalents at end of period	8.2	5.8		56.9
Supplemental cash flows information:
Interest, net of capitalized interest	(192.4)	(184.8)		(180.8)
Income taxes, net	(9.8)	0		5.3
Parent Company [Member]
Net cash flows from operating activities	254	262		246
Cash flows from (used for) investing activities:
Capital contributions to consolidated subsidiaries	(250)	(165)		(90)
Captial repayments from consolidated subsidiaries	130	0		50
Net change in notes receivable from and payable to affiliates	294	2		(23)
Other	10	0		0
Net cash flows from (used for) investing activities	184	(163)		(63)
Cash flows used for financing activities:
Common stock dividends	(267)	(247)		(226)
Proceeds from issuance of common stock, net	27	151		0
Proceeds from issuance of long-term debt	0	0		250
Payments to retire long-term debt	(250)	0		(250)
Net change in commercial paper	52	(1)		45
Other	0	(2)		(2)
Net cash flows from (used for) financing activities	(438)	(99)		(183)
Net increase (decrease) in cash and cash equivalents	0	0		0
Cash and cash equivalents at beginning of period	0	0		0
Cash and cash equivalents at end of period	0	0		0
Supplemental cash flows information:
Interest, net of capitalized interest	(3)	(3)		(11)
Income taxes, net	$ (37)	$ (9)		$ (5)
[1]	Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

Valuation And Qualifying Acc142

Valuation And Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Provision for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	$ 4.8	$ 5.1	$ 4.8
Charged to Expense	[1]	17.4	8.1	11.7
Charged to Other Accounts	[1],[2]	8.8	3	4.1
Deductions	[1],[3]	22.3	11.4	15.5
Ending Balance	[1]	8.7	4.8	5.1
Accumulated Provision for Uncollectible Accounts [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	0.6	0.4	0.7
Charged to Expense	[1]	17.2	8.1	11.5
Charged to Other Accounts	[1],[2]	0	0	0
Deductions	[1],[3]	16.7	7.9	11.8
Ending Balance	[1]	1.1	0.6	0.4
Accumulated Provision for Uncollectible Accounts [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		3.7	4.2	1.7
Charged to Expense		0.1	0	0
Charged to Other Accounts	[2]	8.8	3	4.1
Deductions	[3]	5.5	3.5	1.6
Ending Balance		7.1	3.7	4.2
Accumulated Provision for Other Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	27.1	32.6	38.2
Charged to Expense	[4]	6.1	6.5	12.5
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	8.1	12	18.1
Ending Balance	[4]	25.1	27.1	32.6
Accumulated Provision for Other Reserves [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	9.4	10.6	18.1
Charged to Expense	[4]	1	2.1	3.9
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	1.7	3.3	11.4
Ending Balance	[4]	8.7	9.4	10.6
Accumulated Provision for Other Reserves [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	11.4	16.3	16.2
Charged to Expense	[4]	1.8	0.7	2.5
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	5.1	5.6	2.4
Ending Balance	[4]	$ 8.1	$ 11.4	$ 16.3
[1]	Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.
[2]	Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off.
[3]	Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.
[4]	Other reserves are largely related to injury and damage claims arising in the ordinary course of business.