Interstate Power & Light (IPLDP) 10-K 24 Feb 16 2015 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2015	Jan. 29, 2016	Jun. 30, 2015
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
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		113,465,499
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 6.5
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, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues:
Electric utility	$ 2,770.5	$ 2,713.6	$ 2,689
Gas utility	381.2	517.5	464.8
Other utility	57.9	66.1	71.3
Non-regulated	44	53.1	51.7
Total operating revenues	3,253.6	3,350.3	3,276.8
Operating expenses:
Electric production fuel and purchased power	837.7	877.2	941.8
Electric transmission service	485.3	447.5	418.3
Cost of gas sold	219.1	327.8	276.7
Other operation and maintenance	629.5	665	635.6
Depreciation and amortization	401.3	388.1	370.9
Taxes other than income taxes	103.7	101.1	99.6
Total operating expenses	2,676.6	2,806.7	2,742.9
Operating income (loss)	577	543.6	533.9
Interest expense and other:
Interest expense	187.1	180.6	172.8
Equity (income) loss from unconsolidated investments, net	(33.8)	(40.4)	(43.7)
Allowance for funds used during construction	(36.9)	(34.8)	(30.8)
Interest income and other	(0.7)	(1.8)	(0.4)
Total interest expense and other	115.7	103.6	97.9
Income from continuing operations before income taxes	461.3	440	436
Income tax expense (benefit)	70.4	44.3	53.9
Income from continuing operations, net of tax	390.9	395.7	382.1
Loss from discontinued operations, net of tax	(2.5)	(2.4)	(5.9)
Net income	388.4	393.3	376.2
Preferred dividend requirements of subsidiaries	10.2	10.2	17.9
Net income (loss) attributable to common shareowners	$ 378.2	$ 383.1	$ 358.3
Weighted average number of common shares outstanding (basic and diluted) (in shares)	112.7	110.8	110.8
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)	$ 3.38	$ 3.48	$ 3.29
Loss from discontinued operations, net of tax (in dollars per share)	(0.02)	(0.02)	(0.06)
Net income (in dollars per share)	$ 3.36	$ 3.46	$ 3.23
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 380.7	$ 385.5	$ 364.2
Loss from discontinued operations, net of tax	(2.5)	(2.4)	(5.9)
Net income (loss)	378.2	383.1	358.3
IPL [Member]
Operating revenues:
Electric utility	1,503.8	1,493.3	1,491.8
Gas utility	217.3	296.5	273.9
Other utility	53.4	58.3	53.1
Total operating revenues	1,774.5	1,848.1	1,818.8
Operating expenses:
Electric production fuel and purchased power	428.4	497.3	537.3
Electric transmission service	328.2	323.4	301.4
Cost of gas sold	123.3	185.5	160.3
Other operation and maintenance	389.9	381.1	362.3
Depreciation and amortization	207.2	197.5	191.1
Taxes other than income taxes	55.6	54.1	54.4
Total operating expenses	1,532.6	1,638.9	1,606.8
Operating income (loss)	241.9	209.2	212
Interest expense and other:
Interest expense	96.8	89.9	81.3
Allowance for funds used during construction	(28.2)	(25.9)	(21)
Interest income and other	(0.2)	2.3	(0.3)
Total interest expense and other	68.4	66.3	60
Income from continuing operations before income taxes	173.5	142.9	152
Income tax expense (benefit)	(22.7)	(48.9)	(36.3)
Net income	196.2	191.8	188.3
Preferred dividend requirements of subsidiaries	10.2	10.2	16.3
Net income (loss) attributable to common shareowners	186	181.6	172
Amounts attributable to common shareowners:
Net income (loss)	186	181.6	172
WPL [Member]
Operating revenues:
Electric utility	1,266.7	1,220.3	1,197.2
Gas utility	163.9	221	190.9
Other utility	4.5	7.8	18.2
Total operating revenues	1,435.1	1,449.1	1,406.3
Operating expenses:
Electric production fuel and purchased power	409.3	379.9	404.5
Electric transmission service	157.1	124.1	116.9
Cost of gas sold	95.8	142.3	116.4
Other operation and maintenance	235.4	277.2	258.4
Depreciation and amortization	184.3	181.2	172.2
Taxes other than income taxes	44.5	43.4	41.8
Total operating expenses	1,126.4	1,148.1	1,110.2
Operating income (loss)	308.7	301	296.1
Interest expense and other:
Interest expense	92.4	86.4	85
Equity (income) loss from unconsolidated investments, net	(35.1)	(42.8)	(43.7)
Allowance for funds used during construction	(8.7)	(8.9)	(9.8)
Interest income and other	(0.4)	(0.1)	(0.1)
Total interest expense and other	48.2	34.6	31.4
Income from continuing operations before income taxes	260.5	266.4	264.7
Income tax expense (benefit)	82.9	85.3	85.6
Net income	177.6	181.1	179.1
Net income attributable to noncontrolling interest	1.3	0.7	0
Preferred dividend requirements of subsidiaries	0	0	1.6
Net income (loss) attributable to common shareowners	176.3	180.4	177.5
Amounts attributable to common shareowners:
Net income (loss)	$ 176.3	$ 180.4	$ 177.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 5.8	$ 56.9
Accounts receivable, less allowance for doubtful accounts	397.6	427.3
Production fuel, at weighted average cost	98.8	83.8
Gas stored underground, at weighted average cost	43.3	67.1
Materials and supplies, at weighted average cost	81.4	72.9
Regulatory assets	120.2	68.1
Deferred tax assets	0	150.1
Other	79.7	116.9
Total current assets	826.8	1,043.1
Property, plant and equipment, net	9,519.1	8,938.4
Investments:
Investment in American Transmission Company LLC	293.3	286.5
Other	53	58.4
Total investments	346.3	344.9
Other assets:
Regulatory assets	1,788.4	1,715.6
Deferred charges and other	14.6	21.5
Total other assets	1,803	1,737.1
Total assets	12,495.2	12,063.5
Current liabilities:
Current maturities of long-term debt	313.4	183
Commercial paper	159.8	141.3
Accounts payable	402.4	427.9
Regulatory liabilities	187.1	200.1
Other	296.6	262.4
Total current liabilities	1,359.3	1,214.7
Long-term debt, net (excluding current portion)	3,522.2	3,584.3
Other liabilities:
Deferred tax liabilities	2,381.2	2,321.1
Regulatory liabilities	550.6	621.1
Pension and other benefit obligations	451.8	421.7
Other	306	260.1
Total other liabilities	$ 3,689.6	$ 3,624
Commitments and contingencies (Note 16)
Common equity:
Common stock	$ 1.1	$ 1.1
Additional paid-in capital	1,663	1,509.1
Retained earnings	2,068.9	1,938
Accumulated other comprehensive loss	(0.4)	(0.6)
Shares in deferred compensation trust - 215,093 and 238,935 shares at a weighted average cost of $39.69 and $37.45 per share	(8.5)	(8.9)
Total common equity	3,724.1	3,438.7
Cumulative preferred stock of Interstate Power and Light Company	200	200
Noncontrolling interest	0	1.8
Total equity	3,924.1	3,640.5
Total liabilities and equity	12,495.2	12,063.5
IPL [Member]
Current assets:
Cash and cash equivalents	4.5	5.3
Accounts receivable, less allowance for doubtful accounts	200	216.7
Production fuel, at weighted average cost	60.2	52.7
Gas stored underground, at weighted average cost	18.2	30.8
Materials and supplies, at weighted average cost	45.7	42
Regulatory assets	39.6	38.7
Deferred tax assets	0	104
Other	28.2	65
Total current assets	396.4	555.2
Property, plant and equipment, net	4,925.1	4,554.7
Investments:
Total investments	19.6	19.1
Other assets:
Regulatory assets	1,363	1,319.2
Deferred charges and other	5	2
Total other assets	1,368	1,321.2
Total assets	6,709.1	6,450.2
Current liabilities:
Current maturities of long-term debt	0	150
Commercial paper	0	0
Accounts payable	197.2	259.6
Accounts payable to associated companies	37.7	31.3
Regulatory liabilities	130.9	129.7
Accrued taxes	67.6	45.3
Accrued interest	28.2	25.4
Other	69.5	64.6
Total current liabilities	531.1	705.9
Long-term debt, net (excluding current portion)	1,856.9	1,608
Other liabilities:
Deferred tax liabilities	1,378	1,370.3
Regulatory liabilities	358.3	453.8
Pension and other benefit obligations	160.2	142.4
Other	229.3	185.5
Total other liabilities	$ 2,125.8	$ 2,152
Commitments and contingencies (Note 16)
Common equity:
Common stock	$ 33.4	$ 33.4
Additional paid-in capital	1,407.8	1,242.8
Retained earnings	554.1	508.1
Total common equity	1,995.3	1,784.3
Cumulative preferred stock of Interstate Power and Light Company	200	200
Total equity	2,195.3	1,984.3
Total liabilities and equity	6,709.1	6,450.2
WPL [Member]
Current assets:
Cash and cash equivalents	0.4	46.7
Accounts receivable, less allowance for doubtful accounts	185.4	185.8
Production fuel, at weighted average cost	38.6	31.1
Gas stored underground, at weighted average cost	25.1	36.3
Materials and supplies, at weighted average cost	33.5	29.2
Regulatory assets	80.6	29.4
Prepaid gross receipts tax	39.2	38
Deferred tax assets	0	37.7
Other	20.7	23.2
Total current assets	423.5	457.4
Property, plant and equipment, net	4,103.7	3,938.9
Investments:
Investment in American Transmission Company LLC	293.3	286.5
Other	15.4	19.5
Total investments	308.7	306
Other assets:
Regulatory assets	425.4	396.4
Deferred charges and other	9.1	18.9
Total other assets	434.5	415.3
Total assets	5,270.4	5,117.6
Current liabilities:
Current maturities of long-term debt	0	30.6
Commercial paper	19.9	0
Accounts payable	136	112.9
Accounts payable to associated companies	21.6	25.5
Regulatory liabilities	56.2	70.4
Accrued interest	23.7	24.3
Other	79.5	46.6
Total current liabilities	336.9	310.3
Long-term debt, net (excluding current portion)	1,533.9	1,532.5
Other liabilities:
Deferred tax liabilities	1,005.4	967.1
Regulatory liabilities	192.3	167.3
Capital lease obligations - Sheboygan Falls Energy Facility	83.6	89.4
Pension and other benefit obligations	188.7	180.4
Other	162	155.2
Total other liabilities	$ 1,632	$ 1,559.4
Commitments and contingencies (Note 16)
Common equity:
Common stock	$ 66.2	$ 66.2
Additional paid-in capital	959	959
Retained earnings	731.1	681.7
Total common equity	1,756.3	1,706.9
Noncontrolling interest	11.3	8.5
Total equity	1,767.6	1,715.4
Total liabilities and equity	$ 5,270.4	$ 5,117.6

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	240,000,000	240,000,000
Common stock, shares outstanding (in shares)	113,459,216	110,935,680
Shares in deferred compensation trust (in shares)	215,093	238,935
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 39.69	$ 37.45
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

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 388.4	$ 393.3	$ 376.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	401.3	388.1	370.9
Other amortizations	12.4	54.2	40.2
Deferred tax expense (benefit) and investment tax credits	114.2	55.2	108.3
Equity (income) loss from unconsolidated investments, net	(33.8)	(40.4)	(43.7)
Distributions from equity method investments	30.6	36.4	35.4
Equity component of allowance for funds used during construction	(24.4)	(23.1)	(20.3)
Other	15.7	2	(3.7)
Other changes in assets and liabilities:
Accounts receivable	36.8	48.7	(49.2)
Sales of accounts receivable	(17)	(7)	(101)
Regulatory assets	(104.5)	(439.8)	140.5
Regulatory liabilities	(67.8)	10.8	(90.8)
Deferred taxes	94.6	138.4	101.9
Pension and other benefit obligations	30.1	215.1	(157.4)
Other	(5.4)	59.7	23.7
Net cash flows from operating activities	871.2	891.6	731
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(963.6)	(838.9)	(731.6)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(70.7)	(63.9)	(66.7)
Proceeds from Minnesota electric and natural gas distribution asset sales	139.9	0	0
Proceeds from Franklin County wind farm cash grant	0	0	62.4
Other	(24.8)	(14.9)	(18.8)
Net cash flows used for investing activities	(919.2)	(917.7)	(754.7)
Cash flows from (used for) financing activities:
Common stock dividends	(247.3)	(225.8)	(208.3)
Proceeds from issuance of common stock, net	151.2	0	0
Payments to redeem cumulative preferred stock of subsidiaries	0	0	(211)
Proceeds from issuance of cumulative preferred stock of IPL	0	0	200
Proceeds from issuance of long-term debt	250.7	812.9	250
Payments to retire long-term debt	(183)	(358.5)	(1.5)
Net change in commercial paper	18.5	(138.1)	11.9
Other	6.8	(17.3)	(28.8)
Net cash flows from (used for) financing activities	(3.1)	73.2	12.3
Net increase (decrease) in cash and cash equivalents	(51.1)	47.1	(11.4)
Cash and cash equivalents at beginning of period	56.9	9.8	21.2
Cash and cash equivalents at end of period	5.8	56.9	9.8
Supplemental cash flows information:
Interest, net of capitalized interest	(184.8)	(180.8)	(171.7)
Income taxes, net	0	5.3	9.6
Significant non-cash investing and financing activities:
Accrued capital expenditures	148.3	160.3	103.8
IPL [Member]
Cash flows from operating activities:
Net income	196.2	191.8	188.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	207.2	197.5	191.1
Deferred tax expense (benefit) and investment tax credits	28.9	(11.5)	3
Equity component of allowance for funds used during construction	(18.6)	(17.1)	(13.8)
Other	19.5	11.3	(0.7)
Other changes in assets and liabilities:
Accounts receivable	20.4	43.3	(55.9)
Sales of accounts receivable	(17)	(7)	(101)
Regulatory assets	(76.3)	(272.9)	71.4
Accounts payable	(42.7)	18.8	25.6
Regulatory liabilities	(75.5)	(18.9)	(82.3)
Deferred taxes	82.1	140.4	92.4
Pension and other benefit obligations	17.8	93.8	(74.3)
Other	43	36.6	(11.2)
Net cash flows from operating activities	385	406.1	232.6
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(619.3)	(526)	(400.2)
Proceeds from Minnesota electric and natural gas distribution asset sales	139.9	0	0
Other	(32.5)	(26.7)	(23.1)
Net cash flows used for investing activities	(511.9)	(552.7)	(423.3)
Cash flows from (used for) financing activities:
Common stock dividends	(140)	(140)	(128.1)
Capital contributions from parent	165	90	120
Payments to redeem cumulative preferred stock of subsidiaries	0	0	(150)
Proceeds from issuance of cumulative preferred stock of IPL	0	0	200
Proceeds from issuance of long-term debt	250	250	250
Payments to retire long-term debt	(150)	(38.4)	0
Net change in commercial paper	0	0	(76.3)
Other	1.1	(14.1)	(25)
Net cash flows from (used for) financing activities	126.1	147.5	190.6
Net increase (decrease) in cash and cash equivalents	(0.8)	0.9	(0.1)
Cash and cash equivalents at beginning of period	5.3	4.4	4.5
Cash and cash equivalents at end of period	4.5	5.3	4.4
Supplemental cash flows information:
Interest, net of capitalized interest	(93.9)	(89.8)	(80.7)
Income taxes, net	19.3	20.1	0.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	77	113.2	58.1
WPL [Member]
Cash flows from operating activities:
Net income	177.6	181.1	179.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	184.3	181.2	172.2
Other amortizations	5.3	47.3	29.5
Deferred tax expense (benefit) and investment tax credits	77.6	82.6	89.8
Equity (income) loss from unconsolidated investments, net	(35.1)	(42.8)	(43.7)
Distributions from equity method investments	30.6	36.4	35.4
Other	(5.7)	(7.2)	(6.7)
Other changes in assets and liabilities:
Regulatory assets	(28.2)	(166.9)	69.1
Regulatory liabilities	7.7	29.7	(8.5)
Pension and other benefit obligations	8.3	92	(71.3)
Other	27.4	(9)	(21.6)
Net cash flows from operating activities	449.8	424.4	423.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(344.3)	(312.9)	(331.4)
Other	(13.9)	(7.2)	(4.5)
Net cash flows used for investing activities	(358.2)	(320.1)	(335.9)
Cash flows from (used for) financing activities:
Common stock dividends	(126.9)	(118.7)	(116.3)
Payments to redeem cumulative preferred stock of subsidiaries	0	0	(61)
Proceeds from issuance of long-term debt	0	250	0
Net change in commercial paper	19.9	(183.7)	97.1
Other	(30.9)	(5.7)	(7.4)
Net cash flows from (used for) financing activities	(137.9)	(58.1)	(87.6)
Net increase (decrease) in cash and cash equivalents	(46.3)	46.2	(0.2)
Cash and cash equivalents at beginning of period	46.7	0.5	0.7
Cash and cash equivalents at end of period	0.4	46.7	0.5
Supplemental cash flows information:
Interest, net of capitalized interest	(93.1)	(84.6)	(85)
Income taxes, net	(7.4)	(12.2)	(22.9)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 55.2	$ 38.4	$ 37.7

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, 2012	$ 3,134.9	$ 1,486.4		$ 1.1	$ 33.4	$ 66.2	$ 1,511.2	$ 1,037.8	$ 959.2	$ 1,630.7	$ 415.2	$ 565.9	$ (0.8)	$ (7.3)	$ 0
Beginning balance at Dec. 31, 2012			$ 1,591.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	358.3	172	177.5							358.3	172	177.5
Net income	376.2	188.3	179.1
Common stock dividends	(208.3)	(128.1)	(116.3)							(208.3)	(128.1)	(116.3)
Common stock issued, net	0
Capital contributions from parent		120						120
Preferred stock issuance costs	(5.4)	(5.4)					(5.4)	(5.4)
Other	1.3	3.2	(5.1)				2	0.4	(0.2)		2.8	(4.9)		(0.7)
Other comprehensive income (loss), net of tax	0.6	0	0										0.6
Ending balance at Dec. 31, 2013	3,281.4	1,648.1		1.1	33.4	66.2	1,507.8	1,152.8	959	1,780.7	461.9	622.2	(0.2)	(8)	0
Ending 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)	(140)	(118.7)							(225.8)	(140)	(118.7)
Common stock issued, net	0
Capital contributions from parent		90						90
Contributions from noncontrolling interest			8.6												8.6
Distributions to noncontrolling interest			(0.8)												(0.8)
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	1,784.3	1,706.9	1.1	33.4	66.2	1,509.1	1,242.8	959	1,938	508.1	681.7	(0.6)	(8.9)	8.5
Ending balance at Dec. 31, 2014	3,640.5	1,984.3	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)	(140)	(126.9)							(247.3)	(140)	(126.9)
Common stock issued, net	151.2						151.2
Capital contributions from parent		165						165
Contributions from noncontrolling interest			3.4												3.4
Distributions to noncontrolling interest			(1.9)												(1.9)
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	1,995.3	1,756.3	$ 1.1	$ 33.4	$ 66.2	$ 1,663	$ 1,407.8	$ 959	$ 2,068.9	$ 554.1	$ 731.1	$ (0.4)	$ (8.5)	$ 11.3
Ending balance at Dec. 31, 2015	$ 3,924.1	$ 2,195.3	$ 1,767.6

Consolidated Statements of Com7

Consolidated Statements of Common Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in dollars per share)	$ 2.20	$ 2.04	$ 1.88

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
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, Resources 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 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. Refer to Note 3 for discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets, which were sold in 2015. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which holds Alliant Energy’s investment in ATC. WPL is a direct subsidiary of Alliant Energy and is 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. Refer to Note 6(a) for further discussion of ATC. Resources 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 owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. Refer to Note 6(a) for discussion of ATI, a wholly-owned subsidiary of Resources, which holds a partial interest in WPL Transco. 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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes. Refer to Note 1(q) for details. 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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively. Refer to Note 1(q) for discussion of the changes to IPL’s and WPL’s financial statements. (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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1% 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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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. 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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes. Revenue Recognition - Refer to Note 1(p) for discussion of a new accounting standard issued by FASB in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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) Emission Allowances - Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements
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, Resources 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 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. Refer to Note 3 for discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets, which were sold in 2015. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which holds Alliant Energy’s investment in ATC. WPL is a direct subsidiary of Alliant Energy and is 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. Refer to Note 6(a) for further discussion of ATC. Resources 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 owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. Refer to Note 6(a) for discussion of ATI, a wholly-owned subsidiary of Resources, which holds a partial interest in WPL Transco. 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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes. Refer to Note 1(q) for details. 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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively. Refer to Note 1(q) for discussion of the changes to IPL’s and WPL’s financial statements. (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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1% 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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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. 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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes. Revenue Recognition - Refer to Note 1(p) for discussion of a new accounting standard issued by FASB in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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) Emission Allowances - Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements
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, Resources 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 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. Refer to Note 3 for discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets, which were sold in 2015. WPL’s financial statements include the accounts of WPL and its consolidated subsidiary, WPL Transco, which holds Alliant Energy’s investment in ATC. WPL is a direct subsidiary of Alliant Energy and is 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. Refer to Note 6(a) for further discussion of ATC. Resources 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 owns the non-regulated 99 MW Franklin County wind farm located in Franklin County, Iowa. Refer to Note 6(a) for discussion of ATI, a wholly-owned subsidiary of Resources, which holds a partial interest in WPL Transco. 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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes. Refer to Note 1(q) for details. 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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively. Refer to Note 1(q) for discussion of the changes to IPL’s and WPL’s financial statements. (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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1% 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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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. 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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes. Revenue Recognition - Refer to Note 1(p) for discussion of a new accounting standard issued by FASB in 2014, which provides principles for recognizing revenue. (g) Utility Cost Recovery Mechanisms - Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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) Emission Allowances - Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets are expected to be recovered from customers in future rates; however, the respective carrying costs of these assets are not expected to be recovered from customers in future rates. At December 31, 2015 , IPL and WPL had $30 million and $12 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 debt redemption and clean air compliance projects costs, and emission allowances. 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 include the impacts of qualifying deductions for repairs expenditures and 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 2015 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures, partially offset by a reduction in certain tax-related regulatory assets due to the sales of IPL’s Minnesota electric and natural gas distribution assets in 2015. 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 costs 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 the various regulatory jurisdictions in which IPL and WPL operate. 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 authorized WPL in its Wisconsin retail rate cases for the 2013/2014 and 2015/2016 Test Periods to recover from its electric and gas retail customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during the respective test year periods. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year. In accordance with FERC-approved formula rates, any over- or under-collection of these pension costs each year are refunded to or recovered from customers through subsequent changes to wholesale customer 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. 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. 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 FERC and the PSCW 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 orders previously received by the PSCW and FERC. Continued recovery of the retail portion of the remaining net book value of these EGUs is expected to be addressed in WPL’s next retail electric base rate case. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. 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. The value of these allowances was nominal, which was significantly below the contract price for these allowances. As a result, Alliant Energy and IPL recognized an obligation and offsetting regulatory assets for the amount of the forward contracts that are probable of recovery from IPL’s customers. The current value of these allowances continues to be nominal and significantly below the contract price for these allowances. Environmental-related costs - The IUB has permitted IPL to recover prudently incurred costs by allowing a representative level of MGP costs in the recoverable cost of service component of rates, as determined in its most recent retail gas rate case. Under the current rate-making treatment approved by the PSCW, the MGP expenditures of WPL are deferred and collected from retail gas customers over a five -year period after new rates are implemented. Regulatory assets recorded by IPL and WPL reflect the probable future rate recovery of MGP expenditures. Refer to Note 16(e) for additional details of environmental-related MGP costs. Debt redemption costs - For debt retired early with no subsequent re-issuance, IPL and WPL defer any debt repayment premiums and unamortized debt issuance costs and discounts as regulatory assets. These regulatory assets are amortized over the remaining original life of the debt retired early. Debt repayment premiums and other losses resulting from the refinancing of debt by IPL and WPL are deferred as regulatory assets and amortized over the life of the new debt issued. 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, 2015 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 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7 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 - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. In 2015 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions): Electric tax benefit rider credits $72 Gas tax benefit rider credits 12 $84 Electric tax benefit rider - The IUB has approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in 2011 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 IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues $72 $85 $79 Income tax benefit resulting from decreased taxable income caused by credits 30 35 33 Income tax benefit representing tax benefits realized from electric tax benefit rider 42 50 46 In December 2015, the IUB issued an order authorizing $65 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric customers’ bills in Iowa in 2016 through the electric tax benefit rider. The IUB has authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills 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): 2015 2014 2013 Revenue requirement adjustment $14 $15 $24 In December 2015, the IUB authorized IPL to reduce the $65 million of billing credits on customers’ bills by $15 million in 2016 to recognize the revenue requirement impact of the changes in tax accounting methods. Gas tax benefit rider - The IUB has approved a gas tax benefit rider proposed by IPL, which utilizes approximately $12 million of regulatory liabilities annually to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. Any remaining benefit, including any portion not utilized of the agreed upon amount from January 2013 through December 2015, is expected to be credited to Iowa’s retail gas customers’ bills in 2016. Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues $12 $12 $11 Income tax benefit resulting from decreased taxable income caused by credits 5 5 4 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Refer to Note 11 for additional details regarding IPL’s tax benefit riders. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures incurred by WPL and IPL 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 July 2014 PSCW order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized lower energy efficiency cost recovery amortizations for 2015, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Electric transmission cost recovery - Electric revenues established in WPL’s retail electric rate case (2015/2016 Test Period) included recovery of expected increases in electric transmission service expense largely due to SSR costs expected to be incurred. Due to a revision in MISO’s method to allocate SSR costs, WPL no longer expects to incur certain SSR costs. The difference between actual electric transmission service expense incurred and amounts collected from customers as electric revenues in 2015 are recorded as electric transmission service expense with an offsetting amount recorded to regulatory liabilities due to the escrow treatment authorized for WPL in its 2015/2016 Test Period retail electric rate case. 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. Utility Rate Cases - 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 current levels through the end of 2016. The retail electric base rate case included a return of and a return on costs for environmental controls projects at Columbia Units 1 and 2 and Edgewater Unit 5, generation performance and reliability improvements at Columbia Units 1 and 2, 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 cost 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 require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels during 2015 or 2016 and allows WPL to request a change in retail base rates during this period if its annual regulatory return on common equity falls below a certain level. As of December 31, 2015 , Alliant Energy and WPL did not record any deferred amounts for these provisions. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual retail gas base rates of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain retail electric base rates at their then current levels through the end of 2014. The order included a provision 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, 2015 , Alliant Energy and WPL deferred $8 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. WPL currently expects the deferred amount will be refunded to its customers in a future rate case or other proceeding. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions): Actual Estimated 2014 2015 2016 Billing credits to reduce retail electric customers’ bills $72 $24 $9 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - In December 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $7 million , or approximately 1% , effective January 1, 2016. The increase reflects anticipated increases in retail electric fuel-related costs in 2016, including impacts of increased sales volumes approved in the retail base rate case for 2016. WPL’s 2016 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Deferral of under-collections are reduced to the extent WPL’s actual return on common equity exceeds the most recently authorized return on common equity. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - In December 2014, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $39 million , or approximately 4% , effective January 1, 2015. The increase included $39 million of anticipated increases in retail electric fuel-related costs in 2015 attributable to $25 million for higher retail electric fuel-related costs per MWh anticipated in 2015 and $14 million from the impact of increased sales volumes approved in the retail electric base rate case for 2015. WPL’s 2015 fuel-related costs were subject to deferral if they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of December 31, 2015 , fuel-related costs outside of the approved range were $10 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). As of December 31, 2015 and 2014 , the $28 million of deferred fuel-related costs were included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. In July 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $28 million , or approximately 2% , effective January 1, 2016 to recover the 2014 Test Year deferred fuel-related costs.
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets are expected to be recovered from customers in future rates; however, the respective carrying costs of these assets are not expected to be recovered from customers in future rates. At December 31, 2015 , IPL and WPL had $30 million and $12 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 debt redemption and clean air compliance projects costs, and emission allowances. 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 include the impacts of qualifying deductions for repairs expenditures and 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 2015 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures, partially offset by a reduction in certain tax-related regulatory assets due to the sales of IPL’s Minnesota electric and natural gas distribution assets in 2015. 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 costs 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 the various regulatory jurisdictions in which IPL and WPL operate. 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 authorized WPL in its Wisconsin retail rate cases for the 2013/2014 and 2015/2016 Test Periods to recover from its electric and gas retail customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during the respective test year periods. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year. In accordance with FERC-approved formula rates, any over- or under-collection of these pension costs each year are refunded to or recovered from customers through subsequent changes to wholesale customer 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. 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. 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 FERC and the PSCW 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 orders previously received by the PSCW and FERC. Continued recovery of the retail portion of the remaining net book value of these EGUs is expected to be addressed in WPL’s next retail electric base rate case. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. 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. The value of these allowances was nominal, which was significantly below the contract price for these allowances. As a result, Alliant Energy and IPL recognized an obligation and offsetting regulatory assets for the amount of the forward contracts that are probable of recovery from IPL’s customers. The current value of these allowances continues to be nominal and significantly below the contract price for these allowances. Environmental-related costs - The IUB has permitted IPL to recover prudently incurred costs by allowing a representative level of MGP costs in the recoverable cost of service component of rates, as determined in its most recent retail gas rate case. Under the current rate-making treatment approved by the PSCW, the MGP expenditures of WPL are deferred and collected from retail gas customers over a five -year period after new rates are implemented. Regulatory assets recorded by IPL and WPL reflect the probable future rate recovery of MGP expenditures. Refer to Note 16(e) for additional details of environmental-related MGP costs. Debt redemption costs - For debt retired early with no subsequent re-issuance, IPL and WPL defer any debt repayment premiums and unamortized debt issuance costs and discounts as regulatory assets. These regulatory assets are amortized over the remaining original life of the debt retired early. Debt repayment premiums and other losses resulting from the refinancing of debt by IPL and WPL are deferred as regulatory assets and amortized over the life of the new debt issued. 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, 2015 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 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7 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 - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. In 2015 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions): Electric tax benefit rider credits $72 Gas tax benefit rider credits 12 $84 Electric tax benefit rider - The IUB has approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in 2011 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 IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues $72 $85 $79 Income tax benefit resulting from decreased taxable income caused by credits 30 35 33 Income tax benefit representing tax benefits realized from electric tax benefit rider 42 50 46 In December 2015, the IUB issued an order authorizing $65 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric customers’ bills in Iowa in 2016 through the electric tax benefit rider. The IUB has authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills 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): 2015 2014 2013 Revenue requirement adjustment $14 $15 $24 In December 2015, the IUB authorized IPL to reduce the $65 million of billing credits on customers’ bills by $15 million in 2016 to recognize the revenue requirement impact of the changes in tax accounting methods. Gas tax benefit rider - The IUB has approved a gas tax benefit rider proposed by IPL, which utilizes approximately $12 million of regulatory liabilities annually to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. Any remaining benefit, including any portion not utilized of the agreed upon amount from January 2013 through December 2015, is expected to be credited to Iowa’s retail gas customers’ bills in 2016. Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues $12 $12 $11 Income tax benefit resulting from decreased taxable income caused by credits 5 5 4 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Refer to Note 11 for additional details regarding IPL’s tax benefit riders. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures incurred by WPL and IPL 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 July 2014 PSCW order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized lower energy efficiency cost recovery amortizations for 2015, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Electric transmission cost recovery - Electric revenues established in WPL’s retail electric rate case (2015/2016 Test Period) included recovery of expected increases in electric transmission service expense largely due to SSR costs expected to be incurred. Due to a revision in MISO’s method to allocate SSR costs, WPL no longer expects to incur certain SSR costs. The difference between actual electric transmission service expense incurred and amounts collected from customers as electric revenues in 2015 are recorded as electric transmission service expense with an offsetting amount recorded to regulatory liabilities due to the escrow treatment authorized for WPL in its 2015/2016 Test Period retail electric rate case. 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. Utility Rate Cases - 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 current levels through the end of 2016. The retail electric base rate case included a return of and a return on costs for environmental controls projects at Columbia Units 1 and 2 and Edgewater Unit 5, generation performance and reliability improvements at Columbia Units 1 and 2, 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 cost 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 require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels during 2015 or 2016 and allows WPL to request a change in retail base rates during this period if its annual regulatory return on common equity falls below a certain level. As of December 31, 2015 , Alliant Energy and WPL did not record any deferred amounts for these provisions. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual retail gas base rates of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain retail electric base rates at their then current levels through the end of 2014. The order included a provision 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, 2015 , Alliant Energy and WPL deferred $8 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. WPL currently expects the deferred amount will be refunded to its customers in a future rate case or other proceeding. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions): Actual Estimated 2014 2015 2016 Billing credits to reduce retail electric customers’ bills $72 $24 $9 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - In December 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $7 million , or approximately 1% , effective January 1, 2016. The increase reflects anticipated increases in retail electric fuel-related costs in 2016, including impacts of increased sales volumes approved in the retail base rate case for 2016. WPL’s 2016 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Deferral of under-collections are reduced to the extent WPL’s actual return on common equity exceeds the most recently authorized return on common equity. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - In December 2014, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $39 million , or approximately 4% , effective January 1, 2015. The increase included $39 million of anticipated increases in retail electric fuel-related costs in 2015 attributable to $25 million for higher retail electric fuel-related costs per MWh anticipated in 2015 and $14 million from the impact of increased sales volumes approved in the retail electric base rate case for 2015. WPL’s 2015 fuel-related costs were subject to deferral if they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of December 31, 2015 , fuel-related costs outside of the approved range were $10 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). As of December 31, 2015 and 2014 , the $28 million of deferred fuel-related costs were included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. In July 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $28 million , or approximately 2% , effective January 1, 2016 to recover the 2014 Test Year deferred fuel-related costs.
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8 A portion of the regulatory assets in the above table are not earning a return. These regulatory assets are expected to be recovered from customers in future rates; however, the respective carrying costs of these assets are not expected to be recovered from customers in future rates. At December 31, 2015 , IPL and WPL had $30 million and $12 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 debt redemption and clean air compliance projects costs, and emission allowances. 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 include the impacts of qualifying deductions for repairs expenditures and 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 2015 , Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures, partially offset by a reduction in certain tax-related regulatory assets due to the sales of IPL’s Minnesota electric and natural gas distribution assets in 2015. 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 costs 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 the various regulatory jurisdictions in which IPL and WPL operate. 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 authorized WPL in its Wisconsin retail rate cases for the 2013/2014 and 2015/2016 Test Periods to recover from its electric and gas retail customers an estimated allocated portion of annual costs equal to the costs expected to be incurred during the respective test year periods. IPL and WPL are authorized to recover from their wholesale customers an allocated portion of actual pension costs incurred each year. In accordance with FERC-approved formula rates, any over- or under-collection of these pension costs each year are refunded to or recovered from customers through subsequent changes to wholesale customer 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. 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. 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 FERC and the PSCW 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 orders previously received by the PSCW and FERC. Continued recovery of the retail portion of the remaining net book value of these EGUs is expected to be addressed in WPL’s next retail electric base rate case. Commodity cost recovery - Refer to Note 1(g) for additional details of IPL’s and WPL’s cost recovery mechanisms. 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. The value of these allowances was nominal, which was significantly below the contract price for these allowances. As a result, Alliant Energy and IPL recognized an obligation and offsetting regulatory assets for the amount of the forward contracts that are probable of recovery from IPL’s customers. The current value of these allowances continues to be nominal and significantly below the contract price for these allowances. Environmental-related costs - The IUB has permitted IPL to recover prudently incurred costs by allowing a representative level of MGP costs in the recoverable cost of service component of rates, as determined in its most recent retail gas rate case. Under the current rate-making treatment approved by the PSCW, the MGP expenditures of WPL are deferred and collected from retail gas customers over a five -year period after new rates are implemented. Regulatory assets recorded by IPL and WPL reflect the probable future rate recovery of MGP expenditures. Refer to Note 16(e) for additional details of environmental-related MGP costs. Debt redemption costs - For debt retired early with no subsequent re-issuance, IPL and WPL defer any debt repayment premiums and unamortized debt issuance costs and discounts as regulatory assets. These regulatory assets are amortized over the remaining original life of the debt retired early. Debt repayment premiums and other losses resulting from the refinancing of debt by IPL and WPL are deferred as regulatory assets and amortized over the life of the new debt issued. 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, 2015 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 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7 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 - IPL’s tax benefit riders utilize regulatory liabilities to credit bills of IPL’s Iowa retail electric and gas customers to help offset the impact of rate increases on such customers. These regulatory liabilities are related to tax benefits from tax accounting method changes for repairs expenditures, allocation of mixed service costs, allocation of insurance proceeds from floods in 2008, and cost of removal expenditures. In 2015 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions): Electric tax benefit rider credits $72 Gas tax benefit rider credits 12 $84 Electric tax benefit rider - The IUB has approved an electric tax benefit rider proposed by IPL, which utilizes regulatory liabilities to credit bills of Iowa retail electric customers beginning in 2011 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 IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues $72 $85 $79 Income tax benefit resulting from decreased taxable income caused by credits 30 35 33 Income tax benefit representing tax benefits realized from electric tax benefit rider 42 50 46 In December 2015, the IUB issued an order authorizing $65 million of regulatory liabilities from tax benefits to be credited to IPL’s retail electric customers’ bills in Iowa in 2016 through the electric tax benefit rider. The IUB has authorized IPL to reduce the electric tax benefit rider billing credits on customers’ bills 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): 2015 2014 2013 Revenue requirement adjustment $14 $15 $24 In December 2015, the IUB authorized IPL to reduce the $65 million of billing credits on customers’ bills by $15 million in 2016 to recognize the revenue requirement impact of the changes in tax accounting methods. Gas tax benefit rider - The IUB has approved a gas tax benefit rider proposed by IPL, which utilizes approximately $12 million of regulatory liabilities annually to credit bills of Iowa retail gas customers beginning in January 2013 to help offset the impact of rate increases on such customers. Any remaining benefit, including any portion not utilized of the agreed upon amount from January 2013 through December 2015, is expected to be credited to Iowa’s retail gas customers’ bills in 2016. Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues $12 $12 $11 Income tax benefit resulting from decreased taxable income caused by credits 5 5 4 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7 Refer to Note 11 for additional details regarding IPL’s tax benefit riders. Energy efficiency cost recovery - WPL and IPL collect revenues from their customers to offset certain expenditures incurred by WPL and IPL 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 July 2014 PSCW order for WPL’s 2015/2016 Test Period electric and gas base rate case authorized lower energy efficiency cost recovery amortizations for 2015, which contributed to the decrease in Alliant Energy’s and WPL’s “Energy efficiency cost recovery” regulatory liabilities. Electric transmission cost recovery - Electric revenues established in WPL’s retail electric rate case (2015/2016 Test Period) included recovery of expected increases in electric transmission service expense largely due to SSR costs expected to be incurred. Due to a revision in MISO’s method to allocate SSR costs, WPL no longer expects to incur certain SSR costs. The difference between actual electric transmission service expense incurred and amounts collected from customers as electric revenues in 2015 are recorded as electric transmission service expense with an offsetting amount recorded to regulatory liabilities due to the escrow treatment authorized for WPL in its 2015/2016 Test Period retail electric rate case. 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. Utility Rate Cases - 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 current levels through the end of 2016. The retail electric base rate case included a return of and a return on costs for environmental controls projects at Columbia Units 1 and 2 and Edgewater Unit 5, generation performance and reliability improvements at Columbia Units 1 and 2, 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 cost 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 require WPL to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels during 2015 or 2016 and allows WPL to request a change in retail base rates during this period if its annual regulatory return on common equity falls below a certain level. As of December 31, 2015 , Alliant Energy and WPL did not record any deferred amounts for these provisions. WPL’s Wisconsin Retail Electric and Gas Rate Case (2013/2014 Test Period) - In July 2012, WPL received an order from the PSCW authorizing WPL to implement a decrease in annual retail gas base rates of $13 million effective January 1, 2013, followed by a freeze of such gas base rates through the end of 2014. The order also authorized WPL to maintain retail electric base rates at their then current levels through the end of 2014. The order included a provision 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, 2015 , Alliant Energy and WPL deferred $8 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. WPL currently expects the deferred amount will be refunded to its customers in a future rate case or other proceeding. IPL’s Iowa Retail Electric Rate Settlement Agreement - The IUB approved a settlement agreement in 2014 related to rates charged to IPL’s Iowa retail electric customers. The settlement agreement extends IPL’s Iowa retail electric base rates authorized in its 2009 Test Year rate case through 2016 and provides targeted retail electric customer billing credits of $105 million in aggregate. IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions): Actual Estimated 2014 2015 2016 Billing credits to reduce retail electric customers’ bills $72 $24 $9 WPL’s Retail Fuel-related Rate Filing (2016 Test Year) - In December 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $7 million , or approximately 1% , effective January 1, 2016. The increase reflects anticipated increases in retail electric fuel-related costs in 2016, including impacts of increased sales volumes approved in the retail base rate case for 2016. WPL’s 2016 fuel-related costs will be subject to deferral if they fall outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Deferral of under-collections are reduced to the extent WPL’s actual return on common equity exceeds the most recently authorized return on common equity. WPL’s Retail Fuel-related Rate Filing (2015 Test Year) - In December 2014, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $39 million , or approximately 4% , effective January 1, 2015. The increase included $39 million of anticipated increases in retail electric fuel-related costs in 2015 attributable to $25 million for higher retail electric fuel-related costs per MWh anticipated in 2015 and $14 million from the impact of increased sales volumes approved in the retail electric base rate case for 2015. WPL’s 2015 fuel-related costs were subject to deferral if they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2015 were lower than fuel-related costs used to determine rates for such period resulting in an over-collection of fuel-related costs. As of December 31, 2015 , fuel-related costs outside of the approved range were $10 million and are included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory liabilities table above. WPL’s Retail Fuel-related Rate Filing (2014 Test Year) - Pursuant to a 2013 PSCW order, WPL’s 2014 fuel-related costs were subject to deferral since they were outside an annual bandwidth of plus or minus 2% of the approved annual forecasted fuel-related costs. Retail fuel-related costs incurred by WPL through December 31, 2014 were higher than fuel-related costs used to determine rates for such period resulting in an under-collection of fuel-related costs for 2014 of $33 million (including $28 million outside the approved range for 2014). As of December 31, 2015 and 2014 , the $28 million of deferred fuel-related costs were included in “Commodity cost recovery” in Alliant Energy’s and WPL’s regulatory assets table above. In July 2015, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $28 million , or approximately 2% , effective January 1, 2016 to recover the 2014 Test Year deferred fuel-related costs.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under the MATS Rule and CSAPR. Construction began in 2014 and is expected to be completed in 2016. As of December 31, 2015 and 2014 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $190 million and $90 million , and AFUDC of $8 million and $3 million , respectively, for the scrubber and baghouse in “Construction work in progress” in the above table for Alliant Energy and WPL. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of December 31, 2015 and 2014 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $453 million and $188 million , and AFUDC of $24 million and $4 million , respectively, for Marshalltown 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 April 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. IPL received proceeds of $11 million and a promissory note of $2 million . In July 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 July 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. Refer to Note 19 for further discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets. 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8 In 2014, scrubbers and baghouses were placed in service at IPL’s Ottumwa Unit 1 and George Neal Unit 3, and WPL’s Columbia Units 1 and 2. In 2013, a scrubber and baghouse was placed in service at IPL’s George Neal Unit 4. 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. As of December 31, 2015 , Alliant Energy recorded $130 million on its balance sheet related to the wind farm. Refer to Note 1(i) for discussion of an impairment test performed as of December 31, 2015 related to the wind farm. Refer to Note 5(d) for discussion of a cash grant received in 2013 related to the wind farm. 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, 2015 , Alliant Energy recorded $99 million on its balance sheet related to Sheboygan Falls. Corporate Services and Other - Property, plant and equipment related to Corporate Services includes computer software and the corporate headquarters building located in Madison, Wisconsin. In addition, Corporate Services implemented a new customer billing and information system for IPL and WPL, which was placed in service in the fourth quarter of 2015 and is amortized using the straight-line method over a 12 -year period. As of December 31, 2015 , Alliant Energy recorded capitalized expenditures of $102 million and capitalized interest of $3 million for the customer billing and information system in “Corporate Services and other, net” in the above table for Alliant Energy. Property, plant and equipment related to Transportation includes a short-line railway in Iowa, a barge terminal on the Mississippi River and a coal terminal in Williams, Iowa. 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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under the MATS Rule and CSAPR. Construction began in 2014 and is expected to be completed in 2016. As of December 31, 2015 and 2014 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $190 million and $90 million , and AFUDC of $8 million and $3 million , respectively, for the scrubber and baghouse in “Construction work in progress” in the above table for Alliant Energy and WPL. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of December 31, 2015 and 2014 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $453 million and $188 million , and AFUDC of $24 million and $4 million , respectively, for Marshalltown 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 April 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. IPL received proceeds of $11 million and a promissory note of $2 million . In July 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 July 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. Refer to Note 19 for further discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets. 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8 In 2014, scrubbers and baghouses were placed in service at IPL’s Ottumwa Unit 1 and George Neal Unit 3, and WPL’s Columbia Units 1 and 2. In 2013, a scrubber and baghouse was placed in service at IPL’s George Neal Unit 4.
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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. Utility - Environmental Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5. The scrubber and baghouse reduce SO2 and mercury emissions at the EGU and are expected to help meet requirements under the MATS Rule and CSAPR. Construction began in 2014 and is expected to be completed in 2016. As of December 31, 2015 and 2014 , Alliant Energy and WPL recorded capitalized expenditures for CWIP of $190 million and $90 million , and AFUDC of $8 million and $3 million , respectively, for the scrubber and baghouse in “Construction work in progress” in the above table for Alliant Energy and WPL. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of December 31, 2015 and 2014 , Alliant Energy and IPL recorded capitalized expenditures for CWIP of $453 million and $188 million , and AFUDC of $24 million and $4 million , respectively, for Marshalltown 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 April 2015, IPL completed the sale of its Minnesota natural gas distribution assets (primarily related to property, plant and equipment) to Minnesota Energy Resources Corporation, a subsidiary of Integrys Energy Group, Inc. IPL received proceeds of $11 million and a promissory note of $2 million . In July 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 July 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. Refer to Note 19 for further discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets. 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8 AFUDC related to various construction projects was recognized in the income statements as follows (in millions): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8 In 2014, scrubbers and baghouses were placed in service at IPL’s Ottumwa Unit 1 and George Neal Unit 3, and WPL’s Columbia Units 1 and 2. In 2013, a scrubber and baghouse was placed in service at IPL’s George Neal Unit 4.

Jointly-Owned Electric Utility

Jointly-Owned Electric Utility Plant	12 Months Ended
	Dec. 31, 2015
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8

Receivables

Receivables	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8 (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, seasonal limits on cash proceeds and cash amounts received from the third party. The purchase commitment from the third party to which IPL sells its receivables expires in March 2016. IPL currently expects to amend and extend the purchase commitment. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. In exchange for the receivables sold, IPL receives cash proceeds of up to $180 million from the third party. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current seasonal limit or amount of receivables available for sale, whichever is less. The seasonal limit on cash proceeds as of December 31, 2015 was $150 million . As of December 31, 2015 , IPL sold $181.1 million of receivables to the third party, received $5.0 million in cash proceeds and recorded deferred proceeds of $172.0 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. Refer to Note 14 for discussion of the fair value of deferred proceeds. IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program were as follows (in millions): 2015 2014 2013 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $137.0 $150.0 $170.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 46.7 46.4 105.9 In 2015 , 2014 and 2013 , IPL’s costs incurred related to the sales of accounts receivable program were not material. As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2015 2014 Customer accounts receivable $109.7 $134.8 Unbilled utility revenues 71.3 69.7 Other receivables 0.1 0.1 Receivables sold to third party 181.1 204.6 Less: cash proceeds (a) 5.0 22.0 Deferred proceeds 176.1 182.6 Less: allowance for doubtful accounts 4.1 5.4 Fair value of deferred proceeds $172.0 $177.2 Outstanding receivables past due $18.0 $19.9 (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): 2015 2014 2013 Collections reinvested in receivables $1,812.9 $1,997.9 $1,880.8 Credit losses, net of recoveries 8.8 11.4 11.9 (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 in 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 Resources 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. (d) Franklin County Wind Farm Cash Grant - The ARRA provides incentives for wind projects placed into service between January 1, 2009 and December 31, 2012. In accordance with the ARRA, Alliant Energy filed an application with the U.S. Department of the Treasury in February 2013 requesting a cash grant for a portion of the qualifying project expenditures of the Franklin County wind farm that was placed into service in December 2012. Alliant Energy elected to record the anticipated cash grant as a reduction of the carrying value of the Franklin County wind farm. In 2013, Alliant Energy received $62.4 million of proceeds from the cash grant, which are presented in investing activities in Alliant Energy’s cash flows statement in 2013. The grant proceeds were used by Alliant Energy to reduce short-term borrowings incurred during the construction of the wind farm.
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8 (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, seasonal limits on cash proceeds and cash amounts received from the third party. The purchase commitment from the third party to which IPL sells its receivables expires in March 2016. IPL currently expects to amend and extend the purchase commitment. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. In exchange for the receivables sold, IPL receives cash proceeds of up to $180 million from the third party. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current seasonal limit or amount of receivables available for sale, whichever is less. The seasonal limit on cash proceeds as of December 31, 2015 was $150 million . As of December 31, 2015 , IPL sold $181.1 million of receivables to the third party, received $5.0 million in cash proceeds and recorded deferred proceeds of $172.0 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. Refer to Note 14 for discussion of the fair value of deferred proceeds. IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program were as follows (in millions): 2015 2014 2013 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $137.0 $150.0 $170.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 46.7 46.4 105.9 In 2015 , 2014 and 2013 , IPL’s costs incurred related to the sales of accounts receivable program were not material. As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2015 2014 Customer accounts receivable $109.7 $134.8 Unbilled utility revenues 71.3 69.7 Other receivables 0.1 0.1 Receivables sold to third party 181.1 204.6 Less: cash proceeds (a) 5.0 22.0 Deferred proceeds 176.1 182.6 Less: allowance for doubtful accounts 4.1 5.4 Fair value of deferred proceeds $172.0 $177.2 Outstanding receivables past due $18.0 $19.9 (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): 2015 2014 2013 Collections reinvested in receivables $1,812.9 $1,997.9 $1,880.8 Credit losses, net of recoveries 8.8 11.4 11.9
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8

Investments

Investments	12 Months Ended
	Dec. 31, 2015
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 Carrying Value at Interest at December 31, Equity (Income) / Loss December 31, 2015 2015 2014 2015 2014 2013 Alliant Energy ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) Other Various 0.9 2.3 1.3 2.4 — $302.9 $296.6 ($33.8 ) ($40.4 ) ($43.7 ) WPL ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) $302.0 $294.3 ($35.1 ) ($42.8 ) ($43.7 ) (a) Alliant Energy and WPL have the ability to exercise significant influence over ATC’s financial and operating policies through their 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 2015 2014 2013 2015 2014 2013 Operating revenues $624 $643 $634 $624 $643 $634 Operating income 299 330 334 299 330 334 Net income 186 240 248 202 240 250 As of December 31: Current assets 88 72 87 70 Non-current assets 3,987 3,773 3,977 3,747 Current liabilities 332 315 332 315 Non-current liabilities 2,052 1,871 2,052 1,870 MISO Transmission Owner Return on Equity Complaints - Complaints are currently pending with FERC regarding the level of return on equity that MISO transmission owners, including ATC, should be allowed to utilize in calculating the rates they charge their customers. Alliant Energy and WPL currently anticipate FERC’s decision on the MISO transmission owner complaints will reduce transmission owners’ current return on equity, which is expected to result in lower equity income and dividends from ATC in the future. In 2014, FERC issued an order on the complaints establishing an effective refund date of November 12, 2013. Alliant Energy and WPL have realized $15 million of reductions in the amount of equity income from ATC for the period from November 12, 2013 through December 31, 2015 , including $12 million realized in 2015 and $3 million realized in 2014. WPL’s Noncontrolling Interest - Prior to 2014, WPL owned 100% of WPL Transco, which holds Alliant Energy’s investment in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of Resources, to become a member of WPL Transco in addition to WPL. In 2014, ATI began funding capital contributions that WPL Transco makes to ATC. As of December 31, 2015 , WPL’s and ATI’s ownership interests in WPL Transco were approximately 93% and 7% , respectively. WPL continues to consolidate WPL Transco and as a result, ATI’s ownership interest in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. In 2015 and 2014, 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. ATI’s ownership interest in WPL Transco is expected to increase as a result of future capital contributions to WPL Transco. Alliant Energy’s aggregate ownership percentage in ATC is not expected to change as a result of WPL Transco’s amended operating agreement. (b) Cash Surrender Value of Life Insurance Policies - Various life insurance policies cover certain current and former employees and directors. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4
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. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4
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 Carrying Value at Interest at December 31, Equity (Income) / Loss December 31, 2015 2015 2014 2015 2014 2013 Alliant Energy ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) Other Various 0.9 2.3 1.3 2.4 — $302.9 $296.6 ($33.8 ) ($40.4 ) ($43.7 ) WPL ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) $302.0 $294.3 ($35.1 ) ($42.8 ) ($43.7 ) (a) Alliant Energy and WPL have the ability to exercise significant influence over ATC’s financial and operating policies through their 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 2015 2014 2013 2015 2014 2013 Operating revenues $624 $643 $634 $624 $643 $634 Operating income 299 330 334 299 330 334 Net income 186 240 248 202 240 250 As of December 31: Current assets 88 72 87 70 Non-current assets 3,987 3,773 3,977 3,747 Current liabilities 332 315 332 315 Non-current liabilities 2,052 1,871 2,052 1,870 MISO Transmission Owner Return on Equity Complaints - Complaints are currently pending with FERC regarding the level of return on equity that MISO transmission owners, including ATC, should be allowed to utilize in calculating the rates they charge their customers. Alliant Energy and WPL currently anticipate FERC’s decision on the MISO transmission owner complaints will reduce transmission owners’ current return on equity, which is expected to result in lower equity income and dividends from ATC in the future. In 2014, FERC issued an order on the complaints establishing an effective refund date of November 12, 2013. Alliant Energy and WPL have realized $15 million of reductions in the amount of equity income from ATC for the period from November 12, 2013 through December 31, 2015 , including $12 million realized in 2015 and $3 million realized in 2014. WPL’s Noncontrolling Interest - Prior to 2014, WPL owned 100% of WPL Transco, which holds Alliant Energy’s investment in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of Resources, to become a member of WPL Transco in addition to WPL. In 2014, ATI began funding capital contributions that WPL Transco makes to ATC. As of December 31, 2015 , WPL’s and ATI’s ownership interests in WPL Transco were approximately 93% and 7% , respectively. WPL continues to consolidate WPL Transco and as a result, ATI’s ownership interest in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. In 2015 and 2014, 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. ATI’s ownership interest in WPL Transco is expected to increase as a result of future capital contributions to WPL Transco. Alliant Energy’s aggregate ownership percentage in ATC is not expected to change as a result of WPL Transco’s amended operating agreement. (b) Cash Surrender Value of Life Insurance Policies - Various life insurance policies cover certain current and former employees and directors. At December 31, the cash surrender value of these investments was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2015
Schedule of Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2015 2014 2013 Shares outstanding, January 1 110,935,680 110,943,669 110,987,400 At-the-market offering program 2,186,617 — — Shareowner Direct Plan issuances 303,005 — — Equity-based compensation plans ( Note 12(b) ) 56,378 35,547 (23,374 ) Other (22,464 ) (43,536 ) (20,357 ) Shares outstanding, December 31 113,459,216 110,935,680 110,943,669 At December 31, 2015 , Alliant Energy had a total of 7.3 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 March 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. As of December 31, 2015 , Alliant Energy issued 2,186,617 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. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program. 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-half of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $110.00 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. 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, 2015 , 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 2015 . 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, 2015 , IPL’s amount of retained earnings that were free of dividend restrictions was $554 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. Currently, WPL has a regulatory limitation on distributions to its parent company from an order issued by the PSCW in July 2014. The order prohibits WPL from paying annual common stock dividends to its parent company in excess of $135 million in 2016 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 52.25% for 2016. As of December 31, 2015 , WPL’s amount of retained earnings that were free of dividend restrictions was $135 million for 2016 . 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, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6 Capital Transactions With Subsidiaries - IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0 IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions): 2015 2014 2013 $165.0 $90.0 $120.0 Comprehensive Income - In 2015 , 2014 and 2013 , Alliant Energy’s other comprehensive income (loss) was $0.2 million , ($0.4) million and $0.6 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 2015 , 2014 and 2013 , 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 Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2015 2014 2013 Shares outstanding, January 1 110,935,680 110,943,669 110,987,400 At-the-market offering program 2,186,617 — — Shareowner Direct Plan issuances 303,005 — — Equity-based compensation plans ( Note 12(b) ) 56,378 35,547 (23,374 ) Other (22,464 ) (43,536 ) (20,357 ) Shares outstanding, December 31 113,459,216 110,935,680 110,943,669 At December 31, 2015 , Alliant Energy had a total of 7.3 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 March 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. As of December 31, 2015 , Alliant Energy issued 2,186,617 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. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program. 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-half of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $110.00 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. 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, 2015 , 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 2015 . 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, 2015 , IPL’s amount of retained earnings that were free of dividend restrictions was $554 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. Currently, WPL has a regulatory limitation on distributions to its parent company from an order issued by the PSCW in July 2014. The order prohibits WPL from paying annual common stock dividends to its parent company in excess of $135 million in 2016 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 52.25% for 2016. As of December 31, 2015 , WPL’s amount of retained earnings that were free of dividend restrictions was $135 million for 2016 . 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, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6 Capital Transactions With Subsidiaries - IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0 IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions): 2015 2014 2013 $165.0 $90.0 $120.0 Comprehensive Income - In 2015 , 2014 and 2013 , Alliant Energy’s other comprehensive income (loss) was $0.2 million , ($0.4) million and $0.6 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 2015 , 2014 and 2013 , 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 Share Activity - A summary of Alliant Energy’s common stock activity was as follows: 2015 2014 2013 Shares outstanding, January 1 110,935,680 110,943,669 110,987,400 At-the-market offering program 2,186,617 — — Shareowner Direct Plan issuances 303,005 — — Equity-based compensation plans ( Note 12(b) ) 56,378 35,547 (23,374 ) Other (22,464 ) (43,536 ) (20,357 ) Shares outstanding, December 31 113,459,216 110,935,680 110,943,669 At December 31, 2015 , Alliant Energy had a total of 7.3 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 March 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. As of December 31, 2015 , Alliant Energy issued 2,186,617 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. Alliant Energy currently has no plans to issue any additional common stock through the at-the-market offering program. 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-half of one share of Alliant Energy’s common stock. The rights will be exercisable at an initial price of $110.00 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. 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, 2015 , 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 2015 . 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, 2015 , IPL’s amount of retained earnings that were free of dividend restrictions was $554 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. Currently, WPL has a regulatory limitation on distributions to its parent company from an order issued by the PSCW in July 2014. The order prohibits WPL from paying annual common stock dividends to its parent company in excess of $135 million in 2016 if WPL’s actual 13 -month average common equity ratio (calculated on a financial basis consistent with WPL’s rate cases) would fall below 52.25% for 2016. As of December 31, 2015 , WPL’s amount of retained earnings that were free of dividend restrictions was $135 million for 2016 . 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, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6 Capital Transactions With Subsidiaries - IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0 IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions): 2015 2014 2013 $165.0 $90.0 $120.0 Comprehensive Income - In 2015 , 2014 and 2013 , Alliant Energy’s other comprehensive income (loss) was $0.2 million , ($0.4) million and $0.6 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 2015 , 2014 and 2013 , 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, 2015
Redeemable Preferred Stock	REDEEMABLE PREFERRED STOCK Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Liquidation Preference/Stated Value Shares Authorized Shares Outstanding Series 2015 2014 (in millions) $25 16,000,000 8,000,000 5.1% $200.0 $200.0 IPL - In 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million . The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of additional paid-in capital on Alliant Energy’s and IPL’s balance sheets in 2013. 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. In 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their income statements. Refer to Note 14 for information on the fair value of cumulative preferred stock. WPL - In 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date.
IPL [Member]
Redeemable Preferred Stock	REDEEMABLE PREFERRED STOCK Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Liquidation Preference/Stated Value Shares Authorized Shares Outstanding Series 2015 2014 (in millions) $25 16,000,000 8,000,000 5.1% $200.0 $200.0 IPL - In 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million . The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of additional paid-in capital on Alliant Energy’s and IPL’s balance sheets in 2013. 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. In 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their income statements. Refer to Note 14 for information on the fair value of cumulative preferred stock. WPL - In 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date.
WPL [Member]
Redeemable Preferred Stock	REDEEMABLE PREFERRED STOCK Information related to the carrying value of IPL’s cumulative preferred stock at December 31 was as follows: Liquidation Preference/Stated Value Shares Authorized Shares Outstanding Series 2015 2014 (in millions) $25 16,000,000 8,000,000 5.1% $200.0 $200.0 IPL - In 2013, IPL issued 8,000,000 shares of 5.1% cumulative preferred stock and received proceeds of $200 million . The proceeds were used by IPL to redeem its 8.375% cumulative preferred stock, reduce commercial paper classified as long-term debt by $40 million and for other general corporate purposes. Alliant Energy and IPL incurred $5 million of issuance costs related to this transaction, which were recorded as a reduction of additional paid-in capital on Alliant Energy’s and IPL’s balance sheets in 2013. 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. In 2013, IPL redeemed all 6,000,000 outstanding shares of its 8.375% cumulative preferred stock for $150 million plus accrued and unpaid dividends to the redemption date. Alliant Energy and IPL recorded a $5 million charge in 2013 related to this transaction in “Preferred dividend requirements” in their income statements. Refer to Note 14 for information on the fair value of cumulative preferred stock. WPL - In 2013, WPL redeemed all 1,049,225 outstanding shares of its 4.40% through 6.50% cumulative preferred stock for $61 million plus accrued and unpaid dividends to the redemption date.

Debt

Debt	12 Months Ended
	Dec. 31, 2015
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, 2015 , 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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1% The credit facility agreements and Alliant Energy’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, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48% 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): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes. Five-Year Schedule of Debt Maturities - At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357 At December 31, 2015 , there were no significant sinking fund requirements related to the long-term debt on the balance sheets. Indentures - IPL maintains an indenture related to all of its outstanding senior debentures. WPL maintains an indenture related to all of its outstanding debentures. Sheboygan Power, LLC, Resources’ wholly-owned subsidiary, maintains an indenture related to the issuance of its 5.06% senior secured notes due 2016 to 2024. Optional Redemption Provisions - Alliant Energy and its subsidiaries have certain issuances of long-term debt that contain 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. At December 31, 2015 , the debt issuances that contained these optional redemption provisions included all of IPL’s outstanding senior debentures, all of WPL’s outstanding debentures, Corporate Services’ senior notes due 2022 and Sheboygan Power, LLC’s senior secured notes due 2016 to 2024. Security Provisions - Sheboygan Power, LLC’s 5.06% senior secured notes due 2016 to 2024 are secured by Sheboygan Falls and related assets. Financial Covenant - Alliant Energy’s term loan credit agreement contains a financial covenant, which requires it to maintain a certain debt-to-capital ratio in order to borrow under the agreement. Refer to Note 9(a) for further discussion. Carrying Amount and Fair Value of Long-term Debt - Refer to Note 14 for information on the carrying amount and 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, 2015 , 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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1% The credit facility agreements and Alliant Energy’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, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48% 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): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes. Five-Year Schedule of Debt Maturities - At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357 At December 31, 2015 , there were no significant sinking fund requirements related to the long-term debt on the balance sheets. Indentures - IPL maintains an indenture related to all of its outstanding senior debentures. WPL maintains an indenture related to all of its outstanding debentures. Sheboygan Power, LLC, Resources’ wholly-owned subsidiary, maintains an indenture related to the issuance of its 5.06% senior secured notes due 2016 to 2024. Optional Redemption Provisions - Alliant Energy and its subsidiaries have certain issuances of long-term debt that contain 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. At December 31, 2015 , the debt issuances that contained these optional redemption provisions included all of IPL’s outstanding senior debentures, all of WPL’s outstanding debentures, Corporate Services’ senior notes due 2022 and Sheboygan Power, LLC’s senior secured notes due 2016 to 2024. Security Provisions - Sheboygan Power, LLC’s 5.06% senior secured notes due 2016 to 2024 are secured by Sheboygan Falls and related assets. Financial Covenant - Alliant Energy’s term loan credit agreement contains a financial covenant, which requires it to maintain a certain debt-to-capital ratio in order to borrow under the agreement. Refer to Note 9(a) for further discussion. Carrying Amount and Fair Value of Long-term Debt - Refer to Note 14 for information on the carrying amount and 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, 2015 , 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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1% The credit facility agreements and Alliant Energy’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, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48% 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): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes. Five-Year Schedule of Debt Maturities - At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357 At December 31, 2015 , there were no significant sinking fund requirements related to the long-term debt on the balance sheets. Indentures - IPL maintains an indenture related to all of its outstanding senior debentures. WPL maintains an indenture related to all of its outstanding debentures. Sheboygan Power, LLC, Resources’ wholly-owned subsidiary, maintains an indenture related to the issuance of its 5.06% senior secured notes due 2016 to 2024. Optional Redemption Provisions - Alliant Energy and its subsidiaries have certain issuances of long-term debt that contain 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. At December 31, 2015 , the debt issuances that contained these optional redemption provisions included all of IPL’s outstanding senior debentures, all of WPL’s outstanding debentures, Corporate Services’ senior notes due 2022 and Sheboygan Power, LLC’s senior secured notes due 2016 to 2024. Security Provisions - Sheboygan Power, LLC’s 5.06% senior secured notes due 2016 to 2024 are secured by Sheboygan Falls and related assets. Financial Covenant - Alliant Energy’s term loan credit agreement contains a financial covenant, which requires it to maintain a certain debt-to-capital ratio in order to borrow under the agreement. Refer to Note 9(a) for further discussion. Carrying Amount and Fair Value of Long-term Debt - Refer to Note 14 for information on the carrying amount and fair value of long-term debt outstanding.

Leases

Leases	12 Months Ended
	Dec. 31, 2015
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 2015 , 2014 and 2013 , rental expenses associated with operating leases were not material. At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9
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 2015 , 2014 and 2013 , rental expenses associated with operating leases were not material. At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9
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 2015 , 2014 and 2013 , rental expenses associated with operating leases were not material. At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9 (b) Capital Leases - WPL - In 2005, WPL entered into a 20 -year agreement with Resources’ 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. In 2005, the PSCW approved this affiliated lease agreement with initial monthly lease payments of approximately $1.3 million . The lease payments were based on a 50% debt to capital ratio, a return on equity of 10.9% , a cost of debt based on the cost of senior notes issued by Resources’ Non-regulated Generation business in 2005 and certain costs incurred to construct the facility. In accordance with its order approving the lease agreement, the PSCW reserved the right to review the capital structure, return on equity and cost of debt every five years from the date of the order. No revisions to the lease have been made since its inception. The capital lease asset is amortized using the straight-line method over the 20 -year lease term. Since the inception of the lease in 2005, WPL’s retail and wholesale rates have included recovery of the monthly Sheboygan Falls lease payments. Sheboygan Falls lease expenses were included in WPL’s income statements as follows (in millions): 2015 2014 2013 Interest expense $9.9 $10.4 $10.9 Depreciation and amortization 6.2 6.2 6.2 $16.1 $16.6 $17.1 At December 31, 2015 , WPL’s estimated future minimum capital lease payments for Sheboygan Falls were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Sheboygan Falls $15 $15 $15 $15 $15 $68 $143 $54 $89

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax [Line Items]
Income Taxes	INCOME TAXES Refer to Note 1(c) for discussion of a change implemented in the fourth quarter of 2015 related to IPL’s and WPL’s method of recording income taxes, which was applied retrospectively. Refer to Note 1(p) for discussion of the adoption of an accounting standard to simplify the presentation of deferred taxes on the balance sheet, which was applied prospectively. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind farms. Production tax credits are based on the electricity generated by each wind farm during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0 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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 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 2015 will be approximately $200 million ( $100 million for IPL and $50 million for WPL). Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2015 was primarily due to bonus depreciation deductions estimated at ATC. Regulatory liability tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Carryforwards - At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205 At December 31, 2015 , Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 99% expiring after 2024 . At December 31, 2015 , IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 95% expiring after 2021 . At December 31, 2015 , WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 96% expiring after 2033 . Uncertain Tax Positions - At December 31, 2015 , 2014 and 2013 , 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, 2015 , 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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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 Refer to Note 1(c) for discussion of a change implemented in the fourth quarter of 2015 related to IPL’s and WPL’s method of recording income taxes, which was applied retrospectively. Refer to Note 1(p) for discussion of the adoption of an accounting standard to simplify the presentation of deferred taxes on the balance sheet, which was applied prospectively. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind farms. Production tax credits are based on the electricity generated by each wind farm during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0 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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 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 2015 will be approximately $200 million ( $100 million for IPL and $50 million for WPL). Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2015 was primarily due to bonus depreciation deductions estimated at ATC. Regulatory liability tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Carryforwards - At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205 At December 31, 2015 , Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 99% expiring after 2024 . At December 31, 2015 , IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 95% expiring after 2021 . At December 31, 2015 , WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 96% expiring after 2033 . Uncertain Tax Positions - At December 31, 2015 , 2014 and 2013 , 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, 2015 , 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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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 Refer to Note 1(c) for discussion of a change implemented in the fourth quarter of 2015 related to IPL’s and WPL’s method of recording income taxes, which was applied retrospectively. Refer to Note 1(p) for discussion of the adoption of an accounting standard to simplify the presentation of deferred taxes on the balance sheet, which was applied prospectively. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 % IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind farms. Production tax credits are based on the electricity generated by each wind farm during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0 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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4 Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 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 2015 will be approximately $200 million ( $100 million for IPL and $50 million for WPL). Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2015 was primarily due to bonus depreciation deductions estimated at ATC. Regulatory liability tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Carryforwards - At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205 At December 31, 2015 , Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 99% expiring after 2024 . At December 31, 2015 , IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 95% expiring after 2021 . At December 31, 2015 , WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2034 with 96% expiring after 2033 . Uncertain Tax Positions - At December 31, 2015 , 2014 and 2013 , 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, 2015 , 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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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, 2015
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, and/or through defined contribution plans (including 401(k) savings plans). Qualified and non-qualified non-contributory defined benefit pension plans are currently closed to new hires. 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. 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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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 as of December 31, 2014 and 2015 to utilize new mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015, respectively. 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement. 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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9 Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $1,301.5 $1,113.4 $231.1 $208.7 Service cost 15.9 13.1 5.5 5.2 Interest cost 53.6 54.1 9.1 9.5 Plan participants’ contributions — — 3.1 2.8 Plan amendments — — (0.3 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (70.1 ) 195.8 (9.4 ) 22.3 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Net benefit obligation at December 31 1,206.3 1,301.5 221.4 231.1 Change in plan assets: Fair value of plan assets at January 1 1,018.1 1,022.9 121.6 124.9 Actual return on plan assets (30.2 ) 66.4 (4.9 ) 5.6 Employer contributions 2.2 3.7 4.8 5.7 Plan participants’ contributions — — 3.1 2.8 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Fair value of plan assets at December 31 895.0 1,018.1 106.9 121.6 Under funded status at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $6.1 Other current liabilities (2.6 ) (2.5 ) (6.2 ) (5.6 ) Pension and other benefit obligations (308.7 ) (280.9 ) (111.3 ) (110.0 ) Net amounts recognized at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Amounts recognized in Regulatory Assets and AOCL consist of (a): Net actuarial loss $533.1 $533.4 $59.8 $60.7 Prior service credit (7.2 ) (7.4 ) (5.6 ) (16.7 ) $525.9 $526.0 $54.2 $44.0 (a) Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets. 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. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $603.1 $514.0 $96.4 $87.8 Service cost 8.8 7.2 2.4 2.4 Interest cost 25.0 25.1 3.8 3.9 Plan participants’ contributions — — 1.0 0.9 Plan amendments — — (0.1 ) — Actuarial (gain) loss (32.3 ) 91.4 (4.6 ) 8.6 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Net benefit obligation at December 31 556.1 603.1 91.3 96.4 Change in plan assets: Fair value of plan assets at January 1 484.7 485.9 78.7 81.2 Actual return on plan assets (14.3 ) 32.1 (3.1 ) 3.6 Employer contributions 0.8 1.3 0.2 0.2 Plan participants’ contributions — — 1.0 0.9 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Fair value of plan assets at December 31 422.7 484.7 69.2 78.7 Under funded status at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $— $1.2 Other current liabilities (0.8 ) (0.8 ) — — Pension and other benefit obligations (132.6 ) (117.6 ) (22.1 ) (18.9 ) Net amounts recognized at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $235.5 $233.1 $29.8 $27.9 Prior service credit (2.5 ) (2.6 ) (2.7 ) (8.7 ) $233.0 $230.5 $27.1 $19.2 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $547.6 $460.8 $94.0 $85.6 Service cost 5.8 4.9 2.1 2.0 Interest cost 22.6 22.6 3.7 3.8 Plan participants’ contributions — — 1.6 1.3 Plan amendments — — (0.2 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (30.0 ) 86.7 (3.5 ) 9.2 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Net benefit obligation at December 31 505.9 547.6 89.7 94.0 Change in plan assets: Fair value of plan assets at January 1 440.3 438.8 21.8 21.7 Actual return on plan assets (13.0 ) 28.6 (1.1 ) 1.2 Employer contributions 0.1 0.3 4.4 5.5 Plan participants’ contributions — — 1.6 1.3 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Fair value of plan assets at December 31 386.8 440.3 18.7 21.8 Under funded status at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $4.9 Other current liabilities (0.1 ) (0.1 ) (6.0 ) (5.5 ) Pension and other benefit obligations (119.0 ) (107.2 ) (68.0 ) (71.6 ) Net amounts recognized at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $232.1 $233.5 $23.3 $26.3 Prior service credit (1.2 ) (1.0 ) (2.4 ) (5.6 ) $230.9 $232.5 $20.9 $20.7 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets. 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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4 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, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32% 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, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47% Fair Value Measurements - The following tables report a framework for measuring fair value. The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Investments in securities held in registered investment companies and directly held equity securities are valued at the closing price reported in the active market in which the securities are traded. Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means. Investments in common/collective trusts are valued at the net asset value of shares held by the plans, which is based on the fair market value of the underlying investments in the common/collective trusts. Investments in corporate bonds 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. 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. The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while Alliant Energy, IPL and WPL believe their valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $23.1 $— $23.1 $— $49.3 $— $49.3 $— Equity securities: U.S. large cap core 100.4 100.4 — — 137.2 137.2 — — U.S. large cap value 59.9 — 59.9 — 72.2 — 72.2 — U.S. large cap growth 60.5 — 60.5 — 73.2 — 73.2 — U.S. small cap value 14.2 — 14.2 — 15.2 — 15.2 — U.S. small cap growth 16.0 16.0 — — 15.9 15.9 — — International - developed markets 104.4 52.7 51.7 — 102.9 52.1 50.8 — International - emerging markets 41.2 41.2 — — 47.2 47.2 — — Global asset allocation securities 96.3 52.9 43.4 — 99.9 57.2 42.7 — Risk parity allocation securities 94.0 — 94.0 — 102.5 — 102.5 — Fixed income securities: Corporate bonds — — — — 0.1 — 0.1 — Fixed income funds 284.8 — 284.8 — 302.7 0.2 302.5 — 894.8 $263.2 $631.6 $— 1,018.3 $309.8 $708.5 $— Accrued investment income 0.2 0.1 Due to brokers, net (pending trades with brokers) — (0.3 ) Total pension plan assets $895.0 $1,018.1 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.9 $— $10.9 $— $23.5 $— $23.5 $— Equity securities: U.S. large cap core 47.4 47.4 — — 65.3 65.3 — — U.S. large cap value 28.3 — 28.3 — 34.4 — 34.4 — U.S. large cap growth 28.6 — 28.6 — 34.9 — 34.9 — U.S. small cap value 6.7 — 6.7 — 7.2 — 7.2 — U.S. small cap growth 7.5 7.5 — — 7.6 7.6 — — International - developed markets 49.3 24.9 24.4 — 49.0 24.8 24.2 — International - emerging markets 19.5 19.5 — — 22.5 22.5 — — Global asset allocation securities 45.5 25.0 20.5 — 47.5 27.2 20.3 — Risk parity allocation securities 44.4 — 44.4 — 48.8 — 48.8 — Fixed income securities: Fixed income funds 134.5 — 134.5 — 144.1 0.1 144.0 — 422.6 $124.3 $298.3 $— 484.8 $147.5 $337.3 $— Accrued investment income 0.1 0.1 Due to brokers, net (pending trades with brokers) — (0.2 ) Total pension plan assets $422.7 $484.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.0 $— $10.0 $— $21.3 $— $21.3 $— Equity securities: U.S. large cap core 43.4 43.4 — — 59.3 59.3 — — U.S. large cap value 25.9 — 25.9 — 31.3 — 31.3 — U.S. large cap growth 26.2 — 26.2 — 31.7 — 31.7 — U.S. small cap value 6.1 — 6.1 — 6.6 — 6.6 — U.S. small cap growth 6.9 6.9 — — 6.9 6.9 — — International - developed markets 45.1 22.8 22.3 — 44.5 22.5 22.0 — International - emerging markets 17.8 17.8 — — 20.4 20.4 — — Global asset allocation securities 41.6 22.8 18.8 — 43.2 24.8 18.4 — Risk parity allocation securities 40.6 — 40.6 — 44.3 — 44.3 — Fixed income securities: Fixed income funds 123.1 — 123.1 — 130.9 0.1 130.8 — 386.7 $113.7 $273.0 $— 440.4 $134.0 $306.4 $— Accrued investment income 0.1 — Due to brokers, net (pending trades with brokers) — (0.1 ) Total pension plan assets $386.8 $440.3 At December 31, the fair values of Alliant Energy’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.6 $— $3.6 $— $3.7 $— $3.7 $— Equity securities: U.S. blend 21.1 21.1 — — 35.8 35.8 — — U.S. large cap core 0.9 0.9 — — 2.9 2.9 — — U.S. large cap value 0.5 — 0.5 — 1.5 — 1.5 — U.S. large cap growth 0.5 — 0.5 — 1.6 — 1.6 — U.S. small cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap growth 0.1 0.1 — — 0.4 0.4 — — International - blend 12.5 12.5 — — 14.2 14.2 — — International - developed markets 1.0 0.5 0.5 — 2.2 1.1 1.1 — International - emerging markets 0.4 0.4 — — 1.0 1.0 — — Global asset allocation securities 16.4 16.0 0.4 — 30.3 29.4 0.9 — Risk parity allocation securities 0.9 — 0.9 — 2.2 — 2.2 — Fixed income securities: Fixed income funds 48.9 46.3 2.6 — 25.5 19.0 6.5 — Total OPEB plan assets $106.9 $97.8 $9.1 $— $121.6 $103.8 $17.8 $— At December 31, the fair values of IPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.9 $— $0.9 $— $1.4 $— $1.4 $— Equity securities: U.S. blend 16.6 16.6 — — 27.2 27.2 — — U.S. large cap core 0.1 0.1 — — 0.5 0.5 — — U.S. large cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. large cap growth 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap value — — — — 0.1 — 0.1 — U.S. small cap growth — — — — 0.1 0.1 — — International - blend 10.7 10.7 — — 10.7 10.7 — — International - developed markets 0.1 0.1 — — 0.4 0.2 0.2 — International - emerging markets — — — — 0.2 0.2 — — Global asset allocation securities 6.9 6.9 — — 21.6 21.5 0.1 — Risk parity allocation securities 0.1 — 0.1 — 0.4 — 0.4 — Fixed income securities: Fixed income funds 33.6 33.3 0.3 — 15.5 14.3 1.2 — Total OPEB plan assets $69.2 $67.7 $1.5 $— $78.7 $74.7 $4.0 $— At December 31, the fair values of WPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.3 $— $2.3 $— $1.4 $— $1.4 $— Equity securities: U.S. blend — — — — 3.6 3.6 — — U.S. large cap core — — — — 1.6 1.6 — — U.S. large cap value — — — — 0.8 — 0.8 — U.S. large cap growth — — — — 0.8 — 0.8 — U.S. small cap value — — — — 0.2 — 0.2 — U.S. small cap growth — — — — 0.2 0.2 — — International - blend — — — — 1.4 1.4 — — International - developed markets — — — — 1.2 0.6 0.6 — International - emerging markets — — — — 0.5 0.5 — — Global asset allocation securities 5.4 5.4 — — 3.8 3.3 0.5 — Risk parity allocation securities — — — — 1.1 — 1.1 — Fixed income securities: Fixed income funds 11.0 11.0 — — 5.2 1.8 3.4 — Total OPEB plan assets $18.7 $16.4 $2.3 $— $21.8 $13.0 $8.8 $— 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, 2015 and 2014 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock represented 11.6% and 12.6% of total assets held in 401(k) savings plans at December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5 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 - 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, 2015 , performance shares and restricted stock were outstanding and 3.8 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 and restricted cash awards, to certain key employees. At December 31, 2015 , performance units and performance-contingent cash awards 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. 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): Alli
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, and/or through defined contribution plans (including 401(k) savings plans). Qualified and non-qualified non-contributory defined benefit pension plans are currently closed to new hires. 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. 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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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 as of December 31, 2014 and 2015 to utilize new mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015, respectively. 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement. 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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9 Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $1,301.5 $1,113.4 $231.1 $208.7 Service cost 15.9 13.1 5.5 5.2 Interest cost 53.6 54.1 9.1 9.5 Plan participants’ contributions — — 3.1 2.8 Plan amendments — — (0.3 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (70.1 ) 195.8 (9.4 ) 22.3 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Net benefit obligation at December 31 1,206.3 1,301.5 221.4 231.1 Change in plan assets: Fair value of plan assets at January 1 1,018.1 1,022.9 121.6 124.9 Actual return on plan assets (30.2 ) 66.4 (4.9 ) 5.6 Employer contributions 2.2 3.7 4.8 5.7 Plan participants’ contributions — — 3.1 2.8 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Fair value of plan assets at December 31 895.0 1,018.1 106.9 121.6 Under funded status at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $6.1 Other current liabilities (2.6 ) (2.5 ) (6.2 ) (5.6 ) Pension and other benefit obligations (308.7 ) (280.9 ) (111.3 ) (110.0 ) Net amounts recognized at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Amounts recognized in Regulatory Assets and AOCL consist of (a): Net actuarial loss $533.1 $533.4 $59.8 $60.7 Prior service credit (7.2 ) (7.4 ) (5.6 ) (16.7 ) $525.9 $526.0 $54.2 $44.0 (a) Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets. 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. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $603.1 $514.0 $96.4 $87.8 Service cost 8.8 7.2 2.4 2.4 Interest cost 25.0 25.1 3.8 3.9 Plan participants’ contributions — — 1.0 0.9 Plan amendments — — (0.1 ) — Actuarial (gain) loss (32.3 ) 91.4 (4.6 ) 8.6 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Net benefit obligation at December 31 556.1 603.1 91.3 96.4 Change in plan assets: Fair value of plan assets at January 1 484.7 485.9 78.7 81.2 Actual return on plan assets (14.3 ) 32.1 (3.1 ) 3.6 Employer contributions 0.8 1.3 0.2 0.2 Plan participants’ contributions — — 1.0 0.9 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Fair value of plan assets at December 31 422.7 484.7 69.2 78.7 Under funded status at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $— $1.2 Other current liabilities (0.8 ) (0.8 ) — — Pension and other benefit obligations (132.6 ) (117.6 ) (22.1 ) (18.9 ) Net amounts recognized at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $235.5 $233.1 $29.8 $27.9 Prior service credit (2.5 ) (2.6 ) (2.7 ) (8.7 ) $233.0 $230.5 $27.1 $19.2 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $547.6 $460.8 $94.0 $85.6 Service cost 5.8 4.9 2.1 2.0 Interest cost 22.6 22.6 3.7 3.8 Plan participants’ contributions — — 1.6 1.3 Plan amendments — — (0.2 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (30.0 ) 86.7 (3.5 ) 9.2 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Net benefit obligation at December 31 505.9 547.6 89.7 94.0 Change in plan assets: Fair value of plan assets at January 1 440.3 438.8 21.8 21.7 Actual return on plan assets (13.0 ) 28.6 (1.1 ) 1.2 Employer contributions 0.1 0.3 4.4 5.5 Plan participants’ contributions — — 1.6 1.3 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Fair value of plan assets at December 31 386.8 440.3 18.7 21.8 Under funded status at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $4.9 Other current liabilities (0.1 ) (0.1 ) (6.0 ) (5.5 ) Pension and other benefit obligations (119.0 ) (107.2 ) (68.0 ) (71.6 ) Net amounts recognized at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $232.1 $233.5 $23.3 $26.3 Prior service credit (1.2 ) (1.0 ) (2.4 ) (5.6 ) $230.9 $232.5 $20.9 $20.7 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets. 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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4 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, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32% 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, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47% Fair Value Measurements - The following tables report a framework for measuring fair value. The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Investments in securities held in registered investment companies and directly held equity securities are valued at the closing price reported in the active market in which the securities are traded. Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means. Investments in common/collective trusts are valued at the net asset value of shares held by the plans, which is based on the fair market value of the underlying investments in the common/collective trusts. Investments in corporate bonds 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. 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. The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while Alliant Energy, IPL and WPL believe their valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $23.1 $— $23.1 $— $49.3 $— $49.3 $— Equity securities: U.S. large cap core 100.4 100.4 — — 137.2 137.2 — — U.S. large cap value 59.9 — 59.9 — 72.2 — 72.2 — U.S. large cap growth 60.5 — 60.5 — 73.2 — 73.2 — U.S. small cap value 14.2 — 14.2 — 15.2 — 15.2 — U.S. small cap growth 16.0 16.0 — — 15.9 15.9 — — International - developed markets 104.4 52.7 51.7 — 102.9 52.1 50.8 — International - emerging markets 41.2 41.2 — — 47.2 47.2 — — Global asset allocation securities 96.3 52.9 43.4 — 99.9 57.2 42.7 — Risk parity allocation securities 94.0 — 94.0 — 102.5 — 102.5 — Fixed income securities: Corporate bonds — — — — 0.1 — 0.1 — Fixed income funds 284.8 — 284.8 — 302.7 0.2 302.5 — 894.8 $263.2 $631.6 $— 1,018.3 $309.8 $708.5 $— Accrued investment income 0.2 0.1 Due to brokers, net (pending trades with brokers) — (0.3 ) Total pension plan assets $895.0 $1,018.1 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.9 $— $10.9 $— $23.5 $— $23.5 $— Equity securities: U.S. large cap core 47.4 47.4 — — 65.3 65.3 — — U.S. large cap value 28.3 — 28.3 — 34.4 — 34.4 — U.S. large cap growth 28.6 — 28.6 — 34.9 — 34.9 — U.S. small cap value 6.7 — 6.7 — 7.2 — 7.2 — U.S. small cap growth 7.5 7.5 — — 7.6 7.6 — — International - developed markets 49.3 24.9 24.4 — 49.0 24.8 24.2 — International - emerging markets 19.5 19.5 — — 22.5 22.5 — — Global asset allocation securities 45.5 25.0 20.5 — 47.5 27.2 20.3 — Risk parity allocation securities 44.4 — 44.4 — 48.8 — 48.8 — Fixed income securities: Fixed income funds 134.5 — 134.5 — 144.1 0.1 144.0 — 422.6 $124.3 $298.3 $— 484.8 $147.5 $337.3 $— Accrued investment income 0.1 0.1 Due to brokers, net (pending trades with brokers) — (0.2 ) Total pension plan assets $422.7 $484.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.0 $— $10.0 $— $21.3 $— $21.3 $— Equity securities: U.S. large cap core 43.4 43.4 — — 59.3 59.3 — — U.S. large cap value 25.9 — 25.9 — 31.3 — 31.3 — U.S. large cap growth 26.2 — 26.2 — 31.7 — 31.7 — U.S. small cap value 6.1 — 6.1 — 6.6 — 6.6 — U.S. small cap growth 6.9 6.9 — — 6.9 6.9 — — International - developed markets 45.1 22.8 22.3 — 44.5 22.5 22.0 — International - emerging markets 17.8 17.8 — — 20.4 20.4 — — Global asset allocation securities 41.6 22.8 18.8 — 43.2 24.8 18.4 — Risk parity allocation securities 40.6 — 40.6 — 44.3 — 44.3 — Fixed income securities: Fixed income funds 123.1 — 123.1 — 130.9 0.1 130.8 — 386.7 $113.7 $273.0 $— 440.4 $134.0 $306.4 $— Accrued investment income 0.1 — Due to brokers, net (pending trades with brokers) — (0.1 ) Total pension plan assets $386.8 $440.3 At December 31, the fair values of Alliant Energy’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.6 $— $3.6 $— $3.7 $— $3.7 $— Equity securities: U.S. blend 21.1 21.1 — — 35.8 35.8 — — U.S. large cap core 0.9 0.9 — — 2.9 2.9 — — U.S. large cap value 0.5 — 0.5 — 1.5 — 1.5 — U.S. large cap growth 0.5 — 0.5 — 1.6 — 1.6 — U.S. small cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap growth 0.1 0.1 — — 0.4 0.4 — — International - blend 12.5 12.5 — — 14.2 14.2 — — International - developed markets 1.0 0.5 0.5 — 2.2 1.1 1.1 — International - emerging markets 0.4 0.4 — — 1.0 1.0 — — Global asset allocation securities 16.4 16.0 0.4 — 30.3 29.4 0.9 — Risk parity allocation securities 0.9 — 0.9 — 2.2 — 2.2 — Fixed income securities: Fixed income funds 48.9 46.3 2.6 — 25.5 19.0 6.5 — Total OPEB plan assets $106.9 $97.8 $9.1 $— $121.6 $103.8 $17.8 $— At December 31, the fair values of IPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.9 $— $0.9 $— $1.4 $— $1.4 $— Equity securities: U.S. blend 16.6 16.6 — — 27.2 27.2 — — U.S. large cap core 0.1 0.1 — — 0.5 0.5 — — U.S. large cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. large cap growth 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap value — — — — 0.1 — 0.1 — U.S. small cap growth — — — — 0.1 0.1 — — International - blend 10.7 10.7 — — 10.7 10.7 — — International - developed markets 0.1 0.1 — — 0.4 0.2 0.2 — International - emerging markets — — — — 0.2 0.2 — — Global asset allocation securities 6.9 6.9 — — 21.6 21.5 0.1 — Risk parity allocation securities 0.1 — 0.1 — 0.4 — 0.4 — Fixed income securities: Fixed income funds 33.6 33.3 0.3 — 15.5 14.3 1.2 — Total OPEB plan assets $69.2 $67.7 $1.5 $— $78.7 $74.7 $4.0 $— At December 31, the fair values of WPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.3 $— $2.3 $— $1.4 $— $1.4 $— Equity securities: U.S. blend — — — — 3.6 3.6 — — U.S. large cap core — — — — 1.6 1.6 — — U.S. large cap value — — — — 0.8 — 0.8 — U.S. large cap growth — — — — 0.8 — 0.8 — U.S. small cap value — — — — 0.2 — 0.2 — U.S. small cap growth — — — — 0.2 0.2 — — International - blend — — — — 1.4 1.4 — — International - developed markets — — — — 1.2 0.6 0.6 — International - emerging markets — — — — 0.5 0.5 — — Global asset allocation securities 5.4 5.4 — — 3.8 3.3 0.5 — Risk parity allocation securities — — — — 1.1 — 1.1 — Fixed income securities: Fixed income funds 11.0 11.0 — — 5.2 1.8 3.4 — Total OPEB plan assets $18.7 $16.4 $2.3 $— $21.8 $13.0 $8.8 $— 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, 2015 and 2014 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock represented 11.6% and 12.6% of total assets held in 401(k) savings plans at December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5 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 - 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, 2015 , performance shares and restricted stock were outstanding and 3.8 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 and restricted cash awards, to certain key employees. At December 31, 2015 , performance units and performance-contingent cash awards 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. 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): Alli
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, and/or through defined contribution plans (including 401(k) savings plans). Qualified and non-qualified non-contributory defined benefit pension plans are currently closed to new hires. 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. 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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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 as of December 31, 2014 and 2015 to utilize new mortality tables that were released in 2014 by the Society of Actuaries and updated in 2015, respectively. 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement. 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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9 Net periodic benefit costs are primarily included in “Other operation and maintenance” in the income statements. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $1,301.5 $1,113.4 $231.1 $208.7 Service cost 15.9 13.1 5.5 5.2 Interest cost 53.6 54.1 9.1 9.5 Plan participants’ contributions — — 3.1 2.8 Plan amendments — — (0.3 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (70.1 ) 195.8 (9.4 ) 22.3 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Net benefit obligation at December 31 1,206.3 1,301.5 221.4 231.1 Change in plan assets: Fair value of plan assets at January 1 1,018.1 1,022.9 121.6 124.9 Actual return on plan assets (30.2 ) 66.4 (4.9 ) 5.6 Employer contributions 2.2 3.7 4.8 5.7 Plan participants’ contributions — — 3.1 2.8 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Fair value of plan assets at December 31 895.0 1,018.1 106.9 121.6 Under funded status at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $6.1 Other current liabilities (2.6 ) (2.5 ) (6.2 ) (5.6 ) Pension and other benefit obligations (308.7 ) (280.9 ) (111.3 ) (110.0 ) Net amounts recognized at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Amounts recognized in Regulatory Assets and AOCL consist of (a): Net actuarial loss $533.1 $533.4 $59.8 $60.7 Prior service credit (7.2 ) (7.4 ) (5.6 ) (16.7 ) $525.9 $526.0 $54.2 $44.0 (a) Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets. 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. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $603.1 $514.0 $96.4 $87.8 Service cost 8.8 7.2 2.4 2.4 Interest cost 25.0 25.1 3.8 3.9 Plan participants’ contributions — — 1.0 0.9 Plan amendments — — (0.1 ) — Actuarial (gain) loss (32.3 ) 91.4 (4.6 ) 8.6 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Net benefit obligation at December 31 556.1 603.1 91.3 96.4 Change in plan assets: Fair value of plan assets at January 1 484.7 485.9 78.7 81.2 Actual return on plan assets (14.3 ) 32.1 (3.1 ) 3.6 Employer contributions 0.8 1.3 0.2 0.2 Plan participants’ contributions — — 1.0 0.9 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Fair value of plan assets at December 31 422.7 484.7 69.2 78.7 Under funded status at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $— $1.2 Other current liabilities (0.8 ) (0.8 ) — — Pension and other benefit obligations (132.6 ) (117.6 ) (22.1 ) (18.9 ) Net amounts recognized at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $235.5 $233.1 $29.8 $27.9 Prior service credit (2.5 ) (2.6 ) (2.7 ) (8.7 ) $233.0 $230.5 $27.1 $19.2 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets. 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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $547.6 $460.8 $94.0 $85.6 Service cost 5.8 4.9 2.1 2.0 Interest cost 22.6 22.6 3.7 3.8 Plan participants’ contributions — — 1.6 1.3 Plan amendments — — (0.2 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (30.0 ) 86.7 (3.5 ) 9.2 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Net benefit obligation at December 31 505.9 547.6 89.7 94.0 Change in plan assets: Fair value of plan assets at January 1 440.3 438.8 21.8 21.7 Actual return on plan assets (13.0 ) 28.6 (1.1 ) 1.2 Employer contributions 0.1 0.3 4.4 5.5 Plan participants’ contributions — — 1.6 1.3 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Fair value of plan assets at December 31 386.8 440.3 18.7 21.8 Under funded status at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $4.9 Other current liabilities (0.1 ) (0.1 ) (6.0 ) (5.5 ) Pension and other benefit obligations (119.0 ) (107.2 ) (68.0 ) (71.6 ) Net amounts recognized at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $232.1 $233.5 $23.3 $26.3 Prior service credit (1.2 ) (1.0 ) (2.4 ) (5.6 ) $230.9 $232.5 $20.9 $20.7 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets. 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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4 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, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32% 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, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47% Fair Value Measurements - The following tables report a framework for measuring fair value. The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Investments in securities held in registered investment companies and directly held equity securities are valued at the closing price reported in the active market in which the securities are traded. Level 2 - Pricing inputs are quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means. Investments in common/collective trusts are valued at the net asset value of shares held by the plans, which is based on the fair market value of the underlying investments in the common/collective trusts. Investments in corporate bonds 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. 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. The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while Alliant Energy, IPL and WPL believe their valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $23.1 $— $23.1 $— $49.3 $— $49.3 $— Equity securities: U.S. large cap core 100.4 100.4 — — 137.2 137.2 — — U.S. large cap value 59.9 — 59.9 — 72.2 — 72.2 — U.S. large cap growth 60.5 — 60.5 — 73.2 — 73.2 — U.S. small cap value 14.2 — 14.2 — 15.2 — 15.2 — U.S. small cap growth 16.0 16.0 — — 15.9 15.9 — — International - developed markets 104.4 52.7 51.7 — 102.9 52.1 50.8 — International - emerging markets 41.2 41.2 — — 47.2 47.2 — — Global asset allocation securities 96.3 52.9 43.4 — 99.9 57.2 42.7 — Risk parity allocation securities 94.0 — 94.0 — 102.5 — 102.5 — Fixed income securities: Corporate bonds — — — — 0.1 — 0.1 — Fixed income funds 284.8 — 284.8 — 302.7 0.2 302.5 — 894.8 $263.2 $631.6 $— 1,018.3 $309.8 $708.5 $— Accrued investment income 0.2 0.1 Due to brokers, net (pending trades with brokers) — (0.3 ) Total pension plan assets $895.0 $1,018.1 At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.9 $— $10.9 $— $23.5 $— $23.5 $— Equity securities: U.S. large cap core 47.4 47.4 — — 65.3 65.3 — — U.S. large cap value 28.3 — 28.3 — 34.4 — 34.4 — U.S. large cap growth 28.6 — 28.6 — 34.9 — 34.9 — U.S. small cap value 6.7 — 6.7 — 7.2 — 7.2 — U.S. small cap growth 7.5 7.5 — — 7.6 7.6 — — International - developed markets 49.3 24.9 24.4 — 49.0 24.8 24.2 — International - emerging markets 19.5 19.5 — — 22.5 22.5 — — Global asset allocation securities 45.5 25.0 20.5 — 47.5 27.2 20.3 — Risk parity allocation securities 44.4 — 44.4 — 48.8 — 48.8 — Fixed income securities: Fixed income funds 134.5 — 134.5 — 144.1 0.1 144.0 — 422.6 $124.3 $298.3 $— 484.8 $147.5 $337.3 $— Accrued investment income 0.1 0.1 Due to brokers, net (pending trades with brokers) — (0.2 ) Total pension plan assets $422.7 $484.7 At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.0 $— $10.0 $— $21.3 $— $21.3 $— Equity securities: U.S. large cap core 43.4 43.4 — — 59.3 59.3 — — U.S. large cap value 25.9 — 25.9 — 31.3 — 31.3 — U.S. large cap growth 26.2 — 26.2 — 31.7 — 31.7 — U.S. small cap value 6.1 — 6.1 — 6.6 — 6.6 — U.S. small cap growth 6.9 6.9 — — 6.9 6.9 — — International - developed markets 45.1 22.8 22.3 — 44.5 22.5 22.0 — International - emerging markets 17.8 17.8 — — 20.4 20.4 — — Global asset allocation securities 41.6 22.8 18.8 — 43.2 24.8 18.4 — Risk parity allocation securities 40.6 — 40.6 — 44.3 — 44.3 — Fixed income securities: Fixed income funds 123.1 — 123.1 — 130.9 0.1 130.8 — 386.7 $113.7 $273.0 $— 440.4 $134.0 $306.4 $— Accrued investment income 0.1 — Due to brokers, net (pending trades with brokers) — (0.1 ) Total pension plan assets $386.8 $440.3 At December 31, the fair values of Alliant Energy’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.6 $— $3.6 $— $3.7 $— $3.7 $— Equity securities: U.S. blend 21.1 21.1 — — 35.8 35.8 — — U.S. large cap core 0.9 0.9 — — 2.9 2.9 — — U.S. large cap value 0.5 — 0.5 — 1.5 — 1.5 — U.S. large cap growth 0.5 — 0.5 — 1.6 — 1.6 — U.S. small cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap growth 0.1 0.1 — — 0.4 0.4 — — International - blend 12.5 12.5 — — 14.2 14.2 — — International - developed markets 1.0 0.5 0.5 — 2.2 1.1 1.1 — International - emerging markets 0.4 0.4 — — 1.0 1.0 — — Global asset allocation securities 16.4 16.0 0.4 — 30.3 29.4 0.9 — Risk parity allocation securities 0.9 — 0.9 — 2.2 — 2.2 — Fixed income securities: Fixed income funds 48.9 46.3 2.6 — 25.5 19.0 6.5 — Total OPEB plan assets $106.9 $97.8 $9.1 $— $121.6 $103.8 $17.8 $— At December 31, the fair values of IPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.9 $— $0.9 $— $1.4 $— $1.4 $— Equity securities: U.S. blend 16.6 16.6 — — 27.2 27.2 — — U.S. large cap core 0.1 0.1 — — 0.5 0.5 — — U.S. large cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. large cap growth 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap value — — — — 0.1 — 0.1 — U.S. small cap growth — — — — 0.1 0.1 — — International - blend 10.7 10.7 — — 10.7 10.7 — — International - developed markets 0.1 0.1 — — 0.4 0.2 0.2 — International - emerging markets — — — — 0.2 0.2 — — Global asset allocation securities 6.9 6.9 — — 21.6 21.5 0.1 — Risk parity allocation securities 0.1 — 0.1 — 0.4 — 0.4 — Fixed income securities: Fixed income funds 33.6 33.3 0.3 — 15.5 14.3 1.2 — Total OPEB plan assets $69.2 $67.7 $1.5 $— $78.7 $74.7 $4.0 $— At December 31, the fair values of WPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.3 $— $2.3 $— $1.4 $— $1.4 $— Equity securities: U.S. blend — — — — 3.6 3.6 — — U.S. large cap core — — — — 1.6 1.6 — — U.S. large cap value — — — — 0.8 — 0.8 — U.S. large cap growth — — — — 0.8 — 0.8 — U.S. small cap value — — — — 0.2 — 0.2 — U.S. small cap growth — — — — 0.2 0.2 — — International - blend — — — — 1.4 1.4 — — International - developed markets — — — — 1.2 0.6 0.6 — International - emerging markets — — — — 0.5 0.5 — — Global asset allocation securities 5.4 5.4 — — 3.8 3.3 0.5 — Risk parity allocation securities — — — — 1.1 — 1.1 — Fixed income securities: Fixed income funds 11.0 11.0 — — 5.2 1.8 3.4 — Total OPEB plan assets $18.7 $16.4 $2.3 $— $21.8 $13.0 $8.8 $— 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, 2015 and 2014 . 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock represented 11.6% and 12.6% of total assets held in 401(k) savings plans at December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5 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 - 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, 2015 , performance shares and restricted stock were outstanding and 3.8 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 and restricted cash awards, to certain key employees. At December 31, 2015 , performance units and performance-contingent cash awards 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. 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): Alli

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2015
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 projects, 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 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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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 projects, 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 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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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 projects, 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 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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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, 2015
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock. 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. At each reporting date, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments. 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. At each reporting date, Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. 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 periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 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. 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. 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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock. 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. At each reporting date, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments. 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. At each reporting date, Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. 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 periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 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. 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. 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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Valuation Hierarchy - Fair value measurement accounting establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of the fair value hierarchy and examples of each are as follows: Level 1 - Pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. At each reporting date, Level 1 items included IPL’s 5.1% cumulative preferred stock. 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. At each reporting date, Level 2 items included certain non-exchange traded commodity contracts and substantially all of the long-term debt instruments. 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. At each reporting date, Level 3 items included FTRs, certain non-exchange traded commodity contracts and IPL’s deferred proceeds. 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 periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Risk policies are maintained that govern the use of such derivative instruments. Derivative instruments were not designated as hedging instruments and included the following: Risk management purpose Type of instrument Mitigate pricing volatility for: Electricity purchased to supply customers Electric swap and physical forward contracts (IPL and WPL) Fuel used to supply natural gas-fired EGUs Natural gas swap and physical forward contracts (IPL and WPL) Natural gas supplied to retail customers Natural gas options and physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Fuel used at coal-fired EGUs Coal physical forward contracts (IPL and WPL) Optimize the value of natural gas pipeline capacity Natural gas physical forward contracts (IPL and WPL) Natural gas swap contracts (IPL) Manage transmission congestion costs FTRs (IPL and WPL) Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using monthly or annual auction shadow prices from relevant auctions and were categorized as Level 3. Refer to Note 15 for additional details of derivative assets and derivative liabilities. The fair value measurements of Level 3 derivative instruments include observable and unobservable inputs. The observable inputs are obtained from third-party pricing sources, counterparties and brokers and include bids, offers, historical transactions (including historical price differences between locations with both observable and unobservable prices) and executed trades. The significant unobservable inputs used in the fair value measurement of commodity contracts are forecasted electricity, natural gas and coal prices, and the expected volatility of such prices. Significant changes in any of those inputs would result in a significantly lower or higher fair value measurement. Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 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. 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. 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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9 Unrealized gains and losses from derivative instruments are generally recorded with offsets to regulatory assets or regulatory liabilities, based on fuel and natural gas cost recovery mechanisms, as well as other specific regulatory authorizations. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities resulted in comparable changes to regulatory assets, and the changes in the fair value of derivative assets resulted in comparable changes to regulatory liabilities. Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2015
Derivative [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Purpose - Derivative instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices and transmission congestion costs. Refer to Note 14 for detailed discussion of derivative instruments. Notional Amounts - As of December 31, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018 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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 14 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, 2015 and 2014 , 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, 2015 and 2014 . 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 periodically 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, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018 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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 14 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, 2015 and 2014 , 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, 2015 and 2014 . 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 periodically 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, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018 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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4 Unrealized gains and losses from commodity derivative instruments were recorded with offsets to regulatory assets or regulatory liabilities on the balance sheets. Refer to Notes 2 and 14 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, 2015 and 2014 , 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, 2015 and 2014 . 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, 2015
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 generation maintenance and performance improvements for Marshalltown Combustion Turbine Units 1-3. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, 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, 2015 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $23 million , $7 million and $16 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, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 . 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. On February 12, 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. Plaintiffs have 30 days to seek an appeal of this decision. 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. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The contractual warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016. Limited warranties may be extended in certain cases for warranty work performed. Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of December 31, 2015 , Alliant Energy had $123 million of performance guarantees outstanding with $48 million and $75 million currently expected to expire in 2016 and 2017 , respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects. Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of December 31, 2015 . 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 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. Resources, as the successor to a predecessor entity that owned Whiting Petroleum, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of December 31, 2015 , the present value of the abandonment obligations is estimated at $28 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Resources will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2015 . 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, 2015 . 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 environmental liabilities. At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9 MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 24 and 5 sites, respectively. 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. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2 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 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA. In 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In 2013, the Consent Decree was approved by the Western Wisconsin Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following environmental controls systems: • SCR system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012); • Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014); • Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and • SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 consistent with the Consent Decree. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. In addition, WPL will complete approximately $7 million in environmental mitigation projects. Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. IPL Consent Decree - In July 2015, IPL entered into a Consent Decree with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa to resolve potential claims regarding CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa, while admitting no liability. In September 2015, the Consent Decree was approved by the Northern Iowa Court, thereby resolving all potential claims against IPL. Under the Consent Decree, IPL is required to install the following environmental controls systems: • Scrubber and baghouse at the Ottumwa Generating Station by December 31, 2015 (placed in service in 2014); • Scrubber and baghouse at the Lansing Generating Station by December 31, 2016 (scrubber was placed in service in June 2015 and baghouse was placed in service in 2010); and • SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019. IPL is also required to fuel switch or retire the following EGUs: • M.L. Kapp Generating Station by August 31, 2015 (switched the fuel type from coal to natural gas in June 2015); • Prairie Creek Unit 4 by June 1, 2018; • Burlington Generating Station by December 31, 2021; and • Prairie Creek Units 1 and 3 by December 31, 2025. In addition, IPL is required to either install combined cycle technology at, or retire, the Dubuque and Sutherland Generation Stations by June 1, 2019. IPL previously switched the fuel type from coal to natural gas at these EGUs. 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. Pursuant to the Consent Decree, IPL paid a civil penalty of $1 million in 2015 and will complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover all material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Alliant Energy and IPL currently do not expect to recover costs related to the civil penalty 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 are included below, along with a brief description of these environmental rules. Air Quality - CSAPR is an emissions trading program that requires SO2 and NOx emissions reductions at certain IPL and WPL fossil-fueled EGUs through installation of environmental controls and/or purchases of allowances. Compliance with emission limits began in 2015, with additional emission limits reductions beginning in 2017. Alliant Energy, IPL and WPL are currently in compliance with the Phase I CSAPR emission limits. Ozone NAAQS Rule may require NOx emission reductions in certain non-attainment areas designated by the EPA. The EPA’s final designations of non-attainment areas for this rule are currently expected to be issued by October 2017. Compliance deadlines range from 2020 through 2037 depending on the level of ozone monitored in non-attainment areas. Sheboygan County in Wisconsin is currently the only non-attainment area in Alliant Energy’s service territory. WPL operates Edgewater and Sheboygan Falls in Sheboygan County, Wisconsin. Clean Air Act Section 111(d) establishes standards under Section 111(d) of the CAA, otherwise referred to as the Clean Power Plan, for states to follow in developing plans to reduce CO2 emissions from existing fossil-fueled EGUs. The standards include an interim compliance period from 2022 through 2029 and a final compliance requirement beginning in 2030. In February 2016, the Supreme Court issued a stay of the Clean Power Plan until pending legal challenges are resolved, which places implementation of the final standards on hold indefinitely. Clean Air Act Section 111(b) establishes standards under Section 111(b) of the CAA for CO2 emissions limits for certain new fossil-fueled EGUs. Marshalltown and WPL’s proposed Riverside expansion are expected to be impacted by these standards. Marshalltown is being constructed, and WPL’s proposed Riverside expansion is being designed, to achieve compliance with these standards. Water Quality - Section 316(b) of the Federal Clean Water Act regulates cooling water intake structures and minimizes adverse environmental impacts to fish and other aquatic life. Compliance will be incorporated during periodic facility permit renewal cycles, with final compliance anticipated by 2022. Effluent Limitation Guidelines require changes to discharge limits for wastewater from steam generating facilities. Compliance for existing steam generating facilities will be required after November 1, 2018 but before December 31, 2023, depending on each facility’s wastewater permit renewal cycle, and immediately upon operation for new steam generating facilities constructed after January 2016. Hydroelectric Fish Passage Device - WPL is currently required to install an agency-approved fish passage device at its Prairie du Sac hydro plant by December 31, 2020. Land and Solid Waste - CCR Rule establishes minimum criteria for disposing of CCR in landfills and surface impoundments (ash ponds), and allows for continued operation of ash ponds if they meet certain performance criteria. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in the Midwest region of the U.S. 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. IPL and WPL are typically net buyers of commodities (primarily electricity, coal and natural gas) required to provide regulated electricity and natural gas services to their customers. As a result, IPL and WPL are also subject to credit risk related to their counterparties’ failures to deliver commodities 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 commodity agreements that require credit support from counterparties that exceed certain exposure limits, 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. IPL has a PPA that grants it rights to purchase capacity and the resulting energy from DAEC through December 31, 2025. This PPA exposes Alliant Energy and IPL to risk of counterparty non-performance. However, financial risk is mitigated by IPL’s fuel-related cost recovery mechanisms. Refer to Note 16(b) for further discussion of the DAEC PPA. Based on these credit policies, counterparty diversification and 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.
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 generation maintenance and performance improvements for Marshalltown Combustion Turbine Units 1-3. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, 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, 2015 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $23 million , $7 million and $16 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, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 . 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. On February 12, 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. Plaintiffs have 30 days to seek an appeal of this decision. 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. The indemnification obligations either cease to exist when the statute of limitation for such claims is met or, in the case of RMT’s projects, when the warranty period under the agreements expires. The contractual warranty periods for RMT’s projects generally range from 12 to 60 months with the latest expiring in 2016. Limited warranties may be extended in certain cases for warranty work performed. Alliant Energy also continues to guarantee RMT’s performance obligations related to certain of RMT’s projects that were commenced prior to Alliant Energy’s sale of RMT. As of December 31, 2015 , Alliant Energy had $123 million of performance guarantees outstanding with $48 million and $75 million currently expected to expire in 2016 and 2017 , respectively. The expiration of these performance guarantees may be extended depending on when all valid warranty claims are resolved for the respective projects. Although Alliant Energy has received warranty claims related to certain of these projects, it does not currently believe that material losses are both probable and reasonably estimated, and therefore, has not recognized any material liabilities related to these matters as of December 31, 2015 . 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 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. Resources, as the successor to a predecessor entity that owned Whiting Petroleum, continues to guarantee the partnership obligations of an affiliate of Whiting Petroleum under general partnership agreements in the oil and gas industry, including with respect to the future abandonment of certain platforms off the coast of California and related onshore plant and equipment owned by the partnerships. The guarantees do not include a maximum limit. As of December 31, 2015 , the present value of the abandonment obligations is estimated at $28 million . Alliant Energy is not aware of any material liabilities related to these guarantees of which it is probable that Resources will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2015 . 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, 2015 . 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 environmental liabilities. At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9 MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 24 and 5 sites, respectively. 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. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2 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 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA. In 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In 2013, the Consent Decree was approved by the Western Wisconsin Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following environmental controls systems: • SCR system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012); • Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014); • Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and • SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 consistent with the Consent Decree. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. In addition, WPL will complete approximately $7 million in environmental mitigation projects. Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. IPL Consent Decree - In July 2015, IPL entered into a Consent Decree with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa to resolve potential claims regarding CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa, while admitting no liability. In September 2015, the Consent Decree was approved by the Northern Iowa Court, thereby resolving all potential claims against IPL. Under the Consent Decree, IPL is required to install the following environmental controls systems: • Scrubber and baghouse at the Ottumwa Generating Station by December 31, 2015 (placed in service in 2014); • Scrubber and baghouse at the Lansing Generating Station by December 31, 2016 (scrubber was placed in service in June 2015 and baghouse was placed in service in 2010); and • SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019. IPL is also required to fuel switch or retire the following EGUs: • M.L. Kapp Generating Station by August 31, 2015 (switched the fuel type from coal to natural gas in June 2015); • Prairie Creek Unit 4 by June 1, 2018; • Burlington Generating Station by December 31, 2021; and • Prairie Creek Units 1 and 3 by December 31, 2025. In addition, IPL is required to either install combined cycle technology at, or retire, the Dubuque and Sutherland Generation Stations by June 1, 2019. IPL previously switched the fuel type from coal to natural gas at these EGUs. 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. Pursuant to the Consent Decree, IPL paid a civil penalty of $1 million in 2015 and will complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover all material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Alliant Energy and IPL currently do not expect to recover costs related to the civil penalty 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 are included below, along with a brief description of these environmental rules. Air Quality - CSAPR is an emissions trading program that requires SO2 and NOx emissions reductions at certain IPL and WPL fossil-fueled EGUs through installation of environmental controls and/or purchases of allowances. Compliance with emission limits began in 2015, with additional emission limits reductions beginning in 2017. Alliant Energy, IPL and WPL are currently in compliance with the Phase I CSAPR emission limits. Ozone NAAQS Rule may require NOx emission reductions in certain non-attainment areas designated by the EPA. The EPA’s final designations of non-attainment areas for this rule are currently expected to be issued by October 2017. Compliance deadlines range from 2020 through 2037 depending on the level of ozone monitored in non-attainment areas. Sheboygan County in Wisconsin is currently the only non-attainment area in Alliant Energy’s service territory. WPL operates Edgewater and Sheboygan Falls in Sheboygan County, Wisconsin. Clean Air Act Section 111(d) establishes standards under Section 111(d) of the CAA, otherwise referred to as the Clean Power Plan, for states to follow in developing plans to reduce CO2 emissions from existing fossil-fueled EGUs. The standards include an interim compliance period from 2022 through 2029 and a final compliance requirement beginning in 2030. In February 2016, the Supreme Court issued a stay of the Clean Power Plan until pending legal challenges are resolved, which places implementation of the final standards on hold indefinitely. Clean Air Act Section 111(b) establishes standards under Section 111(b) of the CAA for CO2 emissions limits for certain new fossil-fueled EGUs. Marshalltown and WPL’s proposed Riverside expansion are expected to be impacted by these standards. Marshalltown is being constructed, and WPL’s proposed Riverside expansion is being designed, to achieve compliance with these standards. Water Quality - Section 316(b) of the Federal Clean Water Act regulates cooling water intake structures and minimizes adverse environmental impacts to fish and other aquatic life. Compliance will be incorporated during periodic facility permit renewal cycles, with final compliance anticipated by 2022. Effluent Limitation Guidelines require changes to discharge limits for wastewater from steam generating facilities. Compliance for existing steam generating facilities will be required after November 1, 2018 but before December 31, 2023, depending on each facility’s wastewater permit renewal cycle, and immediately upon operation for new steam generating facilities constructed after January 2016. Hydroelectric Fish Passage Device - WPL is currently required to install an agency-approved fish passage device at its Prairie du Sac hydro plant by December 31, 2020. Land and Solid Waste - CCR Rule establishes minimum criteria for disposing of CCR in landfills and surface impoundments (ash ponds), and allows for continued operation of ash ponds if they meet certain performance criteria. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in the Midwest region of the U.S. 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. IPL and WPL are typically net buyers of commodities (primarily electricity, coal and natural gas) required to provide regulated electricity and natural gas services to their customers. As a result, IPL and WPL are also subject to credit risk related to their counterparties’ failures to deliver commodities 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 commodity agreements that require credit support from counterparties that exceed certain exposure limits, 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. IPL has a PPA that grants it rights to purchase capacity and the resulting energy from DAEC through December 31, 2025. This PPA exposes Alliant Energy and IPL to risk of counterparty non-performance. However, financial risk is mitigated by IPL’s fuel-related cost recovery mechanisms. Refer to Note 16(b) for further discussion of the DAEC PPA. Based on these credit policies, counterparty diversification and 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.
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 generation maintenance and performance improvements for Marshalltown Combustion Turbine Units 1-3. WPL’s projects include the installation of a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions, 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, 2015 , Alliant Energy’s, IPL’s and WPL’s minimum future commitments related to certain contractual obligations for these projects were $23 million , $7 million and $16 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, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 . 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. On February 12, 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. Plaintiffs have 30 days to seek an appeal of this decision. 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 environmental liabilities. At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9 MGP Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. IPL and WPL are currently monitoring and/or remediating 24 and 5 sites, respectively. 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. The amounts recognized as liabilities are reduced for expenditures incurred and are adjusted as further information develops or circumstances change. Costs of future expenditures for environmental remediation obligations are not discounted. At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2 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 2009, the EPA sent a notice of violation to WPL as an owner and the operator of Edgewater, Nelson Dewey and Columbia alleging that the owners of such EGUs failed to comply with appropriate pre-construction review and permitting requirements and as a result violated the PSD program requirements, Title V Operating Permit requirements of the CAA and the Wisconsin SIP. In 2010, the Sierra Club filed complaints against WPL, as owner and operator of Nelson Dewey and Columbia, and separately as owner and operator of Edgewater, based on allegations that modifications were made at the facilities without complying with the PSD program requirements, Title V Operating Permit requirements of the CAA and state regulatory counterparts contained within the Wisconsin SIP designed to implement the CAA. In 2013, WPL, along with the other owners of Edgewater and Columbia, entered into a Consent Decree with the EPA and the Sierra Club to resolve the claims relating to Edgewater, Columbia and Nelson Dewey, while admitting no liability. In 2013, the Consent Decree was approved by the Western Wisconsin Court, thereby resolving all claims against WPL. Under the Consent Decree, WPL is required to install the following environmental controls systems: • SCR system at Edgewater Unit 5 by May 1, 2013 (placed in service in 2012); • Scrubbers and baghouses at Columbia Units 1 and 2 by December 31, 2014 (placed in service in 2014); • Scrubber and baghouse at Edgewater Unit 5 by December 31, 2016; and • SCR system at Columbia Unit 2 by December 31, 2018. WPL is also required to fuel switch or retire Edgewater Unit 4 by December 31, 2018. In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 consistent with the Consent Decree. In addition, the Consent Decree establishes emission rate limits for SO2, NOx and particulate matter for Columbia Units 1 and 2, Nelson Dewey Units 1 and 2, and Edgewater Units 4 and 5. The Consent Decree also includes annual plant-wide emission caps for SO2 and NOx for Columbia, Edgewater and Nelson Dewey. In addition, WPL will complete approximately $7 million in environmental mitigation projects. Final recovery of the costs expected to be incurred related to the Consent Decree will be decided by the PSCW in future rate cases or other proceedings. Alliant Energy and WPL currently expect to recover any material costs incurred by WPL related to compliance with the terms of the Consent Decree from WPL’s electric customers. IPL Consent Decree - In July 2015, IPL entered into a Consent Decree with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa to resolve potential claims regarding CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa, while admitting no liability. In September 2015, the Consent Decree was approved by the Northern Iowa Court, thereby resolving all potential claims against IPL. Under the Consent Decree, IPL is required to install the following environmental controls systems: • Scrubber and baghouse at the Ottumwa Generating Station by December 31, 2015 (placed in service in 2014); • Scrubber and baghouse at the Lansing Generating Station by December 31, 2016 (scrubber was placed in service in June 2015 and baghouse was placed in service in 2010); and • SCR system or equivalent NOx reduction system at the Ottumwa Generating Station by December 31, 2019. IPL is also required to fuel switch or retire the following EGUs: • M.L. Kapp Generating Station by August 31, 2015 (switched the fuel type from coal to natural gas in June 2015); • Prairie Creek Unit 4 by June 1, 2018; • Burlington Generating Station by December 31, 2021; and • Prairie Creek Units 1 and 3 by December 31, 2025. In addition, IPL is required to either install combined cycle technology at, or retire, the Dubuque and Sutherland Generation Stations by June 1, 2019. IPL previously switched the fuel type from coal to natural gas at these EGUs. 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. Pursuant to the Consent Decree, IPL paid a civil penalty of $1 million in 2015 and will complete approximately $6 million in environmental mitigation projects. Alliant Energy and IPL currently expect to recover all material costs incurred by IPL related to the environmental control systems and environmental mitigation projects from IPL’s electric customers. The recovery of such costs will be decided by IPL’s regulators in future rate cases or other proceedings. Alliant Energy and IPL currently do not expect to recover costs related to the civil penalty 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 are included below, along with a brief description of these environmental rules. Air Quality - CSAPR is an emissions trading program that requires SO2 and NOx emissions reductions at certain IPL and WPL fossil-fueled EGUs through installation of environmental controls and/or purchases of allowances. Compliance with emission limits began in 2015, with additional emission limits reductions beginning in 2017. Alliant Energy, IPL and WPL are currently in compliance with the Phase I CSAPR emission limits. Ozone NAAQS Rule may require NOx emission reductions in certain non-attainment areas designated by the EPA. The EPA’s final designations of non-attainment areas for this rule are currently expected to be issued by October 2017. Compliance deadlines range from 2020 through 2037 depending on the level of ozone monitored in non-attainment areas. Sheboygan County in Wisconsin is currently the only non-attainment area in Alliant Energy’s service territory. WPL operates Edgewater and Sheboygan Falls in Sheboygan County, Wisconsin. Clean Air Act Section 111(d) establishes standards under Section 111(d) of the CAA, otherwise referred to as the Clean Power Plan, for states to follow in developing plans to reduce CO2 emissions from existing fossil-fueled EGUs. The standards include an interim compliance period from 2022 through 2029 and a final compliance requirement beginning in 2030. In February 2016, the Supreme Court issued a stay of the Clean Power Plan until pending legal challenges are resolved, which places implementation of the final standards on hold indefinitely. Clean Air Act Section 111(b) establishes standards under Section 111(b) of the CAA for CO2 emissions limits for certain new fossil-fueled EGUs. Marshalltown and WPL’s proposed Riverside expansion are expected to be impacted by these standards. Marshalltown is being constructed, and WPL’s proposed Riverside expansion is being designed, to achieve compliance with these standards. Water Quality - Section 316(b) of the Federal Clean Water Act regulates cooling water intake structures and minimizes adverse environmental impacts to fish and other aquatic life. Compliance will be incorporated during periodic facility permit renewal cycles, with final compliance anticipated by 2022. Effluent Limitation Guidelines require changes to discharge limits for wastewater from steam generating facilities. Compliance for existing steam generating facilities will be required after November 1, 2018 but before December 31, 2023, depending on each facility’s wastewater permit renewal cycle, and immediately upon operation for new steam generating facilities constructed after January 2016. Hydroelectric Fish Passage Device - WPL is currently required to install an agency-approved fish passage device at its Prairie du Sac hydro plant by December 31, 2020. Land and Solid Waste - CCR Rule establishes minimum criteria for disposing of CCR in landfills and surface impoundments (ash ponds), and allows for continued operation of ash ponds if they meet certain performance criteria. (f) Credit Risk - IPL and WPL provide regulated electricity and natural gas services to residential, commercial, industrial and wholesale customers in the Midwest region of the U.S. 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. IPL and WPL are typically net buyers of commodities (primarily electricity, coal and natural gas) required to provide regulated electricity and natural gas services to their customers. As a result, IPL and WPL are also subject to credit risk related to their counterparties’ failures to deliver commodities 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 commodity agreements that require credit support from counterparties that exceed certain exposure limits, 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. IPL has a PPA that grants it rights to purchase capacity and the resulting energy from DAEC through December 31, 2025. This PPA exposes Alliant Energy and IPL to risk of counterparty non-performance. However, financial risk is mitigated by IPL’s fuel-related cost recovery mechanisms. Refer to Note 16(b) for further discussion of the DAEC PPA. Based on these credit policies, counterparty diversification and 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.

Segments Of Business

Segments Of Business	12 Months Ended
	Dec. 31, 2015
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2015 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; 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 Resources and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. Resources’ 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. Certain financial information relating to Alliant Energy’s business segments, services and geographic information was as follows (in millions): 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 Utility Non-Regulated, Alliant Energy 2013 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,689.0 $464.8 $71.3 $3,225.1 $51.7 $3,276.8 Depreciation and amortization 333.0 28.8 1.5 363.3 7.6 370.9 Operating income 444.5 57.3 6.3 508.1 25.8 533.9 Interest expense 166.3 6.5 172.8 Equity income from unconsolidated investments, net (43.7 ) — — (43.7 ) — (43.7 ) Income taxes 49.3 4.6 53.9 Net income attributable to Alliant Energy common shareowners 349.5 8.8 358.3 Total assets 9,018.6 859.3 712.2 10,590.1 502.4 11,092.5 Investments in equity method subsidiaries 279.1 — — 279.1 2.3 281.4 Construction and acquisition expenditures 677.3 47.0 7.3 731.6 66.7 798.3 Services - Alliant Energy’s consolidated operating revenues by segment, which were substantially all related to services, were as follows: 2015 2014 2013 Utility electric operations 85 % 81 % 82 % Utility gas operations 12 % 15 % 14 % Utility other 2 % 2 % 2 % Other 1 % 2 % 2 % 100 % 100 % 100 % Geographic Information - At December 31, 2015 , 2014 and 2013 , Alliant Energy, IPL and WPL did not have any long-lived assets to be held and used in foreign countries. 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. Certain financial information relating to IPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,491.8 $273.9 $53.1 $1,818.8 Depreciation and amortization 173.1 16.5 1.5 191.1 Operating income 173.1 29.8 9.1 212.0 Interest expense 81.3 Income tax benefit (36.3 ) Earnings available for common stock 172.0 Total assets 4,905.3 518.8 369.8 5,793.9 Construction and acquisition expenditures 365.4 27.5 7.3 400.2 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. Certain financial information relating to WPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,197.2 $190.9 $18.2 $1,406.3 Depreciation and amortization 159.9 12.3 — 172.2 Operating income (loss) 271.4 27.5 (2.8 ) 296.1 Interest expense 85.0 Equity income from unconsolidated investments (43.7 ) — — (43.7 ) Income taxes 85.6 Earnings available for common stock 177.5 Total assets 4,113.3 340.5 342.4 4,796.2 Investments in equity method subsidiaries 279.1 — — 279.1 Construction and acquisition expenditures 311.9 19.5 — 331.4
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2015 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; 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 Resources and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. Resources’ 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. Certain financial information relating to Alliant Energy’s business segments, services and geographic information was as follows (in millions): 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 Utility Non-Regulated, Alliant Energy 2013 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,689.0 $464.8 $71.3 $3,225.1 $51.7 $3,276.8 Depreciation and amortization 333.0 28.8 1.5 363.3 7.6 370.9 Operating income 444.5 57.3 6.3 508.1 25.8 533.9 Interest expense 166.3 6.5 172.8 Equity income from unconsolidated investments, net (43.7 ) — — (43.7 ) — (43.7 ) Income taxes 49.3 4.6 53.9 Net income attributable to Alliant Energy common shareowners 349.5 8.8 358.3 Total assets 9,018.6 859.3 712.2 10,590.1 502.4 11,092.5 Investments in equity method subsidiaries 279.1 — — 279.1 2.3 281.4 Construction and acquisition expenditures 677.3 47.0 7.3 731.6 66.7 798.3 Services - Alliant Energy’s consolidated operating revenues by segment, which were substantially all related to services, were as follows: 2015 2014 2013 Utility electric operations 85 % 81 % 82 % Utility gas operations 12 % 15 % 14 % Utility other 2 % 2 % 2 % Other 1 % 2 % 2 % 100 % 100 % 100 % Geographic Information - At December 31, 2015 , 2014 and 2013 , Alliant Energy, IPL and WPL did not have any long-lived assets to be held and used in foreign countries. 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. Certain financial information relating to IPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,491.8 $273.9 $53.1 $1,818.8 Depreciation and amortization 173.1 16.5 1.5 191.1 Operating income 173.1 29.8 9.1 212.0 Interest expense 81.3 Income tax benefit (36.3 ) Earnings available for common stock 172.0 Total assets 4,905.3 518.8 369.8 5,793.9 Construction and acquisition expenditures 365.4 27.5 7.3 400.2 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. Certain financial information relating to WPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,197.2 $190.9 $18.2 $1,406.3 Depreciation and amortization 159.9 12.3 — 172.2 Operating income (loss) 271.4 27.5 (2.8 ) 296.1 Interest expense 85.0 Equity income from unconsolidated investments (43.7 ) — — (43.7 ) Income taxes 85.6 Earnings available for common stock 177.5 Total assets 4,113.3 340.5 342.4 4,796.2 Investments in equity method subsidiaries 279.1 — — 279.1 Construction and acquisition expenditures 311.9 19.5 — 331.4
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2015 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; 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 Resources and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. Resources’ 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. Certain financial information relating to Alliant Energy’s business segments, services and geographic information was as follows (in millions): 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 Utility Non-Regulated, Alliant Energy 2013 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,689.0 $464.8 $71.3 $3,225.1 $51.7 $3,276.8 Depreciation and amortization 333.0 28.8 1.5 363.3 7.6 370.9 Operating income 444.5 57.3 6.3 508.1 25.8 533.9 Interest expense 166.3 6.5 172.8 Equity income from unconsolidated investments, net (43.7 ) — — (43.7 ) — (43.7 ) Income taxes 49.3 4.6 53.9 Net income attributable to Alliant Energy common shareowners 349.5 8.8 358.3 Total assets 9,018.6 859.3 712.2 10,590.1 502.4 11,092.5 Investments in equity method subsidiaries 279.1 — — 279.1 2.3 281.4 Construction and acquisition expenditures 677.3 47.0 7.3 731.6 66.7 798.3 Services - Alliant Energy’s consolidated operating revenues by segment, which were substantially all related to services, were as follows: 2015 2014 2013 Utility electric operations 85 % 81 % 82 % Utility gas operations 12 % 15 % 14 % Utility other 2 % 2 % 2 % Other 1 % 2 % 2 % 100 % 100 % 100 % Geographic Information - At December 31, 2015 , 2014 and 2013 , Alliant Energy, IPL and WPL did not have any long-lived assets to be held and used in foreign countries. 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. Certain financial information relating to IPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,491.8 $273.9 $53.1 $1,818.8 Depreciation and amortization 173.1 16.5 1.5 191.1 Operating income 173.1 29.8 9.1 212.0 Interest expense 81.3 Income tax benefit (36.3 ) Earnings available for common stock 172.0 Total assets 4,905.3 518.8 369.8 5,793.9 Construction and acquisition expenditures 365.4 27.5 7.3 400.2 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. Certain financial information relating to WPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,197.2 $190.9 $18.2 $1,406.3 Depreciation and amortization 159.9 12.3 — 172.2 Operating income (loss) 271.4 27.5 (2.8 ) 296.1 Interest expense 85.0 Equity income from unconsolidated investments (43.7 ) — — (43.7 ) Income taxes 85.6 Earnings available for common stock 177.5 Total assets 4,113.3 340.5 342.4 4,796.2 Investments in equity method subsidiaries 279.1 — — 279.1 Construction and acquisition expenditures 311.9 19.5 — 331.4

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2015
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 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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58 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): 2015 2014 2013 ATC billings to WPL $101 $96 $96 WPL billings to ATC 13 9 12 As of December 31, 2015 and 2014 , WPL owed ATC net amounts of $8 million and $8 million , respectively. WPL’s Sheboygan Falls Lease - Refer to Note 10(b) for discussion of WPL’s Sheboygan Falls lease.
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 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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58 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): 2015 2014 2013 ATC billings to WPL $101 $96 $96 WPL billings to ATC 13 9 12 As of December 31, 2015 and 2014 , WPL owed ATC net amounts of $8 million and $8 million , respectively.
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 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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58 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): 2015 2014 2013 ATC billings to WPL $101 $96 $96 WPL billings to ATC 13 9 12 As of December 31, 2015 and 2014 , WPL owed ATC net amounts of $8 million and $8 million , respectively. WPL’s Sheboygan Falls Lease - Refer to Note 10(b) for discussion of WPL’s Sheboygan Falls lease.

Discontinued Operations and Ass

Discontinued Operations and Assets and Liabilities Held For Sale	12 Months Ended
	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations	DISCONTINUED OPERATIONS AND ASSETS AND LIABILITIES HELD FOR SALE 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): 2015 2014 2013 Operating revenues $— $— $0.9 Operating expenses 4.0 3.7 9.9 Loss before income taxes (4.0 ) (3.7 ) (9.0 ) Income tax benefit (1.5 ) (1.3 ) (3.1 ) Loss from discontinued operations, net of tax ($2.5 ) ($2.4 ) ($5.9 ) Refer to Note 16(d) for further discussion of warranty claims associated with RMT that have resulted in operating expenses subsequent to the sale. In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets, which qualified as held for sale as of December 31, 2014. In July 2015, IPL completed the sale of its Minnesota electric distribution assets. Alliant Energy and IPL evaluated the sales of IPL’s Minnesota electric and natural gas distribution assets and believe such sales did not represent a strategic shift that has, or will have, a major effect on their operational and financial results. As a result, the operating results of IPL’s Minnesota electric and natural gas distribution assets have not been separately classified and reported as discontinued operations in Alliant Energy’s and IPL’s income statements. As of December 31, 2014, Alliant Energy’s and IPL’s balance sheets included assets held for sale related to IPL’s Minnesota natural gas distribution assets recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions): Assets held for sale: Current assets $1.1 Property, plant and equipment, net 11.0 Non-current regulatory assets 7.0 Total assets held for sale 19.1 Liabilities held for sale: Current liabilities 1.0 Other liabilities 7.1 Total liabilities held for sale 8.1 Net assets held for sale $11.0 Refer to Note 3 for further discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets.
IPL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations	DISCONTINUED OPERATIONS AND ASSETS AND LIABILITIES HELD FOR SALE 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): 2015 2014 2013 Operating revenues $— $— $0.9 Operating expenses 4.0 3.7 9.9 Loss before income taxes (4.0 ) (3.7 ) (9.0 ) Income tax benefit (1.5 ) (1.3 ) (3.1 ) Loss from discontinued operations, net of tax ($2.5 ) ($2.4 ) ($5.9 ) Refer to Note 16(d) for further discussion of warranty claims associated with RMT that have resulted in operating expenses subsequent to the sale. In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets, which qualified as held for sale as of December 31, 2014. In July 2015, IPL completed the sale of its Minnesota electric distribution assets. Alliant Energy and IPL evaluated the sales of IPL’s Minnesota electric and natural gas distribution assets and believe such sales did not represent a strategic shift that has, or will have, a major effect on their operational and financial results. As a result, the operating results of IPL’s Minnesota electric and natural gas distribution assets have not been separately classified and reported as discontinued operations in Alliant Energy’s and IPL’s income statements. As of December 31, 2014, Alliant Energy’s and IPL’s balance sheets included assets held for sale related to IPL’s Minnesota natural gas distribution assets recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions): Assets held for sale: Current assets $1.1 Property, plant and equipment, net 11.0 Non-current regulatory assets 7.0 Total assets held for sale 19.1 Liabilities held for sale: Current liabilities 1.0 Other liabilities 7.1 Total liabilities held for sale 8.1 Net assets held for sale $11.0 Refer to Note 3 for further discussion of IPL’s sales of its Minnesota electric and natural gas distribution assets.

Selected Consolidated Quarterly

Selected Consolidated Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2015
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. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $897.4 $717.2 $898.9 $740.1 $952.8 $750.3 $843.1 $804.1 Operating income 152.9 109.0 235.9 79.2 154.2 103.3 194.8 91.3 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 96.6 68.9 180.0 35.2 108.0 62.1 155.2 60.2 Loss from discontinued operations, net of tax — (1.3 ) (0.1 ) (1.1 ) — (0.3 ) (1.9 ) (0.2 ) Net income 96.6 67.6 179.9 34.1 108.0 61.8 153.3 60.0 Earnings per weighted average common share attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 0.87 0.61 1.59 0.31 0.97 0.56 1.40 0.54 Loss from discontinued operations, net of tax — (0.01 ) — (0.01 ) — — (0.02 ) — Net income 0.87 0.60 1.59 0.30 0.97 0.56 1.38 0.54 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. Refer to Note 1(q) for discussion of IPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to IPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $489.0 $382.2 $504.6 $398.7 $528.9 $411.9 $476.2 $431.1 Operating income 65.5 33.8 117.0 25.6 57.5 34.0 93.9 23.8 Net income 50.1 19.0 119.1 8.0 45.3 20.5 104.6 21.4 Earnings available for common stock 47.5 16.5 116.5 5.5 42.7 18.0 102.0 18.9 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. Refer to Note 1(q) for discussion of WPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to WPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $397.1 $324.7 $382.6 $330.7 $410.4 $324.5 $354.4 $359.8 Operating income 80.8 68.3 110.3 49.3 87.7 60.0 93.9 59.4 Net income 45.1 39.7 68.4 24.4 55.2 34.7 57.9 33.3 Earnings available for common stock 44.9 39.2 68.0 24.2 55.2 34.7 57.9 32.6
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. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $897.4 $717.2 $898.9 $740.1 $952.8 $750.3 $843.1 $804.1 Operating income 152.9 109.0 235.9 79.2 154.2 103.3 194.8 91.3 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 96.6 68.9 180.0 35.2 108.0 62.1 155.2 60.2 Loss from discontinued operations, net of tax — (1.3 ) (0.1 ) (1.1 ) — (0.3 ) (1.9 ) (0.2 ) Net income 96.6 67.6 179.9 34.1 108.0 61.8 153.3 60.0 Earnings per weighted average common share attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 0.87 0.61 1.59 0.31 0.97 0.56 1.40 0.54 Loss from discontinued operations, net of tax — (0.01 ) — (0.01 ) — — (0.02 ) — Net income 0.87 0.60 1.59 0.30 0.97 0.56 1.38 0.54 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. Refer to Note 1(q) for discussion of IPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to IPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $489.0 $382.2 $504.6 $398.7 $528.9 $411.9 $476.2 $431.1 Operating income 65.5 33.8 117.0 25.6 57.5 34.0 93.9 23.8 Net income 50.1 19.0 119.1 8.0 45.3 20.5 104.6 21.4 Earnings available for common stock 47.5 16.5 116.5 5.5 42.7 18.0 102.0 18.9 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. Refer to Note 1(q) for discussion of WPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to WPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $397.1 $324.7 $382.6 $330.7 $410.4 $324.5 $354.4 $359.8 Operating income 80.8 68.3 110.3 49.3 87.7 60.0 93.9 59.4 Net income 45.1 39.7 68.4 24.4 55.2 34.7 57.9 33.3 Earnings available for common stock 44.9 39.2 68.0 24.2 55.2 34.7 57.9 32.6
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. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $897.4 $717.2 $898.9 $740.1 $952.8 $750.3 $843.1 $804.1 Operating income 152.9 109.0 235.9 79.2 154.2 103.3 194.8 91.3 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 96.6 68.9 180.0 35.2 108.0 62.1 155.2 60.2 Loss from discontinued operations, net of tax — (1.3 ) (0.1 ) (1.1 ) — (0.3 ) (1.9 ) (0.2 ) Net income 96.6 67.6 179.9 34.1 108.0 61.8 153.3 60.0 Earnings per weighted average common share attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 0.87 0.61 1.59 0.31 0.97 0.56 1.40 0.54 Loss from discontinued operations, net of tax — (0.01 ) — (0.01 ) — — (0.02 ) — Net income 0.87 0.60 1.59 0.30 0.97 0.56 1.38 0.54 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. Refer to Note 1(q) for discussion of IPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to IPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $489.0 $382.2 $504.6 $398.7 $528.9 $411.9 $476.2 $431.1 Operating income 65.5 33.8 117.0 25.6 57.5 34.0 93.9 23.8 Net income 50.1 19.0 119.1 8.0 45.3 20.5 104.6 21.4 Earnings available for common stock 47.5 16.5 116.5 5.5 42.7 18.0 102.0 18.9 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. Refer to Note 1(q) for discussion of WPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to WPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $397.1 $324.7 $382.6 $330.7 $410.4 $324.5 $354.4 $359.8 Operating income 80.8 68.3 110.3 49.3 87.7 60.0 93.9 59.4 Net income 45.1 39.7 68.4 24.4 55.2 34.7 57.9 33.3 Earnings available for common stock 44.9 39.2 68.0 24.2 55.2 34.7 57.9 32.6

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2015
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, 2015 2014 2013 (in millions) Operating revenues $2 $2 $2 Operating expenses 3 3 1 Operating income (loss) (1 ) (1 ) 1 Interest expense and other: Equity earnings from consolidated subsidiaries (379 ) (388 ) (361 ) Interest expense 3 9 11 Interest income (3 ) (2 ) (2 ) Total interest expense and other (379 ) (381 ) (352 ) Income before income taxes 378 380 353 Income tax benefit (1 ) (3 ) (5 ) Net income $379 $383 $358 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, 2015 2014 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $93 $95 Other 9 25 Total current assets 102 120 Investments: Investments in consolidated subsidiaries 3,999 3,721 Other 14 15 Total investments 4,013 3,736 Other assets 20 10 Total assets $4,135 $3,866 LIABILITIES AND EQUITY Current liabilities: Current maturities of long-term debt $250 $— Commercial paper 140 141 Other 12 29 Total current liabilities 402 170 Long-term debt, net (excluding current portion) — 250 Other liabilities 12 11 Common equity: Common stock and additional paid-in capital 1,664 1,510 Retained earnings 2,066 1,934 Shares in deferred compensation trust (9 ) (9 ) Total common equity 3,721 3,435 Total liabilities and equity $4,135 $3,866 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, 2015 2014 2013 (in millions) Net cash flows from operating activities $262 $246 $238 Cash flows used for investing activities: Capital contributions to consolidated subsidiaries (165 ) (90 ) (120 ) Capital repayments from consolidated subsidiaries — 50 95 Net change in notes receivable from affiliates 2 (23 ) 5 Other — — (2 ) Net cash flows used for investing activities (163 ) (63 ) (22 ) Cash flows used for financing activities: Common stock dividends (247 ) (226 ) (208 ) Proceeds from issuance of common stock, net 151 — — Proceeds from issuance of long-term debt — 250 — Payments to retire long-term debt — (250 ) — Net change in commercial paper (1 ) 45 (9 ) Other (2 ) (2 ) 1 Net cash flows used for financing activities (99 ) (183 ) (216 ) 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 ) ($11 ) ($13 ) Income taxes, net (9 ) (5 ) (7 ) 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 Alliant Energy’s 2015 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. Alliant Energy allocates income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. In the fourth quarter of 2015, Alliant Energy changed its method of allocating income tax provisions and related deferred tax assets and liabilities to its subsidiaries from the parent-company-down approach to the modified separate return approach. The change was retrospectively applied to the Parent Company’s Condensed Financial Statements. This tax method change did not impact Alliant Energy’s consolidated financial statements. The change had no impact on Parent Company net income, but impacted the income tax provisions and the equity earnings from consolidated subsidiaries in the Parent Company Condensed Statements of Income, as well as investment in consolidated subsidiaries and deferred tax liabilities on the Parent Company Condensed Balance Sheets. Refer to Note 1(c) for additional information on the tax method change.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts And Reserves	12 Months Ended
	Dec. 31, 2015
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, 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 Year ended December 31, 2013 4.0 13.6 0.6 13.4 4.8 IPL (c) 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 Year ended December 31, 2013 0.7 12.7 — 12.7 0.7 WPL 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 Year ended December 31, 2013 1.8 — 0.6 0.7 1.7 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, 2015 $32.6 $6.5 $— $12.0 $27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 Year ended December 31, 2013 33.4 23.2 — 18.4 38.2 IPL 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 Year ended December 31, 2013 11.6 9.3 — 2.8 18.1 WPL 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 Year ended December 31, 2013 13.5 8.8 — 6.1 16.2 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. (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, 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 Year ended December 31, 2013 4.0 13.6 0.6 13.4 4.8 IPL (c) 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 Year ended December 31, 2013 0.7 12.7 — 12.7 0.7 WPL 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 Year ended December 31, 2013 1.8 — 0.6 0.7 1.7 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, 2015 $32.6 $6.5 $— $12.0 $27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 Year ended December 31, 2013 33.4 23.2 — 18.4 38.2 IPL 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 Year ended December 31, 2013 11.6 9.3 — 2.8 18.1 WPL 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 Year ended December 31, 2013 13.5 8.8 — 6.1 16.2 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. (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, 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 Year ended December 31, 2013 4.0 13.6 0.6 13.4 4.8 IPL (c) 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 Year ended December 31, 2013 0.7 12.7 — 12.7 0.7 WPL 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 Year ended December 31, 2013 1.8 — 0.6 0.7 1.7 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, 2015 $32.6 $6.5 $— $12.0 $27.1 Year ended December 31, 2014 38.2 12.5 — 18.1 32.6 Year ended December 31, 2013 33.4 23.2 — 18.4 38.2 IPL 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 Year ended December 31, 2013 11.6 9.3 — 2.8 18.1 WPL 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 Year ended December 31, 2013 13.5 8.8 — 6.1 16.2 (a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. (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, 2015
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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes.
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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively.
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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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.
Emission Allowances	Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements.
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 that IPL’s customer rates are increased to recover the ARO expenditures. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates included in the most recent depreciation study approved by the PSCW in its May 2012 order and subsequently approved by FERC. 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 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 and Changes in Accounting Principles	Revenue Recognition - In May 2014, FASB issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are currently evaluating the impact of this standard on their financial condition and results of operations. Presentation of Debt Issuance Costs - In April 2015, FASB issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability are presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard, which is applied retrospectively. Refer to Note 1(q) for further discussion. Presentation of Deferred Taxes - In November 2015, FASB issued an accounting standard to simplify the presentation of deferred taxes on the balance sheet. Under the new standard, all deferred tax assets and liabilities are presented as non-current on the balance sheet. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard with prospective application. As such, prior period amounts have not been retrospectively adjusted for this standard. Changes in Accounting Principles - Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of calculating income tax provisions and related deferred tax assets and liabilities for IPL and WPL implemented in the fourth quarter of 2015. Comparative financial statements for prior years have been adjusted to retrospectively apply the new accounting standard related to the presentation of debt issuance costs for Alliant Energy, IPL and WPL, and change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL. There are no required resettlements of cash between the companies for these periods. The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6
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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes.
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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively.
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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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.
Emission Allowances	Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements.
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 that IPL’s customer rates are increased to recover the ARO expenditures. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates included in the most recent depreciation study approved by the PSCW in its May 2012 order and subsequently approved by FERC. 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 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 and Changes in Accounting Principles	Revenue Recognition - In May 2014, FASB issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are currently evaluating the impact of this standard on their financial condition and results of operations. Presentation of Debt Issuance Costs - In April 2015, FASB issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability are presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard, which is applied retrospectively. Refer to Note 1(q) for further discussion. Presentation of Deferred Taxes - In November 2015, FASB issued an accounting standard to simplify the presentation of deferred taxes on the balance sheet. Under the new standard, all deferred tax assets and liabilities are presented as non-current on the balance sheet. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard with prospective application. As such, prior period amounts have not been retrospectively adjusted for this standard. Changes in Accounting Principles - Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of calculating income tax provisions and related deferred tax assets and liabilities for IPL and WPL implemented in the fourth quarter of 2015. Comparative financial statements for prior years have been adjusted to retrospectively apply the new accounting standard related to the presentation of debt issuance costs for Alliant Energy, IPL and WPL, and change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL. There are no required resettlements of cash between the companies for these periods. The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6
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 do have the ability to exercise significant influence over operating and financial policies, are accounted for under the equity method of accounting. 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(n) 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, and assets and liabilities held for sale as of December 31, 2014. Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of recording income taxes implemented in the fourth quarter of 2015 that impacts the separate financial statements of IPL and WPL. As required by GAAP, all prior period financial statements and disclosures presented herein have been restated to reflect these changes.
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 rates. 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 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. The alternative transition method has been elected to calculate the beginning pool of excess tax benefits available to absorb any tax deficiencies associated with recognition of share-based payment awards. Alliant Energy files a consolidated federal income tax return, which includes the aggregate taxable income or loss of Alliant Energy and its subsidiaries. In addition, a combined return including Alliant Energy and all of its subsidiaries is filed in Wisconsin. 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. In the fourth quarter of 2015, IPL and WPL changed their method of calculating their income tax provisions and related deferred tax assets and liabilities from the parent-company-down approach to the modified separate return approach. IPL and WPL believe the new method is preferable to the prior method because income taxes are more reflective of amounts that IPL and WPL would have reported as separate tax return filers, and the new method is more consistent with the way in which IPL’s and WPL’s regulators determine the tax-related components of their cost-based rates. Under the parent-company-down approach, consolidated income taxes were fully allocated to Alliant Energy’s subsidiaries, including IPL and WPL, based on a prorated allocation of separate company results using consolidated tax rates and apportionment factors. Under the modified separate return approach, 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 2015, 2014 or 2013. IPL’s and WPL’s comparative financial statements for prior years have been adjusted to apply the change in method of calculating their income tax provisions and related deferred tax assets and liabilities retrospectively.
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. Corporate Services placed in service a new customer billing and information system for IPL and WPL in 2015, which is amortized over a 12 -year period. The majority of the remaining software is amortized over a 5 -year period. 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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
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: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
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, weather 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. IPL’s and WPL’s customers and generating resources are located in the MISO region. 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 - Certain of Alliant Energy’s subsidiaries serve as collection agents for sales or various other taxes and record revenues on a net basis. Operating revenues do not include the collection of the aforementioned taxes.
Utility Cost Recovery Mechanisms	Electric Production Fuel and Energy Purchases (Fuel-related Costs) - Fuel-related costs are incurred each period 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 coal and natural gas) used during each period to produce electricity at their EGUs, electricity purchased each period from wholesale energy markets (primarily MISO) 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 applicable for IPL’s retail electric customers provide for subsequent adjustments to their electric rates each month for changes in fuel-related costs. Fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction also currently allow IPL to recover prudently incurred costs for emission allowances required to comply with EPA regulations, including the Acid Rain program, through the fuel adjustment clause. Changes in the under-/over-collection of these costs each period 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. The fuel adjustment clause rules applicable to IPL’s Iowa retail jurisdiction currently do not contain a provision for recovery of environmental controls chemical costs to flow through the fuel adjustment clause. Effective February 2014, IPL began recovering the Iowa retail portion of the DAEC PPA costs from its Iowa retail electric customers through the fuel adjustment clause pursuant to a January 2013 IUB order. This PPA does not contain minimum payments for electric generating capacity. WPL Retail - The cost recovery mechanism applicable 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 electric retail rate proceeding or in a separate fuel cost plan approval proceeding. However, if WPL’s actual fuel-related costs fall outside these fuel monitoring ranges during the test period, 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 each period. 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. WPL’s retail fuel-related costs include costs for emission allowances and environmental controls chemicals. IPL and WPL Wholesale - The cost recovery mechanisms applicable 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 each period. 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 and environmental controls chemicals 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 each period to “Electric transmission service” in the income statements. IPL Retail - Electric transmission service expense is recovered from IPL’s Iowa retail electric customers through a transmission cost rider. This cost recovery mechanism provides for annual adjustments to electric rates charged to Iowa electric retail 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 each period. 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 July 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 will be recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements each period. An offsetting amount will be 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 - 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 during each period 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 each period. 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 each period. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers in Iowa through an additional tariff called an EECR factor. EECR factors are revised annually and include 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 each period 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. At the end of each reporting period, derivative instruments representing unrealized gain positions are reported as derivative assets, and derivative instruments representing unrealized loss positions are reported as derivative liabilities. Certain commodity purchase and sales contracts qualify for and have been designated under the normal purchase and sale exception. Based on this designation, such contracts 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, an impairment charge is recognized equal to the amount of the carrying value that was disallowed. If IPL or WPL are disallowed a full or 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, 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. In 2015, declines in forward electricity prices suggested that there may be an impairment indicator for the Franklin County wind farm as a result of exposure to market prices. Alliant Energy performed an impairment test, which included an evaluation of key assumptions, including forward electricity prices, expected output of the wind farm, status of transmission upgrades expected to be completed, the expected life of the wind farm, and likelihood of the sale of the wind farm. Alliant Energy concluded that the estimated undiscounted future cash flows exceeded the carrying value of the Franklin County wind farm as of December 31, 2015, resulting in no impairment. However a further decline in average forward electricity prices of $2 to $3 per MWh over the remaining life of the wind farm could result in an impairment charge that would be material and would likely exceed half of the $130 million carrying value at December 31, 2015 . 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.
Emission Allowances	Emission allowances are granted by the EPA at zero cost and permit the holder of the allowances to emit certain gaseous by-products of fossil fuel combustion, including SO2 and NOx. Purchased emission allowances are recorded as intangible assets at their original cost and evaluated for impairment as long-lived assets to be held and used. Emission allowances allocated or acquired are held primarily for consumption. Amortization of emission allowances recorded in “Electric production fuel and purchased power” in the income statements in 2015 , 2014 and 2013 was not material, and is based upon a weighted average cost for each EPA compliance program category of vintage year utilized during the reporting period. As of December 31, 2015 , future estimated amortization expense for emission allowances was not material for 2016 through 2020 . Cash inflows and outflows related to sales and purchases of emission allowances are presented in investing activities in the cash flows statements.
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 that IPL’s customer rates are increased to recover the ARO expenditures. WPL’s regulatory assets related to AROs are being recovered as a component of depreciation rates included in the most recent depreciation study approved by the PSCW in its May 2012 order and subsequently approved by FERC. 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 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 and Changes in Accounting Principles	Revenue Recognition - In May 2014, FASB issued an accounting standard providing principles for recognizing revenue for the transfer of promised goods or services to customers with the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Alliant Energy, IPL and WPL currently expect to adopt this standard on January 1, 2018 and are currently evaluating the impact of this standard on their financial condition and results of operations. Presentation of Debt Issuance Costs - In April 2015, FASB issued an accounting standard to simplify the presentation of debt issuance costs on the balance sheet. Under the new standard, debt issuance costs related to a recognized debt liability are presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard, which is applied retrospectively. Refer to Note 1(q) for further discussion. Presentation of Deferred Taxes - In November 2015, FASB issued an accounting standard to simplify the presentation of deferred taxes on the balance sheet. Under the new standard, all deferred tax assets and liabilities are presented as non-current on the balance sheet. In the fourth quarter of 2015, Alliant Energy, IPL and WPL elected to early adopt this standard with prospective application. As such, prior period amounts have not been retrospectively adjusted for this standard. Changes in Accounting Principles - Refer to Note 1(p) for discussion of a new accounting standard related to the presentation of debt issuance costs on the balance sheets, which Alliant Energy, IPL and WPL elected to early adopt in the fourth quarter of 2015. In addition, refer to Note 1(c) for discussion of a change in method of calculating income tax provisions and related deferred tax assets and liabilities for IPL and WPL implemented in the fourth quarter of 2015. Comparative financial statements for prior years have been adjusted to retrospectively apply the new accounting standard related to the presentation of debt issuance costs for Alliant Energy, IPL and WPL, and change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL. There are no required resettlements of cash between the companies for these periods. The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6

Summary Of Significant Accoun31

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
Schedule of New Accounting Standards and Changes in Accounting Principles	The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6
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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
Schedule of New Accounting Standards and Changes in Accounting Principles	The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6
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 2015 2014 2013 2015 2014 2013 Electric - generation 3.6% 3.6% 3.6% 3.2% 3.2% 3.3% Electric - distribution 2.4% 2.5% 2.5% 2.7% 2.7% 2.7% Electric - other 4.0% 4.0% 4.0% 4.5% 5.9% 5.0% Gas 3.2% 3.3% 3.4% 2.5% 2.5% 2.5% Other 3.9% 4.3% 4.7% 6.0% 6.0% 5.1%
Schedule of Allowance for Funds Used During Construction Rate	The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows: 2015 2014 2013 IPL (Marshalltown CWIP) (a) 7.9% 8.0% —% IPL (other CWIP) 7.7% 7.8% 8.2% WPL (retail jurisdiction) 8.2% 8.2% 8.2% WPL (wholesale jurisdiction) 7.9% 4.1% 4.5% (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.
Schedule of New Accounting Standards and Changes in Accounting Principles	The following financial statement line items were affected by these changes (in millions): Alliant Energy Originally Effect of New As Balance Sheet as of December 31, 2014 Reported Accounting Standard Adjusted Deferred charges and other $43.9 ($22.4 ) $21.5 Total other assets 1,759.5 (22.4 ) 1,737.1 Total assets 12,085.9 (22.4 ) 12,063.5 Long-term debt, net (excluding current portion) 3,606.7 (22.4 ) 3,584.3 Total liabilities and equity 12,085.9 (22.4 ) 12,063.5 IPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income tax benefit ($51.7 ) $2.8 ($48.9 ) ($37.9 ) $1.6 ($36.3 ) Net income 194.6 (2.8 ) 191.8 189.9 (1.6 ) 188.3 Earnings available for common stock 184.4 (2.8 ) 181.6 173.6 (1.6 ) 172.0 IPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $104.9 $— ($0.9 ) $104.0 Total current assets 556.1 — (0.9 ) 555.2 Deferred charges and other 12.7 (10.7 ) — 2.0 Total other assets 1,331.9 (10.7 ) — 1,321.2 Total assets 6,461.8 (10.7 ) (0.9 ) 6,450.2 Long-term debt, net (excluding current portion) 1,618.7 (10.7 ) — 1,608.0 Deferred tax liabilities 1,341.4 — 28.9 1,370.3 Total other liabilities 2,123.1 — 28.9 2,152.0 Retained earnings 537.9 — (29.8 ) 508.1 Total IPL common equity 1,814.1 — (29.8 ) 1,784.3 Total equity 2,014.1 — (29.8 ) 1,984.3 Total liabilities and equity 6,461.8 (10.7 ) (0.9 ) 6,450.2 January 1, 2014 Retained earnings 493.5 — (31.6 ) 461.9 January 1, 2013 Retained earnings 448.0 — (32.8 ) 415.2 IPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $194.6 ($2.8 ) $191.8 $189.9 ($1.6 ) $188.3 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense (benefit) and investment tax credits (9.7 ) (1.8 ) (11.5 ) 4.2 (1.2 ) 3.0 Other changes in assets and liabilities: Other 32.0 4.6 36.6 (14.0 ) 2.8 (11.2 ) WPL 2014 2013 Income Statements Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Income taxes $85.6 ($0.3 ) $85.3 $87.2 ($1.6 ) $85.6 Net income 180.8 0.3 181.1 177.5 1.6 179.1 Earnings available for common stock 180.1 0.3 180.4 175.9 1.6 177.5 WPL Effect of New Effect of Change in Balance Sheets Originally Accounting Method of Calculating As December 31, 2014 Reported Standard Income Taxes Adjusted Deferred tax assets $37.5 $— $0.2 $37.7 Total current assets 457.2 — 0.2 457.4 Deferred charges and other 29.7 (10.8 ) — 18.9 Total other assets 426.1 (10.8 ) — 415.3 Total assets 5,128.2 (10.8 ) 0.2 5,117.6 Long-term debt, net (excluding current portion) 1,543.3 (10.8 ) — 1,532.5 Deferred tax liabilities 970.0 — (2.9 ) 967.1 Total other liabilities 1,562.3 — (2.9 ) 1,559.4 Retained earnings 678.6 — 3.1 681.7 Total WPL common equity 1,703.8 — 3.1 1,706.9 Total equity 1,712.3 — 3.1 1,715.4 Total liabilities and equity 5,128.2 (10.8 ) 0.2 5,117.6 January 1, 2014 Retained earnings 617.2 — 5.0 622.2 January 1, 2013 Retained earnings 557.6 — 8.3 565.9 WPL 2014 2013 Cash Flows Effect of Change in Effect of Change in Originally Method of Calculating As Originally Method of Calculating As Reported Income Taxes Adjusted Reported Income Taxes Adjusted Cash flows from operating activities: Net income $180.8 $0.3 $181.1 $177.5 $1.6 $179.1 Adjustments to reconcile net income to net cash flows from operating activities: Deferred tax expense and investment tax credits 80.7 1.9 82.6 86.5 3.3 89.8 Other changes in assets and liabilities: Other (6.8 ) (2.2 ) (9.0 ) (16.7 ) (4.9 ) (21.6 ) The change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL did not have a material impact on their income statements or cash flows statements for 2015. The following balance sheet line items for 2015 were affected by this change in method for IPL and WPL (in millions): IPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Deferred tax liabilities $1,346.7 $1,378.0 $31.3 Total other liabilities 2,094.5 2,125.8 31.3 Retained earnings 585.4 554.1 (31.3 ) Total IPL common equity 2,026.6 1,995.3 (31.3 ) Total equity 2,226.6 2,195.3 (31.3 ) WPL As Computed Under As Reported Under Balance Sheet as of December 31, 2015 Parent-company-down Modified Separate Effect of Approach Return Approach Change Other current liabilities $78.2 $79.5 $1.3 Total current liabilities 335.6 336.9 1.3 Deferred tax liabilities 1,010.8 1,005.4 (5.4 ) Total other liabilities 1,637.4 1,632.0 (5.4 ) Retained earnings 727.0 731.1 4.1 Total WPL common equity 1,752.2 1,756.3 4.1 Total equity 1,763.5 1,767.6 4.1 In addition, the following previously reported Selected Consolidated Quarterly Financial Data (Unaudited) for the three months ended were impacted as a result of the change in method of calculating the income tax provisions and related deferred tax assets and liabilities for IPL and WPL (in millions): March 31, 2015 June 30, 2015 September 30, 2015 Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $50.4 $50.1 $19.2 $19.0 $120.0 $119.1 Earnings available for common stock 47.8 47.5 16.7 16.5 117.4 116.5 WPL Net income 44.8 45.1 39.5 39.7 67.9 68.4 Earnings available for common stock 44.6 44.9 39.0 39.2 67.5 68.0 March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Originally As Originally As Originally As Originally As Reported Adjusted Reported Adjusted Reported Adjusted Reported Adjusted IPL Net income $46.0 $45.3 $20.9 $20.5 $105.1 $104.6 $22.6 $21.4 Earnings available for common stock 43.4 42.7 18.4 18.0 102.5 102.0 20.1 18.9 WPL Net income 54.8 55.2 34.6 34.7 61.6 57.9 29.8 33.3 Earnings available for common stock 54.8 55.2 34.6 34.7 61.6 57.9 29.1 32.6

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7
Tax Benefit Riders	In 2015 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions): Electric tax benefit rider credits $72 Gas tax benefit rider credits 12 $84
Electric Tax Benefit Rider	Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues $72 $85 $79 Income tax benefit resulting from decreased taxable income caused by credits 30 35 33 Income tax benefit representing tax benefits realized from electric tax benefit rider 42 50 46
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): 2015 2014 2013 Revenue requirement adjustment $14 $15 $24
Gas Tax Benefit Rider	Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues $12 $12 $11 Income tax benefit resulting from decreased taxable income caused by credits 5 5 4 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7
Customer Billing Credits	IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions): Actual Estimated 2014 2015 2016 Billing credits to reduce retail electric customers’ bills $72 $24 $9
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7
Tax Benefit Riders	In 2015 , Alliant Energy’s and IPL’s “IPL’s tax benefit riders” regulatory liabilities decreased by $84 million as follows (in millions): Electric tax benefit rider credits $72 Gas tax benefit rider credits 12 $84
Electric Tax Benefit Rider	Alliant Energy and IPL recognize an offsetting reduction to income tax expense for the after-tax amounts credited to IPL’s retail electric customers’ bills in Iowa, resulting in no impact to Alliant Energy’s and IPL’s net income from the electric tax benefit rider as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail electric customers’ bills with reduction to electric revenues $72 $85 $79 Income tax benefit resulting from decreased taxable income caused by credits 30 35 33 Income tax benefit representing tax benefits realized from electric tax benefit rider 42 50 46
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): 2015 2014 2013 Revenue requirement adjustment $14 $15 $24
Gas Tax Benefit Rider	Alliant Energy and IPL utilized gas tax benefit rider-related regulatory liabilities to credit IPL’s Iowa retail gas customers’ bills as follows (in millions): 2015 2014 2013 Credit to IPL’s Iowa retail gas customers’ bills with reduction to gas revenues $12 $12 $11 Income tax benefit resulting from decreased taxable income caused by credits 5 5 4 Income tax benefit representing tax benefits realized from gas tax benefit rider 7 7 7
Customer Billing Credits	IPL recorded such billing credits in 2014 and 2015, and estimates billing credits in 2016, as follows (in millions): Actual Estimated 2014 2015 2016 Billing credits to reduce retail electric customers’ bills $72 $24 $9
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 2015 2014 2015 2014 2015 2014 Tax-related $987.7 $955.3 $958.2 $928.0 $29.5 $27.3 Pension and OPEB costs 579.5 570.2 298.1 287.9 281.4 282.3 AROs 92.4 73.7 50.8 41.4 41.6 32.3 Derivatives 70.6 46.9 28.2 28.0 42.4 18.9 WPL’s EGUs retired early 45.0 — — — 45.0 — Commodity cost recovery 35.9 31.1 2.8 0.4 33.1 30.7 Emission allowances 26.9 27.4 26.9 27.4 — — Environmental-related costs 16.4 16.0 11.0 11.5 5.4 4.5 Debt redemption costs 14.3 16.1 9.5 10.9 4.8 5.2 Other 39.9 47.0 17.1 22.4 22.8 24.6 $1,908.6 $1,783.7 $1,402.6 $1,357.9 $506.0 $425.8
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Cost of removal obligations $406.0 $421.7 $260.4 $279.1 $145.6 $142.6 IPL’s tax benefit riders 159.2 243.0 159.2 243.0 — — Energy efficiency cost recovery 48.3 64.3 — — 48.3 64.3 Electric transmission cost recovery 43.5 19.4 21.9 19.4 21.6 — Commodity cost recovery 37.6 15.4 23.5 15.1 14.1 0.3 Other 43.1 57.4 24.2 26.9 18.9 30.5 $737.7 $821.2 $489.2 $583.5 $248.5 $237.7

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8
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): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8
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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8
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): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8
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 2015 2014 2015 2014 2015 2014 Utility: Electric plant: In service: Generation $5,643.7 $5,463.0 $3,011.6 $2,872.4 $2,632.1 $2,590.6 Distribution 4,489.9 4,435.4 2,447.9 2,471.7 2,042.0 1,963.7 Other 311.3 309.1 212.2 215.5 99.1 93.6 Anticipated to be retired early (a) — 157.6 — — — 157.6 Total electric plant 10,444.9 10,365.1 5,671.7 5,559.6 4,773.2 4,805.5 Gas plant in service 1,018.3 946.2 513.6 474.0 504.7 472.2 Other plant in service 530.6 539.3 296.0 298.8 234.6 240.5 Accumulated depreciation (a) (3,939.6 ) (3,923.1 ) (2,152.8 ) (2,124.5 ) (1,786.8 ) (1,798.6 ) Net plant 8,054.2 7,927.5 4,328.5 4,207.9 3,725.7 3,719.6 Leased Sheboygan Falls Energy Facility, net (b) — — — — 58.6 64.7 Construction work in progress 897.5 479.1 578.2 325.0 319.3 154.1 Other, net 18.5 22.3 18.4 21.8 0.1 0.5 Total utility 8,970.2 8,428.9 4,925.1 4,554.7 4,103.7 3,938.9 Non-regulated and other: Non-regulated Generation, net (c) 229.3 240.1 — — — — Corporate Services and other, net (d) 319.6 269.4 — — — — Total non-regulated and other 548.9 509.5 — — — — Total property, plant and equipment $9,519.1 $8,938.4 $4,925.1 $4,554.7 $4,103.7 $3,938.9 (a) In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs. (b) Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014 , respectively. (c) Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014 , respectively. (d) Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014 , 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Equity $24.4 $23.1 $20.3 $18.6 $17.1 $13.8 $5.8 $6.0 $6.5 Debt 12.5 11.7 10.5 9.6 8.8 7.2 2.9 2.9 3.3 $36.9 $34.8 $30.8 $28.2 $25.9 $21.0 $8.7 $8.9 $9.8
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): 2015 2014 2013 IPL: Marshalltown $20.7 $3.7 $— Environmental controls - Ottumwa Unit 1 — 10.6 8.0 Environmental controls - George Neal Units 3 and 4 — 1.4 5.1 Other 7.5 10.2 7.9 28.2 25.9 21.0 WPL: Environmental controls - Edgewater Unit 5 5.1 2.7 — Environmental controls - Columbia Units 1 and 2 — 4.0 7.2 Other 3.6 2.2 2.6 8.7 8.9 9.8 Alliant Energy $36.9 $34.8 $30.8

Jointly-Owned Electric Utilit34

Jointly-Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2015
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8
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, 2015 was as follows (dollars in millions): Accumulated Construction In-service Ownership Electric Provision for Work in Dates Interest % Plant Depreciation Progress IPL Ottumwa Unit 1 1981 48.0 % $481.4 $125.0 $6.5 George Neal Unit 4 1979 25.7 % 184.3 76.3 0.2 George Neal Unit 3 1975 28.0 % 150.0 45.1 0.1 Louisa Unit 1 1983 4.0 % 36.4 21.1 0.1 852.1 267.5 6.9 WPL Columbia Units 1-2 1975-1978 46.2 % 571.9 175.5 34.8 Edgewater Unit 4 1969 68.2 % 102.7 58.2 0.1 674.6 233.7 34.9 Alliant Energy $1,526.7 $501.2 $41.8

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program were as follows (in millions): 2015 2014 2013 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $137.0 $150.0 $170.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 46.7 46.4 105.9
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): 2015 2014 Customer accounts receivable $109.7 $134.8 Unbilled utility revenues 71.3 69.7 Other receivables 0.1 0.1 Receivables sold to third party 181.1 204.6 Less: cash proceeds (a) 5.0 22.0 Deferred proceeds 176.1 182.6 Less: allowance for doubtful accounts 4.1 5.4 Fair value of deferred proceeds $172.0 $177.2 Outstanding receivables past due $18.0 $19.9 (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): 2015 2014 2013 Collections reinvested in receivables $1,812.9 $1,997.9 $1,880.8 Credit losses, net of recoveries 8.8 11.4 11.9
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8
Maximum And Average Outstanding Cash Proceeds	IPL’s maximum and average outstanding cash proceeds related to the sales of accounts receivable program were as follows (in millions): 2015 2014 2013 Maximum outstanding aggregate cash proceeds (based on daily outstanding balances) $137.0 $150.0 $170.0 Average outstanding aggregate cash proceeds (based on daily outstanding balances) 46.7 46.4 105.9
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): 2015 2014 Customer accounts receivable $109.7 $134.8 Unbilled utility revenues 71.3 69.7 Other receivables 0.1 0.1 Receivables sold to third party 181.1 204.6 Less: cash proceeds (a) 5.0 22.0 Deferred proceeds 176.1 182.6 Less: allowance for doubtful accounts 4.1 5.4 Fair value of deferred proceeds $172.0 $177.2 Outstanding receivables past due $18.0 $19.9 (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): 2015 2014 2013 Collections reinvested in receivables $1,812.9 $1,997.9 $1,880.8 Credit losses, net of recoveries 8.8 11.4 11.9
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 2015 2014 2015 2014 2015 2014 Customer $93.8 $88.2 $4.6 $— $81.5 $81.0 Unbilled utility revenues 83.1 85.4 1.2 — 81.9 85.4 Deferred proceeds 172.0 177.2 172.0 177.2 — — Other 53.5 81.6 22.8 39.9 25.7 23.6 Allowance for doubtful accounts (4.8 ) (5.1 ) (0.6 ) (0.4 ) (3.7 ) (4.2 ) $397.6 $427.3 $200.0 $216.7 $185.4 $185.8

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2015
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 Carrying Value at Interest at December 31, Equity (Income) / Loss December 31, 2015 2015 2014 2015 2014 2013 Alliant Energy ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) Other Various 0.9 2.3 1.3 2.4 — $302.9 $296.6 ($33.8 ) ($40.4 ) ($43.7 ) WPL ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) $302.0 $294.3 ($35.1 ) ($42.8 ) ($43.7 ) (a) Alliant Energy and WPL have the ability to exercise significant influence over ATC’s financial and operating policies through their 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 2015 2014 2013 2015 2014 2013 Operating revenues $624 $643 $634 $624 $643 $634 Operating income 299 330 334 299 330 334 Net income 186 240 248 202 240 250 As of December 31: Current assets 88 72 87 70 Non-current assets 3,987 3,773 3,977 3,747 Current liabilities 332 315 332 315 Non-current liabilities 2,052 1,871 2,052 1,870
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 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4
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 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4
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 Carrying Value at Interest at December 31, Equity (Income) / Loss December 31, 2015 2015 2014 2015 2014 2013 Alliant Energy ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) Other Various 0.9 2.3 1.3 2.4 — $302.9 $296.6 ($33.8 ) ($40.4 ) ($43.7 ) WPL ATC (a) 16% $293.3 $286.5 ($34.2 ) ($41.9 ) ($42.7 ) Wisconsin River Power Company 50% 8.7 7.8 (0.9 ) (0.9 ) (1.0 ) $302.0 $294.3 ($35.1 ) ($42.8 ) ($43.7 ) (a) Alliant Energy and WPL have the ability to exercise significant influence over ATC’s financial and operating policies through their 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 2015 2014 2013 2015 2014 2013 Operating revenues $624 $643 $634 $624 $643 $634 Operating income 299 330 334 299 330 334 Net income 186 240 248 202 240 250 As of December 31: Current assets 88 72 87 70 Non-current assets 3,987 3,773 3,977 3,747 Current liabilities 332 315 332 315 Non-current liabilities 2,052 1,871 2,052 1,870
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 2015 2014 2015 2014 2015 2014 Cash surrender value $42.3 $47.0 $18.9 $18.1 $6.4 $11.4

Common Equity (Tables)

Common Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Schedule of Common Equity [Line Items]
Common Stock Activity	A summary of Alliant Energy’s common stock activity was as follows: 2015 2014 2013 Shares outstanding, January 1 110,935,680 110,943,669 110,987,400 At-the-market offering program 2,186,617 — — Shareowner Direct Plan issuances 303,005 — — Equity-based compensation plans ( Note 12(b) ) 56,378 35,547 (23,374 ) Other (22,464 ) (43,536 ) (20,357 ) Shares outstanding, December 31 113,459,216 110,935,680 110,943,669
Schedule of Restricted Net Assets of Subsidiaries	As of December 31, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6
Capital Transactions with Subsidiaries	IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0
Schedule of Capital Contributions	IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions): 2015 2014 2013 $165.0 $90.0 $120.0
IPL [Member]
Schedule of Common Equity [Line Items]
Schedule of Restricted Net Assets of Subsidiaries	As of December 31, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6
Capital Transactions with Subsidiaries	IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0
Schedule of Capital Contributions	IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions): 2015 2014 2013 $165.0 $90.0 $120.0
WPL [Member]
Schedule of Common Equity [Line Items]
Schedule of Restricted Net Assets of Subsidiaries	As of December 31, 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 as follows (in billions): 2015 2014 IPL $1.4 $1.3 WPL 1.6 1.6
Capital Transactions with Subsidiaries	IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions): IPL WPL Resources 2015 2014 2013 2015 2014 2013 2015 2014 2013 Common stock dividends $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $— $— Repayments of capital — — — — — — — 50.0 95.0 Total distributions from common equity $140.0 $140.0 $128.1 $126.9 $118.7 $116.3 $— $50.0 $95.0

Redeemable Preferred Stock (Tab

Redeemable Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2015
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: Liquidation Preference/Stated Value Shares Authorized Shares Outstanding Series 2015 2014 (in millions) $25 16,000,000 8,000,000 5.1% $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: Liquidation Preference/Stated Value Shares Authorized Shares Outstanding Series 2015 2014 (in millions) $25 16,000,000 8,000,000 5.1% $200.0 $200.0

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes.
Schedule of Debt Maturities	At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357
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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes.
Schedule of Debt Maturities	At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357
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 2015 2014 2015 2014 2015 2014 December 31 Commercial paper: Amount outstanding $159.8 $141.3 $— $— $19.9 $— Weighted average interest rates 0.7% 0.4% N/A N/A 0.4% N/A Weighted average remaining maturity 4 days 4 days N/A N/A 4 days N/A Available credit facility capacity $840.2 $858.7 $300.0 $300.0 $380.1 $400.0 Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 For the year ended Maximum amount outstanding (based on daily outstanding balances) $181.2 $353.8 $18.4 $38.0 $24.7 $204.7 Average amount outstanding (based on daily outstanding balances) $119.2 $255.9 $0.2 $0.2 $2.2 $122.9 Weighted average interest rates 0.4% 0.2% 0.4% 0.2% 0.3% 0.1%
Schedule of Debt-To-Capital Ratios	The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2015 were as follows: Alliant Energy IPL WPL Requirement, not to exceed 65% 58% 58% Actual 50% 46% 48%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2015 2014 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures: 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 (a) 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 — 3.3% (Retired in 2015) — — — 150.0 150.0 — 1,875.0 1,875.0 — 1,775.0 1,775.0 — Debentures: 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 Pollution Control Revenue Bonds: 5% (Retired in 2015) — — — 16.0 — 16.0 5.375% (Retired in 2015) — — — 14.6 — 14.6 — — — 30.6 — 30.6 Other: Term loan credit agreement through 2016, 1% at December 31, 2015 250.0 — — 250.0 — — Term loan credit agreement through 2016, 1% at December 31, 2015 60.0 — — 60.0 — — 3.45% senior notes, due 2022 75.0 — — 75.0 — — 5.06% senior secured notes, due 2016 to 2024 56.8 — — 58.9 — — Other, 1% at December 31, 2015, due 2016 to 2025 3.7 — — 3.3 — — 445.5 — — 447.2 — — Subtotal 3,870.5 1,875.0 1,550.0 3,802.8 1,775.0 1,580.6 Current maturities (313.4 ) — — (183.0 ) (150.0 ) (30.6 ) Unamortized debt issuance costs (22.3 ) (11.8 ) (9.9 ) (22.4 ) (10.7 ) (10.8 ) Unamortized debt (discount) and premium, net (12.6 ) (6.3 ) (6.2 ) (13.1 ) (6.3 ) (6.7 ) Long-term debt, net $3,522.2 $1,856.9 $1,533.9 $3,584.3 $1,608.0 $1,532.5 (a) In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million , reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes.
Schedule of Debt Maturities	At December 31, 2015 , debt maturities for 2016 through 2020 were as follows (in millions): 2016 2017 2018 2019 2020 IPL $— $— $350 $— $200 WPL — — — 250 150 Resources 63 5 6 6 7 Alliant Energy parent company 250 — — — — Alliant Energy $313 $5 $356 $256 $357

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2015
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9
IPL [Member]
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9
WPL [Member]
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2015 , future minimum operating lease payments, excluding contingent rentals, were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Alliant Energy $6 $8 $3 $2 $2 $19 $40 IPL 3 3 2 1 1 13 23 WPL 3 5 1 — — — 9
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): 2015 2014 2013 Interest expense $9.9 $10.4 $10.9 Depreciation and amortization 6.2 6.2 6.2 $16.1 $16.6 $17.1
Schedule of Future Minimum Lease Payments for Capital Leases	At December 31, 2015 , WPL’s estimated future minimum capital lease payments for Sheboygan Falls were as follows (in millions): 2016 2017 2018 2019 2020 Thereafter Total Less: amount representing interest Present value of minimum capital lease payments Sheboygan Falls $15 $15 $15 $15 $15 $68 $143 $54 $89

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 %
Production Tax Credits (Net Of State Tax Impacts)	Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0
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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4
Summary Of Tax Credit Carryforwards	At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205
Schedule Of Open Tax Years	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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 %
Production Tax Credits (Net Of State Tax Impacts)	Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0
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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4
Summary Of Tax Credit Carryforwards	At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205
Schedule Of Open Tax Years	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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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 2015 2014 2013 2015 2014 2013 2015 2014 2013 Current tax expense (benefit): Federal $2.0 $36.6 $4.4 ($14.1 ) $8.9 $10.2 $4.7 $2.0 ($0.3 ) State 3.2 9.3 (3.6 ) 11.5 10.4 4.2 0.6 0.8 (4.3 ) IPL’s tax benefit riders (49.0 ) (56.7 ) (52.9 ) (49.0 ) (56.7 ) (52.9 ) — — — Deferred tax expense (benefit): Federal 120.8 83.5 123.9 40.7 10.8 21.7 76.8 81.1 84.0 State 27.9 4.6 15.6 3.3 (7.9 ) (4.0 ) 20.2 20.0 24.1 Production tax credits (33.1 ) (31.3 ) (31.0 ) (14.5 ) (13.8 ) (14.1 ) (18.6 ) (17.5 ) (16.9 ) Investment tax credits (1.4 ) (1.6 ) (1.6 ) (0.6 ) (0.6 ) (0.6 ) (0.8 ) (1.0 ) (1.0 ) Provision recorded as a change in uncertain tax positions: Deferred — — (0.4 ) — — — — — (0.4 ) Provision recorded as a change in accrued interest — (0.1 ) (0.5 ) — — (0.8 ) — (0.1 ) 0.4 $70.4 $44.3 $53.9 ($22.7 ) ($48.9 ) ($36.3 ) $82.9 $85.3 $85.6
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 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 5.2 5.4 5.7 6.2 6.1 6.3 5.1 5.1 5.5 IPL’s tax benefit riders (10.6 ) (12.9 ) (12.1 ) (28.3 ) (39.6 ) (34.8 ) — — — Effect of rate-making on property-related differences (6.8 ) (7.5 ) (6.0 ) (17.2 ) (21.9 ) (15.9 ) (0.5 ) (0.7 ) (0.8 ) Production tax credits (7.2 ) (7.1 ) (7.1 ) (8.3 ) (9.6 ) (9.3 ) (7.1 ) (6.6 ) (6.4 ) Adjustment of prior period taxes 0.8 (1.3 ) (1.3 ) 0.7 (3.0 ) (3.6 ) 0.1 — (0.2 ) Other items, net (1.1 ) (1.5 ) (1.8 ) (1.2 ) (1.2 ) (1.6 ) (0.8 ) (0.8 ) (0.8 ) Overall income tax rate 15.3 % 10.1 % 12.4 % (13.1 %) (34.2 %) (23.9 %) 31.8 % 32.0 % 32.3 %
Production Tax Credits (Net Of State Tax Impacts)	Details regarding production tax credits (net of state tax impacts) related to various wind farms are as follows (dollars in millions): End of Production Nameplate Tax Credit Generation Capacity in MW 2015 2014 2013 Cedar Ridge (WPL) December 2018 68 $4.5 $4.1 $4.2 Bent Tree (WPL) February 2021 201 14.1 13.4 12.7 Subtotal (WPL) 18.6 17.5 16.9 Whispering Willow - East (IPL) December 2019 200 14.5 13.8 14.1 $33.1 $31.3 $31.0
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): 2015 2014 Deferred Deferred Tax Deferred Deferred Tax Alliant Energy Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $2,762.9 $2,762.9 $— $2,627.8 $2,627.8 Investment in ATC — 138.1 138.1 — 131.6 131.6 Net operating losses carryforwards - state (38.3 ) — (38.3 ) (45.7 ) — (45.7 ) Regulatory liability - IPL’s tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (236.4 ) — (236.4 ) (201.0 ) — (201.0 ) Net operating losses carryforwards - federal (250.9 ) — (250.9 ) (332.8 ) — (332.8 ) Other (85.4 ) 157.3 71.9 (88.1 ) 180.1 92.0 ($677.1 ) $3,058.3 $2,381.2 ($768.5 ) $2,939.5 $2,171.0 2015 2014 Current deferred tax assets N/A ($150.1 ) Non-current deferred tax liabilities $2,381.2 2,321.1 Total net deferred tax liabilities $2,381.2 $2,171.0 2015 2014 Deferred Deferred Tax Deferred Deferred Tax IPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,587.8 $1,587.8 $— $1,545.1 $1,545.1 Regulatory liability - tax benefit riders (66.1 ) — (66.1 ) (100.9 ) — (100.9 ) Federal credit carryforwards (81.7 ) — (81.7 ) (66.5 ) — (66.5 ) Net operating losses carryforwards - federal (113.1 ) — (113.1 ) (157.8 ) — (157.8 ) Other (36.7 ) 87.8 51.1 (37.1 ) 83.5 46.4 ($297.6 ) $1,675.6 $1,378.0 ($362.3 ) $1,628.6 $1,266.3 2015 2014 Current deferred tax assets N/A ($104.0 ) Non-current deferred tax liabilities $1,378.0 1,370.3 Total net deferred tax liabilities $1,378.0 $1,266.3 2015 2014 Deferred Deferred Tax Deferred Deferred Tax WPL Tax Assets Liabilities Net Tax Assets Liabilities Net Property $— $1,027.0 $1,027.0 $— $963.0 $963.0 Investment in ATC — 138.9 138.9 — 132.1 132.1 Federal credit carryforwards (95.5 ) — (95.5 ) (76.7 ) — (76.7 ) Net operating losses carryforwards - federal (105.1 ) — (105.1 ) (131.6 ) — (131.6 ) Other (27.8 ) 67.9 40.1 (37.1 ) 79.7 42.6 ($228.4 ) $1,233.8 $1,005.4 ($245.4 ) $1,174.8 $929.4 2015 2014 Current deferred tax assets N/A ($37.7 ) Non-current deferred tax liabilities $1,005.4 967.1 Total net deferred tax liabilities $1,005.4 $929.4
Summary Of Tax Credit Carryforwards	At December 31, 2015 , tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions): Alliant Energy IPL WPL Earliest Tax Deferred Tax Deferred Tax Deferred Expiration Date Carryforwards Tax Assets Carryforwards Tax Assets Carryforwards Tax Assets Federal net operating losses 2030 $732 $251 $336 $113 $300 $105 State net operating losses 2018 766 38 20 1 76 4 Federal tax credits 2022 240 236 85 82 96 96 $525 $196 $205
Schedule Of Open Tax Years	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) 2012 - 2014 Consolidated Iowa income tax returns (b) 2012 - 2014 Wisconsin combined tax returns (c) 2011 - 2014 (a) These federal tax returns 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, 2015
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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.
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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9
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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $1,301.5 $1,113.4 $231.1 $208.7 Service cost 15.9 13.1 5.5 5.2 Interest cost 53.6 54.1 9.1 9.5 Plan participants’ contributions — — 3.1 2.8 Plan amendments — — (0.3 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (70.1 ) 195.8 (9.4 ) 22.3 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Net benefit obligation at December 31 1,206.3 1,301.5 221.4 231.1 Change in plan assets: Fair value of plan assets at January 1 1,018.1 1,022.9 121.6 124.9 Actual return on plan assets (30.2 ) 66.4 (4.9 ) 5.6 Employer contributions 2.2 3.7 4.8 5.7 Plan participants’ contributions — — 3.1 2.8 Gross benefits paid (95.1 ) (74.9 ) (17.7 ) (17.4 ) Fair value of plan assets at December 31 895.0 1,018.1 106.9 121.6 Under funded status at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $6.1 Other current liabilities (2.6 ) (2.5 ) (6.2 ) (5.6 ) Pension and other benefit obligations (308.7 ) (280.9 ) (111.3 ) (110.0 ) Net amounts recognized at December 31 ($311.3 ) ($283.4 ) ($114.5 ) ($109.5 ) Amounts recognized in Regulatory Assets and AOCL consist of (a): Net actuarial loss $533.1 $533.4 $59.8 $60.7 Prior service credit (7.2 ) (7.4 ) (5.6 ) (16.7 ) $525.9 $526.0 $54.2 $44.0 (a) Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets.
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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Compensation expense $10.7 $15.3 $12.0 $5.7 $8.3 $6.2 $4.7 $6.4 $5.2 Income tax benefits 4.4 6.2 4.8 2.4 3.4 2.5 1.9 2.6 2.1
Schedule Of Equity-based Compensation Plans Activity	Information related to fair values of nonvested performance shares and units at December 31, 2015 , by year of grant, were as follows: Performance Shares Performance Units 2015 Grant 2014 Grant 2013 Grant 2015 Grant 2014 Grant 2013 Grant Nonvested awards 45,403 49,719 49,093 17,386 19,440 21,380 Alliant Energy common stock closing price on December 31, 2015 $62.45 $62.45 $62.45 Alliant Energy common stock closing price on grant date $65.09 $53.77 $47.58 Estimated payout percentage based on performance criteria 80 % 125 % 165 % 80 % 125 % 165 % Fair values of each nonvested award $49.96 $78.06 $103.04 $52.07 $67.21 $78.51
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): 2015 2014 Carrying value $8.5 $8.9 Fair market value 13.4 15.9
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 2015 2014 2015 2014 Carrying value $18.3 $17.8 $5.0 $5.2
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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.
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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9
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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $603.1 $514.0 $96.4 $87.8 Service cost 8.8 7.2 2.4 2.4 Interest cost 25.0 25.1 3.8 3.9 Plan participants’ contributions — — 1.0 0.9 Plan amendments — — (0.1 ) — Actuarial (gain) loss (32.3 ) 91.4 (4.6 ) 8.6 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Net benefit obligation at December 31 556.1 603.1 91.3 96.4 Change in plan assets: Fair value of plan assets at January 1 484.7 485.9 78.7 81.2 Actual return on plan assets (14.3 ) 32.1 (3.1 ) 3.6 Employer contributions 0.8 1.3 0.2 0.2 Plan participants’ contributions — — 1.0 0.9 Gross benefits paid (48.5 ) (34.6 ) (7.6 ) (7.2 ) Fair value of plan assets at December 31 422.7 484.7 69.2 78.7 Under funded status at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $— $1.2 Other current liabilities (0.8 ) (0.8 ) — — Pension and other benefit obligations (132.6 ) (117.6 ) (22.1 ) (18.9 ) Net amounts recognized at December 31 ($133.4 ) ($118.4 ) ($22.1 ) ($17.7 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $235.5 $233.1 $29.8 $27.9 Prior service credit (2.5 ) (2.6 ) (2.7 ) (8.7 ) $233.0 $230.5 $27.1 $19.2 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets.
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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Compensation expense $10.7 $15.3 $12.0 $5.7 $8.3 $6.2 $4.7 $6.4 $5.2 Income tax benefits 4.4 6.2 4.8 2.4 3.4 2.5 1.9 2.6 2.1
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 2015 2014 2015 2014 Carrying value $18.3 $17.8 $5.0 $5.2
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 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.47% 4.18% 4.97% 4.30% 3.97% 4.59% Discount rate for net periodic cost 4.18% 4.97% 4.11% 3.97% 4.59% 3.82% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.20% 7.40% 7.40% Rate of compensation increase 3.65 % - 4.50% 3.50 % - 4.50% 3.50 % - 4.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans IPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.50% 4.20% 5.05% 4.28% 3.94% 4.55% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.94% 4.55% 3.76% Expected rate of return on plan assets 7.60% 7.60% 7.60% 6.60% 7.60% 7.50% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% Ultimate trend rate N/A N/A N/A 5.00% 5.00% 5.00% Qualified Defined Benefit Pension Plan OPEB Plans WPL 2015 2014 2013 2015 2014 2013 Discount rate for benefit obligations 4.51% 4.20% 5.05% 4.28% 3.96% 4.56% Discount rate for net periodic cost 4.20% 5.05% 4.20% 3.96% 4.56% 3.81% Expected rate of return on plan assets 7.60% 7.60% 7.60% 4.60% 7.30% 7.20% Rate of compensation increase 3.65% 3.50% 3.50% N/A N/A 3.50% Medical cost trend on covered charges: Initial trend rate (end of year) N/A N/A N/A 7.25% 6.75% 7.00% 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). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan. Alliant Energy Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $15.9 $13.1 $15.7 $5.5 $5.2 $6.3 Interest cost 53.6 54.1 49.0 9.1 9.5 8.5 Expected return on plan assets (a) (75.0 ) (74.9 ) (74.0 ) (8.4 ) (8.3 ) (8.1 ) Amortization of prior service cost (credit) (b) (0.2 ) — 0.2 (11.3 ) (11.9 ) (11.9 ) Amortization of actuarial loss (c) 35.4 19.5 36.2 4.8 2.4 4.9 Additional benefit costs (d) 0.5 — 9.0 — — — $30.2 $11.8 $36.1 ($0.3 ) ($3.1 ) ($0.3 ) IPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $8.8 $7.2 $8.6 $2.4 $2.4 $2.9 Interest cost 25.0 25.1 22.9 3.8 3.9 3.6 Expected return on plan assets (a) (35.8 ) (35.7 ) (35.2 ) (5.7 ) (5.8 ) (5.6 ) Amortization of prior service cost (credit) (b) (0.1 ) — 0.1 (6.1 ) (6.3 ) (6.3 ) Amortization of actuarial loss (c) 15.3 8.0 15.2 2.3 1.1 2.7 Additional benefit costs (d) — — 2.6 — — — $13.2 $4.6 $14.2 ($3.3 ) ($4.7 ) ($2.7 ) WPL Defined Benefit Pension Plans OPEB Plans 2015 2014 2013 2015 2014 2013 Service cost $5.8 $4.9 $5.9 $2.1 $2.0 $2.5 Interest cost 22.6 22.6 20.7 3.7 3.8 3.4 Expected return on plan assets (a) (32.4 ) (32.4 ) (31.9 ) (1.5 ) (1.3 ) (1.3 ) Amortization of prior service cost (credit) (b) 0.2 0.3 0.3 (3.5 ) (3.9 ) (3.9 ) Amortization of actuarial loss (c) 16.8 9.2 17.1 2.2 1.3 1.9 Additional benefit costs (d) 0.5 — 0.6 — — — $13.5 $4.6 $12.7 $3.0 $1.9 $2.6 (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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ( $2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ( $0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.
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 2016 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 $37.4 $4.8 $16.5 $2.6 $17.6 $1.8 Prior service cost (credit) (0.3 ) (4.1 ) (0.2 ) (2.6 ) 0.2 (0.9 ) $37.1 $0.7 $16.3 $— $17.8 $0.9
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 2015 2014 2015 2014 Change in benefit obligation: Net benefit obligation at January 1 $547.6 $460.8 $94.0 $85.6 Service cost 5.8 4.9 2.1 2.0 Interest cost 22.6 22.6 3.7 3.8 Plan participants’ contributions — — 1.6 1.3 Plan amendments — — (0.2 ) — Additional benefit costs 0.5 — — — Actuarial (gain) loss (30.0 ) 86.7 (3.5 ) 9.2 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Net benefit obligation at December 31 505.9 547.6 89.7 94.0 Change in plan assets: Fair value of plan assets at January 1 440.3 438.8 21.8 21.7 Actual return on plan assets (13.0 ) 28.6 (1.1 ) 1.2 Employer contributions 0.1 0.3 4.4 5.5 Plan participants’ contributions — — 1.6 1.3 Gross benefits paid (40.6 ) (27.4 ) (8.0 ) (7.9 ) Fair value of plan assets at December 31 386.8 440.3 18.7 21.8 Under funded status at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $3.0 $4.9 Other current liabilities (0.1 ) (0.1 ) (6.0 ) (5.5 ) Pension and other benefit obligations (119.0 ) (107.2 ) (68.0 ) (71.6 ) Net amounts recognized at December 31 ($119.1 ) ($107.3 ) ($71.0 ) ($72.2 ) Amounts recognized in Regulatory Assets consist of (a): Net actuarial loss $232.1 $233.5 $23.3 $26.3 Prior service credit (1.2 ) (1.0 ) (2.4 ) (5.6 ) $230.9 $232.5 $20.9 $20.7 (a) Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets.
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 2015 2014 2015 2014 Accumulated benefit obligations $1,166.0 $1,255.0 $221.4 $231.1 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 1,166.0 1,255.0 221.4 231.1 Fair value of plan assets 895.0 1,018.1 106.9 121.6 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 1,206.3 1,301.5 N/A N/A Fair value of plan assets 895.0 1,018.1 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2015 2014 2015 2014 Accumulated benefit obligations $531.0 $575.5 $91.3 $96.4 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 531.0 575.5 91.3 96.4 Fair value of plan assets 422.7 484.7 69.2 78.7 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 556.1 603.1 N/A N/A Fair value of plan assets 422.7 484.7 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2015 2014 2015 2014 Accumulated benefit obligations $493.8 $532.5 $89.7 $94.0 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 493.8 532.5 89.7 94.0 Fair value of plan assets 386.8 440.3 18.7 21.8 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 505.9 547.6 N/A N/A Fair value of plan assets 386.8 440.3 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 2015 2014 2015 2014 Regulatory assets $38.0 $38.2 $29.5 $28.0
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $2.6 $0.8 $0.1 OPEB plans 5.8 — 5.5 (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 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $69.5 $74.3 $72.8 $74.3 $78.7 $401.4 OPEB 17.8 18.1 18.2 18.3 18.2 86.9 $87.3 $92.4 $91.0 $92.6 $96.9 $488.3 IPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $32.8 $34.1 $34.8 $34.6 $37.8 $190.8 OPEB 7.6 7.6 7.6 7.5 7.6 36.0 $40.4 $41.7 $42.4 $42.1 $45.4 $226.8 WPL 2016 2017 2018 2019 2020 2021 - 2025 Defined benefit pension benefits $29.1 $29.8 $30.7 $31.1 $32.2 $163.7 OPEB 7.5 7.8 7.8 7.8 7.6 34.7 $36.6 $37.6 $38.5 $38.9 $39.8 $198.4
Recognized Compensation Expense And Income Tax Benefits	A summary of compensation expense (including amounts allocated to IPL and WPL) and the related income tax benefits recognized for share-based compensation awards was as follows (in millions): Alliant Energy IPL WPL 2015 2014 2013 2015 2014 2013 2015 2014 2013 Compensation expense $10.7 $15.3 $12.0 $5.7 $8.3 $6.2 $4.7 $6.4 $5.2 Income tax benefits 4.4 6.2 4.8 2.4 3.4 2.5 1.9 2.6 2.1
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, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $23.1 $— $23.1 $— $49.3 $— $49.3 $— Equity securities: U.S. large cap core 100.4 100.4 — — 137.2 137.2 — — U.S. large cap value 59.9 — 59.9 — 72.2 — 72.2 — U.S. large cap growth 60.5 — 60.5 — 73.2 — 73.2 — U.S. small cap value 14.2 — 14.2 — 15.2 — 15.2 — U.S. small cap growth 16.0 16.0 — — 15.9 15.9 — — International - developed markets 104.4 52.7 51.7 — 102.9 52.1 50.8 — International - emerging markets 41.2 41.2 — — 47.2 47.2 — — Global asset allocation securities 96.3 52.9 43.4 — 99.9 57.2 42.7 — Risk parity allocation securities 94.0 — 94.0 — 102.5 — 102.5 — Fixed income securities: Corporate bonds — — — — 0.1 — 0.1 — Fixed income funds 284.8 — 284.8 — 302.7 0.2 302.5 — 894.8 $263.2 $631.6 $— 1,018.3 $309.8 $708.5 $— Accrued investment income 0.2 0.1 Due to brokers, net (pending trades with brokers) — (0.3 ) Total pension plan assets $895.0 $1,018.1 At December 31, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32%
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, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32% At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.9 $— $10.9 $— $23.5 $— $23.5 $— Equity securities: U.S. large cap core 47.4 47.4 — — 65.3 65.3 — — U.S. large cap value 28.3 — 28.3 — 34.4 — 34.4 — U.S. large cap growth 28.6 — 28.6 — 34.9 — 34.9 — U.S. small cap value 6.7 — 6.7 — 7.2 — 7.2 — U.S. small cap growth 7.5 7.5 — — 7.6 7.6 — — International - developed markets 49.3 24.9 24.4 — 49.0 24.8 24.2 — International - emerging markets 19.5 19.5 — — 22.5 22.5 — — Global asset allocation securities 45.5 25.0 20.5 — 47.5 27.2 20.3 — Risk parity allocation securities 44.4 — 44.4 — 48.8 — 48.8 — Fixed income securities: Fixed income funds 134.5 — 134.5 — 144.1 0.1 144.0 — 422.6 $124.3 $298.3 $— 484.8 $147.5 $337.3 $— Accrued investment income 0.1 0.1 Due to brokers, net (pending trades with brokers) — (0.2 ) Total pension plan assets $422.7 $484.7
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 by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $10.0 $— $10.0 $— $21.3 $— $21.3 $— Equity securities: U.S. large cap core 43.4 43.4 — — 59.3 59.3 — — U.S. large cap value 25.9 — 25.9 — 31.3 — 31.3 — U.S. large cap growth 26.2 — 26.2 — 31.7 — 31.7 — U.S. small cap value 6.1 — 6.1 — 6.6 — 6.6 — U.S. small cap growth 6.9 6.9 — — 6.9 6.9 — — International - developed markets 45.1 22.8 22.3 — 44.5 22.5 22.0 — International - emerging markets 17.8 17.8 — — 20.4 20.4 — — Global asset allocation securities 41.6 22.8 18.8 — 43.2 24.8 18.4 — Risk parity allocation securities 40.6 — 40.6 — 44.3 — 44.3 — Fixed income securities: Fixed income funds 123.1 — 123.1 — 130.9 0.1 130.8 — 386.7 $113.7 $273.0 $— 440.4 $134.0 $306.4 $— Accrued investment income 0.1 — Due to brokers, net (pending trades with brokers) — (0.1 ) Total pension plan assets $386.8 $440.3 At December 31, 2015 , 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% 2% Equity securities: U.S. large cap core 8 % - 18% 11% U.S. large cap value 2.5 % - 12.5% 7% U.S. large cap growth 2.5 % - 12.5% 7% U.S. small cap value 0 % - 4% 1% U.S. small cap growth 0 % - 4% 2% International - developed markets 7 % - 19% 12% International - emerging markets 0 % - 10% 5% Global asset allocation securities 5 % - 15% 11% Risk parity allocation securities 5 % - 15% 10% Fixed income securities 20 % - 40% 32%
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5
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 2015 2014 2013 2015 2014 2013 2015 2014 2013 401(k) costs $24.9 $22.5 $19.2 $12.7 $11.1 $9.9 $11.2 $10.5 $8.5
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 by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $3.6 $— $3.6 $— $3.7 $— $3.7 $— Equity securities: U.S. blend 21.1 21.1 — — 35.8 35.8 — — U.S. large cap core 0.9 0.9 — — 2.9 2.9 — — U.S. large cap value 0.5 — 0.5 — 1.5 — 1.5 — U.S. large cap growth 0.5 — 0.5 — 1.6 — 1.6 — U.S. small cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap growth 0.1 0.1 — — 0.4 0.4 — — International - blend 12.5 12.5 — — 14.2 14.2 — — International - developed markets 1.0 0.5 0.5 — 2.2 1.1 1.1 — International - emerging markets 0.4 0.4 — — 1.0 1.0 — — Global asset allocation securities 16.4 16.0 0.4 — 30.3 29.4 0.9 — Risk parity allocation securities 0.9 — 0.9 — 2.2 — 2.2 — Fixed income securities: Fixed income funds 48.9 46.3 2.6 — 25.5 19.0 6.5 — Total OPEB plan assets $106.9 $97.8 $9.1 $— $121.6 $103.8 $17.8 $— At December 31, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47%
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 by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $0.9 $— $0.9 $— $1.4 $— $1.4 $— Equity securities: U.S. blend 16.6 16.6 — — 27.2 27.2 — — U.S. large cap core 0.1 0.1 — — 0.5 0.5 — — U.S. large cap value 0.1 — 0.1 — 0.3 — 0.3 — U.S. large cap growth 0.1 — 0.1 — 0.3 — 0.3 — U.S. small cap value — — — — 0.1 — 0.1 — U.S. small cap growth — — — — 0.1 0.1 — — International - blend 10.7 10.7 — — 10.7 10.7 — — International - developed markets 0.1 0.1 — — 0.4 0.2 0.2 — International - emerging markets — — — — 0.2 0.2 — — Global asset allocation securities 6.9 6.9 — — 21.6 21.5 0.1 — Risk parity allocation securities 0.1 — 0.1 — 0.4 — 0.4 — Fixed income securities: Fixed income funds 33.6 33.3 0.3 — 15.5 14.3 1.2 — Total OPEB plan assets $69.2 $67.7 $1.5 $— $78.7 $74.7 $4.0 $— At December 31, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47%
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, 2015 , 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% 21% International 0 % - 21% 13% Global asset allocation securities 5 % - 40% 16% Fixed income securities 10 % - 70% 47% At December 31, the fair values of WPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions): 2015 2014 Fair Level Level Level Fair Level Level Level Value 1 2 3 Value 1 2 3 Cash and equivalents $2.3 $— $2.3 $— $1.4 $— $1.4 $— Equity securities: U.S. blend — — — — 3.6 3.6 — — U.S. large cap core — — — — 1.6 1.6 — — U.S. large cap value — — — — 0.8 — 0.8 — U.S. large cap growth — — — — 0.8 — 0.8 — U.S. small cap value — — — — 0.2 — 0.2 — U.S. small cap growth — — — — 0.2 0.2 — — International - blend — — — — 1.4 1.4 — — International - developed markets — — — — 1.2 0.6 0.6 — International - emerging markets — — — — 0.5 0.5 — — Global asset allocation securities 5.4 5.4 — — 3.8 3.3 0.5 — Risk parity allocation securities — — — — 1.1 — 1.1 — Fixed income securities: Fixed income funds 11.0 11.0 — — 5.2 1.8 3.4 — Total OPEB plan assets $18.7 $16.4 $2.3 $— $21.8 $13.0 $8.8 $—
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	Performance shares can be paid out in shares of Alliant Energy’s common stock, cash or a combination of cash and stock. 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. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. A summary of the performance shares activity, with share amounts representing the target number of performance shares, was as follows: 2015 2014 2013 Nonvested shares, January 1 144,424 139,940 145,277 Granted 45,403 51,221 49,093 Vested (45,612 ) (45,235 ) (54,430 ) Forfeited — (1,502 ) — Nonvested shares, December 31 144,215 144,424 139,940 Certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows: 2015 2014 2013 2012 Grant 2011 Grant 2010 Grant Performance shares vested 45,612 45,235 54,430 Percentage of target number of performance shares 167.5 % 147.5 % 197.5 % Aggregate payout value (in millions) $5.1 $3.4 $4.8 Payout - cash (in millions) $3.2 $2.9 $4.4 Payout - common stock shares issued 10,975 4,810 4,177
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	Performance units must be paid out in cash. Each performance unit’s value is based on the average price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units. A summary of the performance unit activity, with amounts representing the target number of performance units, was as follows: 2015 2014 2013 Nonvested units, January 1 63,665 65,912 64,969 Granted 17,837 20,422 22,201 Vested (22,845 ) (20,751 ) (19,760 ) Forfeited (451 ) (1,918 ) (1,498 ) Nonvested units, December 31 58,206 63,665 65,912 Certain performance units vested, resulting in cash payouts as follows: 2015 2014 2013 2012 Grant 2011 Grant 2010 Grant Performance units vested 22,845 20,751 19,760 Percentage of target number of performance units 167.5 % 147.5 % 197.5 % Payout value (in millions) $1.6 $1.2 $1.3
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: 2015 2014 2013 Shares Weighted Average Fair Value Shares Weighted Average Fair Value Shares Weighted Average Fair Value Nonvested shares, January 1 98,812 $50.69 158,922 $42.71 211,651 $32.42 Granted 45,403 65.09 51,221 53.77 49,093 47.58 Vested (a) (49,093 ) 47.58 (90,847 ) 40.91 — — Forfeited (b) — — (20,484 ) 39.85 (101,822 ) 23.67 Nonvested shares, December 31 95,122 59.17 98,812 50.69 158,922 42.71 (a) In 2015, 49,093 performance-contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance-contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met. (b) In 2013, 101,822 performance-contingent restricted shares granted in 2009 were forfeited because the specified performance criteria for such shares were not met. The forfeitures during 2014 were primarily caused by retirements and terminations of participants.
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: 2015 2014 2013 Nonvested awards, January 1 78,930 96,977 59,639 Granted 41,105 42,446 39,530 Vested (a) (37,332 ) (55,517 ) — Forfeited (827 ) (4,976 ) (2,192 ) Nonvested awards, December 31 81,876 78,930 96,977 (a) In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million . In 2014, 34,766 and 20,751 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, 2015
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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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 2015 2014 2015 2014 2015 2014 Balance, January 1 $114.0 $109.7 $51.8 $47.9 $52.4 $52.4 Revisions in estimated cash flows (a) 17.3 — 15.1 — 3.2 — Liabilities settled (8.8 ) (3.4 ) (4.3 ) (1.4 ) (4.5 ) (2.0 ) Liabilities incurred (a) 86.6 3.7 67.8 3.5 18.8 0.2 Accretion expense 4.9 4.0 2.5 1.8 2.0 1.8 Balance, December 31 $214.0 $114.0 $132.9 $51.8 $71.9 $52.4 (a) In April 2015, the EPA published the final CCR Rule, which regulates CCR as a non-hazardous waste and is 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. The 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, 2015
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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9
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 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3
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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9
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 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3
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 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $18.4 $— $2.5 $15.9 $18.4 $38.6 $— $2.6 $36.0 $38.6 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 64.6 — 16.0 48.6 64.6 37.6 — 19.5 18.1 37.6 Long-term debt (including current maturities) 3,835.6 — 4,332.4 3.7 4,336.1 3,767.3 — 4,414.9 3.3 4,418.2 Cumulative preferred stock of IPL 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 IPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $15.5 $— $2.0 $13.5 $15.5 $28.0 $— $2.4 $25.6 $28.0 Deferred proceeds 172.0 — — 172.0 172.0 177.2 — — 177.2 177.2 Liabilities and equity: Derivatives 23.4 — 8.0 15.4 23.4 19.5 — 13.3 6.2 19.5 Long-term debt (including current maturities) 1,856.9 — 2,092.7 — 2,092.7 1,758.0 — 2,053.0 — 2,053.0 Cumulative preferred stock 200.0 206.6 — — 206.6 200.0 200.2 — — 200.2 WPL 2015 2014 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Derivatives $2.9 $— $0.5 $2.4 $2.9 $10.6 $— $0.2 $10.4 $10.6 Liabilities and equity: Derivatives 41.2 — 8.0 33.2 41.2 18.1 — 6.2 11.9 18.1 Long-term debt (including current maturities) 1,533.9 — 1,793.0 — 1,793.0 1,563.1 — 1,908.9 — 1,908.9
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 2015 2014 2015 2014 Beginning balance, January 1 $17.9 $4.4 $177.2 $203.5 Total net gains (losses) included in changes in net assets (realized/unrealized) (63.5 ) 11.1 — — Transfers out of Level 3 0.3 — — — Purchases 36.9 76.7 — — Sales (1.9 ) (2.2 ) — — Settlements (a) (22.4 ) (72.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($32.7 ) $17.9 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($56.0 ) ($0.4 ) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2015 2014 2015 2014 Beginning balance, January 1 $19.4 $14.6 $177.2 $203.5 Total net losses included in changes in net assets (realized/unrealized) (29.6 ) (5.9 ) — — Purchases 33.1 68.8 — — Sales (1.8 ) (2.0 ) — — Settlements (a) (23.0 ) (56.1 ) (5.2 ) (26.3 ) Ending balance, December 31 ($1.9 ) $19.4 $172.0 $177.2 The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31 ($23.1 ) ($9.3 ) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2015 2014 Beginning balance, January 1 ($1.5 ) ($10.2 ) Total net gains (losses) included in changes in net assets (realized/unrealized) (33.9 ) 17.0 Transfers out of Level 3 0.3 — Purchases 3.8 7.9 Sales (0.1 ) (0.2 ) Settlements 0.6 (16.0 ) Ending balance, December 31 ($30.8 ) ($1.5 ) The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 ($32.9 ) $8.9 (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 2015 ($43.1 ) $10.4 ($12.3 ) $10.4 ($30.8 ) $— 2014 (7.0 ) 24.9 (3.2 ) 22.6 (3.8 ) 2.3

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018
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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4
IPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018
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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4
WPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2015 , gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts, FTRs and coal contracts that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Coal MWhs Years MWhs Years Dths Years Tons Years Alliant Energy 5,868 2016-2018 9,880 2016 104,096 2016-2020 4,945 2016-2018 IPL 809 2016 5,622 2016 55,985 2016-2020 1,966 2016-2018 WPL 5,059 2016-2018 4,258 2016 48,111 2016-2020 2,979 2016-2018
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 2015 2014 2015 2014 2015 2014 Current derivative assets $15.1 $30.5 $13.8 $27.4 $1.3 $3.1 Non-current derivative assets 3.3 8.1 1.7 0.6 1.6 7.5 Current derivative liabilities 47.3 28.1 18.5 16.4 28.8 11.7 Non-current derivative liabilities 17.3 9.5 4.9 3.1 12.4 6.4

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 .
Schedule of Environmental Liabilities	At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9 At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2
IPL [Member]
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 .
Schedule of Environmental Liabilities	At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2 At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9
WPL [Member]
Long-term Purchase Commitment [Line Items]
Operating Expense Purchase Obligations	At December 31, 2015 , minimum future commitments related to these operating expense purchase obligations were as follows (in millions): Alliant Energy 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (IPL) (b) $125 $138 $131 $143 $133 $749 $1,419 Other 77 44 44 — — — 165 202 182 175 143 133 749 1,584 Natural gas 173 82 52 43 32 16 398 Coal (c) 129 76 50 12 — — 267 SO2 emission allowances 14 8 — — — — 22 Other (d) 6 2 2 2 2 7 21 $524 $350 $279 $200 $167 $772 $2,292 IPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a): DAEC (b) $125 $138 $131 $143 $133 $749 $1,419 Other 1 — — — — — 1 126 138 131 143 133 749 1,420 Natural gas 95 42 35 28 18 10 228 Coal (c) 70 30 17 4 — — 121 SO2 emission allowances 14 8 — — — — 22 Other (d) 1 — — — — — 1 $306 $218 $183 $175 $151 $759 $1,792 WPL 2016 2017 2018 2019 2020 Thereafter Total Purchased power (a) $76 $44 $44 $— $— $— $164 Natural gas 78 40 17 15 14 6 170 Coal (c) 59 46 33 8 — — 146 Other (d) 2 — — — — — 2 $215 $130 $94 $23 $14 $6 $482 (a) Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions. (b) Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause. (c) 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, 2015 regarding expected future usage, which is subject to change. (d) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015 .
Schedule of Environmental Liabilities	At December 31, 2015 , estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $11 - $28 $9 - $25 $2 - $3 Current and non-current environmental liabilities 15 13 2 At December 31, current environmental liabilities were included in “Other current liabilities” and non-current environmental liabilities were included in “Other liabilities” on the balance sheets as follows (in millions): Alliant Energy IPL WPL 2015 2014 2015 2014 2015 2014 Current environmental liabilities $2.7 $2.0 $1.7 $1.7 $1.0 $0.3 Non-current environmental liabilities 12.8 13.5 11.2 11.9 1.5 1.6 $15.5 $15.5 $12.9 $13.6 $2.5 $1.9

Segments Of Business (Tables)

Segments Of Business (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to Alliant Energy’s business segments, services and geographic information was as follows (in millions): 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 Utility Non-Regulated, Alliant Energy 2013 Electric Gas Other Total Parent and Other Consolidated Operating revenues $2,689.0 $464.8 $71.3 $3,225.1 $51.7 $3,276.8 Depreciation and amortization 333.0 28.8 1.5 363.3 7.6 370.9 Operating income 444.5 57.3 6.3 508.1 25.8 533.9 Interest expense 166.3 6.5 172.8 Equity income from unconsolidated investments, net (43.7 ) — — (43.7 ) — (43.7 ) Income taxes 49.3 4.6 53.9 Net income attributable to Alliant Energy common shareowners 349.5 8.8 358.3 Total assets 9,018.6 859.3 712.2 10,590.1 502.4 11,092.5 Investments in equity method subsidiaries 279.1 — — 279.1 2.3 281.4 Construction and acquisition expenditures 677.3 47.0 7.3 731.6 66.7 798.3
Schedule of Products and Services	Alliant Energy’s consolidated operating revenues by segment, which were substantially all related to services, were as follows: 2015 2014 2013 Utility electric operations 85 % 81 % 82 % Utility gas operations 12 % 15 % 14 % Utility other 2 % 2 % 2 % Other 1 % 2 % 2 % 100 % 100 % 100 %
IPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to IPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,491.8 $273.9 $53.1 $1,818.8 Depreciation and amortization 173.1 16.5 1.5 191.1 Operating income 173.1 29.8 9.1 212.0 Interest expense 81.3 Income tax benefit (36.3 ) Earnings available for common stock 172.0 Total assets 4,905.3 518.8 369.8 5,793.9 Construction and acquisition expenditures 365.4 27.5 7.3 400.2
WPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to WPL’s business segments was as follows (in millions): 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 2013 Electric Gas Other Total Operating revenues $1,197.2 $190.9 $18.2 $1,406.3 Depreciation and amortization 159.9 12.3 — 172.2 Operating income (loss) 271.4 27.5 (2.8 ) 296.1 Interest expense 85.0 Equity income from unconsolidated investments (43.7 ) — — (43.7 ) Income taxes 85.6 Earnings available for common stock 177.5 Total assets 4,113.3 340.5 342.4 4,796.2 Investments in equity method subsidiaries 279.1 — — 279.1 Construction and acquisition expenditures 311.9 19.5 — 331.4

Related Parties (Tables)

Related Parties (Tables)	12 Months Ended
	Dec. 31, 2015
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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2015 2014 2013 ATC billings to WPL $101 $96 $96 WPL billings to ATC 13 9 12
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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58
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 2015 2014 2013 2015 2014 2013 Corporate Services billings $150 $148 $140 $121 $116 $103 Sales credited 10 8 7 24 6 12 Purchases billed 366 422 365 66 125 68
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2015 2014 IPL $93 $84 WPL 54 58
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2015 2014 2013 ATC billings to WPL $101 $96 $96 WPL billings to ATC 13 9 12

Discontinued Operations and A49

Discontinued Operations and Assets and Liabilities Held For Sale (Tables)	12 Months Ended
	Dec. 31, 2015
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): 2015 2014 2013 Operating revenues $— $— $0.9 Operating expenses 4.0 3.7 9.9 Loss before income taxes (4.0 ) (3.7 ) (9.0 ) Income tax benefit (1.5 ) (1.3 ) (3.1 ) Loss from discontinued operations, net of tax ($2.5 ) ($2.4 ) ($5.9 )
Assets and Liabilities Held For Sale on Consolidated Balance Sheets	As of December 31, 2014, Alliant Energy’s and IPL’s balance sheets included assets held for sale related to IPL’s Minnesota natural gas distribution assets recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions): Assets held for sale: Current assets $1.1 Property, plant and equipment, net 11.0 Non-current regulatory assets 7.0 Total assets held for sale 19.1 Liabilities held for sale: Current liabilities 1.0 Other liabilities 7.1 Total liabilities held for sale 8.1 Net assets held for sale $11.0
IPL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets and Liabilities Held For Sale on Consolidated Balance Sheets	As of December 31, 2014, Alliant Energy’s and IPL’s balance sheets included assets held for sale related to IPL’s Minnesota natural gas distribution assets recorded in “Other current assets” and liabilities held for sale recorded in “Other current liabilities” as follows (in millions): Assets held for sale: Current assets $1.1 Property, plant and equipment, net 11.0 Non-current regulatory assets 7.0 Total assets held for sale 19.1 Liabilities held for sale: Current liabilities 1.0 Other liabilities 7.1 Total liabilities held for sale 8.1 Net assets held for sale $11.0

Selected Consolidated Quarter50

Selected Consolidated Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
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. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions, except per share data) Operating revenues $897.4 $717.2 $898.9 $740.1 $952.8 $750.3 $843.1 $804.1 Operating income 152.9 109.0 235.9 79.2 154.2 103.3 194.8 91.3 Amounts attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 96.6 68.9 180.0 35.2 108.0 62.1 155.2 60.2 Loss from discontinued operations, net of tax — (1.3 ) (0.1 ) (1.1 ) — (0.3 ) (1.9 ) (0.2 ) Net income 96.6 67.6 179.9 34.1 108.0 61.8 153.3 60.0 Earnings per weighted average common share attributable to Alliant Energy common shareowners: Income from continuing operations, net of tax 0.87 0.61 1.59 0.31 0.97 0.56 1.40 0.54 Loss from discontinued operations, net of tax — (0.01 ) — (0.01 ) — — (0.02 ) — Net income 0.87 0.60 1.59 0.30 0.97 0.56 1.38 0.54
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. Refer to Note 1(q) for discussion of IPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to IPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $489.0 $382.2 $504.6 $398.7 $528.9 $411.9 $476.2 $431.1 Operating income 65.5 33.8 117.0 25.6 57.5 34.0 93.9 23.8 Net income 50.1 19.0 119.1 8.0 45.3 20.5 104.6 21.4 Earnings available for common stock 47.5 16.5 116.5 5.5 42.7 18.0 102.0 18.9
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. Refer to Note 1(q) for discussion of WPL’s previously reported Selected Consolidated Quarterly Financial Data (Unaudited), which was impacted as a result of a change to WPL’s method of recording income taxes retrospectively adopted in the fourth quarter of 2015. 2015 2014 March 31 June 30 Sep. 30 Dec. 31 March 31 June 30 Sep. 30 Dec. 31 (in millions) Operating revenues $397.1 $324.7 $382.6 $330.7 $410.4 $324.5 $354.4 $359.8 Operating income 80.8 68.3 110.3 49.3 87.7 60.0 93.9 59.4 Net income 45.1 39.7 68.4 24.4 55.2 34.7 57.9 33.3 Earnings available for common stock 44.9 39.2 68.0 24.2 55.2 34.7 57.9 32.6

Condensed Parent Company Fina51

Condensed Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2015
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, 2015 2014 2013 (in millions) Operating revenues $2 $2 $2 Operating expenses 3 3 1 Operating income (loss) (1 ) (1 ) 1 Interest expense and other: Equity earnings from consolidated subsidiaries (379 ) (388 ) (361 ) Interest expense 3 9 11 Interest income (3 ) (2 ) (2 ) Total interest expense and other (379 ) (381 ) (352 ) Income before income taxes 378 380 353 Income tax benefit (1 ) (3 ) (5 ) Net income $379 $383 $358 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, 2015 2014 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $93 $95 Other 9 25 Total current assets 102 120 Investments: Investments in consolidated subsidiaries 3,999 3,721 Other 14 15 Total investments 4,013 3,736 Other assets 20 10 Total assets $4,135 $3,866 LIABILITIES AND EQUITY Current liabilities: Current maturities of long-term debt $250 $— Commercial paper 140 141 Other 12 29 Total current liabilities 402 170 Long-term debt, net (excluding current portion) — 250 Other liabilities 12 11 Common equity: Common stock and additional paid-in capital 1,664 1,510 Retained earnings 2,066 1,934 Shares in deferred compensation trust (9 ) (9 ) Total common equity 3,721 3,435 Total liabilities and equity $4,135 $3,866 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, 2015 2014 2013 (in millions) Net cash flows from operating activities $262 $246 $238 Cash flows used for investing activities: Capital contributions to consolidated subsidiaries (165 ) (90 ) (120 ) Capital repayments from consolidated subsidiaries — 50 95 Net change in notes receivable from affiliates 2 (23 ) 5 Other — — (2 ) Net cash flows used for investing activities (163 ) (63 ) (22 ) Cash flows used for financing activities: Common stock dividends (247 ) (226 ) (208 ) Proceeds from issuance of common stock, net 151 — — Proceeds from issuance of long-term debt — 250 — Payments to retire long-term debt — (250 ) — Net change in commercial paper (1 ) 45 (9 ) Other (2 ) (2 ) 1 Net cash flows used for financing activities (99 ) (183 ) (216 ) 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 ) ($11 ) ($13 ) Income taxes, net (9 ) (5 ) (7 ) 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		12 Months Ended
		Dec. 31, 2015USD ($)customer$ / unitMW	Dec. 31, 2014USD ($)
Asset Impairments:
Non-regulated Generation, net | $	[1]	$ 229.3	$ 240.1
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
Asset Impairments:
Non-regulated Generation, net | $		$ 130
Customer Billing And Information System [Member]
Property, Plant and Equipment:
Property, plant and equipment, useful life		12 years
Software [Member]
Property, Plant and Equipment:
Property, plant and equipment, useful life		5 years
Minimum [Member]
Asset Impairments:
Average forward electricity price (in dollars per MWh) | $ / unit		2
Maximum [Member]
Asset Impairments:
Average forward electricity price (in dollars per MWh) | $ / unit		3
[1]	Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014, respectively.

Summary Of Significant Accoun53

Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Electric - generation [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.60%	3.60%	3.60%
Electric - generation [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.20%	3.20%	3.30%
Electric - distribution [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.40%	2.50%	2.50%
Electric - distribution [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.70%	2.70%	2.70%
Electric - other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.00%	4.00%	4.00%
Electric - other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.50%	5.90%	5.00%
Gas [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.20%	3.30%	3.40%
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%	4.30%	4.70%
Other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	6.00%	6.00%	5.10%

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, 2015	Dec. 31, 2014	Dec. 31, 2013
IPL [Member] | IPL (Marshalltown CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	[1]	7.90%	8.00%	0.00%
IPL [Member] | IPL (other CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		7.70%	7.80%	8.20%
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		7.90%	4.10%	4.50%
[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.

Summary Of Significant Accoun55

Summary Of Significant Accounting Policies Summary Of Significant Accounting Policies (Schedule Of New Accounting Standards And Changes In Accounting Principles) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	$ 0				$ 150.1				$ 0	$ 150.1
Total current assets	826.8				1,043.1				826.8	1,043.1
Deferred charges and other	14.6				21.5				14.6	21.5
Total other assets	1,803				1,737.1				1,803	1,737.1
Total assets	12,495.2				12,063.5				12,495.2	12,063.5	$ 11,092.5
Other current liabilities	296.6				262.4				296.6	262.4
Total current liabilities	1,359.3				1,214.7				1,359.3	1,214.7
Long-term debt, net (excluding current portion)	3,522.2				3,584.3				3,522.2	3,584.3
Deferred tax liabilities	2,381.2				2,321.1				2,381.2	2,321.1
Total other liabilities	3,689.6				3,624				3,689.6	3,624
Retained earnings	2,068.9				1,938				2,068.9	1,938
Total common equity	3,724.1				3,438.7				3,724.1	3,438.7	3,281.4	$ 3,134.9
Total equity	3,924.1				3,640.5				3,924.1	3,640.5
Total liabilities and equity	12,495.2				12,063.5				12,495.2	12,063.5
Income tax expense (benefit)									70.4	44.3	53.9
Net income									388.4	393.3	376.2
Net income (loss) attributable to common shareowners	34.1	$ 179.9	$ 67.6	$ 96.6	60	$ 153.3	$ 61.8	$ 108	378.2	383.1	358.3
Deferred tax expense (benefit) and investment tax credits									114.2	55.2	108.3
Other									(5.4)	59.7	23.7
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					43.9					43.9
Total other assets					1,759.5					1,759.5
Total assets					12,085.9					12,085.9
Long-term debt, net (excluding current portion)					3,606.7					3,606.7
Total liabilities and equity					12,085.9					12,085.9
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(22.4)					(22.4)
Total other assets					(22.4)					(22.4)
Total assets					(22.4)					(22.4)
Long-term debt, net (excluding current portion)					(22.4)					(22.4)
Total liabilities and equity					(22.4)					(22.4)
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	0				104				0	104
Total current assets	396.4				555.2				396.4	555.2
Deferred charges and other	5				2				5	2
Total other assets	1,368				1,321.2				1,368	1,321.2
Total assets	6,709.1				6,450.2				6,709.1	6,450.2
Other current liabilities	69.5				64.6				69.5	64.6
Total current liabilities	531.1				705.9				531.1	705.9
Long-term debt, net (excluding current portion)	1,856.9				1,608				1,856.9	1,608
Deferred tax liabilities	1,378				1,370.3				1,378	1,370.3
Total other liabilities	2,125.8				2,152				2,125.8	2,152
Retained earnings	554.1				508.1				554.1	508.1	461.9	415.2
Total common equity	1,995.3				1,784.3				1,995.3	1,784.3	1,648.1	1,486.4
Total equity	2,195.3				1,984.3				2,195.3	1,984.3
Total liabilities and equity	6,709.1				6,450.2				6,709.1	6,450.2
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income	8	119.1	19	50.1	21.4	104.6	20.5	45.3	196.2	191.8	188.3
Net income (loss) attributable to common shareowners	5.5	116.5	16.5	47.5	18.9	102	18	42.7	186	181.6	172
Deferred tax expense (benefit) and investment tax credits									28.9	(11.5)	3
Other									43	36.6	(11.2)
IPL [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					104.9					104.9
Total current assets					556.1					556.1
Deferred charges and other					12.7					12.7
Total other assets					1,331.9					1,331.9
Total assets					6,461.8					6,461.8
Long-term debt, net (excluding current portion)					1,618.7					1,618.7
Deferred tax liabilities	1,346.7				1,341.4				1,346.7	1,341.4
Total other liabilities	2,094.5				2,123.1				2,094.5	2,123.1
Retained earnings	585.4				537.9				585.4	537.9	493.5	448
Total common equity	2,026.6				1,814.1				2,026.6	1,814.1
Total equity	2,226.6				2,014.1				2,226.6	2,014.1
Total liabilities and equity					6,461.8					6,461.8
Income tax expense (benefit)										(51.7)	(37.9)
Net income		120	19.2	50.4	22.6	105.1	20.9	46		194.6	189.9
Net income (loss) attributable to common shareowners		117.4	16.7	47.8	20.1	102.5	18.4	43.4		184.4	173.6
Deferred tax expense (benefit) and investment tax credits										(9.7)	4.2
Other										32	(14)
IPL [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					(0.9)					(0.9)
Total current assets					(0.9)					(0.9)
Total assets					(0.9)					(0.9)
Deferred tax liabilities	31.3				28.9				31.3	28.9
Total other liabilities	31.3				28.9				31.3	28.9
Retained earnings	(31.3)				(29.8)				(31.3)	(29.8)	(31.6)	(32.8)
Total common equity	(31.3)				(29.8)				(31.3)	(29.8)
Total equity	(31.3)				(29.8)				(31.3)	(29.8)
Total liabilities and equity					(0.9)					(0.9)
Income tax expense (benefit)										2.8	1.6
Net income										(2.8)	(1.6)
Net income (loss) attributable to common shareowners										(2.8)	(1.6)
Deferred tax expense (benefit) and investment tax credits										(1.8)	(1.2)
Other										4.6	2.8
IPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(10.7)					(10.7)
Total other assets					(10.7)					(10.7)
Total assets					(10.7)					(10.7)
Long-term debt, net (excluding current portion)					(10.7)					(10.7)
Total liabilities and equity					(10.7)					(10.7)
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	0				37.7				0	37.7
Total current assets	423.5				457.4				423.5	457.4
Deferred charges and other	9.1				18.9				9.1	18.9
Total other assets	434.5				415.3				434.5	415.3
Total assets	5,270.4				5,117.6				5,270.4	5,117.6
Other current liabilities	79.5				46.6				79.5	46.6
Total current liabilities	336.9				310.3				336.9	310.3
Long-term debt, net (excluding current portion)	1,533.9				1,532.5				1,533.9	1,532.5
Deferred tax liabilities	1,005.4				967.1				1,005.4	967.1
Total other liabilities	1,632				1,559.4				1,632	1,559.4
Retained earnings	731.1				681.7				731.1	681.7	622.2	565.9
Total common equity	1,756.3				1,706.9				1,756.3	1,706.9
Total equity	1,767.6				1,715.4				1,767.6	1,715.4	1,647.4	1,591.3
Total liabilities and equity	5,270.4				5,117.6				5,270.4	5,117.6
Income tax expense (benefit)									82.9	85.3	85.6
Net income	24.4	68.4	39.7	45.1	33.3	57.9	34.7	55.2	177.6	181.1	179.1
Net income (loss) attributable to common shareowners	24.2	68	39.2	44.9	32.6	57.9	34.7	55.2	176.3	180.4	177.5
Deferred tax expense (benefit) and investment tax credits									77.6	82.6	89.8
Other									27.4	(9)	(21.6)
WPL [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					37.5					37.5
Total current assets					457.2					457.2
Deferred charges and other					29.7					29.7
Total other assets					426.1					426.1
Total assets					5,128.2					5,128.2
Other current liabilities	78.2								78.2
Total current liabilities	335.6								335.6
Long-term debt, net (excluding current portion)					1,543.3					1,543.3
Deferred tax liabilities	1,010.8				970				1,010.8	970
Total other liabilities	1,637.4				1,562.3				1,637.4	1,562.3
Retained earnings	727				678.6				727	678.6	617.2	557.6
Total common equity	1,752.2				1,703.8				1,752.2	1,703.8
Total equity	1,763.5				1,712.3				1,763.5	1,712.3
Total liabilities and equity					5,128.2					5,128.2
Income tax expense (benefit)										85.6	87.2
Net income		67.9	39.5	44.8	29.8	61.6	34.6	54.8		180.8	177.5
Net income (loss) attributable to common shareowners		$ 67.5	$ 39	$ 44.6	29.1	$ 61.6	$ 34.6	$ 54.8		180.1	175.9
Deferred tax expense (benefit) and investment tax credits										80.7	86.5
Other										(6.8)	(16.7)
WPL [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					0.2					0.2
Total current assets					0.2					0.2
Total assets					0.2					0.2
Other current liabilities	1.3								1.3
Total current liabilities	1.3								1.3
Deferred tax liabilities	(5.4)				(2.9)				(5.4)	(2.9)
Total other liabilities	(5.4)				(2.9)				(5.4)	(2.9)
Retained earnings	4.1				3.1				4.1	3.1	5	$ 8.3
Total common equity	4.1				3.1				4.1	3.1
Total equity	$ 4.1				3.1				$ 4.1	3.1
Total liabilities and equity					0.2					0.2
Income tax expense (benefit)										(0.3)	(1.6)
Net income										0.3	1.6
Net income (loss) attributable to common shareowners										0.3	1.6
Deferred tax expense (benefit) and investment tax credits										1.9	3.3
Other										(2.2)	$ (4.9)
WPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(10.8)					(10.8)
Total other assets					(10.8)					(10.8)
Total assets					(10.8)					(10.8)
Long-term debt, net (excluding current portion)					(10.8)					(10.8)
Total liabilities and equity					$ (10.8)					$ (10.8)

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended				36 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (67.8)	$ 10.8	$ (90.8)
Electric revenues		2,770.5	2,713.6	2,689
Regulatory liabilities		737.7	821.2
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		$ 30
Period for simple average of actual costs incurred during Test Year		2 years
Increase (decrease) in regulatory liabilities		$ (75.5)	(18.9)	(82.3)
Electric revenues		1,503.8	1,493.3	1,491.8
Regulatory liabilities		489.2	583.5
Billing credits to reduce retail electric customers' bills		24	72
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return		$ 12
Expenditure collection period after new rate implementation		5 years
Increase (decrease) in regulatory liabilities		$ 7.7	29.7	(8.5)
Electric revenues		1,266.7	1,220.3	1,197.2
Regulatory liabilities		248.5	237.7
WPL [Member] | 2013/2014 Test Period Retail Electric And Gas Final Order [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			(13)
Alliant Energy and IPL [Member] | Revenue Requirement Adjustment [Member]
Regulatory Matters [Line Items]
Electric revenues		14	15	24
Alliant Energy and WPL [Member] | Deferral [Member]
Regulatory Matters [Line Items]
Regulatory liabilities		8
Scenario, Forecast [Member] | IPL [Member]
Regulatory Matters [Line Items]
Billing credits to reduce retail electric customers' bills	$ 9				$ 105
Scenario, Forecast [Member] | Alliant Energy and IPL [Member] | Revenue Requirement Adjustment [Member]
Regulatory Matters [Line Items]
Electric revenues	15
Electric [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		(72)	(85)	(79)
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	(65)
Gas [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		(12)
Gas [Member] | Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Matters [Line Items]
Increase (decrease) in regulatory liabilities		$ (12)	(12)	$ (11)
Nelson Dewey Units 1 and 2 and Edgewater Unit Three [Member] | WPL [Member]
Regulatory Matters [Line Items]
Expenditure collection period after new rate implementation		10 years
2014 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Annual bandwidth for fuel-related costs		2.00%
2014 Test Year Retail Electric Fuel Related [Member] | Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 28	28
Under-collection of retail fuel related costs			33
2015/2016 Test Period Retail Electric And Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		(5)
2016 Test Year Retail Electric Fuel Related [Member] | Scenario, Forecast [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount	$ 7
Authorized increase (decrease) in final rates, percent	1.00%
Annual bandwidth for fuel-related costs	2.00%
2015 Test Year Retail Electric Fuel Related [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 39
Authorized increase (decrease) in final rates, percent		4.00%
Annual bandwidth for fuel-related costs		2.00%
2015 Test Year Retail Electric Fuel Related [Member] | Alliant Energy and WPL [Member]
Regulatory Matters [Line Items]
Over-collection of retail fuel-related costs			$ 10
Fuel [Member] | WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 25
Sales [Member] | WPL [Member]
Regulatory Matters [Line Items]
Retail electric fuel-related costs		$ 14

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Regulatory assets	$ 1,908.6	$ 1,783.7
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	987.7	955.3
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	579.5	570.2
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	92.4	73.7
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	70.6	46.9
WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	45	0
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	35.9	31.1
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.9	27.4
Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	16.4	16
Debt redemption costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	14.3	16.1
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	39.9	47
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,402.6	1,357.9
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	958.2	928
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	298.1	287.9
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	50.8	41.4
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	28.2	28
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	2.8	0.4
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	26.9	27.4
IPL [Member] | Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	11	11.5
IPL [Member] | Debt redemption costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	9.5	10.9
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	17.1	22.4
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	506	425.8
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	29.5	27.3
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	281.4	282.3
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	41.6	32.3
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	42.4	18.9
WPL [Member] | WPL's EGUs retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	45	0
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	33.1	30.7
WPL [Member] | Environmental-related costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	5.4	4.5
WPL [Member] | Debt redemption costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	4.8	5.2
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 22.8	$ 24.6

Regulatory Matters (Regulator58

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 737.7	$ 821.2
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	406	421.7
IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	159.2	243
Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48.3	64.3
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	43.5	19.4
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	37.6	15.4
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	43.1	57.4
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	489.2	583.5
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	260.4	279.1
IPL [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	159.2	243
IPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.9	19.4
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	23.5	15.1
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24.2	26.9
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	248.5	237.7
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	145.6	142.6
WPL [Member] | Energy efficiency cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48.3	64.3
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21.6	0
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	14.1	0.3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 18.9	$ 30.5

Regulatory Matters (IPL's Tax B

Regulatory Matters (IPL's Tax Benefit Riders) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	$ (67.8)	$ 10.8	$ (90.8)
Alliant Energy and IPL [Member] | Electric tax benefit rider credits [Member]
Regulatory Assets [Line Items]
Increase (decrease) in regulatory liabilities	(72)
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	$ (84)

Regulatory Matters (Electric Ta

Regulatory Matters (Electric Tax Benefit Rider) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (67.8)	$ 10.8	$ (90.8)
Income tax expense (benefit)	70.4	44.3	53.9
Alliant Energy and IPL [Member] | Electric [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(72)	(85)	(79)
Income tax expense (benefit)	(42)	(50)	(46)
Alliant Energy and IPL [Member] | Electric [Member] | IPL's Tax Benefit Rider Decrease In Taxable Income [Member]
Regulatory Liabilities [Line Items]
Income tax expense (benefit)	$ (30)	$ (35)	$ (33)

Regulatory Matters (Revenue Req

Regulatory Matters (Revenue Requirement Adjustment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Electric revenues	$ 2,770.5	$ 2,713.6	$ 2,689
Alliant Energy and IPL [Member] | Revenue Requirement Adjustment [Member]
Regulatory Liabilities [Line Items]
Electric revenues	$ 14	$ 15	$ 24

Regulatory Matters (Gas Tax Ben

Regulatory Matters (Gas Tax Benefit Rider) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	$ (67.8)	$ 10.8	$ (90.8)
Income tax expense (benefit)	70.4	44.3	53.9
Gas [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(12)
Alliant Energy and IPL [Member] | Gas [Member] | IPL's tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Increase (decrease) in regulatory liabilities	(12)	(12)	(11)
Income tax expense (benefit)	(7)	(7)	(7)
Alliant Energy and IPL [Member] | Gas [Member] | IPL's Tax Benefit Rider Decrease In Taxable Income [Member]
Regulatory Liabilities [Line Items]
Income tax expense (benefit)	$ (5)	$ (5)	$ (4)

Regulatory Matters (Customer Bi

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

Property, Plant and Equipment64

Property, Plant and Equipment (Narrative) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015USD ($)MW	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 897.5	$ 479.1
Allowance for funds used during construction		36.9	34.8	$ 30.8
Non-regulated Generation, net	[1]	229.3	240.1
Corporate Services and other, net	[2]	319.6	269.4
IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		578.2	325
Allowance for funds used during construction		$ 28.2	25.9	21
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		$ 319.3	154.1
Allowance for funds used during construction		$ 8.7	8.9	9.8
Franklin County Wind Farm [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		30 years
Sheboygan Falls Energy Facility [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		35 years
Non-regulated Generation, net		$ 99
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
IPL (FERC formula) [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Authorized return on common equity		10.97%
Edgewater Unit 5 [Member] | Alliant Energy and WPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 190	90
Allowance for funds used during construction		$ 8	3
Marshalltown Generating Station [Member]
Property, Plant and Equipment [Line Items]
Fossil-fueled EGU capacity (in megawatts) | MW		650
Marshalltown Generating Station [Member] | IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction		$ 20.7	3.7	$ 0
Marshalltown Generating Station [Member] | Alliant Energy and IPL [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		453	188
Allowance for funds used during construction		24	$ 4
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
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
Customer Billing And Information System [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life		12 years
Corporate Services and other, net		$ 102
Capitalized interest		$ 3
[1]	Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014, respectively.
[2]	Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014, respectively.

Property, Plant and Equipment65

Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	$ 0	$ 157.6
Total electric plant		10,444.9	10,365.1
Gas plant in service		1,018.3	946.2
Other plant in service		530.6	539.3
Accumulated depreciation	[1]	(3,939.6)	(3,923.1)
Net plant		8,054.2	7,927.5
Construction work in progress		897.5	479.1
Other, net		18.5	22.3
Total utility		8,970.2	8,428.9
Non-regulated Generation, net	[2]	229.3	240.1
Corporate Services and other, net	[3]	319.6	269.4
Total non-regulated and other		548.9	509.5
Total property, plant and equipment		9,519.1	8,938.4
Non-regulated Generation, accumulated depreciation		59	49.5
Corporate Services and other, accumulated depreciation		252.9	229.1
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		5,643.7	5,463
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		4,489.9	4,435.4
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		311.3	309.1
IPL [Member]
Property, Plant and Equipment [Line Items]
Total electric plant		5,671.7	5,559.6
Gas plant in service		513.6	474
Other plant in service		296	298.8
Accumulated depreciation	[1]	(2,152.8)	(2,124.5)
Net plant		4,328.5	4,207.9
Construction work in progress		578.2	325
Other, net		18.4	21.8
Total utility		4,925.1	4,554.7
Total property, plant and equipment		4,925.1	4,554.7
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		3,011.6	2,872.4
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,447.9	2,471.7
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		212.2	215.5
WPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	0	157.6
Total electric plant		4,773.2	4,805.5
Gas plant in service		504.7	472.2
Other plant in service		234.6	240.5
Accumulated depreciation	[1]	(1,786.8)	(1,798.6)
Net plant		3,725.7	3,719.6
Leased Sheboygan Falls Energy Facility, net	[4]	58.6	64.7
Construction work in progress		319.3	154.1
Other, net		0.1	0.5
Total utility		4,103.7	3,938.9
Total property, plant and equipment		4,103.7	3,938.9
Leased Sheboygan Falls Energy Facility, accumulated depreciation		65.2	59.1
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,632.1	2,590.6
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,042	1,963.7
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		$ 99.1	$ 93.6
[1]	In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs.
[2]	Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014, respectively.
[3]	Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014, respectively.
[4]	Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014, respectively.

Property, Plant and Equipment66

Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 36.9	$ 34.8	$ 30.8
Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	24.4	23.1	20.3
Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	12.5	11.7	10.5
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	28.2	25.9	21
IPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	18.6	17.1	13.8
IPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	9.6	8.8	7.2
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	8.7	8.9	9.8
WPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	5.8	6	6.5
WPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 2.9	$ 2.9	$ 3.3

Property, Plant and Equipment67

Property, Plant and Equipment (AFUDC By Project) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 36.9	$ 34.8	$ 30.8
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	28.2	25.9	21
IPL [Member] | Marshalltown Generating Station [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	20.7	3.7	0
IPL [Member] | Ottumwa Unit 1 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0	10.6	8
IPL [Member] | George Neal Units 3 and 4 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0	1.4	5.1
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	7.5	10.2	7.9
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	8.7	8.9	9.8
WPL [Member] | Edgewater Unit 5 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	5.1	2.7	0
WPL [Member] | Columbia Units 1 and 2 [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	0	4	7.2
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 3.6	$ 2.2	$ 2.6

Jointly-Owned Electric Utilit68

Jointly-Owned Electric Utility Plant (Details) $ in Millions	Dec. 31, 2015USD ($)
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	$ 1,526.7
Accumulated Provision for Depreciation	501.2
Construction Work in Progress	41.8
IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	852.1
Accumulated Provision for Depreciation	267.5
Construction Work in Progress	6.9
WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	674.6
Accumulated Provision for Depreciation	233.7
Construction Work in Progress	$ 34.9
Ottumwa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	48.00%
Electric Plant	$ 481.4
Accumulated Provision for Depreciation	125
Construction Work in Progress	$ 6.5
George Neal Unit 4 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	25.70%
Electric Plant	$ 184.3
Accumulated Provision for Depreciation	76.3
Construction Work in Progress	$ 0.2
George Neal Unit 3 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	28.00%
Electric Plant	$ 150
Accumulated Provision for Depreciation	45.1
Construction Work in Progress	$ 0.1
Louisa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	4.00%
Electric Plant	$ 36.4
Accumulated Provision for Depreciation	21.1
Construction Work in Progress	$ 0.1
Columbia Units 1-2 [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	46.20%
Electric Plant	$ 571.9
Accumulated Provision for Depreciation	175.5
Construction Work in Progress	$ 34.8
Edgewater Unit 4 [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	68.20%
Electric Plant	$ 102.7
Accumulated Provision for Depreciation	58.2
Construction Work in Progress	$ 0.1

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of deferred proceeds of receivables sold			$ 172	$ 177.2
Proceeds from Franklin County wind farm cash grant			0	0	$ 62.4
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party			46.7	46.4	105.9
Receivables sold to third party			181.1
Fair value of deferred proceeds of receivables sold			172	177.2
IPL [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party			137	150	170
Seasonal 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
Franklin County Wind Farm [Member] | American Recovery and Reinvestment Act of 2009 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from Franklin County wind farm cash grant					$ 62.4
Receivables Sold [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold to third party			181.1	204.6
Cash proceeds from receivables sold	[1]		5	22
Fair value of deferred proceeds of receivables sold			$ 172	$ 177.2
Scenario, Forecast [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash proceeds to be received from third-party		$ 180
[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, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	$ 93.8	$ 88.2
Unbilled utility revenues	83.1	85.4
Deferred proceeds	172	177.2
Other	53.5	81.6
Allowance for doubtful accounts	(4.8)	(5.1)
Accounts receivable, less allowance for doubtful accounts	397.6	427.3
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	4.6	0
Unbilled utility revenues	1.2	0
Deferred proceeds	172	177.2
Other	22.8	39.9
Allowance for doubtful accounts	(0.6)	(0.4)
Accounts receivable, less allowance for doubtful accounts	200	216.7
WPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer	81.5	81
Unbilled utility revenues	81.9	85.4
Other	25.7	23.6
Allowance for doubtful accounts	(3.7)	(4.2)
Accounts receivable, less allowance for doubtful accounts	$ 185.4	$ 185.8

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 46.7	$ 46.4	$ 105.9
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 137	$ 150	$ 170

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of deferred proceeds		$ 172	$ 177.2
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables sold to third party		181.1
Fair value of deferred proceeds		172	177.2
Receivables Sold [Member] | IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer accounts receivable		109.7	134.8
Unbilled utility revenues		71.3	69.7
Other receivables		0.1	0.1
Receivables sold to third party		181.1	204.6
Less: cash proceeds	[1]	5	22
Deferred proceeds		176.1	182.6
Less: allowance for doubtful accounts		4.1	5.4
Fair value of deferred proceeds		172	177.2
Outstanding receivables past due		$ 18	$ 19.9
[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, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collections reinvested in receivables	$ 1,812.9	$ 1,997.9	$ 1,880.8
Credit losses, net of recoveries	$ 8.8	$ 11.4	$ 11.9

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended		26 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2013
Alliant Energy and WPL [Member]
Schedule of Equity Method Investments [Line Items]
Reduction in equity income from ATC	$ 12	$ 3	$ 15
WPL [Member]
Schedule of Equity Method Investments [Line Items]
WPL's ownership interest in WPL Transco	93.00%		93.00%	100.00%
ATI [Member]
Schedule of Equity Method Investments [Line Items]
ATI's ownership interest in WPL Transco	7.00%		7.00%

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Carrying value		$ 302.9	$ 296.6	$ 281.4
Equity (income) / loss		(33.8)	(40.4)	(43.7)
WPL [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) / loss		$ (35.1)	(42.8)	(43.7)
ATC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	[1]	16.00%
Carrying value	[1]	$ 293.3	286.5
Equity (income) / loss	[1]	$ (34.2)	(41.9)	(42.7)
ATC [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	[1]	16.00%
Carrying value	[1]	$ 293.3	286.5
Equity (income) / loss	[1]	$ (34.2)	(41.9)	(42.7)
Wisconsin River Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Carrying value		$ 8.7	7.8
Equity (income) / loss		$ (0.9)	(0.9)	(1)
Wisconsin River Power Company [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Carrying value		$ 8.7	7.8
Equity (income) / loss		(0.9)	(0.9)	(1)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		0.9	2.3
Equity (income) / loss		1.3	2.4	0
Totals [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		302.9	296.6
Equity (income) / loss		(33.8)	(40.4)	(43.7)
Totals [Member] | WPL [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value		302	294.3
Equity (income) / loss		$ (35.1)	$ (42.8)	$ (43.7)
[1]	Alliant Energy and WPL have the ability to exercise significant influence over ATC’s financial and operating policies through their 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, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues	$ 624	$ 643	$ 634
Operating income	299	330	334
Net income	186	240	248
Current assets	88	72
Non-current assets	3,987	3,773
Current liabilities	332	315
Non-current liabilities	2,052	1,871
WPL [Member]
Operating revenues	624	643	634
Operating income	299	330	334
Net income	202	240	$ 250
Current assets	87	70
Non-current assets	3,977	3,747
Current liabilities	332	315
Non-current liabilities	$ 2,052	$ 1,870

Investments (Cash Surrender Val

Investments (Cash Surrender Value Of Life Insurance Policies) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Cash surrender value	$ 42.3	$ 47
IPL [Member]
Cash surrender value	18.9	18.1
WPL [Member]
Cash surrender value	$ 6.4	$ 11.4

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Common Equity [Line Items]
Shares available for issuance under the Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan	7,300,000
Proceeds from issuance of common stock, net	$ 151.2	$ 0	$ 0
Ownership percentage	15.00%
Initial right entitlement, number of shares of common stock shareholders have the option to purchase (in shares)	0.5
Exercise price, rights (in dollars per share)	$ 110
Percentage of exercise price upon change in beneficial ownership	200.00%
Other comprehensive income (loss)	$ 0.2	(0.4)	0.6
IPL [Member]
Schedule of Common Equity [Line Items]
Retained earnings free of dividend restrictions	$ 554
Common equity ratio, computation of ratio average, number of months	13 months
Common equity ratio	42.00%
Other comprehensive income (loss)	$ 0	0	0
WPL [Member]
Schedule of Common Equity [Line Items]
Retained earnings free of dividend restrictions	$ 135
Common equity ratio, computation of ratio average, number of months	13 months
Other comprehensive income (loss)	$ 0	$ 0	$ 0
Minimum [Member]
Schedule of Common Equity [Line Items]
Ownership percentage	10.00%
2016 [Member] | WPL [Member]
Schedule of Common Equity [Line Items]
Retained earnings free of dividend restrictions	$ 135
Common equity ratio	52.25%
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)	2,186,617	0	0
Proceeds from issuance of common stock, net	$ 133
Fees and commissions from issuance of common stock	$ 2

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1 (in shares)	110,935,680	110,943,669	110,987,400
Common stock issued during the period, Shareowner Direct Plan (in shares)	303,005	0	0
Equity-based compensation plans (in shares)	56,378	35,547	(23,374)
Other (in shares)	(22,464)	(43,536)	(20,357)
Shares outstanding, December 31 (in shares)	113,459,216	110,935,680	110,943,669
At The Market Offering Program [Member]
Common Stock Oustanding [Roll Forward]
Common stock issued during the period, At-the-market offering program (in shares)	2,186,617	0	0

Common Equity (Schedule Of Rest

Common Equity (Schedule Of Restricted Net Assets of Subsidiaries) (Details) - USD ($) $ in Billions	Dec. 31, 2015	Dec. 31, 2014
IPL [Member]
Restricted net assets of subsidiaries	$ 1.4	$ 1.3
WPL [Member]
Restricted net assets of subsidiaries	$ 1.6	$ 1.6

Common Equity (Capital Transact

Common Equity (Capital Transactions With Subsidiaries) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common stock dividends	$ 247.3	$ 225.8	$ 208.3
IPL [Member]
Common stock dividends	140	140	128.1
Repayments of capital	0	0	0
Total distributions from common equity	140	140	128.1
WPL [Member]
Common stock dividends	126.9	118.7	116.3
Repayments of capital	0	0	0
Total distributions from common equity	126.9	118.7	116.3
Resources [Member]
Common stock dividends	0	0	0
Repayments of capital	0	50	95
Total distributions from common equity	$ 0	$ 50	$ 95

Common Equity (Schedule of Capi

Common Equity (Schedule of Capital Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
IPL [Member]
Capital contributions from parent	$ 165	$ 90	$ 120

Redeemable Preferred Stock (Nar

Redeemable Preferred Stock (Narrative) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)Qboard_member$ / shares	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)shares
Temporary Equity [Line Items]
Reduction in commercial paper	$ 18.5	$ (138.1)	$ 11.9
Preferred stock issuance costs			5.4
IPL [Member]
Temporary Equity [Line Items]
Cumulative preferred stock rate	5.10%
Reduction in commercial paper	$ 0	0	(76.3)
Preferred stock issuance costs			$ 5.4
Number of board members to be elected (in members) | board_member	2
Number of quarterly dividend requirements (in quarters) | Q	6
IPL [Member] | Redeemable Preferred Stock [Member] | 5.1% [Member]
Temporary Equity [Line Items]
Preferred stock issued during period (in shares) | shares			8,000,000
Cumulative preferred stock rate	5.10%		5.10%
Preferred stock issued during period, value			$ 200
Preferred stock redemption price per share (in dollars per share) | $ / shares	$ 25
IPL [Member] | Redeemable Preferred Stock [Member] | 8.375% [Member]
Temporary Equity [Line Items]
Cumulative preferred stock rate			8.375%
Preferred stock redeemed during period (in shares) | shares			6,000,000
Preferred stock redeemed during period, value			$ 150
Alliant Energy and IPL [Member] | Redeemable Preferred Stock [Member] | 5.1% [Member]
Temporary Equity [Line Items]
Preferred stock issuance costs			5
Alliant Energy and IPL [Member] | Redeemable Preferred Stock [Member] | 8.375% [Member]
Temporary Equity [Line Items]
Preferred stock redemption charge			5
WPL [Member]
Temporary Equity [Line Items]
Reduction in commercial paper	$ 19.9	$ (183.7)	$ 97.1
WPL [Member] | Redeemable Preferred Stock [Member] | 4.40% through 6.50% [Member]
Temporary Equity [Line Items]
Preferred stock redeemed during period (in shares) | shares			1,049,225
Preferred stock redeemed during period, value			$ 61
WPL [Member] | Redeemable Preferred Stock [Member] | 4.40% [Member]
Temporary Equity [Line Items]
Cumulative preferred stock rate			4.40%
WPL [Member] | Redeemable Preferred Stock [Member] | 6.50% [Member]
Temporary Equity [Line Items]
Cumulative preferred stock rate			6.50%
Long-term debt [Member] | IPL [Member] | Redeemable Preferred Stock [Member] | 5.1% [Member]
Temporary Equity [Line Items]
Reduction in commercial paper			$ 40

Redeemable Preferred Stock (Car

Redeemable Preferred Stock (Carrying Value Of Cumulative Preferred Stock) (Details) - IPL [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2014
Temporary Equity [Line Items]
Series	5.10%
Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Shares Authorized (in shares)	16,000,000
5.1% [Member] | Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Liquidation Preference/Stated Value (in dollars per share)	$ 25
Shares Outstanding (in shares)	8,000,000
Series	5.10%	5.10%
Cumulative preferred stock	$ 200		$ 200

Debt (Narrative) (Details)

Debt (Narrative) (Details)	Dec. 31, 2015USD ($)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	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Commercial paper:
Amount outstanding	$ 159.8	$ 141.3
Weighted average interest rates	0.70%	0.40%
Weighted average remaining maturity	4 days	4 days
Available credit facility capacity	$ 840.2	$ 858.7
IPL [Member]
Commercial paper:
Amount outstanding	0	0
Available credit facility capacity	300	300
WPL [Member]
Commercial paper:
Amount outstanding	$ 19.9	0
Weighted average interest rates	0.40%
Weighted average remaining maturity	4 days
Available credit facility capacity	$ 380.1	$ 400

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 181.2	$ 353.8
Average amount outstanding (based on daily outstanding balances)	$ 119.2	$ 255.9
Weighted average interest rates	0.40%	0.20%
IPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 18.4	$ 38
Average amount outstanding (based on daily outstanding balances)	$ 0.2	$ 0.2
Weighted average interest rates	0.40%	0.20%
WPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 24.7	$ 204.7
Average amount outstanding (based on daily outstanding balances)	$ 2.2	$ 122.9
Weighted average interest rates	0.30%	0.10%

Debt (Schedule Of Debt-To-Capit

Debt (Schedule Of Debt-To-Capital Ratios) (Details)	Dec. 31, 2015
Actual	50.00%
IPL [Member]
Actual	46.00%
WPL [Member]
Actual	48.00%
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, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt issued		$ 3,870.5	$ 3,802.8
Current maturities		(313.4)	(183)
Unamortized debt issuance costs		(22.3)	(22.4)
Unamortized debt (discount) and premium, net		(12.6)	(13.1)
Long-term debt, net		3,522.2	3,584.3
Proceeds from issuance of long-term debt		250.7	812.9	$ 250
3.4% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt		250
Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt issued		1,875	1,775
Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued	[1]	$ 250
Interest rate		3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 250	$ 250
Interest rate		4.70%	4.70%
Senior Debentures [Member] | 3.3% senior debenture, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 150
Interest rate			3.30%
Debentures [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 1,550	$ 1,550
Debentures [Member] | 5% debenture, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 250	$ 250
Interest rate		5.00%	5.00%
Debentures [Member] | 4.6% debenture, due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 150	$ 150
Interest rate		4.60%	4.60%
Debentures [Member] | 2.25% debenture, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 250	$ 250
Interest rate		2.25%	2.25%
Debentures [Member] | 6.25% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 100	$ 100
Interest rate		6.25%	6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 300	$ 300
Interest rate		6.375%	6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 250	$ 250
Interest rate		7.60%	7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 250	$ 250
Interest rate		4.10%	4.10%
Pollution Control Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 30.6
Pollution Control Revenue Bonds [Member] | 5% pollution control revenue bond, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 16
Interest rate			5.00%
Pollution Control Revenue Bonds [Member] | 5.375% pollution control revenue bond, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 14.6
Interest rate			5.375%
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 445.5	$ 447.2
Term Loan Credit Agreement [Member] | Term loan credit agreement through 2016, 1% at December 31, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 250	$ 250
Interest rate		1.00%	1.00%
Senior Notes [Member] | 3.45% senior notes, due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 75	$ 75
Interest rate		3.45%	3.45%
Senior Secured Notes [Member] | 5.06% senior secured notes, due 2016 to 2024 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 56.8	$ 58.9
Interest rate		5.06%	5.06%
Other [Member] | Other, 1% at December 31, 2015, due 2016 to 2025 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 3.7	$ 3.3
Interest rate		1.00%	1.00%
IPL [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 1,875	$ 1,775
Current maturities		0	(150)
Unamortized debt issuance costs		(11.8)	(10.7)
Unamortized debt (discount) and premium, net		(6.3)	(6.3)
Long-term debt, net		1,856.9	1,608
Proceeds from issuance of long-term debt		250	250	250
Repayments of commercial paper		111
IPL [Member] | Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt issued		1,875	1,775
IPL [Member] | Senior Debentures [Member] | 5.875% senior debenture, due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued	[1]	$ 250
Interest rate		3.40%
IPL [Member] | Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 250	$ 250
Interest rate		4.70%	4.70%
IPL [Member] | Senior Debentures [Member] | 3.3% senior debenture, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 150
Interest rate			3.30%
WPL [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 1,550	$ 1,580.6
Current maturities		0	(30.6)
Unamortized debt issuance costs		(9.9)	(10.8)
Unamortized debt (discount) and premium, net		(6.2)	(6.7)
Long-term debt, net		1,533.9	1,532.5
Proceeds from issuance of long-term debt		0	250	$ 0
WPL [Member] | Debentures [Member]
Debt Instrument [Line Items]
Long-term debt issued		1,550	1,550
WPL [Member] | Debentures [Member] | 5% debenture, due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 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 issued		$ 250	$ 250
Interest rate		4.10%	4.10%
WPL [Member] | Pollution Control Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 30.6
WPL [Member] | Pollution Control Revenue Bonds [Member] | 5% pollution control revenue bond, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 16
Interest rate			5.00%
WPL [Member] | Pollution Control Revenue Bonds [Member] | 5.375% pollution control revenue bond, retired in 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued			$ 14.6
Interest rate			5.375%
Franklin County Holdings [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through 2016, 1% at December 31, 2015 [Member]
Debt Instrument [Line Items]
Long-term debt issued		$ 60	$ 60
Interest rate		1.00%	1.00%
[1]	In 2015, IPL issued $250.0 million of 3.4% senior debentures due 2025. The proceeds from the issuance were used by IPL to reduce commercial paper classified as long-term debt by $111 million, reduce cash amounts received from its sales of accounts receivable program and for general corporate purposes.

Debt (Schedule Of Debt Maturiti

Debt (Schedule Of Debt Maturities) (Details) $ in Millions	Dec. 31, 2015USD ($)
2,016	$ 313
2,017	5
2,018	356
2,019	256
2,020	357
IPL [Member]
2,016	0
2,017	0
2,018	350
2,019	0
2,020	200
WPL [Member]
2,016	0
2,017	0
2,018	0
2,019	250
2,020	150
Resources [Member]
2,016	63
2,017	5
2,018	6
2,019	6
2,020	7
Alliant Energy Parent Company [Member]
2,016	250
2,017	0
2,018	0
2,019	0
2,020	$ 0

Leases (Narrative) (Details)

Leases (Narrative) (Details) - Sheboygan Falls Energy Facility [Member] - WPL [Member] $ in Millions	12 Months Ended
	Dec. 31, 2005USD ($)lease_renewal_period_option
Leases [Line Items]
Capital lease, agreement term	20 years
Capital leases, renewal options (in number of renewal periods) | lease_renewal_period_option	2
Affiliated lease agreement monthly payments | $	$ 1.3
Basis for lease payments, debt to capital ratio	50.00%
Basis for lease payments, return on equity ratio	10.90%
Approved agreement terms, review period from date of the order	5 years
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, 2015USD ($)
Operating Leased Assets [Line Items]
2,016	$ 6
2,017	8
2,018	3
2,019	2
2,020	2
Thereafter	19
Total future minimum operating lease payments, excluding contingent rentals	40
IPL [Member]
Operating Leased Assets [Line Items]
2,016	3
2,017	3
2,018	2
2,019	1
2,020	1
Thereafter	13
Total future minimum operating lease payments, excluding contingent rentals	23
WPL [Member]
Operating Leased Assets [Line Items]
2,016	3
2,017	5
2,018	1
2,019	0
2,020	0
Thereafter	0
Total future minimum operating lease payments, excluding contingent rentals	$ 9

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, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Interest expense	$ 9.9	$ 10.4	$ 10.9
Depreciation and amortization	6.2	6.2	6.2
Total lease expenses included in income statements	$ 16.1	$ 16.6	$ 17.1

Leases (Future Minimum Capital

Leases (Future Minimum Capital Lease Payments) (Details) - WPL [Member] - Sheboygan Falls Energy Facility [Member] $ in Millions	Dec. 31, 2015USD ($)
Schedule of Future Lease Payments for Capital Leases [Line Items]
2,016	$ 15
2,017	15
2,018	15
2,019	15
2,020	15
Thereafter	68
Total estimated future minimum capital lease payments	143
Less: amount representing interest	54
Present value of minimum capital lease payments	$ 89

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		99.00%
Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 200
IPL [Member]
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		95.00%
IPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	100
WPL [Member]
Income Tax [Line Items]
Net operating loss carryforwards, percentage expiring		96.00%
WPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 50

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current tax expense (benefit):
Federal	$ 2	$ 36.6	$ 4.4
State	3.2	9.3	(3.6)
Deferred tax expense (benefit):
Federal	120.8	83.5	123.9
State	27.9	4.6	15.6
Production tax credits	(33.1)	(31.3)	(31)
Investment tax credits	(1.4)	(1.6)	(1.6)
Provision recorded as a change in uncertain tax positions, deferred	0	0	(0.4)
Provision recorded as a change in accrued interest	0	(0.1)	(0.5)
Income tax expense (benefit)	70.4	44.3	53.9
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(49)	(56.7)	(52.9)
IPL [Member]
Current tax expense (benefit):
Federal	(14.1)	8.9	10.2
State	11.5	10.4	4.2
Deferred tax expense (benefit):
Federal	40.7	10.8	21.7
State	3.3	(7.9)	(4)
Production tax credits	(14.5)	(13.8)	(14.1)
Investment tax credits	(0.6)	(0.6)	(0.6)
Provision recorded as a change in uncertain tax positions, deferred	0	0	0
Provision recorded as a change in accrued interest	0	0	(0.8)
Income tax expense (benefit)	(22.7)	(48.9)	(36.3)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(49)	(56.7)	(52.9)
WPL [Member]
Current tax expense (benefit):
Federal	4.7	2	(0.3)
State	0.6	0.8	(4.3)
Deferred tax expense (benefit):
Federal	76.8	81.1	84
State	20.2	20	24.1
Production tax credits	(18.6)	(17.5)	(16.9)
Investment tax credits	(0.8)	(1)	(1)
Provision recorded as a change in uncertain tax positions, deferred	0	0	(0.4)
Provision recorded as a change in accrued interest	0	(0.1)	0.4
Income tax expense (benefit)	$ 82.9	$ 85.3	$ 85.6

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.20%	5.40%	5.70%
Effect of rate-making on property-related differences	(6.80%)	(7.50%)	(6.00%)
Production tax credits	(7.20%)	(7.10%)	(7.10%)
Adjustment of prior period taxes	0.80%	(1.30%)	(1.30%)
Other items, net	(1.10%)	(1.50%)	(1.80%)
Overall income tax rate	15.30%	10.10%	12.40%
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	6.20%	6.10%	6.30%
Effect of rate-making on property-related differences	(17.20%)	(21.90%)	(15.90%)
Production tax credits	(8.30%)	(9.60%)	(9.30%)
Adjustment of prior period taxes	0.70%	(3.00%)	(3.60%)
Other items, net	(1.20%)	(1.20%)	(1.60%)
Overall income tax rate	(13.10%)	(34.20%)	(23.90%)
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%	5.50%
Effect of rate-making on property-related differences	(0.50%)	(0.70%)	(0.80%)
Production tax credits	(7.10%)	(6.60%)	(6.40%)
Adjustment of prior period taxes	0.10%	0.00%	(0.20%)
Other items, net	(0.80%)	(0.80%)	(0.80%)
Overall income tax rate	31.80%	32.00%	32.30%
IPL's tax benefit riders [Member]
Effective Tax Rate [Line Items]
IPL’s tax benefit riders	(10.60%)	(12.90%)	(12.10%)
IPL's tax benefit riders [Member] | IPL [Member]
Effective Tax Rate [Line Items]
IPL’s tax benefit riders	(28.30%)	(39.60%)	(34.80%)

Income Taxes (Production Tax Cr

Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)MW	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	$ 33.1	$ 31.3	$ 31
IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.5	13.8	14.1
WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	18.6	17.5	16.9
Cedar Ridge Wind Farm [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	4.5	4.1	4.2
Bent Tree Wind Farm [Member] | WPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	14.1	13.4	12.7
Whispering Willow - East Wind Farm [Member] | IPL [Member]
Production Tax Credits [Line Items]
Production tax credits, net of state tax impacts	$ 14.5	$ 13.8	$ 14.1
Cedar Ridge Wind Farm [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate capacity (in megawatts) | MW	68
Bent Tree Wind Farm [Member] | WPL [Member]
Production Tax Credits [Line Items]
Nameplate capacity (in megawatts) | MW	201
Whispering Willow - East Wind Farm [Member] | IPL [Member]
Production Tax Credits [Line Items]
Nameplate capacity (in megawatts) | MW	200

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets, gross	$ (677.1)	$ (768.5)
Deferred tax liabilities, gross	3,058.3	2,939.5
Deferred tax (assets) and liabilities, net	2,381.2	2,171
Current deferred tax assets	0	(150.1)
Non-current deferred tax liabilities	2,381.2	2,321.1
Deferred tax liabilities, net of deferred tax assets	2,381.2	2,171
IPL [Member]
Deferred tax assets, gross	(297.6)	(362.3)
Deferred tax liabilities, gross	1,675.6	1,628.6
Deferred tax (assets) and liabilities, net	1,378	1,266.3
Current deferred tax assets	0	(104)
Non-current deferred tax liabilities	1,378	1,370.3
Deferred tax liabilities, net of deferred tax assets	1,378	1,266.3
WPL [Member]
Deferred tax assets, gross	(228.4)	(245.4)
Deferred tax liabilities, gross	1,233.8	1,174.8
Deferred tax (assets) and liabilities, net	1,005.4	929.4
Current deferred tax assets	0	(37.7)
Non-current deferred tax liabilities	1,005.4	967.1
Deferred tax liabilities, net of deferred tax assets	1,005.4	929.4
Property [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	2,762.9	2,627.8
Deferred tax (assets) and liabilities, net	2,762.9	2,627.8
Property [Member] | IPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	1,587.8	1,545.1
Deferred tax (assets) and liabilities, net	1,587.8	1,545.1
Property [Member] | WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	1,027	963
Deferred tax (assets) and liabilities, net	1,027	963
Investment In ATC [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	138.1	131.6
Deferred tax (assets) and liabilities, net	138.1	131.6
Investment In ATC [Member] | WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	138.9	132.1
Deferred tax (assets) and liabilities, net	138.9	132.1
Net operating losses carryforward - state [Member]
Deferred tax assets, gross	(38.3)	(45.7)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(38.3)	(45.7)
Regulatory liability - IPL's tax benefit riders [Member]
Deferred tax assets, gross	(66.1)	(100.9)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(66.1)	(100.9)
Regulatory liability - IPL's tax benefit riders [Member] | IPL [Member]
Deferred tax assets, gross	(66.1)	(100.9)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(66.1)	(100.9)
Federal credit carryforwards [Member]
Deferred tax assets, gross	(236.4)	(201)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(236.4)	(201)
Federal credit carryforwards [Member] | IPL [Member]
Deferred tax assets, gross	(81.7)	(66.5)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(81.7)	(66.5)
Federal credit carryforwards [Member] | WPL [Member]
Deferred tax assets, gross	(95.5)	(76.7)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(95.5)	(76.7)
Net operating losses carryforwards - federal [Member]
Deferred tax assets, gross	(250.9)	(332.8)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(250.9)	(332.8)
Net operating losses carryforwards - federal [Member] | IPL [Member]
Deferred tax assets, gross	(113.1)	(157.8)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(113.1)	(157.8)
Net operating losses carryforwards - federal [Member] | WPL [Member]
Deferred tax assets, gross	(105.1)	(131.6)
Deferred tax liabilities, gross	0	0
Deferred tax (assets) and liabilities, net	(105.1)	(131.6)
Other [Member]
Deferred tax assets, gross	(85.4)	(88.1)
Deferred tax liabilities, gross	157.3	180.1
Deferred tax (assets) and liabilities, net	71.9	92
Other [Member] | IPL [Member]
Deferred tax assets, gross	(36.7)	(37.1)
Deferred tax liabilities, gross	87.8	83.5
Deferred tax (assets) and liabilities, net	51.1	46.4
Other [Member] | WPL [Member]
Deferred tax assets, gross	(27.8)	(37.1)
Deferred tax liabilities, gross	67.9	79.7
Deferred tax (assets) and liabilities, net	$ 40.1	$ 42.6

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2015USD ($)
Deferred tax assets, net operating losses	$ 525
IPL [Member]
Deferred tax assets, net operating losses	196
WPL [Member]
Deferred tax assets, net operating losses	205
Federal [Member]
Tax carryforwards, net operating losses	732
Deferred tax assets, net operating losses	251
Tax carryforwards, tax credits	240
Deferred tax assets, tax credits	236
Federal [Member] | IPL [Member]
Tax carryforwards, net operating losses	336
Deferred tax assets, net operating losses	113
Tax carryforwards, tax credits	85
Deferred tax assets, tax credits	82
Federal [Member] | WPL [Member]
Tax carryforwards, net operating losses	300
Deferred tax assets, net operating losses	105
Tax carryforwards, tax credits	96
Deferred tax assets, tax credits	96
State [Member]
Tax carryforwards, net operating losses	766
Deferred tax assets, net operating losses	38
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	20
Deferred tax assets, net operating losses	1
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	76
Deferred tax assets, net operating losses	$ 4

Income Taxes (Schedule Of Uncer

Income Taxes (Schedule Of Uncertain Tax Positions) (Details)	12 Months Ended
	Dec. 31, 2015
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 ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
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	11.60%	12.60%
Percentage of employees accepting voluntary separation package	2.00%
Voluntary employee separation charges	$ 8
Unrecognized compensation cost	$ 3.9
Percentage of base salary and performance-based compensation	100.00%
Performance Shares and Units [Member]
Benefit Plans [Line Items]
Performance period	3 years
Performance Units [Member]
Benefit Plans [Line Items]
Performance multiplier range, lower	0.00%
Performance multiplier range, upper	200.00%
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
WPL [Member]
Benefit Plans [Line Items]
Voluntary employee separation charges	3
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	3.8

Benefit Plans (Assumptions Used

Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.47%	4.18%	4.97%
Discount rate for net periodic cost	4.18%	4.97%	4.11%
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	4.50%	4.20%	5.05%
Discount rate for net periodic cost	4.20%	5.05%	4.20%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.50%	3.50%
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.51%	4.20%	5.05%
Discount rate for net periodic cost	4.20%	5.05%	4.20%
Expected rate of return on plan assets	7.60%	7.60%	7.60%
Rate of compensation increase	3.65%	3.50%	3.50%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	4.30%	3.97%	4.59%
Discount rate for net periodic cost	3.97%	4.59%	3.82%
Expected rate of return on plan assets	6.20%	7.40%	7.40%
Rate of compensation increase			3.50%
Medical cost trend on covered charges, initial trend rate (end of year)	7.25%	6.75%	7.00%
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	4.28%	3.94%	4.55%
Discount rate for net periodic cost	3.94%	4.55%	3.76%
Expected rate of return on plan assets	6.60%	7.60%	7.50%
Rate of compensation increase			3.50%
Medical cost trend on covered charges, initial trend rate (end of year)	7.25%	6.75%	7.00%
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	4.28%	3.96%	4.56%
Discount rate for net periodic cost	3.96%	4.56%	3.81%
Expected rate of return on plan assets	4.60%	7.30%	7.20%
Rate of compensation increase			3.50%
Medical cost trend on covered charges, initial trend rate (end of year)	7.25%	6.75%	7.00%
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%	3.50%	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, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 15.9	$ 13.1	$ 15.7
Interest cost		53.6	54.1	49
Expected return on plan assets	[1]	(75)	(74.9)	(74)
Amortization of prior service cost (credit)		(0.2)	0	0.2
Amortization of actuarial loss	[2]	35.4	19.5	36.2
Additional benefit costs		0.5	0	9	[3]
Total		30.2	11.8	36.1
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		5.5	5.2	6.3
Interest cost		9.1	9.5	8.5
Expected return on plan assets	[1]	(8.4)	(8.3)	(8.1)
Amortization of prior service cost (credit)	[4]	(11.3)	(11.9)	(11.9)
Amortization of actuarial loss	[2]	4.8	2.4	4.9
Additional benefit costs		0	0	0
Total		(0.3)	(3.1)	(0.3)
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		8.8	7.2	8.6
Interest cost		25	25.1	22.9
Expected return on plan assets	[1]	(35.8)	(35.7)	(35.2)
Amortization of prior service cost (credit)		(0.1)	0	0.1
Amortization of actuarial loss	[2]	15.3	8	15.2
Additional benefit costs		0	0	2.6	[3]
Total		13.2	4.6	14.2
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2.4	2.4	2.9
Interest cost		3.8	3.9	3.6
Expected return on plan assets	[1]	(5.7)	(5.8)	(5.6)
Amortization of prior service cost (credit)	[4]	(6.1)	(6.3)	(6.3)
Amortization of actuarial loss	[2]	2.3	1.1	2.7
Additional benefit costs		0	0	0
Total		(3.3)	(4.7)	(2.7)
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		5.8	4.9	5.9
Interest cost		22.6	22.6	20.7
Expected return on plan assets	[1]	(32.4)	(32.4)	(31.9)
Amortization of prior service cost (credit)		0.2	0.3	0.3
Amortization of actuarial loss	[2]	16.8	9.2	17.1
Additional benefit costs		0.5	0	0.6	[3]
Total		13.5	4.6	12.7
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2.1	2	2.5
Interest cost		3.7	3.8	3.4
Expected return on plan assets	[1]	(1.5)	(1.3)	(1.3)
Amortization of prior service cost (credit)	[4]	(3.5)	(3.9)	(3.9)
Amortization of actuarial loss	[2]	2.2	1.3	1.9
Additional benefit costs		0	0	0
Total		$ 3	$ 1.9	2.6
Corporate Service Allocation [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				2.9
Corporate Service Allocation [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				2.2
Cash Balance Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				9
Cash Balance Plan [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				5.5
Cash Balance Plan [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				2.8
Directly assigned defined benefit pension plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				2.6
Directly assigned defined benefit pension plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional benefit costs				$ 0.6
[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 Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
[3]	In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ($2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ($0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.
[4]	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, 2016USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	$ 37.4
Prior service cost (credit)	(0.3)
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	16.5
Prior service cost (credit)	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	16.3
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	17.6
Prior service cost (credit)	0.2
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	17.8
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	4.8
Prior service cost (credit)	(4.1)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	0.7
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	2.6
Prior service cost (credit)	(2.6)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	0
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	1.8
Prior service cost (credit)	(0.9)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	$ 0.9

Benefit Plans (Funded Status of

Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
IPL [Member]
Change in benefit obligation:
Regulatory assets	$ 38	$ 38.2
WPL [Member]
Change in benefit obligation:
Regulatory assets	29.5	28
Pension Plans, Defined Benefit [Member]
Change in benefit obligation:
Net benefit obligation at January 1	1,301.5	1,113.4
Service cost	15.9	13.1	$ 15.7
Interest cost	53.6	54.1	49
Plan participants' contributions	0	0
Plan amendments	0	0
Additional benefit costs	0.5	0
Actuarial (gain) loss	(70.1)	195.8
Gross benefits paid	(95.1)	(74.9)
Net benefit obligation at December 31	1,206.3	1,301.5	1,113.4
Change in plan assets:
Fair value of plan assets at January 1	1,018.1	1,022.9
Actual return on plan assets	(30.2)	66.4
Employer contributions	2.2	3.7
Plan participants' contributions	0	0
Gross benefits paid	(95.1)	(74.9)
Fair value of plan assets at December 31	895	1,018.1	1,022.9
Under funded status at December 31	(311.3)	(283.4)
Pension Plans, Defined Benefit [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	603.1	514
Service cost	8.8	7.2	8.6
Interest cost	25	25.1	22.9
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial (gain) loss	(32.3)	91.4
Gross benefits paid	(48.5)	(34.6)
Net benefit obligation at December 31	556.1	603.1	514
Change in plan assets:
Fair value of plan assets at January 1	484.7	485.9
Actual return on plan assets	(14.3)	32.1
Employer contributions	0.8	1.3
Plan participants' contributions	0	0
Gross benefits paid	(48.5)	(34.6)
Fair value of plan assets at December 31	422.7	484.7	485.9
Under funded status at December 31	(133.4)	(118.4)
Pension Plans, Defined Benefit [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	547.6	460.8
Service cost	5.8	4.9	5.9
Interest cost	22.6	22.6	20.7
Plan participants' contributions	0	0
Plan amendments	0	0
Additional benefit costs	0.5	0
Actuarial (gain) loss	(30)	86.7
Gross benefits paid	(40.6)	(27.4)
Net benefit obligation at December 31	505.9	547.6	460.8
Change in plan assets:
Fair value of plan assets at January 1	440.3	438.8
Actual return on plan assets	(13)	28.6
Employer contributions	0.1	0.3
Plan participants' contributions	0	0
Gross benefits paid	(40.6)	(27.4)
Fair value of plan assets at December 31	386.8	440.3	438.8
Under funded status at December 31	(119.1)	(107.3)
Other Postretirement Benefits Plans [Member]
Change in benefit obligation:
Net benefit obligation at January 1	231.1	208.7
Service cost	5.5	5.2	6.3
Interest cost	9.1	9.5	8.5
Plan participants' contributions	3.1	2.8
Plan amendments	(0.3)	0
Additional benefit costs	0	0
Actuarial (gain) loss	(9.4)	22.3
Gross benefits paid	(17.7)	(17.4)
Net benefit obligation at December 31	221.4	231.1	208.7
Change in plan assets:
Fair value of plan assets at January 1	121.6	124.9
Actual return on plan assets	(4.9)	5.6
Employer contributions	4.8	5.7
Plan participants' contributions	3.1	2.8
Gross benefits paid	(17.7)	(17.4)
Fair value of plan assets at December 31	106.9	121.6	124.9
Under funded status at December 31	(114.5)	(109.5)
Other Postretirement Benefits Plans [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	96.4	87.8
Service cost	2.4	2.4	2.9
Interest cost	3.8	3.9	3.6
Plan participants' contributions	1	0.9
Plan amendments	(0.1)	0
Actuarial (gain) loss	(4.6)	8.6
Gross benefits paid	(7.6)	(7.2)
Net benefit obligation at December 31	91.3	96.4	87.8
Change in plan assets:
Fair value of plan assets at January 1	78.7	81.2
Actual return on plan assets	(3.1)	3.6
Employer contributions	0.2	0.2
Plan participants' contributions	1	0.9
Gross benefits paid	(7.6)	(7.2)
Fair value of plan assets at December 31	69.2	78.7	81.2
Under funded status at December 31	(22.1)	(17.7)
Other Postretirement Benefits Plans [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	94	85.6
Service cost	2.1	2	2.5
Interest cost	3.7	3.8	3.4
Plan participants' contributions	1.6	1.3
Plan amendments	(0.2)	0
Additional benefit costs	0	0
Actuarial (gain) loss	(3.5)	9.2
Gross benefits paid	(8)	(7.9)
Net benefit obligation at December 31	89.7	94	85.6
Change in plan assets:
Fair value of plan assets at January 1	21.8	21.7
Actual return on plan assets	(1.1)	1.2
Employer contributions	4.4	5.5
Plan participants' contributions	1.6	1.3
Gross benefits paid	(8)	(7.9)
Fair value of plan assets at December 31	18.7	21.8	$ 21.7
Under funded status at December 31	$ (71)	$ (72.2)

Benefit Plans (Amounts Recogniz

Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		$ (451.8)	$ (421.7)
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0	0
Other current liabilities		(2.6)	(2.5)
Pension and other benefit obligations		(308.7)	(280.9)
Net amounts recognized at December 31		(311.3)	(283.4)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[1]	533.1	533.4
Prior service credit	[1]	(7.2)	(7.4)
Net amount recognized at December 31	[1]	525.9	526
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		3	6.1
Other current liabilities		(6.2)	(5.6)
Pension and other benefit obligations		(111.3)	(110)
Net amounts recognized at December 31		(114.5)	(109.5)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[1]	59.8	60.7
Prior service credit	[1]	(5.6)	(16.7)
Net amount recognized at December 31	[1]	54.2	44
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		(160.2)	(142.4)
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0	0
Other current liabilities		(0.8)	(0.8)
Pension and other benefit obligations		(132.6)	(117.6)
Net amounts recognized at December 31		(133.4)	(118.4)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[2]	235.5	233.1
Prior service credit	[2]	(2.5)	(2.6)
Net amount recognized at December 31	[2]	233	230.5
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0	1.2
Other current liabilities		0	0
Pension and other benefit obligations		(22.1)	(18.9)
Net amounts recognized at December 31		(22.1)	(17.7)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[2]	29.8	27.9
Prior service credit	[2]	(2.7)	(8.7)
Net amount recognized at December 31	[2]	27.1	19.2
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		(188.7)	(180.4)
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		(119)	(107.2)
Net amounts recognized at December 31		(119.1)	(107.3)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[3]	232.1	233.5
Prior service credit	[3]	(1.2)	(1)
Net amount recognized at December 31	[3]	230.9	232.5
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		3	4.9
Other current liabilities		(6)	(5.5)
Pension and other benefit obligations		(68)	(71.6)
Net amounts recognized at December 31		(71)	(72.2)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[3]	23.3	26.3
Prior service credit	[3]	(2.4)	(5.6)
Net amount recognized at December 31	[3]	$ 20.9	$ 20.7
[1]	Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets.
[2]	Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets.
[3]	Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets.

Benefit Plans (Accumulated Bene

Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 1,166	$ 1,255
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,166	1,255
Fair value of plan assets	895	1,018.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,206.3	1,301.5
Fair value of plan assets	895	1,018.1
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	221.4	231.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	221.4	231.1
Fair value of plan assets	106.9	121.6
IPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	531	575.5
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	531	575.5
Fair value of plan assets	422.7	484.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	556.1	603.1
Fair value of plan assets	422.7	484.7
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	91.3	96.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	91.3	96.4
Fair value of plan assets	69.2	78.7
WPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	493.8	532.5
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	493.8	532.5
Fair value of plan assets	386.8	440.3
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	505.9	547.6
Fair value of plan assets	386.8	440.3
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	89.7	94
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	89.7	94
Fair value of plan assets	$ 18.7	$ 21.8

Benefit Plans (Regulatory Asset

Benefit Plans (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 38	$ 38.2
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 29.5	$ 28

Benefit Plans (Estimated Future

Benefit Plans (Estimated Future Funding) (Details) - Scenario, Forecast [Member] $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	$ 2.6	[1]
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	0.8	[1]
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	0.1	[1]
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	5.8
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	0
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2016	$ 5.5
[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, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	$ 87.3
Expected benefit payments, 2017	92.4
Expected benefit payments, 2018	91
Expected benefit payments, 2019	92.6
Expected benefit payments, 2020	96.9
Expected benefit payments, 2021 - 2025	488.3
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	69.5
Expected benefit payments, 2017	74.3
Expected benefit payments, 2018	72.8
Expected benefit payments, 2019	74.3
Expected benefit payments, 2020	78.7
Expected benefit payments, 2021 - 2025	401.4
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	17.8
Expected benefit payments, 2017	18.1
Expected benefit payments, 2018	18.2
Expected benefit payments, 2019	18.3
Expected benefit payments, 2020	18.2
Expected benefit payments, 2021 - 2025	86.9
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	40.4
Expected benefit payments, 2017	41.7
Expected benefit payments, 2018	42.4
Expected benefit payments, 2019	42.1
Expected benefit payments, 2020	45.4
Expected benefit payments, 2021 - 2025	226.8
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	32.8
Expected benefit payments, 2017	34.1
Expected benefit payments, 2018	34.8
Expected benefit payments, 2019	34.6
Expected benefit payments, 2020	37.8
Expected benefit payments, 2021 - 2025	190.8
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	7.6
Expected benefit payments, 2017	7.6
Expected benefit payments, 2018	7.6
Expected benefit payments, 2019	7.5
Expected benefit payments, 2020	7.6
Expected benefit payments, 2021 - 2025	36
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	36.6
Expected benefit payments, 2017	37.6
Expected benefit payments, 2018	38.5
Expected benefit payments, 2019	38.9
Expected benefit payments, 2020	39.8
Expected benefit payments, 2021 - 2025	198.4
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	29.1
Expected benefit payments, 2017	29.8
Expected benefit payments, 2018	30.7
Expected benefit payments, 2019	31.1
Expected benefit payments, 2020	32.2
Expected benefit payments, 2021 - 2025	163.7
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2016	7.5
Expected benefit payments, 2017	7.8
Expected benefit payments, 2018	7.8
Expected benefit payments, 2019	7.8
Expected benefit payments, 2020	7.6
Expected benefit payments, 2021 - 2025	$ 34.7

Benefit Plans (Allocation Of Pl

Benefit Plans (Allocation Of Plan Assets) (Details)	12 Months Ended
	Dec. 31, 2015
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	2.00%
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	8.00%
Target range allocation, maximum	18.00%
Actual allocation	11.00%
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	2.50%
Target range allocation, maximum	12.50%
Actual allocation	7.00%
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	2.50%
Target range allocation, maximum	12.50%
Actual allocation	7.00%
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	4.00%
Actual allocation	1.00%
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	4.00%
Actual allocation	2.00%
Pension Plans, Defined Benefit [Member] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	7.00%
Target range allocation, maximum	19.00%
Actual allocation	12.00%
Pension Plans, Defined Benefit [Member] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	10.00%
Actual allocation	5.00%
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	11.00%
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	32.00%
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] | Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, minimum	0.00%
Target range allocation, maximum	45.00%
Actual allocation	21.00%
Other Postretirement Benefits Plans [Member] | 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	47.00%

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, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 895	$ 1,018.1	$ 1,022.9
Total plan assets	895	1,018.1
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.1	49.3
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.1	49.3
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] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100.4	137.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100.4	137.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	59.9	72.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	59.9	72.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60.5	73.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60.5	73.2
Pension Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.2	15.2
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.2	15.2
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16	15.9
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16	15.9
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104.4	102.9
Pension Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52.7	52.1
Pension Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	51.7	50.8
Pension Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.2	47.2
Pension Plans, Defined Benefit [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.2	47.2
Pension Plans, Defined Benefit [Member] | International - Emerging Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | International - Emerging Markets [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	96.3	99.9
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52.9	57.2
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43.4	42.7
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94	102.5
Pension Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94	102.5
Pension Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Pension Plans, Defined Benefit [Member] | Corporate Bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Corporate Bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Pension Plans, Defined Benefit [Member] | Corporate Bonds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	284.8	302.7
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	284.8	302.5
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [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]
Fair value of plan assets	894.8	1,018.3
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	263.2	309.8
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	631.6	708.5
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	0.2	0.1
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	422.7	484.7	485.9
Total plan assets	422.7	484.7
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10.9	23.5
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	0	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	10.9	23.5
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] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47.4	65.3
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47.4	65.3
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Core [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Core [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28.3	34.4
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28.3	34.4
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28.6	34.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28.6	34.9
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.7	7.2
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.7	7.2
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.5	7.6
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.5	7.6
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49.3	49
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24.9	24.8
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24.4	24.2
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.5	22.5
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.5	22.5
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [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	45.5	47.5
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	25	27.2
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	20.5	20.3
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44.4	48.8
Pension Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44.4	48.8
Pension Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity 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 Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	134.5	144.1
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	134.5	144
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [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]
Fair value of plan assets	422.6	484.8
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	124.3	147.5
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	298.3	337.3
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	0.1	0.1
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	386.8	440.3	438.8
Total plan assets	386.8	440.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	21.3
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	0	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	10	21.3
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] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43.4	59.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43.4	59.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Core [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Core [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25.9	31.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25.9	31.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	26.2	31.7
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	26.2	31.7
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.1	6.6
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.1	6.6
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.9	6.9
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.9	6.9
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.1	44.5
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.8	22.5
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.3	22
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.8	20.4
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.8	20.4
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [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	41.6	43.2
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	22.8	24.8
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	18.8	18.4
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40.6	44.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40.6	44.3
Pension Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity 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 Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123.1	130.9
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123.1	130.8
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [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]
Fair value of plan assets	386.7	440.4
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113.7	134
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	273	306.4
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	0.1	0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	106.9	121.6	124.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	97.8	103.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9.1	17.8
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	3.6	3.7
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	0	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	3.6	3.7
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] | U.S. Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.1	35.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.1	35.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Blend [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Blend [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9	2.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9	2.9
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Core [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Large Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Value [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Small Cap Growth [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12.5	14.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12.5	14.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Blend [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Blend [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	2.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Developed Markets [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.4	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.4	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Emerging Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | International - Emerging Markets [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	16.4	30.3
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	29.4
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	0.4	0.9
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9	2.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9	2.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | Risk Parity 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 Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48.9	25.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.3	19
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.6	6.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [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	69.2	78.7	81.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67.7	74.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.5	4
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	0.9	1.4
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	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	0.9	1.4
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] | U.S. Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.6	27.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.6	27.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Blend [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] | U.S. Blend [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] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Core [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] | U.S. Large Cap Core [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] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Value [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] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Large Cap Growth [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] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Value [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] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | U.S. Small Cap Growth [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] | U.S. Small Cap Growth [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] | International - Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10.7	10.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10.7	10.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Blend [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] | International - Blend [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] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Developed Markets [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] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | International - Emerging Markets [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] | International - Emerging Markets [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	6.9	21.6
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	6.9	21.5
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	0.1
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Risk Parity 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 Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33.6	15.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33.3	14.3
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	1.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Funds [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	18.7	21.8	$ 21.7
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.4	13
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.3	8.8
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	2.3	1.4
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	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	2.3	1.4
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] | U.S. Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Blend [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] | U.S. Blend [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] | U.S. Large Cap Core [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Core [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Core [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] | U.S. Large Cap Core [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] | U.S. Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Value [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] | U.S. Large Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Large Cap Growth [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] | U.S. Small Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Value [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] | U.S. Small Cap Growth [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | U.S. Small Cap Growth [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] | U.S. Small Cap Growth [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] | International - Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Blend [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Blend [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] | International - Blend [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] | International - Developed Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.6
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Developed Markets [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] | International - Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.5
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | International - Emerging Markets [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] | International - Emerging Markets [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	5.4	3.8
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	5.4	3.3
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	0.5
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] | Risk Parity Allocation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity Allocation Securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity Allocation Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1.1
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Risk Parity 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 Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	5.2
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	1.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3.4
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Funds [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	0	(0.3)
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	(0.2)
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	$ (0.1)

Benefit Plans (Employees Partic

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
401(k) costs	$ 24.9	$ 22.5	$ 19.2
IPL [Member]
401(k) costs	12.7	11.1	9.9
WPL [Member]
401(k) costs	$ 11.2	$ 10.5	$ 8.5

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation expense	$ 10.7	$ 15.3	$ 12
Income tax benefits	4.4	6.2	4.8
IPL [Member]
Compensation expense	5.7	8.3	6.2
Income tax benefits	2.4	3.4	2.5
WPL [Member]
Compensation expense	4.7	6.4	5.2
Income tax benefits	$ 1.9	$ 2.6	$ 2.1

Benefit Plans (Summary Of Perfo

Benefit Plans (Summary Of Performance Shares Activity) (Details) - Performance Shares [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	144,424	139,940	145,277
Granted (in shares/awards)	45,403	51,221	49,093
Vested (in shares/awards)	(45,612)	(45,235)	(54,430)
Forfeited (in shares/awards)	0	(1,502)	0
Nonvested, December 31 (in shares/awards)	144,215	144,424	139,940
Instrument valuation based on shares of common stock, number of shares	1
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%
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	(45,612)
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)	10,975
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(45,235)
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)		4,810
2010 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(54,430)
Vested percentage of the target			197.50%
Cash and stock payout value			$ 4.8
Cash payout value			$ 4.4
Common stock shares from vested performance shares (in shares)			4,177

Benefit Plans (Summary Of Pe117

Benefit Plans (Summary Of Performance Unit Activity) (Details) - Performance Units [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	63,665	65,912	64,969
Granted (in shares/awards)	17,837	20,422	22,201
Vested (in shares/awards)	(22,845)	(20,751)	(19,760)
Forfeited (in shares/awards)	(451)	(1,918)	(1,498)
Nonvested, December 31 (in shares/awards)	58,206	63,665	65,912
Instrument valuation based on shares of common stock, number of shares	1
Performance multiplier range, lower	0.00%
Performance multiplier range, upper	200.00%
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	(22,845)
Vested percentage of the target	167.50%
Cash payout value	$ 1.6
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(20,751)
Vested percentage of the target		147.50%
Cash payout value		$ 1.2
2010 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(19,760)
Vested percentage of the target			197.50%
Cash payout value			$ 1.3

Benefit Plans (Fair Values Of N

Benefit Plans (Fair Values Of Nonvested Performance Shares And Units) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	144,215	144,424	139,940	145,277
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	58,206	63,665	65,912	64,969
2015 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	45,403
Alliant Energy common stock closing price on December 31, 2015 (in dollars per share)	$ 62.45
Estimated payout percentage based on performance criteria	80.00%
Fair values of each nonvested award (in dollars per share)	$ 49.96
2015 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	17,386
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 65.09
Estimated payout percentage based on performance criteria	80.00%
Fair values of each nonvested award (in dollars per share)	$ 52.07
2014 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	49,719
Alliant Energy common stock closing price on December 31, 2015 (in dollars per share)	$ 62.45
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 78.06
2014 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	19,440
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 53.77
Estimated payout percentage based on performance criteria	125.00%
Fair values of each nonvested award (in dollars per share)	$ 67.21
2013 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	49,093
Alliant Energy common stock closing price on December 31, 2015 (in dollars per share)	$ 62.45
Estimated payout percentage based on performance criteria	165.00%
Fair values of each nonvested award (in dollars per share)	$ 103.04
2013 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards (in shares/awards)	21,380
Alliant Energy common stock closing price on grant date (in dollars per share)	$ 47.58
Estimated payout percentage based on performance criteria	165.00%
Fair values of each nonvested award (in dollars per share)	$ 78.51

Benefit Plans (Summary Of Pe119

Benefit Plans (Summary Of Performance Contingent Restricted Stock Activity) (Details) - Performance-Contingent Restricted Stock [Member] - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		98,812	158,922	211,651
Nonvested shares, January 1, weighted average fair value (in dollars per share)		$ 50.69	$ 42.71	$ 32.42
Granted (in shares/awards)		45,403	51,221	49,093
Granted, weighted average fair value (in dollars per share)		$ 65.09	$ 53.77	$ 47.58
Vested (in shares/awards)	[1]	(49,093)	(90,847)	0
Vested, weighted average fair value (in dollars per share)	[1]	$ 47.58	$ 40.91	$ 0
Forfeited (in shares/awards)	[2]	0	(20,484)	(101,822)
Forfeited, weighted average fair value (in dollars per share)	[2]	$ 0	$ 39.85	$ 23.67
Nonvested, December 31 (in shares/awards)		95,122	98,812	158,922
Nonvested shares, December 31, weighted average fair value (in dollars per share)		$ 59.17	$ 50.69	$ 42.71
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(49,093)
2012 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(45,612)
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(45,235)
2009 Grant [Member] | Performace Criteria Not Met [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Forfeited (in shares/awards)				(101,822)
[1]	In 2015, 49,093 performance-contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance-contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.
[2]	In 2013, 101,822 performance-contingent restricted shares granted in 2009 were forfeited because the specified performance criteria for such shares were not met. The forfeitures during 2014 were primarily caused by retirements and terminations of participants.

Benefit Plans (Summary Of Pe120

Benefit Plans (Summary Of Performance Contingent Cash Awards Activity) (Details) - Performance Contingent Cash Awards [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)		78,930	96,977	59,639
Granted (in shares/awards)		41,105	42,446	39,530
Vested (in shares/awards)	[1]	(37,332)	(55,517)	0
Forfeited (in shares/awards)		(827)	(4,976)	(2,192)
Nonvested, December 31 (in shares/awards)		81,876	78,930	96,977
2013 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)		(37,332)
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)			(34,766)
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)			(20,751)
Cash payout value			$ 1.1
[1]	In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 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, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligation	$ 8.5	$ 8.9
Fair market value of deferred compensation obligation	$ 13.4	$ 15.9

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, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligations	$ 18.3	$ 17.8
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligations	$ 5	$ 5.2

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 ($)	Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 114		$ 109.7
Revisions in estimated cash flows	[1]		17.3		0
Liabilities settled			(8.8)		(3.4)
Liabilities incurred		$ 87	86.6	[1]	3.7	[1]
Accretion expense			4.9		4
Balance, December 31			214		114
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			51.8		47.9
Revisions in estimated cash flows	[1]		15.1		0
Liabilities settled			(4.3)		(1.4)
Liabilities incurred		67	67.8	[1]	3.5	[1]
Accretion expense			2.5		1.8
Balance, December 31			$ 132.9		51.8
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			$ 52.4		52.4
Revisions in estimated cash flows	[1]		3.2		0
Liabilities settled			(4.5)		(2)
Liabilities incurred		$ 20	18.8	[1]	0.2	[1]
Accretion expense			2		1.8
Balance, December 31			$ 71.9		$ 52.4
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 is 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. The 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, 2015
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, 2015	Dec. 31, 2014
Assets:
Deferred proceeds	$ 172	$ 177.2
Liabilities and equity:
Long-term debt (including current maturities)	3,870.5	3,802.8
IPL [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	1,875	1,775
WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,550	1,580.6
Level 1 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	206.6	200.2
Level 1 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	206.6	200.2
Level 1 [Member] | WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
Level 2 [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	4,332.4	4,414.9
Cumulative preferred stock of IPL	0	0
Level 2 [Member] | IPL [Member]
Assets:
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	2,092.7	2,053
Cumulative preferred stock of IPL	0	0
Level 2 [Member] | WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,793	1,908.9
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	2.5	2.6
Liabilities and equity:
Derivatives	16	19.5
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	2	2.4
Liabilities and equity:
Derivatives	8	13.3
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0.5	0.2
Liabilities and equity:
Derivatives	8	6.2
Level 3 [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	3.7	3.3
Cumulative preferred stock of IPL	0	0
Level 3 [Member] | IPL [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Cumulative preferred stock of IPL	0	0
Level 3 [Member] | WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	15.9	36
Liabilities and equity:
Derivatives	48.6	18.1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	13.5	25.6
Liabilities and equity:
Derivatives	15.4	6.2
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	2.4	10.4
Liabilities and equity:
Derivatives	33.2	11.9
Carrying Value [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	3,835.6	3,767.3
Cumulative preferred stock of IPL	200	200
Carrying Value [Member] | IPL [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	1,856.9	1,758
Cumulative preferred stock of IPL	200	200
Carrying Value [Member] | WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,533.9	1,563.1
Carrying Value [Member] | Commodity Contracts [Member]
Assets:
Derivatives	18.4	38.6
Liabilities and equity:
Derivatives	64.6	37.6
Carrying Value [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	15.5	28
Liabilities and equity:
Derivatives	23.4	19.5
Carrying Value [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	2.9	10.6
Liabilities and equity:
Derivatives	41.2	18.1
Fair Value [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	4,336.1	4,418.2
Cumulative preferred stock of IPL	206.6	200.2
Fair Value [Member] | IPL [Member]
Assets:
Deferred proceeds	172	177.2
Liabilities and equity:
Long-term debt (including current maturities)	2,092.7	2,053
Cumulative preferred stock of IPL	206.6	200.2
Fair Value [Member] | WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	1,793	1,908.9
Fair Value [Member] | Commodity Contracts [Member]
Assets:
Derivatives	18.4	38.6
Liabilities and equity:
Derivatives	64.6	37.6
Fair Value [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	15.5	28
Liabilities and equity:
Derivatives	23.4	19.5
Fair Value [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	2.9	10.6
Liabilities and equity:
Derivatives	$ 41.2	$ 18.1

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
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		$ 17.9	$ 4.4
Total net gains (losses) included in changes in net assets (realized/unrealized)		(63.5)	11.1
Transfers out of Level 3		0.3	0
Purchases		36.9	76.7
Sales		(1.9)	(2.2)
Settlements		(22.4)	(72.1)
Ending balance, December 31		(32.7)	17.9
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		(56)	(0.4)
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		19.4	14.6
Total net gains (losses) included in changes in net assets (realized/unrealized)		(29.6)	(5.9)
Purchases		33.1	68.8
Sales		(1.8)	(2)
Settlements		(23)	(56.1)
Ending balance, December 31		(1.9)	19.4
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		(23.1)	(9.3)
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		(1.5)	(10.2)
Total net gains (losses) included in changes in net assets (realized/unrealized)		(33.9)	17
Transfers out of Level 3		0.3	0
Purchases		3.8	7.9
Sales		(0.1)	(0.2)
Settlements		0.6	(16)
Ending balance, December 31		(30.8)	(1.5)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		(32.9)	8.9
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1		177.2	203.5
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0
Transfers out of Level 3		0	0
Purchases		0	0
Sales		0	0
Settlements	[1]	(5.2)	(26.3)
Ending balance, December 31		172	177.2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at 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		177.2	203.5
Total net gains (losses) included in changes in net assets (realized/unrealized)		0	0
Purchases		0	0
Sales		0	0
Settlements	[1]	(5.2)	(26.3)
Ending balance, December 31		172	177.2
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at 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 (Fai127

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ (32.7)	$ 17.9	$ 4.4
Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities	(43.1)	(7)
FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	10.4	24.9
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	(1.9)	19.4	14.6
IPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities	(12.3)	(3.2)
IPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	10.4	22.6
WPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	(30.8)	(1.5)	$ (10.2)
WPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative liabilities	(30.8)	(3.8)
WPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 0	$ 2.3

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] T in Thousands, MWh in Thousands, Dekatherms in Thousands	Dec. 31, 2015DekathermsTMWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,868
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	809
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,059
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	9,880
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	5,622
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons)	4,258
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	104,096
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	55,985
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | Dekatherms	48,111
Coal (tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	4,945
Coal (tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	1,966
Coal (tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/Dths/tons) | T	2,979

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 15.1	$ 30.5
Non-current derivative assets	3.3	8.1
Current derivative liabilities	47.3	28.1
Non-current derivative liabilities	17.3	9.5
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	13.8	27.4
Non-current derivative assets	1.7	0.6
Current derivative liabilities	18.5	16.4
Non-current derivative liabilities	4.9	3.1
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	1.3	3.1
Non-current derivative assets	1.6	7.5
Current derivative liabilities	28.8	11.7
Non-current derivative liabilities	$ 12.4	$ 6.4

Commitments And Contingencie130

Commitments And Contingencies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)site
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,292
Time frame for plaintiffs to seek appeal of decision	30 days
Performance guarantees outstanding	$ 123
Present value abandonment obligation	$ 28
Minimum [Member]
Long-term Purchase Commitment [Line Items]
Warranty period	12 months
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Warranty period	60 months
Performance guarantees outstanding, 2016 [Member]
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	$ 48
Performance guarantees outstanding, 2017 [Member]
Long-term Purchase Commitment [Line Items]
Performance guarantees outstanding	75
Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	23
DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,419	[1],[2]
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,792
Maximum indemnification limit	$ 17
Number of sites monitoring and/or remediating (in sites) | site	24
IPL [Member] | Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 7
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 482
Number of sites monitoring and/or remediating (in sites) | site	5
WPL [Member] | Capital Purchase Obligation [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 16
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
Civil Penalty [Member] | IPL [Member]
Long-term Purchase Commitment [Line Items]
Damages awarded	$ 1
[1]	Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.
[2]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.

Commitments And Contingencie131

Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)MW
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,292
Individual commitments incurred	1
Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,584	[1]
DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,419	[1],[2]
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	165	[1]
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	398
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	267	[3]
SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	22
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	21	[4]
2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	524
2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	202	[1]
2016 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125	[1],[2]
2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	77	[1]
2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	173
2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	129	[3]
2016 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	14
2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[4]
2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	350
2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	182	[1]
2017 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1],[2]
2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	82
2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	76	[3]
2017 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8
2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	279
2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	175	[1]
2018 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1],[2]
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	52
2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	50	[3]
2018 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	200
2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1]
2019 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1],[2]
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	43
2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	12	[3]
2019 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	167
2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	133	[1]
2020 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	133	[1],[2]
2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	32
2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
2020 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	772
Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	749	[1]
Thereafter [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	749	[1],[2]
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	16
Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
Thereafter [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	7	[4]
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,792
IPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 1,420	[1]
IPL [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Approved amount of electric power capacity (in megawatts) | MW	431
IPL [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 1,419	[1],[2]
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[1]
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	228
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	121	[3]
IPL [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	22
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[4]
IPL [Member] | 2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	306
IPL [Member] | 2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	126	[1]
IPL [Member] | 2016 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125	[1],[2]
IPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[1]
IPL [Member] | 2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	95
IPL [Member] | 2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	70	[3]
IPL [Member] | 2016 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	14
IPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[4]
IPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	218
IPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1]
IPL [Member] | 2017 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1],[2]
IPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	42
IPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	30	[3]
IPL [Member] | 2017 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8
IPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	183
IPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1]
IPL [Member] | 2018 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1],[2]
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	35
IPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	17	[3]
IPL [Member] | 2018 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	175
IPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1]
IPL [Member] | 2019 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1],[2]
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	28
IPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	4	[3]
IPL [Member] | 2019 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	151
IPL [Member] | 2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	133	[1]
IPL [Member] | 2020 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	133	[1],[2]
IPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	18
IPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | 2020 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
IPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	759
IPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	749	[1]
IPL [Member] | Thereafter [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	749	[1],[2]
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	10
IPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | Thereafter [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	482
WPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	164	[1]
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	170
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	146	[3]
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
WPL [Member] | 2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	215
WPL [Member] | 2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	76	[1]
WPL [Member] | 2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	78
WPL [Member] | 2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	59	[3]
WPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[4]
WPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	130
WPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
WPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	40
WPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	46	[3]
WPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
WPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	94
WPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
WPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	17
WPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	33	[3]
WPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
WPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	23
WPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	15
WPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8	[3]
WPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
WPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	14
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	14
WPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
WPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6
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	6
WPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 0	[4]
[1]	Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.
[2]	Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.
[3]	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, 2015 regarding expected future usage, which is subject to change.
[4]	Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2015.

Commitments And Contingencie132

Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Current environmental liabilities	$ 2.7	$ 2
Non-current environmental liabilities	12.8	13.5
Total environmental liabilities	15.5	15.5
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	11
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	28
IPL [Member]
Current environmental liabilities	1.7	1.7
Non-current environmental liabilities	11.2	11.9
Total environmental liabilities	12.9	13.6
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	9
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	25
WPL [Member]
Current environmental liabilities	1	0.3
Non-current environmental liabilities	1.5	1.6
Total environmental liabilities	2.5	$ 1.9
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	2
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	3
Manufactured Gas Plant [Member]
Total environmental liabilities	15
Manufactured Gas Plant [Member] | IPL [Member]
Total environmental liabilities	13
Manufactured Gas Plant [Member] | WPL [Member]
Total environmental liabilities	$ 2

Segments Of Business (Narrative

Segments Of Business (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015segment
IPL and WPL [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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 804.1	$ 843.1	$ 750.3	$ 952.8	$ 3,253.6	$ 3,350.3	$ 3,276.8
Depreciation and amortization									401.3	388.1	370.9
Operating income (loss)	79.2	235.9	109	152.9	91.3	194.8	103.3	154.2	577	543.6	533.9
Interest expense									187.1	180.6	172.8
Equity (income) loss from unconsolidated investments, net									(33.8)	(40.4)	(43.7)
Income tax expense (benefit)									70.4	44.3	53.9
Net income (loss) attributable to common shareowners	34.1	179.9	67.6	96.6	60	153.3	61.8	108	378.2	383.1	358.3
Total assets	12,495.2				12,063.5				12,495.2	12,063.5	11,092.5
Investments in equity method subsidiaries	302.9				296.6				302.9	296.6	281.4
Construction and acquisition expenditures									1,034.3	902.8	798.3
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	398.7	504.6	382.2	489	431.1	476.2	411.9	528.9	1,774.5	1,848.1	1,818.8
Depreciation and amortization									207.2	197.5	191.1
Operating income (loss)	25.6	117	33.8	65.5	23.8	93.9	34	57.5	241.9	209.2	212
Interest expense									96.8	89.9	81.3
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income (loss) attributable to common shareowners	5.5	116.5	16.5	47.5	18.9	102	18	42.7	186	181.6	172
Total assets	6,709.1				6,450.2				6,709.1	6,450.2
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	330.7	382.6	324.7	397.1	359.8	354.4	324.5	410.4	1,435.1	1,449.1	1,406.3
Depreciation and amortization									184.3	181.2	172.2
Operating income (loss)	49.3	110.3	68.3	80.8	59.4	93.9	60	87.7	308.7	301	296.1
Interest expense									92.4	86.4	85
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									82.9	85.3	85.6
Net income (loss) attributable to common shareowners	24.2	$ 68	$ 39.2	$ 44.9	32.6	$ 57.9	$ 34.7	$ 55.2	176.3	180.4	177.5
Total assets	5,270.4				5,117.6				5,270.4	5,117.6
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,770.5	2,713.6	2,689
Depreciation and amortization									358.6	347	333
Operating income (loss)									514.1	442.4	444.5
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Total assets	10,211.3				9,660.4				10,211.3	9,660.4	9,018.6
Investments in equity method subsidiaries	302				294.3				302	294.3	279.1
Construction and acquisition expenditures									855.8	774.8	677.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,503.8	1,493.3	1,491.8
Depreciation and amortization									187.9	178.7	173.1
Operating income (loss)									218.8	166.8	173.1
Total assets	5,754.1				5,398.3				5,754.1	5,398.3	4,905.3
Construction and acquisition expenditures									561.2	490	365.4
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,266.7	1,220.3	1,197.2
Depreciation and amortization									170.7	168.3	159.9
Operating income (loss)									295.3	275.6	271.4
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Total assets	4,457.2				4,262.1				4,457.2	4,262.1	4,113.3
Investments in equity method subsidiaries	302				294.3				302	294.3	279.1
Construction and acquisition expenditures									294.6	284.8	311.9
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									381.2	517.5	464.8
Depreciation and amortization									31.1	29.9	28.8
Operating income (loss)									34.6	53.8	57.3
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	939.3				913.5				939.3	913.5	859.3
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									106.4	63.2	47
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									217.3	296.5	273.9
Depreciation and amortization									17.5	17	16.5
Operating income (loss)									17.7	25.7	29.8
Total assets	548.2				544.1				548.2	544.1	518.8
Construction and acquisition expenditures									56.7	35.1	27.5
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									163.9	221	190.9
Depreciation and amortization									13.6	12.9	12.3
Operating income (loss)									16.9	28.1	27.5
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	391.1				369.4				391.1	369.4	340.5
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									49.7	28.1	19.5
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									57.9	66.1	71.3
Depreciation and amortization									1.8	1.8	1.5
Operating income (loss)									1.9	14	6.3
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	828.9				993.9				828.9	993.9	712.2
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									1.4	0.9	7.3
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									53.4	58.3	53.1
Depreciation and amortization									1.8	1.8	1.5
Operating income (loss)									5.4	16.7	9.1
Total assets	406.8				507.8				406.8	507.8	369.8
Construction and acquisition expenditures									1.4	0.9	7.3
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									4.5	7.8	18.2
Depreciation and amortization									0	0	0
Operating income (loss)									(3.5)	(2.7)	(2.8)
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	422.1				486.1				422.1	486.1	342.4
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									3,209.6	3,297.2	3,225.1
Depreciation and amortization									391.5	378.7	363.3
Operating income (loss)									550.6	510.2	508.1
Interest expense									189.2	176.3	166.3
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									60.2	36.4	49.3
Net income (loss) attributable to common shareowners									362.3	362	349.5
Total assets	11,979.5				11,567.8				11,979.5	11,567.8	10,590.1
Investments in equity method subsidiaries	302				294.3				302	294.3	279.1
Construction and acquisition expenditures									963.6	838.9	731.6
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,774.5	1,848.1	1,818.8
Depreciation and amortization									207.2	197.5	191.1
Operating income (loss)									241.9	209.2	212
Interest expense									96.8	89.9	81.3
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income (loss) attributable to common shareowners									186	181.6	172
Total assets	6,709.1				6,450.2				6,709.1	6,450.2	5,793.9
Construction and acquisition expenditures									619.3	526	400.2
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,435.1	1,449.1	1,406.3
Depreciation and amortization									184.3	181.2	172.2
Operating income (loss)									308.7	301	296.1
Interest expense									92.4	86.4	85
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									82.9	85.3	85.6
Net income (loss) attributable to common shareowners									176.3	180.4	177.5
Total assets	5,270.4				5,117.6				5,270.4	5,117.6	4,796.2
Investments in equity method subsidiaries	302				294.3				302	294.3	279.1
Construction and acquisition expenditures									344.3	312.9	331.4
Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues									44	53.1	51.7
Depreciation and amortization									9.8	9.4	7.6
Operating income (loss)									26.4	33.4	25.8
Interest (income) expense									(2.1)	4.3	6.5
Equity (income) loss from unconsolidated investments, net									1.3	2.4	0
Income tax expense (benefit)									10.2	7.9	4.6
Net income (loss) attributable to common shareowners									15.9	21.1	8.8
Total assets	515.7				495.7				515.7	495.7	502.4
Investments in equity method subsidiaries	$ 0.9				$ 2.3				0.9	2.3	2.3
Construction and acquisition expenditures									$ 70.7	$ 63.9	$ 66.7

Segments Of Business (Services)

Segments Of Business (Services) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Services	100.00%	100.00%	100.00%
Utility electric operations [Member]
Segment Reporting Information [Line Items]
Services	85.00%	81.00%	82.00%
Utility gas operations [Member]
Segment Reporting Information [Line Items]
Services	12.00%	15.00%	14.00%
Utility other [Member]
Segment Reporting Information [Line Items]
Services	2.00%	2.00%	2.00%
Other [Member]
Segment Reporting Information [Line Items]
Services	1.00%	2.00%	2.00%

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
WPL Owed ATC [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 8	$ 8

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Corporate Service Billings [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 150	$ 148	$ 140
Corporate Service Billings [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	121	116	103
Sales Credited [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	10	8	7
Sales Credited [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	24	6	12
Purchases Billed [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	366	422	365
Purchases Billed [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 66	$ 125	$ 68

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
IPL [Member]
Related Party Transaction [Line Items]
Intercompany payables to Corporate Services	$ 93	$ 84
WPL [Member]
Related Party Transaction [Line Items]
Intercompany payables to Corporate Services	$ 54	$ 58

Related Parties (Related Amount

Related Parties (Related Amounts Billed Between Parties) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ATC Billings To WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 101	$ 96	$ 96
WPL Billings To ATC [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 13	$ 9	$ 12

Discontinued Operations and 140

Discontinued Operations and Assets and Liabilities Held For Sale (Components Of Discontinued Operations In Consolidated Statements Of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]
Operating revenues	$ 0	$ 0	$ 0.9
Operating expenses	4	3.7	9.9
Loss before income taxes	(4)	(3.7)	(9)
Income tax benefit	(1.5)	(1.3)	(3.1)
Loss from discontinued operations, net of tax	$ (2.5)	$ (2.4)	$ (5.9)

Discontinued Operations and 141

Discontinued Operations and Assets and Liabilities Held For Sale (Components Of Assets And Liabilities Held For Sale In Consolidated Balance Sheets) (Details) - Alliant Energy and IPL [Member] - Gas Distribution [Member] $ in Millions	Dec. 31, 2014USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Current assets	$ 1.1
Property, plant and equipment, net	11
Non-current regulatory assets	7
Total assets held for sale	19.1
Current liabilities	1
Other liabilities	7.1
Total liabilities held for sale	8.1
Net assets held for sale	$ 11

Selected Consolidated Quarte142

Selected Consolidated Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 804.1	$ 843.1	$ 750.3	$ 952.8	$ 3,253.6	$ 3,350.3	$ 3,276.8
Operating income	79.2	235.9	109	152.9	91.3	194.8	103.3	154.2	577	543.6	533.9
Income from continuing operations, net of tax	35.2	180	68.9	96.6	60.2	155.2	62.1	108	380.7	385.5	364.2
Loss from discontinued operations, net of tax	(1.1)	(0.1)	(1.3)	0	(0.2)	(1.9)	(0.3)	0	(2.5)	(2.4)	(5.9)
Net income									388.4	393.3	376.2
Net income (loss) attributable to common shareowners	$ 34.1	$ 179.9	$ 67.6	$ 96.6	$ 60	$ 153.3	$ 61.8	$ 108	378.2	383.1	358.3
Income from continuing operations, net of tax (in dollars per share)	$ 0.31	$ 1.59	$ 0.61	$ 0.87	$ 0.54	$ 1.40	$ 0.56	$ 0.97
Loss from discontinued operations, net of tax (in dollars per share)	(0.01)	0	(0.01)	0	0	(0.02)	0	0
Net income (in dollars per share)	$ 0.30	$ 1.59	$ 0.60	$ 0.87	$ 0.54	$ 1.38	$ 0.56	$ 0.97
IPL [Member]
Operating revenues	$ 398.7	$ 504.6	$ 382.2	$ 489	$ 431.1	$ 476.2	$ 411.9	$ 528.9	1,774.5	1,848.1	1,818.8
Operating income	25.6	117	33.8	65.5	23.8	93.9	34	57.5	241.9	209.2	212
Net income	8	119.1	19	50.1	21.4	104.6	20.5	45.3	196.2	191.8	188.3
Net income (loss) attributable to common shareowners	5.5	116.5	16.5	47.5	18.9	102	18	42.7	186	181.6	172
WPL [Member]
Operating revenues	330.7	382.6	324.7	397.1	359.8	354.4	324.5	410.4	1,435.1	1,449.1	1,406.3
Operating income	49.3	110.3	68.3	80.8	59.4	93.9	60	87.7	308.7	301	296.1
Net income	24.4	68.4	39.7	45.1	33.3	57.9	34.7	55.2	177.6	181.1	179.1
Net income (loss) attributable to common shareowners	$ 24.2	$ 68	$ 39.2	$ 44.9	$ 32.6	$ 57.9	$ 34.7	$ 55.2	$ 176.3	$ 180.4	$ 177.5

Condensed Parent Company Fin143

Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 804.1	$ 843.1	$ 750.3	$ 952.8	$ 3,253.6	$ 3,350.3	$ 3,276.8
Operating expenses									2,676.6	2,806.7	2,742.9
Operating income (loss)	$ 79.2	$ 235.9	$ 109	$ 152.9	$ 91.3	$ 194.8	$ 103.3	$ 154.2	577	543.6	533.9
Interest expense and other:
Equity earnings from consolidated subsidiaries									(33.8)	(40.4)	(43.7)
Interest expense									187.1	180.6	172.8
Total interest expense and other									115.7	103.6	97.9
Income from continuing operations before income taxes									461.3	440	436
Income tax benefit									70.4	44.3	53.9
Net income									388.4	393.3	376.2
Parent Company [Member]
Operating revenues									2	2	2
Operating expenses									3	3	1
Operating income (loss)									(1)	(1)	1
Interest expense and other:
Equity earnings from consolidated subsidiaries									(379)	(388)	(361)
Interest expense									3	9	11
Interest income									(3)	(2)	(2)
Total interest expense and other									(379)	(381)	(352)
Income from continuing operations before income taxes									378	380	353
Income tax benefit									(1)	(3)	(5)
Net income									$ 379	$ 383	$ 358

Condensed Parent Company Fin144

Condensed Parent Company Financial Statements (Condensed Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Other	$ 79.7	$ 116.9
Total current assets	826.8	1,043.1
Investments:
Other	53	58.4
Total investments	346.3	344.9
Other assets	1,803	1,737.1
Total assets	12,495.2	12,063.5	$ 11,092.5
Current liabilities:
Current maturities of long-term debt	313.4	183
Commercial paper	159.8	141.3
Other	296.6	262.4
Total current liabilities	1,359.3	1,214.7
Long-term debt, net (excluding current portion)	3,522.2	3,584.3
Other liabilities	306	260.1
Common Equity:
Retained earnings	2,068.9	1,938
Shares in deferred compensation trust	(8.5)	(8.9)
Total common equity	3,724.1	3,438.7	$ 3,281.4	$ 3,134.9
Total liabilities and equity	12,495.2	12,063.5
Parent Company [Member]
Current assets:
Notes receivable from affiliated companies	93	95
Other	9	25
Total current assets	102	120
Investments:
Investments in consolidated subsidiaries	3,999	3,721
Other	14	15
Total investments	4,013	3,736
Other assets	20	10
Total assets	4,135	3,866
Current liabilities:
Current maturities of long-term debt	250	0
Commercial paper	140	141
Other	12	29
Total current liabilities	402	170
Long-term debt, net (excluding current portion)	0	250
Other liabilities	12	11
Common Equity:
Common stock and additional paid-in capital	1,664	1,510
Retained earnings	2,066	1,934
Shares in deferred compensation trust	(9)	(9)
Total common equity	3,721	3,435
Total liabilities and equity	$ 4,135	$ 3,866

Condensed Parent Company Fin145

Condensed Parent Company Financial Statements (Condensed Statements of Cash Flow) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net cash flows from operating activities	$ 871.2	$ 891.6	$ 731
Cash flows used for investing activities:
Other	(24.8)	(14.9)	(18.8)
Net cash flows used for investing activities	(919.2)	(917.7)	(754.7)
Cash flows used for financing activities:
Common stock dividends	(247.3)	(225.8)	(208.3)
Proceeds from issuance of common stock, net	151.2	0	0
Proceeds from issuance of long-term debt	250.7	812.9	250
Payments to retire long-term debt	(183)	(358.5)	(1.5)
Net change in commercial paper	18.5	(138.1)	11.9
Other	6.8	(17.3)	(28.8)
Net cash flows from (used for) financing activities	(3.1)	73.2	12.3
Net increase (decrease) in cash and cash equivalents	(51.1)	47.1	(11.4)
Cash and cash equivalents at beginning of period	56.9	9.8	21.2
Cash and cash equivalents at end of period	5.8	56.9	9.8
Supplemental cash flows information:
Interest, net of capitalized interest	(184.8)	(180.8)	(171.7)
Income taxes, net	0	5.3	9.6
Parent Company [Member]
Net cash flows from operating activities	262	246	238
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries	(165)	(90)	(120)
Captial repayments from consolidated subsidiaries	0	50	95
Net change in notes receivable from affiliates	2	(23)	5
Other	0	0	(2)
Net cash flows used for investing activities	(163)	(63)	(22)
Cash flows used for financing activities:
Common stock dividends	(247)	(226)	(208)
Proceeds from issuance of common stock, net	151	0	0
Proceeds from issuance of long-term debt	0	250	0
Payments to retire long-term debt	0	(250)	0
Net change in commercial paper	(1)	45	(9)
Other	(2)	(2)	1
Net cash flows from (used for) financing activities	(99)	(183)	(216)
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)	(11)	(13)
Income taxes, net	$ (9)	$ (5)	$ (7)

Valuation And Qualifying Acc146

Valuation And Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Provision for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	$ 5.1	$ 4.8	$ 4
Charged to Expense	[1]	8.1	11.7	13.6
Charged to Other Accounts	[1],[2]	3	4.1	0.6
Deductions	[1],[3]	11.4	15.5	13.4
Ending Balance	[1]	4.8	5.1	4.8
Accumulated Provision for Uncollectible Accounts [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	0.4	0.7	0.7
Charged to Expense	[1]	8.1	11.5	12.7
Charged to Other Accounts	[1],[2]	0	0	0
Deductions	[1],[3]	7.9	11.8	12.7
Ending Balance	[1]	0.6	0.4	0.7
Accumulated Provision for Uncollectible Accounts [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		4.2	1.7	1.8
Charged to Expense		0	0	0
Charged to Other Accounts	[2]	3	4.1	0.6
Deductions	[3]	3.5	1.6	0.7
Ending Balance		3.7	4.2	1.7
Accumulated Provision for Other Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	32.6	38.2	33.4
Charged to Expense	[4]	6.5	12.5	23.2
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	12	18.1	18.4
Ending Balance	[4]	27.1	32.6	38.2
Accumulated Provision for Other Reserves [Member] | IPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	10.6	18.1	11.6
Charged to Expense	[4]	2.1	3.9	9.3
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	3.3	11.4	2.8
Ending Balance	[4]	9.4	10.6	18.1
Accumulated Provision for Other Reserves [Member] | WPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[4]	16.3	16.2	13.5
Charged to Expense	[4]	0.7	2.5	8.8
Charged to Other Accounts	[2],[4]	0	0	0
Deductions	[3],[4]	5.6	2.4	6.1
Ending Balance	[4]	$ 11.4	$ 16.3	$ 16.2
[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.
[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.