Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

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	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$25.1		$—		$4.1		$21.0		$25.1		$41.4		$—		$4.6		$36.8		$41.4
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	41.7		—		8.5		33.2		41.7		28.6		—		0.5		28.1		28.6
Long-term debt (incl. current maturities)	4,866.3		—		5,444.6		2.9		5,447.5		4,320.2		—		4,795.7		3.3		4,799.0
Cumulative preferred stock of IPL	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

IPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$17.1		$—		$2.0		$15.1		$17.1		$20.8		$—		$2.8		$18.0		$20.8
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	19.4		—		2.9		16.5		19.4		8.3		—		0.4		7.9		8.3
Long-term debt (incl. current maturities)	2,406.0		—		2,665.7		—		2,665.7		2,153.5		—		2,352.3		—		2,352.3
Cumulative preferred stock	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

WPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$8.0		$—		$2.1		$5.9		$8.0		$20.6		$—		$1.8		$18.8		$20.6
Liabilities and equity:
Derivatives	22.3		—		5.6		16.7		22.3		20.3		—		0.1		20.2		20.3
Long-term debt	1,833.4		—		2,147.9		—		2,147.9		1,535.2		—		1,807.4		—		1,807.4

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
	2017			2016			2017		2016
Beginning balance, January 1		$8.7			($32.7	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(32.9		)	30.7			—		—
Transfers into Level 3	—			0.9			—		—
Transfers out of Level 3	12.2			1.2			—		—
Purchases	28.3			22.0			—		—
Sales	(0.3		)	(1.0		)	—		—
Settlements (a)	(28.2		)	(12.4		)	11.0		39.1
Ending balance, December 31		($12.2	)		$8.7			$222.1		$211.1
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		($31.0	)		$32.7			$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2017			2016			2017		2016
Beginning balance, January 1		$10.1			($1.9	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(14.8		)	7.3			—		—
Transfers into Level 3	—			0.5			—		—
Transfers out of Level 3	3.1			0.2			—		—
Purchases	24.6			20.6			—		—
Sales	(0.2		)	(1.0		)	—		—
Settlements (a)	(24.2		)	(15.6		)	11.0		39.1
Ending balance, December 31		($1.4	)		$10.1			$222.1		$211.1
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		($13.5	)		$8.5			$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2017			2016
Beginning balance, January 1		($1.4	)		($30.8	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(18.1		)	23.4
Transfers into Level 3	—			0.4
Transfers out of Level 3	9.1			1.0
Purchases	3.7			1.4
Sales	(0.1		)	—
Settlements	(4.0		)	3.2
Ending balance, December 31		($10.8	)		($1.4	)
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		($17.5	)		$24.2

(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, coal and diesel fuel 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
2017		($23.5	)		$11.3		($11.5	)		$10.1		($12.0	)		$1.2
2016	(2.3		)	11.0		0.1			10.0		(2.4		)	1.0

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	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$25.1		$—		$4.1		$21.0		$25.1		$41.4		$—		$4.6		$36.8		$41.4
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	41.7		—		8.5		33.2		41.7		28.6		—		0.5		28.1		28.6
Long-term debt (incl. current maturities)	4,866.3		—		5,444.6		2.9		5,447.5		4,320.2		—		4,795.7		3.3		4,799.0
Cumulative preferred stock of IPL	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

IPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$17.1		$—		$2.0		$15.1		$17.1		$20.8		$—		$2.8		$18.0		$20.8
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	19.4		—		2.9		16.5		19.4		8.3		—		0.4		7.9		8.3
Long-term debt (incl. current maturities)	2,406.0		—		2,665.7		—		2,665.7		2,153.5		—		2,352.3		—		2,352.3
Cumulative preferred stock	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

WPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$8.0		$—		$2.1		$5.9		$8.0		$20.6		$—		$1.8		$18.8		$20.6
Liabilities and equity:
Derivatives	22.3		—		5.6		16.7		22.3		20.3		—		0.1		20.2		20.3
Long-term debt	1,833.4		—		2,147.9		—		2,147.9		1,535.2		—		1,807.4		—		1,807.4

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
	2017			2016			2017		2016
Beginning balance, January 1		$8.7			($32.7	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(32.9		)	30.7			—		—
Transfers into Level 3	—			0.9			—		—
Transfers out of Level 3	12.2			1.2			—		—
Purchases	28.3			22.0			—		—
Sales	(0.3		)	(1.0		)	—		—
Settlements (a)	(28.2		)	(12.4		)	11.0		39.1
Ending balance, December 31		($12.2	)		$8.7			$222.1		$211.1
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		($31.0	)		$32.7			$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2017			2016			2017		2016
Beginning balance, January 1		$10.1			($1.9	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(14.8		)	7.3			—		—
Transfers into Level 3	—			0.5			—		—
Transfers out of Level 3	3.1			0.2			—		—
Purchases	24.6			20.6			—		—
Sales	(0.2		)	(1.0		)	—		—
Settlements (a)	(24.2		)	(15.6		)	11.0		39.1
Ending balance, December 31		($1.4	)		$10.1			$222.1		$211.1
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		($13.5	)		$8.5			$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2017			2016
Beginning balance, January 1		($1.4	)		($30.8	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(18.1		)	23.4
Transfers into Level 3	—			0.4
Transfers out of Level 3	9.1			1.0
Purchases	3.7			1.4
Sales	(0.1		)	—
Settlements	(4.0		)	3.2
Ending balance, December 31		($10.8	)		($1.4	)
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		($17.5	)		$24.2

(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, coal and diesel fuel 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
2017		($23.5	)		$11.3		($11.5	)		$10.1		($12.0	)		$1.2
2016	(2.3		)	11.0		0.1			10.0		(2.4		)	1.0

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	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$25.1		$—		$4.1		$21.0		$25.1		$41.4		$—		$4.6		$36.8		$41.4
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	41.7		—		8.5		33.2		41.7		28.6		—		0.5		28.1		28.6
Long-term debt (incl. current maturities)	4,866.3		—		5,444.6		2.9		5,447.5		4,320.2		—		4,795.7		3.3		4,799.0
Cumulative preferred stock of IPL	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

IPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$17.1		$—		$2.0		$15.1		$17.1		$20.8		$—		$2.8		$18.0		$20.8
Deferred proceeds	222.1		—		—		222.1		222.1		211.1		—		—		211.1		211.1
Liabilities and equity:
Derivatives	19.4		—		2.9		16.5		19.4		8.3		—		0.4		7.9		8.3
Long-term debt (incl. current maturities)	2,406.0		—		2,665.7		—		2,665.7		2,153.5		—		2,352.3		—		2,352.3
Cumulative preferred stock	200.0		203.8		—		—		203.8		200.0		194.8		—		—		194.8

WPL	2017										2016
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$8.0		$—		$2.1		$5.9		$8.0		$20.6		$—		$1.8		$18.8		$20.6
Liabilities and equity:
Derivatives	22.3		—		5.6		16.7		22.3		20.3		—		0.1		20.2		20.3
Long-term debt	1,833.4		—		2,147.9		—		2,147.9		1,535.2		—		1,807.4		—		1,807.4

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
	2017			2016			2017		2016
Beginning balance, January 1		$8.7			($32.7	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(32.9		)	30.7			—		—
Transfers into Level 3	—			0.9			—		—
Transfers out of Level 3	12.2			1.2			—		—
Purchases	28.3			22.0			—		—
Sales	(0.3		)	(1.0		)	—		—
Settlements (a)	(28.2		)	(12.4		)	11.0		39.1
Ending balance, December 31		($12.2	)		$8.7			$222.1		$211.1
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		($31.0	)		$32.7			$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2017			2016			2017		2016
Beginning balance, January 1		$10.1			($1.9	)		$211.1		$172.0
Total net gains (losses) included in changes in net assets (realized/unrealized)	(14.8		)	7.3			—		—
Transfers into Level 3	—			0.5			—		—
Transfers out of Level 3	3.1			0.2			—		—
Purchases	24.6			20.6			—		—
Sales	(0.2		)	(1.0		)	—		—
Settlements (a)	(24.2		)	(15.6		)	11.0		39.1
Ending balance, December 31		($1.4	)		$10.1			$222.1		$211.1
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		($13.5	)		$8.5			$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2017			2016
Beginning balance, January 1		($1.4	)		($30.8	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(18.1		)	23.4
Transfers into Level 3	—			0.4
Transfers out of Level 3	9.1			1.0
Purchases	3.7			1.4
Sales	(0.1		)	—
Settlements	(4.0		)	3.2
Ending balance, December 31		($10.8	)		($1.4	)
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		($17.5	)		$24.2

(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, coal and diesel fuel 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
2017		($23.5	)		$11.3		($11.5	)		$10.1		($12.0	)		$1.2
2016	(2.3		)	11.0		0.1			10.0		(2.4		)	1.0