Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):

Alliant Energy	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$14.1		$—		$4.1		$10.0		$14.1		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	46.7		—		7.3		39.4		46.7		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	4,912.5		—		5,366.6		2.5		5,369.1		4,866.3		—		5,444.6		2.9		5,447.5
Cumulative preferred stock of IPL	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

IPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$7.9		$—		$1.7		$6.2		$7.9		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	24.7		—		3.1		21.6		24.7		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,452.2		—		2,635.7		—		2,635.7		2,406.0		—		2,665.7		—		2,665.7
Cumulative preferred stock	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

WPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$6.2		$—		$2.4		$3.8		$6.2		$8.0		$—		$2.1		$5.9		$8.0
Liabilities:
Derivatives	22.0		—		4.2		17.8		22.0		22.3		—		5.6		16.7		22.3
Long-term debt	1,833.7		—		2,102.7		—		2,102.7		1,833.4		—		2,147.9		—		2,147.9

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
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(9.8		)	(35.2		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(7.4		)	(6.3		)	(101.2		)	(62.1		)
Ending balance, March 31		($29.4	)		($32.9	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($9.4	)		($33.7	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($1.4	)		$10.1			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(7.6		)	(12.7		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(6.4		)	(5.6		)	(101.2		)	(62.1		)
Ending balance, March 31		($15.4	)		($8.3	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($7.3	)		($11.4	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net losses included in changes in net assets (realized/unrealized)	(2.2		)	(22.5		)
Settlements	(1.0		)	(0.7		)
Ending balance, March 31		($14.0	)		($24.6	)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($2.1	)		($22.3	)

(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) as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
March 31, 2018		($34.6	)		$5.2		($20.0	)		$4.6		($14.6	)		$0.6
December 31, 2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2

IPL [Member]

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):

Alliant Energy	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$14.1		$—		$4.1		$10.0		$14.1		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	46.7		—		7.3		39.4		46.7		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	4,912.5		—		5,366.6		2.5		5,369.1		4,866.3		—		5,444.6		2.9		5,447.5
Cumulative preferred stock of IPL	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

IPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$7.9		$—		$1.7		$6.2		$7.9		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	24.7		—		3.1		21.6		24.7		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,452.2		—		2,635.7		—		2,635.7		2,406.0		—		2,665.7		—		2,665.7
Cumulative preferred stock	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

WPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$6.2		$—		$2.4		$3.8		$6.2		$8.0		$—		$2.1		$5.9		$8.0
Liabilities:
Derivatives	22.0		—		4.2		17.8		22.0		22.3		—		5.6		16.7		22.3
Long-term debt	1,833.7		—		2,102.7		—		2,102.7		1,833.4		—		2,147.9		—		2,147.9

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
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(9.8		)	(35.2		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(7.4		)	(6.3		)	(101.2		)	(62.1		)
Ending balance, March 31		($29.4	)		($32.9	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($9.4	)		($33.7	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($1.4	)		$10.1			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(7.6		)	(12.7		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(6.4		)	(5.6		)	(101.2		)	(62.1		)
Ending balance, March 31		($15.4	)		($8.3	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($7.3	)		($11.4	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net losses included in changes in net assets (realized/unrealized)	(2.2		)	(22.5		)
Settlements	(1.0		)	(0.7		)
Ending balance, March 31		($14.0	)		($24.6	)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($2.1	)		($22.3	)

(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) as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
March 31, 2018		($34.6	)		$5.2		($20.0	)		$4.6		($14.6	)		$0.6
December 31, 2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2

WPL [Member]

Statement [Line Items]

Fair Value Measurements

Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):

Alliant Energy	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$14.1		$—		$4.1		$10.0		$14.1		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	46.7		—		7.3		39.4		46.7		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	4,912.5		—		5,366.6		2.5		5,369.1		4,866.3		—		5,444.6		2.9		5,447.5
Cumulative preferred stock of IPL	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

IPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$7.9		$—		$1.7		$6.2		$7.9		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	120.9		—		—		120.9		120.9		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	24.7		—		3.1		21.6		24.7		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,452.2		—		2,635.7		—		2,635.7		2,406.0		—		2,665.7		—		2,665.7
Cumulative preferred stock	200.0		198.4		—		—		198.4		200.0		203.8		—		—		203.8

WPL	March 31, 2018										December 31, 2017
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$6.2		$—		$2.4		$3.8		$6.2		$8.0		$—		$2.1		$5.9		$8.0
Liabilities:
Derivatives	22.0		—		4.2		17.8		22.0		22.3		—		5.6		16.7		22.3
Long-term debt	1,833.7		—		2,102.7		—		2,102.7		1,833.4		—		2,147.9		—		2,147.9

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
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(9.8		)	(35.2		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(7.4		)	(6.3		)	(101.2		)	(62.1		)
Ending balance, March 31		($29.4	)		($32.9	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($9.4	)		($33.7	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended March 31	2018			2017			2018			2017
Beginning balance, January 1		($1.4	)		$10.1			$222.1			$211.1
Total net losses included in changes in net assets (realized/unrealized)	(7.6		)	(12.7		)	—			—
Sales	—			(0.1		)	—			—
Settlements (a)	(6.4		)	(5.6		)	(101.2		)	(62.1		)
Ending balance, March 31		($15.4	)		($8.3	)		$120.9			$149.0
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($7.3	)		($11.4	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended March 31	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net losses included in changes in net assets (realized/unrealized)	(2.2		)	(22.5		)
Settlements	(1.0		)	(0.7		)
Ending balance, March 31		($14.0	)		($24.6	)
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31		($2.1	)		($22.3	)

(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) as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
March 31, 2018		($34.6	)		$5.2		($20.0	)		$4.6		($14.6	)		$0.6
December 31, 2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2