Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

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	2018										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		$28.3		$—		$8.9		$19.4		$28.3		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	23.3		—		16.1		7.2		23.3		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	5,502.8		—		5,858.4		2.4		5,860.8		4,866.3		—		5,444.6		2.9		5,447.5

IPL	2018										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		$17.7		$—		$4.0		$13.7		$17.7		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	11.2		—		6.5		4.7		11.2		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,552.3		—		2,691.2		—		2,691.2		2,406.0		—		2,665.7		—		2,665.7

WPL	2018										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		$10.6		$—		$4.9		$5.7		$10.6		$8.0		$—		$2.1		$5.9		$8.0
Liabilities and equity:
Derivatives	12.1		—		9.6		2.5		12.1		22.3		—		5.6		16.7		22.3
Long-term debt (incl. current maturities)	1,834.9		—		2,043.7		—		2,043.7		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
	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.1			(32.9		)	—			—
Transfers out of Level 3 (a)	16.1			12.2			—			—
Purchases	26.7			28.3			—			—
Sales	(0.5		)	(0.3		)	—			—
Settlements (b)	(27.0		)	(28.2		)	(102.7		)	11.0
Ending balance, December 31		$12.2			($12.2	)		$119.4			$222.1
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		$10.7			($31.0	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	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)	(0.5		)	(14.8		)	—			—
Transfers out of Level 3 (a)	11.0			3.1			—			—
Purchases	22.5			24.6			—			—
Sales	(0.4		)	(0.2		)	—			—
Settlements (b)	(22.2		)	(24.2		)	(102.7		)	11.0
Ending balance, December 31		$9.0			($1.4	)		$119.4			$222.1
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		$0.2			($13.5	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.6			(18.1		)
Transfers out of Level 3 (a)	5.1			9.1
Purchases	4.2			3.7
Sales	(0.1		)	(0.1		)
Settlements	(4.8		)	(4.0		)
Ending balance, December 31		$3.2			($10.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$10.5			($17.5	)

(a) Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.

(b) 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, FTR and natural gas 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
2018		$3.2			$9.0		$1.8			$7.2		$1.4			$1.8
2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2

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	2018										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		$28.3		$—		$8.9		$19.4		$28.3		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	23.3		—		16.1		7.2		23.3		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	5,502.8		—		5,858.4		2.4		5,860.8		4,866.3		—		5,444.6		2.9		5,447.5

IPL	2018										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		$17.7		$—		$4.0		$13.7		$17.7		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	11.2		—		6.5		4.7		11.2		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,552.3		—		2,691.2		—		2,691.2		2,406.0		—		2,665.7		—		2,665.7

WPL	2018										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		$10.6		$—		$4.9		$5.7		$10.6		$8.0		$—		$2.1		$5.9		$8.0
Liabilities and equity:
Derivatives	12.1		—		9.6		2.5		12.1		22.3		—		5.6		16.7		22.3
Long-term debt (incl. current maturities)	1,834.9		—		2,043.7		—		2,043.7		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
	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.1			(32.9		)	—			—
Transfers out of Level 3 (a)	16.1			12.2			—			—
Purchases	26.7			28.3			—			—
Sales	(0.5		)	(0.3		)	—			—
Settlements (b)	(27.0		)	(28.2		)	(102.7		)	11.0
Ending balance, December 31		$12.2			($12.2	)		$119.4			$222.1
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		$10.7			($31.0	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	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)	(0.5		)	(14.8		)	—			—
Transfers out of Level 3 (a)	11.0			3.1			—			—
Purchases	22.5			24.6			—			—
Sales	(0.4		)	(0.2		)	—			—
Settlements (b)	(22.2		)	(24.2		)	(102.7		)	11.0
Ending balance, December 31		$9.0			($1.4	)		$119.4			$222.1
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		$0.2			($13.5	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.6			(18.1		)
Transfers out of Level 3 (a)	5.1			9.1
Purchases	4.2			3.7
Sales	(0.1		)	(0.1		)
Settlements	(4.8		)	(4.0		)
Ending balance, December 31		$3.2			($10.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$10.5			($17.5	)

(a) Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.

(b) 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, FTR and natural gas 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
2018		$3.2			$9.0		$1.8			$7.2		$1.4			$1.8
2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2

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	2018										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		$28.3		$—		$8.9		$19.4		$28.3		$25.1		$—		$4.1		$21.0		$25.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	23.3		—		16.1		7.2		23.3		41.7		—		8.5		33.2		41.7
Long-term debt (incl. current maturities)	5,502.8		—		5,858.4		2.4		5,860.8		4,866.3		—		5,444.6		2.9		5,447.5

IPL	2018										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		$17.7		$—		$4.0		$13.7		$17.7		$17.1		$—		$2.0		$15.1		$17.1
Deferred proceeds	119.4		—		—		119.4		119.4		222.1		—		—		222.1		222.1
Liabilities and equity:
Derivatives	11.2		—		6.5		4.7		11.2		19.4		—		2.9		16.5		19.4
Long-term debt (incl. current maturities)	2,552.3		—		2,691.2		—		2,691.2		2,406.0		—		2,665.7		—		2,665.7

WPL	2018										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		$10.6		$—		$4.9		$5.7		$10.6		$8.0		$—		$2.1		$5.9		$8.0
Liabilities and equity:
Derivatives	12.1		—		9.6		2.5		12.1		22.3		—		5.6		16.7		22.3
Long-term debt (incl. current maturities)	1,834.9		—		2,043.7		—		2,043.7		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
	2018			2017			2018			2017
Beginning balance, January 1		($12.2	)		$8.7			$222.1			$211.1
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.1			(32.9		)	—			—
Transfers out of Level 3 (a)	16.1			12.2			—			—
Purchases	26.7			28.3			—			—
Sales	(0.5		)	(0.3		)	—			—
Settlements (b)	(27.0		)	(28.2		)	(102.7		)	11.0
Ending balance, December 31		$12.2			($12.2	)		$119.4			$222.1
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		$10.7			($31.0	)		$—			$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	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)	(0.5		)	(14.8		)	—			—
Transfers out of Level 3 (a)	11.0			3.1			—			—
Purchases	22.5			24.6			—			—
Sales	(0.4		)	(0.2		)	—			—
Settlements (b)	(22.2		)	(24.2		)	(102.7		)	11.0
Ending balance, December 31		$9.0			($1.4	)		$119.4			$222.1
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		$0.2			($13.5	)		$—			$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2018			2017
Beginning balance, January 1		($10.8	)		($1.4	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	9.6			(18.1		)
Transfers out of Level 3 (a)	5.1			9.1
Purchases	4.2			3.7
Sales	(0.1		)	(0.1		)
Settlements	(4.8		)	(4.0		)
Ending balance, December 31		$3.2			($10.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$10.5			($17.5	)

(a) Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.

(b) 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, FTR and natural gas 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
2018		$3.2			$9.0		$1.8			$7.2		$1.4			$1.8
2017	(23.5		)	11.3		(11.5		)	10.1		(12.0		)	1.2