Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2016

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$41.4		$—		$4.6		$36.8		$41.4		$18.4		$—		$2.5		$15.9		$18.4
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	28.6		—		0.5		28.1		28.6		64.6		—		16.0		48.6		64.6
Long-term debt (including current maturities)	4,320.2		—		4,795.7		3.3		4,799.0		3,835.6		—		4,332.4		3.7		4,336.1
IPL’s cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

IPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.8		$—		$2.8		$18.0		$20.8		$15.5		$—		$2.0		$13.5		$15.5
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	8.3		—		0.4		7.9		8.3		23.4		—		8.0		15.4		23.4
Long-term debt (including current maturities)	2,153.5		—		2,352.3		—		2,352.3		1,856.9		—		2,092.7		—		2,092.7
Cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

WPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.6		$—		$1.8		$18.8		$20.6		$2.9		$—		$0.5		$2.4		$2.9
Liabilities and equity:
Derivatives	20.3		—		0.1		20.2		20.3		41.2		—		8.0		33.2		41.2
Long-term debt (including current maturities)	1,535.2		—		1,807.4		—		1,807.4		1,533.9		—		1,793.0		—		1,793.0

Fair Value Measurements Using Significant Unobservable Inputs

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($32.7	)		$17.9			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	30.7			(63.5		)	—		—
Transfers into Level 3	0.9			—			—		—
Transfers out of Level 3	1.2			0.3			—		—
Purchases	22.0			36.9			—		—
Sales	(1.0		)	(1.9		)	—		—
Settlements (a)	(12.4		)	(22.4		)	39.1		(5.2		)
Ending balance, December 31		$8.7			($32.7	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$32.7			($56.0	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($1.9	)		$19.4			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	7.3			(29.6		)	—		—
Transfers into Level 3	0.5			—			—		—
Transfers out of Level 3	0.2			—			—		—
Purchases	20.6			33.1			—		—
Sales	(1.0		)	(1.8		)	—		—
Settlements (a)	(15.6		)	(23.0		)	39.1		(5.2		)
Ending balance, December 31		$10.1			($1.9	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$8.5			($23.1	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2016			2015
Beginning balance, January 1		($30.8	)		($1.5	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	23.4			(33.9		)
Transfers into Level 3	0.4			—
Transfers out of Level 3	1.0			0.3
Purchases	1.4			3.8
Sales	—			(0.1		)
Settlements	3.2			0.6
Ending balance, December 31		($1.4	)		($30.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$24.2			($32.9	)

(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
2016		($2.3	)		$11.0		$0.1			$10.0		($2.4	)		$1.0
2015	(43.1		)	10.4		(12.3		)	10.4		(30.8		)	—

IPL [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$41.4		$—		$4.6		$36.8		$41.4		$18.4		$—		$2.5		$15.9		$18.4
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	28.6		—		0.5		28.1		28.6		64.6		—		16.0		48.6		64.6
Long-term debt (including current maturities)	4,320.2		—		4,795.7		3.3		4,799.0		3,835.6		—		4,332.4		3.7		4,336.1
IPL’s cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

IPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.8		$—		$2.8		$18.0		$20.8		$15.5		$—		$2.0		$13.5		$15.5
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	8.3		—		0.4		7.9		8.3		23.4		—		8.0		15.4		23.4
Long-term debt (including current maturities)	2,153.5		—		2,352.3		—		2,352.3		1,856.9		—		2,092.7		—		2,092.7
Cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

WPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.6		$—		$1.8		$18.8		$20.6		$2.9		$—		$0.5		$2.4		$2.9
Liabilities and equity:
Derivatives	20.3		—		0.1		20.2		20.3		41.2		—		8.0		33.2		41.2
Long-term debt (including current maturities)	1,535.2		—		1,807.4		—		1,807.4		1,533.9		—		1,793.0		—		1,793.0

Fair Value Measurements Using Significant Unobservable Inputs

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($32.7	)		$17.9			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	30.7			(63.5		)	—		—
Transfers into Level 3	0.9			—			—		—
Transfers out of Level 3	1.2			0.3			—		—
Purchases	22.0			36.9			—		—
Sales	(1.0		)	(1.9		)	—		—
Settlements (a)	(12.4		)	(22.4		)	39.1		(5.2		)
Ending balance, December 31		$8.7			($32.7	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$32.7			($56.0	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($1.9	)		$19.4			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	7.3			(29.6		)	—		—
Transfers into Level 3	0.5			—			—		—
Transfers out of Level 3	0.2			—			—		—
Purchases	20.6			33.1			—		—
Sales	(1.0		)	(1.8		)	—		—
Settlements (a)	(15.6		)	(23.0		)	39.1		(5.2		)
Ending balance, December 31		$10.1			($1.9	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$8.5			($23.1	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2016			2015
Beginning balance, January 1		($30.8	)		($1.5	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	23.4			(33.9		)
Transfers into Level 3	0.4			—
Transfers out of Level 3	1.0			0.3
Purchases	1.4			3.8
Sales	—			(0.1		)
Settlements	3.2			0.6
Ending balance, December 31		($1.4	)		($30.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$24.2			($32.9	)

(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
2016		($2.3	)		$11.0		$0.1			$10.0		($2.4	)		$1.0
2015	(43.1		)	10.4		(12.3		)	10.4		(30.8		)	—

WPL [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$41.4		$—		$4.6		$36.8		$41.4		$18.4		$—		$2.5		$15.9		$18.4
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	28.6		—		0.5		28.1		28.6		64.6		—		16.0		48.6		64.6
Long-term debt (including current maturities)	4,320.2		—		4,795.7		3.3		4,799.0		3,835.6		—		4,332.4		3.7		4,336.1
IPL’s cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

IPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.8		$—		$2.8		$18.0		$20.8		$15.5		$—		$2.0		$13.5		$15.5
Deferred proceeds	211.1		—		—		211.1		211.1		172.0		—		—		172.0		172.0
Liabilities and equity:
Derivatives	8.3		—		0.4		7.9		8.3		23.4		—		8.0		15.4		23.4
Long-term debt (including current maturities)	2,153.5		—		2,352.3		—		2,352.3		1,856.9		—		2,092.7		—		2,092.7
Cumulative preferred stock	200.0		194.8		—		—		194.8		200.0		206.6		—		—		206.6

WPL	2016										2015
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$20.6		$—		$1.8		$18.8		$20.6		$2.9		$—		$0.5		$2.4		$2.9
Liabilities and equity:
Derivatives	20.3		—		0.1		20.2		20.3		41.2		—		8.0		33.2		41.2
Long-term debt (including current maturities)	1,535.2		—		1,807.4		—		1,807.4		1,533.9		—		1,793.0		—		1,793.0

Fair Value Measurements Using Significant Unobservable Inputs

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($32.7	)		$17.9			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	30.7			(63.5		)	—		—
Transfers into Level 3	0.9			—			—		—
Transfers out of Level 3	1.2			0.3			—		—
Purchases	22.0			36.9			—		—
Sales	(1.0		)	(1.9		)	—		—
Settlements (a)	(12.4		)	(22.4		)	39.1		(5.2		)
Ending balance, December 31		$8.7			($32.7	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$32.7			($56.0	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
	2016			2015			2016		2015
Beginning balance, January 1		($1.9	)		$19.4			$172.0		$177.2
Total net gains (losses) included in changes in net assets (realized/unrealized)	7.3			(29.6		)	—		—
Transfers into Level 3	0.5			—			—		—
Transfers out of Level 3	0.2			—			—		—
Purchases	20.6			33.1			—		—
Sales	(1.0		)	(1.8		)	—		—
Settlements (a)	(15.6		)	(23.0		)	39.1		(5.2		)
Ending balance, December 31		$10.1			($1.9	)		$211.1		$172.0
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$8.5			($23.1	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
	2016			2015
Beginning balance, January 1		($30.8	)		($1.5	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	23.4			(33.9		)
Transfers into Level 3	0.4			—
Transfers out of Level 3	1.0			0.3
Purchases	1.4			3.8
Sales	—			(0.1		)
Settlements	3.2			0.6
Ending balance, December 31		($1.4	)		($30.8	)
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31		$24.2			($32.9	)

(a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of electric, natural gas and coal commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) at December 31 as follows (in millions):

	Alliant Energy					IPL					WPL
	Excluding FTRs			FTRs		Excluding FTRs			FTRs		Excluding FTRs			FTRs
2016		($2.3	)		$11.0		$0.1			$10.0		($2.4	)		$1.0
2015	(43.1		)	10.4		(12.3		)	10.4		(30.8		)	—