Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Statement [Line Items]

Fair Value Measurements

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

Alliant Energy	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$161.8		$161.8		$—		$—		$161.8		$—		$—		$—		$—		$—
Derivatives	21.9		—		8.2		13.7		21.9		28.3		—		8.9		19.4		28.3
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	28.0		—		27.5		0.5		28.0		23.3		—		16.1		7.2		23.3
Long-term debt (incl. current maturities)	6,144.9		—		6,788.8		2.1		6,790.9		5,502.8		—		5,858.4		2.4		5,860.8

IPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$13.9		$—		$4.1		$9.8		$13.9		$17.7		$—		$4.0		$13.7		$17.7
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	12.2		—		11.7		0.5		12.2		11.2		—		6.5		4.7		11.2
Long-term debt	2,850.5		—		3,135.3		—		3,135.3		2,552.3		—		2,691.2		—		2,691.2

WPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$160.4		$160.4		$—		$—		$160.4		$—		$—		$—		$—		$—
Derivatives	8.0		—		4.1		3.9		8.0		10.6		—		4.9		5.7		10.6
Liabilities:
Derivatives	15.8		—		15.8		—		15.8		12.1		—		9.6		2.5		12.1
Long-term debt (incl. current maturities)	2,181.8		—		2,498.2		—		2,498.2		1,834.9		—		2,043.7		—		2,043.7

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 June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.4			($29.4	)		$178.3		$120.9
Total net losses included in changes in net assets (realized/unrealized)	(0.1		)	(0.2		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Settlements (a)	(4.8		)	(7.8		)	36.3		87.4
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		$—			($0.1	)		$—		$—

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$12.2			($12.2	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(5.7		)	(10.0		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Sales	(0.2		)	—			—		—
Settlements (a)	(10.8		)	(15.2		)	95.2		(13.8		)
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		($2.6	)		($9.7	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.6			($15.4	)		$178.3		$120.9
Total net gains (losses) included in changes in net assets (realized/unrealized)	0.4			(1.6		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Settlements (a)	(3.7		)	(6.4		)	36.3		87.4
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		$0.5			($1.6	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$9.0			($1.4	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(2.8		)	(9.2		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Sales	(0.1		)	—			—		—
Settlements (a)	(8.8		)	(12.8		)	95.2		(13.8		)
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		($0.9	)		($9.0	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended June 30	2019			2018
Beginning balance, April 1		($0.2	)		($14.0	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(0.5		)	1.4
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Settlements	(1.1		)	(1.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($0.5	)		$1.5

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Six Months Ended June 30	2019			2018
Beginning balance, January 1		$3.2			($10.8	)
Total net losses included in changes in net assets (realized/unrealized)	(2.9		)	(0.8		)
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Sales	(0.1		)	—
Settlements	(2.0		)	(2.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($1.7	)		($0.7	)

(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 FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):

	Alliant Energy				IPL				WPL
	Excluding FTRs		FTRs		Excluding FTRs		FTRs		Excluding FTRs		FTRs
June 30, 2019		$2.4		$10.8		$1.4		$7.9		$1.0		$2.9
December 31, 2018	3.2		9.0		1.8		7.2		1.4		1.8

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	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$161.8		$161.8		$—		$—		$161.8		$—		$—		$—		$—		$—
Derivatives	21.9		—		8.2		13.7		21.9		28.3		—		8.9		19.4		28.3
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	28.0		—		27.5		0.5		28.0		23.3		—		16.1		7.2		23.3
Long-term debt (incl. current maturities)	6,144.9		—		6,788.8		2.1		6,790.9		5,502.8		—		5,858.4		2.4		5,860.8

IPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$13.9		$—		$4.1		$9.8		$13.9		$17.7		$—		$4.0		$13.7		$17.7
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	12.2		—		11.7		0.5		12.2		11.2		—		6.5		4.7		11.2
Long-term debt	2,850.5		—		3,135.3		—		3,135.3		2,552.3		—		2,691.2		—		2,691.2

WPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$160.4		$160.4		$—		$—		$160.4		$—		$—		$—		$—		$—
Derivatives	8.0		—		4.1		3.9		8.0		10.6		—		4.9		5.7		10.6
Liabilities:
Derivatives	15.8		—		15.8		—		15.8		12.1		—		9.6		2.5		12.1
Long-term debt (incl. current maturities)	2,181.8		—		2,498.2		—		2,498.2		1,834.9		—		2,043.7		—		2,043.7

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 June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.4			($29.4	)		$178.3		$120.9
Total net losses included in changes in net assets (realized/unrealized)	(0.1		)	(0.2		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Settlements (a)	(4.8		)	(7.8		)	36.3		87.4
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		$—			($0.1	)		$—		$—

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$12.2			($12.2	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(5.7		)	(10.0		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Sales	(0.2		)	—			—		—
Settlements (a)	(10.8		)	(15.2		)	95.2		(13.8		)
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		($2.6	)		($9.7	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.6			($15.4	)		$178.3		$120.9
Total net gains (losses) included in changes in net assets (realized/unrealized)	0.4			(1.6		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Settlements (a)	(3.7		)	(6.4		)	36.3		87.4
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		$0.5			($1.6	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$9.0			($1.4	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(2.8		)	(9.2		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Sales	(0.1		)	—			—		—
Settlements (a)	(8.8		)	(12.8		)	95.2		(13.8		)
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		($0.9	)		($9.0	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended June 30	2019			2018
Beginning balance, April 1		($0.2	)		($14.0	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(0.5		)	1.4
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Settlements	(1.1		)	(1.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($0.5	)		$1.5

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Six Months Ended June 30	2019			2018
Beginning balance, January 1		$3.2			($10.8	)
Total net losses included in changes in net assets (realized/unrealized)	(2.9		)	(0.8		)
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Sales	(0.1		)	—
Settlements	(2.0		)	(2.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($1.7	)		($0.7	)

(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 FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):

	Alliant Energy				IPL				WPL
	Excluding FTRs		FTRs		Excluding FTRs		FTRs		Excluding FTRs		FTRs
June 30, 2019		$2.4		$10.8		$1.4		$7.9		$1.0		$2.9
December 31, 2018	3.2		9.0		1.8		7.2		1.4		1.8

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	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$161.8		$161.8		$—		$—		$161.8		$—		$—		$—		$—		$—
Derivatives	21.9		—		8.2		13.7		21.9		28.3		—		8.9		19.4		28.3
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	28.0		—		27.5		0.5		28.0		23.3		—		16.1		7.2		23.3
Long-term debt (incl. current maturities)	6,144.9		—		6,788.8		2.1		6,790.9		5,502.8		—		5,858.4		2.4		5,860.8

IPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Derivatives		$13.9		$—		$4.1		$9.8		$13.9		$17.7		$—		$4.0		$13.7		$17.7
Deferred proceeds	214.6		—		—		214.6		214.6		119.4		—		—		119.4		119.4
Liabilities:
Derivatives	12.2		—		11.7		0.5		12.2		11.2		—		6.5		4.7		11.2
Long-term debt	2,850.5		—		3,135.3		—		3,135.3		2,552.3		—		2,691.2		—		2,691.2

WPL	June 30, 2019										December 31, 2018
			Fair Value										Fair Value
	Carrying		Level		Level		Level				Carrying		Level		Level		Level
	Amount		1		2		3		Total		Amount		1		2		3		Total
Assets:
Money market fund investments		$160.4		$160.4		$—		$—		$160.4		$—		$—		$—		$—		$—
Derivatives	8.0		—		4.1		3.9		8.0		10.6		—		4.9		5.7		10.6
Liabilities:
Derivatives	15.8		—		15.8		—		15.8		12.1		—		9.6		2.5		12.1
Long-term debt (incl. current maturities)	2,181.8		—		2,498.2		—		2,498.2		1,834.9		—		2,043.7		—		2,043.7

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 June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.4			($29.4	)		$178.3		$120.9
Total net losses included in changes in net assets (realized/unrealized)	(0.1		)	(0.2		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Settlements (a)	(4.8		)	(7.8		)	36.3		87.4
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		$—			($0.1	)		$—		$—

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$12.2			($12.2	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(5.7		)	(10.0		)	—		—
Transfers out of Level 3	3.9			—			—		—
Purchases	13.8			26.7			—		—
Sales	(0.2		)	—			—		—
Settlements (a)	(10.8		)	(15.2		)	95.2		(13.8		)
Ending balance, June 30		$13.2			($10.7	)		$214.6		$208.3
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 June 30		($2.6	)		($9.7	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Three Months Ended June 30	2019			2018			2019		2018
Beginning balance, April 1		$0.6			($15.4	)		$178.3		$120.9
Total net gains (losses) included in changes in net assets (realized/unrealized)	0.4			(1.6		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Settlements (a)	(3.7		)	(6.4		)	36.3		87.4
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		$0.5			($1.6	)		$—		$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net						Deferred Proceeds
Six Months Ended June 30	2019			2018			2019		2018
Beginning balance, January 1		$9.0			($1.4	)		$119.4		$222.1
Total net losses included in changes in net assets (realized/unrealized)	(2.8		)	(9.2		)	—		—
Transfers out of Level 3	2.5			—			—		—
Purchases	9.5			19.3			—		—
Sales	(0.1		)	—			—		—
Settlements (a)	(8.8		)	(12.8		)	95.2		(13.8		)
Ending balance, June 30		$9.3			($4.1	)		$214.6		$208.3
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 June 30		($0.9	)		($9.0	)		$—		$—

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Three Months Ended June 30	2019			2018
Beginning balance, April 1		($0.2	)		($14.0	)
Total net gains (losses) included in changes in net assets (realized/unrealized)	(0.5		)	1.4
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Settlements	(1.1		)	(1.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($0.5	)		$1.5

WPL	Commodity Contract Derivative
	Assets and (Liabilities), net
Six Months Ended June 30	2019			2018
Beginning balance, January 1		$3.2			($10.8	)
Total net losses included in changes in net assets (realized/unrealized)	(2.9		)	(0.8		)
Transfers out of Level 3	1.4			—
Purchases	4.3			7.4
Sales	(0.1		)	—
Settlements	(2.0		)	(2.4		)
Ending balance, June 30		$3.9			($6.6	)
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 June 30		($1.7	)		($0.7	)

(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 FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):

	Alliant Energy				IPL				WPL
	Excluding FTRs		FTRs		Excluding FTRs		FTRs		Excluding FTRs		FTRs
June 30, 2019		$2.4		$10.8		$1.4		$7.9		$1.0		$2.9
December 31, 2018	3.2		9.0		1.8		7.2		1.4		1.8