Debt (Tables)

12 Months Ended

Dec. 31, 2019

Debt Instrument [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):

	Alliant Energy		IPL		WPL
December 31	2019	2018	2019	2018	2019	2018
Commercial paper outstanding	$337.4	$441.2	$—	$50.4	$168.2	$105.5
Commercial paper weighted average interest rates	1.9%	2.8%	N/A	2.8%	1.8%	2.5%
Available credit facility capacity	$662.6	$558.8	$250.0	$199.6	$131.8	$244.5

	Alliant Energy		IPL		WPL
For the year ended	2019	2018	2019	2018	2019	2018
Maximum amount outstanding (based on daily outstanding balances)	$600.6	$446.5	$50.4	$50.4	$195.1	$126.0
Average amount outstanding (based on daily outstanding balances)	$453.5	$221.4	$0.1	$1.5	$92.6	$36.6
Weighted average interest rates	2.5%	2.2%	2.8%	2.3%	2.4%	2.1%

Schedule of Debt-to-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2019 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	48%	48%

Schedule of Long-term Debt

Long-term debt, net as of December 31 was as follows (dollars in millions):

	2019									2018
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
3.65%, due 2020		$200.0			$200.0			$—			$200.0			$200.0			$—
3.25%, due 2024	500.0			500.0			—			500.0			500.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
4.1%, due 2028	500.0			500.0			—			500.0			500.0			—
3.6%, due 2029 (b)	300.0			300.0			—			—			—			—
6.45%, due 2033	100.0			100.0			—			100.0			100.0			—
6.3%, due 2034	125.0			125.0			—			125.0			125.0			—
6.25%, due 2039	300.0			300.0			—			300.0			300.0			—
4.7%, due 2043	250.0			250.0			—			250.0			250.0			—
3.7%, due 2046	300.0			300.0			—			300.0			300.0			—
3.5%, due 2049 (b)	300.0			300.0			—			—			—			—
	3,175.0			3,175.0			—			2,575.0			2,575.0			—
Debentures (a):
4.6%, due 2020	150.0			—			150.0			150.0			—			150.0
2.25%, due 2022	250.0			—			250.0			250.0			—			250.0
3.05%, due 2027	300.0			—			300.0			300.0			—			300.0
3%, due 2029 (c)	350.0			—			350.0			—			—			—
6.25%, due 2034	100.0			—			100.0			100.0			—			100.0
6.375%, due 2037	300.0			—			300.0			300.0			—			300.0
7.6%, due 2038	250.0			—			250.0			250.0			—			250.0
4.1%, due 2044	250.0			—			250.0			250.0			—			250.0
5% (Retired in 2019)	—			—			—			250.0			—			250.0
	1,950.0			—			1,950.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 2% at December 31, 2019 (with Alliant Energy as guarantor)	300.0			—			—			300.0			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)	400.0			—			—			400.0			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)	300.0			—			—			300.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2020 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	38.2			—			—			44.3			—			—
Other, 1% at December 31, 2019, due 2020 to 2025	2.1			—			—			2.4			—			—
	1,115.3			—			—			1,121.7			—			—
Subtotal	6,240.3			3,175.0			1,950.0			5,546.7			2,575.0			1,850.0
Current maturities	(657.2		)	(200.0		)	(150.0		)	(256.5		)	—			(250.0		)
Unamortized debt issuance costs	(36.9		)	(21.0		)	(11.3		)	(32.1		)	(17.2		)	(9.6		)
Unamortized debt (discount) and premium, net	(13.2		)	(6.7		)	(6.0		)	(11.8		)	(5.5		)	(5.5		)
Long-term debt, net (d)		$5,533.0			$2,947.3			$1,782.7			$5,246.3			$2,552.3			$1,584.9

(a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.

(b) In April 2019, IPL issued $300 million of 3.6% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.5% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of IPL’s wind projects.

(c) In June 2019, WPL issued $350 million of 3% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.

(d) There were no significant sinking fund requirements related to the outstanding long-term debt.

Schedule of Maturities of Long-term Debt

At December 31, 2019, long-term debt maturities for 2020 through 2024 were as follows (in millions):

	2020		2021		2022		2023		2024
IPL		$200		$—		$—		$—		$500
WPL	150		—		250		—		—
Corporate Services	—		—		75		—		—
AEF	307		8		8		408		9
Alliant Energy		$657		$8		$333		$408		$509

IPL [Member]

Debt Instrument [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):

	Alliant Energy		IPL		WPL
December 31	2019	2018	2019	2018	2019	2018
Commercial paper outstanding	$337.4	$441.2	$—	$50.4	$168.2	$105.5
Commercial paper weighted average interest rates	1.9%	2.8%	N/A	2.8%	1.8%	2.5%
Available credit facility capacity	$662.6	$558.8	$250.0	$199.6	$131.8	$244.5

	Alliant Energy		IPL		WPL
For the year ended	2019	2018	2019	2018	2019	2018
Maximum amount outstanding (based on daily outstanding balances)	$600.6	$446.5	$50.4	$50.4	$195.1	$126.0
Average amount outstanding (based on daily outstanding balances)	$453.5	$221.4	$0.1	$1.5	$92.6	$36.6
Weighted average interest rates	2.5%	2.2%	2.8%	2.3%	2.4%	2.1%

Schedule of Debt-to-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2019 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	48%	48%

Schedule of Long-term Debt

Long-term debt, net as of December 31 was as follows (dollars in millions):

	2019									2018
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
3.65%, due 2020		$200.0			$200.0			$—			$200.0			$200.0			$—
3.25%, due 2024	500.0			500.0			—			500.0			500.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
4.1%, due 2028	500.0			500.0			—			500.0			500.0			—
3.6%, due 2029 (b)	300.0			300.0			—			—			—			—
6.45%, due 2033	100.0			100.0			—			100.0			100.0			—
6.3%, due 2034	125.0			125.0			—			125.0			125.0			—
6.25%, due 2039	300.0			300.0			—			300.0			300.0			—
4.7%, due 2043	250.0			250.0			—			250.0			250.0			—
3.7%, due 2046	300.0			300.0			—			300.0			300.0			—
3.5%, due 2049 (b)	300.0			300.0			—			—			—			—
	3,175.0			3,175.0			—			2,575.0			2,575.0			—
Debentures (a):
4.6%, due 2020	150.0			—			150.0			150.0			—			150.0
2.25%, due 2022	250.0			—			250.0			250.0			—			250.0
3.05%, due 2027	300.0			—			300.0			300.0			—			300.0
3%, due 2029 (c)	350.0			—			350.0			—			—			—
6.25%, due 2034	100.0			—			100.0			100.0			—			100.0
6.375%, due 2037	300.0			—			300.0			300.0			—			300.0
7.6%, due 2038	250.0			—			250.0			250.0			—			250.0
4.1%, due 2044	250.0			—			250.0			250.0			—			250.0
5% (Retired in 2019)	—			—			—			250.0			—			250.0
	1,950.0			—			1,950.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 2% at December 31, 2019 (with Alliant Energy as guarantor)	300.0			—			—			300.0			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)	400.0			—			—			400.0			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)	300.0			—			—			300.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2020 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	38.2			—			—			44.3			—			—
Other, 1% at December 31, 2019, due 2020 to 2025	2.1			—			—			2.4			—			—
	1,115.3			—			—			1,121.7			—			—
Subtotal	6,240.3			3,175.0			1,950.0			5,546.7			2,575.0			1,850.0
Current maturities	(657.2		)	(200.0		)	(150.0		)	(256.5		)	—			(250.0		)
Unamortized debt issuance costs	(36.9		)	(21.0		)	(11.3		)	(32.1		)	(17.2		)	(9.6		)
Unamortized debt (discount) and premium, net	(13.2		)	(6.7		)	(6.0		)	(11.8		)	(5.5		)	(5.5		)
Long-term debt, net (d)		$5,533.0			$2,947.3			$1,782.7			$5,246.3			$2,552.3			$1,584.9

(a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.

(b) In April 2019, IPL issued $300 million of 3.6% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.5% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of IPL’s wind projects.

(c) In June 2019, WPL issued $350 million of 3% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.

(d) There were no significant sinking fund requirements related to the outstanding long-term debt.

Schedule of Maturities of Long-term Debt

At December 31, 2019, long-term debt maturities for 2020 through 2024 were as follows (in millions):

	2020		2021		2022		2023		2024
IPL		$200		$—		$—		$—		$500
WPL	150		—		250		—		—
Corporate Services	—		—		75		—		—
AEF	307		8		8		408		9
Alliant Energy		$657		$8		$333		$408		$509

WPL [Member]

Debt Instrument [Line Items]

Schedule of Other Short-term Borrowings

Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):

	Alliant Energy		IPL		WPL
December 31	2019	2018	2019	2018	2019	2018
Commercial paper outstanding	$337.4	$441.2	$—	$50.4	$168.2	$105.5
Commercial paper weighted average interest rates	1.9%	2.8%	N/A	2.8%	1.8%	2.5%
Available credit facility capacity	$662.6	$558.8	$250.0	$199.6	$131.8	$244.5

	Alliant Energy		IPL		WPL
For the year ended	2019	2018	2019	2018	2019	2018
Maximum amount outstanding (based on daily outstanding balances)	$600.6	$446.5	$50.4	$50.4	$195.1	$126.0
Average amount outstanding (based on daily outstanding balances)	$453.5	$221.4	$0.1	$1.5	$92.6	$36.6
Weighted average interest rates	2.5%	2.2%	2.8%	2.3%	2.4%	2.1%

Schedule of Debt-to-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2019 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	48%	48%

Schedule of Long-term Debt

Long-term debt, net as of December 31 was as follows (dollars in millions):

	2019									2018
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
3.65%, due 2020		$200.0			$200.0			$—			$200.0			$200.0			$—
3.25%, due 2024	500.0			500.0			—			500.0			500.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
4.1%, due 2028	500.0			500.0			—			500.0			500.0			—
3.6%, due 2029 (b)	300.0			300.0			—			—			—			—
6.45%, due 2033	100.0			100.0			—			100.0			100.0			—
6.3%, due 2034	125.0			125.0			—			125.0			125.0			—
6.25%, due 2039	300.0			300.0			—			300.0			300.0			—
4.7%, due 2043	250.0			250.0			—			250.0			250.0			—
3.7%, due 2046	300.0			300.0			—			300.0			300.0			—
3.5%, due 2049 (b)	300.0			300.0			—			—			—			—
	3,175.0			3,175.0			—			2,575.0			2,575.0			—
Debentures (a):
4.6%, due 2020	150.0			—			150.0			150.0			—			150.0
2.25%, due 2022	250.0			—			250.0			250.0			—			250.0
3.05%, due 2027	300.0			—			300.0			300.0			—			300.0
3%, due 2029 (c)	350.0			—			350.0			—			—			—
6.25%, due 2034	100.0			—			100.0			100.0			—			100.0
6.375%, due 2037	300.0			—			300.0			300.0			—			300.0
7.6%, due 2038	250.0			—			250.0			250.0			—			250.0
4.1%, due 2044	250.0			—			250.0			250.0			—			250.0
5% (Retired in 2019)	—			—			—			250.0			—			250.0
	1,950.0			—			1,950.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 2% at December 31, 2019 (with Alliant Energy as guarantor)	300.0			—			—			300.0			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)	400.0			—			—			400.0			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)	300.0			—			—			300.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2020 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	38.2			—			—			44.3			—			—
Other, 1% at December 31, 2019, due 2020 to 2025	2.1			—			—			2.4			—			—
	1,115.3			—			—			1,121.7			—			—
Subtotal	6,240.3			3,175.0			1,950.0			5,546.7			2,575.0			1,850.0
Current maturities	(657.2		)	(200.0		)	(150.0		)	(256.5		)	—			(250.0		)
Unamortized debt issuance costs	(36.9		)	(21.0		)	(11.3		)	(32.1		)	(17.2		)	(9.6		)
Unamortized debt (discount) and premium, net	(13.2		)	(6.7		)	(6.0		)	(11.8		)	(5.5		)	(5.5		)
Long-term debt, net (d)		$5,533.0			$2,947.3			$1,782.7			$5,246.3			$2,552.3			$1,584.9

(a) Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.

(b) In April 2019, IPL issued $300 million of 3.6% senior debentures due 2029. In September 2019, IPL issued $300 million of 3.5% senior debentures due 2049. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of IPL’s wind projects.

(c) In June 2019, WPL issued $350 million of 3% debentures due 2029. The net proceeds from the issuance were used by WPL to reduce its outstanding commercial paper and retire its $250 million 5% debentures that matured in July 2019.

(d) There were no significant sinking fund requirements related to the outstanding long-term debt.

Schedule of Maturities of Long-term Debt

At December 31, 2019, long-term debt maturities for 2020 through 2024 were as follows (in millions):

	2020		2021		2022		2023		2024
IPL		$200		$—		$—		$—		$500
WPL	150		—		250		—		—
Corporate Services	—		—		75		—		—
AEF	307		8		8		408		9
Alliant Energy		$657		$8		$333		$408		$509