Debt (Tables)

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Line Items]

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	2018	2017	2018	2017	2018	2017
Commercial paper outstanding	$441.2	$320.2	$50.4	$—	$105.5	$25.0
Commercial paper weighted average interest rates	2.8%	2.0%	2.8%	N/A	2.5%	1.5%
Available credit facility capacity	$558.8	$679.8	$199.6	$250.0	$244.5	$325.0

	Alliant Energy		IPL		WPL
For the year ended	2018	2017	2018	2017	2018	2017
Maximum amount outstanding (based on daily outstanding balances)	$446.5	$424.4	$50.4	$20.0	$126.0	$271.2
Average amount outstanding (based on daily outstanding balances)	$221.4	$294.3	$1.5	$0.5	$36.6	$118.2
Weighted average interest rates	2.2%	1.2%	2.3%	1.3%	2.1%	1.0%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	45%	48%

Schedule of Long-term Debt

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

	2018									2017
	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 (b)	500.0			500.0			—			—			—			—
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			—
5.875% (Retired in 2018)	—			—			—			100.0			100.0			—
7.25% (Retired in 2018)	—			—			—			250.0			250.0			—
	2,575.0			2,575.0			—			2,425.0			2,425.0			—
Debentures (a):
5%, due 2019	250.0			—			250.0			250.0			—			250.0
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
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
	1,850.0			—			1,850.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c)	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)(d)	400.0			—			—			—			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d)	300.0			—			—			—			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	44.3			—			—			49.6			—			—
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d)	—			—			—			500.0			—			—
Other, 1% at December 31, 2018, due 2019 to 2025	2.4			—			—			2.9			—			—
	1,121.7			—			—			627.5			—			—
Subtotal	5,546.7			2,575.0			1,850.0			4,902.5			2,425.0			1,850.0
Current maturities	(256.5		)	—			(250.0		)	(855.7		)	(350.0		)	—
Unamortized debt issuance costs	(32.1		)	(17.2		)	(9.6		)	(25.4		)	(14.3		)	(10.5		)
Unamortized debt (discount) and premium, net	(11.8		)	(5.5		)	(5.5		)	(10.8		)	(4.7		)	(6.1		)
Long-term debt, net (e)		$5,246.3			$2,552.3			$1,584.9			$4,010.6			$2,056.0			$1,833.4

(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.

(c) In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

(d) In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

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

Schedule of Debt Maturities

At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):

	2019		2020		2021		2022		2023
IPL		$—		$200		$—		$—		$—
WPL	250		150		—		250		—
Corporate Services	—		—		—		75		—
AEF	6		307		8		8		408
Alliant Energy		$256		$657		$8		$333		$408

IPL [Member]

Debt Disclosure [Line Items]

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	2018	2017	2018	2017	2018	2017
Commercial paper outstanding	$441.2	$320.2	$50.4	$—	$105.5	$25.0
Commercial paper weighted average interest rates	2.8%	2.0%	2.8%	N/A	2.5%	1.5%
Available credit facility capacity	$558.8	$679.8	$199.6	$250.0	$244.5	$325.0

	Alliant Energy		IPL		WPL
For the year ended	2018	2017	2018	2017	2018	2017
Maximum amount outstanding (based on daily outstanding balances)	$446.5	$424.4	$50.4	$20.0	$126.0	$271.2
Average amount outstanding (based on daily outstanding balances)	$221.4	$294.3	$1.5	$0.5	$36.6	$118.2
Weighted average interest rates	2.2%	1.2%	2.3%	1.3%	2.1%	1.0%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	45%	48%

Schedule of Long-term Debt

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

	2018									2017
	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 (b)	500.0			500.0			—			—			—			—
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			—
5.875% (Retired in 2018)	—			—			—			100.0			100.0			—
7.25% (Retired in 2018)	—			—			—			250.0			250.0			—
	2,575.0			2,575.0			—			2,425.0			2,425.0			—
Debentures (a):
5%, due 2019	250.0			—			250.0			250.0			—			250.0
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
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
	1,850.0			—			1,850.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c)	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)(d)	400.0			—			—			—			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d)	300.0			—			—			—			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	44.3			—			—			49.6			—			—
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d)	—			—			—			500.0			—			—
Other, 1% at December 31, 2018, due 2019 to 2025	2.4			—			—			2.9			—			—
	1,121.7			—			—			627.5			—			—
Subtotal	5,546.7			2,575.0			1,850.0			4,902.5			2,425.0			1,850.0
Current maturities	(256.5		)	—			(250.0		)	(855.7		)	(350.0		)	—
Unamortized debt issuance costs	(32.1		)	(17.2		)	(9.6		)	(25.4		)	(14.3		)	(10.5		)
Unamortized debt (discount) and premium, net	(11.8		)	(5.5		)	(5.5		)	(10.8		)	(4.7		)	(6.1		)
Long-term debt, net (e)		$5,246.3			$2,552.3			$1,584.9			$4,010.6			$2,056.0			$1,833.4

(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.

(c) In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

(d) In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

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

Schedule of Debt Maturities

At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):

	2019		2020		2021		2022		2023
IPL		$—		$200		$—		$—		$—
WPL	250		150		—		250		—
Corporate Services	—		—		—		75		—
AEF	6		307		8		8		408
Alliant Energy		$256		$657		$8		$333		$408

WPL [Member]

Debt Disclosure [Line Items]

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	2018	2017	2018	2017	2018	2017
Commercial paper outstanding	$441.2	$320.2	$50.4	$—	$105.5	$25.0
Commercial paper weighted average interest rates	2.8%	2.0%	2.8%	N/A	2.5%	1.5%
Available credit facility capacity	$558.8	$679.8	$199.6	$250.0	$244.5	$325.0

	Alliant Energy		IPL		WPL
For the year ended	2018	2017	2018	2017	2018	2017
Maximum amount outstanding (based on daily outstanding balances)	$446.5	$424.4	$50.4	$20.0	$126.0	$271.2
Average amount outstanding (based on daily outstanding balances)	$221.4	$294.3	$1.5	$0.5	$36.6	$118.2
Weighted average interest rates	2.2%	1.2%	2.3%	1.3%	2.1%	1.0%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	65%	65%
Actual	55%	45%	48%

Schedule of Long-term Debt

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

	2018									2017
	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 (b)	500.0			500.0			—			—			—			—
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			—
5.875% (Retired in 2018)	—			—			—			100.0			100.0			—
7.25% (Retired in 2018)	—			—			—			250.0			250.0			—
	2,575.0			2,575.0			—			2,425.0			2,425.0			—
Debentures (a):
5%, due 2019	250.0			—			250.0			250.0			—			250.0
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
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
	1,850.0			—			1,850.0			1,850.0			—			1,850.0
Other:
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c)	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)(d)	400.0			—			—			—			—			—
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d)	300.0			—			—			—			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)	44.3			—			—			49.6			—			—
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d)	—			—			—			500.0			—			—
Other, 1% at December 31, 2018, due 2019 to 2025	2.4			—			—			2.9			—			—
	1,121.7			—			—			627.5			—			—
Subtotal	5,546.7			2,575.0			1,850.0			4,902.5			2,425.0			1,850.0
Current maturities	(256.5		)	—			(250.0		)	(855.7		)	(350.0		)	—
Unamortized debt issuance costs	(32.1		)	(17.2		)	(9.6		)	(25.4		)	(14.3		)	(10.5		)
Unamortized debt (discount) and premium, net	(11.8		)	(5.5		)	(5.5		)	(10.8		)	(4.7		)	(6.1		)
Long-term debt, net (e)		$5,246.3			$2,552.3			$1,584.9			$4,010.6			$2,056.0			$1,833.4

(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.

(c) In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

(d) In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.

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

Schedule of Debt Maturities

At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):

	2019		2020		2021		2022		2023
IPL		$—		$200		$—		$—		$—
WPL	250		150		—		250		—
Corporate Services	—		—		—		75		—
AEF	6		307		8		8		408
Alliant Energy		$256		$657		$8		$333		$408