Debt (Tables)

12 Months Ended

Dec. 31, 2016

Debt Disclosure [Line Items]

Other Short-Term Borrowings

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

	Alliant Energy		IPL		WPL
December 31	2016	2015	2016	2015	2016	2015
Commercial paper outstanding	$244.1	$159.8	$—	$—	$52.3	$19.9
Commercial paper weighted average interest rates	0.9%	0.7%	N/A	N/A	0.7%	0.4%
Available credit facility capacity	$755.9	$840.2	$300.0	$300.0	$347.7	$380.1

	Alliant Energy		IPL		WPL
For the year ended	2016	2015	2016	2015	2016	2015
Maximum amount outstanding (based on daily outstanding balances)	$251.8	$181.2	$3.1	$18.4	$118.3	$24.7
Average amount outstanding (based on daily outstanding balances)	$179.0	$119.2	$—	$0.2	$38.1	$2.2
Weighted average interest rates	0.6%	0.4%	0.7%	0.4%	0.4%	0.3%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	58%	58%
Actual	53%	47%	49%

Schedule of Long-term Debt

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

	2016									2015
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
5.875%, due 2018		$100.0			$100.0			$—			$100.0			$100.0			$—
7.25%, due 2018	250.0			250.0			—			250.0			250.0			—
3.65%, due 2020	200.0			200.0			—			200.0			200.0			—
3.25%, due 2024	250.0			250.0			—			250.0			250.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
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 (b)	300.0			300.0			—			—			—			—
	2,175.0			2,175.0			—			1,875.0			1,875.0			—
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
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
	1,550.0			—			1,550.0			1,550.0			—			1,550.0
Other:
AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d)	500.0			—			—			—			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a)	53.8			—			—			56.8			—			—
Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			250.0			—			—
Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			60.0			—			—
Other, 1% at December 31, 2016, due 2017 to 2025	3.3			—			—			3.7			—			—
	632.1			—			—			445.5			—			—
Subtotal	4,357.1			2,175.0			1,550.0			3,870.5			1,875.0			1,550.0
Current maturities	(4.6		)	—			—			(313.4		)	—			—
Unamortized debt issuance costs	(23.4		)	(13.7		)	(9.1		)	(22.3		)	(11.8		)	(9.9		)
Unamortized debt (discount) and premium, net	(13.5		)	(7.8		)	(5.7		)	(12.6		)	(6.3		)	(6.2		)
Long-term debt, net (e)		$4,315.6			$2,153.5			$1,535.2			$3,522.2			$1,856.9			$1,533.9

(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 2016, IPL issued $300 million of 3.7% senior debentures due 2046. The proceeds from the issuance were used by IPL to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $100 million and for general corporate purposes.

(c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes.

(d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

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

Schedule of Debt Maturities

At December 31, 2016, debt maturities for 2017 through 2021 were as follows (in millions):

	2017		2018		2019		2020		2021
IPL		$—		$350		$—		$200		$—
WPL	—		—		250		150		—
AEF	5		506		6		7		8
Alliant Energy		$5		$856		$256		$357		$8

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 facilities was as follows (dollars in millions):

	Alliant Energy		IPL		WPL
December 31	2016	2015	2016	2015	2016	2015
Commercial paper outstanding	$244.1	$159.8	$—	$—	$52.3	$19.9
Commercial paper weighted average interest rates	0.9%	0.7%	N/A	N/A	0.7%	0.4%
Available credit facility capacity	$755.9	$840.2	$300.0	$300.0	$347.7	$380.1

	Alliant Energy		IPL		WPL
For the year ended	2016	2015	2016	2015	2016	2015
Maximum amount outstanding (based on daily outstanding balances)	$251.8	$181.2	$3.1	$18.4	$118.3	$24.7
Average amount outstanding (based on daily outstanding balances)	$179.0	$119.2	$—	$0.2	$38.1	$2.2
Weighted average interest rates	0.6%	0.4%	0.7%	0.4%	0.4%	0.3%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	58%	58%
Actual	53%	47%	49%

Schedule of Long-term Debt

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

	2016									2015
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
5.875%, due 2018		$100.0			$100.0			$—			$100.0			$100.0			$—
7.25%, due 2018	250.0			250.0			—			250.0			250.0			—
3.65%, due 2020	200.0			200.0			—			200.0			200.0			—
3.25%, due 2024	250.0			250.0			—			250.0			250.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
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 (b)	300.0			300.0			—			—			—			—
	2,175.0			2,175.0			—			1,875.0			1,875.0			—
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
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
	1,550.0			—			1,550.0			1,550.0			—			1,550.0
Other:
AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d)	500.0			—			—			—			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a)	53.8			—			—			56.8			—			—
Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			250.0			—			—
Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			60.0			—			—
Other, 1% at December 31, 2016, due 2017 to 2025	3.3			—			—			3.7			—			—
	632.1			—			—			445.5			—			—
Subtotal	4,357.1			2,175.0			1,550.0			3,870.5			1,875.0			1,550.0
Current maturities	(4.6		)	—			—			(313.4		)	—			—
Unamortized debt issuance costs	(23.4		)	(13.7		)	(9.1		)	(22.3		)	(11.8		)	(9.9		)
Unamortized debt (discount) and premium, net	(13.5		)	(7.8		)	(5.7		)	(12.6		)	(6.3		)	(6.2		)
Long-term debt, net (e)		$4,315.6			$2,153.5			$1,535.2			$3,522.2			$1,856.9			$1,533.9

(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 2016, IPL issued $300 million of 3.7% senior debentures due 2046. The proceeds from the issuance were used by IPL to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $100 million and for general corporate purposes.

(c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes.

(d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

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

Schedule of Debt Maturities

At December 31, 2016, debt maturities for 2017 through 2021 were as follows (in millions):

	2017		2018		2019		2020		2021
IPL		$—		$350		$—		$200		$—
WPL	—		—		250		150		—
AEF	5		506		6		7		8
Alliant Energy		$5		$856		$256		$357		$8

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 facilities was as follows (dollars in millions):

	Alliant Energy		IPL		WPL
December 31	2016	2015	2016	2015	2016	2015
Commercial paper outstanding	$244.1	$159.8	$—	$—	$52.3	$19.9
Commercial paper weighted average interest rates	0.9%	0.7%	N/A	N/A	0.7%	0.4%
Available credit facility capacity	$755.9	$840.2	$300.0	$300.0	$347.7	$380.1

	Alliant Energy		IPL		WPL
For the year ended	2016	2015	2016	2015	2016	2015
Maximum amount outstanding (based on daily outstanding balances)	$251.8	$181.2	$3.1	$18.4	$118.3	$24.7
Average amount outstanding (based on daily outstanding balances)	$179.0	$119.2	$—	$0.2	$38.1	$2.2
Weighted average interest rates	0.6%	0.4%	0.7%	0.4%	0.4%	0.3%

Schedule of Debt-To-Capital Ratios

The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2016 were as follows:

	Alliant Energy	IPL	WPL
Requirement, not to exceed	65%	58%	58%
Actual	53%	47%	49%

Schedule of Long-term Debt

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

	2016									2015
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures (a):
5.875%, due 2018		$100.0			$100.0			$—			$100.0			$100.0			$—
7.25%, due 2018	250.0			250.0			—			250.0			250.0			—
3.65%, due 2020	200.0			200.0			—			200.0			200.0			—
3.25%, due 2024	250.0			250.0			—			250.0			250.0			—
3.4%, due 2025	250.0			250.0			—			250.0			250.0			—
5.5%, due 2025	50.0			50.0			—			50.0			50.0			—
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 (b)	300.0			300.0			—			—			—			—
	2,175.0			2,175.0			—			1,875.0			1,875.0			—
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
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
	1,550.0			—			1,550.0			1,550.0			—			1,550.0
Other:
AEF term loan credit agreement through 2018, 1% at December 31, 2016 (c)(d)	500.0			—			—			—			—			—
Corporate Services 3.45% senior notes, due 2022 (a)	75.0			—			—			75.0			—			—
Sheboygan Power, LLC 5.06% senior secured notes, due 2017 to 2024 (secured by Sheboygan Falls and related assets) (a)	53.8			—			—			56.8			—			—
Alliant Energy term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			250.0			—			—
Franklin County Holdings LLC term loan credit agreement, 1% at December 31, 2015 (Retired in 2016) (c)	—			—			—			60.0			—			—
Other, 1% at December 31, 2016, due 2017 to 2025	3.3			—			—			3.7			—			—
	632.1			—			—			445.5			—			—
Subtotal	4,357.1			2,175.0			1,550.0			3,870.5			1,875.0			1,550.0
Current maturities	(4.6		)	—			—			(313.4		)	—			—
Unamortized debt issuance costs	(23.4		)	(13.7		)	(9.1		)	(22.3		)	(11.8		)	(9.9		)
Unamortized debt (discount) and premium, net	(13.5		)	(7.8		)	(5.7		)	(12.6		)	(6.3		)	(6.2		)
Long-term debt, net (e)		$4,315.6			$2,153.5			$1,535.2			$3,522.2			$1,856.9			$1,533.9

(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 2016, IPL issued $300 million of 3.7% senior debentures due 2046. The proceeds from the issuance were used by IPL to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt by $100 million and for general corporate purposes.

(c) In 2016, AEF entered into a $500 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement to retire Alliant Energy’s and Franklin County Holdings LLC’s variable-rate term loan credit agreements that matured in 2016, reduce outstanding commercial paper at Alliant Energy and for general corporate purposes.

(d) Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.

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

Schedule of Debt Maturities

At December 31, 2016, debt maturities for 2017 through 2021 were as follows (in millions):

	2017		2018		2019		2020		2021
IPL		$—		$350		$—		$200		$—
WPL	—		—		250		150		—
AEF	5		506		6		7		8
Alliant Energy		$5		$856		$256		$357		$8