Debt (Tables)

9 Months Ended

Sep. 30, 2015

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	Parent
September 30, 2015	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$109.1	$109.1	$—	$—
Weighted average remaining maturity	3 days	3 days	N/A	N/A
Weighted average interest rates	0.4%	0.4%	N/A	N/A
Available credit facility capacity	$890.9	$190.9	$300.0	$400.0

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2015			2014			2015			2014			2015	2014
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$185.0
Average amount outstanding (based on daily outstanding balances)		$122.4			$307.1			$0.5			$0.4		$—		$157.9
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.3		%	N/A	0.1		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$204.7
Average amount outstanding (based on daily outstanding balances)		$114.5			$281.9			$0.2			$0.3		$—		$157.5
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.2		%	N/A	0.1		%

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	Parent
September 30, 2015	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$109.1	$109.1	$—	$—
Weighted average remaining maturity	3 days	3 days	N/A	N/A
Weighted average interest rates	0.4%	0.4%	N/A	N/A
Available credit facility capacity	$890.9	$190.9	$300.0	$400.0

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2015			2014			2015			2014			2015	2014
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$185.0
Average amount outstanding (based on daily outstanding balances)		$122.4			$307.1			$0.5			$0.4		$—		$157.9
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.3		%	N/A	0.1		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$204.7
Average amount outstanding (based on daily outstanding balances)		$114.5			$281.9			$0.2			$0.3		$—		$157.5
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.2		%	N/A	0.1		%

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	Parent
September 30, 2015	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$109.1	$109.1	$—	$—
Weighted average remaining maturity	3 days	3 days	N/A	N/A
Weighted average interest rates	0.4%	0.4%	N/A	N/A
Available credit facility capacity	$890.9	$190.9	$300.0	$400.0

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2015			2014			2015			2014			2015	2014
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$185.0
Average amount outstanding (based on daily outstanding balances)		$122.4			$307.1			$0.5			$0.4		$—		$157.9
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.3		%	N/A	0.1		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$181.2			$353.8			$18.4			$38.0		$—		$204.7
Average amount outstanding (based on daily outstanding balances)		$114.5			$281.9			$0.2			$0.3		$—		$157.5
Weighted average interest rates	0.4		%	0.2		%	0.4		%	0.2		%	N/A	0.1		%