Debt (Tables)

9 Months Ended

Sep. 30, 2014

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, 2014	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$353.8	$169.1	$38.0	$146.7
Weighted average remaining maturity	3 days	3 days	1 day	3 days
Weighted average interest rates	0.2%	0.3%	0.3%	0.1%
Available credit facility capacity	$646.2	$130.9	$262.0	$253.3

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2014			2013			2014			2013			2014			2013
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$—			$185.0			$165.4
Average amount outstanding (based on daily outstanding balances)		$307.1			$228.8			$0.4			$—			$157.9			$140.9
Weighted average interest rates	0.2		%	0.2		%	0.3		%	N/A			0.1		%	0.2		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$26.3			$204.7			$165.4
Average amount outstanding (based on daily outstanding balances)		$281.9			$197.2			$0.3			$1.7			$157.5			$113.4
Weighted average interest rates	0.2		%	0.2		%	0.2		%	0.4		%	0.1		%	0.2		%

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, 2014	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$353.8	$169.1	$38.0	$146.7
Weighted average remaining maturity	3 days	3 days	1 day	3 days
Weighted average interest rates	0.2%	0.3%	0.3%	0.1%
Available credit facility capacity	$646.2	$130.9	$262.0	$253.3

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2014			2013			2014			2013			2014			2013
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$—			$185.0			$165.4
Average amount outstanding (based on daily outstanding balances)		$307.1			$228.8			$0.4			$—			$157.9			$140.9
Weighted average interest rates	0.2		%	0.2		%	0.3		%	N/A			0.1		%	0.2		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$26.3			$204.7			$165.4
Average amount outstanding (based on daily outstanding balances)		$281.9			$197.2			$0.3			$1.7			$157.5			$113.4
Weighted average interest rates	0.2		%	0.2		%	0.2		%	0.4		%	0.1		%	0.2		%

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, 2014	(Consolidated)	Company	IPL	WPL
Commercial paper:
Amount outstanding	$353.8	$169.1	$38.0	$146.7
Weighted average remaining maturity	3 days	3 days	1 day	3 days
Weighted average interest rates	0.2%	0.3%	0.3%	0.1%
Available credit facility capacity	$646.2	$130.9	$262.0	$253.3

	Alliant Energy						IPL						WPL
Three Months Ended September 30	2014			2013			2014			2013			2014			2013
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$—			$185.0			$165.4
Average amount outstanding (based on daily outstanding balances)		$307.1			$228.8			$0.4			$—			$157.9			$140.9
Weighted average interest rates	0.2		%	0.2		%	0.3		%	N/A			0.1		%	0.2		%
Nine Months Ended September 30
Maximum amount outstanding (based on daily outstanding balances)		$353.8			$284.1			$38.0			$26.3			$204.7			$165.4
Average amount outstanding (based on daily outstanding balances)		$281.9			$197.2			$0.3			$1.7			$157.5			$113.4
Weighted average interest rates	0.2		%	0.2		%	0.2		%	0.4		%	0.1		%	0.2		%