Asset Retirement Obligations (AROs)

3 Months Ended

Mar. 31, 2013

Asset Retirement Obligations [Line Items]

Asset Retirement Obligations (AROs)

ASSET RETIREMENT OBLIGATIONS (AROs)

A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):

	Alliant Energy						IPL					WPL
	2013			2012			2013		2012			2013			2012
Balance, January 1		$101.5			$91.1			$45.5		$56.2			$46.9			$34.9
Revisions in estimated cash flows (a)	—			(8.2		)	—		(8.2		)	—			—
Liabilities settled	(0.1		)	(1.0		)	—		(0.9		)	(0.1		)	(0.1		)
Accretion expense	1.0			0.9			0.5		0.5			0.4			0.4
Balance, March 31		$102.4			$82.8			$46.0		$47.6			$47.2			$35.2

(a) For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.

IPL [Member]

Asset Retirement Obligations [Line Items]

Asset Retirement Obligations (AROs)

ASSET RETIREMENT OBLIGATIONS (AROs)

A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):

	Alliant Energy						IPL					WPL
	2013			2012			2013		2012			2013			2012
Balance, January 1		$101.5			$91.1			$45.5		$56.2			$46.9			$34.9
Revisions in estimated cash flows (a)	—			(8.2		)	—		(8.2		)	—			—
Liabilities settled	(0.1		)	(1.0		)	—		(0.9		)	(0.1		)	(0.1		)
Accretion expense	1.0			0.9			0.5		0.5			0.4			0.4
Balance, March 31		$102.4			$82.8			$46.0		$47.6			$47.2			$35.2

(a) For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.

WPL [Member]

Asset Retirement Obligations [Line Items]

Asset Retirement Obligations (AROs)

ASSET RETIREMENT OBLIGATIONS (AROs)

A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):

	Alliant Energy						IPL					WPL
	2013			2012			2013		2012			2013			2012
Balance, January 1		$101.5			$91.1			$45.5		$56.2			$46.9			$34.9
Revisions in estimated cash flows (a)	—			(8.2		)	—		(8.2		)	—			—
Liabilities settled	(0.1		)	(1.0		)	—		(0.9		)	(0.1		)	(0.1		)
Accretion expense	1.0			0.9			0.5		0.5			0.4			0.4
Balance, March 31		$102.4			$82.8			$46.0		$47.6			$47.2			$35.2

(a) For the three months ended March 31, 2012, IPL recorded revisions in estimated cash flows of ($8.2) million based on revised remediation timing and cost information for asbestos remediation at its Sixth Street Generating Station.