Asset Retirement Obligations (AROs)

6 Months Ended

Jun. 30, 2012

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
	2012			2011			2012			2011			2012			2011
Balance, January 1		$91.1			$75.9			$56.2			$43.6			$34.9			$32.3
Revisions in estimated cash flows (a)	(9.9		)	(0.5		)	(9.2		)	(0.2		)	(0.7		)	(0.3		)
Liabilities settled	(1.8		)	(0.3		)	(1.7		)	(0.2		)	(0.1		)	(0.1		)
Liabilities incurred	0.7			3.7			—			2.9			—			0.8
Accretion expense	1.8			2.2			1.0			1.4			0.8			0.8
Balance, June 30		$81.9			$81.0			$46.3			$47.5			$34.9			$33.5

(a) For the six months ended June 30, 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
	2012			2011			2012			2011			2012			2011
Balance, January 1		$91.1			$75.9			$56.2			$43.6			$34.9			$32.3
Revisions in estimated cash flows (a)	(9.9		)	(0.5		)	(9.2		)	(0.2		)	(0.7		)	(0.3		)
Liabilities settled	(1.8		)	(0.3		)	(1.7		)	(0.2		)	(0.1		)	(0.1		)
Liabilities incurred	0.7			3.7			—			2.9			—			0.8
Accretion expense	1.8			2.2			1.0			1.4			0.8			0.8
Balance, June 30		$81.9			$81.0			$46.3			$47.5			$34.9			$33.5

(a) For the six months ended June 30, 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
	2012			2011			2012			2011			2012			2011
Balance, January 1		$91.1			$75.9			$56.2			$43.6			$34.9			$32.3
Revisions in estimated cash flows (a)	(9.9		)	(0.5		)	(9.2		)	(0.2		)	(0.7		)	(0.3		)
Liabilities settled	(1.8		)	(0.3		)	(1.7		)	(0.2		)	(0.1		)	(0.1		)
Liabilities incurred	0.7			3.7			—			2.9			—			0.8
Accretion expense	1.8			2.2			1.0			1.4			0.8			0.8
Balance, June 30		$81.9			$81.0			$46.3			$47.5			$34.9			$33.5

(a) For the six months ended June 30, 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.