Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2015

Schedule of Asset Retirement Obligations [Line Items]

Reconciliation Of Changes In Asset Retirement Obligations

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

	Alliant Energy						IPL						WPL
	2015			2014			2015			2014			2015		2014
Balance, January 1		$114.0			$109.7			$51.8			$47.9			$52.4		$52.4
Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
Liabilities incurred	—			16.5			—			16.3			—		0.2
Accretion expense	1.0			1.0			0.4			0.5			0.4		0.4
Balance, March 31		$112.8			$126.7			$50.0			$64.4			$52.8		$52.8

Asset Retirement Obligations Expected To Be Recognized [Table Text Block]

Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):

	Alliant Energy	IPL	WPL
Estimated ARO increase not to exceed	$85	$75	$10

IPL [Member]

Schedule of Asset Retirement Obligations [Line Items]

Reconciliation Of Changes In Asset Retirement Obligations

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

	Alliant Energy						IPL						WPL
	2015			2014			2015			2014			2015		2014
Balance, January 1		$114.0			$109.7			$51.8			$47.9			$52.4		$52.4
Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
Liabilities incurred	—			16.5			—			16.3			—		0.2
Accretion expense	1.0			1.0			0.4			0.5			0.4		0.4
Balance, March 31		$112.8			$126.7			$50.0			$64.4			$52.8		$52.8

Asset Retirement Obligations Expected To Be Recognized [Table Text Block]

Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):

	Alliant Energy	IPL	WPL
Estimated ARO increase not to exceed	$85	$75	$10

WPL [Member]

Schedule of Asset Retirement Obligations [Line Items]

Reconciliation Of Changes In Asset Retirement Obligations

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

	Alliant Energy						IPL						WPL
	2015			2014			2015			2014			2015		2014
Balance, January 1		$114.0			$109.7			$51.8			$47.9			$52.4		$52.4
Liabilities settled	(2.2		)	(0.5		)	(2.2		)	(0.3		)	—		(0.2		)
Liabilities incurred	—			16.5			—			16.3			—		0.2
Accretion expense	1.0			1.0			0.4			0.5			0.4		0.4
Balance, March 31		$112.8			$126.7			$50.0			$64.4			$52.8		$52.8

Asset Retirement Obligations Expected To Be Recognized [Table Text Block]

Alliant Energy, IPL and WPL currently anticipate recognizing additional AROs in the second quarter of 2015 as a result of the final CCR Rule as follows (in millions):

	Alliant Energy	IPL	WPL
Estimated ARO increase not to exceed	$85	$75	$10