Common Equity (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of Capitalization, Equity [Line Items]

Common Share Activity

A summary of Alliant Energy’s common stock activity was as follows:

Shares outstanding, January 1, 2019	236,063,279
Equity forward agreements	1,090,300
Shareowner Direct Plan issuances	142,090
Equity-based compensation plans	101,478
Other	(2,738	)
Shares outstanding, March 31, 2019	237,394,409

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):

Alliant Energy	Total Alliant Energy Common Equity
									Accumulated			Shares in			Cumulative
			Additional						Other			Deferred			Preferred
	Common		Paid-In			Retained			Comprehensive			Compensation			Stock		Total
	Stock		Capital			Earnings			Income (Loss)			Trust			of IPL		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$2.4		$2,045.5			$2,545.9			$1.7			($9.8	)		$200.0		$4,785.7
Net income attributable to Alliant Energy common shareowners						125.1											125.1
Common stock dividends ($0.355 per share)						(83.7		)									(83.7		)
Equity forward settlements and Shareowner Direct Plan issuances			54.6														54.6
Equity-based compensation plans and other			(0.1		)							0.1					—
Other comprehensive income, net of tax									0.7								0.7
Ending balance, March 31		$2.4		$2,100.0			$2,587.3			$2.4			($9.7	)		$200.0		$4,882.4
Three Months Ended March 31, 2018
Beginning balance, January 1		$2.3		$1,845.5			$2,346.0			($0.5	)		($11.1	)		$200.0		$4,382.2
Net income attributable to Alliant Energy common shareowners						120.9											120.9
Common stock dividends ($0.335 per share)						(77.5		)									(77.5		)
Shareowner Direct Plan issuances			6.3														6.3
Equity-based compensation plans			(0.4		)												(0.4		)
Ending balance, March 31		$2.3		$1,851.4			$2,389.4			($0.5	)		($11.1	)		$200.0		$4,431.5

IPL	Total IPL Common Equity
			Additional					Cumulative
	Common		Paid-In		Retained			Preferred		Total
	Stock		Capital		Earnings			Stock		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$33.4		$2,222.8		$774.5			$200.0		$3,230.7
Earnings available for common stock					53.3					53.3
Common stock dividends					(42.0		)			(42.0		)
Capital contribution from parent			100.0							100.0
Ending balance, March 31		$33.4		$2,322.8		$785.8			$200.0		$3,342.0
Three Months Ended March 31, 2018
Beginning balance, January 1		$33.4		$1,797.8		$678.5			$200.0		$2,709.7
Earnings available for common stock					46.7					46.7
Common stock dividends					(41.9		)			(41.9		)
Ending balance, March 31		$33.4		$1,797.8		$683.3			$200.0		$2,714.5

WPL			Additional					Total
	Common		Paid-In		Retained			Common
	Stock		Capital		Earnings			Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$66.2		$1,309.0		$774.3			$2,149.5
Earnings available for common stock					65.7			65.7
Common stock dividends					(36.0		)	(36.0		)
Ending balance, March 31		$66.2		$1,309.0		$804.0			$2,179.2
Three Months Ended March 31, 2018
Beginning balance, January 1		$66.2		$1,109.0		$706.3			$1,881.5
Earnings available for common stock					54.0			54.0
Common stock dividends					(35.0		)	(35.0		)
Ending balance, March 31		$66.2		$1,109.0		$725.3			$1,900.5

IPL [Member]

Schedule of Capitalization, Equity [Line Items]

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):

Alliant Energy	Total Alliant Energy Common Equity
									Accumulated			Shares in			Cumulative
			Additional						Other			Deferred			Preferred
	Common		Paid-In			Retained			Comprehensive			Compensation			Stock		Total
	Stock		Capital			Earnings			Income (Loss)			Trust			of IPL		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$2.4		$2,045.5			$2,545.9			$1.7			($9.8	)		$200.0		$4,785.7
Net income attributable to Alliant Energy common shareowners						125.1											125.1
Common stock dividends ($0.355 per share)						(83.7		)									(83.7		)
Equity forward settlements and Shareowner Direct Plan issuances			54.6														54.6
Equity-based compensation plans and other			(0.1		)							0.1					—
Other comprehensive income, net of tax									0.7								0.7
Ending balance, March 31		$2.4		$2,100.0			$2,587.3			$2.4			($9.7	)		$200.0		$4,882.4
Three Months Ended March 31, 2018
Beginning balance, January 1		$2.3		$1,845.5			$2,346.0			($0.5	)		($11.1	)		$200.0		$4,382.2
Net income attributable to Alliant Energy common shareowners						120.9											120.9
Common stock dividends ($0.335 per share)						(77.5		)									(77.5		)
Shareowner Direct Plan issuances			6.3														6.3
Equity-based compensation plans			(0.4		)												(0.4		)
Ending balance, March 31		$2.3		$1,851.4			$2,389.4			($0.5	)		($11.1	)		$200.0		$4,431.5

IPL	Total IPL Common Equity
			Additional					Cumulative
	Common		Paid-In		Retained			Preferred		Total
	Stock		Capital		Earnings			Stock		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$33.4		$2,222.8		$774.5			$200.0		$3,230.7
Earnings available for common stock					53.3					53.3
Common stock dividends					(42.0		)			(42.0		)
Capital contribution from parent			100.0							100.0
Ending balance, March 31		$33.4		$2,322.8		$785.8			$200.0		$3,342.0
Three Months Ended March 31, 2018
Beginning balance, January 1		$33.4		$1,797.8		$678.5			$200.0		$2,709.7
Earnings available for common stock					46.7					46.7
Common stock dividends					(41.9		)			(41.9		)
Ending balance, March 31		$33.4		$1,797.8		$683.3			$200.0		$2,714.5

WPL			Additional					Total
	Common		Paid-In		Retained			Common
	Stock		Capital		Earnings			Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$66.2		$1,309.0		$774.3			$2,149.5
Earnings available for common stock					65.7			65.7
Common stock dividends					(36.0		)	(36.0		)
Ending balance, March 31		$66.2		$1,309.0		$804.0			$2,179.2
Three Months Ended March 31, 2018
Beginning balance, January 1		$66.2		$1,109.0		$706.3			$1,881.5
Earnings available for common stock					54.0			54.0
Common stock dividends					(35.0		)	(35.0		)
Ending balance, March 31		$66.2		$1,109.0		$725.3			$1,900.5

WPL [Member]

Schedule of Capitalization, Equity [Line Items]

Changes in Shareowners' Equity

A summary of changes in shareowners’ equity was as follows (in millions):

Alliant Energy	Total Alliant Energy Common Equity
									Accumulated			Shares in			Cumulative
			Additional						Other			Deferred			Preferred
	Common		Paid-In			Retained			Comprehensive			Compensation			Stock		Total
	Stock		Capital			Earnings			Income (Loss)			Trust			of IPL		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$2.4		$2,045.5			$2,545.9			$1.7			($9.8	)		$200.0		$4,785.7
Net income attributable to Alliant Energy common shareowners						125.1											125.1
Common stock dividends ($0.355 per share)						(83.7		)									(83.7		)
Equity forward settlements and Shareowner Direct Plan issuances			54.6														54.6
Equity-based compensation plans and other			(0.1		)							0.1					—
Other comprehensive income, net of tax									0.7								0.7
Ending balance, March 31		$2.4		$2,100.0			$2,587.3			$2.4			($9.7	)		$200.0		$4,882.4
Three Months Ended March 31, 2018
Beginning balance, January 1		$2.3		$1,845.5			$2,346.0			($0.5	)		($11.1	)		$200.0		$4,382.2
Net income attributable to Alliant Energy common shareowners						120.9											120.9
Common stock dividends ($0.335 per share)						(77.5		)									(77.5		)
Shareowner Direct Plan issuances			6.3														6.3
Equity-based compensation plans			(0.4		)												(0.4		)
Ending balance, March 31		$2.3		$1,851.4			$2,389.4			($0.5	)		($11.1	)		$200.0		$4,431.5

IPL	Total IPL Common Equity
			Additional					Cumulative
	Common		Paid-In		Retained			Preferred		Total
	Stock		Capital		Earnings			Stock		Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$33.4		$2,222.8		$774.5			$200.0		$3,230.7
Earnings available for common stock					53.3					53.3
Common stock dividends					(42.0		)			(42.0		)
Capital contribution from parent			100.0							100.0
Ending balance, March 31		$33.4		$2,322.8		$785.8			$200.0		$3,342.0
Three Months Ended March 31, 2018
Beginning balance, January 1		$33.4		$1,797.8		$678.5			$200.0		$2,709.7
Earnings available for common stock					46.7					46.7
Common stock dividends					(41.9		)			(41.9		)
Ending balance, March 31		$33.4		$1,797.8		$683.3			$200.0		$2,714.5

WPL			Additional					Total
	Common		Paid-In		Retained			Common
	Stock		Capital		Earnings			Equity
Three Months Ended March 31, 2019
Beginning balance, January 1		$66.2		$1,309.0		$774.3			$2,149.5
Earnings available for common stock					65.7			65.7
Common stock dividends					(36.0		)	(36.0		)
Ending balance, March 31		$66.2		$1,309.0		$804.0			$2,179.2
Three Months Ended March 31, 2018
Beginning balance, January 1		$66.2		$1,109.0		$706.3			$1,881.5
Earnings available for common stock					54.0			54.0
Common stock dividends					(35.0		)	(35.0		)
Ending balance, March 31		$66.2		$1,109.0		$725.3			$1,900.5