v3.25.2
Common Equity (Changes in Shareowners' Equity) (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance     $ 7,004  
Beginning balance $ 7,093 $ 6,817 7,004 $ 6,777
Net income attributable to Alliant Energy common shareowners 174 87 387 245
Net income     387 245
Common stock dividends (131) (123) (261) (246)
Shareowner Direct Plan issuances 6 6 12 12
Equity-based compensation plans and other 3 3 4 1
Other comprehensive income (loss), net of tax   1 (1) 2
Ending balance 7,145   7,145  
Ending balance $ 7,145 $ 6,791 $ 7,145 $ 6,791
Common stock dividends (in dollars per share) $ 0.5075 $ 0.48 $ 1.015 $ 0.96
Common Stock [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance $ 3 $ 3 $ 3 $ 3
Ending balance 3 3 3 3
Additional Paid-in Capital [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 3,066 3,033 3,060 3,030
Shareowner Direct Plan issuances 6 6 12 12
Equity-based compensation plans and other 3 3 3  
Ending balance 3,075 3,042 3,075 3,042
Retained Earnings [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 4,037 3,791 3,954 3,756
Net income attributable to Alliant Energy common shareowners 174 87 387 245
Common stock dividends (131) (123) (261) (246)
Ending balance 4,080 3,755 4,080 3,755
Accumulated Other Comprehensive Income (Loss) [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 0 2 1 1
Other comprehensive income (loss), net of tax   1 (1) 2
Ending balance 0 3 0 3
Shares in Deferred Compensation Trust [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance (13) (12) (14) (13)
Equity-based compensation plans and other     1 1
Ending balance (13) (12) (13) (12)
IPL [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance     4,461  
Beginning balance 4,527 4,037 4,461 3,974
Net income 98 18 209 81
Common stock dividends (90) (50) (180) (100)
Capital contributions from parent 100 75 145 125
Ending balance 4,635   4,635  
Ending balance 4,635 4,080 4,635 4,080
IPL [Member] | Common Stock [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 33 33 33 33
Ending balance 33 33 33 33
IPL [Member] | Additional Paid-in Capital [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 3,257 2,937 3,212 2,887
Capital contributions from parent 100 75 145 125
Ending balance 3,357 3,012 3,357 3,012
IPL [Member] | Retained Earnings [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 1,237 1,067 1,216 1,054
Net income 98 18 209 81
Common stock dividends (90) (50) (180) (100)
Ending balance 1,245 1,035 1,245 1,035
WPL [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance     4,101  
Beginning balance 4,136 3,995 4,101 3,897
Net income 87 64 198 156
Common stock dividends (43) (49) (119) (98)
Capital contributions from parent     0 55
Ending balance 4,180   4,180  
Ending balance 4,180 4,010 4,180 4,010
WPL [Member] | Common Stock [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 66 66 66 66
Ending balance 66 66 66 66
WPL [Member] | Additional Paid-in Capital [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 2,533 2,533 2,533 2,478
Capital contributions from parent       55
Ending balance 2,533 2,533 2,533 2,533
WPL [Member] | Retained Earnings [Member]        
Changes in Shareowners' Equity Roll Forward [Line Items]        
Beginning balance 1,537 1,396 1,502 1,353
Net income 87 64 198 156
Common stock dividends (43) (49) (119) (98)
Ending balance $ 1,581 $ 1,411 $ 1,581 $ 1,411