v2.4.0.6
Consolidated Statements of Common Equity (USD $)
In Millions, unless otherwise specified
Total
IPL [Member]
WPL [Member]
Common Stock [Member]
Common Stock [Member]
IPL [Member]
Common Stock [Member]
WPL [Member]
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
IPL [Member]
Additional Paid-in Capital [Member]
WPL [Member]
Retained Earnings [Member]
Retained Earnings [Member]
IPL [Member]
Retained Earnings [Member]
WPL [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
Deferred Compensation, Share-based Payments [Member]
Beginning balance at Dec. 31, 2009 $ 2,772.6 $ 1,330.0 $ 1,254.7 $ 1.1 $ 33.4 $ 66.2 $ 1,499.1 $ 1,042.2 $ 768.9 $ 1,281.7 $ 254.4 $ 419.6 $ (1.4) $ (7.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 287.6 128.0 149.0             287.6 128.0 149.0    
Common stock dividends 174.6   109.5             174.6   109.5    
Capital contributions from parent   50.0 75.0         50.0 75.0          
Repayment of capital to parent   (118.2)           (118.2)            
Common stock issued, repurchased and other, net 8.0   0.1       7.7   0.1         0.3
Ending balance at Dec. 31, 2010 2,893.6 1,389.8 1,369.3 1.1 33.4 66.2 1,506.8 974.0 844.0 1,394.7 382.4 459.1   (7.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 73.5 21.7 43.6                      
Ending balance at Mar. 31, 2011                            
Beginning balance at Dec. 31, 2010 2,893.6 1,389.8 1,369.3 1.1 33.4 66.2 1,506.8 974.0 844.0 1,394.7 382.4 459.1 (1.4) (7.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 303.6 124.3 160.2             303.6 124.3 160.2    
Common stock dividends 188.1 73.4 112.1             188.1 73.4 112.1    
Capital contributions from parent   54.0 25.0         54.0 25.0          
Repayment of capital to parent   (100.7)           (100.7)            
Common stock issued, repurchased and other, net 3.3 0.4         4.0 0.4           (0.7)
Other comprehensive income, net of tax 0.6                       0.6  
Ending balance at Dec. 31, 2011 3,013.0 1,394.4 1,442.4 1.1 33.4 66.2 1,510.8 927.7 869.0 1,510.2 433.3 507.2 (0.8) (8.3)
Beginning balance at Sep. 30, 2011                            
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 57.0 6.6 41.9                      
Ending balance at Dec. 31, 2011 3,013.0 1,394.4 1,442.4 1.1 33.4 66.2                
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 34.9 (4.7) 31.1                      
Ending balance at Mar. 31, 2012                            
Beginning balance at Dec. 31, 2011 3,013.0 1,394.4 1,442.4 1.1 33.4 66.2 1,510.8 927.7 869.0 1,510.2 433.3 507.2   (8.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 319.8 137.6 162.4             319.8 137.6 162.4    
Common stock dividends 199.3 122.9 112.0             199.3 122.9 112.0    
Capital contributions from parent   110.0 90.0         110.0 90.0          
Common stock issued, repurchased and other, net 1.4 0.1 0.2       0.4 0.1 0.2         1.0
Ending balance at Dec. 31, 2012 3,134.9 1,519.2 1,583.0 1.1 33.4 66.2 1,511.2 1,037.8 959.2 1,630.7 448.0 557.6 (0.8) (7.3)
Beginning balance at Sep. 30, 2012                            
Increase (Decrease) in Stockholders' Equity [Roll Forward]                            
Net income attributable to Alliant Energy common shareowners 68.3 22.4 40.2                      
Ending balance at Dec. 31, 2012 $ 3,134.9 $ 1,519.2 $ 1,583.0 $ 1.1 $ 33.4 $ 66.2             $ (0.8)