XML 100 R1.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Document And Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Jan. 31, 2020
Jun. 30, 2019
Entity Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2019    
Document Transition Report false    
Entity Registrant Name ALLIANT ENERGY CORP    
Entity Central Index Key 0000352541    
Entity Incorporation, State or Country Code WI    
Entity Address, Address Line One 4902 N. Biltmore Lane    
Entity Address, City or Town Madison    
Entity Address, State or Province WI    
Entity Address, Postal Zip Code 53718    
City Area Code 608    
Local Phone Number 458-3311    
Entity File Number 1-9894    
Entity Tax Identification Number 39-1380265    
Title of 12(b) Security Common Stock, $0.01 Par Value    
Trading Symbol LNT    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 11,600.0
Entity Common Stock, Shares Outstanding   245,031,019  
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Amendment Flag false    
Documents Incorporated by Reference
Portions of the Proxy Statement relating to Alliant Energy Corporation’s 2020 Annual Meeting of Shareowners are, or will be upon filing with the Securities and Exchange Commission, incorporated by reference into Part III hereof.
    
IPL [Member]      
Entity Information [Line Items]      
Entity Registrant Name INTERSTATE POWER & LIGHT CO    
Entity Central Index Key 0000052485    
Entity Incorporation, State or Country Code IA    
Entity Address, Address Line One Alliant Energy Tower    
Entity Address, City or Town Cedar Rapids    
Entity Address, State or Province IA    
Entity Address, Postal Zip Code 52401    
City Area Code 319    
Local Phone Number 786-4411    
Entity File Number 1-4117    
Entity Tax Identification Number 42-0331370    
Title of 12(b) Security 5.100% Series D Cumulative Perpetual Preferred Stock, $0.01 Par Value    
Trading Symbol IPLDP    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     0.0
Entity Common Stock, Shares Outstanding   13,370,788  
WPL [Member]      
Entity Information [Line Items]      
Entity Registrant Name WISCONSIN POWER & LIGHT CO    
Entity Central Index Key 0000107832    
Entity Incorporation, State or Country Code WI    
Entity Address, Address Line One 4902 N. Biltmore Lane    
Entity Address, City or Town Madison    
Entity Address, State or Province WI    
Entity Address, Postal Zip Code 53718    
City Area Code 608    
Local Phone Number 458-3311    
Entity File Number 0-337    
Entity Tax Identification Number 39-0714890    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 0.0
Entity Common Stock, Shares Outstanding   13,236,601