|
Utility Rate Cases (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | 1 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Dec. 31, 2012
|
Dec. 31, 2011
|
Dec. 31, 2010
|
Dec. 31, 2012
2012 Test Year Retail Electric Fuel Related Request Final Order [Member]
|
Dec. 31, 2012
WPL [Member]
|
Dec. 31, 2011
WPL [Member]
|
Dec. 31, 2010
WPL [Member]
|
Dec. 31, 2012
WPL [Member]
WPL's Edgewater Unit 5 Purchase [Member]
|
May 31, 2012
WPL [Member]
2013/2014 Test Period Retail Electric And Gas Rate Request [Member]
|
Dec. 31, 2012
WPL [Member]
2013/2014 Test Period Retail Electric And Gas Rate Request [Member]
WPL's Edgewater Unit 5 Purchase [Member]
|
Jan. 31, 2011
WPL [Member]
2011 Test Year Retail Electric Request Final Order [Member]
|
Dec. 31, 2010
WPL [Member]
2011 Test Year Retail Electric Request Final Order [Member]
|
Dec. 31, 2010
WPL [Member]
2010 Test Year Retail Electric Fuel Related Request [Member]
|
Jun. 30, 2010
WPL [Member]
2010 Test Year Retail Electric Fuel Related Request [Member]
|
Dec. 31, 2010
WPL [Member]
2010 Test Year Retail Electric Fuel Related Request [Member]
|
Dec. 31, 2012
WPL [Member]
2013 Test Year Retail Electric Fuel Related Request [Member]
|
Dec. 31, 2012
WPL [Member]
2013 Test Year Retail Electric Fuel Related Request [Member]
|
Dec. 31, 2011
WPL [Member]
2012 Test Year Retail Electric Fuel Related Request Final Order [Member]
|
Dec. 31, 2012
WPL [Member]
2012 Test Year Retail Electric Fuel Related Request Final Order [Member]
|
Dec. 31, 2012
IPL [Member]
|
Dec. 31, 2011
IPL [Member]
|
Dec. 31, 2010
IPL [Member]
|
Nov. 30, 2012
IPL [Member]
2011 Test Year Retail Gas IA, Request [Member]
|
Jun. 30, 2012
IPL [Member]
2011 Test Year Retail Gas IA, Request [Member]
|
May 31, 2012
IPL [Member]
2011 Test Year Retail Gas IA, Request [Member]
|
Dec. 31, 2012
IPL [Member]
2011 Test Year Retail Gas IA, Request [Member]
|
Dec. 31, 2012
IPL [Member]
2011 Test Year Retail Gas IA, Request [Member]
Tax Benefit Rider [Member]
|
Feb. 28, 2011
IPL [Member]
2009 Test Year Retail Electric IA, Request [Member]
|
Mar. 31, 2010
IPL [Member]
2009 Test Year Retail Electric IA, Request [Member]
|
Dec. 31, 2011
IPL [Member]
2009 Test Year Retail Electric IA, Request [Member]
|
Jul. 31, 2010
IPL [Member]
2009 Test Year Retail Electric MN, Request [Member]
|
Nov. 30, 2011
IPL [Member]
2009 Test Year Retail Electric MN, Final Order [Member]
|
Nov. 30, 2011
IPL [Member]
2009 Test Year Retail Electric MN, Final Order [Member]
Higher Base Rates [Member]
|
Nov. 30, 2011
IPL [Member]
2009 Test Year Retail Electric MN, Final Order [Member]
Renewable Energy Rider [Member]
|
Nov. 30, 2011
IPL [Member]
2009 Test Year Retail Electric MN, Final Order [Member]
IPL Electric Transmission Assets Sale [Member]
|
|
| Utility Rate Cases [Line Items] | |||||||||||||||||||||||||||||||||||
| Reduction in annual rates for its customers, amount | $ 13 | $ 36 | |||||||||||||||||||||||||||||||||
| Jointly owned utility plant, proportionate ownership share | 25.00% | 25.00% | |||||||||||||||||||||||||||||||||
| Increase in annual rates for its customers, amount | 8 | 4 | 11 | 114 | 11 | 8 | 2 | 1 | |||||||||||||||||||||||||||
| Increase in annual rates for its customers, percentage | 1.00% | 4.00% | 10.00% | ||||||||||||||||||||||||||||||||
| Increase in interim rates for its customers, amount | 9 | 9 | 5 | 9 | 119 | 14 | |||||||||||||||||||||||||||||
| Decrease in annual electric retail rates | 1 | 29 | |||||||||||||||||||||||||||||||||
| Reduction in interim rates for its customers, amount | 5 | ||||||||||||||||||||||||||||||||||
| Requested rate increase, adjustment period subsequent to test year | 12 months | 12 months | |||||||||||||||||||||||||||||||||
| Proposed gas tax benefit rider, term | 3 years | ||||||||||||||||||||||||||||||||||
| Increase in interim rates for its customers, percentage | 3.00% | ||||||||||||||||||||||||||||||||||
| Gas revenue | 396.3 | 476.7 | 480.6 | 169.6 | 200.4 | 206.3 | 226.7 | 276.3 | 274.3 | 5.0 | |||||||||||||||||||||||||
| Revenue refunded to customers, including interest | 5 | ||||||||||||||||||||||||||||||||||
| Decrease in annual rate for its customers, percentage | 3.00% | ||||||||||||||||||||||||||||||||||
| Rate at which fuel costs will be monitored | 2.00% | 2.00% | |||||||||||||||||||||||||||||||||
| Refunds anticipated to be used to offset fuel related cost changes in 2014 | $ 11 | ||||||||||||||||||||||||||||||||||