|
Receivables (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | 12 Months Ended | 1 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Dec. 31, 2012
|
Dec. 31, 2011
|
Dec. 31, 2012
Whiting Petroleum Corporation [Member]
|
Dec. 31, 2011
Whiting Petroleum Corporation [Member]
|
Dec. 31, 2012
IPL [Member]
|
Dec. 31, 2011
IPL [Member]
|
Dec. 31, 2012
IPL [Member]
Maximum [Member]
|
Dec. 31, 2011
IPL [Member]
Maximum [Member]
|
Dec. 31, 2010
IPL [Member]
Maximum [Member]
|
Dec. 31, 2012
IPL [Member]
March 2012 Through March 2014 [Member]
Maximum [Member]
|
Dec. 31, 2012
IPL [Member]
March 2012 Through March 2014 [Member]
Minimum [Member]
|
Dec. 31, 2011
IPL and WPL [Member]
|
Dec. 31, 2012
Franklin County Wind Project [Member]
American Recovery and Reinvestment Act of 2009 [Member]
|
Feb. 28, 2013
Franklin County Wind Project [Member]
American Recovery and Reinvestment Act of 2009 [Member]
Subsequent Event [Member]
|
|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||||||||||||||
| Cash proceeds to be received from third-party | $ 160.0 | $ 160.0 | $ 160.0 | $ 180.0 | $ 150.0 | |||||||||
| Receivables sold | 198.4 | 195.3 | ||||||||||||
| Obligations to pay on tax benefits, percentage | 90.00% | |||||||||||||
| Customer accounts receivable and unbilled revenues | 94.9 | 88.1 | 27.0 | 27.0 | 95.0 | 75.2 | ||||||||
| Customer accounts receivable, financing payment term | 5 years | |||||||||||||
| Cash grant request, percentage of qualifying project expenditures | 30.00% | |||||||||||||
| Accounts receivable, expected amount due | 209.4 | 114.9 | 62.0 | |||||||||||
| Decrease in non-regulated generation property, plant and equipment | 62 | |||||||||||||
| Timing difference between book and tax basis related to expected grant proceeds, percentage | 50.00% | |||||||||||||
| Permanent timing difference between book and tax basis related to expected grant proceeds, percentage | 50.00% | |||||||||||||
| Long-term deferred income tax asset recorded | $ 20 | |||||||||||||