v2.4.0.6

Investments (Summary Financial Information) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Operating revenues | $ 611 | $ 575 | $ 564
Operating income | 326 | 307 | 307
Net income | 234 | 218 | 226
Current assets | 67 | 62 |
Non-current assets | 3,321 | 3,100 |
Current liabilities | 252 | 299 |
Non-current liabilities | 1,652 | 1,490 |
WPL [Member] |  |  |
Operating revenues | 611 | 575 | 564
Operating income | 325 | 308 | 308
Net income | 239 | 226 | 221
Current assets | 66 | 61 |
Non-current assets | 3,292 | 3,071 |
Current liabilities | 252 | 299 |
Non-current liabilities | $ 1,651 | $ 1,487 |

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