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v2.4.1.9

Investments (Summary Financial Information) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Operating revenues | $ 643 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue | $ 634 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue | $ 611 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
Operating income | 330 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss | 334 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss | 326 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss
Net income | 240 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss | 248 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss | 234 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
Current assets | 72 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentAssets | 86 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentAssets |
Non-current assets | 3,773 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentAssets | 3,553 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentAssets |
Current liabilities | 315 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentLiabilities | 383 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentLiabilities |
Non-current liabilities | 1,871 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentLiabilities | 1,682 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentLiabilities |
WPL [Member] |  |  |
Operating revenues | 643 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue / dei_LegalEntityAxis = lnt_WplMember | 634 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue / dei_LegalEntityAxis = lnt_WplMember | 611 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue / dei_LegalEntityAxis = lnt_WplMember
Operating income | 330 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss / dei_LegalEntityAxis = lnt_WplMember | 334 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss / dei_LegalEntityAxis = lnt_WplMember | 325 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationGrossProfitLoss / dei_LegalEntityAxis = lnt_WplMember
Net income | 240 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 250 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 239 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / dei_LegalEntityAxis = lnt_WplMember
Current assets | 70 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentAssets / dei_LegalEntityAxis = lnt_WplMember | 84 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentAssets / dei_LegalEntityAxis = lnt_WplMember |
Non-current assets | 3,747 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentAssets / dei_LegalEntityAxis = lnt_WplMember | 3,527 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentAssets / dei_LegalEntityAxis = lnt_WplMember |
Current liabilities | 315 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentLiabilities / dei_LegalEntityAxis = lnt_WplMember | 383 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationCurrentLiabilities / dei_LegalEntityAxis = lnt_WplMember |
Non-current liabilities | $ 1,870 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentLiabilities / dei_LegalEntityAxis = lnt_WplMember | $ 1,681 us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNoncurrentLiabilities / dei_LegalEntityAxis = lnt_WplMember |

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