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Related Parties (Narrative) (Details) (WPL Owed ATC [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
WPL Owed ATC [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 7.0	$ 6.0

Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

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