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Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
IPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collections reinvested in receivables	$ 475.8	$ 435.0	$ 1,017.2	$ 926.3
Credit losses, net of recoveries	$ 3.9	$ 2.0	$ 6.4	$ 3.9

X

- Definition

Collections reinvested related to sales of accounts receivable program.

+ References

No definition available.

+ Details

Name:	lnt_CollectionsReinvestedInReceivables
Namespace Prefix:	lnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Credit losses, net of recoveries related to sales of accounts receivable program.

+ References

No definition available.

+ Details

Name:	lnt_CreditLossesNetOfRecoveries
Namespace Prefix:	lnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration