Related Parties (Sales Credited And Purchases Billed) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
IPL [Member] | Scoa Sales Credited [Member]
Amounts billed between related parties	$ 6.3	$ 7.9	$ 26.0	$ 22.2
WPL [Member] | Scoa Sales Credited [Member]
Amounts billed between related parties	7.2	7.6	23.5	19.7
IPL [Member] | Scoa Purchases Billed [Member]
Amounts billed between related parties	93.0	88.2	238.4	263.0
WPL [Member] | Scoa Purchases Billed [Member]
Amounts billed between related parties	$ 20.1	$ 17.4	$ 56.4	$ 60.5