Notes Receivable (Disclosure of Delinquency Status of EnerBank's Consumer Loans) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Total Outstanding	$ 480	[1]	$ 386	[1]
EnerBank USA [Member]
Past Due 30-59 Days	1
Past Due Over 90 Days	1
Total Delinquent	2
Current	478
Total Outstanding	$ 480		$ 386

[1] Includes current portion of notes receivable of $19 million at December 31, 2011 and $11 million at December 31, 2010.