Notes Receivable (Disclosure of Delinquency Status of EnerBank's Consumer Loans) (Details) (EnerBank USA [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
EnerBank USA [Member]
Past Due 30-59 Days	$ 1		$ 1
Past Due Over 90 Days	1		1
Total Delinquent	2		2
Current	475		478
Total Outstanding	477	[1]	480	[1]
Loans modified as troubled debt restructurings	$ 1		$ 1

[1] Includes current portion of notes receivable of $24 million at March 31, 2012 and $19 million at December 31, 2011.