Notes Receivable (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sale of notes receivable	$ 48
Current notes receivable	128	$ 98
EnerBank notes receivable held for sale	16	41
EnerBank [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sale of notes receivable	48
Current notes receivable	144	138
Delinquent loans	8	5
Loans modified as troubled debt restructurings	1	1
Receivables Held For Sale [Member] | EnerBank [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current notes receivable	$ 16	$ 41