Notes Receivable (Narrative) (Details) - USD ($) $ in Millions |
Sep. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| EnerBank notes receivable held for sale | $ 41 | $ 16 |
| EnerBank [Member] | ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| Unearned income | 82 | 82 |
| Delinquent loans | 10 | 8 |
| Loans modified as troubled debt restructurings | 1 | 1 |
| Receivables Held For Sale [Member] | EnerBank [Member] | ||
| Accounts, Notes, Loans and Financing Receivable [Line Items] | ||
| EnerBank notes receivable held for sale | 41 | 16 |
| Unearned income | $ 8 | $ 3 |