Debt (Schedule of Debt Extinguishment) (Details) - Senior Notes [Member] - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Mar. 31, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Extinguishment of Debt [Line Items] | ||||
| Notes Purchased | $ 933 | $ 793 | $ 933 | $ 793 |
| 9.95% Senior Notes Due 2038 [Member] | ||||
| Extinguishment of Debt [Line Items] | ||||
| Notes Purchased | 441 | 0 | ||
| 10.20% Senior Notes Due 2039 [Member] | ||||
| Extinguishment of Debt [Line Items] | ||||
| Notes Purchased | 492 | 0 | ||
| 9.70% Senior Notes Due 2018 [Member] | ||||
| Extinguishment of Debt [Line Items] | ||||
| Notes Purchased | $ 0 | $ 793 | ||