Retirement Benefits (Components of Expense (Income)) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
Mar. 31, 2016 |
Mar. 31, 2015 |
|
| Pension Plans, Defined Benefit [Member] | ||||
| Components of Expense (Income) | ||||
| Service cost | $ 3 | $ 3 | $ 6 | $ 6 |
| Interest cost | 31 | 39 | 63 | 78 |
| Expected return on plan assets | (59) | (61) | (119) | (121) |
| Prior service credit | (1) | 0 | (1) | (1) |
| Net actuarial loss | 20 | 18 | 39 | 36 |
| Net benefit expense (income) | (6) | (1) | (12) | (2) |
| Other Postretirement Benefit Plans, Defined Benefit [Member] | ||||
| Components of Expense (Income) | ||||
| Service cost | 1 | 1 | 1 | 1 |
| Interest cost | 2 | 3 | 3 | 4 |
| Expected return on plan assets | (1) | (1) | (1) | (1) |
| Prior service credit | 0 | (1) | 0 | (2) |
| Net actuarial loss | 2 | 1 | 4 | 3 |
| Net benefit expense (income) | $ 4 | $ 3 | $ 7 | $ 5 |