Schedule of Net Periodic Benefit Cost Components (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Pension Plan Asset | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | $ 8 | $ 9 | $ 24 | $ 28 |
| Interest cost | 20 | 19 | 60 | 56 |
| Expected return on plan assets | (24) | (24) | (72) | (73) |
| Amortization of actuarial loss | 7 | 6 | 21 | 19 |
| Net periodic pension benefit cost | 11 | 10 | 33 | 30 |
| Other Postretirement Benefit Cost | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | 3 | 3 | 9 | 10 |
| Interest cost | 7 | 7 | 22 | 22 |
| Expected return on plan assets | (7) | (6) | (20) | (19) |
| Amortization of prior service credit | (3) | (4) | (1) | |
| Amortization of actuarial loss | 1 | 1 | 3 | 4 |
| Net periodic pension benefit cost | $ 1 | $ 5 | $ 10 | $ 16 |