Pension and Other Post-Retirement Benefits - Schedule of Net Periodic Benefit Cost Components (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Pension Plan Asset | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Service cost | $ 9 | $ 9 |
| Interest cost | 19 | 20 |
| Expected return on plan assets | (25) | (24) |
| Amortization of actuarial loss | 7 | 9 |
| Net periodic pension benefit cost | 10 | 14 |
| Other Postretirement Benefit Cost | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Service cost | 3 | 3 |
| Interest cost | 6 | 7 |
| Expected return on plan assets | (7) | (7) |
| Amortization of prior service credit | (5) | (5) |
| Amortization of actuarial loss | 1 | 3 |
| Net periodic pension benefit cost | $ (2) | $ 1 |