Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Pension Benefits | ||
| Components of net periodic benefit cost: | ||
| Service cost | $ 36 | $ 31 |
| Interest cost | 18 | 19 |
| Expected return on plan assets | (26) | (26) |
| Amortization – prior service credit | (8) | (10) |
| Amortization – actuarial loss (gain) | 9 | 9 |
| Amortization - settlement loss | 1 | 0 |
| Net periodic benefit cost | 30 | 23 |
| Other Benefits | ||
| Components of net periodic benefit cost: | ||
| Service cost | 7 | 7 |
| Interest cost | 7 | 8 |
| Expected return on plan assets | 0 | 0 |
| Amortization – prior service credit | (1) | (1) |
| Amortization – actuarial loss (gain) | 0 | 0 |
| Amortization - settlement loss | 0 | 0 |
| Net periodic benefit cost | $ 13 | $ 14 |