Benefit or Income Cost Related to Pension and Postretirement Health Care and Life Insurance Plans (Detail) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2016 |
Jun. 30, 2017 |
Jun. 30, 2016 |
|
| Pension | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | $ 70 | $ 76 | $ 140 | $ 156 |
| Amortization of prior service cost (credit) | 9 | 3 | 19 | 2 |
| Expected return on plan assets | (316) | (257) | (632) | (528) |
| Interest cost | 171 | 170 | 342 | 356 |
| Remeasurement loss, net | 1,257 | 1,422 | ||
| Net periodic benefit (income) cost | (66) | 1,249 | (131) | 1,408 |
| Health Care And Life | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | 37 | 52 | 74 | 113 |
| Amortization of prior service cost (credit) | (235) | (113) | (470) | (186) |
| Expected return on plan assets | (13) | (13) | (26) | (28) |
| Interest cost | 165 | 197 | 330 | 421 |
| Remeasurement loss, net | 2,293 | 2,293 | ||
| Net periodic benefit (income) cost | $ (46) | $ 2,416 | $ (92) | $ 2,613 |