Defined Benefit Pension and Other Postretirement Plans - Additional Information (Detail) $ in Millions |
3 Months Ended |
|---|---|
|
Mar. 31, 2018
USD ($)
| |
| Pension Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Employer contributions | $ 0 |
| Other Pension Plan | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Benefits paid | 6 |
| Other Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Benefits paid | $ 8 |