Pension and Other Postretirement Benefits - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 16
Other Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	9
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	$ 23