Contingencies and Commitments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) Project	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Environmental remediation reserve balance, current	$ 33	$ 44
Active or future remediation for siginficant sites	212	214
Remediation reserve balance	$ 276	280	$ 294
Massena, New York [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period	4 years
Massena, New York [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period	8 years
Sherwin, Texas [Member]
Loss Contingencies [Line Items]
Beginning of expected term for reuse of residue bed	8 years
Ending of expected term for reuse of residue bed	12 years
Other Sites [Member]
Loss Contingencies [Line Items]
Number of remediation projects | Project	35
Remediation reserve balance	$ 64	$ 66