Commitments and Contingencies - Additional Information (Detail) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($)
Minimum
Commitments and Contingencies Disclosure [Line Items]
Losses for environmental liabilities	$ 10
Maximum
Commitments and Contingencies Disclosure [Line Items]
Losses for environmental liabilities	$ 25

The adjustment to exclude the noncash portion of, and include cash payments for environmental costs when calculating operating cash flows under the indirect method. The adjustment can include the increase (decrease) during an accounting period in total estimated obligations recorded for probable future loss attributable to environmental contamination issues.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Name:	us-gaap_EnvironmentalExpenseAndLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration