Financial Instruments - Additional Information (Detail) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Estimated amount reclassified from other comprehensive income and reduce interest expense	$ 20

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80845-113994

Name:	us-gaap_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration