Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

No definition available.

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

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASU 2016-01
Defined Benefit Plan Disclosure [Line Items]
Reclassification of accumulated other comprehensive income related to marketable securities into beginning retained earnings	$ 46.1
ASU 2017-07
Defined Benefit Plan Disclosure [Line Items]
Reclassification of corporate expense to other components of net periodic pension and OPEB cost		$ 0.8	$ 0.3