Revenue from Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Uncollected amounts receivable	$ 54	$ 56
Accrued interest and other liabilities [Member]
Disaggregation Of Revenue [Line Items]
Deferred revenue	$ 43	$ 43

Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

No definition available.

Name:	us-gaap_DeferredRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant