Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($) segments
Business Acquisition [Line Items]
Number of business segments \| segments	3
Zohar [Member]
Business Acquisition [Line Items]
Aggregate claim amount	$ 919
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments	393
Outstanding bonds	3,000
Puerto Rico [Member] \| CABs [Member]
Business Acquisition [Line Items]
Outstanding bonds	$ 3,300

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration