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.

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Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions		12 Months Ended
	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($) segments	Dec. 31, 2017
Business Acquisition [Line Items]
Number of business segments \| segments		3
MBIA UK [Member]
Business Acquisition [Line Items]
Sale effective date			Jan. 10, 2017
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments		$ 393
Outstanding bonds		3,300
Additional claim payment amount		$ 66
Puerto Rico [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Claims payments	$ 59