Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions	3 Months Ended
Mar. 31, 2017 USD ($) segments	Mar. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of operating segments \| segments	3
Fixed-to-Floating rate Surplus Notes	14.00%
Income (loss) before income taxes	$ (120)	$ (101)
Proceeds from Senior Lenders	325
Zohar II [Member]
Business Acquisition [Line Items]
Claims payments	770
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments	24
Mbia Inc [Member]
Business Acquisition [Line Items]
Proceeds from subordinated financing	38
Mbia Corp [Member] \| Zohar II [Member]
Business Acquisition [Line Items]
Claims payments	60
Assured Guaranty Corp [Member]
Business Acquisition [Line Items]
Payment for sale of subsidiary	23
Assured Guaranty Corp [Member] \| Zohar II [Member]
Business Acquisition [Line Items]
Outstanding bonds	347
MBIA UK [Member]
Business Acquisition [Line Items]
Gain recorded on adjustment of carrying value to fair value less costs to sell	$ 5
Income (loss) before income taxes		$ 9
Sale effective date	Jan. 10, 2017

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Date the entity disposed of a business or a group of assets, in CCYY-MM-DD format.

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