Business Developments And Risks And Uncertainties (Loss On Sale Transaction) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Income Statement [Abstract]
Difference between the carrying value and the fair value of MBIA UK	$ (270)	[1]
Costs to sell	(8)
Total pre-tax loss on adjusting MBIA UK to its fair value less costs to sell	$ (278)

[1] Includes $97 million of losses related to items that continue to be included in accumulated other comprehensive income (loss) until ultimate sale.