Insurance Premiums (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance Premiums [Line Items]
Premiums receivable	$ 409	$ 792	$ 875
Weighted average risk-free rate	2.80%	2.70%
Weighted average expected collection term of the premiums receivable, years	10 years 25 days	9 years 29 days
Reinsurance premiums payable	$ 26	$ 38
Other Liabilities [Member] | MBIA UK [Member]
Insurance Premiums [Line Items]
Reinsurance premiums payable	$ 6