Insurance Regulations And Dividends (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Insurance Regulations And Dividends [Line Items]
Percentage of policyholders' surplus	10.00%
Percentage of adjusted net investment income	100.00%
Dividends from subsidiaries	$ 118	$ 114
Minimum [Member]
Insurance Regulations And Dividends [Line Items]
Policyholders' surplus	65
MBIA Corp [Member]
Insurance Regulations And Dividends [Line Items]
Statutory net loss	323
Statutory capital	492	885
Policyholders' surplus	238
Contingency reserves	$ 254
Statutory net income		25
MBIA Corp [Member] | Loss Reserves And Unearned Premium Reserves [Member]
Insurance Regulations And Dividends [Line Items]
Percentage of loss reserves and unearned premium reserve required to be invested in qualifying assets	50.00%
MBIA Corp [Member] | Policyholders Surplus [Member]
Insurance Regulations And Dividends [Line Items]
Unassigned surplus	$ (1,800)	(1,400)
Statutory surplus negative impact	$ 112	75
Maximum percentage of statutory net admitted assets invested in subsidiaries	60.00%
National [Member]
Insurance Regulations And Dividends [Line Items]
Statutory capital	$ 3,500	3,400
Policyholders' surplus	2,700
Contingency reserves	745
Statutory net income	192	$ 284
MBIA UK [Member]
Insurance Regulations And Dividends [Line Items]
Loss recorded on adjustment of carrying value to fair value less costs to sell	$ 114