Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		$ 365		$ 365		$ 577
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal	[1]	10,642		10,642		11,160
Policyholder (Benefits) And Claims Incurred Net		77	$ 46	99	$ 40
Total excess spread recoveries		363		363		571
Contract claims on ineligible mortgage loans inception to date, incurred loss on transactions		430		430
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		546		546		516
Expected recoveries of future payments		91		91		100
First Lien R M B S Reserves [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		327		327		277
First Lien R M B S Reserves [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		18		18		5
Second Lien Rmbs And Heloc And Ces [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Addition to case basis reserves if losses remain at peak levels				26
Second Lien Rmbs And Heloc And Ces [Member] | Excess Spread [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		319		319		382
Total excess spread recoveries		408		408		499
Expected recoveries of future payments		13		13		24
Second Lien Rmbs And Heloc And Ces [Member] | Excess Spread [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		75		75		87
Total excess spread recoveries		76		76		93
Expected recoveries of future payments		1		1		6
U S Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		58		58		45
Insurance loss recoverable		2		2		4
Policyholder (Benefits) And Claims Incurred Net		9	$ 8	18	$ 2
U S Public Finance Insurance [Member] | General obligations
Loss And Loss Adjustment Expense Reserves [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal		59,900		59,900		70,000
U S Public Finance Insurance [Member] | General obligations | Classified [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal		1,100		1,100		79
Second Lien R M B S Securitizations [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		47		47		51
Second Lien R M B S Securitizations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		$ 16		$ 16		$ 16

[1] Represents contractual principal and interest payments due by the issuer of the obligations insured by MBIA.