Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended									0 Months Ended				0 Months Ended					6 Months Ended		0 Months Ended	6 Months Ended		24 Months Ended	6 Months Ended					6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013		Jun. 30, 2014 Loss And Lae Reserves [Member]	Dec. 31, 2013 Loss And Lae Reserves [Member]	Jun. 30, 2014 Classified [Member] Loss And Lae Reserves [Member]	Dec. 31, 2013 Classified [Member] Loss And Lae Reserves [Member]	May 31, 2014 First Lien R M B S Reserves [Member]	Jun. 30, 2014 First Lien R M B S Reserves [Member] Loss And Lae Reserves [Member]	Dec. 31, 2013 First Lien R M B S Reserves [Member] Loss And Lae Reserves [Member]	Dec. 31, 2013 First Lien R M B S Reserves [Member] Variable Interest Entity Primary Beneficiary [Member]	May 31, 2014 First Lien R M B S Reserves [Member] ALT-A [Member]	May 31, 2014 First Lien R M B S Reserves [Member] Foreclosure [Member]	May 31, 2014 First Lien R M B S Reserves [Member] Real Estate Owned [Member]	May 31, 2014 First Lien R M B S Reserves [Member] Bankruptcy [Member]	May 31, 2014 Rmbs And Heloc And Ces [Member]	Nov. 30, 2014 Rmbs And Heloc And Ces [Member]	Jun. 30, 2014 Rmbs And Heloc And Ces [Member]	Mar. 31, 2015 Rmbs And Heloc And Ces [Member] Scenario Forecast [Member]	Nov. 30, 2014 Rmbs And Heloc And Ces [Member] Scenario Forecast [Member]	Nov. 30, 2014 Rmbs And Heloc And Ces [Member] Scenario Forecast [Member] Minimum [Member]	May 31, 2016 Rmbs And Heloc And Ces [Member] Scenario Forecast [Member] Maximum [Member]	Nov. 30, 2014 Rmbs And Heloc And Ces [Member] Scenario Forecast [Member] Rate Reduction [Member]	Jun. 30, 2014 Rmbs And Heloc And Ces [Member] Excess Spread [Member]	Dec. 31, 2013 Rmbs And Heloc And Ces [Member] Excess Spread [Member]	Jun. 30, 2014 Rmbs And Heloc And Ces [Member] Excess Spread [Member] Variable Interest Entity Primary Beneficiary [Member]	Dec. 31, 2013 Rmbs And Heloc And Ces [Member] Excess Spread [Member] Variable Interest Entity Primary Beneficiary [Member]	Jun. 30, 2014 U S Public Finance Insurance [Member]	Dec. 31, 2013 U S Public Finance Insurance [Member]	Jun. 30, 2014 U S Public Finance Insurance [Member] General obligations	Dec. 31, 2013 U S Public Finance Insurance [Member] General obligations	Jun. 30, 2014 U S Public Finance Insurance [Member] General obligations Classified [Member]	Dec. 31, 2013 U S Public Finance Insurance [Member] General obligations Classified [Member]	Jun. 30, 2014 Second Lien R M B S Securitizations [Member] Loss And Lae Reserves [Member]	Dec. 31, 2013 Second Lien R M B S Securitizations [Member] Loss And Lae Reserves [Member]	Jun. 30, 2014 Second Lien R M B S Securitizations [Member] Variable Interest Entity Primary Beneficiary [Member]	Dec. 31, 2013 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									$ 554	$ 641	$ 554	$ 641		$ 237	$ 241	$ 2																	$ 70	$ 87					$ 118	$ 126	$ 18	$ 43
Insurance loss recoverable																													569	647	168	183	14	13
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal	15,595	[1]		15,595	[1]		14,264	[1]																											113,200	124,900	154	161
Policyholder (Benefits) And Claims Incurred Net	12		188	62		(6)																											3
Total excess spread recoveries																													577	681	173	190
Expected recoveries of future payments									159	206																			8	34	5	7
Assumed roll rate for loans																		90.00%	90.00%	75.00%
90+ day roll rate to loss set stress scenario													90.00%
Percentage of roll to loss after declining over a 24-month period																	25.00%
Assumed roll rate for ninety plus day delinquent loans excluding foreclosure and real estate owned																					95.00%
Period of elevated delinquency and loss for base case, beginning, months																						6
Percentage of loans in 30-59 days delinquent bucket																					10.00%
Percentage of loans charged-off																					30.00%
Percentage of Current Roll to Loss for the transaction																					3.00%
Decrease in percentage of Current Roll to Loss for transaction																									25.00%			0.75%
Current Roll to Loss																								0.00%
Period of elevated delinquency and loss for stress case, additional months																										6	24
Addition to case basis reserves if losses remain at peak levels																							$ 60

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