Fair Value Of Financial Instruments (Fair Value And Carrying Value Of Assets And Liabilities That Are Disclosed At Fair Value But Not Reported At Fair Value On Company's Consolidated Balance Sheets) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Variable Interest Entity [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Variable interest entity notes	$ 7,039		$ 7,124
Value Disclosed At Fair Value Not Recorded At Fair Value [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Other investments	9		9
Accrued investment income	40	[1]	43	[1]
Receivable for investments sold	3	[1]	17	[1]
Net cash collateral pledged	58	[1]	66	[1]
Total assets	2,869		2,809
Investment agreements	1,126		1,175
Medium-term notes	944		860
Long-term debt	801		692
Payable for investments purchased	51	[2]	50	[2]
Accrued interest expense	34	[2]	19	[2]
Total liabilities	6,209		5,943
Gross	466		650
Ceded	100		97
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments held-to-maturity	2,759		2,674
Variable interest entity notes	3,253		3,147
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Accrued investment income	40	[1]	43	[1]
Receivable for investments sold	3	[1]	17	[1]
Net cash collateral pledged	58	[1]	66	[1]
Total assets	101		126
Payable for investments purchased	51	[2]	50	[2]
Accrued interest expense	13	[2]	9	[2]
Total liabilities	64		59
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Long-term debt	801		692
Accrued interest expense	21	[2]	10	[2]
Total liabilities	822		702
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Other investments	9		9
Total assets	2,768		2,683
Investment agreements	1,126		1,175
Medium-term notes	944		860
Total liabilities	5,323		5,182
Gross	466		650
Ceded	100		97
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Variable Interest Entity [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments held-to-maturity	2,759		2,674
Variable interest entity notes	3,253		3,147
Carrying Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Other investments	9		9
Accrued investment income	40	[1]	43	[1]
Receivable for investments sold	3	[1]	17	[1]
Net cash collateral pledged	58	[1]	66	[1]
Total assets	2,936		2,964
Investment agreements	915		944
Medium-term notes	1,396		1,433
Long-term debt	1,661		1,662
Payable for investments purchased	51	[2]	50	[2]
Accrued interest expense	103	[2]	70	[2]
Total liabilities	7,587		7,624
Gross	(318)		143
Ceded	87		91
Carrying Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments held-to-maturity	2,826		2,829
Variable interest entity notes	$ 3,461		$ 3,465

[1] Reported within "Other assets" on MBIA's consolidated balance sheets.

[2] Reported within "Other liabilities" on MBIA's consolidated balance sheets.