Fair Value Of Financial Instruments (Fair Value Hierarchy Table Presents The Company's Assets And Liabilities At Fair Value Not Recorded On The Company's Consolidated Balance Sheet) (Detail) (Value Disclosed At Fair Value Not Recorded At Fair Value [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments	$ 9		$ 9
Accrued investment income	42	[1]	43	[1]
Receivable for investments sold	12	[1]	17	[1]
Net cash collateral pledged	55	[1]	66	[1]
Total assets	2,808		2,809
Investment agreements	931		1,175
Medium-term notes	1,018		860
Securities Loaned Or Sold Under Agreements To Repurchase	0		0
Long-term debt	1,371		692
Payable for investments purchased	43	[2]	50	[2]
Accrued interest payable	109	[2]	19	[2]
Total liabilities	6,437		5,943
Gross	3,677		650
Ceded	85		97
Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Variable interest entity notes	2,965		3,147
Investments held-to-maturity	2,690		2,674
Long-term debt			0
Fair Value Inputs Level 1 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments	0		0
Accrued investment income	42	[1]	43	[1]
Receivable for investments sold	12	[1]	17	[1]
Net cash collateral pledged	55	[1]	66	[1]
Total assets	109		126
Investment agreements	0		0
Medium-term notes	0		0
Securities Loaned Or Sold Under Agreements To Repurchase	0		0
Long-term debt	0		0
Payable for investments purchased	43	[2]	50	[2]
Accrued interest payable	9	[2]	9	[2]
Total liabilities	52		59
Gross	0		0
Ceded	0		0
Fair Value Inputs Level 1 [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Variable interest entity notes	0		0
Investments held-to-maturity	0		0
Long-term debt			0
Fair Value Inputs Level 2 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments	0		0
Accrued investment income	0	[1]	0	[1]
Receivable for investments sold	0	[1]	0	[1]
Net cash collateral pledged	0	[1]	0	[1]
Total assets	0		0
Investment agreements	0		0
Medium-term notes	0		0
Securities Loaned Or Sold Under Agreements To Repurchase	0		0
Long-term debt	1,371		692
Payable for investments purchased	0	[2]	0	[2]
Accrued interest payable	100	[2]	10	[2]
Total liabilities	1,471		702
Gross	0		0
Ceded	0		0
Fair Value Inputs Level 2 [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Variable interest entity notes	0		0
Investments held-to-maturity	0		0
Long-term debt			0
Fair Value Inputs Level 3 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments	9		9
Accrued investment income	0	[1]	0	[1]
Receivable for investments sold	0	[1]	0	[1]
Net cash collateral pledged	0	[1]	0	[1]
Total assets	2,699		2,683
Investment agreements	931		1,175
Medium-term notes	1,018		860
Securities Loaned Or Sold Under Agreements To Repurchase	0		0
Long-term debt	0		0
Payable for investments purchased	0	[2]	0	[2]
Accrued interest payable	0	[2]	0	[2]
Total liabilities	4,914		5,182
Gross	3,677		650
Ceded	85		97
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Variable interest entity notes	2,965		3,147
Investments held-to-maturity	2,690		2,674
Long-term debt			0
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments	9		9
Accrued investment income	42	[1]	43	[1]
Receivable for investments sold	12	[1]	17	[1]
Net cash collateral pledged	55	[1]	66	[1]
Total assets	2,936		2,964
Investment agreements	775		944
Medium-term notes	1,373		1,433
Securities Loaned Or Sold Under Agreements To Repurchase	0		0
Long-term debt	1,524		1,662
Payable for investments purchased	43	[2]	50	[2]
Accrued interest payable	125	[2]	70	[2]
Total liabilities	6,957		7,624
Gross	2,507		143
Ceded	85		91
Carrying Reported Amount Fair Value Disclosure [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Variable interest entity notes	3,117		3,465
Investments held-to-maturity	2,818		2,829
Long-term debt			$ 0

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

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