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) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Investments held-to-maturity, fair value		$ 573	$ 2,401
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Total assets		0	0
Total liabilities		0	0
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Accrued investment income	[1]	41	38
Receivable for investments sold	[1]	23	26
Total assets		64	64
Long-term debt		976	762
Payable for investments purchased	[2]	50	36
Total liabilities		1,026	798
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments		3	3
Total assets		576	2,404
Investment agreements		571	595
Medium-term notes		485	534
Total liabilities		1,833	3,725
Gross		3,141	3,093
Ceded		107	94
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Investments held-to-maturity, fair value		573	2,401
Variable interest entity notes		777	2,596
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Other investments		3	3
Accrued investment income	[1]	41	38
Receivable for investments sold	[1]	23	26
Total assets		957	2,756
Investment agreements		418	462
Medium-term notes		826	855
Long-term debt		1,975	1,889
Payable for investments purchased	[2]	50	36
Total liabilities		4,159	5,931
Gross		1,329	1,530
Ceded		52	56
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Investments held-to-maturity, fair value		890	2,689
Variable interest entity notes		890	2,689
Fair 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		3	3
Accrued investment income	[1]	41	38
Receivable for investments sold	[1]	23	26
Total assets		640	2,468
Investment agreements		571	595
Medium-term notes		485	534
Long-term debt		976	762
Payable for investments purchased	[2]	50	36
Total liabilities		2,859	4,523
Gross		3,141	3,093
Ceded		107	94
Fair Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Investments held-to-maturity, fair value		573	2,401
Variable interest entity notes		$ 777	$ 2,596

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

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