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		Mar. 31, 2017	Dec. 31, 2016
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale			$ 555
Variable Interest Entity Primary Beneficiary [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Investments held-to-maturity, fair value		$ 879	876
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]
Other investments		2	2
Accrued investment income	[1]	37	40
Receivable for investments sold	[1]	52
Assets held for sale		0	306
Total assets		91	348
Long-term debt		1,047	1,030
Payable for investments purchased	[2]	89	32
Total liabilities		1,473	1,062
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | 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		337
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]
Total assets		879	876
Investment agreements		496	508
Medium-term notes		456	478
Total liabilities		1,826	1,868
Gross		2,499	2,638
Ceded		35	18
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		879	876
Variable interest entity notes		874	882
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		2	3
Accrued investment income	[1]	37	40
Receivable for investments sold	[1]	52
Assets held for sale		0	306
Total assets		981	1,239
Investment agreements		390	399
Medium-term notes		726	794
Long-term debt		2,034	1,986
Payable for investments purchased	[2]	89	32
Total liabilities		4,450	4,101
Gross		986	995
Ceded		43	43
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	890
Variable interest entity notes		1,211	890
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		2	2
Accrued investment income	[1]	37	40
Receivable for investments sold	[1]	52
Assets held for sale		0	306
Total assets		970	1,224
Investment agreements		496	508
Medium-term notes		456	478
Long-term debt		1,047	1,030
Payable for investments purchased	[2]	89	32
Total liabilities		3,299	2,930
Gross		2,499	2,638
Ceded		35	18
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		879	876
Variable interest entity notes		$ 1,211	$ 882

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

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