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, 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		$ 897		876
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]	28		40
Receivable for investments sold	[1]	49
Assets held for sale				306
Total assets		969		1,239
Investment agreements		350		399
Medium-term notes		771		794
Long-term debt		2,093		1,986
Payable for investments purchased	[2]	74		32
Interest payable for derivatives	[2]	15
Total liabilities		4,515		4,101
Gross		1,015		995
Ceded		36		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		1,212		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	[1]	2
Accrued investment income	[1]	28		40
Receivable for investments sold		49
Assets held for sale				306
Total assets		976		1,224
Investment agreements		453		508
Medium-term notes		497		478
Long-term debt		1,054		1,030
Payable for investments purchased	[2]	74		32
Interest payable for derivatives	[2]	15
Total liabilities		3,343		2,930
Gross		2,116		2,638
Ceded		71		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		897		876
Variable interest entity notes		1,250		882
Fair Value [Member] | 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	[1]	2
Accrued investment income	[1]	28		40
Receivable for investments sold		49
Assets held for sale				306
Total assets		79		348
Long-term debt		1,054		1,030
Payable for investments purchased	[2]	74		32
Interest payable for derivatives	[2]	15
Total liabilities		1,496		1,062
Fair Value [Member] | 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		353
Fair Value [Member] | 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		897		876
Investment agreements		453		508
Medium-term notes		497		478
Total liabilities		1,847		1,868
Gross		2,116		2,638
Ceded		71		18
Fair Value [Member] | 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		897		876
Variable interest entity notes		$ 897		$ 882

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

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