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		Jun. 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		$ 894	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]	3
Assets held for sale		0	306
Total assets		42	348
Long-term debt		1,055	1,030
Payable for investments purchased	[2]	20	32
Interest payable for derivatives	[2]	18
Total liabilities		1,422	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		329
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		894	876
Investment agreements		471	508
Medium-term notes		490	478
Total liabilities		1,855	1,868
Gross		2,376	2,638
Ceded		50	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		894	876
Variable interest entity notes		894	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]	3
Assets held for sale		0	306
Total assets		932	1,239
Investment agreements		365	399
Medium-term notes		753	794
Long-term debt		2,061	1,986
Payable for investments purchased	[2]	20	32
Interest payable for derivatives	[2]	18
Total liabilities		4,422	4,101
Gross		1,092	995
Ceded		31	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		1,205	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]	3
Assets held for sale		0	306
Total assets		936	1,224
Investment agreements		471	508
Medium-term notes		490	478
Long-term debt		1,055	1,030
Payable for investments purchased	[2]	20	32
Interest payable for derivatives	[2]	18
Total liabilities		3,277	2,930
Gross		2,376	2,638
Ceded		50	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		894	876
Variable interest entity notes		$ 1,223	$ 882

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

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