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, 2015	Dec. 31, 2014
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale		$ 0	$ 802
Investments held-to-maturity, fair value		2,580	2,632
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]	42	43
Receivable for investments sold	[1]	62	69
Total assets		104	138
Long-term debt		978	1,172
Payable for investments purchased	[2]	7	42
Total liabilities		985	1,214
Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Fair Value Inputs Level 2 [Member] | Facilities [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale			26
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	4
Total assets		2,583	2,636
Investment agreements		649	705
Medium-term notes		614	801
Total liabilities		4,000	4,285
Gross		3,830	4,051
Ceded		105	109
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		2,580	2,632
Variable interest entity notes		2,737	2,779
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	4
Accrued investment income	[1]	42	43
Receivable for investments sold	[1]	62	69
Total assets		2,831	2,899
Investment agreements		513	547
Medium-term notes		913	1,004
Long-term debt		1,854	1,810
Payable for investments purchased	[2]	7	42
Total liabilities		6,011	6,160
Gross		1,817	1,959
Ceded		60	65
Carrying Reported Amount Fair Value Disclosure [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Facilities [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale			26
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		2,724	2,757
Variable interest entity notes		2,724	2,757
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	4
Accrued investment income	[1]	42	43
Receivable for investments sold	[1]	62	69
Total assets		2,687	2,774
Investment agreements		649	705
Medium-term notes		614	801
Long-term debt		978	1,172
Payable for investments purchased	[2]	7	42
Total liabilities		4,985	5,499
Gross		3,830	4,051
Ceded		105	109
Fair Value [Member] | Value Disclosed At Fair Value Not Recorded At Fair Value [Member] | Facilities [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale			26
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		2,580	2,632
Variable interest entity notes		$ 2,737	$ 2,779

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

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