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, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Assets held for sale	$ 22		$ 802
Investments held-to-maturity, fair value	2,635		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	43	[1]	43	[1]
Receivable for investments sold	67	[1]	69	[1]
Total assets	132		138
Long-term debt	1,113		1,172
Payable for investments purchased	71	[2]	42	[2]
Total liabilities	1,184		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	22		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	4		4
Total assets	2,639		2,636
Investment agreements	711		705
Medium-term notes	753		801
Total liabilities	4,240		4,285
Gross	3,874		4,051
Ceded	103		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	2,635		2,632
Variable interest entity notes	2,776		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	4		4
Accrued investment income	43	[1]	43	[1]
Receivable for investments sold	67	[1]	69	[1]
Total assets	2,878		2,899
Investment agreements	538		547
Medium-term notes	928		1,004
Long-term debt	1,828		1,810
Payable for investments purchased	71	[2]	42	[2]
Total liabilities	6,107		6,160
Gross	1,846		1,959
Ceded	61		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	22		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	2,742		2,757
Variable interest entity notes	2,742		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	4		4
Accrued investment income	43	[1]	43	[1]
Receivable for investments sold	67	[1]	69	[1]
Total assets	2,771		2,774
Investment agreements	711		705
Medium-term notes	753		801
Long-term debt	1,113		1,172
Payable for investments purchased	71	[2]	42	[2]
Total liabilities	5,424		5,499
Gross	3,874		4,051
Ceded	103		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	22		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	2,635		2,632
Variable interest entity notes	$ 2,776		$ 2,779

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

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