Insurance In Force (Schedule Of Insurance In Force By Type Of Bond, Excluding Transactions Guaranteed By MBIA Corp. On Behalf Of Various Investment Management Services And Other Affiliated Companies) (Detail) - USD ($) $ in Billions		Dec. 31, 2018	Dec. 31, 2017
Insurance in Force		$ 128.1	$ 154.9
Gross Par Amount		69.8	87.0
U S [Member]
Insurance in Force		118.8	143.4
Non-United States [Member]
Insurance in Force		9.3	11.5
Global Public Finance [Member]
Insurance in Force		119.6	144.2
Gross Par Amount		64.2	79.7
Global Public Finance [Member] | U S [Member]
Insurance in Force		111.6	134.0
Gross Par Amount		57.9	71.9
Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		8.0	10.2
Gross Par Amount		6.3	7.8
Global Structured Finance [Member]
Insurance in Force		8.5	10.7
Gross Par Amount		5.6	7.3
General Obligation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[1]	34.2	42.8
Gross Par Amount	[1]	17.3	22.9
General Obligation - Lease [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		4.0	5.1
Gross Par Amount		3.0	3.8
Municipal Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		14.2	17.7
Gross Par Amount		9.5	11.8
Tax-Backed [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		24.0	26.5
Gross Par Amount		11.2	12.4
Transportation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		12.0	15.2
Gross Par Amount		4.8	6.9
Transportation [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		3.0	4.5
Gross Par Amount		2.5	3.6
Higher Education [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		2.5	3.2
Gross Par Amount		1.7	2.1
Health Care [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		1.7	2.6
Gross Par Amount		1.2	1.8
Military Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		15.8	16.3
Gross Par Amount		7.2	7.3
Investor-Owned Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[2]	2.0	3.1
Gross Par Amount	[2]	1.3	2.0
Municipal Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		0.3	0.4
Gross Par Amount		0.2	0.3
Other Public Finance [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[3]	0.9	1.1
Gross Par Amount	[3]	0.5	0.6
Other Public Finance [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force	[4]	0.1	0.2
Gross Par Amount	[4]	0.1	0.1
International Utilities [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		1.4	1.7
Gross Par Amount		1.2	1.4
Sovereign Related And Sub-Sovereign [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force	[5]	3.5	3.8
Gross Par Amount	[5]	2.5	2.7
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Insurance in Force	[6]	0.5	0.5
Gross Par Amount	[6]	0.4	0.4
Residential Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		3.4	4.7
Gross Par Amount		2.5	3.6
Commercial Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		0.6	0.7
Gross Par Amount		0.3	0.3
Consumer Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force		0.5	0.9
Gross Par Amount		0.4	0.7
Corporate Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force	[7]	3.5	3.9
Gross Par Amount	[7]	$ 2.0	$ 2.3

[1] Includes general obligation unlimited and limited (property) tax bonds, general fund obligation bonds and pension obligation bonds of states, cities, counties, schools and special districts.

[2] Includes investor owned utilities, industrial development and pollution control revenue bonds.

[3] Includes certain non-profit enterprises, stadium related financing and student loans.

[4] Includes municipal owned entities backed by sponsoring local government and tax backed transactions.

[5] Includes regions, departments or their equivalent in each jurisdiction as well as sovereign owned entities that are supported by a sovereign state, region or department.

[6] Includes a transaction (represented by structured pools of CRE assets) that does not include typical CDO structuring characteristics, such as tranched credit risk, cash flow waterfalls, or interest and over-collateralization coverage tests.

[7] As of December 31, 2018, includes structured insurance securitizations of $2.2 billion and $1.0 billion of insurance in force and gross par amount, respectively. As of December 31, 2017, includes structured insurance securitizations of $2.3 billion and $1.1 billion of insurance in force and gross par amount, respectively.