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, 2020	Dec. 31, 2019
Insurance in Force		$ 91.4	$ 107.5
Gross Par Amount		49.6	58.9
U S [Member]
Insurance in Force		84.5	99.4
Non-United States [Member]
Insurance in Force		6.9	8.1
Global Public Finance [Member]
Insurance in Force		87.4	100.7
Gross Par Amount		46.7	54.6
Global Public Finance [Member] | U S [Member]
Insurance in Force		81.5	93.7
Gross Par Amount		41.9	48.9
Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		5.9	7.0
Gross Par Amount		4.8	5.7
Global Structured Finance [Member]
Insurance in Force		4.0	6.8
Gross Par Amount		2.9	4.3
General Obligation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[1]	25.0	29.1
Gross Par Amount	[1]	12.1	14.3
General Obligation - Lease [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		2.4	3.1
Gross Par Amount		1.9	2.3
Municipal Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		10.6	12.0
Gross Par Amount		7.3	8.1
Tax-Backed [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		15.7	17.7
Gross Par Amount		7.9	9.2
Transportation [Member] | Non-United States [Member]
Insurance in Force		2.1	2.7
Gross Par Amount		1.8	2.3
Transportation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		9.2	10.6
Gross Par Amount		3.0	3.9
Higher Education [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		1.5	2.2
Gross Par Amount		1.1	1.5
Health Care [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		1.2	1.4
Gross Par Amount		0.8	1.0
Military Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		14.8	15.2
Gross Par Amount		7.0	7.1
Investor-Owned Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[2]	0.9	1.4
Gross Par Amount	[2]	0.6	0.9
Municipal Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		0.1	0.2
Gross Par Amount		0.1	0.1
Other Public Finance [Member] | Non-United States [Member]
Insurance in Force	[3]	0.1	0.2
Gross Par Amount	[3]	0.1	0.1
Other Public Finance [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[4]	0.1	0.8
Gross Par Amount	[4]	0.1	0.5
International Utilities [Member] | Non-United States [Member]
Insurance in Force		0.9	1.1
Gross Par Amount		0.8	1.0
Sovereign Related And Sub-Sovereign [Member] | Non-United States [Member]
Insurance in Force		2.8	3.0
Gross Par Amount		2.1	2.3
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Insurance in Force		0.4	0.4
Gross Par Amount		0.3	0.3
Residential Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		2.0	2.5
Gross Par Amount		1.5	1.8
Commercial Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		0.5	0.5
Gross Par Amount		0.2	0.2
Consumer Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force		0.3	0.4
Gross Par Amount		0.3	0.3
Corporate Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force	[5]	0.8	3.0
Gross Par Amount	[5]	$ 0.6	$ 1.7

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

[4] Includes certain non-profit enterprises, stadium related financing.

[5] As of December 31, 2020, all remaining insurance in force and gross par relating to structured insurance securitizations was terminated. As of December 31, 2019, includes structured insurance securitizations of $2.1 billion and $1.0 billion of insurance in force and gross par amount, respectively.