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 Affiliated Companies) (Detail) - USD ($) $ in Billions		Dec. 31, 2016	Dec. 31, 2015
Insurance in Force		$ 235.9	$ 326.6
% of Insurance in Force		100.00%	100.00%
U S [Member]
Insurance in Force		$ 205.5	$ 290.3
% of Insurance in Force		87.10%	88.90%
Non-United States [Member]
Insurance in Force		$ 30.4	$ 36.3
% of Insurance in Force		12.90%	11.10%
Global Public Finance [Member]
Insurance in Force		$ 220.3	$ 301.4
% of Insurance in Force		93.40%	92.30%
Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 191.5	$ 267.5
% of Insurance in Force		81.20%	81.90%
Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		$ 28.8	$ 33.9
% of Insurance in Force		12.20%	10.40%
Global Structured Finance [Member]
Insurance in Force		$ 15.6	$ 25.2
% of Insurance in Force		6.60%	7.70%
General Obligation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[1]	$ 64.6	$ 89.4
% of Insurance in Force	[1]	27.40%	27.40%
General Obligation - Lease [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 12.2	$ 20.0
% of Insurance in Force		5.20%	6.10%
Municipal Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 26.1	$ 41.8
% of Insurance in Force		11.00%	12.80%
Tax-Backed [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 33.0	$ 41.6
% of Insurance in Force		14.00%	12.70%
Tax-Backed [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		$ 0.2	$ 0.2
% of Insurance in Force		0.10%	0.10%
Transportation [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 21.7	$ 28.9
% of Insurance in Force		9.20%	8.80%
Transportation [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		$ 7.1	$ 7.6
% of Insurance in Force		3.00%	2.30%
Higher Education [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 6.8	$ 13.5
% of Insurance in Force		2.90%	4.10%
Health Care [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 4.2	$ 6.6
% of Insurance in Force		1.80%	2.00%
Military Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 16.8	$ 17.3
% of Insurance in Force		7.10%	5.30%
Investor-Owned Utilities [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[2]	$ 3.7	$ 5.4
% of Insurance in Force	[2]	1.60%	1.70%
Municipal Housing [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force		$ 0.7	$ 1.5
% of Insurance in Force		0.30%	0.50%
Other Public Finance [Member] | Global Public Finance [Member] | U S [Member]
Insurance in Force	[3]	$ 1.7	$ 1.5
% of Insurance in Force	[3]	0.70%	0.50%
International Utilities [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force		$ 10.1	$ 12.1
% of Insurance in Force		4.30%	3.70%
Sovereign Related And Sub-Sovereign [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force	[4]	$ 11.3	$ 13.7
% of Insurance in Force	[4]	4.80%	4.20%
Local Governments [Member] | Global Public Finance [Member] | Non-United States [Member]
Insurance in Force	[5]	$ 0.1	$ 0.3
% of Insurance in Force	[5]	0.00%	0.10%
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Insurance in Force	[6]	$ 2.7	$ 6.4
% of Insurance in Force	[6]	1.10%	1.90%
Residential Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		$ 6.3	$ 8.0
% of Insurance in Force		2.70%	2.50%
Commercial Mortgage Backed Securities [Member] | Global Structured Finance [Member]
Insurance in Force		$ 0.7	$ 0.9
% of Insurance in Force		0.30%	0.30%
Consumer Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force		$ 1.2	$ 1.6
% of Insurance in Force		0.50%	0.50%
Corporate Asset Backed [Member] | Global Structured Finance [Member]
Insurance in Force	[7]	$ 4.7	$ 8.3
% of Insurance in Force		2.00%	2.50%
Structured Insurance Securitizations [Member]
Insurance in Force		$ 2.6	$ 5.1

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

[5] Includes municipal owned entities backed by sponsoring local government.

[6] Includes transactions (represented by structured pools of primarily investment grade corporate credit risks or CRE assets) that do not include typical CDO structuring characteristics, such as tranched credit risk, cash flow waterfalls, or interest and over-collateralization coverage tests.

[7] Includes $2.6 billion and $5.1 billion of structured insurance securitizations as of December 31, 2016 and 2015, respectively.