Insurance in Force (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Transactions guaranteed by MBIA on behalf of affiliated companies		$ 2,000
Aggregate amount of insurance in force ceded to reinsurers		4,200	$ 5,100
Aggregate amount of insured par outstanding ceded to reinsurers		2,194	2,700
Ceding commissions from reinsurance	[1]	317	370	$ 480
Insurance in Force		128,100	154,900
Gross Par Amount		69,800	$ 87,000
U S Public Finance Insurance [Member]
Guarantor Obligations [Line Items]
Aggregate amount of insured par outstanding ceded to reinsurers		1,700
Structured Finance And International Insurance [Member]
Guarantor Obligations [Line Items]
Aggregate amount of insured par outstanding ceded to reinsurers		$ 499
Financial Guaranty Insurance Company [Member]
Guarantor Obligations [Line Items]
Financial guaranty maturity year		2058
Investment agreements, MTNs and other affiliated contracts [Member]
Guarantor Obligations [Line Items]
Financial guaranty maturity year		2037

[1] Represents the sum of third-party financial guarantee net premiums earned, net investment income, insurance-related fees and reimbursements and other fees.