Debt (Long-Term Debt) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Accrued interest		$ 751	$ 624
Debt issuance costs		(15)	(16)
Total		2,249	2,121
6.400% Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[1]	$ 265	265
Long-term debt, interest rate		6.40%
Long-term debt, maturity year		2022
Initial Callable date		Aug. 15, 2006
7.000% Debentures Due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 46	46
Long-term debt, interest rate		7.00%
Long-term debt, maturity year		2025
7.150% Debentures Due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 100	100
Long-term debt, interest rate		7.15%
Long-term debt, maturity year		2027
6.625% Debentures Due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 141	141
Long-term debt, interest rate		6.625%
Long-term debt, maturity year		2028
5.700% Senior Notes Due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 21	21
Long-term debt, interest rate		5.70%
Long-term debt, maturity year		2034
Surplus Notes Due 2033 [Member]
Debt Instrument [Line Items]
Surplus notes outstanding	[3]	$ 940	$ 940
Long-term debt, maturity year		2033
Callable date for fifth anniversary of initial callable date		Jan. 15, 2023
MBIA Inc. Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate		5.70%
Long-term debt, maturity year		2034

[1] Callable on or after August 15, 2006 at par.

[2] Callable anytime at the greater of par or the present value of the remaining scheduled payments of principal and interest.

[3] Contractual interest rate is based on three month LIBOR plus 11.26%