Common and Preferred Stock (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	2 Months Ended	12 Months Ended
	Feb. 21, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Warrants exercised		11,850,000
Warrant exercise price		$ 9.59
Warrants outstanding		0
Fair value of warrants			$ 6
Shares repurchased under share repurchase program, average price per share		$ 8.21	$ 7.55
Preferred stock shares issued		0	0
Preferred stock shares outstanding		0	0
Preferred Stock Par Or Stated Value Per Share		$ 1	$ 1
StockIssuedDuringPeriodSharesTreasuryStockReissued		1,300,000
Remaining amount available under repurchase program		$ 202	$ 250
Treasury stock shares acquired		5,800,000	43,000,000
SubsequentEvent [Member]
Class of Stock [Line Items]
Shares repurchased under share repurchase program, average price per share	$ 8.94
Remaining amount available under repurchase program	$ 198
Treasury stock shares acquired	500,000
MBIA Insurance Corporation [Member]
Class of Stock [Line Items]
Preferred Stock Par Or Stated Value Per Share		$ 1,000
Preferred stock liquidation preference		100,000
Preferred Stock [Member] | MBIA Insurance Corporation [Member]
Class of Stock [Line Items]
Shares repurchased under share repurchase program, average price per share		$ 10,900
Preferred stock shares issued		2,759
Preferred stock repurchased during period shares		1,444
Preferred stock, carrying value issued and outstanding		$ 28
Face value of repurchased preferred stock		10.90%
Dividend rate on preferred stock determined rate		LIBOR plus 200 basis points
2016 Repurchase Authorization [Member]
Class of Stock [Line Items]
Authorized repurchase of common stock, value		$ 100
Stock repurchase program cancelled amount		13
June 27, 2017 Repurchase Authorization [Member]
Class of Stock [Line Items]
Authorized repurchase of common stock, value		250
November 3, 2017 Repurchase Authorization [Member]
Class of Stock [Line Items]
Authorized repurchase of common stock, value		$ 250
Unaffiliated Investors [Member] | MBIA Insurance Corporation [Member]
Class of Stock [Line Items]
Preferred stock shares outstanding		1,315