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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 |

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