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The Company and its Subsidiaries - Additional Information (Detail) |  |  |  |  | 6 Months Ended | 12 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 15, 2018 | Feb. 12, 2018 USD ($) $ / shares shares | Feb. 02, 2018 | Dec. 11, 2017 | Jun. 30, 2018 Insurers $ / shares shares | Dec. 31, 2017 $ / shares shares | Jun. 29, 2018 USD ($) | Jun. 14, 2018 | Dec. 31, 2016 shares | May 11, 2015 $ / shares shares | Jan. 05, 2015 shares | Jan. 30, 2014 shares | Mar. 19, 2012 $ / shares shares
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Plan Effective Date |  |  |  |  | Mar. 19, 2012 |  |  |  |  |  |  |  |
Common stock, par value | $ / shares |  |  |  |  | $ 0.00001 | $ 0.00001 |  |  |  | $ 0.00001 |  |  | $ 0.00001
Expected merger close date |  |  |  |  | Jul. 31, 2018 |  |  |  |  |  |  |  |
Common stock, shares authorized |  |  |  |  | 3,500,000,000 | 3,500,000,000 |  |  |  | 3,500,000,000 |  |  | 500,000,000
Preferred stock, shares authorized |  |  |  |  | 10,000,000 |  |  |  |  | 10,000,000 |  |  | 5,000,000
Convertible preferred stock, par value | $ / shares |  |  |  |  | $ 0.00001 |  |  |  |  | $ 0.00001 |  |  | $ 0.00001
Common stock, shares issued |  | 21,197,619 |  |  | 216,664,908 | 206,714,132 |  |  |  |  |  |  |
Common stock, shares outstanding |  |  |  |  | 216,664,908 | 206,714,132 |  |  |  |  |  |  |
WMMRC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of primary mortgage insurers | Insurers |  |  |  |  | 7 |  |  |  |  |  |  |  |
Reinsurance agreement termination date |  |  | Feb. 02, 2018 |  |  |  |  |  |  |  |  |  |
Redeemable Convertible Series B Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, redemption date |  |  |  |  | Oct. 05, 2019 |  |  |  |  |  |  |  |
Preferred stock dividend rate | 5.00% |  |  |  |  | 3.00% |  |  |  |  |  |  |
Preferred stock, shares issued |  |  |  |  | 600,000 | 600,000 |  |  |  |  | 600,000 |  |
Preferred stock, shares outstanding |  |  |  |  | 600,000 | 600,000 |  |  | 600,000 |  |  |  |
Amendment Effective Date |  |  |  |  | Jan. 05, 2018 |  |  |  |  |  |  |  |
Redeemable Convertible Series B Preferred Stock [Member] | Amended and Restated Certificate of Incorporation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, redemption date |  |  |  |  | Oct. 05, 2019 |  |  |  |  |  |  |  |
Preferred stock dividend rate |  |  |  |  | 5.00% |  |  |  |  |  |  |  |
Redeemable Convertible Series B Preferred Stock [Member] | Certificate of Amendment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Amendment Effective Date |  |  |  | Jan. 05, 2018 |  |  |  |  |  |  |  |  |
Convertible Series A Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible preferred stock, par value | $ / shares |  |  |  |  | $ 0.00001 | $ 0.00001 |  |  |  |  |  |  |
Convertible preferred stock, shares issued |  |  |  |  | 1,000,000 | 1,000,000 |  |  |  |  |  | 1,000,000 |
Convertible preferred stock, shares outstanding |  |  |  |  | 1,000,000 | 1,000,000 |  |  |  |  |  |  |
Merger Sub [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issued aggregate principal amount | $ |  |  |  |  |  |  | $ 1,700,000,000 |  |  |  |  |  |
Senior Notes due 2021 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  | 6.50% |  |  |  |  |
Senior Notes due 2022 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  |  | 6.50% |  |  |  |  |
Notes due 2023 [Member] | Merger Sub [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  | 8.125% |  |  |  |  |  |
Issued aggregate principal amount | $ |  |  |  |  |  |  | $ 950,000,000 |  |  |  |  |  |
Notes due 2026 [Member] | Merger Sub [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  |  |  |  | 9.125% |  |  |  |  |  |
Issued aggregate principal amount | $ |  |  |  |  |  |  | $ 750,000,000 |  |  |  |  |  |
WMIH Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares issued |  | 21,197,619 |  |  |  |  |  |  |  |  |  |  |
Merger Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Merger agreement date |  | Feb. 12, 2018 |  |  |  |  |  |  |  |  |  |  |
Share price, without interest | $ / shares |  | $ 18.00 |  |  |  |  |  |  |  |  |  |  |
Aggregate amount of merger consideration | $ |  | $ 1,200,000,000 |  |  |  |  |  |  |  |  |  |  |
Merger Agreement [Member] | WMIH Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued, fully paid and nonassessable shares |  | 12.7793 |  |  |  |  |  |  |  |  |  |  |
Common stock, par value | $ / shares |  | $ 0.00001 |  |  |  |  |  |  |  |  |  |  |

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