The Company and its Subsidiaries - Additional Information (Detail) $ / shares in Units, $ in Billions				3 Months Ended	12 Months Ended
	Feb. 12, 2018 USD ($) $ / shares shares	Feb. 02, 2018	Dec. 11, 2017	Mar. 31, 2018 Insurers $ / shares shares	Dec. 31, 2017 $ / shares shares	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
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			206,714,132	206,714,132
Common stock, shares outstanding				206,714,132	206,714,132
WMMRC [Member]
Related Party Transaction [Line Items]
Number of primary mortgage insurers | Insurers				7
Reinsurance agreement termination date		Feb. 02, 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
Redeemable Convertible Series B Preferred Stock [Member]
Related Party Transaction [Line Items]
Preferred stock, redemption date				Oct. 05, 2019
Preferred stock dividend rate					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
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 | $	$ 1.2
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