Residential Investment Securities - Unrealized Loss Position (Detail) $ in Thousands		Jun. 30, 2017 USD ($) Securities	Dec. 31, 2016 USD ($) Securities
Unrealized Loss Position For:
Estimated Fair Value	[1]	$ 56,374,847	$ 58,742,859
Gross Unrealized Losses	[1]	$ (1,100,921)	$ (1,361,566)
Number of Securities | Securities	[1]	1,487	1,422
Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	[1]	$ 50,551,597	$ 52,465,045
Gross Unrealized Losses	[1]	$ (871,480)	$ (1,094,957)
Number of Securities | Securities	[1]	1,432	1,368
Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months
Unrealized Loss Position For:
Estimated Fair Value	[1]	$ 5,823,250	$ 6,277,814
Gross Unrealized Losses	[1]	$ (229,441)	$ (266,609)
Number of Securities | Securities	[1]	55	54

[1] Excludes interest-only mortgage-backed securities.