Summary of Interest Income Recognition Methodology for Residential Investment Securities (Detail)	6 Months Ended
	Jun. 30, 2017
Agency Mortgage-backed Securities | Fixed Rate Pass-through
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Effective yield	[1],[2]
Agency Mortgage-backed Securities | Adjustable-rate Pass-through
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Effective yield	[1],[2]
Agency Mortgage-backed Securities | CMO
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Effective yield	[1],[2]
Agency Mortgage-backed Securities | Debentures
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Contractual Cash Flows	[1]
Agency Mortgage-backed Securities | Interest-only
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]
Residential Credit Securities Mortgage Backed Securities | CRT
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]
Residential Credit Securities Mortgage Backed Securities | Legacy
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]
Residential Credit Securities Mortgage Backed Securities | NPL/RPL
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]
Residential Credit Securities Mortgage Backed Securities | New Issue
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]
Residential Credit Securities Mortgage Backed Securities | New Issue Interest Only
Mortgage-Backed Securities Portfolio:
Interest Income Methodology	Prospective	[3]

[1] Changes in fair value are recognized in Other comprehensive income (loss) on the accompanying Consolidated Statements of Comprehensive Income (Loss).

[2] Effective yield is recalculated for differences between estimated and actual prepayments and the amortized cost is adjusted as if the new effective yield had been applied since inception.

[3] Changes in fair value are recognized in Net unrealized gains (losses) on investments measured at fair value through earnings on the accompanying Consolidated Statements of Comprehensive Income (Loss).