Repurchase Agreements - Remaining Maturities, Collateral Types and Weighted Average Rate (Detail) - USD ($) $ in Thousands		Jun. 30, 2016		Dec. 31, 2015
Repurchase Agreements:
Repurchase agreements		$ 53,868,385		$ 56,230,860	[1]
Weighted Average Rate		1.02%		0.90%
Credit Risk Transfer Securities
Repurchase Agreements:
Repurchase agreements		$ 123,760		$ 142,853
Non Agency MBS
Repurchase Agreements:
Repurchase agreements		660,915		435,581
Commercial Loan [Member]
Repurchase Agreements:
Repurchase agreements		304,867		179,428
Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		52,778,843		$ 55,472,998
1 day
Repurchase Agreements:
Repurchase agreements		$ 7,506,405
Weighted Average Rate		0.91%		0.00%
1 day | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		$ 7,506,405
2 to 29 days
Repurchase Agreements:
Repurchase agreements		$ 12,706,560		$ 20,467,487
Weighted Average Rate		0.81%		0.69%
2 to 29 days | Credit Risk Transfer Securities
Repurchase Agreements:
Repurchase agreements		$ 53,590		$ 83,664
2 to 29 days | Non Agency MBS
Repurchase Agreements:
Repurchase agreements		221,210		260,359
2 to 29 days | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		12,431,760		20,123,464
30 to 59 days
Repurchase Agreements:
Repurchase agreements		$ 7,014,305		$ 8,023,209
Weighted Average Rate		0.95%		0.74%
30 to 59 days | Credit Risk Transfer Securities
Repurchase Agreements:
Repurchase agreements		$ 70,170		$ 59,189
30 to 59 days | Non Agency MBS
Repurchase Agreements:
Repurchase agreements		197,005		65,374
30 to 59 days | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		6,747,130		7,898,646
60 to 89 days
Repurchase Agreements:
Repurchase agreements		$ 5,970,102		$ 4,125,426
Weighted Average Rate		0.86%		0.74%
60 to 89 days | Non Agency MBS
Repurchase Agreements:
Repurchase agreements		$ 223,289		$ 78,833
60 to 89 days | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		5,746,813		4,046,593
90 to 119 days
Repurchase Agreements:
Repurchase agreements		$ 6,179,055		$ 4,846,580
Weighted Average Rate		0.82%		0.60%
90 to 119 days | Non Agency MBS
Repurchase Agreements:
Repurchase agreements		$ 19,411
90 to 119 days | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements		6,159,644		$ 4,846,580
Over 120 days
Repurchase Agreements:
Repurchase agreements	[2]	$ 14,491,958		$ 18,768,158
Weighted Average Rate		1.44%	[2]	1.33%
Over 120 days | Non Agency MBS
Repurchase Agreements:
Repurchase agreements	[2]			$ 31,015
Over 120 days | Commercial Loan [Member]
Repurchase Agreements:
Repurchase agreements	[2]	$ 304,867		179,428
Over 120 days | Agency Mortgage Backed Securities
Repurchase Agreements:
Repurchase agreements	[2]	$ 14,187,091		$ 18,557,715

[1] Derived from the audited consolidated financial statements at December 31, 2015.

[2] Approximately 9% and 14% of the total repurchase agreements had a remaining maturity over 1 year as of June 30, 2016 and December 31, 2015, respectively.