Repurchase Agreements (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Repurchase Agreements
Repurchase Agreements Number of Counterparties	26		26
Balance of repurchase agreements	$ 8,339,297,000	[1]	$ 8,752,472,000	[1]
Repurchase agreements
Repurchase Agreements
Weighted average remaining term-to-interest rate reset of borrowings under repurchase agreements	25 days		28 days
Effective repricing period	24 months		5 months
Balance of repurchase agreements	8,339,297,000	[2],[3]	8,752,472,000	[2]
Weighted Average Interest Rate (as a percent)	0.77%		0.85%
Maturity Overnight [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	0	[3]
Weighted Average Interest Rate (as a percent)	0.00%
Maturity up to 30 days [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	6,508,863,000	[3]
Weighted Average Interest Rate (as a percent)	0.55%
Maturity 30 to 90 Days [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	1,245,007,000	[3]
Weighted Average Interest Rate (as a percent)	1.25%
Maturity Over 90 Days to 12 Months [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	343,902,000	[3]
Weighted Average Interest Rate (as a percent)	1.87%
Maturity Over 12 Months [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	241,525,000	[3]
Weighted Average Interest Rate (as a percent)	2.67%
Interest Rate Reset within 30 Days [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	7,064,598,000	[2]	6,293,802,000	[2]
Weighted Average Interest Rate (as a percent)	0.68%		0.71%
Interest Rate Reset Over 30 Days to 3 Months [Member] | Repurchase agreements
Repurchase Agreements
Balance of repurchase agreements	1,274,699,000	[2]	2,458,670,000	[2]
Weighted Average Interest Rate (as a percent)	1.31%		1.21%
Agency MBS | Repurchase agreements
Repurchase Agreements
Fair Value of securities pledged as collateral under repurchase agreements	6,068,447,000		6,678,384,000
Balance of repurchase agreements	5,750,053,000		6,353,489,000
Weighted average haircut (as a percent)	4.89%	[4]	4.80%	[4]
Non-Agency MBS | Repurchase agreements
Repurchase Agreements
Fair Value of securities pledged as collateral under repurchase agreements	3,663,523,000	[5],[6]	3,463,128,000	[5],[6]
Non-Agency MBS acquired from consolidated VIEs	1,885,000,000		1,860,000,000
Balance of repurchase agreements	2,206,586,000	[5]	1,988,172,000	[5]
Weighted average haircut (as a percent)	32.48%	[4]	30.49%	[4]
Non-Agency MBS | Linked Transactions
Repurchase Agreements
Linked repurchase agreements	102,700,000		35,300,000
U.S. Treasuries | Repurchase agreements
Repurchase Agreements
Fair Value of securities pledged as collateral under repurchase agreements	383,743,000		408,833,000
Balance of repurchase agreements	$ 382,658,000		$ 410,811,000
Weighted average haircut (as a percent)	1.65%	[4]	1.74%	[4]

[1] The fair value of securities pledged against the Company’s repurchase agreements was $10.116 billion and $10.550 billion at December 31, 2013 and 2012, respectively.

[2] At December 31, 2013 and 2012, the Company had repurchase agreements of $102.7 million and $35.3 million, respectively, that were linked to Non-Agency MBS purchases and accounted for as Linked Transactions, and as such, the linked repurchase agreements are not included in the above table.

[3] At December 31, 2013, the Company had repurchase agreements of $102.7 million that were linked to Non-Agency MBS purchases and accounted for as Linked Transactions, and as such, the linked repurchase agreements are not included in the above table.

[4] Haircut represents the percentage amount by which the collateral value is contractually required to exceed the loan amount on the Company’s repurchase agreements borrowings.

[5] Does not reflect Non-Agency MBS and repurchase agreement borrowings that are components of Linked Transactions.

[6] Includes $1.885 billion and $1.860 billion of Non-Agency MBS acquired from consolidated VIEs at December 31, 2013 and 2012, respectively, that are eliminated from the Company’s consolidated balance sheets.