Repurchase Agreements (Details) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Repurchase Agreements
Balance of repurchase agreements	$ 8,125,723,000	[1]	$ 8,339,297,000	[1]
Securities Sold under Agreements to Repurchase
Repurchase Agreements
Weighted average remaining term-to-interest rate reset of borrowings under repurchase agreements	26 days		25 days
Effective repricing period	21 months		24 months
Balance of repurchase agreements	8,125,723,000	[2],[3]	8,339,297,000	[2]
Agency Mortgage Backed Securities | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	5,417,797,000		5,750,053,000
Fair Value of securities pledged as collateral under repurchase agreements	5,698,202,000		6,068,447,000
Weighted average haircut (as a percent)	4.70%	[4]	4.89%	[4]
Non-Agency Mortgage Backed Securities | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	2,263,910,000	[5]	2,206,586,000	[5]
Fair Value of securities pledged as collateral under repurchase agreements	3,454,698,000	[5],[6]	3,663,523,000	[5],[6]
Weighted average haircut (as a percent)	28.48%	[4]	32.48%	[4]
Non-Agency MBS acquired from consolidated VIEs	1,276,000,000		1,885,000,000
U.S. Treasuries | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	444,016,000		382,658,000
Fair Value of securities pledged as collateral under repurchase agreements	$ 442,370,000		$ 383,743,000
Weighted average haircut (as a percent)	1.41%	[4]	1.65%	[4]

[1] The fair value of securities pledged against the Company’s repurchase agreements was $9.595 billion and $10.116 billion at September 30, 2014 and December 31, 2013, respectively.

[2] At September 30, 2014 and December 31, 2013, the Company had repurchase agreements of $791.8 million and $102.7 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. (See Note 5)

[3] At September 30, 2014, the Company had repurchase agreements of $791.8 million that were linked to Non-Agency MBS purchases and were accounted for as Linked Transactions, and as such, the linked repurchase agreements are not included in the above table. (See Note 5)

[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 $1.276 billion and $1.885 billion of Non-Agency MBS acquired from consolidated VIEs at September 30, 2014, and December 31, 2013, respectively, that are eliminated from the Company’s consolidated balance sheets.