Repurchase Agreements (Details) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Repurchase Agreements
Balance of repurchase agreements	$ 8,384,101,000	[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	28 days		25 days
Effective repricing period	24 months		24 months
Balance of repurchase agreements	8,384,101,000	[2],[3]	8,339,297,000	[2]
Weighted Average Interest Rate (as a percent)	0.69%		0.77%
Overnight | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	0	[3]
Weighted Average Interest Rate (as a percent)	0.00%
Within 30 days | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	6,453,126,000	[3]
Weighted Average Interest Rate (as a percent)	0.47%
Over 30 days to 90 days | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	1,184,772,000	[3]
Weighted Average Interest Rate (as a percent)	1.14%
Over 90 days to 12 months | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	746,203,000	[3]
Weighted Average Interest Rate (as a percent)	1.89%
Within 30 days | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	6,993,651,000	[2]	7,064,598,000	[2]
Weighted Average Interest Rate (as a percent)	0.57%		0.68%
Over 30 days to 3 months | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	1,175,229,000	[2]	1,274,699,000	[2]
Weighted Average Interest Rate (as a percent)	1.14%		1.31%
Over 3 months to 12 months | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	215,221,000	[2]	0	[2]
Weighted Average Interest Rate (as a percent)	1.84%		0.00%
Agency Mortgage Backed Securities | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	5,757,074,000		5,750,053,000
Fair Value of securities pledged as collateral under repurchase agreements	6,074,987,000		6,068,447,000
Weighted average haircut (as a percent)	4.69%	[4]	4.89%	[4]
Non Agency Mortgage Backed Securities | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	2,187,998,000	[5]	2,206,586,000	[5]
Fair Value of securities pledged as collateral under repurchase agreements	3,698,181,000	[5],[6]	3,663,523,000	[5],[6]
Weighted average haircut (as a percent)	32.50%	[4]	32.48%	[4]
Non-Agency MBS acquired from consolidated VIEs	1,955,000,000		1,885,000,000
Non Agency Mortgage Backed Securities | Linked Transactions
Repurchase Agreements
Linked repurchase agreements	387,500,000		102,700,000
U.S. Treasuries | Securities Sold under Agreements to Repurchase
Repurchase Agreements
Balance of repurchase agreements	439,029,000		382,658,000
Fair Value of securities pledged as collateral under repurchase agreements	$ 446,375,000		$ 383,743,000
Weighted average haircut (as a percent)	1.40%	[4]	1.65%	[4]

[1] The fair value of securities pledged against the Company’s repurchase agreements was $10.220 billion and $10.116 billion at June 30, 2014 and December 31, 2013, respectively.

[2] At June 30, 2014 and December 31, 2013, the Company had repurchase agreements of $387.5 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 June 30, 2014, the Company had repurchase agreements of $387.5 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 $1.955 billion and $1.885 billion of Non-Agency MBS acquired from consolidated VIEs at June 30, 2014, and December 31, 2013, respectively, that are eliminated from the Company’s consolidated balance sheets.