Repurchase Agreements - Narrative (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Repurchase Agreements:
Repurchase agreements - outstanding	$ 69,610,722,000	$ 61,781,001,000	[1]
Repurchase agreements - weighted average borrowing rates	1.61%	2.33%
Repurchase agreements - weighted average remaining maturities (in days)	159 days	204 days
Secured financings and interest rate swaps - collateral held, estimated fair value	73,300,000,000	67,900,000,000
Secured financings and interest rate swaps - collateral held, accrued interest	$ 230,100,000	$ 222,100,000

[1] Derived from the audited consolidated financial statements at December 31, 2013.