Repurchase Agreements - Narrative (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013		Jan. 31, 2014
Repurchase Agreements:
Repurchase agreements - outstanding	$ 64,543,949,000	$ 61,781,001,000	[1]	$ 399,500,000
Repurchase agreements - weighted average borrowing rates	2.43%	2.33%
Repurchase agreements - weighted average remaining maturities (in days)	187 days	204 days
Repurchase agreements - collateral held, fair value	68,500,000,000	67,900,000,000
Repurchase agreements - accrued interest	$ 227,000,000	$ 222,100,000

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