Investment Securities Summary of Unrealized Losses on Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	$ 6,886,836	[1]	$ 637,004
Less than 12 months - Unrealized Losses	(152,383)	[1]	(1,663)
12 months or longer - Fair Value of Investments	154,250	[1]	8,163
12 months or longer - Unrealized Losses	(8,015)	[1]	(270)
Fair Value of Investments	7,041,086	[1]	645,167
Unrealized Losses	(160,398)	[1]	(1,933)
U.S. agency debentures
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	1,821,045
Less than 12 months - Unrealized Losses	(40,785)
12 months or longer - Fair Value of Investments	0
12 months or longer - Unrealized Losses	0
Fair Value of Investments	1,821,045
Unrealized Losses	(40,785)
Residential mortgage-backed securities | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	1,480,870		22,831
Less than 12 months - Unrealized Losses	(14,029)		(107)
12 months or longer - Fair Value of Investments	19,830		0
12 months or longer - Unrealized Losses	(2,112)		0
Fair Value of Investments	1,500,700		22,831
Unrealized Losses	(16,141)		(107)
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Fixed rate
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	2,098,137		461,397
Less than 12 months - Unrealized Losses	(79,519)		(995)
12 months or longer - Fair Value of Investments	134,420		0
12 months or longer - Unrealized Losses	(5,903)		0
Fair Value of Investments	2,232,557		461,397
Unrealized Losses	(85,422)		(995)
Residential mortgage-backed securities | Agency-issued collateralized mortgage obligations | Variable rate
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	109,699		0
Less than 12 months - Unrealized Losses	(123)		0
12 months or longer - Fair Value of Investments	0		7,908
12 months or longer - Unrealized Losses	0		(4)
Fair Value of Investments	109,699		7,908
Unrealized Losses	(123)		(4)
Agency-issued commercial mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	464,171		150,581
Less than 12 months - Unrealized Losses	(17,423)		(489)
12 months or longer - Fair Value of Investments	0		0
12 months or longer - Unrealized Losses	0		0
Fair Value of Investments	464,171		150,581
Unrealized Losses	(17,423)		(489)
Municipal bonds and notes
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	3,404		2,098
Less than 12 months - Unrealized Losses	(21)		(11)
12 months or longer - Fair Value of Investments	0		0
12 months or longer - Unrealized Losses	0		0
Fair Value of Investments	3,404		2,098
Unrealized Losses	(21)		(11)
Equity securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months - Fair Value of Investments	909,510		97
Less than 12 months - Unrealized Losses	(483)		(61)
12 months or longer - Fair Value of Investments	0		255
12 months or longer - Unrealized Losses	0		(266)
Fair Value of Investments	909,510		352
Unrealized Losses	$ (483)		$ (327)

[1] As of December 31, 2013, we identified a total of 220 investments that were in unrealized loss positions, of which eight investments totaling $154 million with unrealized losses of $8 million have been in an impaired position for a period of time greater than 12 months. As of December 31, 2013, we do not intend to sell any impaired debt or equity securities prior to recovery of our adjusted cost basis, and it is more likely than not that we will not be required to sell any of our securities prior to recovery of our adjusted cost basis. Based on our analysis as of December 31, 2013, we deem all impairments to be temporary, and therefore changes in value for our temporarily impaired securities as of the same date are included in other comprehensive income. Market valuations and impairment analyses on assets in the available-for-sale securities portfolio are reviewed and monitored on a quarterly basis.