Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014 Investment		Sep. 30, 2013 Investment		Sep. 30, 2014 Investment		Sep. 30, 2013 Investment		Dec. 31, 2013 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 86,211,000		$ 196,782,000		$ 438,116,000		$ 288,132,000
Gross losses on investment securities	(80,567,000)		(8,920,000)		(265,880,000)		(32,271,000)
(Losses) gains on investment securities, net	5,644,000		187,862,000		172,236,000		255,861,000
Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	5,444,000	[1]	143,840,000	[1]
Gross losses on investment securities	(52,264,000)	[1]	(75,000)	[1]
Net gains (losses) on securities	(49,800,000)				(21,700,000)
Realized gains					66,500,000
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	300,000		400,000		700,000		1,200,000
Number of other-than-temporary impaired investments	5		12		22		37
Number of investments	281		293		281		293		288
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	45,000	[2]	317,000	[2]	642,000	[2]	3,167,000	[2]
Gross losses on investment securities	(1,035,000)	[2]	(98,000)	[2]	(18,052,000)	[2]	(2,218,000)	[2]
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	69,044,000		35,826,000		268,483,000		107,546,000
Gross losses on investment securities	(25,584,000)		(1,575,000)		(76,243,000)		(17,020,000)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,779,000		5,180,000		11,334,000		8,020,000
Gross losses on investment securities	(1,233,000)		(587,000)		(3,274,000)		(2,241,000)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities					136,010,000	[1]	148,185,000	[1]
Gross losses on investment securities					(166,051,000)	[1]	(2,609,000)	[1]
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,239,000		6,569,000		8,767,000		14,038,000
Gross losses on investment securities	(179,000)		(1,944,000)		(1,219,000)		(2,421,000)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,641,000		5,016,000		7,706,000		6,806,000
Gross losses on investment securities	(272,000)	[3]	(689,000)	[3]	(781,000)	[3]	(1,462,000)	[3]
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	19,000		34,000		5,174,000		370,000
Gross losses on investment securities	$ 0		$ (3,952,000)		$ (260,000)		$ (4,300,000)

[1] Other securities (fair value accounting) includes net losses of $49.8 million for the three months ended September 30, 2014, and net losses of $21.7 million (including $66.5 million of realized gains) for the nine months ended September 30, 2014, attributable to one public company, FireEye. The extent to which any unrealized gains (or losses) will become realized is subject to a variety of factors, including among other things, changes in prevailing market prices and the timing of any sales or distribution of securities, which are subject to our securities sales and governance processes and may also be constrained by lock-up agreements. None of the FireEye related investments currently are subject to a lock-up agreement.

[2] Includes realized gains (losses) on sales of available-for-sale equity securities that are recognized in the income statement. Unrealized gains (losses) on available-for-sale fixed income and equity securities are recognized in other comprehensive income. The cost basis of available-for-sale securities sold is determined on a specific identification basis.

[3] cludes OTTI losses of $0.3 million from the declines in value for 5 of the 281 investments and $0.4 million from the declines in value for 12 of the 293 investments, respectively. For the nine months ended September 30, 2014 and 2013, includes OTTI losses of $0.7 million from the declines in value for 22 of the 281 investments and $1.2 million from the declines in value for 37 of the 293 investments, respectively. We concluded that any declines in value for the remaining investments were temporary, and as such, no OTTI was required to be recognized.