Schedule of Investment Securities Classified as Current and Long-Term (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment [Line Items]
Amortized Cost	$ 9,119	$ 8,928
Gross Unrealized Gains	736	542
Gross Unrealized Losses	(8)	(17)
Total debt securities, Fair Value	9,847	9,453
Debt Securities \| Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,890	2,709
Gross Unrealized Gains	185	149
Gross Unrealized Losses	(4)	(2)
Total debt securities, Fair Value	3,071	2,856
Debt Securities \| Residential Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	33	46
Gross Unrealized Gains	2	0
Gross Unrealized Losses	(1)	(2)
Total debt securities, Fair Value	34	44
Debt Securities \| Commercial Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	615	356
Gross Unrealized Gains	44	25
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	659	381
Debt Securities \| Asset-backed Securities
Investment [Line Items]
Amortized Cost	66	82
Gross Unrealized Gains	2	1
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	68	83
Debt Securities \| Corporate Debt Securities
Investment [Line Items]
Amortized Cost	3,394	3,329
Gross Unrealized Gains	402	262
Gross Unrealized Losses	(2)	(11)
Total debt securities, Fair Value	3,794	3,580
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| U.S. Treasury And Agency Obligations
Investment [Line Items]
Amortized Cost	602	705
Gross Unrealized Gains	16	20
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	618	725
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	1,519	1,701
Gross Unrealized Gains	85	85
Gross Unrealized Losses	(1)	(2)
Total debt securities, Fair Value	$ 1,603	$ 1,784

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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