Schedule of Investment Securities Classified as Current and Long-Term (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Investment [Line Items]
Amortized Cost	$ 8,984	$ 9,119
Gross Unrealized Gains	430	736
Gross Unrealized Losses	(88)	(8)
Total debt securities, Fair Value	9,326	9,847
Debt Securities \| Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,933	2,890
Gross Unrealized Gains	113	185
Gross Unrealized Losses	(18)	(4)
Total debt securities, Fair Value	3,028	3,071
Debt Securities \| Residential Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	27	33
Gross Unrealized Gains	1	2
Gross Unrealized Losses	0	(1)
Total debt securities, Fair Value	28	34
Debt Securities \| Commercial Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	557	615
Gross Unrealized Gains	23	44
Gross Unrealized Losses	(7)	0
Total debt securities, Fair Value	573	659
Debt Securities \| Asset-backed Securities
Investment [Line Items]
Amortized Cost	53	66
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	0
Total debt securities, Fair Value	53	68
Debt Securities \| Corporate Debt Securities
Investment [Line Items]
Amortized Cost	3,423	3,394
Gross Unrealized Gains	239	402
Gross Unrealized Losses	(29)	(2)
Total debt securities, Fair Value	3,633	3,794
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| U.S. Treasury And Agency Obligations
Investment [Line Items]
Amortized Cost	568	602
Gross Unrealized Gains	9	16
Gross Unrealized Losses	(6)	0
Total debt securities, Fair Value	571	618
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	1,423	1,519
Gross Unrealized Gains	44	85
Gross Unrealized Losses	(27)	(1)
Total debt securities, Fair Value	$ 1,440	$ 1,603

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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