Schedule of Investment Securities Classified as Current and Long-Term (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Amortized Cost	$ 9,050	$ 9,072
Gross Unrealized Gains	553	516
Gross Unrealized Losses	(31)	(41)
Total debt securities, Fair Value	9,572us-gaap_AvailableForSaleSecurities	9,547us-gaap_AvailableForSaleSecurities
Debt Securities \| Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,628	2,931
Gross Unrealized Gains	132	140
Gross Unrealized Losses	(4)	(3)
Total debt securities, Fair Value	2,756	3,068
Debt Securities \| Residential Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	16	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	16	17
Debt Securities \| Commercial Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	890	846
Gross Unrealized Gains	21	16
Gross Unrealized Losses	(20)	(19)
Total debt securities, Fair Value	891	843
Debt Securities \| Asset-backed Securities
Investment [Line Items]
Amortized Cost	138	28
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	139	29
Debt Securities \| Corporate Debt Securities
Investment [Line Items]
Amortized Cost	3,318	3,432
Gross Unrealized Gains	333	299
Gross Unrealized Losses	(5)	(13)
Total debt securities, Fair Value	3,646	3,718
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| U.S. Treasury And Agency Obligations
Investment [Line Items]
Amortized Cost	356	365
Gross Unrealized Gains	10	10
Gross Unrealized Losses	0	(1)
Total debt securities, Fair Value	366	374
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	1,704	1,453
Gross Unrealized Gains	56	50
Gross Unrealized Losses	(2)	(5)
Total debt securities, Fair Value	$ 1,758	$ 1,498

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name Accounting Standards Codification

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