Schedule of Investment Securities Classified as Current and Long-Term (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Amortized Cost	$ 9,018	$ 9,072
Gross Unrealized Gains	218	516
Gross Unrealized Losses	(126)	(41)
Total debt securities, Fair Value	9,110	9,547
Debt Securities \| Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,611	2,931
Gross Unrealized Gains	61	140
Gross Unrealized Losses	(4)	(3)
Total debt securities, Fair Value	2,668	3,068
Debt Securities \| Residential Mortgage-backed securities
Investment [Line Items]
Amortized Cost	13	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total debt securities, Fair Value	13	17
Debt Securities \| Commercial Mortgage-backed securities
Investment [Line Items]
Amortized Cost	1,024	846
Gross Unrealized Gains	2	16
Gross Unrealized Losses	(41)	(19)
Total debt securities, Fair Value	985	843
Debt Securities \| Asset-backed securities
Investment [Line Items]
Amortized Cost	264	28
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(2)	0
Total debt securities, Fair Value	263	29
Debt Securities \| Corporate debt securities
Investment [Line Items]
Amortized Cost	2,873	3,432
Gross Unrealized Gains	140	299
Gross Unrealized Losses	(55)	(13)
Total debt securities, Fair Value	2,958	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	331	365
Gross Unrealized Gains	2	10
Gross Unrealized Losses	(1)	(1)
Total debt securities, Fair Value	332	374
Debt Securities \| U.S. Treasury And Other U.S. Government Corporations And Agencies \| Mortgage-backed securities
Investment [Line Items]
Amortized Cost	1,902	1,453
Gross Unrealized Gains	12	50
Gross Unrealized Losses	(23)	(5)
Total debt securities, Fair Value	$ 1,891	$ 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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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