Schedule of Investment Securities Classified as Current and Long-Term (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Amortized Cost	$ 8,624	$ 9,072
Gross Unrealized Gains	348	516
Gross Unrealized Losses	(92)	(41)
Fair Value	8,880	9,547
Debt Securities \| Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,563	2,931
Gross Unrealized Gains	92	140
Gross Unrealized Losses	(14)	(3)
Fair Value	2,641	3,068
Debt Securities \| Residential Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	14	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	14	17
Debt Securities \| Commercial Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	965	846
Gross Unrealized Gains	9	16
Gross Unrealized Losses	(30)	(19)
Fair Value	944	843
Debt Securities \| Asset-backed securities
Investment [Line Items]
Amortized Cost	162	28
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Fair Value	163	29
Debt Securities \| Corporate debt securities
Investment [Line Items]
Amortized Cost	3,239	3,432
Gross Unrealized Gains	211	299
Gross Unrealized Losses	(31)	(13)
Fair Value	3,419	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	336	365
Gross Unrealized Gains	1	10
Gross Unrealized Losses	0	(1)
Fair Value	337	374
Debt Securities \| U.S. Treasury and other U.S. government corporations and agencies: \| Mortgage-backed securities
Investment [Line Items]
Amortized Cost	1,345	1,453
Gross Unrealized Gains	34	50
Gross Unrealized Losses	(17)	(5)
Fair Value	$ 1,362	$ 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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