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Schedule of Investment Securities Classified as Current and Long-Term (Detail) - USD ($) $ in Millions | Mar. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Investment [Line Items] |  |
Amortized Cost | $ 9,451 | $ 9,018
Gross Unrealized Gains | 291 | 218
Gross Unrealized Losses | (64) | (126)
Fair Value | 9,678 | 9,110
Debt Securities | Tax-exempt municipal securities |  |
Investment [Line Items] |  |
Amortized Cost | 2,967 | 2,611
Gross Unrealized Gains | 74 | 61
Gross Unrealized Losses | (3) | (4)
Fair Value | 3,038 | 2,668
Debt Securities | Residential Mortgage-Backed Securities |  |
Investment [Line Items] |  |
Amortized Cost | 11 | 13
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Fair Value | 11 | 13
Debt Securities | Commercial Mortgage-Backed Securities |  |
Investment [Line Items] |  |
Amortized Cost | 885 | 1,024
Gross Unrealized Gains | 7 | 2
Gross Unrealized Losses | (33) | (41)
Fair Value | 859 | 985
Debt Securities | Asset-backed securities |  |
Investment [Line Items] |  |
Amortized Cost | 252 | 264
Gross Unrealized Gains | 1 | 1
Gross Unrealized Losses | 0 | (2)
Fair Value | 253 | 263
Debt Securities | Corporate debt securities |  |
Investment [Line Items] |  |
Amortized Cost | 2,870 | 2,873
Gross Unrealized Gains | 187 | 140
Gross Unrealized Losses | (27) | (55)
Fair Value | 3,030 | 2,958
Debt Securities | U.S. Treasury and other U.S. government corporations and agencies: | U.S. Treasury and agency obligations |  |
Investment [Line Items] |  |
Amortized Cost | 451 | 331
Gross Unrealized Gains | 2 | 2
Gross Unrealized Losses | 0 | (1)
Fair Value | 453 | 332
Debt Securities | U.S. Treasury and other U.S. government corporations and agencies: | Mortgage-backed securities |  |
Investment [Line Items] |  |
Amortized Cost | 2,015 | 1,902
Gross Unrealized Gains | 20 | 12
Gross Unrealized Losses | (1) | (23)
Fair Value | $ 2,034 | $ 1,891

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