v3.8.0.1

Short-term and Long-term Investments, Restricted Deposits - Fair Value of Available-for-Sale Investments in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Unrealized Losses |  |
Less than 12 months | $ (17) | $ (59)
12 Months or longer | (14) | (1)
Fair Value |  |
Less than 12 months | 2,658 | 3,218
12 Months or longer | 689 | 89
U.S. Treasury securities and obligations of U.S. government corporations and agencies |  |
Unrealized Losses |  |
Less than 12 months | (1) | (1)
12 Months or longer | (1) | 0
Fair Value |  |
Less than 12 months | 222 | 215
12 Months or longer | 79 | 2
Corporate securities |  |
Unrealized Losses |  |
Less than 12 months | (6) | (12)
12 Months or longer | (4) | (1)
Fair Value |  |
Less than 12 months | 1,044 | 1,020
12 Months or longer | 185 | 39
Municipal securities |  |
Unrealized Losses |  |
Less than 12 months | (7) | (35)
12 Months or longer | (3) | 0
Fair Value |  |
Less than 12 months | 943 | 1,423
12 Months or longer | 175 | 30
Asset-backed securities |  |
Unrealized Losses |  |
Less than 12 months | (1) | (1)
12 Months or longer | 0 | 0
Fair Value |  |
Less than 12 months | 228 | 101
12 Months or longer | 28 | 18
Residential mortgage-backed securities |  |
Unrealized Losses |  |
Less than 12 months | (1) | (5)
12 Months or longer | (5) | 0
Fair Value |  |
Less than 12 months | 109 | 188
12 Months or longer | 171 | 0
Commercial mortgage- backed securities |  |
Unrealized Losses |  |
Less than 12 months | (1) | (5)
12 Months or longer | (1) | 0
Fair Value |  |
Less than 12 months | 112 | 271
12 Months or longer | 51 | 0
Investments |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Investments And Restricted Deposits Contractual Maturities Within One Year Fair Value | $ 474 | $ 500

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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