Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Securities (Parenthetical) (Detail) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
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| Fair Value Disclosures [Abstract] | ||
| Investment held for more than 12 months | $ 46 | $ 10 |
| Securities in unrealized loss position | $ 2 | $ 1 |
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- References No definition available.
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