Fair Value Measurements - Summary of Fair Value and Carrying Value of Financial Assets and Liabilities (Footnotes) (Details) - USD ($) $ in Millions |
Sep. 30, 2018 |
Dec. 31, 2017 |
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| Fair Value Disclosures [Abstract] | ||
| Amortized cost of investments | $ 169 | $ 153 |
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- Definition This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- References No definition available.
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