Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions |
Sep. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Fair Value Disclosures [Abstract] | ||
| Life insurance contracts and other private equity investments, which approximates fair value | $ 520 | $ 311 |
| X | ||||||||||
- Definition Life insurance contracts and cost method investments fair value disclosure No definition available.
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| X | ||||||||||
- References No definition available.
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