Summary of Significant Accounting Policies Indefinite LIved Intangible Assets (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
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| Intangible Assets Disclosure [Abstract] | |||
| Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) | $ 30 | $ 0 | $ 0 |
| X | ||||||||||
- Definition Intangible Assets Disclosure [Abstract] No definition available.
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| X | ||||||||||
- Definition Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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