Investments - Carrying Value of Equity Investments Without Readily Determinable Fair Values (Details) $ in Millions |
3 Months Ended | 9 Months Ended |
|---|---|---|
|
Sep. 30, 2018
USD ($)
|
Sep. 30, 2018
USD ($)
|
|
| Equity Securities without Readily Determinable Fair Value [Roll Forward] | ||
| Carrying value, beginning of period | $ 859 | $ 872 |
| Additions | 0 | 23 |
| Sales | (718) | (718) |
| Downward adjustments for observable price changes and impairment | 0 | (20) |
| Foreign currency translation and other | (3) | (19) |
| Carrying value, end of period | 138 | 138 |
| Cumulative downward adjustments for price changes and impairment | $ 81 | $ 81 |