Derivative Instruments - Notional Amounts of Derivatives Outstanding (Details) - USD ($) $ in Millions |
Sep. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Derivatives, Fair Value [Line Items] | ||
| Notional amount | $ 8,110 | $ 6,739 |
| Foreign Exchange Contract | Designated as Hedging Instrument | Cash Flow Hedging | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional amount | 1,857 | 1,990 |
| Foreign Exchange Contract | Designated as Hedging Instrument | Net Investment Hedging | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional amount | 1,002 | 0 |
| Foreign Exchange Contract | Not Designated as Hedging Instrument | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional amount | 2,851 | 2,349 |
| Interest Rate Contract | Designated as Hedging Instrument | Fair Value Hedging | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional amount | $ 2,400 | $ 2,400 |