Derivative Instruments - Notional Amounts of Derivatives Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional amount	$ 7,928	$ 8,231
Foreign Exchange Contract | Designated as Hedging Instrument | Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Notional amount	1,646	1,510
Foreign Exchange Contract | Designated as Hedging Instrument | Net Investment Hedging
Derivatives, Fair Value [Line Items]
Notional amount	150	804
Foreign Exchange Contract | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional amount	3,732	3,517
Interest Rate Contract | Designated as Hedging Instrument | Fair Value Hedging
Derivatives, Fair Value [Line Items]
Notional amount	$ 2,400	$ 2,400