Financial Instruments (Fair Values of Outstanding Derivative Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative Assets:
Derivative assets	$ 596	$ 628
Derivative Liabilities:
Derivative liabilities	13	16
Level 2
Derivative Assets:
Derivative assets	596	628
Derivative Liabilities:
Derivative liabilities	13	16
Level 2 | Foreign exchange contracts | Prepaid revenue share, expenses and other assets, current and non-current
Derivative Assets:
Derivative assets	596	628
Level 2 | Foreign exchange contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	13	14
Level 2 | Interest rate contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	0	2
Fair Value of Derivatives Designated as Hedging Instruments | Level 2
Derivative Assets:
Derivative assets	539	626
Derivative Liabilities:
Derivative liabilities	4	3
Fair Value of Derivatives Designated as Hedging Instruments | Level 2 | Foreign exchange contracts | Prepaid revenue share, expenses and other assets, current and non-current
Derivative Assets:
Derivative assets	539	626
Fair Value of Derivatives Designated as Hedging Instruments | Level 2 | Foreign exchange contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	4	1
Fair Value of Derivatives Designated as Hedging Instruments | Level 2 | Interest rate contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	0	2
Fair Value of Derivatives Not Designated as Hedging Instruments | Level 2
Derivative Assets:
Derivative assets	57	2
Derivative Liabilities:
Derivative liabilities	9	13
Fair Value of Derivatives Not Designated as Hedging Instruments | Level 2 | Foreign exchange contracts | Prepaid revenue share, expenses and other assets, current and non-current
Derivative Assets:
Derivative assets	57	2
Fair Value of Derivatives Not Designated as Hedging Instruments | Level 2 | Foreign exchange contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	9	13
Fair Value of Derivatives Not Designated as Hedging Instruments | Level 2 | Interest rate contracts | Accrued expenses and other liabilities, current and non-current
Derivative Liabilities:
Derivative liabilities	$ 0	$ 0