Significant Accounting Policies - Cumulative effect of the revenue accounting changes made (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Current and long-term assets:
Prepaid expenses and other current assets	$ 292		$ 269
Current and long-term liabilities:
Deferred merchant bookings	4,327		3,219
Deferred income taxes	69		329
Stockholders' equity:
Retained earnings	$ 517		331
ASU 2014-09
Current and long-term assets:
Accounts receivable, net		$ 1,826
Prepaid expenses and other current assets		268
Long-term investments and other assets		842
Current and long-term liabilities:
Deferred merchant bookings		3,838
Accrued expenses and other current liabilities		701
Deferred income taxes		326
Stockholders' equity:
Retained earnings		323
ASU 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Current and long-term assets:
Accounts receivable, net			1,866
Prepaid expenses and other current assets			269
Long-term investments and other assets			845
Current and long-term liabilities:
Deferred merchant bookings			3,219
Accrued expenses and other current liabilities			1,265
Deferred income taxes			329
Stockholders' equity:
Retained earnings			$ 331
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Current and long-term assets:
Accounts receivable, net		(40)
Prepaid expenses and other current assets		(1)
Long-term investments and other assets		(3)
Current and long-term liabilities:
Deferred merchant bookings		619
Accrued expenses and other current liabilities		(564)
Deferred income taxes		(3)
Stockholders' equity:
Retained earnings		$ (8)