Summary of Significant Accounting Policies - Other Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Advertising expense	$ 310	$ 281	$ 135
Deferred Revenue & Deposits [Abstract]
Deferred revenue, rate payable to developer upon utilization of virtual currency	70.00%
Deferred revenue	$ 62	28
Deposits	28	28
Total deferred revenue and deposits	$ 90	$ 56