Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Summary of Significant Accounting Policies
Contract cost capitalized during the period	$ 46	$ 67	$ 128	$ 159
Amortization expense related to the programs	33	$ 21	89	$ 52
Total costs capitalized	$ 340		$ 340		$ 300
Maximum
Summary of Significant Accounting Policies
Period of deferral for the portion of subscriber fees that are deferred			1 year