Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Contract cost capitalized during the period	$ 162	$ 207	$ 183
Amortization expense related to the programs	123	76	$ 28
Total costs capitalized	$ 339	$ 300
Maximum
Summary of Significant Accounting Policies
Period of deferral for the portion of subscriber fees that are deferred	1 year