Summary of Significant Accounting Policies - Principles of Consolidation and Research and Development (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant accounting policies
Maturity period of cash equivalents	90 days
Advertising Costs
Advertising expenses	$ 432	$ 520	$ 426
Research and Development
Research and development costs	$ 24	$ 21	$ 24
Minimum
Property and Equipment
Useful life of property and equipment	2 years
Business Combinations
Amortization of finite lived intangible assets useful life	5 years
Maximum
Property and Equipment
Useful life of property and equipment	40 years
Business Combinations
Amortization of finite lived intangible assets useful life	20 years
Long-Term Deferred Revenue, Distribution and Carriage Payments
Deferred upfront payment, amortization period	10 years