Summary of Significant Accounting Policies - Allowance for Sales Returns (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Sales returns	$ 2,336	$ 2,434	$ 1,861
Sales returns, beginning balance		137	98
Additions, charged to earnings			1,027
Deductions			(1,023)
Acquisition of HSN			35
Sales returns, ending balance			137
Stock-based compensation	71	88	123
Cumulative Effect, Period of Adoption, Adjusted Balance
Sales returns, beginning balance	266	267
Additions, charged to earnings	2,336	2,434
Deductions	(2,341)	(2,435)
Sales returns, ending balance	$ 261	$ 266	$ 267