Schedule II: Valuation and Qualifying Accounts Schedule II: Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Trade Receivables [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 763	$ 1,032	$ 356
Additions/Charged to Expense	7,682	9,287	6,934
Valuation Allowances and Reserves, Deductions	7,990	9,556	6,258
Balance at End of Period	455	763	1,032
Allowance for Sales Returns [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	195	371	171
Additions/Charged to Expense	23	(141)	219
Valuation Allowances and Reserves, Deductions	56	35	19
Balance at End of Period	162	195	371
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	126	6	9
Additions/Charged to Expense	72	120	0
Valuation Allowances and Reserves, Deductions	36	0	3
Balance at End of Period	$ 162	$ 126	$ 6