Description of Business and Accounting Policies - Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Contract with Customer, Refund Liability	$ 623	$ 468	$ 567
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Contract with Customer, Right to Recover Product	519	406	411
Sales Returns and Allowances [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Additions to allowance for returns	2,300	1,800	1,500
Deductions to allowance for returns	$ 2,300	$ 1,900	$ 1,500