Accounts Receivable and Finance Receivables - Finance receivables by delinquency aging category (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 30, 2017
Finance receivables held for investment by delinquency aging
60 + days contractual delinquency as a percentage of finance receivables	6.57%	4.00%
Less than 31 days past due
Finance receivables held for investment by delinquency aging
Financing receivable held for investment	$ 705	$ 791
31-60 days past due
Finance receivables held for investment by delinquency aging
Financing receivable held for investment	35	25
61- 90 days past due
Finance receivables held for investment by delinquency aging
Financing receivable held for investment	40	14
Over 90 days past due
Finance receivables held for investment by delinquency aging
Financing receivable held for investment	$ 12	$ 20