Summary of Significant Accounting Policies Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Trade receivables		$ 7,158	$ 6,896
Contract liabilities (included in accrued expenses)	$ 67	$ 75	$ 67
Change in Contract with Customer, Liability [Abstract]
Contract liabilities (included in accrued expenses) beginning balance	67
Loyalty program earnings and gift card issuances	90
Redemption and breakage	(82)
Contract liabilities (included in accrued expenses) ending balance	$ 75

Contract with Customer Liaiblity Redemption and Breakage

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

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Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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