Leases - Schedule of Impact of Lease Standard (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property and equipment, net	$ 1,314		$ 1,394
Operating lease assets, net	809
Total assets	16,096		15,913
Operating lease liabilities	184
Operating lease liabilities, noncurrent	651
Accrued expenses and other current liabilities	1,915		2,267
Other noncurrent liabilities	150		253
Total liabilities	4,960		4,489
Retained earnings	$ 11,140		$ 11,485
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property and equipment, net		$ (81)
Operating lease assets, net		839
Total assets		758
Operating lease liabilities		191
Operating lease liabilities, noncurrent		670
Accrued expenses and other current liabilities		(10)
Other noncurrent liabilities		(95)
Total liabilities		756
Retained earnings		$ 2