Accounts Payable and Other Current Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts Payable and Other Current Liabilities [Abstract]
Short-term Lease Commitment, Amount	$ 474	$ 0
Short-term operating lease liabilities	415	371
Accounts payable	234	208
Accrued marketing and commissions, current	194	192
Employee-related Liabilities, Current	148	200
Deferred Revenue, Current	176	140
Public liability and property damage insurance liabilities, current	149	149
Other	445	433
Accounts payable and other current liabilities	$ 2,235	$ 1,693