Other Liabilities - Schedule of Other Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other Liabilities Disclosure [Abstract]
Program surplus	$ 549	$ 446
Pension obligations	165	215
Other long-term tax liabilities	397	480
Deferred employee compensation and benefits	117	113
Insurance reserves	162	131
Other	80	107
Other liabilities, noncurrent	$ 1,470	$ 1,492