Revenue - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Effect on operating expenses	$ 2,506	$ 2,292	$ 4,927	$ 4,595
Effect on operating income	797	817	1,955	1,581
Cumulative effect recognized on initial application of the new guidance	$ 3,538		$ 3,538		$ 2,709
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Effect on net revenues		(32)		(71)
Effect on operating expenses		(33)		(73)
Effect on operating income		$ 1		$ 2
Cumulative effect recognized on initial application of the new guidance						$ (8)