Basis of Presentation - Narrative (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2016
Adoption of ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment of accounting principle		$ (149)
Retained Earnings | Adoption of ASU 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment of accounting principle	$ 372
Retained Earnings | Adoption of ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment of accounting principle	$ 4
Retained Earnings | Adoption of ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment of accounting principle		$ (149)	$ 264