Basis of Presentation Policies (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	$ 356	$ 0
Operating lease liability	362
Build-to-suit lease liability	389
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	356
Operating lease liability	$ 362
Capitalized construction costs		217
Build-to-suit lease liability		$ 219