Basis of Presentation and Accounting Policies - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	$ 694
Operating lease liabilities	$ 787
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets		$ 710
Operating lease liabilities		$ 710