Summary of Significant Accounting Policies Accounting Standards Adoption 2016-02 (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets, net	$ 455
Operating Lease, Liability	$ 504
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets, net		$ 441
Operating Lease, Liability		$ 490