Accounting Policies (Details) - USD ($) $ in Millions	Jan. 01, 2019	Mar. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease liability		$ 2,198
Operating		$ 2,041
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease liability	$ 2,100
Operating	2,000
Accounting Standards Update 2016-02 [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of ASU adoptions, pretax	$ 83