Income Taxes, Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits
Unrecognized tax benefits	$ 897	$ 970	$ 941	$ 936
Tax refund claims not yet filed but that we intend to file	(29)	(277)
Interest and penalties	100	88
Liability for unrecognized tax benefits presented in our balance sheets	$ 968	$ 781