Income Tax (Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 1,113	$ 1,322
General business tax credit carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	1,343
General business tax credit carryforward | 2019-2023
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
General business tax credit carryforward | 2024-2028
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
General business tax credit carryforward | 2029-2033
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	203
General business tax credit carryforward | 2034-2038
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	1,140
General business tax credit carryforward | Indefinite
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	25
Foreign Tax Authority | 2019-2023
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Foreign Tax Authority | 2024-2028
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	2
Foreign Tax Authority | 2029-2033
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Foreign Tax Authority | 2034-2038
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Foreign Tax Authority | Indefinite
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	23
Other tax credit carryforward
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	145
Other tax credit carryforward | 2019-2023
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Other tax credit carryforward | 2024-2028
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Other tax credit carryforward | 2029-2033
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Other tax credit carryforward | 2034-2038
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	0
Other tax credit carryforward | Indefinite
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 145