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Note 8. Short And Long-Term Debt Other Debt Facilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity	$ 125
Unsecured Letter of Credit Facility [Member]
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity	74	$ 131
Outstanding letter of credit	69	$ 127
Unsecured Letter of Credit Facility [Member] \| September 2018
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity	8
Unsecured Letter of Credit Facility [Member] \| December 2019
Line of Credit Facility [Line Items]
Letter of Credit, borrowing capacity	$ 66