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Income Taxes, Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Other income tax disclosures      
Net accrued interest and penalties $ 19 $ 15  
Interest and penalties expense related to unrecognized income tax benefits 3 (2) $ 1
Effect of unrecognized tax benefit on income tax expense $ 38 $ 29 $ 25
Federal income tax rate 35.00% 35.00% 35.00%
Future tax year      
Other income tax disclosures      
Federal income tax rate 21.00%    
State      
Other income tax disclosures      
All audit periods prior to this year are closed 2013    
Federal      
Other income tax disclosures      
All audit periods prior to this year are closed 2013