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Investment Securities (Details 1) - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Available-for-sale investment securities with gross unrealized losses and length of time    
Estimated Fair Value, Less than 12 months $ 0 $ 224
Estimated Fair Value, 12 months or more 1,050 873
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]    
Gross Unrealized Losses, Less than 12 Months 0 (2)
Gross Unrealized Losses, 12 months or more (10) (16)
U.S. States and Political Subdivisions Debt Securities [Member]    
Available-for-sale investment securities with gross unrealized losses and length of time    
Estimated Fair Value, Less than 12 months 0 0
Estimated Fair Value, 12 months or more 52 82
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]    
Gross Unrealized Losses, Less than 12 Months 0 0
Gross Unrealized Losses, 12 months or more (1) (1)
U.S. Government treasury obligations [Member]    
Available-for-sale investment securities with gross unrealized losses and length of time    
Estimated Fair Value, Less than 12 months 0 224
Estimated Fair Value, 12 months or more 998 791
Available For Sale Securities Continuous Unrealized Aggregate Losses [Abstract]    
Gross Unrealized Losses, Less than 12 Months 0 (2)
Gross Unrealized Losses, 12 months or more $ (9) $ (15)