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Fair Value Measurements (Quantitative Information About Level 3 Measurements) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Investment securities available-for-sale [1] $ 10,787 $ 10,519
Recurring    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Investment securities available-for-sale 10,787 10,519
Recurring | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Investment securities available-for-sale 54 77
Recurring | State and municipal securities | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Investment securities available-for-sale [2] $ 7 $ 9
Recurring | State and municipal securities | Minimum | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Unobservable Input, Discount rate [2] 4.00% 3.00%
Unobservable Input, Workout period [2] 1 year 1 year
Recurring | State and municipal securities | Maximum | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Unobservable Input, Discount rate [2] 6.00% 8.00%
Unobservable Input, Workout period [2] 2 years 2 years
Recurring | Equity and other non-debt securities | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Investment securities available-for-sale [2] $ 47 $ 67
Recurring | Equity and other non-debt securities | Minimum | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Unobservable Input, Discount rate [2] 7.00% 4.00%
Unobservable Input, Workout period [2] 1 year 1 year
Recurring | Equity and other non-debt securities | Maximum | Level 3    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Unobservable Input, Discount rate [2] 9.00% 9.00%
Unobservable Input, Workout period [2] 2 years 1 year
[1] Included auction-rate securities at amortized cost and fair value of $55 million and $54 million, respectively, as of December 31, 2016 and $76 million and $77 million, respectively, as of December 31, 2015.
[2] Auction-rate securities.