Investment Securities (Available-for-sale and Held-to-maturity Securities, Unrealized Losses) (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2016
USD ($)
security
Sep. 30, 2015
USD ($)
Sep. 30, 2016
USD ($)
security
Sep. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]          
Purchase of investment securities available-for-sale     $ 203,000,000 $ 783,000,000  
Sales of AFS securities $ 115,000,000 $ 0 290,000,000 0  
Sales of AFS securities, realized gain (loss) 3,000,000   4,000,000    
Non-cash reclassification of investment securities AFS to HTM   1,100,000,000 0 1,136,000,000  
Transfer of available-for-sale securities to held-to-maturity, premium   8,000,000      
Unrealized holding gain (loss), net of tax included in transfer   5,000,000      
Gain (loss) related to transfer of HTM securities   0      
Purchase of investment securities HTM 0 10,000,000 15,000,000 10,000,000  
Proceeds from sale of held-to-maturity securities 0        
Maturity of HTM securities   25,000,000 126,000,000 38,000,000  
Available-for-sale Securities Pledged as Collateral 918,000,000   918,000,000   $ 14,000,000
Agency - Commercial          
Schedule of Available-for-sale Securities [Line Items]          
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value $ 0   $ 0   $ 0
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Positions | security 0   0   0
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months or Over, Unrealized Loss $ 0   $ 0   $ 0
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value $ 20,000,000   $ 20,000,000   $ 471,000,000
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Positions | security 2   2   27
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss $ 0   $ 0   $ (2,000,000)
Agency - Residential          
Schedule of Available-for-sale Securities [Line Items]          
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value $ 0   $ 0   $ 0
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Positions | security 0   0   0
Held-to-maturity Securities, Unrealized Loss Position with Duration 12 Months or Over, Unrealized Loss $ 0   $ 0   $ 0
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value $ 19,000,000   $ 19,000,000   $ 547,000,000
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Positions | security 2   2   50
Held-to-maturity Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss $ 0   $ 0   $ (4,000,000)
US Government-sponsored Enterprises Debt Securities          
Schedule of Available-for-sale Securities [Line Items]          
Purchase of investment securities available-for-sale 136,000,000 59,000,000 203,000,000 $ 783,000,000  
Non-cash reclassification of investment securities AFS to HTM   $ 462,000,000      
Agency - Commercial          
Schedule of Available-for-sale Securities [Line Items]          
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value $ 6,000,000   $ 6,000,000   $ 0
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Securities | security 1   1   0
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Unrealized Loss $ 0   $ 0   $ 0
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value $ 0   $ 0   $ 482,000,000
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Securities | security 0   0   27
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss $ 0   $ 0   $ (3,000,000)
Agency - Residential          
Schedule of Available-for-sale Securities [Line Items]          
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value $ 0   $ 0   $ 8,000,000
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Securities | security 0   0   2
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Unrealized Loss $ 0   $ 0   $ 0
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value $ 75,000,000   $ 75,000,000   $ 224,000,000
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Securities | security 6   6   15
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss $ 0   $ 0   $ (2,000,000)
Municipal obligations          
Schedule of Available-for-sale Securities [Line Items]          
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Fair Value $ 0   $ 0    
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Number of Securities | security 0   0    
Available-for-sale Securities, Unrealized Loss Position with Duration 12 Months and Over, Unrealized Loss $ 0   $ 0    
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Fair Value $ 1,000,000   $ 1,000,000    
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Number of Securities | security 1   1    
Available-for-Sale Securities, Unrealized Loss Position with Duration Under 12 Months, Unrealized Loss $ 0   $ 0