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Summary of Significant Accounting Policies Fee and Other Income (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Gain Contingencies [Line Items]                      
Fee and other income $ 431 $ 1,194 $ 353 $ 249 $ 414 $ 175 $ 174 $ 203 $ 2,227 $ 966 $ 1,348
Private Label Securities Settlements [Member]                      
Gain Contingencies [Line Items]                      
Fee and other income                 $ 975 $ 245 $ 21