v3.8.0.1
Segment Information (Operating Income of Reportable Segments) (Reconciling Items) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]      
Other trading account assets $ 336 $ (17) $ (524)
Segment Reconciling Items      
Segment Reporting Information [Line Items]      
Terminated hedges of foreign currency earnings (15) 39 284
Current period yield adjustments 434 466 475
Principal source of earnings (8) 74 123
Other trading account assets 184 (95) (94)
Foreign currency exchange movements (135) (154) 69
Other activities $ (20) $ (18) $ 9