Quarterly report pursuant to Section 13 or 15(d)

Derivatives - Derivatives Designated as Accounting Hedges - Fair Value Hedges (Details)

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Derivatives - Derivatives Designated as Accounting Hedges - Fair Value Hedges (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Effect of Fair Value Hedges on Results of Operations [Abstract]        
Derivative $ 1,095 $ 545 $ 491 $ 3,896
Hedged Item (1,230) (687) (840) (4,257)
Hedge Ineffectiveness (135) (142) (349) (361)
Interest rate risk on long-term debt | Interest expense        
Effect of Fair Value Hedges on Results of Operations [Abstract]        
Derivative 272 1,263 (478) 3,924
Hedged Item (422) (1,380) 144 (4,234)
Hedge Ineffectiveness (150) (117) (334) (310)
Interest rate and foreign currency risk on long-term debt | Interest expense        
Effect of Fair Value Hedges on Results of Operations [Abstract]        
Derivative 901 (495) 1,024 344
Hedged Item (877) 487 (1,010) (359)
Hedge Ineffectiveness 24 (8) 14 (15)
Interest rate risk on AFS securities | Interest income        
Effect of Fair Value Hedges on Results of Operations [Abstract]        
Derivative (80) (215) (63) (366)
Hedged Item 70 198 33 330
Hedge Ineffectiveness (10) (17) (30) (36)
Price risk on commodity inventory | Trading gain (loss)        
Effect of Fair Value Hedges on Results of Operations [Abstract]        
Derivative 2 (8) 8 (6)
Hedged Item (1) $ 8 (7) 6
Hedge Ineffectiveness $ 1   $ 1 $ 0