Annual report pursuant to Section 13 and 15(d)

Accumulated Other Comprehensive Income (Loss) - Change in Accumulated OCI (Details)

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Accumulated Other Comprehensive Income (Loss) - Change in Accumulated OCI (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance $ 266,195 $ 255,615 $ 243,476  
Net change 206 (1,930) (110)  
Ending Balance 267,146 266,195 255,615  
Debit Valuation Adjustments        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (767) (611)    
Cumulative adjustment for accounting change       $ (1,226)
Net change (293) (156) 615  
Ending Balance (1,060) (767) (611)  
Derivatives        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (895) (1,077) (1,661)  
Net change 64 182 584  
Ending Balance (831) (895) (1,077)  
Employee Benefit Plans        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (3,480) (2,956) (3,350)  
Net change 288 (524) 394  
Ending Balance (3,192) (3,480) (2,956)  
Foreign currency        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (879) (792) (669)  
Net change 86 (87) (123)  
Ending Balance (793) (879) (792)  
Accumulated Other Comprehensive Income (Loss)        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (7,288) (5,358) (4,022)  
Cumulative adjustment for accounting change       $ (1,226)
Net change 206 (1,930) (110)  
Ending Balance (7,082) (7,288) (5,358)  
Debt securities | Available-for-sale securities        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance (1,299) 16 1,641  
Net change 91 (1,315) (1,625)  
Ending Balance (1,208) (1,299) 16  
Equity securities | Available-for-sale securities        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Beginning Balance 32 62 17  
Net change (30) (30) 45  
Ending Balance $ 2 $ 32 $ 62