v3.8.0.1
Employee Benefit Plans (Status of Prepaid Benefits Costs and Accrued Benefit Liabilities Included in Other Assets and Other Liabilities) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension Benefits      
Change in benefit obligation      
Benefit obligation at the beginning of period $ (12,917) $ (12,221)  
Service cost (284) (253) $ (244)
Interest cost (476) (498) (469)
Plan participants’ contributions 0 0  
Medicare Part D subsidy receipts 0 0  
Amendments 0 (3)  
Actuarial gains (losses), net (871) (602)  
Settlements 57 24  
Special termination benefits (4) (2)  
Benefits paid 723 681  
Foreign currency changes and other (66) (43)  
Benefit obligation at end of period (13,838) (12,917) (12,221)
Change in plan assets      
Fair value of plan assets at beginning of period 12,861 12,541  
Actual return on plan assets 1,329 883  
Employer contributions 202 187  
Plan participants’ contributions 0 0  
Disbursement for settlements (57) (24)  
Benefits paid (723) (681)  
Foreign currency changes and other 43 (45)  
Fair value of plan assets at end of period 13,655 12,861 12,541
Funded status at end of period (183) (56)  
Amounts recognized in the Statements of Financial Position      
Prepaid benefit cost 2,645 2,538  
Accrued benefit liability (2,828) (2,594)  
Net amount recognized (183) (56)  
Items recorded in “Accumulated other comprehensive income (loss)” not yet recognized as a component of net periodic (benefit) cost:      
Transition obligation 0 0  
Prior service cost (22) (25)  
Net actuarial loss 3,611 3,481  
Net amount not recognized 3,589 3,456  
Accumulated benefit obligation (13,190) (12,300)  
Other Postretirement Benefits      
Change in benefit obligation      
Benefit obligation at the beginning of period (2,084) (2,159)  
Service cost (20) (19) (20)
Interest cost (82) (91) (86)
Plan participants’ contributions (30) (31)  
Medicare Part D subsidy receipts (9) (10)  
Amendments (9) 0  
Actuarial gains (losses), net 69 46  
Settlements 0 0  
Special termination benefits 0 0  
Benefits paid 172 181  
Foreign currency changes and other (3) (1)  
Benefit obligation at end of period (1,996) (2,084) (2,159)
Change in plan assets      
Fair value of plan assets at beginning of period 1,531 1,584  
Actual return on plan assets 212 82  
Employer contributions 14 15  
Plan participants’ contributions 30 31  
Disbursement for settlements 0 0  
Benefits paid (172) (181)  
Foreign currency changes and other 0 0  
Fair value of plan assets at end of period 1,615 1,531 $ 1,584
Funded status at end of period (381) (553)  
Amounts recognized in the Statements of Financial Position      
Prepaid benefit cost 0 0  
Accrued benefit liability (381) (553)  
Net amount recognized (381) (553)  
Items recorded in “Accumulated other comprehensive income (loss)” not yet recognized as a component of net periodic (benefit) cost:      
Transition obligation 0 0  
Prior service cost 10 1  
Net actuarial loss 344 557  
Net amount not recognized 354 558  
Accumulated benefit obligation $ (1,995) $ (2,084)