v3.8.0.1
Employee Benefit Plans (Amounts Recorded in Accumulated Other Comprehensive Income not yet Recognized) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension Benefits      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year $ 3,456    
Amortization for the period 191 $ 181 $ 168
Deferrals for the period (871) (602)  
Impact of foreign currency changes and other 66 43  
Balance, end of period 3,589 3,456  
Pension Benefits | Transition Obligation      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 0 0 0
Amortization for the period 0 0 0
Deferrals for the period 0 0 0
Impact of foreign currency changes and other 0 0 0
Balance, end of period 0 0 0
Pension Benefits | Prior Service Cost      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year (25) (33) (42)
Amortization for the period 3 6 8
Deferrals for the period 0 3 0
Impact of foreign currency changes and other 0 (1) 1
Balance, end of period (22) (25) (33)
Pension Benefits | Net Actuarial (Gain) Loss      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 3,481 3,173 2,946
Amortization for the period (191) (181) (168)
Deferrals for the period 323 473 405
Impact of foreign currency changes and other (2) 16 (10)
Balance, end of period 3,611 3,481 3,173
Other Postretirement Benefits      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 558    
Amortization for the period 36 41 38
Deferrals for the period 69 46  
Impact of foreign currency changes and other 3 1  
Balance, end of period 354 558  
Other Postretirement Benefits | Transition Obligation      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 0 0 0
Amortization for the period 0 0 0
Deferrals for the period 0 0 0
Impact of foreign currency changes and other 0 0 0
Balance, end of period 0 0 0
Other Postretirement Benefits | Prior Service Cost      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 1 (1) (8)
Amortization for the period 0 2 5
Deferrals for the period 9 0 2
Impact of foreign currency changes and other 0 0 0
Balance, end of period 10 1 (1)
Other Postretirement Benefits | Net Actuarial (Gain) Loss      
Pension And Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Before Tax [Roll Forward]      
Balance, beginning of year 557 621 600
Amortization for the period (36) (41) (38)
Deferrals for the period (179) (23) 63
Impact of foreign currency changes and other 2 0 (4)
Balance, end of period $ 344 $ 557 $ 621