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Postretirement Benefit Plans (Accumulated Benefit Obligation) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Pension Benefit Plan [Member] | Principal pension plans [Member]    
Accumulated Benefit Obligation [Abstract]    
Accumulated Benefit Obligation $ 61,631 $ 50,967
Plan Assets For Plans With Assets Less Than Abo [Abstract]    
Accumulated Benefit Obligation 61,631 50,967
Pension Benefit Plan [Member] | Supplemental Employee Retirement Plan, Defined Benefit [Member]    
Accumulated Benefit Obligation [Abstract]    
Accumulated Benefit Obligation 5,070 3,946
Plan Assets For Plans With Assets Less Than Abo [Abstract]    
Accumulated Benefit Obligation 5,070 3,946
Projected benefit obligation 6,632 5,162
Pension Benefit Plan [Member] | Other Pension Plans [Member]    
Accumulated Benefit Obligation [Abstract]    
Accumulated Benefit Obligation 14,790 12,629
Plan Assets For Plans With Assets Less Than Abo [Abstract]    
Accumulated Benefit Obligation 14,790 12,629
Pension Benefit Plan [Member] | Funded Plans With Assets Less Than ABO [Member]    
Accumulated Benefit Obligation [Abstract]    
Accumulated Benefit Obligation 67,676 60,715
Plan Assets For Plans With Assets Less Than Abo [Abstract]    
Defined Benefit Plan Fair Value Of Plan Assets 53,126 57,430
Accumulated Benefit Obligation 67,676 60,715
Projected benefit obligation 70,354 63,532
Pension Benefit Plan [Member] | Unfunded Plans [Member]    
Accumulated Benefit Obligation [Abstract]    
Accumulated Benefit Obligation 6,719 5,243
Plan Assets For Plans With Assets Less Than Abo [Abstract]    
Accumulated Benefit Obligation 6,719 5,243
Projected benefit obligation 8,342 $ 6,512
Retiree Benefit Plan [Member]    
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates    
APBO 1% Increase 977  
APBO 1% Decrease (810)  
Service and interest cost 1% Increase 56  
Service and interest cost 1% Decrease $ (47)