v3.19.3.a.u2
Pension And Postretirement Benefits (Other Changes Recognized in Other Comprehensive Income) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]      
Prior service (cost) credit $ 3,457 $ 830 $ 1,083
Amortization of prior service cost (credit) (1,459) (1,322) (988)
Adoption of ASU 2018-02 [1] 0    
ASU 2018-02 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Adoption of ASU 2018-02   1,529  
Pension Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Balance at beginning of year 447 571 575
Prior service (cost) credit 0 (37) (30)
Amortization of prior service cost (credit) (86) (87) (76)
Total recognized in other comprehensive (income) loss (86) (124) (106)
Balance at end of year 361 447 571
Pension Benefit [Member] | ASU 2018-02 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Adoption of ASU 2018-02 0 0 102
Postretirement Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Balance at beginning of year 6,086 6,456 5,089
Prior service (cost) credit 3,457 864 1,120
Amortization of prior service cost (credit) (1,372) (1,234) (907)
Total recognized in other comprehensive (income) loss 2,085 (370) 213
Balance at end of year 8,171 6,086 6,456
Postretirement Benefit [Member] | ASU 2018-02 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Adoption of ASU 2018-02 $ 0 $ 0 $ 1,154
[1]
With the adoption of ASU 2016-01, the unrealized (gains) losses on our equity investments are reclassified to retained earnings (see Note 1).