Employee Benefit Plans - Benefit Obligations, Fair Value of Plan Assets and Funded Status (Details) - USD ($)
$ in Millions |
12 Months Ended |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Pension Benefits |
|
|
|
| Change in Benefit Obligation |
|
|
|
| Benefit obligation at beginning of period |
$ 19,809
|
$ 21,696
|
|
| Service cost |
0
|
0
|
$ 0
|
| Interest cost |
833
|
781
|
853
|
| Actuarial loss (gain) |
1,678
|
(1,560)
|
|
| Benefits paid, including lump sums and annuities |
(1,107)
|
(1,093)
|
|
| Participant contributions |
0
|
0
|
|
| Curtailment |
0
|
0
|
|
| Settlements |
(14)
|
(15)
|
|
| Benefit obligation at end of period |
21,199
|
19,809
|
21,696
|
| Change in Fair Value of Plan Assets |
|
|
|
| Fair value of plan assets at beginning of period |
13,459
|
14,744
|
|
| Actual gain (loss) on plan assets |
2,485
|
(700)
|
|
| Employer contributions |
1,022
|
523
|
|
| Participant contributions |
0
|
0
|
|
| Benefits paid, including lump sums and annuities |
(1,107)
|
(1,093)
|
|
| Settlements |
(14)
|
(15)
|
|
| Fair value of plan assets at end of period |
15,845
|
13,459
|
14,744
|
| Funded Status of Plan |
|
|
|
| Funded status at end of period |
(5,354)
|
(6,350)
|
|
| Other Postretirement and Postemployment Benefits |
|
|
|
| Change in Benefit Obligation |
|
|
|
| Benefit obligation at beginning of period |
3,225
|
3,504
|
|
| Service cost |
83
|
85
|
87
|
| Interest cost |
137
|
126
|
138
|
| Actuarial loss (gain) |
226
|
(142)
|
|
| Benefits paid, including lump sums and annuities |
(315)
|
(306)
|
|
| Participant contributions |
23
|
26
|
|
| Curtailment |
0
|
(68)
|
|
| Settlements |
0
|
0
|
|
| Benefit obligation at end of period |
3,379
|
3,225
|
3,504
|
| Change in Fair Value of Plan Assets |
|
|
|
| Fair value of plan assets at beginning of period |
637
|
866
|
|
| Actual gain (loss) on plan assets |
134
|
(72)
|
|
| Employer contributions |
159
|
152
|
|
| Participant contributions |
23
|
26
|
|
| Benefits paid, including lump sums and annuities |
(346)
|
(335)
|
|
| Settlements |
0
|
0
|
|
| Fair value of plan assets at end of period |
607
|
637
|
$ 866
|
| Funded Status of Plan |
|
|
|
| Funded status at end of period |
$ (2,772)
|
$ (2,588)
|
|