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, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in benefit obligation
Benefit obligation at the beginning of period	$ (13,185)	$ (13,838)
Service cost	(291)	(314)	$ (284)
Interest cost	(489)	(448)	(476)
Plan participants’ contributions	0	0
Medicare Part D subsidy receipts	0	0
Amendments	0	(3)
Actuarial gains (losses), net	(1,499)	611
Settlements	45	27
Special termination benefits	(26)	(1)
Benefits paid	831	797
Foreign currency changes and other	(23)	(16)
Benefit obligation at end of period	(14,637)	(13,185)	(13,838)
Change in plan assets
Fair value of plan assets at beginning of period	12,807	13,655
Actual return on plan assets	1,681	(224)
Employer contributions	280	219
Plan participants’ contributions	0	0
Disbursement for settlements	(45)	(27)
Benefits paid	(831)	(797)
Foreign currency changes and other	14	(19)
Fair value of plan assets at end of period	13,906	12,807	13,655
Funded status at end of period	(731)	(378)
Amounts recognized in the Statements of Financial Position
Prepaid benefit cost	2,204	2,458
Accrued benefit liability	(2,935)	(2,836)
Net amount recognized	(731)	(378)
Items recorded in “Accumulated other comprehensive income (loss)” not yet recognized as a component of net periodic (benefit) cost:
Prior service cost	(12)	(15)
Net actuarial loss	4,191	3,829
Net amount not recognized	4,179	3,814
Accumulated benefit obligation	(13,934)	(12,560)
Other Postretirement Benefits
Change in benefit obligation
Benefit obligation at the beginning of period	(1,876)	(1,996)
Service cost	(22)	(23)	(20)
Interest cost	(78)	(70)	(82)
Plan participants’ contributions	(21)	(25)
Medicare Part D subsidy receipts	(7)	(9)
Amendments	(27)	(32)
Actuarial gains (losses), net	(124)	96
Settlements	0	0
Special termination benefits	(1)	0
Benefits paid	165	182
Foreign currency changes and other	(2)	1
Benefit obligation at end of period	(1,993)	(1,876)	(1,996)
Change in plan assets
Fair value of plan assets at beginning of period	1,432	1,615
Actual return on plan assets	264	(70)
Employer contributions	5	44
Plan participants’ contributions	21	25
Disbursement for settlements	0	0
Benefits paid	(165)	(182)
Foreign currency changes and other	0	0
Fair value of plan assets at end of period	1,557	1,432	$ 1,615
Funded status at end of period	(436)	(444)
Amounts recognized in the Statements of Financial Position
Prepaid benefit cost	0	4
Accrued benefit liability	(436)	(448)
Net amount recognized	(436)	(444)
Items recorded in “Accumulated other comprehensive income (loss)” not yet recognized as a component of net periodic (benefit) cost:
Prior service cost	65	41
Net actuarial loss	341	408
Net amount not recognized	406	449
Accumulated benefit obligation	(1,993)	(1,877)
Annuity Contracts | Pension Benefits
Change in benefit obligation
Benefit obligation at the beginning of period	(18)
Benefit obligation at end of period	$ (22)	$ (18)