Employee Benefit Plans (Net Periodic Benefit Costs and Other Changes Recognized in OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other changes in plan assets and benefit obligations recognized in OCI:
Income (loss) from discontinued operations, net of income tax	$ 0	$ 0	$ (986)
Total recognized in OCI	(30)	(263)	(144)
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	214	223	238
Interest costs	425	391	429
Settlement and curtailment costs	0	(1)	4
Expected return on plan assets	(489)	(533)	(516)
Amortization of net actuarial (gains) losses	201	182	195
Amortization of prior service costs (credit)	(15)	(3)	(1)
Total net periodic benefit costs (credit)	336	259	349
Other changes in plan assets and benefit obligations recognized in OCI:
Net actuarial (gains) losses	231	244	149
Prior service costs (credit)	3	(110)	(1)
Amortization of net actuarial (gains) losses	(201)	(182)	(195)
Amortization of prior service (costs) credit	15	3	1
Disposal of subsidiary	0	0	(30)
Total recognized in OCI	48	(45)	(76)
Total recognized in net periodic benefit costs and OCI	384	214	273
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	5	6	6
Interest costs	53	55	76
Settlement and curtailment costs	2	0	2
Expected return on plan assets	(67)	(71)	(72)
Amortization of net actuarial (gains) losses	(48)	(34)	0
Amortization of prior service costs (credit)	(12)	(20)	(22)
Total net periodic benefit costs (credit)	(67)	(64)	(10)
Other changes in plan assets and benefit obligations recognized in OCI:
Net actuarial (gains) losses	(138)	(248)	(146)
Prior service costs (credit)	0	(7)	0
Amortization of net actuarial (gains) losses	48	34	0
Amortization of prior service (costs) credit	12	20	22
Disposal of subsidiary	0	0	2
Total recognized in OCI	(78)	(201)	(122)
Total recognized in net periodic benefit costs and OCI	$ (145)	$ (265)	$ (132)