Employee Benefit Plans (Obligations and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Change in benefit obligations:
Benefit obligations at January 1,	$ 11,950	$ 10,591
Service costs	226	214	$ 223
Interest costs	363	425	391
Plan participants’ contributions	0	0
Plan amendments	0	3
Net actuarial (gains) losses	928	1,360
Acquisition, divestitures, settlements and curtailments	(55)	(5)
Benefits paid	(589)	(647)
Effect of foreign currency translation	50	9
Benefit obligations at December 31,	12,873	11,950	10,591
Change in plan assets
Estimated fair value of plan assets at January 1,	10,230	8,948
Actual return on plan assets	1,491	1,619
Acquisition, divestitures and settlements	(55)	(5)
Plan participants’ contributions	0	0
Employer contributions	155	311
Benefits paid	(589)	(647)
Effect of foreign currency translation	24	4
Estimated fair value of plan assets at December 31,	11,256	10,230	8,948
Over (under) funded status at December 31,	(1,617)	(1,720)
Amounts recognized in the consolidated balance sheets
Other assets	390	147
Other liabilities	(2,007)	(1,867)
Net amount recognized	(1,617)	(1,720)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	2,780	3,009
Prior service costs (credit)	(86)	(100)
AOCI, before income tax	2,694	2,909
Accumulated benefit obligation	12,510	11,616
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations at January 1,	1,289	1,324
Service costs	5	5	6
Interest costs	42	53	55
Plan participants’ contributions	32	32
Plan amendments	0	0
Net actuarial (gains) losses	(15)	(31)
Acquisition, divestitures, settlements and curtailments	0	(3)
Benefits paid	(101)	(93)
Effect of foreign currency translation	0	2
Benefit obligations at December 31,	1,252	1,289	1,324
Change in plan assets
Estimated fair value of plan assets at January 1,	1,468	1,360
Actual return on plan assets	89	173
Acquisition, divestitures and settlements	0	(3)
Plan participants’ contributions	32	32
Employer contributions	4	(2)
Benefits paid	(101)	(93)
Effect of foreign currency translation	0	1
Estimated fair value of plan assets at December 31,	1,492	1,468	$ 1,360
Over (under) funded status at December 31,	240	179
Amounts recognized in the consolidated balance sheets
Other assets	756	617
Other liabilities	(516)	(438)
Net amount recognized	240	179
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	(327)	(359)
Prior service costs (credit)	1	(2)
AOCI, before income tax	(326)	(361)
Changes to financial assumptions [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses	851	1,200
Changes to financial assumptions [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses	103	66
Changes to demographic assumptions [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses	31
Changes to demographic assumptions [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses	4
Changes to Plan Experience [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses	46	103
Changes to Plan Experience [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses	$ (122)	$ (97)