Employee Benefit Plans (Obligations and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in benefit obligations:
Benefit obligations at January 1,	$ 10,591	$ 11,409
Service costs	214	223	$ 238
Interest costs	425	391	429
Plan participants’ contributions	0	0
Plan amendments	3	(110)
Net actuarial (gains) losses	1,360	(713)
Acquisition, divestitures, settlements and curtailments	(5)	(6)
Benefits paid	(647)	(623)
Effect of foreign currency translation	9	20
Benefit obligations at December 31,	11,950	10,591	11,409
Change in plan assets
Estimated fair value of plan assets at January 1,	8,948	9,688
Actual return on plan assets	1,619	(423)
Acquisition, divestitures and settlements	(5)	(5)
Plan participants’ contributions	0	0
Employer contributions	311	306
Benefits paid	(647)	(623)
Effect of foreign currency translation	4	5
Estimated fair value of plan assets at December 31,	10,230	8,948	9,688
Over (under) funded status at December 31,	(1,720)	(1,643)
Amounts recognized in the consolidated balance sheets
Other assets	147	135
Other liabilities	(1,867)	(1,778)
Net amount recognized	(1,720)	(1,643)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	3,009	2,979
Prior service costs (credit)	(100)	(118)
AOCI, before income tax	2,909	2,861
Accumulated benefit obligation	11,616	10,301
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations at January 1,	1,324	1,674
Service costs	5	6	6
Interest costs	53	55	76
Plan participants’ contributions	32	30
Plan amendments	0	(7)
Net actuarial (gains) losses	(31)	(348)
Acquisition, divestitures, settlements and curtailments	(3)	13
Benefits paid	(93)	(97)
Effect of foreign currency translation	2	(2)
Benefit obligations at December 31,	1,289	1,324	1,674
Change in plan assets
Estimated fair value of plan assets at January 1,	1,360	1,434
Actual return on plan assets	173	(27)
Acquisition, divestitures and settlements	(3)	16
Plan participants’ contributions	32	32
Employer contributions	(2)	4
Benefits paid	(93)	(97)
Effect of foreign currency translation	1	(2)
Estimated fair value of plan assets at December 31,	1,468	1,360	$ 1,434
Over (under) funded status at December 31,	179	36
Amounts recognized in the consolidated balance sheets
Other assets	617	373
Other liabilities	(438)	(337)
Net amount recognized	179	36
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	(359)	(269)
Prior service costs (credit)	(2)	(14)
AOCI, before income tax	(361)	(283)
Changes to financial assumptions [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses	1,200	(796)
Changes to financial assumptions [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses	66	(192)
Changes to demographic assumptions [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses		23
Changes to demographic assumptions [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses		(48)
Changes to Plan Experience [Member] | Pension Benefits
Change in benefit obligations:
Net actuarial (gains) losses	103	60
Changes to Plan Experience [Member] | Other Postretirement Benefits
Change in benefit obligations:
Net actuarial (gains) losses	$ (97)	$ (108)