Employee Benefit Plans (Obligations and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Change in benefit obligations:
Benefit obligations at January 1,	$ 11,409	$ 10,741
Service costs	223	238	$ 272
Interest costs	391	429	423
Plan participants’ contributions	0	0
Plan amendments	(110)	0
Net actuarial (gains) losses	(713)	595
Acquisition, divestitures, settlements and curtailments	(6)	(27)
Benefits paid	(623)	(600)
Effect of foreign currency translation	20	33
Benefit obligations at December 31,	10,591	11,409	10,741
Change in plan assets
Estimated fair value of plan assets at January 1,	9,688	9,009
Actual return on plan assets	(423)	968
Acquisition, divestitures and settlements	(5)	(30)
Plan participants’ contributions	0	0
Employer contributions	306	329
Benefits paid	(623)	(600)
Effect of foreign currency translation	5	12
Estimated fair value of plan assets at December 31,	8,948	9,688	9,009
Over (under) funded status at December 31,	(1,643)	(1,721)
Amounts recognized in the consolidated balance sheets
Other assets	135	59
Other liabilities	(1,778)	(1,780)
Net amount recognized	(1,643)	(1,721)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	2,979	2,917
Prior service costs (credit)	(118)	(11)
AOCI, before income tax	2,861	2,906
Accumulated benefit obligation	10,301	10,996
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations at January 1,	1,674	1,759
Service costs	6	6	9
Interest costs	55	76	82
Plan participants’ contributions	30	33
Plan amendments	(7)	0
Net actuarial (gains) losses	(348)	(95)
Acquisition, divestitures, settlements and curtailments	13	0
Benefits paid	(97)	(107)
Effect of foreign currency translation	(2)	2
Benefit obligations at December 31,	1,324	1,674	1,759
Change in plan assets
Estimated fair value of plan assets at January 1,	1,434	1,386
Actual return on plan assets	(27)	125
Acquisition, divestitures and settlements	16	(1)
Plan participants’ contributions	32	33
Employer contributions	4	(2)
Benefits paid	(97)	(107)
Effect of foreign currency translation	(2)	0
Estimated fair value of plan assets at December 31,	1,360	1,434	$ 1,386
Over (under) funded status at December 31,	36	(240)
Amounts recognized in the consolidated balance sheets
Other assets	373	160
Other liabilities	(337)	(400)
Net amount recognized	36	(240)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	(269)	(55)
Prior service costs (credit)	(14)	(27)
AOCI, before income tax	$ (283)	$ (82)