Employee Benefit Plans (Obligations and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Change in benefit obligations:
Benefit obligations at January 1,	$ 10,741	$ 10,293
Service costs	238	272	$ 275
Interest costs	429	423	414
Plan participants’ contributions	0	0
Net actuarial (gains) losses	595	362
Acquisition, divestitures, settlements and curtailments	(27)	(37)
Change in benefits	0	(11)
Benefits paid	(600)	(582)
Effect of foreign currency translation	33	21
Benefit obligations at December 31,	11,409	10,741	10,293
Change in plan assets
Estimated fair value of plan assets at January 1,	9,009	8,603
Actual return on plan assets	968	618
Acquisition, divestitures and settlements	(30)	(7)
Plan participants’ contributions	0	0
Employer contributions	329	374
Benefits paid	(600)	(582)
Effect of foreign currency translation	12	3
Estimated fair value of plan assets at December 31,	9,688	9,009	8,603
Over (under) funded status at December 31,	(1,721)	(1,732)
Amounts recognized in the consolidated balance sheets
Other assets	59	3
Other liabilities	(1,780)	(1,735)
Net amount recognized	(1,721)	(1,732)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	2,917	2,993
Prior service costs (credit)	(11)	(11)
AOCI, before income tax	2,906	2,982
Accumulated benefit obligation	10,996	10,340
Other Postretirement Benefits
Change in benefit obligations:
Benefit obligations at January 1,	1,759	1,892
Service costs	6	9	17
Interest costs	76	82	89
Plan participants’ contributions	33	30
Net actuarial (gains) losses	(95)	(115)
Acquisition, divestitures, settlements and curtailments	0	18
Change in benefits	0	(43)
Benefits paid	(107)	(111)
Effect of foreign currency translation	2	(3)
Benefit obligations at December 31,	1,674	1,759	1,892
Change in plan assets
Estimated fair value of plan assets at January 1,	1,386	1,382
Actual return on plan assets	125	75
Acquisition, divestitures and settlements	(1)	(1)
Plan participants’ contributions	33	30
Employer contributions	(2)	13
Benefits paid	(107)	(111)
Effect of foreign currency translation	0	(2)
Estimated fair value of plan assets at December 31,	1,434	1,386	$ 1,382
Over (under) funded status at December 31,	(240)	(373)
Amounts recognized in the consolidated balance sheets
Other assets	160	1
Other liabilities	(400)	(374)
Net amount recognized	(240)	(373)
Accumulated other comprehensive (income) loss:
Net actuarial (gains) losses	(55)	89
Prior service costs (credit)	(27)	(49)
AOCI, before income tax	$ (82)	$ 40