Employee Benefit Plans (Narrative) (Details) shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 02, 2018 employee
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement		$ 48
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment		51
Number of retirees | employee					3,800
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax		$ 0	$ (117)	$ 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Increase (Decrease) for Plan Amendment				18
Percentage of non-matching employer's contribution to eligible participants (as a percent)		1.00%
Employer's Common stock held under 401 (k) plan (in shares) | shares		8
Market value of employer's Common stock held under 401 (k) plan		$ 384
Cash dividend received on employer's Common stock held under 401 (k) plan		$ 12
Plan Amendment, Effect on AOCI				164
Plan amendment - effect on funded status				182
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	100.00%	100.00%	100.00%
Defined Benefit Plan, Plan Assets, Payment for Settlement		$ 10	$ 528
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement		(35)	528
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax	$ (117)	(96)	(117)	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment		0	1	0
Accumulated other comprehensive income, unrecognized prior service cost (credit)		133
Accumulated other comprehensive income, unrecognized actuarial losses		572
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		20
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		37
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit obligation	2,000	2,300	2,000
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	1,900	2,200	1,900
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	1,900	2,200	1,900
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	1,400	1,600	1,400
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	1,800	2,100	1,800
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets	1,300	1,500	1,300
Accumulated benefit obligation	$ 2,200	2,600	2,200
Contributions and expected future benefit payments		27
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement		(3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax		(3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment		0	$ 0	$ 0
Accumulated other comprehensive income, unrecognized prior service cost (credit)		15
Accumulated other comprehensive income, unrecognized actuarial losses		47
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		14
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		$ 5
Annual rate of increase in per capita cost of covered health care benefits assumed for transition period (as a percent)		6.90%
Annual rate for per capita cost of covered health care benefits assumed for 2025 and thereafter (as a percent)		4.50%
Year ultimate rate assumed for per capita cost of health care benefits is to be reached		2026
Contributions and expected future benefit payments		$ 16
Other Pension Plan Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	12.00%	11.00%	12.00%
Other Pension Plan Assets [Member] | Foreign Plan [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation		41.00%