Employee Benefit Plans (Narrative) (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 02, 2018 employee
Defined Benefit Plan Disclosure [Line Items]
Number of retirees | employee				3,800
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax	$ (117)
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	9
Market value of employer's Common stock held under 401 (k) plan	$ 388
Cash dividend received on employer's Common stock held under 401 (k) plan	$ 13
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%
Defined Benefit Plan, Plan Assets, Payment for Settlement	$ 528	$ 6
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement	528	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax	(117)	0	$ 5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	1	0	$ 0
Accumulated other comprehensive income, unrecognized prior service cost (credit)	150
Accumulated other comprehensive income, unrecognized actuarial losses	517
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year	19
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year	20
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit obligation	2,000	2,700
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	1,900	2,700
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	1,900	2,600
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	1,400	2,000
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	1,800	2,500
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets	1,300	1,900
Accumulated benefit obligation	2,200	3,000
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	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement, after tax	0
Service years			30 years
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	0	$ 0	$ 38
Accumulated other comprehensive income, unrecognized prior service cost (credit)	31
Accumulated other comprehensive income, unrecognized actuarial losses	27
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year	15
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year	$ 2
Annual rate of increase in per capita cost of covered health care benefits assumed for transition period (as a percent)	7.30%
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	$ 13
Other Pension Plan Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset allocation	12.00%	2.00%