Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 108
Interest cost	731	695
Expected return on plan assets	(965)	(1,002)
Amortization of prior service credits	(20)	(14)
Recognized net actuarial loss	161	282
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(92)	69
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	24
Interest cost	49	49
Expected return on plan assets	(2)	(2)
Amortization of prior service credits	(9)	(32)
Recognized net actuarial loss	(11)	(3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	46	36
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	78	82
Operating Income (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	22	22
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	93	42
Other Income [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	27	24
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	15	40
Operating Income (Loss) Before Taxes [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	$ 49	$ 46