Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 93	$ 81	$ 92
Interest cost	179	185	174
Expected return on plan assets	(262)	(253)	(248)
Prior service credit	(1)	(1)	(1)
Actuarial (gain) loss	55	32	74
Curtailment gain			1
Net periodic benefit cost (income)	64	44	92
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	21	19	24
Interest cost	47	50	48
Expected return on plan assets	(75)	(72)	(68)
Prior service credit	(5)	(5)	(5)
Actuarial (gain) loss	(6)	(11)	5
Curtailment gain			0
Net periodic benefit cost (income)	$ (18)	$ (19)	$ 4