Retirement Benefits (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Components of Net Periodic Benefit Cost (Table Amounts) [Abstract]
Service cost	$ 424	$ 446	$ 484
Interest cost	1,234	1,284	1,224
Expected return on plan assets	(1,885)	(1,853)	(1,975)
Amortization of:
Prior service credit	(57)	(60)	(60)
Net loss from previous years	712	714	682
Other	4	0	0
Net periodic benefit cost	432	531	355
Medical and Life Benefits
Components of Net Periodic Benefit Cost (Table Amounts) [Abstract]
Service cost	23	30	35
Interest cost	84	94	94
Expected return on plan assets	(89)	(86)	(89)
Amortization of:
Prior service credit	(22)	(22)	(28)
Net loss from previous years	9	16	27
Other	1	0	0
Net periodic benefit cost	$ 6	$ 32	$ 39