Retirement Benefits (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Unamortized Benefit plan Costs (Table Amounts) [Abstract]
Change in net actuarial loss	$ (571)	$ 912	$ 501
Amortization of:
Prior service credit	79	82	88
Net loss from previous years	(721)	(730)	(709)
Tax expense (benefit) related to above items	383	(89)	45
Change in unamortized benefit plan costs	(830)	175	(75)
Pension Benefits
Changes in Unamortized Benefit plan Costs (Table Amounts) [Abstract]
Change in net actuarial loss	(476)	1,003	626
Amortization of:
Prior service credit	57	60	60
Net loss from previous years	(712)	(714)	(682)
Tax expense (benefit) related to above items	365	(121)	(1)
Change in unamortized benefit plan costs	(766)	228	3
Medical and Life Benefits
Changes in Unamortized Benefit plan Costs (Table Amounts) [Abstract]
Change in net actuarial loss	(95)	(91)	(125)
Amortization of:
Prior service credit	22	22	28
Net loss from previous years	(9)	(16)	(27)
Tax expense (benefit) related to above items	18	32	46
Change in unamortized benefit plan costs	$ (64)	$ (53)	$ (78)