Retirement Benefits (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization of:
Prior service credit	$ 79	$ 79	$ 82
Tax expense (benefit) related to above items	(19)	(35)	(20)
Change in unamortized benefit plan costs	60	44	62
Pension Benefits
Amortization of:
Prior service credit	58	57	60
Tax expense (benefit) related to above items	(14)	(26)	(11)
Change in unamortized benefit plan costs	44	31	49
Medical and Life Benefits
Amortization of:
Prior service credit	21	22	22
Tax expense (benefit) related to above items	(5)	(9)	(9)
Change in unamortized benefit plan costs	$ 16	$ 13	$ 13