Retirement Benefits Unamortized Prior Service Credit Rollforward (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amortization of:
Prior service credit	$ 55	$ 62	$ 79
Tax expense (benefit) related to above items	(14)	(15)	(19)
Change in unamortized benefit plan costs	41	47	60
Pension Benefits
Amortization of:
Prior service credit	59	59	58
Tax expense (benefit) related to above items	(15)	(14)	(14)
Change in unamortized benefit plan costs	44	45	44
Medical and Life Benefits
Amortization of:
Prior service credit	(4)	3	21
Tax expense (benefit) related to above items	1	(1)	(5)
Change in unamortized benefit plan costs	$ (3)	$ 2	$ 16