Retirement Benefits Funded Status of Plan Assets (Liabilities) (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets
Fair value of plan assets at beginning of year	$ 32,038
Fair value of plan assets at end of year	35,967	$ 32,038
Amounts Recognized on the Balance Sheet
Non-current liability	(6,498)	(6,979)
Pension Benefits
Change in plan assets
Fair value of plan assets at beginning of year	30,646	27,150
Net gain on plan assets	4,802	5,025
Employer contributions	851	221
Participant contributions	8	8
Benefits paid	(1,865)	(1,763)
Acquired plan assets	0	0
Other	10	5
Fair value of plan assets at end of year	34,452	30,646	$ 27,150
Change in projected benefit obligation
Projected benefit obligation at beginning of year	36,914	32,231
Service cost	409	367	404
Interest cost	1,226	1,360	1,226
Participant contributions	8	8
Actuarial loss	3,455	4,708
Benefits paid	(1,865)	(1,763)
Acquired benefit obligation	0	0
Other	35	3
Projected benefit obligation at end of year	40,182	36,914	32,231
Funded status	(5,730)	(6,268)
Amounts Recognized on the Balance Sheet
Non-current assets	211	124
Current liability	(180)	(173)
Non-current liability	(5,761)	(6,219)
Medical and Life Benefits
Change in plan assets
Fair value of plan assets at beginning of year	1,392	1,247
Net gain on plan assets	218	234
Employer contributions	36	42
Participant contributions	24	24
Benefits paid	(155)	(156)
Acquired plan assets	0	0
Other	0	1
Fair value of plan assets at end of year	1,515	1,392	1,247
Change in projected benefit obligation
Projected benefit obligation at beginning of year	2,048	1,930
Service cost	17	16	21
Interest cost	67	80	76
Participant contributions	24	24
Actuarial loss	115	159
Benefits paid	(155)	(156)
Acquired benefit obligation	0	0
Other	3	(5)
Projected benefit obligation at end of year	2,119	2,048	$ 1,930
Funded status	(604)	(656)
Amounts Recognized on the Balance Sheet
Non-current assets	179	151
Current liability	(46)	(47)
Non-current liability	$ (737)	$ (760)