Retirement Benefits (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets
Fair value of plan assets at beginning of year	$ 28,564
Fair value of plan assets at end of year	28,397	$ 28,564
Amounts Recognized on the Balance Sheet
Non-current liability	(5,755)	(5,511)
Pension Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	31,967	30,409
Service cost	404	388	$ 390
Interest cost	1,226	1,250	1,302
Plan participants’ contributions	9	11
Actuarial (gain) loss	(2,561)	1,544
Benefits paid	(1,685)	(1,617)
Acquired benefit obligation	2,895	0
Other	(24)	(18)
Projected benefit obligation at end of year	32,231	31,967	30,409
Change in plan assets
Fair value of plan assets at beginning of year	27,226	24,384
Net gain on plan assets	(1,043)	3,885
Employer contributions	370	596
Plan participants’ contributions	9	11
Benefits paid	(1,685)	(1,617)
Acquired plan assets	2,293	0
Other	(20)	(33)
Fair value of plan assets at end of year	27,150	27,226	24,384
Funded status	(5,081)	(4,741)
Amounts Recognized on the Balance Sheet
Non-current assets	77	82
Current liability	(164)	(154)
Non-current liability	(4,994)	(4,669)
Medical and Life Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	2,110	2,100
Service cost	21	20	29
Interest cost	76	85	95
Plan participants’ contributions	25	24
Actuarial (gain) loss	(211)	26
Benefits paid	(148)	(144)
Acquired benefit obligation	50	0
Other	7	(1)
Projected benefit obligation at end of year	1,930	2,110	2,100
Change in plan assets
Fair value of plan assets at beginning of year	1,338	1,208
Net gain on plan assets	(65)	208
Employer contributions	38	45
Plan participants’ contributions	25	24
Benefits paid	(148)	(144)
Acquired plan assets	58	0
Other	1	(3)
Fair value of plan assets at end of year	1,247	1,338	$ 1,208
Funded status	(683)	(772)
Amounts Recognized on the Balance Sheet
Non-current assets	124	112
Current liability	(46)	(42)
Non-current liability	$ (761)	$ (842)