Retirement Benefits (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in plan assets
Fair value of plan assets at beginning of year	$ 25,103
Fair value of plan assets at end of year	25,592	$ 25,103
Amounts Recognized on the Balance Sheet
Non-current liability	(6,818)	(6,172)
Pension Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	29,182	30,525
Service cost	446	484	$ 457
Interest cost	1,284	1,224	1,260
Plan participants’ contributions	11	10
Actuarial (gain) loss	1,026	(1,602)
Benefits paid	(1,480)	(1,428)
Other	(60)	(31)
Projected benefit obligation at end of year	30,409	29,182	30,525
Change in plan assets
Fair value of plan assets at beginning of year	23,950	25,063
Net gain on plan assets	1,867	(258)
Employer contributions	81	578
Plan participants’ contributions	11	10
Benefits paid	(1,480)	(1,428)
Other	(45)	(15)
Fair value of plan assets at end of year	24,384	23,950	25,063
Funded status	(6,025)	(5,232)
Amounts Recognized on the Balance Sheet
Non-current assets	2	18
Current liability	(146)	(142)
Non-current liability	(5,881)	(5,108)
Medical and Life Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	2,181	2,398
Service cost	30	35	34
Interest cost	94	94	99
Plan participants’ contributions	20	22
Actuarial (gain) loss	(80)	(219)
Benefits paid	(146)	(151)
Other	1	2
Projected benefit obligation at end of year	2,100	2,181	2,398
Change in plan assets
Fair value of plan assets at beginning of year	1,153	1,216
Net gain on plan assets	97	(5)
Employer contributions	83	68
Plan participants’ contributions	20	22
Benefits paid	(146)	(151)
Other	1	3
Fair value of plan assets at end of year	1,208	1,153	$ 1,216
Funded status	(892)	(1,028)
Amounts Recognized on the Balance Sheet
Non-current assets	87	79
Current liability	(42)	(43)
Non-current liability	$ (937)	$ (1,064)