Retirement Benefits (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in plan assets
Fair value of plan assets at end of year	$ 26,279	$ 25,273
Amounts Recognized on the Balance Sheet
Non-current liability	(6,555)	(2,954)
Pension Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	25,972	27,746
Service cost	457	516	522
Interest cost	1,260	1,117	1,184
Plan participants’ contributions	19	12
Plan amendments	0	0
Actuarial (gain) loss	4,273	(2,063)
Benefits paid	(1,409)	(1,365)
Other	(47)	9
Projected benefit obligation at end of year	30,525	25,972	27,746
Change in plan assets
Fair value of plan assets at beginning of year	24,098	22,962
Net gain on plan assets	2,298	1,907
Employer contributions	78	579
Plan participants’ contributions	19	12
Benefits paid	(1,409)	(1,365)
Other	(21)	3
Fair value of plan assets at end of year	25,063	24,098	22,962
Funded status	(5,462)	(1,874)
Amounts Recognized on the Balance Sheet
Non-current assets	3	117
Current liability	(133)	(122)
Non-current liability	(5,332)	(1,869)
Medical and Life Benefits
Change in projected benefit obligation
Projected benefit obligation at beginning of year	2,224	2,448
Service cost	34	36	34
Interest cost	99	96	109
Plan participants’ contributions	50	77
Plan amendments	(92)	0
Actuarial (gain) loss	258	(219)
Benefits paid	(186)	(227)
Other	11	13
Projected benefit obligation at end of year	2,398	2,224	2,448
Change in plan assets
Fair value of plan assets at beginning of year	1,175	1,062
Net gain on plan assets	108	137
Employer contributions	57	114
Plan participants’ contributions	50	77
Benefits paid	(186)	(227)
Other	12	12
Fair value of plan assets at end of year	1,216	1,175	1,062
Funded status	(1,182)	(1,049)
Amounts Recognized on the Balance Sheet
Non-current assets	80	72
Current liability	(39)	(36)
Non-current liability	$ (1,223)	$ (1,085)