Postretirement Benefit Plans (Cost of Pension Plans) (Details) - Postretirement Benefit Costs [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefit Plan [Member] | Principal pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 367	$ 299	$ 728	$ 617
Prior service cost amortization	51	54	103	108
Expected return on plan assets	(827)	(800)	(1,652)	(1,601)
Interest cost on benefit obligation	696	687	1,391	1,373
Net actuarial (gain) loss amortization	820	642	1,645	1,283
Net curtailment / other gain	0	0	71	0
Pension plans cost	1,107	882	2,286	1,780
Pension Benefit Plan [Member] | Other Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	95	105	200	219
Prior service cost amortization	0	2	0	3
Expected return on plan assets	(205)	(199)	(414)	(396)
Interest cost on benefit obligation	130	148	263	294
Net actuarial (gain) loss amortization	71	50	145	99
Pension plans cost	91	106	194	219
Retiree Benefit Plan [Member] | Principal Retiree Health and Life Insurance Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	51	40	92	84
Prior service cost amortization	34	99	67	197
Expected return on plan assets	(12)	(13)	(24)	(25)
Interest cost on benefit obligation	100	110	201	220
Net actuarial (gain) loss amortization	2	(43)	3	(86)
Net curtailment / other gain	(196)	0	(192)	0
Pension plans cost	$ (21)	$ 193	$ 147	$ 390