Postretirement Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Disclosure of other pension plans includes pension plans with pension assets or obligations in excess of threshold amount	$ 50		$ 50
Defined Benefit Plan, Plan Amendments			586
Defined Benefit Plan Actuarial Gain Loss			290
Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	304	362	921	1,145
Prior service cost amortization	54	62	162	185
Expected return on plan assets	(792)	(875)	(2,393)	(2,625)
Interest cost on benefit obligation	687	615	2,060	1,845
Net actuarial (gain) loss amortization	642	916	1,925	2,748
Net curtailment / other gain	65	0	65	0
Pension plans cost	960	1,080	2,740	3,298
Other Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	91	130	310	330
Prior service cost amortization	1	2	4	6
Expected return on plan assets	(200)	(170)	(596)	(496)
Interest cost on benefit obligation	149	135	443	392
Net actuarial (gain) loss amortization	50	85	149	256
Pension plans cost	91	182	310	488
Principal Retiree Health and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	41	43	125	168
Prior service cost amortization	88	98	285	294
Expected return on plan assets	(12)	(15)	(37)	(45)
Interest cost on benefit obligation	106	101	326	309
Net actuarial (gain) loss amortization	(38)	(16)	(124)	(28)
Net curtailment / other gain	48	0	48	0
Pension plans cost	$ 233	$ 211	$ 623	$ 698