Postretirement Benefit Plans (Cost of Pension Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Principal pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 291	$ 367	$ 606	$ 728
Prior service cost amortization	76	51	152	103
Expected return on plan assets	(836)	(827)	(1,670)	(1,652)
Interest cost on benefit obligation	735	696	1,469	1,391
Net actuarial gain (loss) amortization	612	820	1,224	1,645
Curtailment loss	(1)	0	(1)	71
Pension plans costs	877	1,107	1,780	2,286
Other pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	118	95	231	200
Prior service cost amortization	0	0	1	0
Expected return on plan assets	(259)	(205)	(522)	(414)
Interest cost on benefit obligation	168	130	340	263
Net actuarial gain (loss) amortization	65	71	129	145
Pension plans costs	92	91	177	194
Principal retiree benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	27	51	52	92
Prior service cost amortization	41	(34)	82	(67)
Expected return on plan assets	(11)	(12)	(22)	(24)
Interest cost on benefit obligation	63	100	126	201
Net actuarial gain (loss) amortization	(14)	2	(27)	3
Curtailment loss	0	196	0	192
Pension plans costs	$ 24	$ (21)	$ 47	$ 147