Postretirement Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cost of Pension Plans
Prior service cost amortization		$ (646)
Net actuarial (gain) loss amortization		(3,962)
Principal pension plans
Cost of Pension Plans
Prior service cost amortization		(246)
Net actuarial (gain) loss amortization		(3,664)
Other Pension Plan, Defined Benefit [Member]
Cost of Pension Plans
Prior service cost amortization		(7)
Net actuarial (gain) loss amortization		(343)
Principal Retiree Health and Life Insurance Plans [Member]
Cost of Pension Plans
Prior service cost amortization		(393)
Net actuarial (gain) loss amortization		45
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of total pension assets disclosed		99.00%
Pension Plan Participants
Active employees		128,000
Vested former employees		229,000
Retirees and beneficiaries		263,000
Total pension plan participants		620,000
Funding Policy
Amount Expected To Be Contributed To Fund Company Pension Plan	528	0	433
Weighted average discount rate used for determination of costs	7.50%	8.00%	8.00%	8.00%
Pension Benefit Plan [Member] | Postretirement Benefit Costs [Member]
Cost of Pension Plans
Service cost for benefits earned		1,970	1,779	1,498
Prior service cost amortization		253	287	207
Expected return on plan assets		(4,163)	(4,394)	(4,543)
Interest cost on benefit obligation		2,983	2,993	3,176
Net actuarial (gain) loss amortization		4,007	3,701	2,486
Pension plans cost		5,050	4,366	2,824
Pension Benefit Plan [Member] | Principal pension plans
Pension Plan Participants
Active employees		94,000
Vested former employees		184,000
Retirees and beneficiaries		230,000
Total pension plan participants		508,000
Actuarial assumptions
Discount rate		4.85%	3.96%	4.21%	5.28%
Compensation increases		4.00%	3.90%	3.75%	4.25%
Expected return on assets		7.50%	8.00%	8.00%	8.00%
Funding Policy
Expected Future Benefit Payments And Administrative Expenses	244
Expected return on assets		7.50%	8.00%	8.00%	8.00%
Pension Benefit Plan [Member] | Principal pension plans | Postretirement Benefit Costs [Member]
Cost of Pension Plans
Service cost for benefits earned		1,535	1,387	1,195
Prior service cost amortization		246	279	194
Expected return on plan assets		(3,500)	(3,768)	(3,940)
Interest cost on benefit obligation		2,460	2,479	2,662
Net actuarial (gain) loss amortization		3,664	3,421	2,335
Pension plans cost		4,405	3,798	2,446
Pension Benefit Plan [Member] | Other Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Disclosure of other pension plans includes pension plans with pension assets or obligations in excess of threshold amount		40
Minimum Pension Assets Or Obligations		50
Pension Plan Participants
Active employees		34,000
Vested former employees		45,000
Retirees and beneficiaries		33,000
Total pension plan participants		112,000
Actuarial assumptions
Discount rate		4.39%	3.92%	4.42%	5.11%
Compensation increases		3.76%	3.30%	4.31%	4.44%
Expected return on assets		6.92%	6.82%	7.09%	7.25%
Funding Policy
Amount Expected To Be Contributed To Fund Company Pension Plan	800	673
Expected Future Benefit Payments And Administrative Expenses		225
Expected return on assets		6.92%	6.82%	7.09%	7.25%
Pension Benefit Plan [Member] | Other Pension Plan, Defined Benefit [Member] | Postretirement Benefit Costs [Member]
Cost of Pension Plans
Service cost for benefits earned		435	392	303
Prior service cost amortization		7	8	13
Expected return on plan assets		(663)	(626)	(603)
Interest cost on benefit obligation		523	514	514
Net actuarial (gain) loss amortization		343	280	151
Pension plans cost		645	568	378
Retiree Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirees and beneficiaries		198,000
Funding Policy
Weighted average discount rate used for determination of costs		3.77%	3.94%
Retiree Benefit Plan [Member] | Postretirement Benefit Costs [Member]
Cost of Pension Plans
Service cost for benefits earned		229	219	216
Prior service cost amortization		393	518	647
Expected return on plan assets		(60)	(73)	(97)
Interest cost on benefit obligation		410	491	604
Net actuarial (gain) loss amortization		(45)	32	(110)
Net curtailment / other gain		0	(101)	0
Pension plans cost		927	1,086	1,260
Retiree Benefit Plan [Member] | Principal Retiree Health and Life Insurance Plans [Member]
Actuarial assumptions
Discount rate		4.61%	3.74%	4.09%	5.15%
Compensation increases		4.00%	3.90%	3.75%	4.25%
Expected return on assets		7.00%	7.00%	7.00%	8.00%
Funding Policy
Retiree Health Plan Postretirement Health Benefit Contributions		$ 545
Ultimate declining initial healthcare trend rate		5.00%
Expected return on assets		7.00%	7.00%	7.00%	8.00%
Initial healthcare trend rate		6.00%	6.50%	7.00%	7.00%