Postretirement Plans (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Y	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Moving average of plan assets, years	5
Amount by which fair value of plan assets exceeds market-related value of plan assets (MRVA)	$ 1,813
Derivative net notional amount for fixed income as percentage of total plan assets	3.50%	18.30%
Derivative net notional amount for global equity, currency overlay and commodities as a percentage of total plan assets	2.00%	(2.20%)
Expense for defined contribution plans	764	742	708
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation (ABO) for all pension plans	75,655	63,491
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Pension Plans [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	48.00%	49.00%
Pension Plans [Member] | Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	5.00%	5.00%
Pension Plans [Member] | Real estate and real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	9.00%	8.00%
Pension Plans [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	5.00%	5.00%
Pension Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	29.00%	29.00%
Pension Plans [Member] | Level 3 [Member] | Fixed Income Securities [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	7	21
Pension Plans [Member] | Level 3 [Member] | Fixed Income Securities [Member] | Mortgage backed and asset backed [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	8
Pension Plans [Member] | Level 3 [Member] | Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(3)
Pension Plans [Member] | Level 3 [Member] | Real estate and real assets [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	198	243
Pension Plans [Member] | Level 3 [Member] | Real estate and real assets [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(38)	71
Pension Plans [Member] | Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(48)	283
Pension Plans [Member] | Level 3 [Member] | Private Equity and Other Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held		422
Pension Plans [Member] | Level 3 [Member] | Equity Securities [Member] | Common Or Collective Or Pooled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(24)
Pension Plans [Member] | Adoption of new mortality assumptions [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	2,500
Other Postretirement Benefits Plans [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	40.00%
Other Postretirement Benefits Plans [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, actual plan asset allocations	60.00%
Other Postretirement Benefits Plans [Member] | Adoption of new mortality assumptions [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	$ 200