Retirement Benefits (Narrative) (Details) (USD $)	3 Months Ended				9 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Nov. 01, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Change Due to Subsequent Interim Measurement	7.87	.041
Retiree Medical Plan, Net Gain Loss at Remeasurement		$ 124,000,000
Retiree medical plan, assumptions used calculating net periodic benefit cost, change due to subsequent interim measurement		3.80%
Defined Benefit Plan, Effect of Settlements and Curtailments on Accumulated Benefit Obligation		(6,600,000,000)			(6,600,000,000)
Defined Benefit Plans, Actuarial Loss at Remeasurement		(1,900,000,000)
Retiree medical plan, effect of plan amendment on accumulated benefit obligation		(1,200,000,000)			(1,200,000,000)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments		1,800,000,000
Recognized Unamortized Prior Service Cost		(58,000,000)
Retiree Medical Plan, Plan Amendment Gain		1,900,000,000
Recognized Unamortized Prior Service Cost - Retiree Medical		157,000,000
Employer contributions to defined benefit pension plans	86,000,000	86,000,000	86,000,000	6,500,000
Defined Benefit Plan, Contributions by Employer September 2012		6,900,000
Super Saver 401(k) Company Match						5.50%
Principal terms of new business, headcount reduced					10,000
Retiree Medical Plan, Curtailment Gain Loss		(33,000,000)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		8,900,000,000			8,900,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 211,000,000			$ 211,000,000