Summary of Significant Accounting Policies (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Loss
Unamortized benefit plan costs, net of tax benefit of $3,395 in 2014 and $1,972 in 2013	$ (5,316)	$ (3,000)
Cumulative translation adjustment	(41)	18
Net unrealized gain (loss) on marketable securities and cash flow hedges, net of tax	1	(2)
Total accumulated other comprehensive loss	(5,356)	(2,984)
Unamortized benefit plan costs - Tax Benefit	3,395	1,972
Unamortized benefit plan, actuarial loss, net of tax	5,600	3,300
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	$ 145	$ 319	$ 204