Employee Postretirement Benefits (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Pension Plans
Service cost		$ 38	$ 46	$ 53
Interest cost		187	279	257
Expected return on plan assets(a)	[1]	(215)	(332)	(331)
Recognized net actuarial loss		75	100	120
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments		0	0	(32)
Settlements		1,357	20	1
Other		(10)	(3)	1
Net periodic benefit cost		1,432	110	69
Other Postretirement Benefit Plans
Service cost		12	13	17
Interest cost		32	35	32
Expected return on plan assets(a)		0	0	0
Recognized net actuarial loss		0	0	3
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments		0	0	0
Settlements		0	0	0
Other		(1)	(1)	(2)
Net periodic benefit cost		$ 43	$ 47	$ 50

[1] The expected return on plan assets is determined by multiplying the fair value of plan assets at the remeasurement date, typically the prior year-end adjusted for estimated current year cash benefit payments and contributions, by the expected long-term rate of return.