Benefit Plans (Amounts Recorded in Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	$ (3,280)	$ (2,682)	$ (1,378)	$ (2,040)
Accumulated Defined Benefit Plans Adjustment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(2,010)	(2,040)	$ (1,273)	$ (2,414)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(3,501)	(3,582)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	209	241
Accumulated Defined Benefit Plans Adjustment, Net Deferred Tax Impact [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	1,282	1,301
Pension [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(1,726)	(1,623)
Pension [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(2,805)	(2,637)
Pension [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	(22)	(23)
Pension [Member] | Accumulated Defined Benefit Plans Adjustment, Net Deferred Tax Impact [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	1,101	1,037
Postretirement Benefit Plan [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(216)	(341)
Postretirement Benefit Plan [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(588)	(823)
Postretirement Benefit Plan [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	231	264
Postretirement Benefit Plan [Member] | Accumulated Defined Benefit Plans Adjustment, Net Deferred Tax Impact [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	141	218
Postemployment Benefit Plans [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(68)	(76)
Postemployment Benefit Plans [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(108)	(122)
Postemployment Benefit Plans [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	0	0
Postemployment Benefit Plans [Member] | Accumulated Defined Benefit Plans Adjustment, Net Deferred Tax Impact [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	$ 40	$ 46