Benefit Plans (Amounts Recorded in Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	$ (2,048)	$ (2,010)
Net loss [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(3,537)	(3,501)
Prior service costs/credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	176	209
Deferred Income Taxes [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	1,313	1,282
Pension [Member] | Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(1,752)	(1,726)
Pension [Member] | Net loss [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(2,857)	(2,805)
Pension [Member] | Prior service costs/credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	(19)	(22)
Pension [Member] | Deferred Income Taxes [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	1,124	1,101
Postretirement Benefit Plan [Member] | Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(233)	(216)
Postretirement Benefit Plan [Member] | Net loss [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(581)	(588)
Postretirement Benefit Plan [Member] | Prior service costs/credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prior service (cost) credit	195	231
Postretirement Benefit Plan [Member] | Deferred Income Taxes [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	153	141
Postemployment Benefit Plans [Member] | Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated other comprehensive losses	(63)	(68)
Postemployment Benefit Plans [Member] | Net loss [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(99)	(108)
Postemployment Benefit Plans [Member] | Prior service costs/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] | Deferred Income Taxes [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred income taxes	$ 36	$ 40