Employee Benefit Plans, Amounts Recognized in Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	$ (471)	$ 367	$ (228)
Prior service cost arising during the year	(1)		(9)
Remeasurement due to plan amendments		371
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	34	57	34
Prior service cost (credit)	(40)	(33)	(20)
Curtailment and settlement loss	3	1	12
Net gain (loss) on pension and other postretirement benefits, before-tax amount	(475)	763	(211)
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	(434)	290	(245)
Prior service cost arising during the year	(1)	0	(9)
Remeasurement due to plan amendments	0	328	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	35	57	33
Prior service cost (credit)	(22)	(19)	3
Curtailment and settlement loss	3	1	12
Net gain (loss) on pension and other postretirement benefits, before-tax amount	(419)	657	(206)
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	(37)	77	17
Prior service cost arising during the year	0	0	0
Remeasurement due to plan amendments	0	43	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	(1)	0	1
Prior service cost (credit)	(18)	(14)	(23)
Curtailment and settlement loss	0	0	0
Net gain (loss) on pension and other postretirement benefits, before-tax amount	$ (56)	$ 106	$ (5)