Employee Benefit Plans, Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net (gain) loss reclassified into income:
Net gain (loss) on pension and other postretirement benefits, before-tax amount	$ 57	$ (475)	$ 763
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	24	(434)	290
Prior service cost arising during the year	(22)	(1)	0
Remeasurement due to plan amendments	0	0	328
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	62	35	57
Prior service credit	(22)	(22)	(19)
Curtailment and settlement loss	7	3	1
Net gain (loss) on pension and other postretirement benefits, before-tax amount	49	(419)	657
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	26	(37)	77
Prior service cost arising during the year	0	0	0
Remeasurement due to plan amendments	0	0	43
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	0	(1)	0
Prior service credit	(18)	(18)	(14)
Curtailment and settlement loss	0	0	0
Net gain (loss) on pension and other postretirement benefits, before-tax amount	$ 8	$ (56)	$ 106