Employee Benefit Plans, Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net (gain) loss reclassified into income:
Net gain (loss) on pension and other postretirement benefits, before-tax amount	$ (98)	$ 57	$ (475)
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	(145)	24	(434)
Prior service cost arising during the year	0	(22)	(1)
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	49	62	35
Prior service credit	(20)	(22)	(22)
Curtailment and settlement loss	0	7	3
Net gain (loss) on pension and other postretirement benefits, before-tax amount	(116)	49	(419)
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss) arising during the year	35	26	(37)
Prior service cost arising during the year	0	0	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	(1)	0	(1)
Prior service credit	(16)	(18)	(18)
Curtailment and settlement loss	0	0	0
Net gain (loss) on pension and other postretirement benefits, before-tax amount	$ 18	$ 8	$ (56)