Employee Benefit Plans, Pre-Tax Amounts in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Pension Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Prior service credit	$ (166)	$ (210)
Net actuarial (gain) loss	783	876
Total	617	666
Other Postretirement Benefit Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Prior service credit	(75)	(92)
Net actuarial (gain) loss	(31)	(6)
Total	$ (106)	$ (98)