Employee Benefit Plans, Pre-Tax Amounts in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Pension Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	$ 878	$ 783
Prior service credit	(145)	(166)
Total	733	617
Other Postretirement Benefit Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	(66)	(31)
Prior service credit	(58)	(75)
Total	$ (124)	$ (106)