Employee Benefit Plans, Net Periodic Benefit Costs Amortized from Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Pension Plans [Member]
Pension and Other Postretirement Benefit Plans Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year
Amortization of net actuarial (gain) loss	$ 66
Amortization of prior service credit	(19)
Total	47
Other Postretirement Benefit Plans [Member]
Pension and Other Postretirement Benefit Plans Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year
Amortization of net actuarial (gain) loss	(2)
Amortization of prior service credit	(11)
Total	$ (13)