Benefit Plans (Estimated Future Minimum Benefit Payments to Participants) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 178
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	178
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	177
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	178
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	178
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	883
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	3
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	2
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	2
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	2
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	2
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 3