Benefit Plans (Estimated Future Minimum Benefit Payments to Participants) (Details) $ in Millions	Dec. 31, 2015 USD ($)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 180
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	183
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	184
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	183
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	185
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	915
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	4
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	4
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	3
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	3
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	2
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 7