Benefit Plans (Schedule of estimated amounts to be recognized from Accumulated other comprehensive income into net periodic cost (benefit) during next fiscal year) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	$ 0
Amortization of net actuarial (gain) loss	36
Total estimated amounts to be recognized	36
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	(2)
Amortization of net actuarial (gain) loss	0
Total estimated amounts to be recognized	$ (2)