Benefit Plans (Narrative) (Details) - Pension [Member] $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Additional employer contributions	$ 10
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	10
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	$ 30