Benefit Plans (Narrative) (Details) - Pension [Member] $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Additional employer contributions	$ 8
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	20
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	$ 40