Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Increase to liabilities	$ (18)	$ 25
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase to liabilities	250
Employer contributions	3
Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	30
Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Anticipated additional employer contributions	75
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase to liabilities	$ 70