Employee Benefit Plans (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) year
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer | $	$ 155
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description | $	$ 50
Other Postretirement Benefits | Minimum
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Arrangement with Individual, Requisite Age | year	50
Deferred Compensation Arrangement with Individual, Requisite Service Period	10 years
Other Postretirement Benefits | Maximum
Defined Benefit Plan Disclosure [Line Items]
Deferred Compensation Arrangement with Individual, Requisite Age | year	55
Deferred Compensation Arrangement with Individual, Requisite Service Period	20 years