Employee Benefit Plans (Narrative) (Details) - USD ($)				1 Months Ended	12 Months Ended
	Jan. 01, 2018	Jan. 01, 2017	Jan. 01, 2016	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fixed earnings credit given to all new participants in pension and postretirement plans					3.00%
Minimum annual earnings credit per participant					$ 2,000
Percentage of bonds with highest yields excluded from calculation of yield curve for pension plan assumptions					10.00%
Percentage of bonds with lowest yields excluded from calculation of yield curve for pension plan assumptions					40.00%
Expected long-term return on plan assets	6.00%	6.38%	6.75%
Expected long-term return on plan assets in 2019					5.75%
Defined Contribution Plan, eligible compensation for deferral in absence of election otherwise (percent)					4.00%
Defined Contribution Plan, employee benefit plan expense					$ 139,000,000	$ 125,000,000	$ 122,000,000
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contribution				$ 200,000,000	$ 200,000,000	200,000,000
Pension plan, decline in discount rate (percent)					0.50%
Nonqualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contribution					$ 24,000,000	$ 24,000,000
Pension plan, decline in discount rate (percent)					0.50%