Employee Incentive, Retirement, Deferred Compensation, and Career Achievement Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Service cost	$ 8	$ 6	$ 8
Interest cost	1	1	0
Net benefit cost	$ 9	$ 7	$ 8