Employee Incentive, Retirement, Deferred Compensation, and Career Achievement Plans (Schedule of Changes in Projected Benefit Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 26	$ 17
Benefit cost	9	7	$ 8
Actuarial (gain)/loss	9	2
Projected benefit obligation at the end of year	$ 44	$ 26	$ 17