Intangible Assets and Goodwill (Changes in Carrying Amount of Goodwill as Allocated to Reportable Segments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning balance	$ 1,227	$ 1,227
Goodwill acquired and other changes during the period	0	0
Ending balance	1,227	1,227
Investor Services [Member]
Goodwill [Roll Forward]
Beginning balance	1,096	1,096
Goodwill acquired and other changes during the period	0	0
Ending balance	1,096	1,096
Advisor Services [Member]
Goodwill [Roll Forward]
Beginning balance	131	131
Goodwill acquired and other changes during the period	0	0
Ending balance	$ 131	$ 131