Loans to Banking Clients and Related Allowance for Loan Losses (Changes in Allowance for Loan Losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 48	$ 56	$ 54
Charge-offs	(5)	(11)	(16)
Recoveries	3	4	2
Provision for loan losses	(4)	(1)	16
Balance at end of period	42	48	56
Residential real estate mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	34	36	40
Charge-offs	(3)	(5)	(7)
Recoveries	2	2	2
Provision for loan losses	(4)	1	1
Balance at end of period	29	34	36
Home equity lines of credit [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	14	20	14
Charge-offs	(2)	(6)	(9)
Recoveries	1	2
Provision for loan losses		(2)	15
Balance at end of period	$ 13	$ 14	$ 20