Bank Loans and Related Allowance for Loan Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 14,316	$ 13,392
Past due and other nonaccrual loans	49	49
Total loans	14,365	13,441
Allowance for loan losses	31	42	$ 48	$ 56
Total bank loans — net	14,334	13,399
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	18	11
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	3	3
>90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	28	35
Residential real estate mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,304	8,092
Past due and other nonaccrual loans	30	35
Total loans	8,334	8,127
Allowance for loan losses	20	29	34	36
Total bank loans — net	8,314	8,098
Residential real estate mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	11	9
Residential real estate mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	1	2
Residential real estate mortgages [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	18	24
Home equity loans and lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,720	2,942
Past due and other nonaccrual loans	15	13
Total loans	2,735	2,955
Allowance for loan losses	11	13	$ 14	$ 20
Total bank loans — net	2,724	2,942
Home equity loans and lines of credit [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	4	1
Home equity loans and lines of credit [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	1	1
Home equity loans and lines of credit [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	10	11
Pledged asset lines [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,228	2,320
Past due and other nonaccrual loans	4
Total loans	3,232	2,320
Total bank loans — net	3,232	2,320
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	3
Pledged asset lines [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	1
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	64	38
Past due and other nonaccrual loans		1
Total loans	64	39
Total bank loans — net	$ 64	39
Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans		$ 1