Bank Loans and Related Allowance for Loan Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 15,376	$ 14,316
Past due and other nonaccrual loans	53	49
Total loans	15,429	14,365
Allowance for loan losses	26	31		$ 42	$ 48
Total bank loans — net	15,403	14,334	[1]
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	21	18
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	6	3
>90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	26	28
Residential real estate mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,100	8,304
Past due and other nonaccrual loans	34	30
Total loans	9,134	8,334
Allowance for loan losses	17	20		29	34
Total bank loans — net	9,117	8,314
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	15	11
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	3	1
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	16	18
Home equity loans and lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,336	2,720
Past due and other nonaccrual loans	14	15
Total loans	2,350	2,735
Allowance for loan losses	8	11		$ 13	$ 14
Total bank loans — net	2,342	2,724
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	2	4
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	2	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	10
Pledged asset lines [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,846	3,228
Past due and other nonaccrual loans	5	4
Total loans	3,851	3,232
Total bank loans — net	3,851	3,232
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	4	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	1
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	94	64
Total loans	94	64
Allowance for loan losses	1
Total bank loans — net	$ 93	$ 64

[1] Adjusted for the retrospective adoption of ASU 2015-03. See New Accounting Standards in Note 2 for additional information.