Bank Loans and Related Allowance for Loan Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 16,448,000,000	$ 15,376,000,000
Past due and other nonaccrual loans	56,000,000	53,000,000
Total loans	16,504,000,000	15,429,000,000
Allowance for loan losses	26,000,000	26,000,000	$ 31,000,000	$ 42,000,000
Total bank loans - net	16,478,000,000	15,403,000,000
Loans accruing interest contractually 90 days or more past due	0	0
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	18,000,000	21,000,000
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	9,000,000	6,000,000
>90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	29,000,000	26,000,000
First Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,983,000,000	9,100,000,000
Past due and other nonaccrual loans	33,000,000	34,000,000
Total loans	10,016,000,000	9,134,000,000
Allowance for loan losses	16,000,000	17,000,000	20,000,000	29,000,000
Total bank loans - net	10,000,000,000	9,117,000,000
First Mortgage [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	14,000,000	15,000,000
First Mortgage [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	2,000,000	3,000,000
First Mortgage [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	17,000,000	16,000,000
HELOC's [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,928,000,000	2,336,000,000
Past due and other nonaccrual loans	15,000,000	14,000,000
Total loans	1,943,000,000	2,350,000,000
Allowance for loan losses	8,000,000	8,000,000	11,000,000	$ 13,000,000
Total bank loans - net	1,935,000,000	2,342,000,000
HELOC's [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	0	2,000,000
HELOC's [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	2,000,000
HELOC's [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	12,000,000	10,000,000
Pledged asset lines [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,361,000,000	3,846,000,000
Past due and other nonaccrual loans	8,000,000	5,000,000
Total loans	4,369,000,000	3,851,000,000
Allowance for loan losses	0	0
Total bank loans - net	4,369,000,000	3,851,000,000
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	4,000,000	4,000,000
Pledged asset lines [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	4,000,000	1,000,000
Pledged asset lines [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	176,000,000	94,000,000
Past due and other nonaccrual loans	0	0
Total loans	176,000,000	94,000,000
Allowance for loan losses	2,000,000	1,000,000	$ 0
Total bank loans - net	174,000,000	93,000,000
Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
First Mortgage And Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs	$ 77,000,000	$ 78,000,000
First Mortgage And Home Equity [Member] | California [Member] | Loans Geographic Area [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Concentration risk percentage	48.00%	48.00%