Bank Loans and Related Allowance for Loan Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Past Due [Line Items]
Current	$ 16,863,000,000	$ 16,580,000,000
Past due and other nonaccrual loans	49,000,000	50,000,000
Total loans	16,912,000,000	16,630,000,000
Allowance for loan losses	17,000,000	21,000,000	$ 19,000,000	$ 26,000,000	$ 26,000,000	$ 26,000,000
Total bank loans – net	16,895,000,000	16,609,000,000
Loans 90 days past due and still accruing	0	0
30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	25,000,000	27,000,000
60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	3,000,000
More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	21,000,000	20,000,000
First Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Current	10,607,000,000	10,349,000,000
Past due and other nonaccrual loans	33,000,000	35,000,000
Total loans	10,640,000,000	10,384,000,000
Allowance for loan losses	10,000,000	14,000,000	12,000,000	17,000,000	17,000,000	16,000,000
Total bank loans – net	10,630,000,000	10,370,000,000
First Mortgage [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	20,000,000	21,000,000
First Mortgage [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	2,000,000	2,000,000
First Mortgage [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	11,000,000	12,000,000
HELOCs [Member]
Financing Receivable, Past Due [Line Items]
Current	1,208,000,000	1,493,000,000
Past due and other nonaccrual loans	12,000,000	12,000,000
Total loans	1,220,000,000	1,505,000,000
Allowance for loan losses	4,000,000	5,000,000	5,000,000	7,000,000	7,000,000	8,000,000
Total bank loans – net	1,216,000,000	1,500,000,000
HELOCs [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	3,000,000
HELOCs [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	1,000,000	1,000,000
HELOCs [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	8,000,000	8,000,000
Pledged asset lines [Member]
Financing Receivable, Past Due [Line Items]
Current	4,876,000,000	4,558,000,000
Past due and other nonaccrual loans	2,000,000	3,000,000
Total loans	4,878,000,000	4,561,000,000
Allowance for loan losses	0	0
Total bank loans – net	4,878,000,000	4,561,000,000
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	2,000,000	3,000,000
Pledged asset lines [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Pledged asset lines [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member]
Financing Receivable, Past Due [Line Items]
Current	172,000,000	180,000,000
Past due and other nonaccrual loans	2,000,000	0
Total loans	174,000,000	180,000,000
Allowance for loan losses	3,000,000	2,000,000	$ 2,000,000	$ 2,000,000	$ 2,000,000	$ 2,000,000
Total bank loans – net	171,000,000	178,000,000
Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	0	0
Other [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	2,000,000	0
First Mortgage and HELOC [Member]
Financing Receivable, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs	$ 71,000,000	$ 73,000,000
First Mortgage and HELOC [Member] | Loans, Geographic Area [Member] | California [Member]
Financing Receivable, Past Due [Line Items]
Concentration risk percentage	46.00%	47.00%