Bank Loans and Related Allowance for Credit Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Past Due [Line Items]
Current		$ 23,709,000,000	$ 18,173,000,000
Past due and other nonaccrual loans		134,000,000	57,000,000
Total loans		23,843,000,000	18,230,000,000
Allowance for credit losses		30,000,000	18,000,000	$ 21,000,000	$ 26,000,000
Total bank loans – net	[1]	23,813,000,000	18,212,000,000
Loans accruing interest contractually 90 days or more past due		0	0
30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		38,000,000	30,000,000
60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		7,000,000	5,000,000
>90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		89,000,000	22,000,000
Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current		15,627,000,000	12,770,000,000
Past due and other nonaccrual loans		119,000,000	51,000,000
Total loans		15,746,000,000	12,821,000,000
Allowance for credit losses		27,000,000	15,000,000	19,000,000	24,000,000
Total bank loans – net		15,719,000,000	12,806,000,000
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		28,000,000	26,000,000
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		2,000,000	5,000,000
Residential Real Estate [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		89,000,000	20,000,000
First Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Current		14,804,000,000	11,665,000,000
Past due and other nonaccrual loans		100,000,000	39,000,000
Total loans		14,904,000,000	11,704,000,000
Allowance for credit losses		22,000,000	11,000,000	14,000,000	16,000,000
Total bank loans – net		14,882,000,000	11,693,000,000
First Mortgage [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		27,000,000	24,000,000
First Mortgage [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		1,000,000	4,000,000
First Mortgage [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		72,000,000	11,000,000
HELOC's [Member]
Financing Receivable, Past Due [Line Items]
Current		823,000,000	1,105,000,000
Past due and other nonaccrual loans		19,000,000	12,000,000
Total loans		842,000,000	1,117,000,000
Allowance for credit losses		5,000,000	4,000,000	5,000,000	8,000,000
Total bank loans – net		837,000,000	1,113,000,000
HELOC's [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		1,000,000	2,000,000
HELOC's [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
HELOC's [Member] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		17,000,000	9,000,000
Pledged asset lines [Member]
Financing Receivable, Past Due [Line Items]
Current		7,901,000,000	5,202,000,000
Past due and other nonaccrual loans		15,000,000	4,000,000
Total loans		7,916,000,000	5,206,000,000
Allowance for credit losses		0	0
Total bank loans – net		7,916,000,000	5,206,000,000
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		10,000,000	4,000,000
Pledged asset lines [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		5,000,000	0
Pledged asset lines [Member] | >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		181,000,000	201,000,000
Past due and other nonaccrual loans		0	2,000,000
Total loans		181,000,000	203,000,000
Allowance for credit losses		3,000,000	3,000,000	$ 2,000,000	$ 2,000,000
Total bank loans – net		178,000,000	200,000,000
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] | >90 Days Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans		0	2,000,000
First Mortgage And Home Equity [Member]
Financing Receivable, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs		$ 72,000,000	$ 74,000,000
First Mortgage And Home Equity [Member] | Loans Geographic Area [Member] | California [Member]
Financing Receivable, Past Due [Line Items]
Concentration risk percentage		45.00%	45.00%

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.