Bank Loans and Related Allowance for Credit Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	$ 31,583,000,000	$ 23,843,000,000
Allowance for credit losses	13,000,000	30,000,000	$ 13,000,000	$ 30,000,000	$ 30,000,000	$ 18,000,000
Total bank loans – net	31,570,000,000	23,813,000,000
Loans 90 days past due and still accruing	0	0
Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	31,489,000,000	23,709,000,000
Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	94,000,000	134,000,000
30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	35,000,000	38,000,000
60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	12,000,000	7,000,000
More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	47,000,000	89,000,000
Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,978,000,000	15,746,000,000
Allowance for credit losses	10,000,000	27,000,000	10,000,000	27,000,000	26,000,000	15,000,000
Total bank loans – net	19,968,000,000	15,719,000,000
Residential Real Estate [Member] | Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,903,000,000	15,627,000,000
Residential Real Estate [Member] | Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	75,000,000	119,000,000
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	25,000,000	28,000,000
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	3,000,000	2,000,000
Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	47,000,000	89,000,000
First Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,290,000,000	14,904,000,000
First Mortgage [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,290,000,000	14,904,000,000
Allowance for credit losses	8,000,000	22,000,000	8,000,000	21,000,000	22,000,000	11,000,000
Total bank loans – net	19,282,000,000	14,882,000,000
First Mortgage [Member] | Residential Real Estate [Member] | Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,226,000,000	14,804,000,000
First Mortgage [Member] | Residential Real Estate [Member] | Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	64,000,000	100,000,000
First Mortgage [Member] | Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	25,000,000	27,000,000
First Mortgage [Member] | Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	3,000,000	1,000,000
First Mortgage [Member] | Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	36,000,000	72,000,000
HELOCs [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	688,000,000	842,000,000
HELOCs [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	688,000,000	842,000,000
Allowance for credit losses	2,000,000	5,000,000	2,000,000	6,000,000	4,000,000	4,000,000
Total bank loans – net	686,000,000	837,000,000
HELOCs [Member] | Residential Real Estate [Member] | Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	677,000,000	823,000,000
HELOCs [Member] | Residential Real Estate [Member] | Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	11,000,000	19,000,000
HELOCs [Member] | Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	1,000,000
HELOCs [Member] | Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	1,000,000
HELOCs [Member] | Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	11,000,000	17,000,000
Pledged asset lines [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	11,412,000,000	7,916,000,000
Allowance for credit losses	0	0
Total bank loans – net	11,412,000,000	7,916,000,000
Pledged asset lines [Member] | Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	11,393,000,000	7,901,000,000
Pledged asset lines [Member] | Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	19,000,000	15,000,000
Pledged asset lines [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	10,000,000	10,000,000
Pledged asset lines [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	9,000,000	5,000,000
Pledged asset lines [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	0
Other [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	193,000,000	181,000,000
Allowance for credit losses	3,000,000	3,000,000	$ 3,000,000	$ 3,000,000	$ 4,000,000	$ 3,000,000
Total bank loans – net	190,000,000	178,000,000
Other [Member] | Current [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	193,000,000	181,000,000
Other [Member] | Total Past Due And Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	0
Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	0
Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	0
Other [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Total nonperforming assets	0	0
First Mortgage and HELOC [Member]
Financing Receivable, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs	$ 85,000,000	$ 72,000,000
First Mortgage and HELOC [Member] | Loans, Geographic Area [Member] | California [Member] | Geographic Concentration Risk [Member]
Financing Receivable, Past Due [Line Items]
Concentration risk percentage	45.00%	45.00%