Bank Loans and Related Allowance for Credit Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	$ 20,841,000,000	$ 18,173,000,000
Past due and other nonaccrual loans	60,000,000	57,000,000
Total loans	20,901,000,000	18,230,000,000
Allowance for credit losses	30,000,000	18,000,000	$ 29,000,000	$ 19,000,000	$ 21,000,000	$ 21,000,000
Total bank loans – net	20,871,000,000	18,212,000,000
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	29,000,000	30,000,000
60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	8,000,000	5,000,000
More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	23,000,000	22,000,000
Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current	14,924,000,000	12,770,000,000
Past due and other nonaccrual loans	50,000,000	51,000,000
Total loans	14,974,000,000	12,821,000,000
Allowance for credit losses	26,000,000	15,000,000	25,000,000	17,000,000	19,000,000	19,000,000
Total bank loans – net	14,948,000,000	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	26,000,000	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	4,000,000	5,000,000
Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	20,000,000	20,000,000
First Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total loans	13,993,000,000	11,704,000,000
First Mortgage [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current	13,952,000,000	11,665,000,000
Past due and other nonaccrual loans	41,000,000	39,000,000
Total loans	13,993,000,000	11,704,000,000
Allowance for credit losses	22,000,000	11,000,000	21,000,000	12,000,000	14,000,000	14,000,000
Total bank loans – net	13,971,000,000	11,693,000,000
First Mortgage [Member] | Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	25,000,000	24,000,000
First Mortgage [Member] | Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	4,000,000
First Mortgage [Member] | Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	13,000,000	11,000,000
HELOCs [Member]
Financing Receivable, Past Due [Line Items]
Total loans	981,000,000	1,117,000,000
HELOCs [Member] | Residential Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current	972,000,000	1,105,000,000
Past due and other nonaccrual loans	9,000,000	12,000,000
Total loans	981,000,000	1,117,000,000
Allowance for credit losses	4,000,000	4,000,000	4,000,000	5,000,000	5,000,000	5,000,000
Total bank loans – net	977,000,000	1,113,000,000
HELOCs [Member] | Residential Real Estate [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
HELOCs [Member] | Residential Real Estate [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] | Residential Real Estate [Member] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	7,000,000	9,000,000
Pledged asset lines [Member]
Financing Receivable, Past Due [Line Items]
Current	5,727,000,000	5,202,000,000
Past due and other nonaccrual loans	7,000,000	4,000,000
Total loans	5,734,000,000	5,206,000,000
Allowance for credit losses	0	0
Total bank loans – net	5,734,000,000	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	3,000,000	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	4,000,000	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	190,000,000	201,000,000
Past due and other nonaccrual loans	3,000,000	2,000,000
Total loans	193,000,000	203,000,000
Allowance for credit losses	4,000,000	3,000,000	$ 4,000,000	$ 2,000,000	$ 2,000,000	$ 2,000,000
Total bank loans – net	189,000,000	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] | More Than 90 Days Past Due and Other Nonaccrual Loans [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	2,000,000
First Mortgage and HELOC [Member]
Financing Receivable, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs	$ 78,000,000	$ 74,000,000
First Mortgage and HELOC [Member] | Loans, Geographic Area [Member] | California [Member]
Financing Receivable, Past Due [Line Items]
Concentration risk percentage	45.00%	45.00%