Bank Loans and Related Allowance for Credit Losses (Composition of Bank Loans and Delinquency Analysis by Loan Segment) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	$ 19,480,000,000	$ 18,173,000,000
Past due and other nonaccrual loans	70,000,000	57,000,000
Total loans	19,550,000,000	18,230,000,000
Allowance for credit losses	29,000,000	18,000,000	$ 21,000,000	$ 21,000,000
Total bank loans – net	19,521,000,000	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	40,000,000	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
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
First Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Current	12,751,000,000	11,665,000,000
Past due and other nonaccrual loans	47,000,000	39,000,000
Total loans	12,798,000,000	11,704,000,000
Allowance for credit losses	21,000,000	11,000,000	14,000,000	14,000,000
Total bank loans – net	12,777,000,000	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	32,000,000	24,000,000
First Mortgage [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	3,000,000	4,000,000
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	12,000,000	11,000,000
HELOCs [Member]
Financing Receivable, Past Due [Line Items]
Current	1,055,000,000	1,105,000,000
Past due and other nonaccrual loans	12,000,000	12,000,000
Total loans	1,067,000,000	1,117,000,000
Allowance for credit losses	4,000,000	4,000,000	5,000,000	5,000,000
Total bank loans – net	1,063,000,000	1,113,000,000
HELOCs [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past due and other nonaccrual loans	2,000,000	2,000,000
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	9,000,000	9,000,000
Pledged asset lines [Member]
Financing Receivable, Past Due [Line Items]
Current	5,458,000,000	5,202,000,000
Past due and other nonaccrual loans	9,000,000	4,000,000
Total loans	5,467,000,000	5,206,000,000
Allowance for credit losses	0	0
Total bank loans – net	5,467,000,000	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	6,000,000	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	3,000,000	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	216,000,000	201,000,000
Past due and other nonaccrual loans	2,000,000	2,000,000
Total loans	218,000,000	203,000,000
Allowance for credit losses	4,000,000	3,000,000	$ 2,000,000	$ 2,000,000
Total bank loans – net	214,000,000	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	2,000,000	2,000,000
First Mortgage and HELOC [Member]
Financing Receivable, Past Due [Line Items]
Unamortized premiums and discounts and direct origination costs	$ 77,000,000	$ 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%