Bank Loans and Related Allowance for Loan Losses (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total bank loans	$ 18,230	$ 16,630
First Mortgage and Home Equity Loans and Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral	10,500
Adjustable Rate First Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of mortgages	$ 10,500
Percent of loans with interest-only payments	26.00%
Percent of interest only adjustable rate	68.00%
Adjustable Rate First Mortgage [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed rate interest rate period	3 years
Interest-only reset period	3 years
Adjustable Rate First Mortgage [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed rate interest rate period	10 years
HELOC's [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Loan Term	30 years
Financing Receivable, Initial Draw Period	10 years
Financing Receivable, Convert to Amortizing Loans, Period	20 years
Total bank loans	$ 1,117	$ 1,505
Percent of loan balance outstanding, borrowers paid only minimum interest due	52.00%
Home Equity Secured By Second Liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total bank loans	$ 905