Bank Loans and Related Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 18	$ 21	$ 26
Charge-offs	0	0	(1)
Recoveries	1	2	2
Provision for loan losses	10	(5)	(6)
Balance at end of period	30	18	21
Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	1	0	0
Balance at end of period		1	0
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	15	19	24
Charge-offs	0	0	0
Recoveries	1	2	2
Provision for loan losses	10	(6)	(7)
Balance at end of period	27	15	19
Residential Real Estate [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	1	0	0
Balance at end of period		1	0
First Mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	11	14	16
Charge-offs	0	0	0
Recoveries	1	1	1
Provision for loan losses	9	(4)	(3)
Balance at end of period	22	11	14
First Mortgage [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	1	0	0
Balance at end of period		1	0
HELOC's [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4	5	8
Charge-offs	0	0	0
Recoveries	0	1	1
Provision for loan losses	1	(2)	(4)
Balance at end of period	5	4	5
HELOC's [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	0	0	0
Balance at end of period		0	0
Other [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	3	2	2
Charge-offs	0	0	(1)
Recoveries	0	0	0
Provision for loan losses	0	1	1
Balance at end of period	3	3	2
Other [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 0	0	0
Balance at end of period		$ 0	$ 0