Bank Loans and Related Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 30	$ 19	$ 18	$ 21
Recoveries			1	2
Provision for loan losses	0	(2)	10	(6)
Balance at end of period	30	17	30	17
Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			1	0
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	26	17	15	19
Recoveries			1	2
Provision for loan losses	1	(3)	10	(7)
Balance at end of period	27	14	27	14
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
First Mortgage [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	22	12	11	14
Recoveries			1	1
Provision for loan losses	(1)	(2)	8	(5)
Balance at end of period	21	10	21	10
First Mortgage [Member] | 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
HELOCs [Member] | Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4	5	4	5
Recoveries			0	1
Provision for loan losses	2	(1)	2	(2)
Balance at end of period	6	4	6	4
HELOCs [Member] | Residential Real Estate [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	0
Other [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4	2	3	2
Recoveries			0	0
Provision for loan losses	(1)	1	0	1
Balance at end of period	$ 3	$ 3	3	3
Other [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			$ 0	$ 0