Bank Loans and Related Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 29	$ 21	$ 18	$ 21
Charge-offs	0	0	0	0
Recoveries	1	1	1	2
Provision for loan losses	0	(3)	10	(4)
Balance at end of period	30	19	30	19
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	25	19	15	19
Charge-offs	0	0	0	0
Recoveries	1	1	1	2
Provision for loan losses	0	(3)	9	(4)
Balance at end of period	26	17	26	17
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	21	14	11	14
Charge-offs	0	0	0	0
Recoveries	1	1	1	1
Provision for loan losses	0	(3)	9	(3)
Balance at end of period	22	12	22	12
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
Charge-offs	0	0	0	0
Recoveries	0	0	0	1
Provision for loan losses	0	0	0	(1)
Balance at end of period	4	5	4	5
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
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	0	0	1	0
Balance at end of period	$ 4	$ 2	4	2
Other [Member] | Adoption of ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			$ 0	$ 0