Bank Loans and Related Allowance for Loan Losses (Changes in Allowance for Loan Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 27	$ 26	$ 26	$ 26
Charge-offs	(1)	(2)	(1)	(2)
Recoveries	1	2	1	2
Provision for loan losses	(1)	0	0	0
Balance at end of period	26	26	26	26
First Mortgage [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	17	17	16	17
Charge-offs	0	(1)	0	(1)
Recoveries	0	1	0	1
Provision for loan losses	0	0	1	0
Balance at end of period	17	17	17	17
HELOCs [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	7	8	8	8
Charge-offs	0	(1)	0	(1)
Recoveries	1	1	1	1
Provision for loan losses	(1)	0	(2)	0
Balance at end of period	7	8	7	8
Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	3	1	2	1
Charge-offs	(1)	0	(1)	0
Recoveries	0	0	0	0
Provision for loan losses	0	0	1	0
Balance at end of period	$ 2	$ 1	$ 2	$ 1