Guaranteed Benefit Features (Information On Guaranteed Death Benefit Features) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Return of Net Deposits [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 88,627	$ 101,601
Net amount at risk	$ 1,563	$ 71
Average attained age of contract holders	65 years	65 years
Minimum Return [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 76	$ 92
Net amount at risk	$ 17	$ 13
Average attained age of contract holders	78 years	77 years
Guaranteed minimum return	5.00%	5.00%
Anniversary Contract Value [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 21,713	$ 25,763
Net amount at risk	$ 2,401	$ 384
Average attained age of contract holders	72 years	71 years