Guaranteed Benefit Features (Information On Guaranteed Death Benefit Features) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018	[1]
Return of Net Deposits [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value		$ 95,670	$ 89,783
Net amount at risk	[2]	$ 209	$ 1,002
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		$ 95	$ 88
Net amount at risk	[2]	$ 16	$ 18
Average attained age of contract holders		77 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		$ 25,031	$ 23,365
Net amount at risk	[2]	$ 596	$ 2,007
Average attained age of contract holders		71 years	71 years

[1] Our variable contracts with guarantees may offer more than one type of guarantee in each contract; therefore, the amounts listed are not mutually exclusive.

[2] Represents the amount of death benefit in excess of the account balance that is subject to market fluctuations.