Guaranteed Benefit Features (Account Balances Of Variable Annuity Contracts With Guarantees Invested In Separate Accounts) (Details) - Variable Annuity [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Account Balances Of Variable Annuity Contracts With Guarantees Invested In Separate Accounts [Line Items]
Total	$ 121,110	$ 109,182
Percent of total variable annuity separate account values	99.00%	99.00%
Domestic Equity [Member]
Account Balances Of Variable Annuity Contracts With Guarantees Invested In Separate Accounts [Line Items]
Total	$ 59,647	$ 52,244
International Equity [Member]
Account Balances Of Variable Annuity Contracts With Guarantees Invested In Separate Accounts [Line Items]
Total	20,837	17,396
Fixed Income [Member]
Account Balances Of Variable Annuity Contracts With Guarantees Invested In Separate Accounts [Line Items]
Total	$ 40,626	$ 39,542