Life Policy And Investment Contract Reservess (Reserve In Addition To The Account Balance Based On Expected No-Lapse Guarantee Benefits And Expected Policy Assessments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 2,729	$ 2,671
Life Policy Reserves
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,127	1,056
Life Policy Reserves | Ordinary/Traditional Life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,080	1,011
Life Policy Reserves | Other Life Policy Reserves
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	47	45
Investment contract reserves
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	1,602	1,615
Investment contract reserves | Deferred Annuities
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	835	861
Investment contract reserves | Universal Life
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	601	578
Investment contract reserves | Structured Settlements
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	160	170
Investment contract reserves | Other Investment Contract Reserves
Liability for Future Policy Benefit, by Product Segment
Life policy and investment contract reserves	$ 6	$ 6