Investments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments [Abstract]
Non-income producing fixed maturity securities	$ 0	$ 54
Investments that exceed ten percent of stockholders' equity	0	0
Limited partnership investments	2,371	2,548
Undistributed earnings of limited partnership investments	$ 523	$ 687
Percentage of limited partnerships reported on a current basis	60.00%
Percentage of limited partnerships reported on a one month lag	18.00%
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	68.00%	70.00%
Limited partnerships invested in private debt and equity	27.00%	26.00%
Percentage of equity related limited partnership hedge fund strategies	55.00%
Percentage of multistrategy approach limited partnership hedge fund strategies	26.00%
Percentage of distressed investments limited partnership hedge fund strategies	17.00%
Percentage of fixed income limited partnership hedge fund strategies	2.00%
Carrying value of ten largest limited partnerships	$ 1,168	$ 1,221
Carrying value of limited partnerships as percentage of aggregate partnership equity	4.00%	3.00%
Income As Percentage Of Change In Partnership Equity For All Limited Partnerships	4.00%	3.00%	4.00%
Derivative, Collateral, Right to Reclaim Cash	$ 0	$ 0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative, Notional Amount	174	179
Derivative Liability, Fair Value, Gross Liability	(3)	(5)
Commercial mortgage loans past due or in non-accrual status	0	0
Valuation allowances recorded on commercial mortgage loans	0	0
Future capital call commitments for limited partnership investments	380
Mortgage loan commitments	20
Commitments to purchase or fund privately placed debt securities	130
Commitments to sell various privately placed debt securities	121
Carrying value of securities deposited under requirements of regulatory authorities	2,300	2,800
Cash and securities deposited as collateral for letters of credit	514	364
Carrying value of assets deposited to secure reinsurance and third party obligations	$ 261	$ 263