Investments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments [Abstract]
Non-income producing fixed maturity securities	$ 54	$ 0
Investments that exceed ten percent of stockholders' equity	0	0
Fixed maturity securities and equity securities in the energy and metals and mining sectors, at fair value	2,533
Fixed maturity securities and equity securities in the energy and metals and mining sectors, amortized cost or cost basis	2,658
Fixed maturity securities and equity securities in the energy and metals and mining sectors, at fair value, unrealized loss position	1,340
Fixed maturity securities and equity securities in the energy and metals and mining sectors, amortized cost or cost basis, unrealized loss position	1,554
Limited partnership investments	2,548	2,937
Undistributed earnings of limited partnership investments	$ 687	$ 1,040
Percentage of limited partnerships reported on a current basis	63.00%
Percentage of limited partnerships reported on a one month lag	16.00%
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	70.00%	73.00%
Limited partnerships invested in private debt and equity	26.00%	23.00%
Percentage of equity related limited partnership hedge fund strategies	54.00%
Percentage of multistrategy approach limited partnership hedge fund strategies	28.00%
Percentage of distressed investments limited partnership hedge fund strategies	16.00%
Percentage of fixed income limited partnership hedge fund strategies	2.00%
Carrying value of ten largest limited partnerships	$ 1,221	$ 1,492
Carrying value of limited partnerships as percentage of aggregate partnership equity	3.00%	4.00%
Income As Percentage Of Change In Partnership Equity For All Limited Partnerships	3.00%	4.00%	4.00%
Derivative, Collateral, Right to Reclaim Cash	$ 0	$ 0
Derivative, Collateral, Obligation to Return Cash	0	0
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	398
Mortgage loan commitments	12
Commitments to purchase or fund privately placed debt securities	138
Commitments to sell various privately placed debt securities	67
Carrying value of securities deposited under requirements of regulatory authorities	2,800	3,000
Cash and securities deposited as collateral for letters of credit	364	361
Carrying value of assets deposited to secure reinsurance and third party obligations	$ 263	$ 302